Paludidraco and Cymatosaurus in the LRT

It’s been awhile since we looked at anything wet.
A new robust-ribbed sauropterygian, Paludidraco ( Fig. 1, Middle Triassic) does indeed share many traits with Simosaurus, as described by Chaves et al. 2018.

A welcome confirmation!
Due to its tiny dentition, Paludidraco was originally considered a likely filter feeder, distinct from related, long-toothed nothosaurs and plesiosaurs. Simosaurus also has relatively tiny teeth, but on a larger skull and fewer in number. That’s evolution at work!

Isn’t it great to see these two related taxa together? Doesn’t it make compare and contrast so much easier? See the evolution of the human ear bones from primitive jaw bones illustration here for another great example of comparative anatomy.

Figure 1. Simosaurus compared to Paludidraco. Isn’t it great to see these two related taxa together? Doesn’t it make compare and contrast so much easier? 

Chaves et al. 2018 provided
a cladogram of marine reptile relationships (Fig. 2). Most of these taxa are also included in the large reptile tree ( LRT, 1261 taxa, subsets Figs. 3, 4), which includes many times more taxa and more marine reptiles. Missing from the Chavez team cladogram (Fig. 2) is the genus/taxon Anningsaura, which links nothosaurs to pistosaurs + plesiosaurs in the LRT. The Chaves et al. cladogram, nests Cymatosaurus (Fig. 4) and Corosaurus basal to Pistosaurus + plesiosaurs.

Figure 2. Paludidraco cladogram from Chaves et al. 2018 with arrows showing how taxa nest in the LRT. Taxon exclusion is the problem here. See figure 3.

The Chaves et al. 2018 cladogram
(Fig. 2) excludes many pertinent taxa, so much so that important interrelationships were missed, based on the authority of the LRT (Fig. 3), which minimizes taxon exclusion due to its wider gamut of taxon inclusion. Several taxa in the Chaves et all cladogram would shift positions when tested with more taxa (arrows in Fig. 2) as the LRT shows (Fig. 3).

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria). Paludidraco was not added when this graphic was created, but has since been added. Sharp-eyed readers will see Vancleavea here.

Cymatosaurus
had to be added to the LRT (Fig. 4) to test it fairly against the Chavez team cladogram (Fig. 2). Only the skull is known (AFAIK) from three different species.

FIgure 4. The addition of Cymatosaurus is more of an insertion, that changes nothing else in the tree topology. Here it nests on the nothosaur side of Simosaurus, not close to plesiosaurs.

Despite the many offshoot traits
found in Anningsaura, the rest of its traits nest it firmly at the base of the pistosaurs + plesiosaurs, where Chaves et al. nests Cymatosaurus. In the LRT Cymatosaurus nests close to Paludidraco, but more on the nothosaur side than the plesiosaur side.

References
Chaves C de M, Ortega F and Pérez‐García A 2018. New highly pachyostotic nothosauroid interpreted as a filter-feeding Triassic marine reptile. Biology Letters. 14 (8): 20180130.
Maisch MW 2014. A well preserved skull of Cymatosaurus (Reptilia: Sauropterygia) from the uppermost Buntsandstein (Middle Triassic) of Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen. 272 (2): 213–224.

wiki/Paludidraco

Excuses for not posting last week…

1. I finally wrote another paper and submitted it. That took all week.
2. There wasn’t much other paleo news to get excited about (unless I missed something?).

Now that I’m back to looking at other things,
all I see is a pachypleurosaur with small hands and feet of uncertain affinities, Dawazisaurus (Cheng, Wu, Sato and Shan 2016). I note the authors did not test it against Hanosaurus and Dianmeisaurus, where it nested in the large reptile tree.

I’m pleased and surprised to see that readership does not flag
on quiet weeks. And for some reason Sunday was a big day. Thank you all for your continued interest.

References
Cheng Y-N, Wu X-C, Sato T, Shan H-Y 2016. Dawazisaurus brevis, a new eosauropterygian from the Middle Triassic of Yunnan, China. Acta Geologica Sinica (English) 90:401-424.

 

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

Diandongosaurus – pachypleurosaur/placodont transitional taxon

Just found another paper on Diandongosaurus the day after, August 30, 2015. See below.

