Eorhynchochelys: a giant eunotosaur, not a stem turtle

Figure 1. Skull of Eorhynchochelys sinensis with DGS colors applied to bones. These differ somewhat from the original bone drawing. This is a standard eunotosaur skull, not a pareiasaur or turtle skull. I see tiny premaxillary teeth, btw.

Li, Fraser, Rieppel and Wu 2018
introduce Eorhynchochelys sinensis (Figs. 1,2), which they describe in their headline as ‘a  Triassic stem turtle’ and in their abstract as ‘a Triassic turtle.’ Unfortunately, Eorhynchochelys is not related to turtles. Instead it is a spectacular giant eunotosaur (sister to Eunotosaurus).

Figure 2. Eorhynchochelys in situ alongside manus, pes, pectoral and pelvic girdle, plus Eunotosaurus to scale. By convergence Eorhynchochelys resembles Cotylorhychus.

The problem is, once again, taxon exclusion.
Li et al. employed far too few taxa (Fig. 3) and no pertinent turtle ancestor taxa (see Fig. 4).

Figure 3. Cladogram of turtle relationships by Li et al. 2018. Yellow-green areas are lepidosauromorphs in the LRT demonstrating the mix of clades present here due to massive taxon exclusion. The LRT has 40x more taxa.

We know exactly from which taxa turtles arise.
In the large reptile tree (LRT, 1271 taxa, Fig. 4): 1) hard shell turtles arise from the small, horned pareiasaur, Elginia. The basalmost hard shell turtle is Niolamia, not Proganochelys. 2) soft shell turtles arise from the small, horned pareiasaurs, Sclerosaurus and Arganaceras. The basalmost soft shell turtle is Odontochelys. None of these taxa have temporal fenestrae. We looked at turtle origins earlier here. Turtle origins were published online in the form of a manuscript earlier here.

Figure 4. Subset of the LRT focusing on turtle origins and unrelated eunotosaurs.

Unrelated
Pappochelys nests with basal placodonts. Eunotosaurus nests with the caseid clade, close to Acleistorhinus and Australothyris, all taxa with a lateral temporal fenestra. Li et al. suggested that this lateral temporal fenestra indicated that turtles were diapsids. That has been falsified by the LRT which shows that turtles never had temporal fenestra all the way back to Devonian tetrapods.

Eorhynchochelys sinensis (Li et al. 2018; Late Triassic) was considered the earliest known stem turtle with a toothless beak, but here nests as a giant aquatic eunotosaur with tiny premaxillary teeth. In size and overall build it converges with Cotylorhynchus.

References
Li C, Fraser NC, Rieppel O and Wu X-C 2018. A Triassic stem turtle with an edentulous beak. Nature 560:476–479.

More evidence that Meiolania is a basal turtle

Figure 1. Meiolania, the most primitive of known turtles, has lateral forelimbs, like non turtles. Extant turtle elbows point anteriorly. 

Earlier we looked at the bizarre and seeming highly derived skulls of Meiolania (Fig. 1) and Niolamia, (Fig. 2) two large late-surviving meiolanid turtles that are only known from rather recent fossil material following an undocumented origin in the Late Permian or Early Triassic.  They both nested as sisters to Elginia (Fig. 2; Late Permian), a toothed turtle sister with horns. So the horns and frills are primitive, not derived.

Figure 2. Comparing the skulls of Elginia, with teeth, and the turtle, Niolamia, toothless.

Here’s a review
of various turtle ancestor candidates in graphic format (Fig. 3). A candidate touted by several recent authors, Eunotosaurus, is among those shown.

Figure 3. In traditional studies Eunotosaurus nests at the base of turtles, but that is only in the absence of the taxa shown here and correctly scored. Here Eunotosaurus is convergent with turtles, but not related. Turtles arise from small pareiasaurs.

Cervical count
Pareiasaurs have 6 cervicals. Turtles have 8, several of which are tucked inside the shell. Proganochelys, often touted as the most basal turtle, has 8 cervicals. Horned Meiolania, at the base of the hard-shell turtles has 6 cervicals with ribs and 2 without ribs according to Gaffney (1985; Fig. 4). Most living turtles do not have cervical ribs. In Proganochelys cervical ribs are much reduced.

Note that in Odontochelys (Fig. 3 a similar situation arises where the all the vertebrae anterior to the expanded ribs are considered cervicals, even though two are posterior to the scapula. Similarly, in Proganchelys (Fig. 3) the last cervical is posterior to the scapula. In other tetrapods (let me know if I am forgetting any), all the cervicals are anterior to the scapula and a few dorsal vertebrae typically appear anterior to the scapulae. The tucking of the scapula beneath the ribs of turtles is a recurring problem with many offering insight.

