SVP abstracts 14: Phylogeny of the Eosauropterygia reviewed

Lin et al. 2020 bring us a new phylogeny
of the Eosauropterygia (defined as: Pachypleurosaurus (Fig. 1) and descendants, or Sauropterygia sans Placodontia).

Figure 1. Pachypleurosaurus had more than two sacrals all converging on a tiny ilium.

From the Lin et all 2020 abstract:
“During the last two decades, abundant Triassic sauropterygians have been reported from Europe and southwestern China, which greatly improve our understanding of the diversity and stratigraphic, as well as paleogeographic, distribution of Triassic sauropterygians. The phylogeny of Sauropterygia was also repeatedly analyzed with the description of each new species. Except for Placodontia, however, various analyses of sauropterygian interrelationships have yielded incongruent results, especially with regards to the monophyly of Pachypleurosauridae and Eusauropterygia (= Eosauropterygia sans Pachypleurosauridae) which were alternatively supported or rejected by different analyses.”

“The incongruent results of these analyses were probably caused by the implementation of different character codings, based primarily on the same data matrix taken from a global parsimony analysis by Rieppel about 20 years ago, which was based almost exclusively on European material. Since we have a large number of new specimens from the rest of the world, it is high time to reexamine the phylogeny of the entire group, or at least of the eosauropterygians, in order to assess whether and how the newly described taxa affect overall tree topology.”

Figure 2. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Continuing from the Lin et all 2020 abstract:
“Given that the ingroup relationships of Placodontia is well established, we herein focus on reanalyzing the interrelationships of Eosauropterygia, which is the sister clade of the Placodontia within the Sauropterygia. We present a comprehensive phylogenetic hypothesis for Eosauropterygia based on a cladistic analysis of 137 characters coded for four outgroup and 49 ingroup taxa, including nearly all currently recognized Triassic eosauropterygian genera. This is the most inclusive phylogenetic analysis of Eosauropterygia to date.”

Does it include the taxa listed above (Fig. 1). If not, add them.

“The new phylogenetic hypothesis of Eosauropterygia suggests that Pachypleurosauridae is the sister taxon of Eusauropterygia, and their monophyly as traditionally upheld is reestablished.”

Which taxon is the last common ancestor? In the large reptile tree (LRT, 1751+ taxa, subset Fig. 2) indicates that Eusauropterygia is indeed monophyletic and arises from a series of pachypleurosaurs. This is distinct from the Lin et al. results which recovers a monophyletic Pachypleurosauridae.

“Furthermore, the monophyly of the genus Nothosaurus as traditionally conceived is not supported, whereas the monophyly of Lariosaurus is obtained if the lariosaurian affinity of N. juvenilis, N. youngi, and N. winkelhorsti is accepted. In this study, the monophyletic Pistosauroidea excludes Corosaurus and Cymatosaurus. The latter two genera are found to form a clade that represents the basal-most members of Eusauropterygia. The new phylogenetic hypothesis is mostly in good accordance with the stratigraphic distribution of the genera.”

I cannot comment further on a cladogram I have not seen. Overall the LRT recovers a traditional cladogram, with the exception of a short list of non-tradtional outgroups, like the Mesosauria, Thalattosauria and Ichthyosauria along with a long list of basal aquatic diapsids. The clade Enaliosauria is traditionally considered obsolete, but the LRT recovers it as a monophyletic clade. Turtles are not closely related when the valid, tested turtle sisters and ancestors are included in the taxon list. The initial radiation of sauropterygians evidently occurred prior to the Early Triassic given the diversity present in the Early Triassic and the diversity of mesosaurs in the Late Permian.

---

References
Lin W, Jiang D, Rieppel O, Motany R, Tintori A, Sun Z and Zhou M 2020. Phylogeny of the Eosauropterygia (Diapsida: Sauropterygia) incorporating recent discoveries from South China.  SVP Abstracts 2020.

wiki/Sauropterygia

Acostasaurus enters the LRT

Pérez and Noé 2017 described
a near complete 3D skull, a complete hindlimb and several vertebrae of a eusauropterygian, Acostasaurus (Fig. 1), they considered it a 4-5m long, snort-snouted pliosaur, one of many ‘pliosaurs’ found in Barremian (Early Cretaceous) Columbia. 

Figure 1. Acostasaurus skull from Pérez and Noé 2017, colors added.

