Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China

Abstract

During the last decade, abundant ichthyopterygian material has been found from the Triassic of South China as well as the Upper Jurassic and Lower Cretaceous of Europe and South America, significantly expanDing our knowledge of ichthyopterygian diversity through the Mesozoic. Previous phylogenetic hypotheses of the group no longer account for these extensive additions, necessitating a new phylogenetic framework for the entire Ichthyopterygia to enable evolutionary studies of the group. We present here a comprehensive phylogenetic hypothesis for Ichthyopterygia based on cladistic analysis of 163 characters coded for 59 ingroup and five outgroup taxa. The monophyly of Ichthyopterygia is strongly supported by a Bremer index value of 7. Five major groups of Ichthyopterygia during the Triassic, viz., Grippioidea, Cymbospondylidae, Mixosauridae, Shastasauridae, and Toretocnemidae, are well supported by Bremer index values between 3 and 5. Major clades that evolved in the Triassic, incluDing Merriamosauria, Euichthyosauria, and Parvipelvia, are also robustly supported, whereas most post-Triassic clades are very weakly supported with a Bremer index value of 1, with a few exceptions, such as Thunnosauria and Ophthalmosauridae. The traditional Shastasauridae is expanded to comprise six genera but excludes Callawayia, which is more closely related to Parvipelvia than to Shastasauridae. C. wolonggangensis is a shastasaurid but does not form a monophyletic clade with Callawayia neoscapularis or Guizhouichthyosaurus tangae as previously asserted. The new phylogenetic hypothesis is generally consistent with the stratigraphic occurrences of each taxon especially for the Triassic taxa.

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Journal of Vertebrate Paleontology
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Phylogeny of the Ichthyopterygia incorporating
recent discoveries from South China
Cheng Ji, Da-Yong Jiang, Ryosuke Motani, Olivier Rieppel, Wei-Cheng Hao &
Zuo-Yu Sun
To cite this article: Cheng Ji, Da-Yong Jiang, Ryosuke Motani, Olivier Rieppel, Wei-Cheng Hao
& Zuo-Yu Sun (2015): Phylogeny of the Ichthyopterygia incorporating recent discoveries from
South China, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2015.1025956
To link to this article: http://dx.doi.org/10.1080/02724634.2015.1025956
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ARTICLE
PHYLOGENY OF THE ICHTHYOPTERYGIA INCORPORATING RECENT DISCOVERIES
FROM SOUTH CHINA
CHENG JI,
1,2
DA-YONG JIANG,*
,2,3
RYOSUKE MOTANI,
4
OLIVIER RIEPPEL,
5
WEI-CHENG HAO,
2
and ZUO-YU SUN
2
1
Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese
Academy of Sciences, Nanjing 210008, People’s Republic of China, chengji@nigpas.ac.cn;
2
Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, Department of Geology and Geological Museum,
Peking University, Beijing 100871, People’s Republic of China, djiang@pku.edu.cn;
3
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of
Sciences, Nanjing 210008, People’s Republic of China;
4
Department of Geology, University of California, Davis, California 95616, U.S.A., rmotani@ucdavis.edu;
5
Section of Earth Sciences, Integrative Research Center, The Field Museum, Chicago, Illinois 60605-2496, U.S.A,
orieppel@fieldmuseum.org
ABSTRACT—During the last decade, abundant ichthyopterygian material has been found from the Triassic of South China
as well as the Upper Jurassic and Lower Cretaceous of Europe and South America, significantly expanding our knowledge of
ichthyopterygian diversity through the Mesozoic. Previous phylogenetic hypotheses of the group no longer account for these
extensive additions, necessitating a new phylogenetic framework for the entire Ichthyopterygia to enable evolutionary studies
of the group. We present here a comprehensive phylogenetic hypothesis for Ichthyopterygia based on cladistic analysis of 163
characters coded for 59 ingroup and five outgroup taxa. The monophyly of Ichthyopterygia is strongly supported by a Bremer
index value of 7. Five major groups of Ichthyopterygia during the Triassic, viz., Grippioidea, Cymbospondylidae, Mixosauridae,
Shastasauridae, and Toretocnemidae, are well supported by Bremer index values between 3 and 5. Major clades that evolved in
the Triassic, including Merriamosauria, Euichthyosauria, and Parvipelvia, are also robustly supported, whereas most post-
Triassic clades are very weakly supported with a Bremer index value of 1, with a few exceptions, such as Thunnosauria and
Ophthalmosauridae. The traditional Shastasauridae is expanded to comprise six genera but excludes Callawayia,whichismore
closely related to Parvipelvia than to Shastasauridae. ‘C.’wolonggangensis is a shastasaurid but does not form a monophyletic
clade with Callawayia neoscapularis or Guizhouichthyosaurus tangae as previously asserted. The new phylogenetic hypothesis is
generally consistent with the stratigraphic occurrences of each taxon especially for the Triassic taxa.
http://zoobank.org/urn:lsid:zoobank.org:pub:901B6FB6-2D80-4AE9-B017-A0226175AFDA
SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP
Citation for this article: Ji, C., D.-Y. Jiang, R. Motani, O. Rieppel, W.-C. Hao, and Z.-Y. Sun. 2015. Phylogeny of the
Ichthyopterygia incorporating the recent discoveries from South China. Journal of Vertebrate Paleontology. DOI: 10.1080/
02724634.2015.1025956.
INTRODUCTION
The Ichthyopterygia is a group of reptiles secondarily adapted
to aquatic life that spanned from the Early Triassic to early Late
Cretaceous (McGowan, 1991; Motani et al., 1996). Derived
members of the clade are known for their fish-shaped body pro-
files. The group has been known for over 200 years and is widely
distributed among multiple localities all over the world. Ich-
thyopterygians adapted to marine life through numerous
extreme modifications of the basic reptilian skeletal design,
which eventually led them to become the dominant marine pred-
ators in Mesozoic oceans. Cladistic reconstruction of ichthyop-
terygian phylogeny has been discussed since 1982, based on
selected taxa and characters (see Motani, 1999, and Maisch and
Matzke, 2000, for historical reviews). The first comprehensive
phylogenetic analyses of Ichthyopterygia were offered by Motani
(1999), Maisch and Matzke (2000), and Sander (2000), and many
analyses have been subsequently published for selected sub-
groups within the clade (Fern
andez, 1999, 2007; Nicholls and
Manabe, 2001; Fr€
obisch et al., 2006, 2013; Jiang et al., 2006;
Maisch et al., 2006; Druckenmiller and Maxwell, 2010; Maxwell,
2010, 2012; Caine and Benton, 2011; Fischer et al., 2011b, 2013,
2014; Thorne et al., 2011; Maxwell et al., 2012; Ji et al., 2013).
During the previous century, the number of reported Triassic
ichthyopterygians were fewer and not as well preserved com-
pared with those of post-Triassic forms. Although plenty of
specimens were collected, the ones that were described were less
complete. During the last 15 years, abundant material has been
reported from the Triassic of North America (Nicholls and Man-
abe, 2001, 2004; Fr€
obisch et al., 2006, 2013; Cuthbertson et al.,
2013a, 2013b, 2014) and especially from South China (Li, 1999;
Yin et al., 2000; Li and You, 2002; Chen and Cheng, 2003; Nich-
olls et al., 2003; Pan et al., 2004; Jiang et al., 2006, 2007, 2008;
Maisch et al., 2006, 2008; Chen et al., 2007; Shang et al., 2009;
Sander et al., 2011; Ji et al., 2013), ranging from the Anisian
(Middle Triassic) to the Carnian (Upper Triassic). The Chinese
materials are exceptionally well preserved from multiple
*Corresponding author.
Journal of Vertebrate Paleontology e1025956 (18 pages)
Óby the Society of Vertebrate Paleontology
DOI: 10.1080/02724634.2015.1025956
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locations and stratigraphic occurrences. At least nine different
genera and species have been described, which greatly expanded
the diversity and stratigraphic and paleogeographic distribution
of Triassic ichthyopterygians. However, phylogenetic relation-
ships within the Ichthyopterygia have not been well established
except in a limited number of subgroups such as mixosaurs
(Jiang et al., 2006). In addition, abundant ichthyosaur material
has been reported from the Upper Jurassic to Lower Cretaceous
of South America, North America, Europe, and Middle East
(Fern
andez, 1999; Bardet and Fern
andez, 2000; Maxwell and
Caldwell, 2006a, 2006b; Druckenmiller and Maxwell, 2010; Max-
well, 2010; Maxwell et al., 2012; Fischer et al., 2011a, 2011b,
2011c, 2012, 2013, 2014; Fern
andez and Maxwell, 2012; Martin
et al., 2012).