Diandongosaurus acutidentatus (Shang et al. 2011, IVPP V 17761) was originally considered, “neither a pachpleurosau nor a nothosauroid; it might be the sister group of the clade consisting of Wumengosaurus, the nothosauroid and those taxa traditionally considered as pachypleurosaurs.”

Shang et all are almost correct.
Despite its very pachypleurosaur-ish overall appeance (Fig. 2), Diandongosaurus nested at the base of the Placodontia in the large reptile tree.

Figure 1. Diandongosaurus skull. The DGS method shows the dorsal and palatal views of the in situ specimen.

Using DGS,
the skull of Diandongosaurus (Fig. 1) is only slightly different than originally described. The prefrontal does not meet the postfrontal in this or any other basal sauropterygian. The premaxilla/maxilla suture is shifted slightly forward so that the premaxilla has only 4 teeth.

Figure 2. 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.

While we’re discussing the base of the Sauropterygia…
I realized that all sister taxa of Cartorhynchus (Fig. 4) have about 19 cervicals and 19 dorsals. Originally I had reconstructed Cartorhynchus withe its pectoral girdle close to the skull, where it was found in situ. But the pectoral girdle was much wider than the ribs in that area. Of course crushing is involved, but if you move the pectoral girdle closer to the 19th cervical, then everything appears to fit a little better (Fig. 3). Those posterior cervical ribs were dorsalized, indistinct from the dorsal ribs based on available data. Perhaps a closer look would show the line of demarcation.

Figure 2. Cartorhynchus reconstruction in lateral and dorsal views with new lateral view skull and pectoral girdle. 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.

You might remember 
Cartorhynchus (Motani et al. 2014) was originally considered a type of basal ichthyosaur. Having a short neck was part of that decision. Lacking the correct generic sister taxa (Fig. 4) was also part of that decision. A few score revisions nested Cartorhynchus as a sister to Qianxisaurus, which also has poorly ossified manual digits.

Figure 4, Subset of the large reptile tree: the marine younginiformes, including the Enaliosauria (Sauropterygia + Mesosauria + Thalattosauria + Ichthyosauria)

A second paper on Diandongosaurus 
(Sato et al. 2013) just came to my attention, restudied on the basis of a new specimen, also in ventral view.  It is preserved straight as an arrow. (Fig. 5).

Figure 5. Sato et al. specimen of Diandongosaurus.

The Sato et al team
nested their specimen at the base of the nothosauroids (Nothosaurus, Corosaurus, Lariosaurus), but they did not include Palatodonta, Pappochelys and other basal placodonts. Instead they used Placodus and Cyamodus to represent all placodonts. The Sato et al. team also used many suprageneric taxa, except among the pachypleurosaurs.

By duplicating the deletion
of all but two placodonts, the large reptile tree recovered Diandongosaurus at the base of the the Sauropterygia, basal to Pachypleurosaurus. So no change there. However, Placodus and Cyamodus now nested between Wangosaurus and Simosaurus among the basal plesiosaurs, one node away from the nothosaurs.

By duplicating the taxon list 
of Sato et all. (as best as I could using 25 similar or the same taxa) Diandongosaurus did not change its nesting between Anarosaurus and Pachypleurosaurus. Likewise, the sauropterygians did not change their topology. However, other taxa were all over the place. The soft shell turtle, Odontochelys, nested at the base with the thalattosaur, Askeptosaurus. The rhynchosaur, Hyperodapedon and the choristodere, Champsosaurus nested with the placodonts, Placodus and Cyamodus. Claudiosaurus nested with Prolacerta, Trilophosaurus, Iguana (representing Squamata) and Proterosuchus (representing Archosauriformes). These odd nestings demonstrate the importance of having a broad gamut study to enable a verifiable narrowing of focus on a subset of that broad gamut study. Otherwise, its just scattershot, as shown above.