Figure 4. Meiolania cervicals. Did Gaffney follow tradition when he identified 8 cervicals here? Only 6 have ribs (yellow) and the shape changes between 6 and 7.

There are several different possible nesting sites
for turtles with regard to living reptiles (including mammals and birds, Fig. 5). Only the LRT (in yellow) has not made it to the academic literature (after several tries) because it is the only tree topology that splits Archosauromorpha from Lepidosauromorpha in the Viséan, further in the past than other workers venture to place reptiles that still look like amphibians. Until we get the basic topology down and agreed upon, it is going to be difficult to nest turtles properly.

Figure 5. Various hypotheses regarding turtle origins. The LRT is added in yellow. Most studies show Synapsida as the basal dichotomy, whereas the LRT divides Lepidosauromorpha from Archosauromorpha together with two separate origins for diapsid reptiles.

References
Gaffney ES 1985. The cervical and caudal vertebrae of the cryptodiran turtle, Meiolania platyceps, form the Pleistocene of Lord Howe Island, Australia. American Museum Novitates 2805:1-29.

Eunotosaurus not a stem turtle – SVP abstracts 2016

Yet another confirmation
made 5 years later than this Oct 01, 2011 blog post.

Figure 1. The nesting of Microleter with Delorhynchus, Acleistorhinus and Eunotosaurus.

From the Hirayama R and Nakajima abstract:

“Eunotosaurus africanus has been often hypothesized as an ancestral form for turtles, as they share the wider dorsal ribs and highly reduced number of axial skeletons of body portion (1). Recent research points out further synapomorphies such as the T-shaped cross section of dorsal ribs shared with Triassic stem turtles such as Pappochelys, (2) Odontochelys, and Proganochelys. Nonetheless, this theory has a serious weak point—in E. africanus, the gastralia were absent, or very poorly developed as reported in just a few specimens, if any. (3) Ontogenetic studies of extant turtles strongly suggest that the chelonian shell was formed as a result of association of both carapacial (dorsal vertebrae and ribs) and plastral (pectoral girdle and gastralia) elements, with reduction of distal portion of dorsal ribs. This scenario seems to be supported by the body plan of Triassic stem turtles (4). E. africanus, however, has uniquely developed distal part of dorsal ribs. Dorsal vertebrae of E. africanus indicate a horizontal movement of the body and the presence of intercostal muscles. E. africanus has a unique overlapping of dorsal ribs, unknown in any stem turtles. (5) A T-shaped cross-section of dorsal ribs is observed in several tetrapods such as ankylosaurs (Ornithisuchia (sic)), armadillos, and anteaters (Xenarthra), not unique to E. africanus and stem turtles. In conclusion, E. africanus has its own uniquely derived defensive body structure, exclusively depending on dorsal ribs, not probable as an ancestral form to the turtle body plan. (6)

Fiigure 2. The turtle mimic Eunotosaurus from the Middle Permian was actually closer to Acleistorhinus.

Notes

1. In the LRT Eunotosaurus nests with Acleistorhinus and Microleter, far from turtles, which arise twice from phylogenetically miniaturized pareiasaurs like Elginia and Sclerosaurus.
2. In the LRT Pappochelys nests with basal placodonts like Palatodonta, even further from turtles.
3. This is a false presumption. Gastralia do not become the plastron in turtles, which arises in both clades of turtles.
4. A large gamut phylogenetic analysis clears this problem up. Sclerosaurus is Middle Triassic. Elginia is Late Permian, both with origins much earlier.
5. Excellent point. Too bad we have no post-crania for LRT sister taxa.
6. Too bad that the authors do not tell us what Eunotosaurus is in their analysis (if they produced one). The nesting of Eunotosaurus with Acleistorhinus occurs when both are present in the inclusion set and bones are correctly identified. That does not happen very often in academic publications.

References

Hirayama R and Nakajima Y 2016. Is Eunotosaurus africanus really ancestral to turtles? Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.

The origin of the anapsid skull of modern turtles

Earlier we looked at Bever et. al. 2015, a paper that purported to provide an answer for the anapsid origin of turtles by unsealing the temporal fenestra of purported ancestors, like Eunotosaurus (Figs. 1-3). As you might recall with incredulity, the authors actually peeled back the supratemporal to expose what they considered a hopeful upper temporal fenestra.

Even earlier we looked at Lyson et al 2014 (ome of these authors are the heavy-hitters and grand old men of paleontology), who examined the ribs of Eunotosaurus and considered them homologs of turtle ribs. They sure look like turtle ribs, but like other reptiles (e.g. Sinosaurophargis, Minmi and Henodus) this was by convergence. Those authors need to broaden their search.