The extensive addition of new genera and species has been
accompanied by phylogenetic analyses of subgroups within the
Ichthyopterygia, based mainly on Motani (1999) and Maisch and
Matzke (2000). These restricted analyses resulted in conflicting
tree topologies, sometimes partially blurring the large-scale phy-
logenetic framework of the Ichthyopterygia. It is high time to
reexamine the phylogeny of the entire group after 15 years to
assess if and how the newly discovered taxa affect overall tree
topology, and to find which of the proposed subgroup topologies
are congruent with a large-scale data set. Thus, a comprehensive
phylogenetic analysis of Ichthyopterygia based on a broad set of
taxa and characters is now necessary to provide a framework for
further evolutionary studies within Ichthyopterygia. We present
here a cladistic analysis of a data matrix comprising 163 charac-
ters for 59 taxa, including nearly all Triassic ichthyopterygian gen-
era and most post-Triassic genera. This is the most inclusive
phylogenetic analysis of the Ichthyopterygia to date.
HISTORICAL REVIEW
Motani (1999) and McGowan and Motani (2003) gave com-
prehensive reviews of research on the interrelationships
among ichthyopterygians published by the end of the last
century. Since then, many analyses have been presented by
researchers based on selected taxa within Ichthyopterygia,
but only a few on the entire group. We here briefly review
those analyses that are more inclusive. Motani (1999) and
Maisch and Matzke (2000) each gave a comprehensive analy-
sis of Ichthyopterygia, mainly at the genus level; the latter
differed from the former mainly in the different interpreta-
tion of character evolution and a slight increase in the num-
ber of taxa and characters included. Motani (1999) employed
five non-ichthyopterygian diapsids as outgroup taxa and dem-
onstrated the monophyly of Ichthyopterygia while testing the
effects of outgroup selection on ingroup topology. Maisch
and Matzke (2000) did not use any outgroup for the data
matrix but employed an all-zero ancestor. Removal of the
all-zero ancestor will result in different tree topologies for
Early Triassic taxa (Utatsusaurus, Grippia, Chaohusaurus,
Thaisaurus,andParvinatator), as stated in McGowan and
Motani (2003). Sander (2000) presented a phylogeny of
selected well-known taxa based on many metric (propor-
tional) characters, but it is not clear if he found discrete gaps
in the continuous metric data that would justify the recogni-
tion of discrete character states. Proportion characters should
be treated with caution and are usually analyzed based on
histograms of their distribution to establish discrete states
whenever possible.
As more taxa were reported, especially from the Middle to
Upper Triassic of South China, the Upper Triassic of British
Columbia, and the Upper Jurassic to Lower Cretaceous of South
America, North America, Europe, and Australia, the phylogenies
of some subgroups within Ichthyopterygia have been analyzed
based on morphological characters. As a result, our knowledge
of the diversity of basal and highly derived ichthyosaurs has been
greatly enriched during the last decade (Nicholls and Manabe,
2001; Jiang et al., 2006; Fern
andez, 2007; Maxwell, 2010; Fischer
et al., 2012, 2013). A species-level taxonomy of some ichthyop-
terygians such as Mixosauridae and Ophthalmosauridae was also
established (Jiang et al., 2006; Maxwell, 2010). In contrast, the
monophyly and ingroup topology of Shastasauridae have been
interpreted variously between different analyses (Callaway, 1989;
Motani, 1999; Maisch and Matzke, 2000; Sander et al., 2011;
Thorne et al., 2011). The Shastasauridae of Callaway (1989) was
shown to be polyphyletic and was consequently redefined by
Motani (1999) to include Besanosaururs, Shastasaurus,andSho-
nisaurus only, whereas no monophyletic group is supported in
Maisch and Matzke (2000). Sander et al. (2011) gave a new inter-
pretation of this group by combining Guanlingsaurus liangae and
Shonisaurus sikanniensis with Shastasaurus, based on analysis of
a modified data matrix taken from Motani (1999). Thorne et al.
(2011) provided a majority-rule consensus tree of Ichthyopterygia
based on a modified data matrix taken from Motani (1999) and
more recent publications, and presented a monophyletic clade
Shastasauridae comprising Besanosaurus, Guizhouichthyosaurus,
Shastasaurus, Shonisaurus,andCallawayia.
New material from the Jurassic to Lower Cretaceous
revealed higher diversity of Ichthyosauria during this period
than previously thought. Caine and Benton (2011) reported
new materials from the Lower Jurassic of England and pro-
posed a tree topology for Jurassic ichthyosaurs based mainly on
prior data sets. A rapid radiation was recognized during the
Late Jurassic, giving rise to more than seven genera (Drucken-
miller and Maxwell, 2010; Fischer et al., 2013). These genera,
however, are mostly monotypic. Fern
andez (2007) conducted
phylogenetic analyses of nine genera and found two monophy-
letic groups within Ophthalmosauridae: one including
Aegirosaurus and Ophthalmosaurus, the other including Bra-
chypterygius, Caypullisaurus, and Platypterygius. Druckenmiller
and Maxwell (2010) analyzed the species-level phylogeny of
Ophthalmosauridae with additional taxa found after Fern
andez
(2007) and questioned the monophyly of the species within
Ophthalmosaurus and Platypterygius, respectively. Fischer et al.
(2013) conducted a comprehensive phylogenetic analysis of Par-
vipelvia using Mikadocephalus as the outgroup. They recognized
the presence of Aalenian ‘Ophthalmosaurid Radiation’ and Kim-
meridgian ‘Platypterygiine Radiation,’ both of which occurred
before the Cretaceous. This analysis included nearly all the taxa
from the latest Triassic to the Late Cretaceous and demonstrated
that ichthyosaurs of the Cretaceous were more diverse than tra-
ditionally thought. However, the only outgroup taxon was so
incompletely known that it was coded for only 35 of the 66 char-
acters, leaving much ambiguity in character polarization.
MATERIALS AND METHODS
Character Selection—We used 163 discrete morphological
characters, of which 34 are multistate. The derivation and defini-
tion of characters are given in Supplementary Data 1.
Ingroup Selection—Nearly all ichthyopterygian genera were
included in the analysis, resulting in a total of 59 ingroup taxa, of
which 11 were subsequently removed in a second analysis. The
following genera were coded at the species level to test the
monophyly of each genus: Mixosaurus, Phalarodon, Cymbo-
spondylus, Shonisaurus, Qianichthyosaurus, Leptonectes, Platyp-
terygius, and Ophthalmosaurus. Most of the new species
reported from the Triassic since Motani (1999) and Maisch and
Matzke (2000) are within or related to these genera, necessitat-
ing a species-level phylogenetic analysis in order to resolve their
interrelationships.
Outgroup Selection—We adopted five outgroup taxa from
Motani (1999) for character polarization, whereas the position of
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the Ichthyopterygia within the Amniota is beyond the scope of
the current study.
Analysis—Mesquite 2.74 (Maddison and Maddison, 2010) was
used for constructing the character matrix (Supplementary Data
1). All characters were equally weighted, and all multistate char-
acters were considered unordered. The data matrix was analyzed
using both TNT 1.1 (Goloboff et al., 2008) and PAUP (Swofford,
2002). A heuristic search algorithm was used in PAUP by run-
ning 20,000 replicates of random addition sequences and TBR
branch swapping, holding 10 trees at a time. A branch-and-
bound search was conducted under the constraint of the strict
consensus tree from the heuristic search. New technology
searches were performed in TNT at level 10, with 100 hits, 100
replications, 10 drifts, holding 10 trees per replicate, and using
rule-3 collapse. The TNT search was followed by Bremer support
estimation. The strict consensus trees were computed in TNT, as
shown in Figures 1 and 2. The Bremer support analysis included
trees that are within 10 steps of the shortest trees.
We ran two analyses based on different combinations of
ingroup taxa. In the first analysis, all taxa in the data matrix were
included. In the second analysis, those taxa that could not be
coded for 1/3 of the characters (54.3 out of 163 characters) were
excluded (see Table S1 for more details), namely, Parvinatator,
Acamptonectes, Maiaspondylus, Arthropterygius, Malawania,
Chacaicosaurus, Mollesaurus, Leninia, Thalattoarchon, Palvennia,
and Sisteronia. Inclusion of these taxa will only cause more poly-
tomy because they contain a large number of missing data. Excep-
tions were made to include the following species in the analysis
despite the incompleteness of character coding: Cymbospondylus
nichollsi, Mixosaurus kuhnschnyderi, Phalarodon callawayia,and
Shonisaurus sikanniensis. These species were necessary to test the
monophyly of their respective genus, whereas the presence of
well-known sister taxa prevented them from confusing the out-
come of the analysis. Hudsonelpidia was also included because its
unique stratigraphy and phylogenetic position made it necessary
to stabilize the basal node of Parvipelvia.
