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ARTICLE
UTILITY AND VALIDITY OF MIDDLE AND LATE TRIASSIC
‘LAND VERTEBRATE FAUNACHRONS’
EMILY J. RAYFIELD,
1
PAUL M. BARRETT,
*,2
and ANDREW R. MILNER
2
1
Department of Earth Sciences, University of Bristol, Queens Road, Bristol BS8 1RJ, United Kingdom;
2
Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom;
P.Barrett@nhm.ac.uk
ABSTRACT—A tetrapod-based biochronologic framework for the terrestrial Triassic, which subdivides the Triassic into
eight ‘Land Vertebrate Faunachrons’ (LVFs), has been proposed and developed by Lucas and coworkers. In a recent
article, these authors reiterated their support for this scheme and used this opportunity to respond to criticisms dealing
with the validity and utility of Triassic LVFs. This article is a reply to Lucas and colleagues and demonstrates that many
aspects of this Triassic biochronology are dependent on: (1) subjective opinions regarding the taxonomic assignments of
key specimens; and (2) unjustified extrapolation of correlations on the basis of geographically restricted endemics.
Furthermore, it is suggested that the methodological basis for recognizing the onset of a particular LVF, the identification
of the ‘first appearance datum’ for those taxa deemed to be biochronologically significant, leads to imprecision in
correlation and potential ambiguity in dating. Finally, it is argued that geographic information systems are ideal tools for
testing biostratigraphic hypotheses.
INTRODUCTION
In a series of papers over the past two decades, Lucas and
coworkers proposed, developed, and refined a globally appli-
cable biochronologic framework for the terrestrial Triassic (e.g.,
Lucas, 1990, 1993, 1998; Lucas and Hunt, 1993; Huber et al.,
1993; Lucas et al., 2007a). This scheme is based on tetrapod
occurrences and subdivides the Triassic Period into eight Land
Vertebrate Faunachrons (LVFs): some of these are cross refer-
enced with the standard global chronostratigraphic scale by
means of fortuitous discoveries of index taxa in well-dated
marine deposits (Lucas and Heckert, 2000). The onset of each
LVF is characterized by the first appearance datum (FAD) of
a specific tetrapod taxon (termed the ‘FAD taxon’ hereafter)
and a series of index taxa have been proposed to character-
ize each LVF thereby permitting cross-correlation between
assemblages. The duration of each LVF is defined as the time
between the first appearance of the FAD taxon for that LVF
and the first appearance of the FAD taxon for the succeed-
ing LVF.
To test the utility of this biostratigraphic scheme, Rayfield
et al. (2005) used a geographic information system (GIS) to
analyze the spatial and temporal distribution of FAD taxa and
index taxa in the Middle and Late Triassic of western Europe
and North America and to test for environmental and facies
biases that might affect the utility of these tetrapods for bio-
stratigraphic correlations. This study concluded that several taxa
were either useful or potentially useful regional index fossils for
specific intervals (e.g., Eocyclotosaurus in the Anisian and some
aetosaurs and phytosaurs in the Norian and Rhaetian), in agree-
ment with the conclusions of Lucas and coworkers. However, it
was noted that in many cases the proposed FAD taxa and index
taxa were geographically restricted endemics that were not
appropriate for use in global correlations (Rayfield et al., 2005).
Furthermore, Rayfield et al. (2005) demonstrated that this Tri-
assic tetrapod biostratigraphic scheme was hampered by taxo-
nomic instability (caused by disagreement over taxon diagnoses
and specimen referrals) and the use of taxa with broad or poorly
constrained temporal distributions. Index taxa should, by defini-
tion, be widespread, abundant, easy to characterize, monophy-
letic, and temporally restricted (e.g., ammonites, conodonts,
palynomorphs, and graptolites). However, many of the taxa used
to support the Triassic LVF framework violate these established
criteria. Consequently, large-scale macroevolutionary or paleo-
ecological hypotheses and global biostratigraphic correlations
based on this scheme should be treated with caution (although
on some regional scales Triassic LVFs appear to have some
utility).
Lucas and coworkers recently provided an update on the
current status of their proposed Triassic biostratigraphy and
concluded that it remained “a robust tool for both global
and regional age assignment and correlation” (Lucas et al.,
2007a:229). In an Appendix to this article these authors provided
an extensive point-by-point rebuttal of Rayfield et al. (2005) and
stated that the conclusions of the latter study could be rejected
on the basis that it was “replete with factual errors, selective use
of the literature, misrepresentations, and misinterpretations”
(Lucas et al., 2007a:237). Here, we provide a reply to these criti-
cisms and accusations. We refrain from answering each of the 76
individual criticisms listed by Lucas et al. (2007a) as many of
these points are repeated within this list, or are merely opinions
advanced by Lucas and colleagues rather than factual inaccura-
cies (see below, for several examples). Rather, we will focus on
the broader conceptual issues highlighted by Lucas et al.
(2007a), namely the utility of GIS to assess biostratigraphy, the
concepts of LVFs and FAD taxa, supposed errors in taxonomic
records, taxonomic and temporal uncertainty regarding occur-
rences of FAD taxa and index taxa (including the issue of ‘cla-
dotaxonomic diagnoses’), and problems of endemism in global
correlation.
*
Corresponding author.