Some of those purported Columbian ‘pliosaurs’
turned out to be giant sisters to more basal eusauropterygians in the large reptile tree (LRT, 1430 taxa). You might remember (here) the giant Sachicasaurus nested with Nothosaurus and (here) the very large Bobosaurus nested with the smaller Corosaurus.

In the LRT
Acostasaurus nests with Anningsaura (Fig. 2) apart from the pliosaurs in the LRT.

Figure 6. Anningasaura colorized from an old engraving. No other aquatic taxon has such bizarrely curved teeth. This taxon is closely related to Hauffiosaurus.

The authors compared Acostasaurus
with Simolestes a taxon not yet added to the LRT. Look for it soon.

Figure 4. Subset of the LRT focusing on Eusauropterygians (pachypleurosaurs, nothosaurs, plesiosaurs and kin).

---

References
Gómez Pérez M and Noè LF 2017. Cranial anatomy of a new pliosaurid Acostasaurus pavachoquensis from the Lower Cretaceous of Colombia, South America. Palaeontographica Abteilung A. 310 (1–2): 5–42. doi:10.1127/pala/2017/0068.

wiki/Acostasaurus

Bobosaurus enters the LRT

Figure 1. Bobosaurus in situ with colors added. See figure 2 for a reconstruction. Colors help segregate the elements.

Bobosaurus forojuliensis (Dalla Vecchia 2006; Fabbri, Dalla Vecchia and Cau 2014; Dalla Vecchia 2016/2017; Late Triassic, Early Carnian; MFSN 27285; Figs. 1, 2) is a large eusauropterygian originally considered close to Pistosaurus and among pistosaurians, closer to plesiosaurians. It was originally assumed to have large flippers despite lacking large flipper elements.

Here
in the large reptile tree (LRT, 1430 taxa), high–spined Bobosaurus nests as a 3x larger sister to Corosaurus with small hands and feet, not flippers. The pectoral elements were overlooked or considered ribs. Corosaurus was among the taxa tested in Fabri, Dalla Vecchia and Cau 2014. Not sure yet how the topologies differed, but they nested turtles between Claudiosaurus and Lepidosauriformes (like Icarosaurus) + Ichthyopterygia, a hypothesis of relationships not confirmed by the LRT.

Figure 2. Bobosaurus reconstructed to scale alongside the 3x smaller Corosaurus. Both share tall spines, small hands, a tiny ilium and other traits not found in sister taxa or pistosaurids. Not all ribs are shown.

In a similar story,
earlier we looked at another large eusauropterygian, Sachicasaurus, that was originally considered a small-handed pliosaur, but nested in the LRT with the more primitive Nothosaurus. 

Figure 4. Subset of the LRT focusing on Eusauropterygians (pachypleurosaurs, nothosaurs, plesiosaurs and kin).

---

References
Dalla Vecchia FM 2006. A new sauropterygian reptile with plesiosaurian affinity from the Late Triassic of Italy. Rivista Italiano Paleontaleontologia, Stratigraphia 112 (2): 207-25.
Dalla Vecchia FM 2016. Comments on the skeletal anatomy of the Triassic reptile Bobosaurus forojuliensis (Sauropterygia, Pistosauroidea). Gortania Geologia, Paleontolgia, Paletnologia 38:39–75.
Fabbri M, Dalla Vecchia FM and Cau A 2014. New information on Bobosaurus forojuliensis (Reptilia: Sauropterygia): implications for plesiosaurian evolution. Historical Biology 26 (5): 661-9.

wiki/Bobosaurus

Cartorhynchus: rebuilding the small ichthyosaur mimic

Mistakes were made here
earlier while reconstructing Cartorhynchus, the basal sauropterygian ichthyosaur-mimic. Those mistakes are corrected here (Figs. 1, 2) and already updated in earlier posts. All of these repairs further cement the relationship of Cartorhynchus to its sister, Sclerocormus  (Fig. 3) and its ancestral sister, Qianxisaurus (Fig. 4), taxa nesting near the base of the Eosauropterygia, not the Ichthyopterygia in the large reptile tree (LRT, 1401 taxa).

Figure 1. New tracing and reconstruction of the basal sauropterygian with weak flippers, Cartorhynchus. Note the flipped maxilla, now convex ventrally. The pectoral girdle is rebuilt based on that of Qianxisaurus. See text for details. Compare pectoral elements to Qianxisaurus in figure 5.

