On the Steinmanellidae (Bivalvia: Myophorelloidea); their palaeobiogeography, evolution and classification

Abstract

The trigoniid group "Pseudo-Quadratae" was introduced for Cretaceous descendents of Myophorellidae with a convergent resemblance to Tethyan Quadratotrigoniinae (= Quadratae). Subsequently it was made the basis of the subfamily Steinmanellinae, which herein is elevated to family rank. The earliest record of the group is from the Early-Middle Kimmeridgian of the Tethyan Realm (American Province), from where it spread into the Boreal and Gondwanic realms. Steinmanellids rose to dominance in the cool temperate waters of the Andean Province, and the latter represents their centre of diversification. They are absent from the predominantly cold circum-polar waters of Southern and Eastern Gondwana, i.e. the Antarctic and Maorian provinces, as well as from the Australasian Province. The evolution of the group is tracked and two lineages identified, comprising 47 nominal species assigned to 14 genera, 9 of which are new: Stoyanowella, Philippiella, Garatella, Weaverella, Neuquenella, Pseudoyaadia, Popenoella, Louella, and Tashiroella. One lineage (Yaadiinae nov.) migrated northwards from its Tethyan origin into the Cordilleran Province of the Boreal Realm and thence, in the Late Cretaceous, to the Oriental Province, surviving in both biochores into the Maastrichtian. The second lineage, the subfamily Steinmanellinae, appeared in the Early-Middle Kimmeridgian of the American Province, but its centre of diversification was in the Andean Province where it appeared in the Early Tithonian and survived until the Late Hauterivian. From there it migrated eastwards into the Ethiopian Province, reaching as far as India, where it is recorded only from the Late Valanginian and Barremian. © 2017 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.

Full text

On the Steinmanellidae (Bivalvia: Myophorelloidea); their palaeobio-
geography, evolution and classification
Michael R. Cooper and Héctor A. Leanza
With 7 figures
Abstract: The trigoniid group “Pseudo-Quadratae” was introduced for Cretaceous descendents of Myophorellidae with a
convergent resemblance to Tethyan Quadratotrigoniinae (= Quadratae). Subsequently it was made the basis of the subfam-
ily Steinmanellinae, which herein is elevated to family rank. The earliest record of the group is from the Early-Middle
Kimmeridgian of the Tethyan Realm (American Province), from where it spread into the Boreal and Gondwanic realms.
Steinmanellids rose to dominance in the cool temperate waters of the Andean Province, and the latter represents their centre
of diversification. They are absent from the predominantly cold circum-polar waters of Southern and Eastern Gondwana, i.e.
the Antarctic and Maorian provinces, as well as from the Australasian Province. The evolution of the group is tracked and
two lineages identified, comprising 47 nominal species assigned to 14 genera, 9 of which are new: Stoyanowella, Philippiella,
Garatella, Weaverella, Neuquenella, Pseudoyaadia, Popenoella, Louella, and Tashiroella. One lineage (Yaadiinae nov.)
migrated northwards from its Tethyan origin into the Cordilleran Province of the Boreal Realm and thence, in the Late
Cretaceous, to the Oriental Province, surviving in both biochores into the Maastrichtian. The second lineage, the subfamily
Steinmanellinae, appeared in the Early-Middle Kimmeridgian of the American Province, but its centre of diversification
was in the Andean Province where it appeared in the Early Tithonian and survived until the Late Hauterivian. From there it
migrated eastwards into the Ethiopian Province, reaching as far as India, where it is recorded only from the Late Valanginian
and Barremian.
Key words: Bivalvia, Trigoniida, Myophorelloidea, Steinmanellidae, evolution, classification, new taxa.
1. Introduction
Early workers referred all large “knobby trigoniids” to
the “section Quadratae” (AgAssiz 1840; Lycett 1872),
and cox (1952, 1969) assigned them to only two gen-
era, Steinmanella and Yaadia, thereby “…confounding
lineages that can be distinguished over a long period
of geological time” (sAuL 1978: 5). steinmAnn (1881,
1882) was the first to appreciate that the Gondwanic
representatives were phylogenetically distinct from
European Quadratae and introduced the term “Pseudo-
Quadratae” for South American Trigonia transitoria
steinmAnn and South African T. herzogi goLdfuss,
the only two representatives known at that time.
Subsequently the concept and range of the group was
extended by the addition of species from the Ethiopian
Province, T. mamillata Kitchin (1903) from India,
T. holubi Kitchin (1908) from South Africa, and T.
hennigi LAnge (1914) from East Africa. As a result
c
ricKmAy
(1930) established the genus Steinmanella,
with T. holubi as type, and dietrich (1933) introduced
Transitrigonia for Andean T. transitoria. Later, r
ennie
(1936) and cox (1952, 1969) synonymized the two gen-
era, Savelʼev (1958) included Steinmanella in the syn-
onymy of Quadratotrigonia and PouLton (1977) treated
it as a subgenus of Myophorella. However, the descrip-
tion of still more species resulted in their resurrection
at the subgeneric level (c
AmAcho
& o
Livero
1985; H.A.
LeAnzA 1993) and revealed a far more complex evolu-
tionary history than first envisaged. As a result cooPer
©2017 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de
DO I : 10.1127/ njgpa/20 17/0683 007 7-7 749/2 017/068 3 $ 5.75
N. Jb. Geol. Paläont. Abh. 285/3 (2017), 313–335 Article
Stuttgart, September 2017
E
eschweizerbart_xxx

314 M.R. Cooper and H.A. Leanza
(1991) introduced the subfamily Steinmanellinae for
this predominantly Gondwanic group, which includes
the largest-known trigoniids, and their Boreal off-
shoots. However, taxonomic lumping has obfuscated
the diversification and complexity of the group and the
purpose of this paper, therefore, is to track the evolu-
tionary history of steinmanellids and to represent their
diversity in an appropriate taxonomy which replicates
genealogy. Again we would reiterate (cf. cooPer 2015)
that in phylogenetic taxonomy, taxonomic rank is not
discretionary, but it is pre-determined by evolutionary
position. Suggestions we have oversplit the group re-
flect a Linnean approach in which taxonomic limits
are subjectively pre-determined, and hence do not ac-
curately replicate genealogy. We stress also that, due to
rampant convergence, palaeobiogeographical consid-
erations are fundamental to generic identification (cf.
c
ooPer
1915: 15), as are seemingly “trivial characters”.
This work is dedicated to Dr renAto reyes-BiAnchi, and to
the memory of Dr e
rneSto
P
eréz
d
ʼa
ngelo
, foremost stu-
dents of the Steinmanellidae.
2. Palaeobiogeography
Steinmanellids are strongly provincial bivalves first
recorded from the Early-Middle Kimmeridgian of the
American Province (crAgin 1897, 1905). However,
their centre of diversification is the Andean Province
(with 22 nominal species) where they appeared in
the Early Tithonian and from where they have been
recorded and figured by many workers (steinmAnn
1881, 1882; PhiLiPPi 1899; BurcKhArdt 1900a, b, 1903;
hAuPt 1907; douviLLé 1910; Lisson 1930; WeAver
1931; A.f. L
eAnzA
1941; L
AmBert
1944; A.F. L
eAnzA
& c
AsteLLAro
1955; c
orvALán
& P
érez
1958; L
evy
1969; r
eyes
& P
érez
1978; r
eyes
et al. 1981; P
érez
et al. 1981; c
AmAcho
& o
Livero
1985; H.A. L
eAnzA
& gArAte 1987; Lo forte 1988; Pérez & reyes 1989;
h.A. LeAnzA 1993; Luci 2010; Luci & LAzo 2012;
LAzo & Luci 2013). From here the group migrated
eastwards, entering the Ethiopian Province in the Late
Valanginian and surviving into the Barremian. Here it
is recorded from South Africa (g
oLdfuss
1837; K
itchin
1908; rennie 1936; cooPer 1979, 1991), East Africa
(LAnge 1914) and India (Kitchin 1903; rudrA et al.
2007). A second group penetrated the Cordilleran
Province in the Middle Valanginian where it persisted
into the Maastrichtian (g
ABB
1864, 1876; W
hiteAves
1879; PAcKArd 1921; cricKmAy 1930; Anderson 1938,
1958; PouLton 1977; sAuL 1978, 1991; scott 2007).
From there steinmanellids migrated westwards, reach-
ing the Oriental Province in the Cenomanian where,
again, they persisted into the Maastrichtian (y
ehArA
1923a, b; KuBotA 1955; KoBAyAshi & AmAno 1955;
n
AKAno
1958, 1961; h
AyAmi
1975; t
Ashiro
1978, 1988,
1992; morozumi et al. 1981; tAshiro & morozumi 1983;
tAshiro & KAno 1989). The group was extinct before
the end of the Maastrichtian in both the Cordilleran and
Oriental provinces.
Palaeomagnetic data (Kent & irving 2010) indi-
cate that North America underwent mainly north-
ward drift throughout the Jurassic and Cretaceous,
with the Gulf of Mexico positioned at 15° N of lati-
tude in the Late Jurassic (160 Ma) and at about 22° N
in the Early Cretaceous (120 Ma). This suggests that
Kimmeridgian-Tithonian Stoyanowella n.g. lived in
subtropical to warm temperate waters on the Tropic of
Cancer, between 35-40° N of latitude. Early Cretaceous
North American yaadiines inhabited temperate waters
between 45-60° N of latitudes, suggesting adaptation
to somewhat cooler waters (Fig. 1). As the southern tip
of the Yucatán Peninsula was positioned on the Tropic
of Capricorn at 30° S of latitude at the beginning of the
Jurassic 220 Ma ago, much of the Gondwanic Realm
experienced cool temperate and subpolar conditions for
most of the Jurassic and Cretaceous. Obviously north-
ward drift of Gondwana during the Late Cretaceous
would have seen progressive warming of water condi-
tions during this period.
Steinmanellids have a bipolar distribution,
Yaadiinae nov. favouring cool temperate waters in the
Boreal Realm (cf. c
ooPer
2015 for trigoniid palaeo-
biogeographical map) and Steinmanellinae inhabiting
similar waters in the Gondwanic Realm. However,
whereas the former preferred high-energy nearshore
environments with coarse-clastic sediments (sAuL
1978), the latter favoured low-energy sticky-clay fa-
cies of lagoonal and back-barrier origin (L
Azo
2003;
pers. observ.). The family avoided tropical warm-water
ecosystems dominated by reef-building corals, calcare-
ous algae, microbial bioherms, orbitoline foraminifers
and rudistid bivalves. Undoubtedly, their absence from
southern and eastern Gondwana, i.e. the Antarctic and
Maorian provinces, is also environmentally induced, to
avoid very cold circum-polar waters. Conditions in the
Australasian Province were also detrimental to stein-
manellids, but the precise reasons unknown.
Nominal species referred to Steinmanellidae from
the different faunal provinces used here (see cooPer
2015: 14, fig. 1) are as follows:
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 315
Oriental Province
ainuana yABe & nAgAo, deckeina KABo tA, japonica
yehArA, jimboi KoBAyAshi & AmAno, kimurai toKun ugA &
shimizu, lymani KoBAyAshi & AmAno, obsoleta KoBAyAshi
& A
mAno
, sanukiensis n
AKAno
, shinoharai K
oBAyAshi
&
AmAno, tanii tAshiro & morozumi.
Cordilleran Province
brandti s
AuL
, californiana P
AcKArd
, colusaensis A
nderson
,
fitchi PAcKArd, hemphilli Anderson, jonesi sAuL, leana
gABB, lewisagassizi cricKmAy, perrinsmithi Anderson,
pinea s
AuL
, robusta s
AuL
, wheelerensis A
nderson
, white-
avesi PAcKArd.
American Province
maloneana s
toyAnoW
, sologureni f
eLix
, vyschetzkii c
rAgin
.
Andean Province
caicayensis L
Azo
& L
uci
, erycina P
hiLiPPi
, haupti L
AmBert
,
herzogi reyes (non goLdfuss), katterfeldensis cAmAcho &
oLivero, lepida PhiLiPPi, neuquensis BurcKhArdt, pehuen-
mapuensis H.A. LeAnzA, posadensis cAmAcho & oLivero,
quintucoensis WeAver, raimondii Lisson, splendida A.F.
LeAnzA, steinmanni PhiLiPPi, subquadrata Luci & LAzo,
transitoria steinmAnn, vacaensis WeAver.
Fig. 1. The palaeobiogeographical distribution of steinmanellid bivalves (Hauterivian continental reconstruction after o
Wen
1983). Trigoniid palaeobiogeographical provinces are after cooPer (2015). The lines of latitude are for the Barremian (120
Ma) taken from Kent & irving (2010).
eschweizerbart_xxx