Journal of Vertebrate Paleontology 29(1):80–87, March 2009
#2009 by the Society of Vertebrate Paleontology
80
USE OF GEOGRAPHIC INFORMATION SYSTEMS
IN BIOCHRONOLOGY
Lucas et al. (2007a:237) stated that “GIS is not able to test
biochronology.” However, these authors provide no evidence
(or discussion) in support of this opinion. Geographic informa-
tion systems represent a well-established tool with the capability
to store, manage, visualize, and analyze spatial data (Burrough
and McDonnell, 1998; Longley et al. 2001) and GIS is beginning
to be used in various paleontological contexts (Barnosky et al.,
2005; Rode and Lieberman, 2005; Jennings and Hasiotis, 2006;
Oheim, 2007). Contrary to the assertion of Lucas et al. (2007a)
GIS lends itself well to testing biostratigraphic correlations, as
distributions of proposed index taxa in space, as well as time,
need to be determined to test their utility for correlations be-
tween, as well as within, regions. Use of GIS in this context can
demonstrate whether proposed index taxa or FAD taxa are suf-
ficiently widespread in a particular timeslice for use in global
correlation. Critically, we used GIS to analyse not only spatial
data, but also the temporal distributions of taxa. This was
achieved by timeslicing the spatial distributions of proposed
FAD taxa and index taxa within the GIS: this permitted us to
examine if these taxa were restricted to specific biochronologic
or chronostratigraphic intervals or if they had broader temporal
distributions. GIS was also used to analyze the spatial relation-
ships between different variables such as environment, facies,
fauna, and flora within the dataset in order to search for poten-
tial biases that may have distorted any potential biochronologi-
cal signals. Consequently, we argue that GIS is a powerful and
appropriate tool for testing LVF concepts (contra Lucas et al.,
2007a). Using these methods we were able to demonstrate that
many of the index taxa and FAD taxa that form the basis of
Triassic LVFs were either spatially restricted or had broad tem-
poral distributions, thereby undermining their utility in biostrati-
graphic correlations (Rayfield et al., 2005).
VALIDITY AND UTILITY OF LAND
VERTEBRATE FAUNACHRONS
The Faunachron Concept
Faunachrons are determined by the FADs of particular fossil
taxa. The end of a faunachron is determined not by the extinc-
tion of the FAD taxon for a particular LVF, but by the appear-
ance of the FAD taxon for the successive LVF (e.g., Lucas, 1998;
Lucas et al., 2007a). If FAD taxa were temporally distinct, this
would provide a clear division between LVFs and would form a
strong basis for the erection of a biochronologic scheme. In
many cases, however, the total ranges of FAD taxa from tempo-
rally adjacent LVFs overlap significantly, potentially blurring
the boundaries between these units for the following reasons.
First, the FAD definition will often lead to ambiguity in dating.
LVF determination is reliable when the younger FAD taxon
coexists with the preceding FAD taxon; however, if the younger
FAD taxon is absent for some reason (e.g., poor fossil record,
taphonomic bias), even in the presence of other index taxa for
the younger LVF, the assemblage would erroneously be assigned
to the older LVF. Second, to establish a reliable series of LVFs,
a substantially complete section is required in order to accurate-
ly record faunal succession through time and to document the
occurrences of the FAD taxa for each LVF. Where such sections
are available LVFs can indeed represent a robust local biochro-
nology, though caution is still necessary in their implementation
(e.g., Parker, 2006). However, such sections are generally rare
and many of the sedimentary sequences that have yielded Meso-
zoic terrestrial tetrapods are temporally and spatially fragmen-
ted. These sequences are often bounded by (or contain) hiatuses,
unconformities, or other types of non-comparable depositio-
nal units (e.g., marine units, volcanic units). Consequently,
correlations between geographically distant and/or incomplete
sequences can be problematic as it might be impossible to com-
pare them over a sufficiently long timescale to capture the ap-
pearance of successive FAD taxa. In addition, breaks within
sequences may obscure first appearances of FAD taxa, leading
to incorrect correlations. Thus, the FAD taxon concept may be
unreliable when attempting to date assemblages with a less than
complete fossil record. Finally, biostratigraphic frameworks
based on macrofossils are most robust when they can be tied to
the geologic timescale by independent lines of evidence, such as
radiometric dating or magnetostratigraphy, as in the example of
the widely used North American Land Mammal Ages (e.g.,
Woodburne and Swisher, 1995). However, independent age
assessments are conspicuously absent for many Triassic LVFs:
for example, independent dates for LVFs based on assemblages
from the southwestern USA are currently limited to one radio-
metric date (Riggs et al., 2003) and limited palynological corre-
lations (e.g., Litwin et al., 1991).
Different LVF definitions have been provided by Lucas and
coworkers over the past 10 years, thereby shifting the paradigm
that other workers need to test. For example, Lucas (1998:349)
stated “The type tetrapod assemblage is the primary basis
for characterization of the LVF”. In contrast, Lucas et al.
(2007a:237) state that LVFs “have a characteristic tetrapod as-
semblage, but they are not temporally coextensive with
assemblage zones of tetrapod fossils.” The latter argument is
nonsensical, however, because biostratigraphers routinely use
index fossils to correlate assemblages: moreover, this procedure
has been adopted frequently to strengthen the Triassic tetrapod
LVF framework (e.g., Lucas, 1998; Lucas et al., 2007a). To give
one example, Lucas et al. (2007a:238) used the following occur-
rence to provide a global correlation for the Anisian-aged Per-
ovkan LVF: “Were the Moenkopi erythrosuchid identified as
Shansisuchus, it would support a China-western North America
correlation, which is a global terrestrial correlation across Mid-
dle Triassic Pangea.” This correlation is not based on the FAD
taxon for the Perovkan LVF (the temnospondyl Eocycloto-
saurus), but on one of the proposed index taxa for this assem-
blage, the archosaur Shansisuchus. As a result, Lucas et al.
contravene their own protocols (2007a:237), by relying on index
taxa (which are potentially more broadly distributed in time) to
identify a LVF correlation between these regions. Moreover,
this example also highlights another key problem with
LVF index taxa, which is that they are frequently subject to
conflicting taxonomic assignments (see below for more exam-
ples). In this particular case, the proposed correlation hinges on
the assignment of the ‘Moenkopi erythrosuchid’ to the Chinese
taxon Shansisuchus. If this referral is correct, then it might sup-
port a global correlation if index taxa are accepted as useful in
this respect. However, Nesbitt et al. (2006), a paper that includes
Lucas as a coauthor, noted that this specimen lacks diagnostic
features, and identified the material as an indeterminate basal
archosauriform, severely undermining this proposed global cor-
relation.