Cartorhynchus lenticarpus (Motani et al. 2014; Early Triassic) was originally considered a strange basal ichthyosauriform and a suction feeder. Here it nests with Sclerocormus and Qianxisaurus as a basal eosauropterygian representing a new clade of ichthyosaur-mimics with a very early appearance of flipper-like limbs. Neotony played a part in the appearance of a short rostrum, large eyes, short neck, poorly ossified phalanges and small size. The supratemporal was large here, and the splenial can be seen in lateral view, though just barely. These are also results of neotony as most sauropterygians lack them. The outgroup taxon, Pachypleurosaurus, fuses the large supratemporal and squamosal

Ichthyosaurs have the following traits by convergence.
Ichthyosaurs have robust scleral rings (eyeball bones) while most eosauropterygians do not. Distinct from most eosauropterygians and like ichthyosaurs, Qianxisaurus has small supratemporals and gracile scleral rings. The splenials are not visible in the present exposure. Like Cartorhynchus, the digits of Qianxisaurus are not well developed. 

Figure 2. Cartorhynchus reconstruction in lateral and dorsal views with new lateral view skull and old invalid dorsal view skull. The new pectoral girdle is in place here. The flippers seem to be relatively immobile. The tail was the main propulsive organ. Neotony created this sauropterygian with large eyes, short snout, short neck and digit-less limbs.

The premaxilla
of Cartorhynchus was tiny, ideal for nipping small food items. Small teeth were present, contra the original interpretation. The naris and orbit were quite large, distinct from all candidate sister taxa. The in situ maxilla was taphonomically flipped, so Cartorhynchus actually had a ventrally convex maxilla. The heavy ribs and flat bottom make Cartorhynchus look like a bottom feeder. The elevated dorsal neural spines suggest a dorsal fin (Fig. 2). The small scapula and coracoid suggest a weak, passive pectoral flipper. A long tail was probably present, as in its larger sister, Sclerocormus (Fig. 3). This would have been the primary propulsive organ. Note the lack of large flippers in Sclerocormus. Qianxisaurus is the last known common ancestor.

Figure 3. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms.

Qianxisaurus chajiangensis (Cheng et al. 2012; Fig. 4) is a Middle Triassic basal eosauropterygian based on a virtually complete articulated skeleton with all digits poorly ossified. Cheng et al. 2012 nested Qianxisaurus as derived from a sister to Wumengosaurus, a taxon that nested closer to thalattosaurs, ichthyosaurs and mesosaurs in the LRT. The Cheng et al. (2012) study had some odd nestings including Kuehneosauridae (rib gliders) a little too close to turtles and thalattosaurs. The LRT widely separated these taxa, as befitting their utterly distinct morphologies.

Figure 4. Slight changes to the temple region of Qianxisaurus shows the reappearance of the suptratemporal, which had been lost in more primitive taxa only to be reacquired here and further elaborated in Cartorhynchus.

The LRT
nests Qianxisaurus between Pachypleurosaurus and Lariosaurus. Pistosaurus nests as an outgroup in the Cheng et al. (2012) tree, but closer to Simosaurus in the LRT.

The upper temporal fenestrae of Qianxisaurus
were smaller than in Pachypleurosaurus. The supratemporal formed the posterior rim without fusion to the squamosal. In Qianxisaurus the retroarticular process of the mandible was smaller than in related taxa. The teeth of Qixiansaurus were unusual with a slightly constricted cylinder and short conical crown.

Despite the small size of the ilium
at least four sacrals were present.

The Cartorhynchus-like pectoral girdle of Qianxisaurus.
The scapula (green Fig. 5) had a slim strap-like morphology. The clavicles were broader laterally, meeting medially in an arch shape, as in Cartorhynchus (Fig. 1).

Figure 5. The Qianxisaurus pectoral girdle is ancestral to the Cartorhynchus pectoral girdle with similarly shaped elements. Compare to figure 1. Interclavicle is hidden in situ and hypothetical here based on phylogenetic bracketing. 

Mimic taxa
appear occasionally in the LRT, which, so far, has been able to lump and split mimics by testing them against all available candidate sisters. Motari et al. 2014, for all his experience and expertise in ichthyosaurs, failed to add basal eosauropterygians, like Qianxisaurus, to their taxon lists and so was not able to consider this possibility. Better not to assume things, but to let the software perform an unbiased analysis starting with a wide gamut of taxa like the LRT.

Correcting mistakes
is part of the scientific process, whether they be internal or external. 