316 M.R. Cooper and H.A. Leanza
Ethiopian Province
hennigi LAnge, herzogi goLdfuss, holubi Kitchin, kensleyi
cooPer, mamillata Kitchin.
With regard to the Andean Province, Tithonian
Trigonia copiapina PhiLiPPi (1899: 71, pl. 32, fig. 1;
P
érez
& r
eyes
1989: 22), T. stolpi P
hiLiPPi
(1899: 81, pl.
35, fig. 6; Pérez & reyes 1989: 17) and T. erycina var.
irregularis P
hiLiPPi
(1899: 66, pl. 32, fig. 3) are based on
generically-indeterminate internal moulds whose type
specimens are lost (Pérez & reyes 1989). The holo-
type of Neocomian T. williamsi PhiLiPPi (1899: 72, pl.
32, fig. 4; Pérez & reyes 1989: 24) is also lost and its
curious shape with prominent umbones is not a feature
of steinmanellines; it may be teratological. Trigonia
clavellata PhiLiPPi (non PArKinson) 1899: 63, pl. 29,
figs. 3, 4) was assigned to Steinmanella by Pérez &
reyes (1989: 9, pl. 1, fig. 15) but the species was based
upon two fragments both of which do not preserve the
ornament of the area or escutcheon and hence are ge-
nerically indeterminate. Moreover, the Aptian age of
the material suggests it may be myophorelline. Here
all these species are regarded as nomina dubia and are
not discussed further.
Trigonia amarali PhiLiPPi (1899: 67, pl. 30, fig.
6; Pérez & reyes 1989: 22) (Fig. 4J) is based on a
medium-sized (L = 57 mm), moderately inequilateral,
Tithonian specimen with a pyriform shape, strongly-
rounded anterior with umbones positioned well back,
and prominent transverse costellae to the escutcheon.
Its shape is unlike that of any steinmanelline and it ap-
pears closer to Japanese material currently assigned to
Heterotrigonia. We do not regard it a steinmanelline.
3. Systematic palaeontology
Repositories of material referred to here are as follows:
BMNH – Natural History Museum, London; DNSM –
Natural Science Museum, Durban; MOZ – Museo Juan
Olsacher, Zapala; SAM – South African Museum, Cape
Town; MLP – Museo de La Plata; UO – Condon Museum,
University of Oregon, Eugene; USNMNH – Smithsonian
Institute, Washington.
Superfamily Myophorelloidea KoBAyAshi, 1954
Family Steinmanellidae cooPer, 1991
(nom. transl. herein ex Steinmanellinae)
Diagnosis: Moderately large to very large, thick-shelled,
strongly inequilateral, moderately inflated, subquadratic
to rectangular and subovate with obliquely subtruncate re-
spiratory margin, low subterminal umbones, moderately-
incurved opisthogyrous beaks and relatively large ligament
nymph; anterior face commonly flat, either unornamented
or with upward-concave extensions of flank costae and nar-
row lunule; escutcheon moderately wide, with commarginal
or transverse rows of nodes; broad, flat, generally bipar-
tite area with nodate inner, median and marginal carinae
in early to middle growth; area with commarginal costel-
lae continuous from flank in earliest growth but in middle
growth with growth striae which may persist to maturity
(Yaadiinae nov.) or give way to strong irregular commar-
ginal rugae (Steinmanellinae); antecarinal sulcus narrow
in early growth, obsolete later when areal rugae commonly
extend onto posterodorsal flank; flanks with oblique, curved
to almost straight, nodate costae, generally narrower than
interspaces, with large subcircular to elliptical nodes which
may become drawn out and attenuated ventrally; LV with
weak lath-like anterior tooth. Early-Late Kimmeridgian –
Maastrichtian.
Discussion: As recognized by steinmAnn (1882), and many
subsequent workers, the similarity of steinmanellids to
Quadratotrigoniinae is convergent. In the latter there are
V-shaped flank costae in early growth, the longitudinal fur-
row to the area is closer to the marginal than to the inner
carina, and internally there are pits to the posteroventral
commissure (Kitchin 1903).
The early growth stages of steinmanellids, with nodate
carinae and curved rows of flank nodes, point indubitably
to an origin in Jurassic Myophorellidae (steinmAnn 1882;
Kitchi n 1908; renni e 1936; KoBAyAshi & AmAno 1955;
Savelʼev 1958; nAKAno 1968; reyes et al. 1981; cooPer
Fig. 2. Hypothesized relationships among Steinmanellidae. It is important to appreciate that the phenotypic discontinuities
represented by the gaps between adjacent branches of the cladogram are inherently unequal and hence an indication only
of affiliation among known members and not necessarily a very close evolutionary relationship. 1. Moderately large, thick-
shelled, elongate-ovate, moderately inflated, low subterminal umbones, moderately-incurved opisthogyrous beaks, relatively
large ligament nymph; gently-convex anterior margin, long convex ventral margin, obliquely subtruncate respiratory margin,
long almost straight posterodorsal margin; escutcheon moderately wide, with transverse rows of nodes; narrow flattened
anterior face with fine rib extensions; bipartite area with nodate inner, median and marginal carinae, median carina weaker
than others; area beaded in early growth, later with irregular growth rugae which may extend onto posterodorsal flank;
marginal carina nodate, nodes increasing in size posteriorly; antecarinal sulcus lacking; flanks with gently curved nodate
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 317
costae with opisthocline dorsal stems. 2. Subquadratic; anterior margin subvertical, almost straight, posterodorsal margin
short; escutcheon large, with transverse rows of enlarged nodes; entire area nodate. 3. Elongate-subovate; escutcheon with
commarginal (oblique) rows of beads; escutcheon carina with enlarged nodes becoming increasing elongate posteriorly. 4.
Area non-tuberculate, with irregular growth rugae in middle to later growth; nodate median carina obsolete in later growth;
ribs strongly curved, with relatively-small nodes. 5. Elongate-ovate, with convex anterior margin; flank costae without dorsal
stems, terminating mostly along anterior margin, becoming subtangential to ventral margin in later growth, flank nodes
decreasing in size and becoming increasingly crowded posteriorly. 6. Moderately large to large, subtrigonal, with straight,
vertical anterior margin, ribbed anterior face; relatively short, straight posterodorsal margin; flank costae strongly curved,
mostly intersecting anterior margin, sometimes with gaps and enlarged and irregular nodes on anterolateral shoulders. 7.
Large to very large, subrectangular, with subparallel ventral and posterodorsal margins; narrow unornamented anterior face;
narrow antecarinal space in early to middle growth, becoming obsolete later with encroachment of growth rugae from area;
flank costae with nodes increasing in size posteriorly and becoming irregular anterolaterally, with gaps and occasional larger
tubercles. 8. Very large, massive, very elongate-ovate to subrectangular; anterior margin inclined, with acute umbonal angle;
ligament nymph relatively small; flank costae straight, relatively distant, posteriorly opisthocline, mostly terminating along
ventral margin, nodes increasing in size posteriorly; escutcheon with transverse or commarginal costellae. 9. Ovate-elongate;
escutcheon relatively broad, in early growth with transverse nodate costae, nodes becoming oblique in middle growth and
hence commarginal; in earliest growth area with commarginal costellae; nodate median and marginal carinae obsolete in
middle to later growth when area ornamented by growth striae only; curved flank costae narrower than interspaces, about half
terminating on anterolateral shoulder in disconnected double row of enlarged tubercles. 10. Moderately large; anterolateral
corner subangular; escutcheon subtabulate, with transverse rows of nodes; inner carina with strong transverse bars which in
early growth extend across inner area to reach longitudinal furrow; area with fine diagonal (commarginal) costellae on outer
part; narrow unornamented antecarinal space; flanks with 1-2 vertical rows of enlarged tubercles on anterolateral shoulders
more-or-less separated from weakly-curved, oblique flank costae with large nodes. 11. Anterior margin convex, with rounded
anterolateral corner, round anterolateral shoulders lacking enlarged tubercles and convex anterior face; umbones positioned
back from anterior, posterodorsal margin concave; narrow shallowly-sunken escutcheon smooth or with strong subtransverse
costellae continuous from area; very-large ligament nymph; juvenile ribbing of area may form complicated chevrons; nodate
marginal carinae evanescing in later growth. 12. Elongate-subovate, with fastigiate anterior face; posterodorsal margin almost
straight; escutcheon large, in early growth with bar-like transverse costae, later unornamented and poorly discriminated
from area, fastigiate on conjoined valves; inner carina non-tuberculate, marked only by a change in slope; area broad, gently
convex, with fine oblique costellae and longitudinal groove in early growth only; curved flank costae numerous, broader
than interspaces, with small uniform nodes, in later growth cutting obliquely across growth striae anteriorly, forming zigzags
anteroventrally. 13. Subquadratic to subovate; escutcheon with oblique costellae meeting commissure in posteriorly-directed
chevrons; nodate inner, median and marginal carinae evanescing in later growth; area with commarginal costellae in earli-
est growth, later with growth striae only; strongly-curved nodate flank costae, narrower than interspaces, most terminating
along anterior margin, nodes tending to elongate and coalesce in later growth to become segmented subcommarginal cords.
14. Very narrow, short, unornamented escutcheon; nodate inner, median and marginal carinae restricted to early growth
(primitive) or obsolete (derived); broad bipartite area unornamented; nodate flank costae evanescing posteriorly in middle
to later growth leaving flanks with growth striae only.
eschweizerbart_xxx