Taxonomic Uncertainty
Rayfield et al. (2005) highlighted many instances of taxonomic
uncertainty in discussions of Triassic tetrapod LVFs and demon-
strated that this was a major problem for the global utility of this
scheme. Lucas et al. (2007a) drew attention to a total of 13 errors
in the Rayfield et al. database relating to either incorrect age or
locality assignments for various index taxa and suggested that
these errors cast doubt on the validity of the conclusions in the
latter study. Although we are willing to concede that some errors
may have been inadvertently incorporated into our database, it
should be noted that these errors (where substantiated) should
be viewed in the context of a data compilation that included over
RAYFIELD ET AL.—TRIASSIC TETRAPOD BIOSTRATIGRAPHY 81
1800 individual entries: as a result, such errors are unlikely to
substantively undermine the overall conclusions of our previous
study. Moreover, as we discuss below, many of these alleged
errors are the result of taxonomic uncertainty, including conflicts
between authorities over issues of taxonomic splitting/lumping
and the validity of key taxa (see below). We stand by our origi-
nal conclusion that taxonomic instability hampers the use of the
Triassic LVF scheme at a global and, in some instances, regional
level and illustrate these issues with several examples.
Lucas’ use of temnospondyls as the basis of faunachrons and
his selective citation and use of literature is a case in point. Much
of this concerns the use of Mastodonsaurus as both an FAD
taxon and an index taxon for the Berdyankian (Ladinian-aged)
LVF, and Metoposaurus as an index taxon for the early Carnian-
aged Otischalkian LVF. Despite the fact that highest occur-
rences are not critical to the concept of LVFs, Lucas et al.
(2007a) have particular problems with late records of both these
genera, presumably because these reduce their resolution as in-
dex taxa. The following observations focus on Mastodonsaurus
as an example of the eclectic citation of taxonomic work on this
genus by Lucas et al.(2007a). The controversies relating to
Metoposaurus will be discussed fully by ARM and R. R. Schoch
elsewhere.
The Mastodonsauridae sensu stricto are restricted to the Tri-
assic of Eurasia and range from the early Anisian Upper Bunt-
sandstein to the late Carnian Schilfsandstein. The family was
founded on the basis of Ladinian material of Mastodonsaurus
giganteus, first named in 1828, but the description of an Anisian
mastodonsaurid in 1923 has generated an unresolved splitting-
lumping division in the literature. Wepfer (1923) described his
new taxon as Mastodonsaurus cappelensis and this was followed
by Romer (1947), Welles and Cosgriff (1965), Paton (1974),
Milner et al. (1990), and Damiani (2001). Sa
¨ve-So
¨derbergh
(1935) separated the Anisian material as the new genus Hepta-
saurus and was followed in this by Ochev (1966), Kamphausen
(1989), Maryanska and Shishkin (1996), Schoch (1999), and
Schoch and Milner (2000). However, Schoch (1999:27) did not
actually study Wepfer’s surviving material (much was destroyed
in WW2) as part of his revision of Mastodonsaurus, noting it as a
future project. The differential diagnosis of Heptasaurus is based
on very few features, some of which may be size-related, because
M./H. cappelensis attained only 50 cm skull length at the type
locality whereas M. giganteus grew to 1.25 m in length. Damiani
(2001) could distinguish the two species only on orbit shape and
size and Schoch (1999), despite maintaining separate genera,
could distinguish them only on orbit shape, snout breadth, and
centrum shape: all of these character-states could be size-linked.
Damiani (2001:410) observed that the genera appeared to have
been maintained on stratigraphic grounds as much as morpho-
logical grounds. This is where the use of Mastodonsaurus as a
basis for an LVF becomes highly problematic, due to the invoca-
tion of circular reasoning.
Lucas (1998, 1999) has based the Berdyankian LVF on the
‘splitters’ interpretation of the European mastodonsaurids, i.e.,
the earlier Heptasaurus succeeded by the later Mastodonsaurus.