Figure 1. This looks like Eunotosaurus (fossilized at left) is the ancestor to the extant turtle (in vivo at right), but phylogenetic analysis tells us this is just a case of convergence.

Unfortunately,
both Bever et al. and Lyson et al. essentially ignored the verified ancestors of turtles among small horned pareiasaurs (Figs. 1, 2) like Sclerosaurus and Elginia. This likely happened because the authors put all their effort and enthusiasm into Eunotosaurus, which, among many other reptiles, was convergent with turtles in several regards.

We’ve seen bias and propaganda like this before
whenever workers discuss the archosaur ancestry of pterosaurs, the Lagerpeton ancestry of dinosaurs, the diadectid ancestry of reptiles, the synapsid ancestry of caseids and other nestings not verified by the large gamut study at ReptileEvolution.com. In the latter study turtles are provided 660+ candidate taxa to nest with, including Eunotosaurus and other shelled reptiles. And with these choices, turtles nest with small horned pareiasaurs.

Figure 2. Click to enlarge. Above: Taxa employed by Bever et al. to promote their view of a diapsid origin for the turtle skull. Below: what the large reptile tree recovers. Note that Bever et al. mislabel the supratemporal and squamosal and they omit the best candidates for turtle ancestry. Eunotosaurus is a sister to Acleistorhinus. For more details, see the large reptile tree. Elginia, a key transitional taxon at the base of the hard shell turtles, is not shown here. Use the links below to find it at ReptileEvolution.com

In like fashion, Lyson et al. 2015 ignored 
better, closer, more parsimonious ancestral candidates among the small pareiasaurs in their post-cranial studies (Fig. 2). I know those broad ribs are tempting, but a suite of 228 traits indicates that turtles do not nest with Eunotosaurus. By convergence, Diadectes and Stephanosphondylus have broad anterior ribs on narrow stems, and neither is more closely related to either Eunotosaurus or turtles. The origin of the soft shell or hard shell turtle shell is still unknown or unpublished. The Bever et al cladogram (Fig. 2) is old school. It does not echo the results of the large reptile tree.

Figure 3. Click to enlarge. From Lyson et al. 2014 with yellow boxes added for missing taxa.

A further problem
All prior studies, and I mean ALL prior studies, mislabeled the supratemporal and squamosal in Proganochelys and other living turtle. Even Gaffney 1983 mislabeled the horns of Meiolania as squamosal horns. Unfortuantely alll prior workers have ignored the correct labeling of the supratemporal horns of Elginia, which is a sister to the most basal hard shell turtle, Meiolania. No prior workers have published on the dual origin of soft shell and hard shell turtles. As you can see (Figs. 2, 4) the basalmost turtles are widely divergent in morphology. We still expect to find the Archaeopteryx of turtles. Despite Lyson’s quote, he doesn’t have it in Eunotosaurus. He has its crafty impostor.

Lee 1997 had it right.
That turtle origin study should not ignored. Lee found that pareiasaurs made good ancestors to turtles.

First things first.
Lepidosaur diapsids are not related to archosaur diapsids. This goes back to the origin of reptiles. So there is a lot of work to be done out there. That work has already been done here.

Figure 4. Dorsal views of bolosaur, diadectid, pareiasaur, turtle and lanthanosuchian skulls. The disappearance of the turtle orbit in lateral view occurs only in hard shell turtles.

Getting back to our headline:
The anapsid skull of modern turtles evolved from the horned anapsid skulls of small pareiasaurs without rib modifications (based on Sclerosaurus, Fig. 4). We don’t have postcrania for Elginia and the ribs of Bunostegos have not been published. We would like to have those ribs. We don’t have them at present.

References
Bever GS, Lyson TR, Field DJ and Bhullar 2015. Evolutionary origin of the turtle skull. Nature 525, 239–242 (10 September 2015) doi:10.1038/nature14900
Gaffney ES 1983. The cranial morphology of the extinct horned turtle, Meiolania platyceps, from the Pleistocene of Lord Howe Island, Australia. Bulletin of the AMNH 175, article 4: 361-480.
Lee MSY 1997. Pareiasaur phylogeny and the origin of turtles. Zoological Journal of the Linnean Society 120: 197-280.
Lyson TR, Bever GS, Bhullar B-AS, Joyce WG, Gauthier JA 2010. Transitional fossils and the origin of turtles. Biology Letters 6:830-833. online PDF
Lyson TR, Bever GS, Scheyer TM, Hsiang AY, Gauthier JA 2013. Evolutionary Origin of the Turtle Shell. Current Biology 23(12):1113-1119.
Lyson TR,  Schachner ER, Botha-Brink J, Scheyer TM, Lambertz M, Bever GS, Rubidge B, and de Queiroz K 2014. Origin of the unique ventilatory apparatus of turtles. Nature Communications. November 7, 2014. 5:5211. DOI: 10.1038/ncomms6211