Institutional Abbreviations—AGM, Anhui Geological
Museum, Hefei, People’s Republic of China; GMR, Weiwei
Paleontological Research and Development Center, Guiyang,
People’s Republic of China; GNG, Guanling National Geopark
of Fossil Biota, Guanling County, People’s Republic of China;
IVPP, Institute of Vertebrate Paleontology and Paleoanthropol-
ogy, Academia Sinica, Beijing, People’s Republic of China;
MCSNM, Museo Civico di Storia Naturale di Milano, Milan,
Italy; PIMUZ, Pal€
aontologisches Institut und Museum, Uni-
versit€
at Z€
urich, Zurich, Switzerland; ROM, Royal Ontario
Museum, Toronto, Ontario, Canada; RTMP, Royal Tyrrell
Museum of Palaeontology, Drumheller, Alberta, Canada;
UCMP, University of California Museum of Paleontology, Ber-
keley, California, U.S.A.; SPCV, Wuhan (former Yichang) Insti-
tute of Geology and Mineral Resources, China Geological
Survey, Wuhan, Hubei, China.
RESULTS
In the first analysis, the heuristic search in PAUP found
2,180,061 most parsimonious trees (tree length D538 steps, con-
sistency index [CI] D0.3741, retention index [RI] D0.7776)
(strict consensus tree, Fig. 1), of which 247 were found by a new
technology search in TNT. The topology of Triassic ichthyop-
terygians is mostly resolved, whereas post-Triassic taxa form a
polytomy. Only two monophyletic clades were obtained, includ-
ing the sister group of Excalibosaurus and Eurhinosaurus, and
the three species of Leptonectes, respectively. Thalattoarchon
appears to be closely related to the cymbospondylids. However,
this clade is weakly supported, with a Bremer value of 1.
In the second analysis, a heuristic search in PAUP reported 90
most parsimonious trees (MPTs; tree length D501 steps, CI D
0.4012, RI D0.7862), of which six were duplicates. Therefore, it
found 84 MPTs (strict consensus tree, Fig. 2). The New Technol-
ogy Search recovered the same 84 most parsimonious trees. Five
major clades of Triassic ichthyosaurs are robustly supported as
monophyletic, including Grippioidea, Cymbospondylidae, Mixo-
sauridae, Shastasauridae, and Toretocnemidae. The topology of
post-Triassic ichthyosaurs, especially the ingroup topology of
Thunnosauria, is resolved in the second analysis, but the Bremer
values are low. We hereafter base our discussion on the better-
resolved topology (Fig. 2) unless otherwise stated.
The Ichthyopterygia is well supported as a monophyletic clade
(Bremer support D7 steps) and is diagnosed by the following 14
characters: (10-1) nasal anteriorly extending beyond external
naris; (36-1) anterior terrace of upper temporal fenestra present;
(44-1) ectopterygoid absent; (47-1) angular lateral exposure at its
medium depth much shallower than surangular; (67-1) clavicle
length beyond distal end of the body long; (78-1) coracoid fora-
men absent; (80-1) coracoid posterior notch or cavity present;
(100-1) intermedium as wide as long or wider than long; (101-1)
interdigital separation absent; (102-1) metacarpal I peripheral
shaft largely reduced; (126) wide distal femur blade present;
(153-1) neural spine articulation in tail present; (155-1) caudal
peak present; and (160-1) tail stem count 1/2 or more that of the
presacral count.
Because many new taxa have been erected in the past decade,
a revised classification of the Ichthyopterygia based on the strict
consensus tree from the analysis is given below. Diagnoses are
given based on unambiguously changing characters at each inter-
node and autapomorphic characters that were not included in
the data matrix. The Triassic taxa are mainly at the species level
because most species represent monotypic genera. The following
figures are for better explanation of the characters used in the
analysis for the skull (Figs. 3, 4) and hind limb (Fig. 5).
SYSTEMATIC PALEONTOLOGY
ICHTHYOPTERYGIA Owen, 1840
Genus CHAOHUSAURUS Young and Dong, 1972
Type Species—Chaohusaurus geishanensis Young and Dong,
1972.
Referred Species—Chaohusaurus chaoxianensis (Chen, 1985);
C. zhangjiawanensis Chen et al., 2013.
Diagnosis—Quadratojugal taller than long; snout relatively slen-
der; maxilla with multiple tooth rows; posterior tooth crown
rounded; interclavicle posterior process absent; clavicle orientation
at proximal end transverse; ulnar facet of humerus posterodistally
deflected and radius facet distally orientated; anteroproximal promi-
nence of radius extensively developed; distal carpal I absent; pubis
obturator foramen partially open; small body size of less than 1 m.
Locality and Horizon—Lower Triassic (Spathian) of Anhui
Province, China.
Discussion—Chaohusaurus chaoxianensis was synonymized
with C. geishanensis by Motani and You (1998). However, it was
recently resurrected based on additional specimens by Motani
et al. (2015a).
GRIPPIOIDEA nov.
Definition—The last common ancestor of Utatsusaurus hataii
and Grippia longirostris, and all its descendants.
Diagnosis—External naris dorsal orientation; no contact
between prefrontal and postfrontal; anterior orbital margin
irregular; jugal quadratojugal lateral contact absent; pterygoid
transverse flange anterolateral; lower temporal arch composed
of jugal and quadratojugal; manual pisiform present.
Genus UTATSUSAURUS Shikama, Kamei, and Murata, 1978
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FIGURE 1. Strict consensus tree of the phylogenetic relationships among ichthyopterygians under the complete data matrix from TNT. The Bremer
values are listed above the node. Abbreviations: Cymb., Cymbospondylus; Mixo., Mixosaurus; Phar., Phalarodon; Calla., Callawayia; Shon., Shoni-
saurus; Qian., Qianichthyosaurus; Lept., Leptonectes; Opht., Ophthalmosaurus; Plat., Platypterygius.
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Type Species—Utatsusaurus hataii Shikama, Kamei, and Mur-
ata, 1978.
Referred Species—Type species only.
Diagnosis—Tooth size relative to skull width small; humerus
proximal and distal width nearly equal; propodial Cepipodial
longer than manus; medium-sized ichthyopterygian, approaching
3 m in total length.
FIGURE 2. Strict consensus tree of the phylogenetic relationships among ichthyopterygians with removal of eleven poorly known taxa from TNT.
The Bremer values are listed above the node. See text for explanations.
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Locality and Horizon—Lower Triassic (Spathian) of Miyagi,
Japan; Lower Triassic of British Columbia, Canada.
GRIPPIIDAE Wiman, 1933
Definition—The last common ancestor of Grippia longirostris
and Gulosaurus helmi, and all its descendants.
Diagnosis—Maxilla with multiple tooth rows; posterior
tooth crown rounded; supratemporal-postorbital contact pres-
ent; proximal manual phalanges not closely packed
proximodistally.
Genus GRIPPIA Wiman, 1929
Type Species—Grippia longirostris Wiman, 1929.
Referred Species—Type species only.
Diagnosis—Small-sized ichthyosaur; tooth size relatively
small, round; metacarpal I lunate, without a shaft; posterior dor-
sal rib facet bicipital.
Locality and Horizon—Lower Triassic (Spathian) of
Spitsbergen.
Genus GULOSAURUS Cuthbertson et al., 2013a
Type Species—Gulosaurus helmi Cuthbertson et al., 2013a.
Referred Species—Type species only.
Diagnosis—Premaxilla ventral process long; postfrontal
extends medially over the anterior-most margin of the upper
temporal fenestra; squamosal participation in the upper tempo-
ral fenestra absent; scapula posterior extension absent; anterior
teeth cylindrical rather than conical; coracoid facet on scapula
equal or smaller than glenoid facet of scapula; intermedium lon-
ger than wide.
FIGURE 3 Skulls of eight ichthyopterygians in lateral view. A,Utatsusaurus hataii (Motani, 1999); B,Mixosaurus panxianensis (modified after Jiang
et al., 2006); C,Cymbospondylus piscosus (based on UCMP 9950); D,‘Callawayia’ wolonggangensis (based on SPCV 10306); E,Guizhouichthyosau-
rus tangae (modified after Maisch et al., 2008, and Pan et al., 2004); F,Qianichthyosaurus zhoui (modified from Nicholls et al., 2003); G,Ichthyosaurus
communis (after Motani, 1999); H,Platypterygius australis (after Kear, 2005). Abbreviations: a, angular; d, dentary; exn, external naris; f, frontal; j,
jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; prf, prefrontal; pm, premaxilla; po, postorbital; pof, postfrontal; q, quadrate; qj, quadratojugal; sq,
squamosal; sa, surangular; sp, splenial; st, supratemporal; utf, upper temporal fenestra.
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Locality and Horizon—Lower Triassic of British Columbia,
Canada.