In the ‘lumpers’ interpretation, the FAD of Mastodonsaurus,
defining the Berdyankian LVF, occurs in the Upper Buntsand-
stein and coincides with the FAD of Eocyclotosaurus, which
defines the preceding Perovkan LVF. All Anisian mastodon-
saurid material would then fall within the genus Mastodonsaurus
and the Perovkan and Berdyankian LVFs would either become
synonymous or require profound redefinition. Only by treating
all Anisian mastodonsaurid material as either Heptasaurus or
indeterminate, can this family be used to distinguish Perovkan
and Berdyankian LVFs. This appears to be the basis of Lucas
et al.’s (2007a:points 8 and 33 [in part]) rejection of the presence
of Mastodonsaurus in the Anisian Bromsgrove Sandstone
Formation of England as not ‘verified’ (their point 8) or
‘documented’ (their point 33), Paton’s (1974) description appar-
ently not qualifying as documentation. Their statement appears
to be an act of faith that, because this material has not been
rigorously revised post-Schoch (1999), it will never be assignable
and, if it is, it will prove not to be Mastodonsaurus. In fact,
Schoch (1999:27) commented that the circumorbital fragments
of the Bromsgrove Sandstone mastodonsaurid described by
Paton (1974:figs 5 and 7b) resemble those of M. giganteus more
than the generalised condition in H. cappelensis. Schoch also
noted that, although H.cappelensis is not known from skulls
longer than 50 cm in the type assemblage, massive mastodon-
saurid material of M. giganteus size does occur in the Anisian of
Germany: for example, ‘Mastodonsaurus ingens’ described by
Trusheim (1937) from the Anisian of Gambach is a mandible
from a 90 cm long skull that was assigned to Heptasaurus
cappelensis purely on the basis of stratigraphy rather than
morphology. If the situation exists that Anisian M. giganteus-like
material is being assigned to Heptasaurus on stratigraphic
grounds, it can hardly be satisfactory to use Heptasaurus and
Mastodonsaurus as biochronological markers even if one does
accept that the trivial differences between them might merit
generic separation.
Lucas et al.’s (2007a) assertion (their overlapping points 9 and
33), that there are no records of Mastodonsaurus in the late
Carnian Schilfsandstein, cannot be reconciled with the available
data as published or observed by ARM and R. Schoch. The
taxon Mastodonsaurus keuperinus was described from the Schilf-
sandstein by Fraas (1913) and although some of Fraas’s speci-
mens have proved to be indeterminate (Schoch, 1999:26; Schoch
and Milner, 2000:143), the snout tip (Staatliches Museum fu
¨r
Naturkunde Stuttgart specimen 4947) has been prepared further
and is indistinguishable from that of Mastodonsaurus giganteus
(Schoch and Milner 2000:143): moreover, the specimen and tax-
on was synonymised by Damiani (2001) with M. giganteus. The
basis for Lucas et al.’s rejection of a Schilfsandstein Mastodon-
saurus is not stated; either they were unaware of this specimen
and associated literature or they believed it to be indeterminate.
Given that the specimen is from the same basin as M. giganteus,
is from a succeeding horizon, and is morphologically indistin-
guishable from Mastodonsaurus, there seems no logical basis
other than for it to be a relict Mastodonsaurus. This falsifies
their points 9 and 33 (in part) and it makes Mastodonsaurus an
imperfect index fossil for the Berdyankian in that it extends into
the Adamanian (late Carnian) LVF.
The twin problems of taxonomic consensus and degree of
endemism also bedevil Lucas’s (1998) confident use of Masto-
donsaurus to characterise and correlate the Berdyankian LVF
across Europe and Russia, because there is no general agree-
ment on the generic status of the Russian material described as
Mastodonsaurus torvus. This was named as a species of Masto-
donsaurus by Konzhukova (1955) and referred to that genus by
Ochev (1972), Schoch and Milner (2000), and Damiani (2001).
However Novikov and Shishkin (1992) and Maryanska and
Shishkin (1996:74) treat it as a new genus to be redescribed. This
has not happened, but Shishkin’s 48 years of research on Triassic
temnospondyls would suggest that this is a serious alternative.
Damiani’s (2001) continued ‘lumping’ of the Russian material
with M. giganteus, uses criteria that also apply to the Anisian
material so that acceptance of the Russian material as Masto-
donsaurus would also entail acceptance of the Anisian material
as such. Thus, the status of the Russian mastodonsaurid material
is not sufficiently resolved that it can form the safe basis for
correlation of an LVF.
The general problem with use of the genus Mastodonsaurus
for biochronological purposes is that Schoch’s (1999) detailed
revision of the Ladinian M. giganteus has not been followed by
comparable revisions of the earlier and later German material
or the Russian material. The generic status of these other
82 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 29, NO. 1, 2009
assemblages is a matter of historical accident and expediency
rather than recent rigorous taxonomic analysis. Lucas (1998,
1999; Lucas et al., 2007a) has taken an eclectic selection of the
mastodonsaurid literature that supports the geographical ‘lump-
ing’ and chronological ‘splitting’ that his biochronological pro-
posal requires. Lucas et al. (2007a) use the terms ‘verified/
unverified’ and ‘documented’ in a self-serving manner to distin-
guish between the taxonomic observations that support the Ber-
dyankian LVF, and those that do not.
Other classic examples of taxonomic conflict that have had
crucial importance to LVF definitions concern the lumping or
splitting of the phytosaur Pseudopalatus (=Redondasaurus?) and
the aetosaur Typothorax coccinarum (=Redondasuchus reseri?).
‘Pseudopalatus-grade’ phytosaurs are considered index taxa of
the Norian-aged Revueltian LVF. Several authorities contend
that Pseudopalatus can be distinguished from Redondasaurus,
the FAD taxon of the proceeding Rhaetian-aged Apachean
LVF, by the morphology of the supratemporal fenestrae: the
fenestrae are visible in dorsal view in Pseudopalatus, but are not
visible in Redondasaurus (Hunt and Lucas, 1993a; Hungerbu
¨h-
ler, 2002; Spielmann et al., 2006a). Conversely, other workers
have concluded that the type specimen of Redondasaurus is
merely a poorly preserved skull of Pseudopalatus, rending the
former a junior synonym of the latter (Long and Murry, 1995).