318 M.R. Cooper and H.A. Leanza
1991), from which they differ most obviously in their larger
size, robust shell and ornamented escutcheon. n
AKAno
(1968)
looked to Orthogonia for the progenitor of Yaadia, whereas
s
AuL
(1978) favoured myophorellines with enlarged shoulder
tubercles, i.e. Scaphogonia and Scaphotrigonia. However,
this latter character has occurred repeatedly in myophorel-
loid evolution and is highly convergent (cf. c
ooPer
2011), and
the precise antecedent of steinmanellids remains unknown
since they are separated by a moderate phenotypic disconti-
nuity from other myophorelloids. Hypothesized relationships
among the steinmanellid genera recognized here are shown
as Fig. 2.
Subfamily Steinmanellinae cooPer, 1991
Diagnosis: Moderately large to very large; escutcheon no-
date, either in transverse (primitive) or commarginal (de-
rived) rows; area primitively nodate or not, later with coarse,
irregular, commarginal rugae in middle to later growth, com-
monly extending onto posterodorsal flank with obsolescence
of marginal carina. Early-Late Kimmeridgian – Barremian.
Discussion: Steinmanelline bivalves are characteristic of
Western Gondwana (Andean and Ethiopian provinces)
(cAmAcho & oLivero 1985; cooPer 1991; H.A. LeAnzA
1993). Their diversity has long been recognized and, follow-
ing multivariate analysis, r
eyes
et al. (1981) distinguished 3
major groups: the (A) transitoria, (B) erycina and (C) stein-
manni groups, with S. splendida remaining isolated but with
strong affinities with the transitoria group.
Within the transitoria group (A), reyes et al. (1981)
distinguished 3 subgroups, A
1
comprising transitoria, cu-
racoensis, quintucoensis and herzogi, A2 made up of va-
caensis, and A3 with neuquensis and raimondii. Within the
erycina group (B) they recognized two subgroups, B1 made
up of erycina and haupti, and B
2
consisting only of neuquen-
sis (excluding the forms described by WeAver and LAmBert)
which was considered intermediate between the erycina and
transitoria groups. The steinmanni group (C) consisted only
of the nominate species. Subsequently a number of subgenera
were introduced to encompass this variation (cf. c
AmAcho
& o
Livero
1985; H.A. L
eAnzA
1993), but these taxa have
failed to gain acceptance on the grounds they were “… rather
poorly defined” (Luci & LAzo 2012: 104). Here we provide
new diagnoses.
Genus Stoyanowella nov.
Etymology: For Dr. ALexAnder A. stoyAnoW (1879-1974),
monographer of the Early Cretaceous faunas of southeastern
Arizona (cf. Lee & schroter 1977).
Type species: Trigonia vyschetzkii crAgin, 1893; by original
designation herein.
Stoyanowella vyschetzkii (crAgin, 1893)
Fig. 3A, B
Diagnosis of genus: Moderately large, subovate, longer
than high with near-terminal umbones and gently-convex
anterior margin curving evenly into long convex ventral
margin; respiratory margin obliquely subtruncate and long
posterodorsal margin almost straight; escutcheon broad,
with nodate transverse costellae; narrow flattened anterior
face with fine ribs; bipartite area with nodate inner, median
and marginal carinae, median row weaker than others and
nodes of marginal carina increasing in size posteriorly and
becoming more elongate; in early growth area with com-
marginal rows of beads which, in middle to later growth,
coalesce to produce irregular growth rugae which may ex-
tend onto the posterodorsal flank; marginal carina nodate,
nodes increasing in size posteriorly, extending onto outer
flank; antecarinal sulcus lacking; flanks with gently curved
nodate costae, nodes rounded to elliptical, increasing in size
posteriorly, often with single very large node near ventral
margin; flank costae with thin, finely tuberculate, opistho-
cline dorsal stems. Early-Late Kimmeridgian.
Referred species: S. maloneana (s
toyAnoW
1949: 72 (pars),
pl. 9, figs. 1-2 only) (Fig. 3C, D).
Discussion: Stoyanowella n.g. is endemic to the American
Province (Texas). As the oldest member of the Pseudo-
Quadratae, and the only non-Gondwanic representative,
S. vyschetzkii has a critical bearing on the origin of the
fa mily. crAgin (1893) introduced the species for material
from the Malone Formation of Texas. These trigoniids oc-
cur in the lower part of the formation which was dated on
the basis of the associated ammonites to the Early-Middle
Kimmeridgian (ALBritton 1937; imLAy 1980). However,
Fig. 3. A, B – Stoyanowella vyschetzkii (crAgin), lectotype (A) and paralectotype (B), after crAgin (1905). C, D –
Stoyanowella maloneana (s
toyAnoW
), the holotype after s
cott
(2007). E-F, L, M – Philippiella erycina (P
hiLiPPi
). E-F,
a hypotype figured by WeAver (1931); L, the lost syntype for which the species was created, after Ph iLiPPi (1899); M, the
lectotype selected by Pérez & reyes (1989). G, H – Splenditrigonia splendida (A.F. LeAnzA), the holotype, MLP-4128. I,
V – Philippiella haupti (LAmBert); I, a topotype after H.A. LeAnzA (1993); V, the lectotype after LAmBert (1944). J, K –
“Trigonia” sologureni f
eLix
, the holotype by monotypy, after f
eLix
(1891). N – “Trigonia” volckmanni P
hiLiPPi
, the holotype
after Pérez & reyes (1989). O-Q – Garatella quintucoensis (WeAver), the lectotype designated herein, after Luci & LAzo
(2012). R – Garatella neuquensis (B
urcKhAr dt
), the holotype, after L
uci
& L
Azo
(2012). S, T – Garatella subquadrata
(Luci & LAzo), the holotype after Luci & LAzo (2012). U – Garatella raimondii (Lisson), the holotype, after Lisson (1930).
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 319
Fig. 3.
eschweizerbart_xxx