ICHTHYOSAURIA Blainville, 1835
Diagnosis—Sagittal eminence present but small, involving
only the parietal; anterior processes of parietals narrowly sepa-
rated anteriorly, forming parietal fork, and frontal dorsally visi-
ble along the pineal foramen; ulna peripheral shaft notched or
absent; iliac blade plate-like; posterior dorsal centra discoidal;
sacral ribs absent.
CYMBOSPONDYLIDAE von Huene, 1948
Definition—The last common ancestor of Cymbospondylus
piscosus and Xinminosaurus catactes, and all its descendants.
Diagnosis—Clavicle length beyond distal to main body short;
coracoid foramen present; coracoid anterior margin notched;
presacral count 55 or more.
Genus CYMBOSPONDYLUS Leidy, 1868
Type Species—Cymbospondylus piscosus Leidy, 1868.
Referred Species—Cymbospondylus buchseri Sander, 1989; C.
nichollsi Fr€
obisch et al., 2006.
Diagnosis—Large size, possibly over 9 m in adult; frontal
entering the upper temporal fenestra; supratemporal anterome-
dial extension long; coronoid region slightly elevated; no dental
FIGURE 4. Skulls of eight ichthyopterygians in dorsal view. A,Utatsusaurus hataii (after Motani, 1999); B,Mixosaurus panxianensis (modified from
Yang, 2009, unpublished dissertation); C,Cymbospondylus piscosus (based on UCMP 9950); D,‘Callawayia’ wolonggangensis (based on SPCV
10305); E,Guizhouichthyosaurus tangae (modified from Maisch et al., 2006); F,Guanlingsaurus liangae (based on GNG dq-50); G,Ichthyosaurus
communis (after Motani, 1999); H,Platypterygius australis (after Kear, 2005). Abbreviations: see Figure 3.
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groove; anterodorsal margin of scapula emarginated; humerus
proximal and distal width nearly equal.
CYMBOSPONDYLUS PISCOSUS Leidy, 1868
Diagnosis—Cymbospondylus with long and robust snout, orbit
relatively small, cheek region wide, postfrontal large and medi-
ally extended over anterior-most margin of upper temporal
fenestra, and dentary labial shelf.
Locality and Horizon—Middle Triassic (Anisian) of Nevada,
U.S.A.
CYMBOSPONDYLUS BUCHSERI Sander, 1989
Diagnosis—Cymbospondylus with supratemporal and postor-
bital in contact, short humerus, and postorbital not entering
upper temporal fenestra.
Locality and Horizon—Middle Triassic (Early Ladinian) of
Monte San Giorgio, Switzerland.
CYMBOSPONDYLUS NICHOLLSI Fr€
obisch et al., 2006
Diagnosis—Cymbospondylus with long nasal posterior process
extending into the upper temporal fenestra, supratemporal and
postorbital in contact, and parietal foramen restricted within
parietals.
Locality and Horizon—Middle Triassic (Anisian) of Nevada,
U.S.A.
Genus XINMINOSAURUS Jiang et al., 2008
Type Species—Xinminosaurus catactes Jiang et al., 2008.
Referred Species—Type species only.
Diagnosis—Bulbous and laterally compressed teeth in multi-
ple rows on maxilla; replacement teeth appearing outside of
pulp cavity and forming a second tooth row; interclavicle pos-
terior process absent; coracoid wider than long; distal facet of
ulna greatly expanded; distal carpals III and IV fused; distal
carpal I and distal tarsal I absent; metacarpals I–IV and
phalanges hourglass-shaped, shaft present at least in the proxi-
mal elements.
Locality and horizon—Middle Triassic (Anisian) of Guizhou,
South China.
HUENEOSAURIA Maisch and Matzke, 2000
Definition—The last common ancestor of Mixosaurus corna-
lianus and Ophthalmosaurus icenicus, and all its descendants.
Diagnosis—Postorbital posterodorsal corner round or absent;
postorbital participation in upper temporal fenestra; basioccipi-
tal/atlas articulation convex posteriorly; clavicle proximal end
transverse to saggittal plane; maximum phalangeal count seven
or more.
MIXOSAURIDAE Baur, 1887
Definition—The last common ancestor of Mixosaurus corna-
lianus and Phalarodon fraasi, and all its descendants.
Diagnosis—Premaxilla posteriorly pointed, without dorsal or
ventral process, scarcely entering external naris; maxilla contact-
ing prefrontal; nasal short, not contacting postfrontal; frontal
dorsal exposure large; supraorbital crest on prefrontal and post-
frontal present; parietal supratemporal process short; parietal
ridge present; long sagittal crest reaching nasal, formed by parie-
tal, frontal, and nasal; large anterior terrace of upper temporal
fenestra, reaching nasal and exposure of upper temporal fenestra
small; interclavicle posterior process triangular; metacarpal I
peripheral shaft absent; manual pisiforms I and II present; pubis
and ischium median symphysis present; pubis more than twice as
large as ischium; remarkably high and narrow neural spines;
mid-caudal vertebral centra with increased size.
Discussion—In Motani (1999:479), Mixosauridae was defined
as “The last common ancestor of Mixosaurus cornalianus and M.
nordenskioeldii, and all its descendants.” However, M. norden-
skioeldii was considered nomen dubium in Schmitz (2005)
because the type specimen is not diagnostic and the com-
mendable attempts (Nicholls et al., 1999; Schmitz et al., 2004)
FIGURE 5. Hind limb morphology of selected Ichthyopterygians. A,Chaohusaurus geishanensis (after AGM MT10011); B,Mixosaurus panxianen-
sis (modified after Jiang et al., 2006); C,Xinminosaurus catactes (after Jiang et al., 2008); D,Cymbospondylus piscosus (after Merriam, 1908); E,Besa-
nosaurus leptorhynchus (based on Besanosaurus leptorhynchus MCSNM BES SC 999); F,Guizhouichthyosaurus tangae (based on GMR 009); G,
Guanlingsaurus liangae (based on GMR 014); H,Shastasaurus pacificus (after Merriam, 1908); I,Californosaurus perrini (after Merriam, 1902); J,Sho-
nisaurus popularis (after Camp, 1980); K,Qianichthyosaurus xingyiensis (modified from Yang et al., 2013); L,Eurhinosaurus longirostris (based on
ROM 55094). Abbreviations:fe, femur; fi, fibula; ti, tibia.
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were not in accordance with ICZN. Therefore, the definition of
this group is here revised as above; for the ingroup relationship
interpretation, see the analysis by Jiang et al. (2006).
Genus MIXOSAURUS Baur, 1887
Type Species—Mixosaurus cornalianus (Bassani, 1886).
Referred Species—Mixosaurus kuhnschnyderi (Brinkmann,
1998) and M. panxianensis Jiang et al., 2006.
Diagnosis—Posterior tooth crown rounded rather than
conical.
Locality and Horizon—Middle Triassic (Anisian to Ladinian)
of Italy, Switzerland, and South China.
Genus PHALARODON Merriam, 1910
Type Species—Phalarodon fraasi Merriam, 1910.
Referred Species—Phalarodon atavus (Quenstedt, 1852) and
P. callawayi Schmitz et al., 2004.
FIGURE 6. Stratigraphic record of Ichthyopterygia. Black bars were used when the stratigraphy of a taxon is described with accuracy at stage level
or finer. Black bars spanning over two stages indicate occurrence of fossils from two different stages or on the boundary. Gray bar (Gulosaurus) indi-
cates uncertain stratigraphic occurrence from two or more stages. Stratigraphy here follows the International Commission on Stratigraphy.
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Diagnosis—Narial shelf present; dental groove only present
anteriorly and absent posteriorly; dental labial shelf present;
tooth with laterally compressed horizontal section (circular in P.
callawayi); posterior tooth crown flat (conical in P. atavus).
Locality and Horizon—Middle Triassic (Anisian to Ladinian)
of Germany, Poland, U.S.A., and South China.
MERRIAMOSAURIA Motani, 1999
Definition—The last common ancestor of Shastasaurus pacif-
icus and Ichthyosaurus communis, and all its descendants.
Diagnosis—Postfrontal medial extension over the anterior mar-
gin of the upper temporal fenestra; quadratojugal taller than long;
scapula anterior process absent, anterior margin slightly convex or
nearly straight; coracoid facet on scapula equal to or smaller than
glenoid facet; coracoid foramen absent; coracoid concave anteri-
orly and posteriorly; humerus distal and proximal width nearly
equal; radius peripheral shaft reduced or absent; metacarpal I not
ossified; metacarpal III shaft absent; manual digit II distal ele-
ments peripheral shaft notched or absent; pes digit I absent; proxi-
mal manual phalanges widely spaced along the proximodistal axis;
shape of the posterior surface of the ulna rounded; notching of the
anterior facet of leading elements of forefin in adult.
SHASTASAURIDAE Merriam, 1902
Definition—The last common ancestor of Shastasaurus and
Besanosaurus, and all its descendants.