References
Cheng YN, Wu XC, Sato T and Shan HY 2012. A new eosauropterygian (Diapsida, Sauropterygia) from the Triassic of China. Journal of Vertebrate Paleontology. 32 (6): 1335. doi:10.1080/02724634.2012.695983
Jiang D-Y, Motani R, Huang J-D, Tintori A, Hu Y-C, Rieppel O, Fraser NC, Ji C, Kelley NP, Fu W-L and Zhang R 2016. A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction. Nature Scientific Reports online here.
Motani R et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866

wiki/Qianxisaurus
wiki/Cartorhynchus
wiki/Sclerocormus

 

Libonectes enters the LRT

After applying colors to
the bones in a photograph of the skull of Libonectes (Fig. 1, Turonian, early Late Cretaceous, Welles 1949, originally Elasmosaurus morgani), the Carpenter 1997 drawing was added to gauge similarities and difference. A transparent GIF makes this easy. Comparisons to the earlier (Late Triassic) Yunguisaurus and Thalassiodracon are instructional. These taxa also rotate the orbits anteriorly, providing binocular vision. The pterygoid (dark green) pops out slightly behind the jugal.

Figure 1. The skull of Libonectes. Freehand drawing from Carpenter 1997. DGS colors added here. Some parts of the original fossil may be restored. The fossil may be more fully prepared than this now. Note the slight differences between the fossil and drawing. The orbits appear to permit binocular vision.

Libonectes morgani, (Welles 1949, Elasmosaurus morgani, Carpenter 1997) an elasmosaur of the Turonian, early Late Cretaceous. In the large reptile tree (LRT, 1399 taxa) this skull nests with the skull-less Albertonectes (Fig. 2) and Plesiosaurus (Fig. 3) at first with no resolution owing to the lack of common traits between the skull-only and skull-less taxa.

Figure 2. Plesiosaurus skull in several views representing two specimens alongside the pectoral girdle. Data comes only from this drawing, not the fossil itself, which I have not yet seen.

Later the post-crania of Libonectes is added
and the two elasmosaurs now nest together sharing fore limbs slightly longer than hind limbs (Fig. 3) among several other less obvious traits. Neck length, much longer with more vertebrae than in Plesiosaurus, scores the same, “Presacral vertebrae, 31 or more” in the LRT.

Figure 3. Libonectes flippers. 2nd frame shows PILs. Terrestrial tetrapods flex and extend along continuous PILs. The in vivo misalignment of phalanges in Libonectes largely prevents flexion and extension, creating a large stiff flipper at misaligned PILs. Those that are more proximal are continuous, permitting a limited amount of flexion and extension.

Sachs and Kears 2017
bring us images and descriptions of the post-crania of Libonectes, a Late Cretaceous elasmosaur, one of the sauropterygian plesiosaurs, similar in most respects to the other tested elasmosaur, Albertonectes, which we looked at earlier here.

Distinct from terrestrial tetrapods
that flex and extend their phalanges along continuous PILs, the in vivo misalignment of phalanges in Libonectes largely prevents flexion and extension, creating a stiffer flipper at the misaligned PILs. Note, those that are more proximal are continuous, permitting more flexion and extension.

PILs were first documented
in Peters 2000. Many taxa may be distinguished by their fore and hind PIL patterns as also shown for pterosaurs in Peters 2011.

It is worth noting (and scoring)
that the forelimbs are slightly larger than the hind limbs in elasmosaurs, distinct from other sauropterygians, convergent with many ichthyosaurs, sea turtles and perhaps other taxa I am overlooking presently (overlooking some birds and all bats and pterosaurs for the moment, because they fly).

Figure 4. Elasmosaurid origins. The long neck preceded the flippers in this clade of vertical feeders.

We looked at hypothetical elasmosaur swimming techniques
a few months ago here.

References
Carpenter K 1999. Revision of North American elasmosaurs from the Cretaceous of the western interior. Paludicola, 2(2): 148-173.
Sachs S and Kear BP 2017. Redescription of the elasmosaurid plesiosaurian Libonectes atlasense from the Upper Cretaceous of Morocco. Cretaceous Research 74:205–222.
Welles SP 1949. A new elasmosaur from the Eagle Ford Shale of Texas. Fondren
Science Series, Southern Methodist University 1: 1-28.

wiki/Albertonectes
wiki/Libonectes

The skull of Sclerocormus reinterpreted.