320 M.R. Cooper and H.A. Leanza
it was only later (crAgin 1905: 56, pl. 8, figs. 1-2, pl. 9,
figs. 1-3) that the species was described in detail and fig-
ured for the first time. crAgin recognized that the absence
internally of commissural pits precluded assignment to
Quadratotrigonia and considered T. vyschetzkii related to
T. transitoria, while acknowledging that none “… has the
condition of Trigonia transitoria steinmAnn in which the
untuberculated median carina is barely indicated, whereas
the solid costellae are strongly sculptured in the posterior
part of the areas”. s
toyAnoW
(1949) referred T. vyschetzkii to
the Pseudo-Quadratae, and nAKAno (1961), sAuL (1978) and
scott (2007) assigned it to the genus Steinmanella without
discussion.
stoyAnoW (1949: 72) restudied Craginʼs type material
and suggested that at least 3 species were involved. His de-
terminations were as follows:
pl. 8, fig. 1, pl. 9, fig. 3 – Trigonia sp. (USNMNH-28967).
pl. 8, fig. 2 – lectotype of Trigonia vyschetzkii
(USNMNH-28967) (Fig. 2A).
pl. 9, fig. 1 – holotype of Trigonia maloneana stoyAnoW
(usnmnh-92020) (Fig. 3C, D).
pl. 9, fig. 2 – T. maloneana var. (USNMNH-28967).
This assessment was refuted by sAuL (1978) and scott
(2007) both of whom, without in-depth analysis, admitted
only one species. However, there are differences; S. malo-
neana lacks opisthocline stems to its flank costae and a flat-
tened anterior face (cf. crAgin 1905, pl. 9, fig. 2), and has
coarser flank tubercles. Moreover, scott (2007) considered
Trigonia vyschetzkii most similar to Late Aptian T. guildi
stoyAnoW (1949: 75, pl. 12, figs. 1-2) but the latter is clearly
a member of the Quadratotrigoniinae, with V-shaped flank
costae in early growth. Given its abundance, and the criti-
cal position of Stoyanowella n.g. in steinmanellid phylogeny
and, indeed, its significance to the suggested monophyly of
the group, the Malone material warrants further collecting
and thorough re-analysis, especially since S. vyschetzkii “…
was found by scores, in one or two places being agglomerat-
ed in beds, mingled more or less with other fossils. Between
75 and 100 specimens of it are represented from this tract.
But if the shells of other Malone fossils, as here preserved,
prove fragile under the rigorous temperature changes of a
plateau climate, that of Trigonia vyschetzkii is so especially,
and of the large number collected many are in half-released
fragments, and comparatively few make even tolerably fair
cabinet specimens” (crAgin 1905: 57).
crAgin (1905: 57) suggested that Trigonia sologureni
feLix (1891: 179, pl. 27, fig. 2) “approached” some specimens
of S. vyschetzkii. However, the Mexican species is based on
an internal mould (Fig. 3J, K) which is shorter, more inflated
and subquadratic and, without more information, is generi-
cally unidentifiable. It is a nomen dubium.
At present there is no known ancestor for Stoyanowella
n.g. Unfortunately the genus Myophorella as currently inter-
preted (c
ox
1969) is a sac-name for a number of generically-
distinct clades, i.e. a taxonomic mess, and hence comparison
with steinmanellines virtually impossible. Certainly there
is a high degree of convergence among the two groups,
e.g. “Trigonia” keepingi L
ycett
(1877: 196, pl. 35, figs. 1,
2). Among potential myophorelline candidates, Tethyan
Trigonia clavellata (J. soWer By, 1815) (Lycett 1872: 18, pl.
1, figs. 1, 2), a junior homonym of T. clavellata P
ArKinson
(1811), comes closest, being moderately large and similarly
robust, with 3 well-developed nodate carinae, but its elon-
gate-ovate shape, unornamented escutcheon, lack of growth
rugae to the area and absence of opisthocline dorsal stems
to the flank costae immediately distinguish it. However,
according to chAmBerLAin’s comments of the etheLdred
Benett (1831) collection (cited by torrens et al. 2000: 110),
the forms of T. clavellata from the Oxford Clay “… involve
a much greater amount of differences than that which in
other forms of the genus is regarded as of specific impor-
tance”. Thus, without taxonomic revision, T. clavellata is
also almost impossible to interpret; s. s
chneider
(in litt.)
regards it a junior subjective synonym of T. nodulosa B
AyLe
.
Promyophorella has a similarly wide area to Stoyanowella
n.g. but is much smaller and thin-shelled, with an unorna-
mented escutcheon, fine commarginal lirae to the area and
it lacks a beaded median carina.
Since Stoyanowella n.g. is separated from all known
myophorellines by a moderate phenotypic discontinuity here
the subfamily Steinmanellinae is elevated to family rank.
Genus Splenditrigonia H.A. LeAnzA, 1993
Type species: Trigonia splendida A. F. LeAnzA 1941: 225, pl.
1, figs. 1, 2; by original designation.
Splenditrigonia splendida (A.f. LeAnzA, 1941)
Fig. 3G, H
Diagnosis of genus: Like Stoyanowella n.g. but subquadrat-
ic; escutcheon large, wide, with subtransverse rows of en-
larged nodes; broad bipartite area with rows of small nodes
in both subcommarginal and diagonal rows which persist to
maturity; nodate median and marginal carinae obsolete in
middle to later growth; antecarinal sulcus lacking; posterior
flank costae with short opisthocline dorsal stems meeting
marginal carina at very acute angle. Early Tithonian.
Discussion: Splenditrigonia is a monotypic Andean endemic
(Argentina) introduced as a subgenus of Steinmanella but
here elevated to generic rank. Its nodate area distinguishes
it from all but Philippiella n.g. With respect to its origin it is
important to recall Cr aginʼs (1905: 56) observation that the
areal ornamentation of S. vyschetzkii “…. shows considerable
mutability, and a variety occurs in which the entire area is
covered with small compressed tubercles”. This latter vari-
ant has neither been figured nor described, nor has it been
shown to be conspecific, but it certainly makes S. vyschetzkii
a strong candidate for the origin of Splenditrigonia.
cooPer (1991) united Vaugoniinae and Quadrato-
trigoniinae as Vaugoniidae on the basis of their V-shaped
flank costae in early growth, an inferred apomorphy, with
Quadratotrigonia separated by its quadratic shape and
nodate areal ornament. However, the apparent presence
of Stoyanowella “variants” with nodate areas raises the
possibility that Steinmanellinae and Quadratotrigoniinae
may be sister taxa, and it is the V-shaped flank costae of
Vaugoniinae that are convergent. Clearly better knowledge
of the Malone fauna is critical to unraveling this quandary.
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 321
Genus Philippiella nov.
Etymology: In memory of Dr. r
oduLfo
A
mAndo
P
hiLiPPi
(1808-1904), University of Chile, monographer of the
Jurassic-Cretaceous bivalves of Chile.
Type species: Trigonia erycina P
hiLiPPi
1899: 66, pl. 30, figs.
3, 5; WeAver 1931: 259, pl. 21, figs. 109-110; LAmBert 1944:
379, pl. 8, fig. 4; reyes et al. 1981: 38, pl. 2, figs. 3-8; Pérez
& reyes 1989: 9, pl. 1, figs. 5, 10; H.A. LeAnzA 1993: 44, pl.
7, fig. 1; by original designation herein.
Philippiella erycina (PhiLiPPi, 1899)
Fig. 3E, F, L
Diagnosis of genus: Like Splenditrigonia but subrectangu-
lar to elongate-subovate, longer than high, with commarginal
rows of beads to the escutcheon, and small nodes to the area;
flank costae terminate mostly along the ventral margin, with
relatively long, opisthocline dorsal stems and smaller nodes.
Late Tithonian.
Referred species: P. haupti (LAmBert 1944: 381, pl. 5, fig.
7; H.A. LeAnzA 1993: 44, pl. 6, figs. 1, 2) (Fig. 3I).
Discussion: Philippiella n.g. is endemic to the Andean
Province (Chile, Argentina) and comprises two closely-re-
lated Late Tithonian (Corongoceras alternans Zone) species
(H.A. LeAnzA 1993). The genus corresponds to the B1 group
of reyes et al. (1981) which is morphometrically well sepa-
rated from ancestral S. splendida, with derived characters
placing it closer to Garatella n.g.
Trigonia erycina was based upon an almost-complete
specimen (P
hiLiPPi
1899, pl. 30, fig. 3) (Fig. 3L) which ap-
pears to have been lost. As a result Pérez & reyes (1989: 9)
selected the second imperfect syntype (pl. 1, fig. 5), identi-
fied as T. erycina var., as lectotype. Trigonia erycina var.
irregularis PhiLiPPi (1899: 66, pl. 32, fig. 3; Pérez & reyes
1989: 22) and T. volckmanni (PhiLiPPi 1899: 72, pl. 32, fig.
5; Pérez & rey es 1989: 10, pl. 2, figs. 17, 18) (Fig. 3N), are
based on poorly-preserved specimens and both have been
included in the synonymy of P. erycina.
Genus Garatella nov.
Etymology: For the late Dr. José i. gArAte zuBiLLAgA
(Zapala), in recognition of his contribution to the knowledge
of trigoniids in the Neuquén Basin of Argentina.
Type species: Trigonia quintucoensis WeAver (1931: 248, pl.
21, fig. 111, pl. 23, figs. 119-125; BMNH-C.119 is selected
here as lectotype; by original designation.
Garatella quintucoensis (WeAver, 1931)
Fig. 3O-Q
Diagnosis of genus: Like Philippiella n.g. but larger (Lmax
= 120 mm), subquadratic, almost as high as long, with sub-
terminal umbones, straight subvertical anterior margin and
rounded anteroventral corner; escutcheon carina persistent,
nodes becoming increasingly elongate with growth; non-
tuberculate area with irregular growth rugae which, in mid-
dle to later growth, absorb the nodate marginal carina and
extend well onto the flank, displaying a prominent furrow
below the marginal carina posteriorly expanded; flank costae
strongly curved, terminating mostly along the anterior and
anteroventral margins. Late Berriasian – Early Valanginian.
Referred species: G. neuquensis (BurcKhArdt 1903: 74,
pl. 14, figs. 4-6); LAzo & Luci 2013: 113, fig. 11) (Fig. 3R),
G. raimondii (Lisson 1930: 15, pl. 8, figs. 1-2) (Fig. 3U),
G. subquadrata (Luci & LAzo 2012: 110, figs. 9, 10; = T.
neuquensis WeAver (non BurcKhArdt) 1931: 253, pl. 22, figs.
112-114) (Fig. 3S).
Discussion: Garatella n.g. is endemic to the Andean
Province (Argentina, Peru). It corresponds to the A3 group
of reyes et al. (1981) and is easily distinguished from
Philippiella n.g., to which it is morphometrically closest (cf.
reyes et al. 1981), and Splenditrigonia by the lack of nodes
to the area. Garatella quintucoensis retains long, thin, opis-
thocline, dorsal stems to the flank costae not seen in the
other referred species, but a feature of Philippiella n.g., and
is assumed to be the most primitive member of the group.
The apomorphic characters of Garatella n.g. foreshadow
Weaverella n.g.
Contrary to Luci & LAzo (2012), the holotype of G.
neuquensis (Fig. 3R) is not an “anterior fragment”. That the
areal growth rugae extend well onto the posterodorsal flank
shows that it is an almost complete specimen, albeit some-
what corroded, with a broad antecarinal space crossed by
growth rugae from the area.
Peruvian S. raimondii (Fig. 3U) is based on material <36
mm in length and may be juvenile, as a result of which its
status has been questioned. Contrary to LAzo (2003), how-
ever, the name is legitimate and nomenclaturally available
since it was correctly introduced. Moreover, the type locality
is geographically well separated from other steinmanellines,
and the species may well prove valid. Topotypic material is
required.
Genus Weaverella nov.
Etymology: For Dr chArLes edWin WeAver (1880-1958) (cf.
L
Azo
2009), whose seminal work on the Jurassic-Cretaceous
palaeontology and stratigraphy of west-central Argentina has
formed the starting point for much subsequent research.
Type species: Trigonia transitoria var. curacoensis W
eAver
1931: 243, pl. 22, figs. 115-118; Luci & LAzo 2012: 104, figs.
5, 6; LAzo & Luci 2013: 70, fig. 5); by original designation
herein.
Weaverella curacoensis (WeAver, 1931)
Fig. 4A-C
Diagnosis of genus: Elongate-subovate, posteriorly
produced, with well-rounded anteroventral margin; ligament
eschweizerbart_xxx