Note—In McGowan and Motani (2003:70), the clade was
defined as “the last common ancestor of Shastasaurus and
Shonisaurus, and all its descendants.” Because Guanlingsaurus
appeared closely related to the former two genera and Besano-
saurus appears as the nearest outgroup in the phylogenetic anal-
ysis, Shastasauridae is here defined as including all of the genera
above. It ranged through the early Ladinian, with a few members
still present in the Norian (Nicholls and Manabe, 2004; Drucken-
miller and Kelley, 2010; Ji et al., 2012).
Diagnosis—Body size of over 6 m; presacral count over 55;
scapula axis and glenoid facet not parallel, forming an angle of
about 60 degrees; coracoid wider than long; radius relatively
wide, about 1.5 times width of ulna; ulna contiguous shaft both
reduced; radioulnar foramen absent; pubis foramen mostly
within pubis but open on one side; wide distal femur blade.
Genus BESANOSAURUS Dal Sasso and Pinna, 1996
Type Species—Besanosaurus leptorhynchus Dal Sasso and
Pinna, 1996.
Referred Species—Type species only.
Diagnosis—Size about 6 m, skull relatively small; teeth small;
snout extremely slender; maxilla prefrontal contact present;
humerus and ulna round, radius nearly quadrangular, slightly
larger than ulna, and contiguous shaft notched or absent; pubis
foramen nearly closed.
Locality and Horizon—Middle Triassic (Early Ladinian) of
Besano, Italy.
Genus GUIZHOUICHTHYOSAURUS Cao and Luo in Yin
et al., 2000
Type Species—Guizhouichthyosaurus tangae CaoandLuoin
Yin et al., 2000.
Referred Species—Type species only.
Diagnosis—Size over 5 m; long and robust snout; narrow and
long groove anterior to external naris; scapula without proximal
shaft; hind fin digit II proximal phalanges remarkably smaller
than distal ones; an accessory element present distal to the
ulnare, but much smaller than adjacent carpals.
Locality and Horizon—Middle Triassic (late Ladinian) to Late
Triassic (Carnian) of Guizhou, China.
‘CALLAWAYIA’wolonggangensis Chen et al., 2007
Diagnosis—Medium-sized ichthyosaur, skull (mandible)
length around 70 cm; snout long and slender; narrow groove
anterior to external naris present; nasal large, extending nearly
to parietal foramen; cheek region short.
Locality and Horizon—Upper Triassic (Carnian) of Guizhou,
China.
Remarks—This species was originally referred to Callawayia
because it possessed the parietal shelf and a straight anterior
margin of scapula, which were also reported in Callawayia neo-
scapularis. However, the scapula in ‘C.’ wolonggangensis is not
complete anteriorly and the anterior striations are radial instead
of parallel to the margin, which is similar to Guizhouichthyosau-
rus and Shastasaurus. Besides, ‘Callawayia’ wolonggangensis
lacks the diagnostic features of C. neoscapularis such as presence
of a parietal shelf and absence of maxilla dorsal lamina. Thus,
‘Callawayia’ wolonggangensis shares no synapomorphies with
Callawayia neoscapularis, which is the type species, and the phy-
logenetic topology does not support their monophyly.
SHASTASAURINAE Merriam, 1908
Definition—The last common ancestor of Shastasaurus and
Guanlingsaurus, and all its descendants.
Diagnosis—Squamosal participation in upper temporal fenes-
tra; edentulous in adult; dental groove absent; scapula proximal
shaft present; intercoracoid facet long, medial margin relatively
straight; metacarpal V not ossified.
Genus SHASTASAURUS Merriam, 1895
Type Species—Shastasaurus pacificus Merriam, 1895.
Referred Species—Type species only.
Diagnosis—Contact between nasal and postfrontal narrow;
orbit anteroposteriorly elongated; cheek narrow; radiale anterior
notch present.
Locality and Horizon—Upper Triassic (Carnian) of Califor-
nia, U.S.A., and Mexico.
Discussion—McGowan (1994) reviewed the species and
assigned them all to the type species because no significant fea-
tures were available based on the incomplete specimens. There-
fore, S. pacificus is at present the only valid species of the genus.
Genus GUANLINGSAURUS Yin in Yin et al., 2000
Type Species—Guanlingsaurus liangae Yin in Yin et al., 2000.
Referred Species—Type species only.
Diagnosis—Over 11 m long in adult; presacral count around
80; extremely short and edentulous snout; parietal foramen
located within parietals; forelimb with no more than three digits;
phalanges widely separated from each other; pubis foramen
wide; fibular posterior flange present.
Locality and Horizon—Upper Triassic (Carnian) of Guizhou,
China.
Genus SHONISAURUS Camp, 1976
Type Species—Shonisaurus popularis Camp, 1976.
Referred Species—Shonisaurus sikanniensis Nicholls and
Manabe, 2004.
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Diagnosis—Over 15 m long in adult; radius and ulna contigu-
ous shaft present; ulna remarkably longer than wide; radioulnar
foramen present; fibular posterior flange present.
Locality and Horizon—Upper Triassic (Carnian) of Nevada,
U.S.A; Upper Triassic (Norian) of British Columbia, Canada.
EUICHTHYOSAURIA Motani, 1999
Definition—All merriamosaurians more closely related to Ich-
thyosaurus communis than to Shastasaurus pacificus.
Diagnosis—Humerus with two distal articular facets, nearly
equal in length; anterior notch of radiale present; pubis obturator
foramen wide; sudden decrease in height of the mid-caudal ver-
tebrae; tail stem vertebral size about 1/2 of the largest dorsal ver-
tebrae or less; anterior caudal count about 2/3 of the prepelvic
count or more; radiale anterior notch present.
Genus CALIFORNOSAURUS Kuhn, 1934
Type Species—Californosaurus perrini (Merriam, 1902).
Referred Species—Type species only.
Diagnosis—Dorsal centra discoidal yet thick, with height/
length ratio about 1.6–1.7; humerus anterior flange reduced prox-
imally; radius and ulna of equal size; ilium with anteromedial
prominence; rib facets not confluent with the anterior facet in
any centra.
Locality and Horizon—Upper Triassic (Carnian) of Califor-
nia, U.S.A.
Genus CALLAWAYIA Maisch and Matzke, 2000
Type Species—Callawayia neoscapularis (McGowan, 1994).
Referred Species—Type species only.
Diagnosis—Frontal participation in upper temporal fenestra;
distal ulna facet of humerus deflecting posterodistally but radius
facet distally; radius facet on humerus larger than ulna facet;
ulna medium-sized; radius much larger than ulna; manual pisi-
form present; presacral count 55 or more; coracoid wider than
long.
Locality and Horizon—Upper Triassic (Norian) of British
Columbia, Canada.
TORETOCNEMIDAE Maisch and Matzke, 2000
Definition—The last common ancestor of Toretocnemus and
Qianichthyosaurus, and all its descendants.
Diagnosis—Scapula posterior extension absent; coracoid ante-
rior nearly round or polygonal, without anterior or posterior
notch; intercoracoid facet long and straight; radius and ulna of
equal size and elongated, with contiguous shaft present and
peripheral shaft greatly reduced or absent; phalanges polygonal
and closely packed; pubis obturator foramen completely
enclosed in pubis; femur strongly constricted medially, forming a
narrow shaft; femur anterodistal expansion, forming a distinctive
structure at the distal end; tibia contiguous shaft greatly reduced
or absent; digit II in line with digits III and IV; posterior dorsal
rib facet bicipital.
Genus TORETOCNEMUS Merriam, 1903
Type Species—Toretocnemus californicus Merriam, 1903.
Referred Species—Type species only.
Diagnosis—Tridactyl forefin and hind fin; pubis and ischium
meet medially in well-defined symphysis.
Locality and Horizon—Upper Triassic (Carnian to Norian) of
U.S.A.
Genus QIANICHTHYOSAURUS Li, 1999
Type Species—Qianichthyosaurus zhoui Li, 1999.
Referred Species—Qianichthyosaurus xingyiensis Ji et al. in
Yang et al., 2013.
Diagnosis—Premaxilla posterior end pointed, with both dorsal
and ventral processes absent; tridactyl forefin with one accessory
digit and tetradactyl hind fin; tibia contiguous shaft complete.
Locality and Horizon—Middle (late Ladinian) to Upper Trias-
sic (Carnian) of Guizhou, China.
PARVIPELVIA Motani, 1999
Definition—The last common ancestor of Macgowania, Hud-
sonelpidia, and Ichthyosaurus, and all its descendants.
Diagnosis—Maxilla dorsal lamina absent; maxilla external
naris contact absent; scapula anteroproximal extension toward
clavicle present; humerus anterior flange reduced proximally;
ulna contiguous shaft notched or absent; ulna relatively short;
only one posterior manual accessory digit; pubis styloidal;
ischium plate-like, wider transversely than long sagittally; ante-
rodorsal rib facets not confluent in any of the centra; posterior
gastralia absent.