Microleter mckinzieorum Tsuji et al., 2010

Microleter (Fig. 1) was described a few years ago (Tsuji et al. 2010) as an Early Permian parareptile (an invalid multiphyletic assembly of early reptiles). Tsuji et al. nested Microleter between millerettids and Acleistorhinus + Lanthanosuchus (another unnatural assembly).

Figure 1. Microleter in situ and reconstructed with a larger lateral temporal fenestra than originally reconstructed. The skull is 3 cm long. That’s a pair of fused vomers and a left pterygoid (dorsal view) at lower right. Freehand original reconstruction by Tsuji et al. 2010 at upper left. Note the expansion of the quadratojugal/squamosal in the freehand drawing compared to the in situ tracing. Note the reduction of the postorbital in the freehand drawing. Note the absence of the splenial in the freehand drawing.

Character analysis
Tsuji et al. used the matrix of Modesto et al. (2009) which was based on Mülller and Tsuki (2007) consisting of 30 taxa and 137 characters. Both numbers are too small. The analysis recovered six trees in which Microleter nested in an unresolved polygamy with Australothyris and Acleistorhinus  + Lanthanosuchus at the base of the ‘ankyramorphan parareptiles’ (another unnatural assembly).

The large reptile tree (575 taxa, completely resolved) found Microleter nested between Delorhynchus and Eunotosaurus + Acleistorhinus. The clade Australothyris + Feeserpeton is the proximal outgroup. The caseasaurs and millerettids are more distant.

Figure 2. The nesting of Microleter with Delorhynchus, Acleistorhinus and Eunotosaurus.

With insight Tsuji et al report, “As it is becoming increasingly clear, temporal fenestration is actually a common phenomenon among parareptiles, quite a departure for a group once termed Anapsida.”

Oddly,
Tsuji et al. include mesosaurs in their parareptilia and do not give them temporal fenestra. Oddly Tsuji et al nest Procolophon with Owenetta. Oddly they nest Eudibamus with Belebey. Oddly Tsuji et al nest Acleistorhinus with Lanthanosuchus, but not Eunotosaurus.They think the anapsid condition re-evolved in pareiasaurs. That’s not true. The ‘parareptile’ pseudoclade is a mess. It’s time for a thorough cleaning with more taxa.

Notably
the pterygoids produced a circular opening between them, as in Eunotosaurus, but not so exaggerated. Acleistorhinus does not have this trait. Here (Fig. 1), based on self-evident transfer techniques, the lateral temporal fenestra is reconstructed larger than Tsuji et al. drew it freehand. The lacrimal may not have contacted the naris according to the reconstruction where the maxilla contacts the nasal.

References
Linda A. Tsuji; Johannes Muller; Robert R. Reisz (2010). “Microleter mckinzieorum gen. et sp. nov. from the Lower Permian of Oklahoma: the basalmost parareptile from Laurasia”. Journal of Systematic Palaeontology 8 (2): 245–255.

The skull of Eunotosaurus CT scanned – still not a turtle ancestor!

Fiigure 1. The turtle mimic Eunotosaurus from the Middle Permian was actually closer to Acleistorhinus.

Before yesterday,
the best images of the skull of Eunotosaurus were simple drawings (Fig. 1). Now, thanks to Bever et al. (2015) we have CT scans of several skulls in several views (Fig. 2). For those we are all most grateful!

Figure 2. Click to enlarge. Eunotosaurus from CT scans. Left column, DGS tracings with restoration to in vivo positions. Middle column, CT scans from Bever et al. Right column, top, reconstructions by Bever et al. Bottom, juvenile skull with incorrect scale bar and correct scale bar.

Bever et al. reports, “If turtles are closely related to the other living reptiles then we would expect the fossil record to produce early turtle relatives with diapsid skulls. That expectation remained unfulfilled for a long time, but we can now draw the well-supported and satisfying conclusion that Eunotosaurus is the diapsid turtle. The skull of Eunotosaurus grows in such a way that its diapsid nature is obvious in juveniles but almost completely obscured in adults.”

The important word
in that paragraph is “IF.” Turtles are related to other living reptiles, but they are not either kind of diapsid (lepidosaur or archosaur). And, as you’ll see, the skull of Eunotosaurus does not grow in such a way that its diapsid nature is obvious. Bever et al. made several mistakes in their observations and analyses, as will be shown.