322 M.R. Cooper and H.A. Leanza
Fig. 4. A-C – Weaverella curacoensis (WeAver), the lectotype designated herein, BMNH-C.119, after Luci & LA zo (2012,
fig. 8. 1-3). D – Weaverella lepida (PhiLiPPi), the holotype by monotypy, after PhiLiPPi (1899). E, F – Weaverella steinmanni
(P
hiLiPPi
); E, the holotype by monotypy, after P
hiLiPPi
(1899); f, the neotype selected herein, MOZ P-0917, after H.A. L
eAnzA
& gArAte (1987). G – Steinmanella holubi (Kitchin), a topotype figured by cooPer (1991). H – Steinmanella mamillata
(Kitchin), the lectotype designated herein after Kitchin (1903). I, J – Neuquenella pehuenmapuensis (H.A. LeAnzA), a
topotype after Luci & LAzo (2012). K, L – Steinmanella caicayensis Luci & LAzo, the holotype, after Luci & LAzo (2012).
M – Neuquenella kensleyi (cooPer), an unnumbered adult topotype in the DNSM.
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 323
nymph relatively large; escutcheon with commarginal rows
of ellipsoidal nodes replaced by growth rugae and striae in
middle to later growth; escutcheon carina with enlarged
nodes becoming increasing elongate posteriorly, evanescing
in maturity; area with weak, nodate, median and marginal
carinae, small and weak nodes transversely elongate in
middle growth, becoming obsolete later when growth rugae
from area extend onto posterodorsal flank; antecarinal
sulcus in early growth only, later obsolete; flank costae
strongly curved, terminating mostly along anterior margin
with concave-upward extensions on anterior face, becoming
subtangential to ventral margin in later growth, meeting area
at acute angle; tubercles to flank costae relatively small,
decreasing in size and becoming increasingly crowded
posteriorly. Early Valanginian – Early Hauterivian,
?Barremian.
Referred species: W. lepida (P
hiLiPPi
1899: 67, pl. 30, fig.
4; Pérez & reyes 1989: 10, pl. 1, fig. 11) (Fig. 3D), W. s tein-
manni (P
hiLiPPi
1899: 64, pl. 30, figs. 1, 2; H.A. L
eAnzA
&
g
ArAte
1987: 216, pl. 13, figs. 1, 2; H.A. L
eAnzA
1993: 42, pl.
13, figs. 1, 10; non Lisson 1930: 6, pl. 2, figs. 1-3) (Fig. 4E-F)
Discussion: Weaverella n.g. is endemic to the Andean
Province (Chile, Argentina), corresponding to the A2 and C
groups of reyes et al. (1981). It differs most obviously from
Garatella n.g. in it elongate-subovate shape, long posterodor-
sal margin, well-rounded anteroventral corner, strongly-con-
vex ventral margin, areal rugae not passing substantially onto
the flank, lack of dorsal stems to the flank costae and smaller
flank tubercles.
Although included in the synonymy of W. curacoensis
by H.A. L
eAnzA
(1993), W. steinmanni (Fig. 4E-F) differs in
its earlier loss of median and marginal carinae, the smaller
nodes to its flank costae, and the finer, more-regular rugae
to its area. P
hiLLiPi
(1899) gave its imprecise type locality
as “… declivi oriental Andium chillianensium” but P
érez
& reyes (1989: 10) suggested it most likely came from the
Valanginian at Puerta Curaco in Neuquén, Argentina, from
where it was recorded by H.A. LeAnzA & gAr Ate (1987).
Here the specimen figured by H.A. L
eAnzA
& g
ArAte
(1987,
pl. 13, figs. 1, 2), MOZ-P0917, is selected as neotype, and the
type locality becomes Puerta Curaco with the type horizon
the Mulichinco Formation of late Early Valanginian Lissonia
riveroi and early Late Valanginian Olcostephanus atherstoni
zones. We interpret Weaverella n.g. to include the steinmanni
group (C) of reyes et al. (1981).
Genus Neuquenella nov.
Etymology: From Neuquén (Argentina), the province
from where the type species was collected in the Pilmatué
Member of the Agrio Formation.
Type species: Steinmanella (Macrotrigonia) pehuenmapu-
ensis H.A. L
eAnzA
(1998: 57, pl. 1, figs. 1-7; L
Azo
2003: 1076,
figs. 6.1-6.11; LAzo & Luci 2013: 70, fig. 6); by original des-
ignation herein.
Neuquenella pehuenmapuensis (h.A. LeAnzA, 1998)
Fig. 4I, J
Diagnosis for genus: Moderately large, subtrigonal, with
prominent terminal umbones, straight vertical anterior mar-
gin, flat narrow anterior face crossed by concave-up rib ter-
minations, and short, straight posterodorsal margin; escutch-
eon not sunken, fastigiate on conjoined valves; curved flank
costae strongly oblique, mostly intersecting anterior margin,
sometimes forming enlarged double nodes on anterolateral
shoulder. Late Late Valanginian.
Referred species: N. kensleyi (cooPer 1979: 58. fig. 8) (Fig.
4M).
Discussion: Pandemic to the Andean (Argentina) and
Ethiopian (South Africa) provinces. Nequenella n.g. dif-
fers from Weaverella n.g. most obviously in its subtrigonal
shape and straight vertical anterior margin, with irregular
and sometimes enlarged tubercles along the anterior mar-
gin. Neuquenella kensleyi (Fig. 4M) differs from N. pe-
huenmapuensis in its smaller size and more-curved flank
costae, with fused and doubled tubercles on the anterolat-
eral shoulders separated by a short gap. This latter character
is seen also in some specimens of N. pehuemapuensis (cf.
WeAver 1931, pl. 21, fig. 106) and also younger (Barremian)
Pseudoyaadia hennigi (L
Ange
) (see below). It was introduced
as a species of Macrotrigonia but differs from the latter in
its smaller size, vertical anterior margin and trigonal shape.
Genus Steinmanella cricKmAy, 1930
= Steinmannella KoBAyAshi & AmAno, 1955, nomen
vanum.
= Steinmannaea cricKmAy, 1962, unnecessary re-
placement name.
Type species: Trigonia holubi Kitchin 1908: 103, pl. 4, fig.
2; cAmAcho & oLi vero 1985: 48, pl. 1, figs. 1, 2; cooPer
1991: 16, figs. 6-8; by original designation.
Steinmanella holubi (Kitchin, 1908)
Fig. 4G
Diagnosis for genus: Large to very large, subquadratic to
subrectangular, longer than high, with straight vertical to
slightly prosocline anterior margin, small inconspicuous
near-terminal umbones, perpendicular to obtuse umbonal
angle and narrow unornamented anterior face with rounded
shoulders; ventral and posterodorsal margins subparallel;
ligament nymph large (l/L = 0.25); maximum inflation
slightly anterior of anterolateral shoulders; escutcheon long,
very narrow, with commarginal rows of ellipsoidal nodes,
largest adjacent to commissure; in early to middle growth
broad bipartite area unornamented but for conspicuous
nodate inner, median and marginal carinae, nodes becom-
ing elongated in middle growth and replaced by irregular
eschweizerbart_xxx

324 M.R. Cooper and H.A. Leanza
Fig. 5.
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 325
growth rugae in maturity; narrow antecarinal space in early
to middle growth, becoming obsolete later with encroach-
ment of tubercles from flank and rugae from area; flank
costae moderately curved, mostly terminating along ventral
margin, with crowded nodes increasing in size posteriorly
but decreasing in size and becoming ellipsoidal ventrally;
tuberculation somewhat irregular anteroventrally, sometimes
with intercalated rows and enlarged nodes separated by gaps.
Early Late Valanginian.
Referred species: S. caicayensis L
Azo
& L
uci
(2013: 65. fig.
4) (Fig. 4K, L), S. cf. caicayensis Luci & LAzo (= Trigonia
transitoria stein mAnn 1882 (non 1881), after steinmAnn
(1882) (Fig. 5G, H), S. mamillata (Kitchin 1903: 100, pl. 9,
figs. 8, 9, pl. 10, figs. 1-3) (Fig. 4H).
Discussion: Steinmanella is pandemic to the Andean
and Ethiopian provinces (Argentina, South Africa, India).
According to rudrA et al. (2007) the type horizon of
S. mamillata is Late Valanginian in age, not Tithonian-
Berriasian as previously believed (cooPer 1979, 1991).
Palaeobiogeographical considerations indicate that the pro-
genitor of S. mamillata lies in some Ethiopian steinmanel-
line, with its subquadratic shape, straight vertical anterior
margin (not preserved in the lectotype) and curved flank
costae indicating assignment to Steinmanella, contrary to
the view of cAmAcho & oLivero (1985).
Steinmanella differs from Weaverella n.g. in its larger
size, subquadratic to subrectangular shape with straight
subvertical anterior margin, weakly curved ventral mar-
gin subparallel to posterodorsal margin, lesser inflation,
relatively smaller ligament nymph, prominent inner, median
and marginal carinae in early to middle growth with well-
spaced nodes, and less-curved flank costae which become
irregularly nodate anteriorly in later growth, with gaps and
enlarged nodes.
Genus Transitrigonia dietrich, 1933
Type species: Trigonia transitoria steinmAnn 1881: 260, pl.
13, fig. 3; by monotypy.
Transitrigonia transitoria (steinmAnn, 1881)
Fig. 5E, F
Diagnosis of genus: Very large, massive, strongly inequi-
lateral, elongate-ovate to subrectangular, with subparallel
posterodorsal and ventral margins and low insignificant
umbones; anterior margin subvertical to opisthocline with
acute umbonal angle, curving imperceptibly into long gen-
tly-convex ventral margin; escutcheon with commarginal or
transverse rows of nodes; escutcheon carina with prominent
nodes becoming increasing elongate in middle growth; area
with commarginal costellae in earliest growth which eva-
nesce later; nodate median carina becomes obsolete in later
growth when irregular commarginal growth rugae cross
area; marginal carina nodate, nodes becoming elongate in
middle growth and obsolete in later growth when growth
rugae from the area cross onto the posterodorsal flank; an-
tecarinal sulcus in early to middle growth becoming obsolete
later; flank costae weakly curved, almost straight, posterior-
ly opisthocline, mostly terminating along the ventral margin,
effaced from anterior face; nodes to flank costae increase in
size posteriorly. Late Valanginian – Early Barremian.
Referred species: T. herzogi (g
oLdfuss
1837: 193, pl. 137,
fig. 5; steinmAnn 1882: 219, pls. 7-9; Kitchin 1908: 101, pl.
5, fig. 1; c
AmAcho
& o
Livero
1985: 53, pl. 2, fig. 2, pl. 3, fig.
3; cooPer 1991: 19, figs. 9-12) (Fig. 5D), T. katterfeldensis
(cAmAcho & oLivero 1985: 53, pl. 2, figs. 3-4) (Fig. 5A, B),
T. maxima (cAmAcho & oLivero 1985: 58, pl. 1, fig. 5, pl. 3,
fig. 1) (Fig. 5C), T. posadensis (cAmAcho & oLivero 1985:
55, pl. 4, figs. 1, 3) (Fig. 5I), T. vacaensis (WeAver 1931:
251, pl. 24, figs. 126-130; H.A. LeAnzA 1993: 45, pl. 15, figs.
6-7, pl. 16, fig. 13) (Fig. 5K), T. sp. (= herzogi r
eyes
(non
goLdfuss) 1970: 15, pl. 3, figs. 2-3, pl. 4, figs. 1-3).
Discussion: Transitrigonia is pandemic to the Andean
(Chile, Argentina) and Ethiopian (South Africa) provinces,
with most species Middle to Late Hauterivian. It includes
the A
2
group of r
eyes
et al. (1981). The genus holds a special
place in steinmanellid classification since the type species,
together with T. herzogi goLdfuss, formed the basis for rec-
ognition of the group Pseudo-Quadratae, and corresponds to
the A1 group of reyes et al. (1981).
As interpreted here Transitrigonia differs from Wea-
verella n.g. most obviously in its very large size, posterior
elongation with very long posterodorsal margin, subrectan-
gular shape, straight anterior margin, subparallel posterodor-
sal and ventral margins, straighter more-distant flank costae
which do not curve strongly forwards but terminate mostly
along the ventral margin, and prominent rounded nodes to
the flank costae that increase in size posteriorly.
Transitrigonia transitoria was based (s
teinmAnn
1881:
260, pl. 13, fig. 3) on a specimen said to have come from
the Lower? Cretaceous of Caracoles, Bolivia. However,
Caracoles is 55 km northeast of Antofagasta (c. S 23°02’ –
Fig. 5. A, B – Transitrigonia katterfeldensis (c
AmAcho
& o
Livero
), the holotype after c
AmAcho
& o
Livero
(1985). C –
Transitrigonia maxima (cAmAcho & oLivero), the holotype after cAmAcho & oLiv ero (1985). D – Transitrigonia herzogi
(g
oLdfuss
), the provisional neotype after c
ooPer
(1991). E, F – Transitrigonia transitoria (s
teinmAnn
), the holotype by
monotypy, after s
teinmAnn
(1881). G, H – Steinmanella cf. caicayensis L
uci
& L
Azo
(= Trigonia transitoria s
teinmAnn
1882 (non 1881), after steinmAnn (1882). I – Transitrigonia posadensis (cAmAcho & oLivero), the holotype after cAmAcho
& o
Livero
(1985). J – “Trigonia” amarali P
hiLiPPi
, the holotype by monotypy, after P
hiLiPPi
(1899). K – Transitrigonia
vacaensis (WeAver), the lectotype designated herein, after WeAver (1931).
eschweizerbart_xxx