Genus MACGOWANIA Motani, 1999
Type Species—Macgowania janiceps (McGowan, 1996a).
Referred Species—Type species only.
Diagnosis—Humerus constriction unremarkable as in Ichthyo-
saurus, but manus without digital bifurcation or accessory digits
S4–S5; manual digit V closely contacting digit VI.
Locality and Horizon—Upper Triassic (Norian) of British
Columbia, Canada.
Genus HUDSONELPIDIA McGowan, 1995
Type Species—Hudsonelpidia brevirostris McGowan, 1995.
Referred Species—Type species only.
Diagnosis—Short snout; high, narrow dorsal neural spines;
humerus slender, slightly longer than femur; iliac anteromedial
prominence present; pubis triangular rather than plate-like and
longer than wide; ischium plate-like, wider than pubis, and con-
cave anteroposteriorly; posterior extent of fibula much posterior
to femur.
Locality and Horizon—Upper Triassic (Norian) of British
Columbia, Canada.
TEMNODONTOSAUROIDEA McGowan and Motani,
2003
Definition—The last common ancestor of Temnodontosaurus
platyodon and Leptonectes tenuirostris, and all its descendants.
Genus TEMNODONTOSAURUS Lydekker, 1889
Type Species—Temnodontosaurus platyodon (Conybeare,
1822).
Referred Species—Temnodontosaurus trigonodon (Theodori,
1834), T. crassimanus (Blake, 1876), T. eurycephalus McGowan,
1974, T. acutirostris (Owen, 1840), and T. azerguensis Martin
et al., 2012.
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Diagnosis—Large size of usually 7–12 m in adult; long and
robust snout, snout ratio usually <0.65 but >0.59; maxilla ante-
rior process extending as far anteriorly as the nasal; nasal parietal
contact lateral to frontal present; anterodistal margin of femur
slightly enlarged; phalanges roughly hexagonal.
Locality and Horizon—Lower Jurassic (Hettangian-Toarcian)
of England, Belgium, and France.
LEPTONECTIDAE Maisch, 1998
Definition—The last common ancestor of Eurhinosaurus
longirostris and Leptonectes tenuirostris, and all its descendants.
Diagnosis—Sagittal crest absent; cheek facing posteriorly than
laterally; rostrum and mandible slender; overbite to varying
degrees; tooth size relative to skull below 0.05; tibia and fibula
widely separated.
Genus LEPTONECTES McGowan, 1996b
Type Species—Leptonectes tenuirostris (Conybeare, 1822).
Referred Species—Leptonectes solei (McGowan, 1993) and L.
moorei McGowan and Milner, 1999.
Diagnosis—Orbit large; angular lateral exposure at its maxi-
mum depth much deeper than surangular; coronoid region
slightly elevated; root of tooth without strong striations; humerus
with constricted shaft, widely expanded distally with leading
edge facet that is usually prominent; radioulnar foramen present;
phalanges rounded and well spaced distally; forelimb longer than
but less than twice hind limb; femur medially constricted, form-
ing a slender shaft region; pubis and ischium separate or partially
fused.
Locality and Horizon—Upper Triassic (Rhaetian) to Lower
Jurassic (Hettangian to Pliensbachian) of England, France, and
Switzerland.
Genus EXCALIBOSAURUS McGowan, 1986
Type Species—Excalibosaurus costini McGowan, 1986.
Referred Species—Type species only.
Diagnosis—Size 6 m; snout and mandible slender; mandible
shorter than skull but longer than 50% of the latter; prominent
acromion process of scapula present; forefin with three digits and
one postaxial accessory digit; number of phalanges in longest
digit of forefin <16; ischium and pubis not fused.
Locality and Horizon—Lower Jurassic (Sinemurian) of
England.
Genus EURHINOSAURUS Abel, 1909
Type Species—Eurhinosaurus longirostris (Mantell, 1851).
Referred Species—Type species only.
Diagnosis—Size about 7 m in adult; snout and mandible slen-
der; mandible much shorter than skull, <60% of skull length;
maxilla and external naris contact present; basioccipital with
extensive extracondylar area; basioccipital peg present; pubis
and ischium not fused; forefin with four digits and one postaxial
accessory digit; pisiform present; forefin and hind fin equally
long and slender; number of elements in longest digit of forefin
>17; wide space between tibia and fibula.
Locality and Horizon—Lower Jurassic (Toarcian) of England,
Germany, France, and Switzerland.
Genus SUEVOLEVIATHAN Maisch, 1998
Type Species—Suevoleviathan disinteger (von Huene, 1926).
Referred Species—S. integer (Bronn, 1844).
Diagnosis—Size of over 4 m in adult; forefin digits splayed dis-
tally; single row of digits between digits IV and V present; iliac
blade plate-like, with anterior process; pubis slender and curved;
ischium subrectangular; posterodorsal rib facet single-headed.
Locality and Horizon—Lower Jurassic (Toarcian) of Germany
and France.
Genus HAUFFIOPTERYX Maisch, 2008
Type Species—Hauffiopteryx typicus (von Huene, 1931).
Referred Species—Type species only.
Diagnosis—Total length about 3 m; <46 presacral vertebrae;
relatively short and slender snout; slight overbite; nasal not con-
tacting postfrontal; nasal forming dorsal margin of external naris;
prefrontal entering external naris; jugal not contacting quadrato-
jugal; cheek facing posteriorly rather than laterally; scapula ante-
roproximal extension toward clavicle absent; one postaxial
accessory digit.
Locality and Horizon—Lower Jurassic (Toarcian) of Germany
and England.
THUNNOSAURIA Motani, 1999
Definition—The last common ancestor of Stenopterygius
quadriscissus and Ichthyosaurus communis, and all its
descendants.
Diagnosis—Quadratojugal small, largely covered by squamo-
sal and postorbital; humerus anterior flange absent; radiale ante-
rior margin not notched; manual pisiform present; forefin at least
twice as long as hind fin.
Genus ICHTHYOSAURUS de la Beche and Conybeare,
1821
Type Species—Ichthyosaurus communis de la Beche and Con-
ybeare, 1821.
Referred Species—Ichthyosaurus breviceps Owen, 1881, I.
conybeari Lydekker, 1888 and I. anningae Lomax and Massare,
2015.
Diagnosis—Sagittal eminence absent; frontal and postfrontal
separated by prefrontal; squamosal absent; basioccipital with
extensive extracondylar area; basioccipital peg well developed;
coracoid posterior concavity present; forefin with no fewer than
four digits, mostly over five; ulnare equal or larger than interme-
dium; digital bifurcation present; phalanges numerous and
closely packed; pubis and ischium not fused.
Locality and Horizon—Upper Triassic (Rhaetian) to Lower
Jurassic (Hettangian to Pliensbachian) of England and Switzerland.
Genus STENOPTERYGIUS Jaekel, 1904
Type Species—Stenopterygius quadriscissus (Quenstedt,
1856).
Referred Species—Stenopterygius triscissus (Quenstedt, 1856),
S. uniter von Huene, 1931, and S. aaleniensis Maxwell et al.,
2012.
Diagnosis—Frontal and postfrontal separated by prefrontal;
scapula with prominent acromial angle; forefin with four to six
digits; single row of digits between digits IV and V present
(absent in some individuals); phalanges closely packed proxi-
mally; notching of leading edge in some elements; ischium and
pubis fused; presacral vertebrae 44–46.
Locality and Horizon—Lower Jurassic (Toarcian) of England,
Luxembourg, Switzerland, Germany, and France.
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OPHTHALMOSAURIDAE Baur, 1887
Definition—The last common ancestor of Brachypterygius and
Ophthalmosaurus, and all its descendants.
Diagnosis—Descending process of the nasal on the dorsal bor-
der of the nares present; extracondylar area of basioccipital
reduced; stapes proximal head massive, as large or larger
than opisthotic; tooth root smooth, with no striations; angular
largely exposed laterally, reaching as far anteriorly as the suran-
gular; prominent acromion process of scapula present; extra
zeugopodial element anterior to radius, and digit distal to it;
pubis and ischium completely fused; chevrons in apical region
absent.
Genus AEGIROSAURUS Bardet and Fern
andez, 2000
Type Species—Aegirosaurus leptospondylus (Wagner, 1853)
Referred Species—Type species only.
Diagnosis—Snout long and slender; coracoid anterior margin
without notch; humerus wider distally than proximally, with
three distal facets, the middle one for the intermedium being
smallest, the anterior and posterior ones for the radius and ulna;
ulna much larger than radius; intermedium longer than wide; six
digits, elements in longest digit probably >20; phalanges polygo-
nal rather than rounded, tightly packed; ischium and pubis
completely fused, without a foramen.