Hungerbu
¨hler et al. (2003) supported the latter conclusion, on
the basis of a skull referred to Pseudopalatus that possesses
supratemporal fenestra morphology intermediate between that
of Pseudopalatus and Redondasaurus. If accepted, this synonymy
would undermine the utility of Redondasaurus as an FAD taxon
for the Apachean, as it would (by definition if included in the
same genus) represent another ‘Pseudopalatus-grade’ phytosaur,
a ‘taxon’ that is proposed to be diagnostic for the earlier Revuel-
tian LVF.
Similarly, the aetosaur Redondasuchus reseri, another index
taxon of the Apachean LVF, is also subject to taxonomic insta-
bility. Long and Murry (1995) considered this taxon to be a
synonym of Typothorax coccinarum, which would extend the
range of T.coccinarum, (the FAD taxon of the Revueltian) into
the Apachean, rendering both of these LVFs unstable. More-
over, Martz (2002: see also Parker, 2007) suggested that R.reseri
may represent a separate species of Typothorax –T.reseri (thus
preserving its biostratigraphic utility), while Spielmann et al.
(2006b) have asserted that Redondasuchus is a valid genus.
These taxonomic disagreements hinge largely on the semantics
of the degree of ‘arcing’ or ‘flexure’ of the osteoderms and on
the size of the specimens. However, is has been shown that the
degree of osteoderm curvature varies throughout the aetosaur
carapace within individuals (e.g., Parker, 2007). Moreover, as
Redondasuchus is smaller than adult Typothorax it is conceiv-
able that the former taxon represents juvenile individuals of the
latter. Given this taxonomic instability, and the fact that both
taxa are restricted to the western United States, the Apachean
LVF is certainly problematic for global biochronological corre-
lation, as also admitted by Lucas et al. (2007a:232).
Some of the taxonomic criticisms levelled at Rayfield et al.
(2005) are either in error or conflict with other published opi-
nions. For example, Lucas et al. (2007a:238) stated that, in con-
trast to the Rayfield et al. (2005) database, “Typothorax
coccinarum (indeed, no aetosaur) has ever been documented
from the Sloan Canyon Formation.” However, both Hunt and
Lucas (1989) and Long and Murry (1995:101, 218 and 235) list
Typothorax from Wedding Cake Butte, Sloan Canyon, Big
Cimarron Valley, Union County, New Mexico (this record is
also referred to as an indeterminate aetosaur by Hunt and Lucas
[1993b]). A further criticism of the database states that “There
are no records of Typothorax coccinarum in the Trujillo Forma-
tion” (Lucas et al., 2007a:238), yet Lucas et al. (2002) explicitly
assign osteoderms from the Trujillo Formation in east-central
New Mexico to T.coccinarum and note that this material is the
“stratigraphically lowest occurrence (LO) of that taxon” (Lucas
et al. 2002:221 and 230) and further state that “Hunt (1991,
2001a,b) also discussed MDM [Mesalands Dinosaur Museum]
specimens of T.coccinarum from the Trujillo Formation”. Simi-
larly, Lucas et al. (2007a:238) claim that T.coccinarum is absent
from the Tres Lagunas Member of the Santa Rosa Formation:
however, Long and Murry (1995:234) note such an occurrence.
Hunt and Lucas (1995; see also Lucas et al., 2002) dismissed the
Tres Lagunas record, suggesting it was from the Garita Creek
Formation. However, the material mentioned by Long and
Murry (1995) is an unnumbered specimen housed in the Univer-
sity of New Mexico (UNM), whereas the specimens that Hunt
and Lucas (1995; Lucas et al., 2002) discuss are in the collections
of the New Mexico Museum of Natural History and Science (the
latter specimens also listed by Long and Murry [1995], who
correctly attribute them to the Garita Creek Formation). Hunt
and Lucas (1995; Lucas et al., 2002) do not mention the UNM
specimen in their discussions, perhaps suggesting that the latter
authors have overlooked the Tres Lagunas record. This under-
scores the difficulty of sourcing information on some of the
rapidly changing taxonomic identities applied to material that
plays a prominent role in establishing LVF correlations. Finally,
some records have been reassigned to other species at a later
date: for example, T. coccinarum from the Garita Creek Forma-
tion (Hunt and Lucas, 1995; Long and Murry, 1995) was
renamed T. antiquum by Lucas et al. (2002) and this new species
was later proposed as the FAD taxon of the Lamyan sub-LVF, a
subdivision of the Adamanian LVF (Hunt et al., 2005). How-
ever, reinterpretation of the T. antiquum type material led Park-
er (2006) to conclude that the two Typothorax species were
synonymous. If this synonymy is accepted it extends the strati-
graphic range of Typothorax into strata that Lucas and collea-
gues consider Adamanian in age (Hunt et al., 2005), weakening
the use of this aetosaur as the FAD taxon of the Revueltian and
also rendering the Lamyan sub-LVF redundant (Parker, 2006;
see also Irmis, 2005).
Given that serious taxonomic issues, such as those outlined
above, surround many of the FAD and index taxa that define
the Triassic LVF framework, we suggest that a high proportion
of these taxa are unsuitable for use in biostratigraphic correlation
(see Rayfield et al. [2005] for additional examples). Taxa used
in correlations should be easy to distinguish to avoid ambiguity in
the resulting age assignments. This is especially true given the
difficulties in reliably identifying the isolated and often fragmen-
tary specimens that usually form the basis for these correlations.