326 M.R. Cooper and H.A. Leanza
W 69°) and thus actually in northern Chile. It was found in
a similar grey marly limestone to Heteraster oblongus (de
Luc) and Janira sp. [= Neithea cf. atava (roemer)], the lat-
ter a typically Neocomian (Berriasian – Barremian) species
(dhondt 1973). Stoyanowʼs (1949: 69) subsequent selection
of the original of steinmAnn (1882, pl. 8, fig. 3) (Fig. 5G, H)
as lectotype is invalid, since S
teinm ann
ʼs (1881) specimen
was the holotype by monotypy.
Although T. transitoria is a widely-cited Andean spe-
cies, at present only the holotype can be assigned here with
confidence. According to LAzo & Luci (2013: 74) they re-
ceived photographs of the holotype of T. transitoria from the
Philipps-Universität Marburg (Germany), but our similar re-
quest went unanswered, both by the university and Dr L
Azo
.
As illustrated by s
teinmAnn
, the holotype of T. transitoria
is medium-sized (L = c. 60 mm; measured from the plate
and assumed to be figured approximately in natural size like
the ammonite on the same plate), small for a steinmanellid
and hence probably immature. It is posteriorly very elongate
(H/L = 0.63), subrectangular, with maximum inflation close
to midlength (W/H = 0.34), and with small, low, anteriorly-
positioned umbones, moderately-incurved beaks and a broad
anterior face with rounded anterolateral shoulders. The al-
most straight, subvertical anterior margin curves evenly into
the long gently-convex ventral margin which is subparallel
to the long, straight posterodorsal margin; the respiratory
margin is obliquely subtruncate. There is a large ligament
nymph (l/L = 0.39), much longer than wide (w/l = 0.10). The
escutcheon is relatively large, shallowly sunken, with indis-
tinct (?due to erosion), elongate, commarginal nodes. The
nodes to the escutcheon carina become increasingly elon-
gate posteriorly, eventually passing into the growth rugae
of the area. In early to middle growth the bipartite area has
a prominent longitudinal furrow flanked by a nodate me
-
dian carina, the nodes becoming absorbed by commarginal
growth rugae in later growth. The marginal carina is nodate,
the nodes not increasing markedly in size posteriorly. There
is a shallow antecarinal sulcus which persists to the posterior
margin and is not crossed by growth rugae from the area.
There are feeble, very short, opisthocline dorsal stems to the
flank costae which are distant, slightly curved, and coarsely
tuberculate, with only four tubercles per rib at midlength.
The ribs are narrower than the interspaces, with tubercles
increasing in size posteriorly, and most (66%) terminating
along the ventral margin. Factors which suggest the holo-
type is immature include its relatively small size, persistent
antecarinal sulcus and areal rugae failing to cross onto the
posterodorsal flank.
In our view, T. transitoria has been badly misinterpreted
by previous workers. Material subsequently referred to this
species by its author (steinmAnn 1882: 221, pl. 7, figs. 3, 4,
pl. 8, figs. 1-3) (Fig. 5G, H), and on which interpretation
of the species has been based, came from the Bío Bío re
-
gion, some 1400 km to the south of Caracoles, at the same
latitude as the Argentinean Neuquén Basin. It comprised 5
fairly well-preserved specimens in the collection of the for-
mer Mining Office in Munich (but these could not be found
by Dr S. schneider, in litt.), from three different localities as
follows: 2 specimens from Cordillera (Nevados) de Chillán
(S 36°18’), together with Ptychomya, 1 specimen from Baños
de Chillán, and 2 specimens from near the Antuco volcano
(S 37°16’). All were from unknown stratigraphical levels and
different localities to the holotype and hence cannot be re-
garded as topotypes. Their true identity awaits re-analysis.
We place the material assigned to S. transitoria by Luci &
LAzo (2012) in Weaverella n.g.
As recognized by s
teinmAnn
(1881), and confirmed by
morphometrical analysis (r
eyes
et al. 1981), T. transitoria is
closely allied to South African T. herzogi, a species placed in
the subgenus Macrotrigonia by c
AmAcho
& o
Livero
(1985).
The latter taxon was introduced for the Hauterivian S. (M.)
katterfeldensis (Fig. 5A, B), which seems to differ from T.
herzogi mainly in its younger age, curved flank costae and
in having subtransverse costellae to the escutcheon. The
ornament of the escutcheon is unknown in the other two
species assigned to the subgenus by c
AmAcho
& o
Livero
(1985), and both T. h erzogi and T. vacaensis differ in having
commarginal rows of nodes. Moreover, immature T. maxi-
ma (c
AmAcho
& o
Livero
1985, pl. 1, fig. 5) has a strongly
convex ventral margin and looks much like a very large
Weaverella n.g. For the present we treat Macrotrigonia as
a synonym of Transitrigonia but better knowledge of the
Argentine material, which is from the Middle Hauterivian
to Early Barremian, is required.
Transitrigonia herzogi, the earliest species in the genus
(early Late Valanginian), shares with Steinmanella a heavy
robust shell, unornamented anterior face, subparallel ventral
and posterodorsal margins, and flank costae that become
irregularly nodate anteroventrally, with variable gaps and
enlarged nodes. We believe they are sister taxa.
Genus Pseudoyaadia nov.
Etymology: The generic name refers to its superficial (con-
vergent) resemblance to Yaadia.
Type species: Trigonia hennigi L
Ange
(1914: 238, pl. 19, fig.
3; r
ennie
1936: 347, pl. 43, figs. 1-3, pl. 44, fig. 1), by original
designation herein.
Pseudoyaadia hennigi (LAnge, 1914)
Fig. 6J
Diagnosis for genus: Large (Lmax = 130 mm), posteriorly
elongate (H/L = 0.63), ovate, with low, inconspicuous, near-
terminal umbones and small incurved opisthogyrous beaks;
anterior margin gently convex, inclined, with acute umbonal
angle and flat, narrow, unornamented anterior face; long (l
= 28 mm) narrow lunule (w/l = 0.25); anteroventral corner
rounded, ventral margin convex, broad oblique respira-
tory margin gently convex, and long posterodorsal margin
straight; ligament nymph relatively long (l = 32 mm), narrow
(w/l = 0.18); escutcheon relatively broad, in early growth with
transverse nodate costae, the nodes becoming smaller and
oblique in middle growth and hence commarginal; in earliest
growth area with commarginal costellae with prominent no-
date escutcheon, median and marginal carinae, nodes of me-
dian and marginal carinae obsolete in middle to later growth
when area is ornamented by growth striae only; curved flank
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 327
costae oblique, narrower than interspaces, with large rounded
nodes, about half terminating on anterolateral shoulder in a
disconnected double row of enlarged tubercles. Barremian.
Discussion: Pseudoyaadia n.g. is endemic to the Ethiopian
(Zululand, Tanzania) Province. Superficially it greatly re-
sembles Yaadia but their disjunct distribution and vast geo-
graphical separation suggests the similarity is due to con-
vergence. However, the possibility that it may be a case of
bipolar distribution (cf. dAmBoreneA et al. 2013) should be
investigated. It differs from Yaadia most obviously in lack-
ing bar-like ribs to the inner area in early growth. In addi-
tion it differs in being larger, with an acute umbonal angle,
rounded anterolateral corner, sparser more-distant flank
costae and the early loss of median and marginal carinae. It
differs from all other Steinmanellinae in lacking irregular
growth rugae to the area. Pseudoyaadia n.g. appears above
a stratigraphical discontinuity and hence its immediate ante-
cedent is unknown. However, its acute umbonal angle, sparse
flank costae terminating mainly along the ventral margin,
and transverse costae to the escutcheon are features of some
Transitrigonia, e.g. T. katterfeldensis (cAmAcho & oLivero
(1985), and a double row of tubercles along the anterolateral
shoulder is a feature of Neuquenella kensleyi (cooPer).
Subfamily Yaadiinae nov.
Diagnosis: Moderately large, mostly subovate, with small
low anteriorly-positioned umbones and opisthogyrous beaks;
straight vertical to rounded anterior margin, convex ventral
margin, obliquely-subtruncate respiratory margin and long
shallowly-concave to almost-straight posterodorsal mar-
gin; escutcheon moderately wide, shallowly-sunken with
transverse costellae which evanesces medially in derived
members; nodate inner and marginal carinae, evanescing in
middle to later growth in derived members; commarginal
ribs of inner area in early growth persist in middle to later
growth as bar-like transverse nodes on inner carina; area
with growth striae only in middle to later growth; flanks
with curved rows of uniform nodes, primitively enlarged on
anterolateral shoulder. ?Middle Valanginian, Hauterivian –
Maastrichtian.
Discussion: Yaadiines are restricted to the Boreal Realm.
They first appeared in the Middle Valanginian of the
Cordilleran Province (northern California, Oregon, British
Columbia, Queen Charlotte Island), from where they spread
into the Oriental Province (Japan) in the Cenomanian. The
subfamily persisted into the Maastrichtian in both provinces,
and its origin has been inferred to lie in Steinmanellinae
(cooPer 1991). Since transverse costellae to the escutch-
eon are a character shared both with Splenditrigonia and
Stoyanowella n.g., palaeobiogeographical considerations
suggest an early split from Steinmanellinae and that the ori-
gin of Yaadiinae nov. may in fact lie close to Kimmeridgian
Stoyanowella n.g.
Typically yaadiines are found in medium- to coarse-
grained, immature, pebbly sandstones of nearshore high-
energy environments (inner sublittoral zone) suggestive of
water depths of 7-40 m, “… and are absent from the finer
grained more basinward deposits” (sAuL 1978: 17). Thus
their ecological requirements are different from most stein-
manellines.
Genus Yaadia cricKmAy, 1930
Type species: Trigonia lewisagassizi c
ricKmAy
1930: 50,
pl. 13, figs. 1, 2; s
AuL
1991: 27, text-figs. 8, 10; by original
designation.
Yaadia lewisagassizi (cricKmAy, 1932)
Fig. 6A, B
Diagnosis of genus: Moderately large to large, thick-shelled,
subquadratic, longer than high with subterminal umbones
and opisthogyrous beaks; straight vertical anterior margin,
long gently-convex ventral margin, obliquely subtruncate re-
spiratory margin and long essentially straight posterodorsal
margin; anterior face flat, with extensions of flank costae;
escutcheon relatively broad, subtabulate, extending most of
posterodorsal length, with transverse or commarginal rows
of beads, or smooth; inner carina with strong, bar-like trans-
verse nodes which in early growth extend across inner area
to reach longitudinal furrow; bipartite area with persistent,
nodate, median and marginal carinae, ornamented only in
early growth with transverse bars from escutcheon on inner
part, and fine commarginal) costellae on outer part; nar-
row unornamented antecarinal space; flanks with nodate
commarginal costellae in early growth, later with 1-2 ver-
tical rows of enlarged tubercles on anterolateral shoulders
more-or-less separated from weakly-curved, oblique flank
costae with large rounded to ellipsoidal nodes. ?Middle
Valanginian, Hauterivian – Cenomanian.
Referred species: Y. jonesi sAuL (1978: 29, pl. 1, figs., 1-8,
pl. 2, figs. 1, 2, pl. 11, fig. 1, text-fig. 11) (Fig. 6C), Y. leana
(gABB 1876: 312; = Trigonia gibboniana gABB (non LeA)
1864: 190, pl. 25, fig. 178, pl. 31, fig. 262; sAuL 1978: 33,
pl. 4, figs. 1-8, pl. 5, figs. 1-4, pl. 11, fig. 2, text-fig. 13a, b;
= Trigonia colusaensis Anderson 1958: 110, pl. 1, fig. 6; =
Trigonia wheelerensis Anderson 1958: 116) (Fig. 6F, G), Y.
whiteavesi (PAcKArd 1921: 21, pl. 6, fig. 2 only; sAuL 1978:
31, pl. 2, figs. 3-5, pl. 3, figs. 1-6, text-fig. 12; = Trigonia per-
rinsmithi Anderson 1958: 110, pl. 2, fig. 7) (Fig. 6D).
Discussion: Yaadia is typical of the Cordilleran Province
(British Columbia, Oregon, northern California). Due to
poor knowledge of the type species, recognized only by the
tectonically-distorted holotype, some might regard Yaadia
as a nomen dubium. However, it is clearly congeneric with
slightly younger Y. jonesi s
AuL
(Fig. 6C) which, in our opin-
ion, validates the generic characteristics of Yaadia. Although
a poorly-known species Y. lewisagassizi differs from its im-
mediate descendent and closest ally, Y. jonesi, in having two
rows of enlarged shoulder tubercles rather than just one.
Future work may show these differences represent no more
than intraspecific variation and, with better material, the two
species may be shown to be conspecific.
eschweizerbart_xxx