Locality and Horizon—Upper Jurassic (Tithonian) of
Germany.
Genus OPHTHALMOSAURUS Seeley, 1874
Type Species—Ophthalmosaurus icenicus Seeley, 1874.
Referred Species—Ophthalmosaurus natans (Marsh, 1879).
Diagnosis—Humerus with three distal facets, the anterior one
articulating with a preaxial accessory element; phalanges
rounded, not tightly packed, free margins rugose; elements in
longest digit probably <20; teeth not firmly attached and usually
lost to a certain extent; orbit large, orbital ratio >0.20; parietal
ridge present; ventral notch in the extracondylar area of the
basioccipital; pelvic girdle bipartite, ischium and pubis fused
with a foramen in the middle.
Locality and Horizon—Middle to Upper Jurassic (Callovian to
Tithonian) of England, Russia, France, U.S.A., Mexico, and
Argentina.
Discussion—The genus Ophthalmosaurus is not supported as a
monophyletic clade in this analysis, which has been suggested in
previous research (Druckenmiller and Maxwell, 2010; Fischer
et al., 2013). However, the Bremer value is pretty low in the
ingroup topology of Ophthalmosauridae, and the topology easily
changes or collapses when adding or removing other taxa. There-
fore, no assignment or further discussion is made here for this
genus.
Genus SVELTONECTES Fischer et al., 2011b
Type Species—Sveltonectes insolitus Fischer et al., 2011b.
Referred Species—Type species only.
Diagnosis—Parietal supratemporal process long; basiptery-
goid processes short, giving basisphenoid a square outline in dor-
sal view; scapula with anterior acromion process; coracoid
anterior margin notched; humerus with two distal facets; phalan-
ges polygonal and closely packed; forefin preaxial and postaxial
accessory digits present; femur with three distal facets, anterior
one for the accessory digit; hind fin with anterior and posterior
accessory digits.
Locality and Horizon—Lower Cretaceous (Barremian) of Russia.
Genus ATHABASCASAURUS Druckenmiller and Maxwell,
2010
Type Species—Athabascasaurus bitumineus Druckenmiller
and Maxwell, 2010.
Referred Species—Type species only.
Diagnosis—Size 3.5 m (estimated); maxilla dorsal lamina pres-
ent; lacrimal lacks a process entering the external naris; frontal
small and not excluded from upper temporal fenestra; postor-
bital overlapped dorsally by triangular flange of postfrontal; den-
tition with extremely light ridging of the enamel; presacral count
near 42; ischium and pubis fused, ischiopubis foramen absent.
Locality and Horizon—Lower Cretaceous (Albian) of
Canada.
Genus BRACHYPTERYGIUS von Huene, 1922
Type Species—Brachypterygius extremus (Boulenger, 1904).
Referred Species—B. cantabrigiensis (Lydekker, 1888)
Diagnosis—Long snout; no contact between jugal and quadra-
tojugal laterally; teeth numerous, robust, and well anchored in
dental grooves; humerus with distal facets of similar size, the
middle one for the intermedium and anterior and posterior ones
for radius and ulna; no fewer than five digits, but likely not
exceeding six; probably one preaxial and one postaxial accessory
digit; phalanges nearly rectangular.
Locality and Horizon—Upper Jurassic (Kimmeridgian) to
Lower Cretaceous (Albian) of England and Russia.
Genus CRYOPTERYGIUS Druckenmiller et al., 2012
Type Species—Cryopterygius kristiansenae Druckenmiller
et al., 2012.
Diagnosis—Size estimated to 5.5 m; 52 presacral vertebrae;
premaxilla and lacrimal not entering the external naris; maxilla
with extensive lateral exposure along the tooth row, extending
posteriorly to the midpoint of the orbit; postorbital posterodorsal
corner broad and triangular; coracoid facet on scapula equal to
or smaller than glenoid facet of scapula; humerus with two distal
facets, ulnar facet deflecting posterodistally, and radial facet dis-
tally; manual pisiform absent; ischiopubis expanded and not
fused distally; femur with two distal facets.
Locality and Horizon—Upper Jurassic (Tithonian) of Norway.
Genus PLATYPTERYGIUS von Huene, 1922
Type Species—Platypterygius platydactylus (Broili, 1907).
Referred Species—Platypterygius campylodon (Carter, 1846),
P. americanus (Nace, 1939), P. australis (M’Coy, 1867), P. sachi-
carum (P
aramo, 1997), P. hercynicus (Kuhn, 1946), and P. hau-
thali (von Huene, 1927).
Diagnosis—Maxilla and prefrontal contact present; postfron-
tal medial extension not over anterior margin of upper temporal
fenestra; frontal entering upper temporal fenestra; squamosal
absent; teeth set in sockets at least anteriorly; humerus with up
to four facets (anterior and posterior for pre- and postaxial
accessory digits); more than seven digits in forefin, including
more than one preaxial accessory digit; phalanges polygonal and
closely packed, number of elements in longest digit of forefin
>17; ischium and pubis fused; femur with two or three distal
facets.
Locality and Horizon—Lower to Upper Cretaceous (Berria-
sian to Cenomanian) of Australia, Canada, U.S.A., Argentina,
England, Germany, France, and Russia.
Ji et al.—Phylogeny of the Ichthyopterygia (e1025956-13)
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Discussion—P. americanus and P. australis do not form a clade
in the current analysis, which has been suggested in previous
research (Druckenmiller and Maxwell, 2010; Fisher et al.,
2013a). However, due to the incomplete specimens of this
period, this topology is not stable (Bremer value very low),
although Platypterygius is known from plenty of complete speci-
mens. No assignment or further discussion is made here.
Genus CAYPULLISAURUS Fern
andez, 1997
Type Species—Caypullisaurus bonapartei Fern
andez, 1997.
Referred Species—Type species only.
Diagnosis—No contact between supratemporal and postor-
bital; basioccipital extracondylar area reduced; teeth reduced
and probably absent; postorbital region broad; humerus with
three distal facets, the anterior one articulating with a preaxial
accessory element; facet for ulna smaller than radial facet and
set off obliquely; phalanges polygonal and closely packed; ele-
ments in longest digit probably >24; hind fin preaxial and postax-
ial accessory digits present.
Locality and Horizon—Upper Jurassic (Tithonian) of
Argentina.
DISCUSSION
The goal of this study is to reanalyze the phylogeny of the Ich-
thyopterygia. With the addition of new taxa reported during the
last decade, the current study is the most comprehensive phylo-
genetic analysis of the Ichthyopterygia (48 ingroup taxa) to date.
The resulting tree is robustly supported in the Triassic part, with
high Bremer support values found in all major clades, such as
Parvipelvia (Bremer support D6 steps), Merriamosauria (5),
Grippioidea (5), Ichthyosauria (3), and Euichthyosauria (3). All
major family-level clades are also well supported in the Triassic
part of the tree, as in Mixosauridae (5), Cymbospondylidae (3),
Toretocnemidae (3), and Shastasauridae (3). This robustness of
the Triassic part is one of the greatest advances made in the pres-
ent study over previous phylogenetic hypotheses. In contrast, the
post-Triassic part is weakly supported, with most nodes having a
Bremer support of only 1 step. Thunnosauria (Bremer value D3
steps) and Ophthalmosauridae (6) are the major clades that are
highly supported in this analysis compared with the weak
ingroup topology. Leptonectes is a monophyletic group contain-
ing three species (Bremer value D3 steps), L. tenuirostris, L.
moorei, and L. solei, respectively.
The current analysis has included the new taxa reported
recently and especially expanded the evolutionary topology of
Triassic ichthyopterygians. In contrast to previous topologies
(e.g., Motani, 1999; Maish and Matzke, 2000), Chaohusaurus
appears as the most basal genus. This is mainly because many
complete specimens of Chaohusaurus have been found during
the past five years and revealed new morphological information
of this group (Chen et al., 2014; Motani et al., 2015a, 2015b).
New evidence from ammonoids suggests that the first occurrence
of Chaohusaurus was in Procolumbites Zone (Ji et al., 2015),
which is older than Utatsusaurus (Subcolumbites Zone) (Shi-
kama et al., 1978). The clade of Grippioidea nov. in the current
analysis is well supported with a Bremer value of 5 steps and
seven characters listed above. The four genera of ichthyoptery-
gians from the Early Triassic were located in four different
regions (South China, Japan, British Columbia of Canada, and
Spitsbergen, respectively), suggesting a fast diversification after
their first appearance and geographic diffusion.