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms. The odd thing about this genus is really the short neck, not the small head.

Yesterday we looked at the new basal sauropterygian with a tiny head, Sclerocormus (Figs. 1, 2). Originally Jiang et al. 2016 considered Sclerocormus ‘a large aberrant stem ichthyosauriform,’ but their cladogram did not have the stem ichthyosauriforms recovered by the 684-taxa reptile tree, Wumengosaurus, Thaisaurus and Xinminosaurus.

Basal sauropterygians often have a tiny skull. 
Check out these examples: Pachypleurosaurus, Keichousaurus, Plesiosaurus, Albertonectes. Given this pattern, the odd thing about Sclerocormus is its short neck, not its tiny skull. The outgroup, Qianxisaurus has a skull about equal to the cervical series.

As noted previously
the terms ‘aberrant’ or ‘engimatic’ usually translate into “somewhere along the way we made a huge mistake, but don’t know what to do about it.” For the same reason, pterosaurs are widely considered ‘aberrant’ archosaurs, Vancleavea is an ‘aberrant’ archosauriform, Daemonosaurus and Chilesaurus are aberrant theropods and caseasaurs are ‘aberrant’ synapsids. All of these taxa also nest elsewhere in the large reptile tree.

Moreover
several of the Jiang et al interpretations of the skull could not by confirmed by DGS tracings (Fig. 2). Others were just fine.

Figure 2. Sclerocormus skull as originally interpreted and reinterpreted here.

Reinterpretations

1. Jiang et al. nasals  >  nasals + premaxillae
2. Jiang et al. premaxilla (lower portion)   >  anterior maxilla
3. Jiang et al. premaxilla (upper portion)  >   left dentary
4. Jiang et al. missed the right dentary and all teeth
5. Jiang et al. missed the occipitals (postparietals, tabulars, supra occipital)
6. Jiang et al. maxilla   >   lacrimal
7. Jiange et al. scapula    >  coracoid + scapula
8. Jiang et al. mandible elements? are confirmed as actual mandible elements
9. Jiang et al. left postfrontal   >   postorbital
10. Jiang et al. left squamosal and postfrontal   >  left posterior mandible elements

Phylogenetically
here are the stem ichthyosaurs and a sampling if ichthyosaurs (Fig. 3). Note where hupehsuchids nest, as derived utatsusaurs and shastasaurs. Cartorhynchus and Sclerocormus (Fig. 1) do not nest here.

Figure 2. Subset of the large reptile tree focusing on ichthyosaurs. Note most of the more derived ichthyosaurs from Marek et al. 2015, are not listed here. So we’re not comparing apples to apples here.

References
Jiang D-Y, Motani R, Huang J-D, Tintori A, Hu Y-C, Rieppel O, Fraser NC, Ji C, Kelley NP, Fu W-L and Zhang R 2016. A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction. Nature Scientific Reports online here.

A new ichthyosaur mimic: Sclerocormus

A new Nature paper
by Jiang et al. 2016 introduces Sclerocormus, a large sister to the much smaller Cartorhynchus. Like a marine Cotylorhynchus, this odd basal sauropterygian had a tiny skull not much larger than that of its much smaller, big-headed sister (Fig. 1).

Figure 1. Large Sclerocormus and its much smaller sister, Cartorhynchus. These nest with basal sauropterygians, not ichthyosauriforms. Click to enlarge. Note the skull size of the two are within a short range.

These two nested
with Qianxisaurus, a basal sauropterygian/pachypleurosaur, not basal ichthyosauriforms. The authors are still in the dark about ichthyosaur ancestors. You can trace them, or any taxon, back to basal tetrapods here.

Figure 2. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

The authors
report that Sclerocormus had no teeth and that the nasals extended to the tip of the rostrum. I have to disagree with both observation given the photographic data and lack of similarity in sister. They also misidentified a few bones. Their big scapula is a posterior coronoid + smaller scapula.

More coming in later posts.

References
Jiang D-Y, Motani R, Huang J-D, Tintori A, Hu Y-C, Rieppel O, Fraser NC, Ji C, Kelley NP, Fu W-L and Zhang R 2016. A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction. Nature Scientific Reports online here.