328 M.R. Cooper and H.A. Leanza
Fig. 6.
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 329
A feature not emphasized by s
AuL
(1978), but clearly evident
in the Middle to Late Hauterivian Y. jonesi (s
AuL
1978, pl.
1, fig. 8) (Fig. 6C) and in the Early Albian Y. whiteavesi
(PouLton 1977, pl. 1, figs. 14, 15) (Fig. 6D) are subtrans-
verse rows of beaded costellae to the escutcheon. This
primitive character, shared with Stoyanowella n.g. and
Splenditrigonia, is less consistent in Y. leana (gABB) but is
still displayed by some individuals (sAuL 1978, pl. 4, fig. 4).
Yaadia has a superficial resemblance to the myophorel-
line Scaphotrigonia (Fig. 6K, L), but the latter is smaller,
with an unornamented escutcheon and straighter flank cos-
tae, and lacks a median nodate carina and nodate escutcheon
and marginal carina which are present only in early growth.
We regard the similarity as due to convergence.
The species lewisagassizi → jonesi → whiteavesi →
leana form a Middle Valanginian to Early Turonian evo-
lutionary series. Yaadia differs from its possible progenitor
Stoyanowella n.g. in its straight subvertical anterior mar-
gin, near-terminal umbones and doubled rows of enlarged
tubercles to the anterolateral shoulders. It differs from
Steinmanella in its smaller size, narrower more-rounded
respiratory margin, curved marginal carina, sparser, more
distant flank costae with 1-2 well-developed vertical rows
of enlarged tubercles on the anterolateral shoulders, lack of
growth rugae to the area in later growth and presence of bar-
like transverse nodes to the inner area and escutcheon carina.
Genus Popenoella nov.
= Packardella KoBAyAshi & AmAno, 1955, a nomen
nudum.
Etymology: For W.P. P
oPenoe
, in recognition of his work on
the Cretaceous stratigraphy and palaeontology of the Pacific
Coast of North America.
Type species: Trigonia hemphilli Anderson 1958: 115, pl.
52, fig. 9; s
AuL
1978: 50, pl. 10, figs. 2-9, pl. 11, figs. 3, 6,
text-figs. 8, 19; by original designation herein.
Popenoella hemphilli (Anderson, 1958)
Fig. 6N, O
Diagnosis of genus: Like Yaadia but with rounded antero-
lateral margin, umbones positioned further back, anterior
face not flattened, rounded anterolateral shoulders without
enlarged tubercles; narrow shallowly-sunken escutcheon
smooth (primitive), or with strong subtransverse costellae
continuous from area (derived); very large ligament nymph;
juvenile ribbing of area may form complicated chevrons;
nodate marginal carinae evanescing in later growth. Late
Turonian – Early Maastrichtian.
Referred species: P. branti sAuL (1978: 43, pl. 7, figs.
3-10, pl. 8, fig. 1, pl. 11, fig. 5, text-fig. 16), P. californiana
(P
AcKArd
1921: 17, pl. 2, fig. 2; s
AuL
1978: 39, pl. 5, figs. 5-8,
pl. 6, figs. 1, 2, pl. 11, fig. 4, text-fig. 14), P. pinea s
AuL
(1978:
42, pl. 6, figs. 3-6, pl. 7, figs. 1, 2, text-fig. 15), P. robusta
(sAuL 1978: 47, pl. 9, figs. 2-4, 6, text-fig. 18), P. tryoniana
(gABB 1864: 188, pl. 25, fig. 176; WhiteAves 1879: 161, pl.
18, fig. 7; P
AcKArd
1921: 19, pl. 4, fig. 4; s
AuL
1978: 45, pl. 8,
figs. 2-7, pl. 9, fig. 1, text-fig. 17).
Discussion: Popenoella n.g. is endemic to the Cordilleran
Province (northern California, Oregon, British Columbia),
quite obviously with an origin in Yaadia. s
AuL
(1978: 27)
declined to name this group on the grounds that “…it tends
to obscure their direct relationship to Yaadia”. The writers
have the opposite view, that this genus is necessary to taxo-
nomically reflect the significant evolutionary change within
this lineage. Quite obviously the primitive species more-
closely approach ancestral Yaadia, but the two genera be-
come increasingly divergent with time so that Maastrichtian
P. hemphilli is very different from Y. lewisagassizi and Y.
jonesi. Its sparser costation and coarse flank tubercles im-
mediately distinguish it from Louella n.g.
KoBAyAshi & AmAno (1955: 193) considered the species
californiana, tryoniana, fitchi, leana and whiteavesi an en-
demic group closely allied to, but distinct from, Japanese
Yeharella. They distinguished the North American group as
a “Packardella section” in which “” the effacement of the
sculpture was more advanced” (p. 198). While we recognize
this grouping also, unfortunately they failed to designate a
type species and their name is a nomen nudum.
The holotype of P. tryoniana (gABB) has a very dif-
ferent aspect to the other species of Popenoella n.g., with
subdued flank ornament and two conspicuous radiating
grooves which correspond to the antecarinal sulcus and the
longitudinal furrow to the area. This is due to exfoliation of
the outermost shell layer (cf. s
AuL
1978). Likewise the lost
holotype of P. californiana (P
AcKArd
) also seems to have had
the outermost shell layer exfoliated, and problems associated
with its identification were dealt with by sAuL (1978).
Fig. 6. A, B – Yaadia lewisagassizi c
ricKmAy
; A, the holotype after c
ricKmAy
(1932); B, a reconstruction after s
AuL
(1978). C.
Yaadia jonesi s
AuL
, a restoration. D – Yaadia whiteavesi (P
AcKArd
), the lectotype designated herein, after P
ouLton
(1977). E,
H, I, M – Louella fitchi (PAcKArd). E, cast of the holotype, UO-26859; H-I, cast of the paratype, UO-26910; M, the holotype
of Trigonia branneri Anderson, after Anderson (1958). F, G – Yaadia leana (gABB), USNMNH-241677, a juvenile showing
the bar-like ribs to the outer area and inner escutcheon, an apomorphic character for Yaadiinae. J – Pseudoyaadia hennigi
(L
Ange
), the unnumbered SAM specimen figured by r
ennie
(1936) from the Barremian of Zululand. K, L – Scaphotrigonia
navis (L
AmArcK
), an unnumbered BMNH specimen. N-O – Popenoella hemphilli (A
nderson
), the holotype, after A
nderson
(1958).
eschweizerbart_xxx