Xinminosaurus is from the Anisian (Middle Triassic) of Guiz-
hou, South China (Jiang et al., 2008). Compared with contempo-
raneous ichthyosaurs such as mixosaurs and Cymbospondylus,it
exhibits more primitive features in the limbs, such as elongated
phalanges. The phylogenetic analysis suggests a relationship
between Xinminosaurus and Cymbospondylus and the reestab-
lished Cymbospondylidae is based on three characters (listed in
Systematic Paleontology). However, the topology within Cym-
bospondylidae is not strongly supported (Bremer support of only
1 step) because C. nichollsi and Xinminosaurus are not
completely preserved, missing most of the skull morphology.
New material is required to support the ingroup topology.
Mixosauridae is a group of ichthyosaurs diagnosed by a combi-
nation of unique features and has a wide geographic distribution.
Recent discoveries from multiple localities reveal new informa-
tion on mixosaur morphology and taxonomy (Maisch and
Matzke, 1997, 1998, 2000, 2001, 2005; Maisch et al., 2003; Nich-
olls et al., 1999; Schmitz, 2005; Jiang et al., 2006, 2007; Kolb
et al., 2011; Liu et al., 2011, 2013). Here it is a monophyletic
clade formed by Mixosaurus and Phalarodon. The ingroup topol-
ogy is nearly identical to Jiang et al. (2006) except that the
ingroup topology of Mixosaurus is not resolved in the current
analysis. M. kuhnschnyderi is coded for only 23 out of 163 char-
acters, resulting in the polytomy of this clade.
In the present analysis, Shastasauridae is expanded to include
the traditional shastasaur Shastasaurus and Shonisaurus and the
taxa from South China, Guizhouichthyosaurus, Guanlingsaurus,
and ‘C.’ wolonggangensis. This group is diagnosed based on the
combination of features listed above. Shang and Li (2009)
assigned Guizhouichthyosaurus tangae to Shastasaurus based on
the following features: rather short vertebrae; cervical vertebrae
with bicipital rib facet; presence of chevrons; long and slender
clavicle, slightly curved posteriorly; coracoid axe-shaped and
asymmetrical; scapula anterior flange well developed; relatively
short humerus, radius, and ulna; notch present on the anterior
margin of humerus and radius; radius much bigger than ulna;
posterior margin of radius and anterior margin of ulna slightly
concaved; and rather big radiale. However, features such as short
vertebrae, cervical vertebrae with bicipital rib facet, and scapula
anterior flange well developed are common features in all mer-
riamosaurians or even ichthyosaurians. The unique morphology
of the humerus, radius, and ulna is a synapomorphy of the Shas-
tasauridae. The occurrence of a notch on the anterior margin of
the humerus and radius is more complicated and variable (Chen
and Cheng, 2003; Shang and Li, 2009; C.J., pers. observ.) which is
not a proper diagnosis of this species. Above all, the current
analysis does not support the monophyletic clade of Guizhouich-
thyosaurus and Shastasaurus. Compared with the abundant
materials of Guizhouichthyosaurus from South China, Shasta-
saurus includes only poorly preserved specimens, but the former
can still be easily distinguished from the latter by the presence of
shallow groove anterior to the external naris and the relatively
small proximal elements on the digit II of hind limb.
Callawayia neoscapularis, from the Norian (Late Triassic) of
British Columbia, was proposed to be closely related with Shas-
tasauridae by previous workers. In the phylogenetic hypothesis
of Nicholls and Manabe (2001), Callawayia forms the sister
group of Shonisaurus, with Shastasaurus as the next clade out.
However, although Callawayia has a high presacral count of
over 60 and a similar forefin pattern as Shastasauridae, it already
has more derived cranial features, such as the absence of a max-
illa dorsal lamina and presence of a parietal ridge. The femur of
Callawayia is different from that of Shastasauridae and similar to
that of Toretocnemus. It is constricted medially, and distally
much wider than proximally, but not as much as in Toretocne-
mus. The preserved outline of the right femur of RTMP
94.380.11 (Nicholls and Manabe, 2001:fig. 11) is not genuine but
a result of compression (pers. observ., C. J.). Therefore, Calla-
wayia is more likely an intermediate between Shastasauridae
and the more derived Parvipelvia. This is also in accordance with
its stratigraphic occurrence.
Recently, much new material has been collected from the
Early Triassic of Chaohu, South China, suggesting a much higher
Ji et al.—Phylogeny of the Ichthyopterygia (e1025956-14)
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diversity in this period than previously supposed (e.g., Motani
et al., 2014, 2015a, 2015b). Further study of this new material
may change the topology of the Early Triassic ichthyosaurs.
Since the first record from multiple localities of the late Early
Triassic, ichthyosaurs diversified fast and exhibited a remarkably
high level of disparity during the Anisian. Large-bodied ichthyo-
saurs of over 6 m might have existed already by the end of the
Olenekian (Wiman, 1910; Scheyer et al., 2014), and the largest
ichthyosaurs, with an estimated length of over 20 m, appeared in
the Norian, namely, Shonisaurus sikanniensis (Nicholls and Man-
abe, 2004). Many types of dentition in the Ichthyopterygia all
emerged during the Triassic, indicating the widest range of tro-
phic adaptations within this group (Motani, 2005). The largest
ichthyosaurs Shonisaurus and the top predator Himalayasaurus,
both appeared during the Late Triassic—coinciding with the
appearance of the parvipelvian ichthyosaurs Hudsonelpidia and
Macgowania. Triassic ichthyopterygians were not less diverse
than post-Triassic forms as previously believed (Callaway, 1989).
Although the Triassic was shorter than half of the post-Triassic
history of ichthyopterygians (51 vs. 107 million years), there
were as many genera (21 vs. 24) in the Triassic. The number of
species was smaller (31 vs. 38), but this difference is not as great
as the difference in temporal duration.
The tree topology within Parvipelvia, especially of Thunnosau-
ria, is nearly fully resolved but weakly supported, mainly because
many taxa do not have a complete skeleton preserved. Some taxa
(e.g., Mollesaurus and Acamptonectes) are excluded from this
study because the specimens are too fragmentary to supply suffi-
cient morphological data (note that we only included those taxa
for which 1/3 or more of the characters are known). The current
analysis supports the major aspects of the topology of Fischer
et al. (2013) such as the monophyly of Neoichthyosauria and
Thunnosauria, but some differences are also shown. That Hauf-
fiopteryx is located within Stenopterygiidae (Maisch, 2008) is not
supported. It appears outside Thunnosauria, which is in accor-
dance with the hypothesis of Caine and Benton (2011) and Fischer
et al. (2013). Ophthalmosauridae is the most stable clade of the
post-Triassic topology, with a Bremer index of 6. However,
although the clades of ophthalmosaurids and platypterygids are
found in the strict consensus tree, the ingroup topology is weakly
supported and easily collapses when adding or removing a new
taxon. The true picture will only emerge when complete speci-
mens of these poorly known taxa become available.
According to the stratigraphic occurrences of each taxon, the
Middle Jurassic radiation that they document is still remarkable,
but the Late Jurassic radiation may have occurred in separate
clades. Given that we did not recode all the character states of
parvipelvians, the most likely reason behind this discrepancy is
the character polarization that was mentioned earlier. However,
because Bremer values for clades within Parvipelvia are unani-
mously low except for Thunnosauria and Ophthalmosauridae,
the topology presented here requires future corroboration. More
informative characters, and redescription of historical materials,
are required to improve the phylogenetic hypothesis in the
future.
The phylogenetic analysis is in approximate accordance with
the stratigraphic distribution of each taxon, especially for those
of the Triassic (Fig. 6). During the past decade, many new taxa
have been reported from both Triassic and post-Triassic and
from multiple localities, which greatly increased our knowledge
on the diversity and stratigraphy of the Ichthyopterygia. How-
ever, many ghost lineages still exist in the Ichthyopterygia, espe-
cially within the Thunnosauria.
ACKNOWLEDGMENTS
This research was supported by Projects 41372016 and
41402014 from the National Natural Science Foundation of
China, Project 123102 from State Key Laboratory of Palaeobiol-
ogy and Stratigraphy (Nanjing Institute of Geology and Palaeon-
tology, Chinese Academy of Sciences), and Project
20120001110072 from the Research Fund for the Doctoral Pro-
gram of Higher Education to D.Y.J. C.J was supported by a
grant from the China Scholarship Council for one-year research
in the U.S.A. We thank J.-l. Li, C. Li, Q.-h. Shang, and F. Zheng
(IVPP), G.-z. Yin (GMR), X.-h. Chen and L. Cheng (YIGMR),
P. Holroyd (UCMP), B. Strilisky (RTMP), B. Adams (NSM), G.
Teruzzi (MCSNM), K. Seymour (ROM), H. Furrer (BIMUZ),
and R. Schoch (SMNS) for providing access to the specimens in
their care. We thank C. McGowan for providing photographs. C.
J. thanks N. Kelley for helpful discussion on the manuscript. We
thank the two anonymous reviewers for critical comments and
suggestions that helped improve the manuscript.
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