Dianmeisaurus: perhaps not a new pachypleurosaur

A new paper
by Shang and Li (2015) presents an exquisitely preserved small (< 50cm) Middle Triassic pachpleurosaur (basal sauropterygian, IVPP V 18630) they name Dianmeisaurus (Fig. 1-3, pdf online here). Shang and Li noted resemblance to contemporary specimens attributed to Diandongosaurus Shang et al., 2011 and Dianopachysaurus Liu et al., 2011a, both similarly without a constricted snout and with a large orbit and small upper temporal fenestra. They reported the new genus, Dianmeisaurus, is characterized by extremely narrow frontals and a mandibular articulation close to the occipital condyle, a large and stout anterolateral process of the clavicle, the proximal ulna is much wider than the distal end and 41 presacral vertebrae. Other traits are distinct from one sister or the other.

Phylogenetic analysis
Shang and Li added this new taxon to a flawed cladogram by x and nested Dianmeisaurus between Diandongosaurus and Majiashanosaurus with 49 MPTs. Keichousaurus and Dianopachysaurus are also clade members close to the base of the Nothsauroidea.

By contrast,
I added Dianmeisaurus to the large reptile tree and found it nested with Keichousaurus and Hanosaurus at the base of the Nothosauroidea. Since the post-crania is completely visible (except for the ilium) the differences are all in the skull, which is exposed ventrally and only slightly disarticulated. Note the rather vague tracing by Shang and Li. By contrast, I traced more bones. They had first hand access to the fossil itself. I worked from published images using DGS (digital graphic segregation) and created a reconstruction in several views that closely match sister taxa.

Figure 1. Dianmeisaurus with tracing by Shang and Li 2015 and with tracings using DGS bottom from right to left: mandible and occiput, ventral view of dorsal elements, palatal elements, and at left all combined. Above are reconstructions in dorsal, lateral and palatal views. Note the differences with the original tracing. Click to enlarge. The depth of the premaxilla and length of the pmx teeth are guesses as dimensions are largely hidden by the overlying dentaries.

Distinct from Shang and Li 
I found the preorbital and postorbital regions sub equal. The pterygoids and and palatines are narrower. The maxillary processes are wider. Circumorbital bones are defined. A posterior parietal and occiput are separated and identified.

In the large reptile tree
Dianmeisaurus is similar to Hanosaurus, but differs from Keichousaurus in the following traits:

1. Orbit not > lateral temporal fenestra
2. Pineal foramen ≥ 0.20 minimum parietal length
3. Posterior parietal > 40º in dorsal view
4. Last maxillary tooth extends to posterior orbit
5. Phalanx number on pedal digit 4: five
6. Pedal 4.1 length/width less than 3/1.

Dianmeisaurus is similar to Keichousaurus, but differs from Hanosaurus in the following traits:

1. Orbit ≥ rostrum

Keichousaurus is similar to Hanosaurus, but differs from Dianmeisaurus in the following traits:

1. Frontal and parietal fusion

Other traits,
such as humerus vs. femur length, are not preserved or exposed in all three taxa. Keichousaurus traits are based on a published drawing. The current loss of resolution could be due to bad data, or could resolve itself with more pertinent taxa. Based on the above traits, Dianmeisaurus appears to be closer to Hanosaurus, which closely resemble one another. If congeneric, they are not conspecific.

Personal note
This is the 1500th blog post for this WordPress site.

References
Shang Q-H and Li C 2015. A new small-sized eosauropterygian (Diapsida:Sauropterygia) from the Middle Triassic of Luoping, Yunnan, southwestern China. Vertebrata PalAsiatica 10:265-280. online pdf here

SVP 14 – a new Diandongosaurus

Liu et al 2015
redescribe the basal sauropterygian/placodont Diandongosaurus with a new specimen.

Figure 1. Diandongosaurus exposed in ventral view, skull in dorsal view. Note the small size. At 72 dpi this image is 6/10 the original size.The last common ancestor of Diandongosaurus and Pachypleurosaurus was a sister to Anarosaurus at the base of the Sauropterygia.