Lucas et al. (2007a,b) reject the practice of ‘cladotaxonomy,’
which they define as the diagnosis of taxa within a phylogenetic
context. However, these authors conflate the generation of phy-
logenetic hypotheses and the consequent recognition of mono-
phyletic clades of taxa with the practice of alpha taxonomy,
whereas these are actually logically independent activities. Al-
though Lucas et al. are correct to infer that many systematists
use phylogenetic analyses to provide a context for taxonomy,
they seem not to appreciate that autapomorphies are phylogen-
etically uninformative characters that are not dependent on tree
topology. Recognition of this distinction would remove most of
Lucas et al.’s (2007a,b) objections to cladotaxonomy, which
seem to stem largely from a general mistrust of parsimony-based
character analysis and the cladograms such analyses generate
(e.g., Heckert and Lucas, 2003, 2006). Moreover, these authors
offer the observation that cladograms ignore variation in char-
acters, but are apparently unaware that there are ways of scoring
characters to incorporate this information (e.g., Wiens, 1999;
Harris et al., 2003a,b). Instead, these authors advocate less rigor-
ously defined taxon definitions that are rooted in more general
phenetic resemblances and that do not necessarily define
taxa as discrete monophyletic units, a standpoint that fuels
RAYFIELD ET AL.—TRIASSIC TETRAPOD BIOSTRATIGRAPHY 83
disagreements over taxon validity between Lucas and coworkers
and other specialists working on Triassic tetrapods.
One such example concerns confusion over phytosaur speci-
mens that have been referred to the taxa Paleorhinus and Para-
suchus (Hunt and Lucas, 1991; Lucas et al., 2007b). Hunt and
Lucas (1991) synonymized many phytosaur genera and species
from the USA, Germany, Morocco, and India with Paleorhinus,
a genus based on material from the Popo Agie Formation in
Wyoming, and suggested that Paleorhinus could be used as a
global FAD taxon for the Otischalkian LVF. These referred taxa
included the Indian genus Parasuchus (Lydekker, 1885), which
Hunt and Lucas (1991) regarded as a nomen dubium (however,
it should be noted that nomina dubia cannot be referred to other
taxa as, by definition, they should lack identifying features).
Subsequently, a neotype specimen was proposed for Parasuchus
(Chatterjee, 2001) and this better material allowed more explicit
comparisons with Paleorhinus. Following this nomenclatural re-
vision, Lucas et al. (2007b) retained the named species of Paleor-
hinus but referred them to Parasuchus and argued that the latter
genus could be identified on the basis of four diagnostic charac-
ters relating to the nares, orbit shape, and quadrate foramen.
One of these characters (external nares positioned rostral to the
antorbital fenestra) was used by Hunt and Lucas (1991) to refer
a partial phytosaur snout from the well-dated late Carnian
Opponitzer Schichten of Austria to Parasuchus (‘Paleorhinus’):
this referral allowed these authors to link Parasuchus to the
global standard timescale and provide a date for the Otischalk-
ian LVF. However, none of the diagnostic features of Parasu-
chus listed by Hunt and Lucas (1991: see also Lucas et al., 2007b)
are autapomorphies and all have a wider distribution among
basal phytosaurs and other archosaurs (e.g., Padian, 1994; Irmis,
2005; Fara and Hungerbu
¨hler, 2000; Hungerbu
¨hler, 2001a; H.-D.
Sues, pers. comm., 2004): as a result the monophyly of Parasu-
chus has not been established. As the fragmentary specimen
from the Opponitzer Schichten can only be identified on the
basis of an archosaur symplesiomorphy it could be referable to
any non-phytosaurid phytosaur (Hungerbu
¨hler, 2001b), thus sev-
ering the only link between the FAD taxon of the Otischalkian
and the marine record. Moreover, Hungerbu
¨hler (2001a) sug-
gested that the taxonomic status of Paleorhinus was ambiguous,
as the genotype specimen is poorly preserved and possesses no
clear autapomorphies that could be used to support either its
recognition as a valid taxon distinct from other basal phytosaurs
or its proposed synonymy with Parasuchus. This conclusion
would also invalidate the use of Paleorhinus as a FAD taxon for
the Otischalkian. Finally, it is notable that a specimen referred
to Paleorhinus has been discovered in the Cooper Canyon For-
mation of Texas (Lehman and Chatterjee, 2005), a unit that is
regarded as Revueltian in age, emphasizing the potentially
broad temporal distribution of this taxon.
Opinions on the validity (or not) of the species previously
referred to Paleorhinus are currently deadlocked, a situation
that will only be resolved by either acceptance of the ‘cladotaxo-
nomic’ concept by Lucas and coworkers, or by a revision of the
genus Parasuchus/Paleorhinus that identifies either autapomor-
phies or a unique combination of character states that the major-
ity of phytosaur workers would regard as diagnostic. Lucas et al.
(2007a) censure Rayfield et al. (2005) for following the ‘clado-
taxonomic approach.’ However, we believe that taxa should be
distinguished on the basis of clear autapomorphies or unique
character combinations to ensure their distinctiveness and valid-
ity. This is especially important where such taxa should be easily
and unambiguously identifiable, as in biostratigraphic schemes,
as it will prevent confusion and enhance precision.
Finally, many of the proposed correlations that underpin the
global Triassic LVF framework (Lucas, 1998; Lucas et al., 2007a)
are based on the identification of FAD taxa or index taxa that
are ‘grade-level’ referrals that equate to the use of paraphyletic
taxa: for example, ‘Rutiodon-grade’ phytosaurs have been used
to determine the Adamanian LVF (however, it should be noted
that no other workers recognize the presence of Rutiodon in
North America: Long and Murry [1995; see also Hungerbu
¨hler,
2000] referred ‘Rutiodon’ material from the southwestern USA
to Leptosuchus, while the type species Rutiodon carolinensis,
from the eastern USA, has been synonymized with Angistorhi-
nus [Hungerbu
¨hler and Sues, 2001]). This practice stems, at least
in part, from rejection of ‘cladotaxonomy.’ Lucas et al.