330 M.R. Cooper and H.A. Leanza
Genus Louella nov.
Etymology: For Dr LoueLLA r. sAuL (Los Angeles County
Museum), eminent American malacologist and monographer
of the genus Yaadia.
Type species: Trigonia fitchi PAcKArd 1921: 20, pl. 6, fig. 3,
pl. 7, fig. 2; = T. branneri Anderson 1958: 112, pl. 17, fig. 5
(Fig. 6M); by original designation herein.
Louella fitchi (PAcKArd, 1921)
Fig. 6E, H, I, M
Diagnosis for genus: Moderately large, elongate-subovate,
with insignificant subterminal umbones and convex anterior
margin; anterior face fastigiate; respiratory margin obliquely
subtruncate; long posterodorsal margin straight shallowly
sunken; escutcheon large, shallowly sunken, in early growth
with bar-like transverse costae (primitive) or fine oblique
costellae continuous from area (derived), later unornament-
ed and not discriminated from area, fastigiate on conjoined
valves; inner carina non-tuberculate, marked only by change
in slope; area broad, convex, with fine oblique costellae in
early growth; longitudinal furrow to area present only in
early growth; curved flank costae numerous, broader than
interspaces, with small uniform nodes, in later growth cut-
ting obliquely across the growth striae anteriorly and form-
ing zigzags ventrally. Early – Middle Turonian.
Description: The holotype is medium-sized (L = 68 mm),
elongate-ovate, strongly inequilateral, longer than high (H/L
= 0.81), inflated (W/H = 0.46), with low subterminal umbo-
nes. The subvertical anterior margin passes rapidly into the
moderately-convex ventral margin, the respiratory margin
is not preserved, but growth striae indicate it was obliquely
subtruncate, and the long posterodorsal margin is very-
shallowly sunken. The escutcheon is defined only in earliest
growth, with transverse bars, later not discriminated from
the area. The broad flat area has nodate carinae only in earli-
est growth, later with commarginal striae only. The flanks
are ornamented with 15 conspicuous, curved oblique cos-
tae, broader than the interspaces, bearing regularly-disposed,
crowded, small nodes. The holotype of T. b ran neri Anderson
shows the flank costae becoming zigzag anteroventrally in
later growth (Fig. 6M).
Referred species: L? jimboi (KoBAyAshi & AmA no 1955:
204, pl. 13, fig. 4).
Discussion: This genus is known with certainty only from
the Cordilleran Province (Oregon, northern California), but
may be present also in the Oriental Province (Japan). As
noted by s
AuL
(1978: 13), Trigonia fitchi “… is obviously not
a Yaadia”. She tentatively assigned it to Litschkovitrigonia,
but the latter is a member of Quadratotrigoniinae endemic
to the Central Asian Province with V-shaped flank costae
in early growth. The transverse bars to the escutcheon of L.
fitchi point to an origin in Yaadia.
Louella n.g. differs from Yaadia in its convex anterior
margin, fastigiate anterior face and posterodorsal region on
conjoined valves, round anterolateral shoulders without en-
larged tubercles, escutcheon non-discriminated in middle
to later growth, early loss of nodate carinae to the area, and
numerous, closely-spaced flank costae with crowded uni-
form nodes.
sAuL (1978: 53, pl. 12, figs. 2-7, text-fig. 20) figured
Turonian material from the Hornbrook Formation, Siskiyou
County, Klamath River, California, as L? fitchi. However, it
differs from the holotype of L. fitchi in having fine diago-
nal costellae to the escutcheon and area in early to middle
growth. Whether this is due to better preservation, or a dif-
ferent species is involved, remains to be determined.
Densicostate Steinmanella (Yeharella) jimboi KoBA-
yAshi & AmAno (1955: 204, pl. 13, fig. 4) is based on an
internal mould which has been assigned tentatively to
Litschkovitrigonia (sAuL 1978; tAshiro & morozumi 1982),
but the latter genus is an Asiatic endemic. Poor illustration
and inadequate description hinder proper identification of Y.
jimboi but dense geniculate ribbing suggests it may belong
here. Just as likely, however, the similarity could be due to
convergence.
Genus Yeharella KoBAyAshi & AmAno, 1955
Type species: Trigonia japonica y
ehArA
1923a: 10, pl. 6,
figs. 6, 7; 1923b: 83, pl. 12, figs. 3, 4; KoBAyAshi & AmAno
1955: 201, pl. 14, figs. 1-3, pl. 15, fig. 4; h
AyAmi
1975: 112,
pl. 5, fig. 12; = sanukiensis nAKAno 1958: 86, pl. 13, fig. 1;
by original designation.
Yeharella japonica (yehArA, 1923a)
Fig. 7
Diagnosis of genus: Moderately large to large, subquadratic
to subovate, longer than high, with low insignificant anterior-
ly-positioned umbones; anterior and ventral margins convex,
oblique respiratory margin gently convex, long posterodorsal
margin shallowly concave to straight; escutcheon narrow,
shallowly sunken, with oblique costellae meeting at com-
missure in posteriorly-directed chevrons; inner, median and
marginal carinae nodate in early to middle growth, evanesc-
ing later with rounding of marginal carina; broad bipartite
area with commarginal costellae in earliest growth, later with
growth striae only; narrow antecarinal space, evanescing in
later growth; strongly-curved nodate flank costae, narrower
than interspaces, most terminating along anterior commis-
sure, nodes tending to elongate and coalesce in later growth
to become segmented subcommarginal cords. Cenomanian
– Maastrichtian.
Referred species: Y. ainuana (yABe & nAgAo 1928: 84,
pl. 16, fig. 20; KoBAyAshi & AmA no 1955: 204), Y. deckeina
(KuBotA 1955: 14, pl. 1, figs. 1, 2; nAKAno 1958: 87, pl. 13,
fig. 2, pl. 14, fig. 1), Y. kimurai (toKunugA & shimizu 1926:
189, pl. 27, figs. 3, 4; KoBAyAshi & AmAno 1955: 205, pl. 13,
figs. 1, 2), Y. lymani (KoBAyAshi & AmAno 1955: 203, pl. 13,
fig. 3), Y. obsoleta (K
oBAyAshi
& A
mAno
1955: 202, pl. 14,
figs. 4, 5), Y. sinoharai (KoBAyAshi & AmAno 1955: 207, pl.
15, figs. 1-3; hAyAmi 1975: 114, pl. 5, fig. 13).
eschweizerbart_xxx

On the Steinmanellidae (Bivalvia: Myophorelloidea) 331
Fig. 7. Hypothesized relationships among species of Yeharella and Tashiroella n.g., adapted from tAshiro & KAno (1989)
and tAshiro (1992). Note the significant phenotypic discontinuity separating Cenomanian Yeharella ainuana (JimBo) and
Albian Yaadia whiteavesi (PAcKArd).
eschweizerbart_xxx

332 M.R. Cooper and H.A. Leanza
Discussion: Yeharella is an Oriental endemic (Japan).
KoBAyAshi & AmAno (1955) looked to Steinmanella for the
origin of the genus, whereas s
AuL
(1978) favoured Yaadia.
The writers reject the suggestion (sAuL 1978; tAshiro 1992)
that Yeharella is a synonym of Yaadia since it constitutes a
divergent Oriental group that evolved in parallel with other
steinmanellid lineages. According to t
Ashiro
& K
Ano
(1989)
Yeharella comprises 3 lineages (clades) which evolved in
parallel for much of the later Cretaceous, one of which is
here made the basis of a new genus. The taxonomic status of
the other two lineages remains to be determined.
Yeharella is first known from the Cenomanian-Turonian
(tAshiro 1988) and hence, if its ancestry lies in Yaadia,
must be sought in older species of Yaadia, in particular
the Albian-Cenomanian Y. whiteavesi (PAcKArd) (Fig. 6D).
However, the earliest Yeharella, Y. ainuana, differs mark-
edly from Y. whiteavesi in its smaller size, ovate shape, con-
vex anterior without flattened anterior face, lack of bar-like
transverse nodes to the inner area which persist as the inner
carina in middle to later growth, lack of enlarged tubercles
on the anterolateral shoulders and gap separating them from
the remainder of the flank, and fine oblique costellae to the
area and escutcheon. The differences point to a moderate
phenotypic discontinuity and derivation of Yeharella from
Yaadia is conjectural rather than compelling.
Barremian Pseudoyaadia hennigi (LAnge) is the only
Gondwanic steinmanellid that can be entertained as a can-
didate for the ancestor of Yeharella. However, it differs from
Y. a inua na in its large size, very robust shell, subrectangular
shape, with straighter more-distant flank costae with larger
well-discriminated nodes, prominent nodate inner carina
which persists almost to maturity, enlarged anterolateral
shoulder tubercles, and coarse transverse costellae to the es-
cutcheon. The two are separated by a moderate phenotypic
discontinuity and vastly disjunct distributions.
Steinmanella (Setotrigonia) KoBAyAshi & AmAno (1955)
was introduced as a monotypic subgenus for a species from
the Campanian of Japan. However, tAshiro & morozumi
(1982: 6, 7) pointed out that the holotype of S. sinoharai
(KoBAyAshi & AmAno) is based on the external mould of a
left valve, not a right valve as interpreted by KoBAyAshi &
AmAno (1955). Hence it is the anterior not posterior part of
a valve. Consequently they judged S. sinoharai “… not to be
so different from Yaadia japonica (y
ehArA
)”, which is from
the same stratigraphical level. Here Setotrigonia sinoharai
is considered a nomen dubium, and Setotrigonia is regarded
as a subjective junior synonym of Yeharella.
Genus Tashiroella nov.
Fig. 7
Etymology: For Professor mAsAyuKi tAshiro (Kochi
University), pre-eminent expert on Japanese Mesozoic bi-
valves.
Type species: Yaadia tanii t
Ashiro
& m
orozumi
1982: 5,
pl. 3, fig. 1; tAshiro 1992: 146, pl. 39, fig. 7; by original
designation herein.
Tashiroella tanii (tAshiro & morozumi, 1982)
Fig. 7
Diagnosis of genus: Like Yeharella but with very narrow,
short, unornamented escutcheon; nodate inner, median and
marginal carinae restricted to early growth (primitive) or
obsolete (derived); broad bipartite area unornamented; no-
date flank costae covering entire flank in early growth, eva-
nescing posteriorly in middle to later growth. Campanian
– Maastrichtian.
Referred species: T. koshikiana (tAshiro & KAno 1989: 7,
pl. 1, figs. 1-3, pl. 2, figs. 1-4, pl. 3, fig. 1, text-fig. 2; tAshiro
1992: 150, pl. 45, fig. 7, erroneously labelled Y. koshikiji-
mensis).
Discussion: Endemic to the Oriental Province (Japan). The
type species is markedly different from contemporaneous
species of Yeharella, i.e. Y. obsoleta (KoBAyAshi & AmAno)
and Y. japonica (yehArA), and Popenoella n.g., i.e P. hemp-
hilli (Anderson), and obviously represents the end members
of a different phyletic line. t
Ashiro
& K
Ano
(1989) looked to
Coniacian Yeharella kimurai (KoBAyAshi & AmA no) for the
origin of the genus, implying that Yeharella and Tashiroella
n.g. evolved in parallel for much of the later Cretaceous.
Acknowledgements
The writers are grateful to Drs noeL morris, ron cLeeveLy
and Jon todd (Natural History Museum, London), Mr
fred coLLier and the late Dr B.F. KensLey (Smithsonian
Institution, Washington), Dr herBi e KLinger (South
African Museum, Cape Town), Dr. LeAndro Pérez and Dr.
JAvi er echeverríA (Universidad Nacional de La Plata) and
Professors n
ormAn
m. s
AvAge
and W
iLLiAm
o
rr
(Eugene,
Oregon) who facilitated access to material in their care and
provided every assistance. Mrs E.H. g
reyLing
is thanked
for help with the photography, and A.M. r
ivoLtA
(MACN,
Buenos Aires) helped in different stages of this paper. Drs.
simon schneider and roBert W. scott reviewed the manu-
script, providing insightful comments which improved the
paper.
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Addresses of the authors:
m
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ooPer
, Durban Natural Science Museum, P/
Bag 4085, Durban 4001, South Africa;
e-mail: mikecooper1946@gmail.com
héctor A. LeA nzA, Departamento de Geología, Museo
Argentino de Ciencias Naturales, CONICET, Av. Angel
Gallardo 470, 1405 Buenos Aires, Argentina;
e-mails: hleanza@macn.gov.ar, hectorleanza@gmail.com
eschweizerbart_xxx

eschweizerbart_xxx