From the abstract
“The eosauropterygian Diandongosaurus acutidentatus, first reported from the Upper Member of the Guanling Formation (Anisian, Middle Triassic) at Luoping, Yunnan Province, southwestern China, is a small pachypleurosaur-like form characterized by the following features: enlarged and procumbent teeth in the premaxilla and anterior portion of the dentary, fang-like maxillary teeth, clavicle with a distinct anterolateral process, 19 cervical and 19 dorsal vertebrae, and ungual phalanges of the pes extremely expanded. Except for the distinct anterolateral process of the clavicle, this taxon is very similar to Dinopachysaurus dingi, which is from the same locality and the same stratigraphic level, and of similar body size. Herein we describe a new, nearly complete skeleton of Diandongosaurus, which provides new information on the ventral side of the skull, the pectoral girdle and hind limbs. The posterior process of the interclavicle is absent, and the
coracoid foramen is present in the new specimen, features that cannot be seen in the holotype. The anterolateral process of the clavicle is more slender than that of the holotype. Furthermore, the phalangeal formula of the pes of the new specimen is 2-3-4-5-3, whereas the preserved phalangeal formula of the holotype is 2-3-4-6-4, and thus has a higher count for the fourth and fifth digits. The new specimen also shows that there are no vomerine teeth, the ‘anterior interpterygoid vacuity’ is absent, but a natural oval shaped ‘posterior interpterygoid vacuity’ is present, different from the referred specimen,
NMNS-000933-F03498. The results of our phylogenetic analysis also suggest Diandongosaurus is an eosauropterygian, closely related to the Eusauropterygia, and grouped together with Majiashanosaurus to form the sister-group of the Eusauropterygia.”

Different than the Liu et al. study,
the large reptile tree nests Diandongosaurus at the base of the Placodontia, derived from Anarosaurus, as described here. Shifting this specimen to the node suggested by Liu et al. adds 33 steps to the shortest tree.

Figure 2. Diandongosaurus subset of the large reptile family tree, nesting at the base of the Placodontia, yet still retaining its basal sauropterygian looks.

References
Liu et al. 2015. A new specimen of Diandongosaurus acutidentatus (Sauropterygia) from the Middle Triassic of Yunnan, China. Journal of Vertebrate Paleontology abstracts.

 

At the nothosaur/plesiosaur node

A cover story and rapid communication in the latest Journal of Vertebrate Paleontology features Wangosaurus (Ma et al. 2015, Fig. 1), a long-necked, short-faced sauropterygian with short fingers and toes.

[Unfortunately, Wangosaurus in the urban dictionary is “a complete jackass.”] But let’s concentrate on the fossil, which is virtually complete and wonderfully preserved.

Figure 1. Wangosaurus. Click to enlarge. Note the short fingers and toes.

Sister taxa
In the Ma et al paper, Wangosaurus nested as a sister Yungisaurus (Figs. 2, 3) and both were considered pistosaurids, the clade transitional between nothosaurs and plesiosaurs, despite their morphological differences.

Figure 2. The Ma et al. tree that nested Wangosaurus with Yungisaurus as a pistosaurid. Colors were added. Yellow = enaliosauria in the large reptile tree. Blue = protorosaurs + archosauriformes. Pink = lepidosauromorphs.

In the large reptile tree (subset Fig. 4), Yungisaurus also nests between Pistosaurus and Plesiosaurus, but Wangosaurus nests in a much more basal node, between nothosaurs and Simosaurus, still close to the nesting in the Ma et al. paper (Fig. 2).

Figure 3. Yungisaurus in situ and closeups of the skull and flippers. This is a much larger sauropterygian with longer toes transformed into flippers. Interesting to see the rear flippers larger than the forelimbs. So does that tell us something about their swimming technique?  

The Ma et al. tree is based on earlier work by Jiang et al. (2014 – featuring the basal placodont Majianshanosaurus), which is an updated version of Neenan et al. (2013). Note the differences in the skulls of Wangosaurus and Yungisaurus. Those don’t look like close relatives to me and their scores confirm those suspicions.

 

Figure 4. The enaliosaur/marine reptile subset of the large reptile tree. Note there are intervening taxa here between Wangosaurus and Youngisaurus.

The Ma et al. tree employs suprageneric taxa (always a problem). You’ll note that turtles and lepidosauriformes are the proximal outgroup taxa to sauropterygians here. That is not supported by the large reptile tree. I also find it odd that the marine reptiles Claudiosaurus and Hovasaurus nest so far from the rest of their natural clade in the Ma et al. tree, and separate from one another.

References
Cheng Y-N,  Sato T, Wu X-C and Li C 2006. First complete pistosaurid from the Triassic of China. Journal of Vertebrate Paleontology 6(2):501-504.
Ma L-T, Jiang D-Y, Rieppel O, Motani R and Tintori A 2015. A new pistosaurid (Reptilia, Sauropterygia) from the late Landinian Xingyi marine reptile level, southwestern China. Journal of Vertebrate Paleontology 35(1): e881832.