(2007a:238) admit that such correlations are “less than desir-
able,” but frequently use this reasoning (see Lucas et al.
2007a:233). Rayfield et al. (2005) noted that grade-level correla-
tions are weak and inappropriate for high-resolution biochronol-
ogy, a conclusion that we reiterate here. Paraphyletic taxa can
create major problems in biostratigraphic correlations by arbi-
trarily including or excluding specimens from consideration.
Such taxa are, by definition, weakly defined morphologically as
they are based on a plexus of taxa, rather than a single taxon. In
addition, specimens referred to ‘grade-level’ taxa are usually
identified on the basis of gestalt, rather than rigorously defined
diagnostic features, increasing the probably of errors in identifi-
cation. Consequently, there is no guarantee that all specimens
referred to a paraphyletic taxon represent the same biological
entities as the proposed index taxon (see Angielczyk and Kur-
kin, 2003). Finally, paraphyletic taxon may exist over much lon-
ger timescales than either FAD taxa or index taxa due to their
incorporation of several lineages, severely reducing chronologic
accuracy.
Endemism
The aim of the Triassic LVF system is to create a global
biochronologic framework. However, many of the proposed in-
dex taxa and FAD taxa are endemic to the United States or
southern Africa, and this is obviously problematic for global
correlations. For example, until recently, the Russian dicynodont
Shansiodon was the FAD taxon for the Anisian-aged Perovkan
LVF (e.g., Lucas, 1998). However, difficulties in dating the Rus-
sian sequences led Lucas et al. (2007a) to propose Eocycloto-
saurus, from the early Anisian of western Europe and North
America, as a replacement FAD taxon for this LVF. Given the
limited European and North American distribution of Eocyclo-
tosaurus, correlations with assemblages in China and Russia are
inherently weak, especially if the ‘Moenkopi erythrosuchid’ is
not referable to the Chinese erythrosuchid Shansisuchus (Nes-
bitt et al., 2006: see above). Furthermore, Lucas et al. (2007a)
reiterate that there are no Berdyankian (late Ladinian to early
Carnian-aged) assemblages in North America and three of the
five Berdyankian index taxa are endemic to South America
(German and Russian records of two of these taxa, Dinodonto-
saurus and Stahleckeria are non-diagnostic: King, 1988; Lucas
and Wild, 1995). Therefore global correlation of both Middle
Triassic LVFs is untenable (see Rayfield et al., 2005).
Of the proposed index taxa for the Otischalkian LVF, Dos-
wellia is known only from the USA (but may be useful for
correlation between the western and eastern USA, if not for
global correlations), and Longosuchus occurs in an even more
restricted geographical area (parts of Texas: Long and Murry,
1995). Previous attempts to extend the geographical range of the
latter taxon are no longer considered valid as material previously
referred to Longosuchus from North Carolina can be distin-
guished as the genus Lucasuchus based on paramedian osteo-
derm morphology (Parker, 2007). A further record of
Longosuchus/Lucasuchus from Morocco (Lucas, 1998) does not
possess any diagnostic characters of this taxon (W. G. Parker,
pers. comm., 2007). As discussed above, the taxonomy of the
Revueltian forms Typothorax coccinarum and Pseudopalatus is
contentious: furthermore, these taxa are also geographically
84 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 29, NO. 1, 2009
restricted to the western USA. As a result, even if a taxonomic
consensus were reached regarding the synonymy or separation
of these taxa, endemism would still prevent the use of these
species as the FAD taxon and index taxon of a globally applica-
ble Revueltian LVF. The same comments apply to the Apa-
chean LVF taxa Redondasaurus and Rendondasuchus (Rayfield
et al., 2005). Endemism severely undermines the global utility of
these Triassic LVFs, although in some cases they are potentially
useful within specific regions, such as the western USA.
Uncertainty in Temporal Ranges
One of the major problems with the Triassic LVF scheme
relates to discrepancies or ambiguities in the known temporal
ranges of some FAD and index taxa. These ambiguities often
arise as a result of taxonomic confusion, which results from the
use of index taxa that are inadequately diagnosed, paraphyletic
or identified on the basis of nondiagnostic material. An excellent
example of these issues is provided by discussions over the age
of the Bluewater Creek Member of the Chinle Formation (Lucas
et al., 2007a). Attempts to date this unit have been based on the
famous and extensively studied fauna recovered from the Pla-
cerias/Downs quarry in Arizona, which has yielded the remains
of Leptosuchus (‘Rutiodon’) the FAD taxon for the Adamanian
LVF, as well as Desmatosuchus haplocerus, which has been pro-
posed as index taxon for this interval (Hunt et al., 1993; Lucas
et al., 1997). Other members of the Bluewater Creek fauna
include the Otischalkian FAD taxon Parasuchus (‘Paleorhinus’)
and the Otischalkian index taxon Angistorhinus (Hunt et al.,
1993; Lucas et al., 1997). Lucas et al. (1997, 2007a) acknowledge
the contemporaneous occurrences of Otischalkian and Adama-
nian taxa in the Bluewater Creek Member and state that this
situation represents “what may be expected in as good a fossil
record as the Chinle Group” (Lucas et al., 2007a:231). However,
we argue that these temporal overlaps diminish the utility of
both sets of taxa as indicators of either Otischalkian or Adama-
nian time.
In an attempt to explain the combined occurrence of Parasu-
chus (‘Paleorhinus’) and Leptosuchus (‘Rutiodon’), Lucas et al.