References
Motani R et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866
Sato T, Cheng Y-N, Wu X-C and Shan H-Y 2013. Diandongosaurus acutidentatus Shang, Wu & Li, 2011 (Diapsida: Sauropterygia) and the relationships of Chinese eosauropterygians. Geological Magazine 151:121-133.
Shang Q-H, Wu X-C and Li C 2011. A new eosauropterygian from Middle Triassic of Eastern Yunnan Province, Southwestern China. Vertebrata PalAsiatica 49(2):155-171.

 

wiki/Cartorhynchus

Qianxisaurus. A new big pachypleurosaur.

A recent paper by Cheng et al. 2012 describes a new Middle Triassic sauropterygian, Qianxisaurus chajiangensis, based on a virtually complete (missing some manus digits) articulated skeleton. The teeth are unusual with a slightly constricted peduncle and short conical crowns. The upper temporal fenestrae were small, smaller than in Pachypleurosaurus, an outgroup taxon in the large reptile tree, and much smaller than in Lariosaurus, its closest relative. The retroarticular process was smaller than in related taxa.

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 large reptile tree. The Cheng et al. (2012) had some odd nestings including Kuehneosauridae (rib gliders) a little too close to turtles and thalattosaurs (Fig. x). The large reptile tree widely separated these taxa, as befitting their utterly distinct morphologies.

Figure x. Click to enlarge.  In response to a comment, I modified my statement about kuehneosaurs and turtles. Even so, note there are no taxa closer to the kuehneosaur/rhynchocepalian/ squamate clade than turtles and thalattosaurs in the Cheng et al. (2012) tree. This is incorrect. Some of these taxa have no business being listed here in a study of sauropterygians, like rhynchosaurs, kuehneosaurs and turtles (based on the large reptile tree). Other key taxa, like mesosaurs and Pachypleurosaurus, are missing.

There’s not a lot that should go wrong with an excellently preserved, completely articulated specimen — unless the included taxa are not related and excluded taxa are. Cheng et al. (2012) determined that Qianxisaurus was neither a pachypleurosaur nor a nothosauroid, but formed the sister group of the clade ‘Nothosauriformes’ without Wumengosaurus and Hanosaurus. The large reptile tree, employing far fewer sauropterygians, nested Qianxisaurus between Pachypleurosaurus and Lariosaurus. Pistosaurs nest as outgroups in the Cheng et al. (2012) tree, but nest as  a sister to Simosaurus in the large reptile tree, a major difference.

The present tracing of the skull of Qianxisaurus using the DGS method revealed more details and different details than in the Cheng et al. (2012) tracing (Fig. 1), including the presence of postparietals, tabulars and tiny supratemporals. The premaxilla contacted the frontals and split the nasals. Lacrimals were identified in Qianxisaurus, but these fuse to the maxilla in more derived taxa.

Figure 1. The skull of Qinxiansaurus. Below: the specimen in situ from Cheng et al. (2012). Middle: Original tracing by Cheng et al. (2012). Above: Using the DGS method other details emerge that were previously overlooked. Note the presence of supratemporals (bright green) and lacirmals (pink). Tiny inset: Pachypleurosaurus skull preserved in virtually the same configuration. The axis is re-identified and the former axis is now considered vertebra #3.

Perhaps one of the reasons why Qianxisaurus was not nested as a pachypleurosaur by Cheng et al. (2012) can be attributed to their interpretations of the skull that differ from the present interpretations. I found very few differences between Qianxisaurus and Pachypleurosaurus other than the lean of the quadrates.

Figure 2. Interpreting the disarticulated pedal elements of Qianxisaurus. The pes thus restored is very close to that of Lariosaurus.

The skull of Pachypleurosaurus is very small, and crushed, so overlooking super tiny bones like the supratemporal can be forgiven. The much larger Qianxisaurus offers a last look at these bones before they disappear in more derived taxa. The premaxilla between the nares needs to be reexamined in nothosaurs and other pachypleurosaurs because this area is prone to damage.

The unusual teeth suggest an unusual diet, but not one that led to any great new clades.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data. If I made any mistakes, I’ll clear them up when you send me the evidence.

References
Cheng Y-N, Wu X-C, Sato T, Shan H-Y 2012. A new eosauropterygian (Diapsida, Sauropterygia) from the Triassic of China. Journal of Vertebrate Paleontology 32(6):1335-1349.