(2007a:232 and 239) claimed that “The Bluewater Creek record
of Paleorhinus (=Parasuchus) may be Otischalkian”, based upon
the following reasoning. The aetosaur Stagonolepis was formerly
proposed as an Adamanian index taxon (e.g., Lucas, 1998) and
the Blasensandstein of Germany was considered to represent an
Otischalkian deposit based on the presence of Parasuchus
(Lucas, 1998:365). Subsequently, Heckert and Lucas (2000) re-
ferred Ebrachosaurus, from the Blasensandstein, to Stagonole-
pis, and argued for an Adamanian age for this deposit (Heckert
and Lucas, 2002). Stagonolepis has since been described from
purported Otischalkian-aged deposits in Poland (Dzik, 2001;
Dzik and Sulej, 2007; Lucas et al., 2007c), and this led Lucas
et al. (2007a) to reconsider the Blasensandstein as Otischalkian
in age and to conclude that Stagonolepis was, therefore, no lon-
ger an Adamanian index taxon (Lucas et al., 2007c:252). Howev-
er, as Stagonolepis had been stated to be present in Otischalkian
strata from Poland, Lucas et al. (2007a) concluded that the Blue-
water Creek Member may also be Otischalkian, thereby remov-
ing the problematic appearance of Paleorhinus in younger strata.
It is clear that such arguments are inherently circular and imply
that taxonomic assignments can be changed on the basis of pre-
ferred biochronologic interpretations. In addition, this line of
reasoning ignores the fact that the Bluewater Creek Member
yields specimens of the FAD taxon for the Adamanian (Lepto-
suchus). Following the criteria proposed by Lucas et al. (2007a),
the Bluewater Creek should be regarded as Adamanian in age,
as LVFs are defined by the first appearances of taxa (Leptosu-
chus) rather than the last appearances of the FAD taxa from the
preceding LVF (Parasuchus). As a consequence, Lucas et al.
(2007a) violate their own biostratigraphic criteria in an attempt
to circumvent problems caused by the mixture of taxa present in
the Placerias/Downs quarry.
Moreover, the utility of Stagonolepis as an index fossil is high-
ly problematic. Specimens referred to this taxon have been re-
covered from the Sonela Member of the Chinle Formation: this
unit also yields individuals of Typothorax coccinarum, which
suggests that Stagonolepis may range beyond the Adamanian
into the Revueltian LVF (Parker, 2006). Recent work on Stago-
nolepis has also demonstrated that the genus may be paraphy-
letic (Desojo, 2005; Parker, 2007) and thus unsuitable for global
correlation purposes. Finally, as defined by Lucas and cowor-
kers, Stagonolepis has a wide distribution in strata assigned to
both the Otischalkian and Adamanian LVFs (Rayfield et al.,
2005). Ironically, the problematic occurrence of Parasuchus in
the Bluewater Creek Member disappears if this record is
regarded as an indeterminate phytosaur (Padian, 1994; Irmis,
2005), but Lucas and coworkers do not accept this interpretation
and retain its identity as Parasuchus (e.g., Lucas et al., 2007a,b).
Angistorhinus,Leptosuchus, and Stagonolepis are not the only
taxa to occupy both Otischalkian and Adamanian LVFs. The
rhynchosaur Scaphonyx (now mostly referred to as Hyperodape-
don), which was originally considered to be an Adamanian index
taxon, is now known to have existed through a longer, well-
documented temporal range that is considered to represent an
extended time interval encompassing the Otischalkian and Ada-
manian (Lucas et al., 2002). On the basis of the aforementioned
evidence, we conclude that both of these LVFs are unstable and
that there is strong evidence for amalgamating the Otischalkian
and Adamanian (Langer, 2005; Rayfield et al., 2005).
CONCLUSIONS
In spite of claims to contrary (Lucas et al., 2007a), there is
currently little evidence to support the use of LVFs as the basis
for a stable global biochronologic framework during the Middle
and Late Triassic (see also Langer 2005; Rayfield et al., 2005).
Although Lucas et al. (2007a) provide an extensive critique of the
data presented by Rayfield et al. (2005) these objections do not
significantly alter or undermine the conclusions of the latter study.
Many of the criticisms listed by Lucas et al. (2007a) represent
idiosyncratic interpretations of taxonomic, stratigraphic, and
methodological issues that are not shared by other authors work-
ing on Triassic tetrapods (e.g., Long and Murry, 1995; Hungerbu
¨h-
ler, 2001a,b, 2002; Martz, 2002; Milner and Schoch, 2004; Irmis,
2005; Langer, 2005; Nesbitt et al., 2006; Parker, 2006, 2007; Schoch,
2007). Here, we clarify and validate the use of GIS in the testing of
biochronologic hypotheses and reiterate that the utility of Triassic
LVFs is undermined by continuing and fundamental problems.
These problems include: reliance on FAD and index taxa with
poor diagnoses and controversial taxonomies; uncertainty or ex-
tensive overlap in the temporal ranges of key taxa, which render
them unfit for use as time-restricted index fossils; and the ende-
mism of many proposed FAD and index taxa, which restricts their
utility to regional biochronologic correlations.
ACKNOWLEDGMENTS
We thank many colleagues for discussion on the issues raised
herein including (but not limited to) R. J. Butler, N. C. Fraser,
M. C. Langer, and H.-D. Sues. In particular we thank the refer-
ees, W. G. Parker and R. B. Irmis, for their extensive and helpful
comments on a previous version of this paper.
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RAYFIELD ET AL.—TRIASSIC TETRAPOD BIOSTRATIGRAPHY 87