Bever et al. note that “Eunotosaurus africanus, a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive postcranial skeleton shares many unique features with the shelled body plan of turtles.

What Bever et al. fail to note
is that such an armored postcrania has evolved several times independently within the Reptilia. In addition to Eunotosaurus and turtles there are Sinosaurosphargis, Henodus and Cyamodus,  not to mention ankylosaurs, aetosaurs, armadillos and pangolins.

Bever et al. note: “Scepticism regarding the status of Eunotosaurus as the earliest stem turtle arises from the possibility that these shell-related features are the products of evolutionary convergence.”

True.
The large reptile tree indicates these shell-related features are convergent in the above-named taxa.

Figure 3. Sister taxa according to Bever et al. Eunotosaurus purportedly nests between the diapsid, Ascerosodontosaurus, and the turtles. The large reptile tree, on the other hand, finds that only the turtles are related to each other. Click to enlarge.

Bever et al. note: “Our phylogenetic analyses indicate strong cranial support for Eunotosaurus as a critical transitional form in turtle evolution. Furthermore, we find unexpected evidence that Eunotosaurus is a diapsid reptile in the process of becoming secondarily anapsid.”

That’s big news.
Worthy of a Nature paper, if valid. At it happens, secondary anapsids do occur in mesosaurs and ankylosaurs, but not turtles. The large reptile tree indicates turtle ancestors were always anapsids. And that Eunotosaurus and kin were all synapsid in skull morphology, but were not related to the real synapsids: pelycosaurs + therpasids + mammals (pan-mammals). Bever et al. did not test enough taxa or pertinent taxa. Most importantly, even if Eunotosaurus juveniles did have an upper temporal fenestra (Figs. 4, 5), they did so alone. All their closest sisters did not and adult Eunotosaurus did not have the upper temporal fenestra, but instead had a bone in that area.

Figure 4. Juvenile Eunotosaurus showing purported left upper temporal fenestra left by an absent supratemporal.

Bever et al. note: “This is important because categorizing the skull based on the number of openings in the complex of dermal bone covering the adductor chamber has long held sway in amniote systematics, and still represents a common organizational scheme for teaching the evolutionary history of the group.”

Held sway?? What Bever et al. fail to note
is that several of these skull morphologies arose more than once by convergence. This fact is not commonly known, but recovered in the large reptile tree. Remind yourself not to follow anyone who holds “held sway” up as evidence.

Figure 5. Eunotosaurus juvenile right side showing purported absent supratemporal. At right a possible displaced supratemporal is identified as bump on the otherwise humpless parietal that pretty well fits the opening left by its taphonomic shift.

Bever et al. note: “Our results suggest that Eunotosaurus represents a crucially important link in a chain that will eventually lead to consilience in reptile systematics, paving the way for synthetic studies of amniote evolution and development.”

Actually
Eunotosaurus currently represents a dead end in the large reptile tree.

The Bever et al figure 1 
misidentifies several bones on the skull of Proganochelys. They mistakenly follow the original bone identifications, where were changed here.

1. The postorbital + postfrontal was mistakenly labeled ‘postorbital.’
2. The tabular was mislabeled ‘supratemporal.’
3. The supratemporal was mislabeled ‘squamosal.’
4. The squamosal was mislabeled ‘quadratojugal.’
5. The quadratojugal was not separated from the jugal.

In support of this,
the long Eunotosaurus supratemporal is actually homologous to the mislabeled ‘squamosal’ (actually the supratemporal) of Proganochelys (same shape, same placement), despite their separation on the large reptile tree. Noting that would have added evidence to the Bever et al claims, but they let that one pass and stuck to the old paradigm. Basal turtles, like Elginia and Meiolania, and pre-tuirtles like Sclerosaurus and Arganaceras, had supratemporal horns, not squamosal horns.

The Bever et al cladogram (their figure 1) has several errors.

1. Eothyris is not a member of the Pan-mammals (Synapsida), but is in the Milleretta and Casea clade.
2. The term ‘Parareptilia’ does not represent a monophyletic clade.
3. Youngina does not belong on this cladogram of several Lepidosauromorpha, but belongs on another branch, the Archosauromorpha.
4. Elginia is a more basal and earlier stem turtle than Proganochelys, but is omitted in the cladogram.
5. Some of the drawings used are inaccurate, but that may matter only a wee bit.

Bever et al. report, “The skull of Eunotosaurus is relatively short and wide. Its compact snout bears approximately 23 robust, subthecodont marginal teeth and nasals that are longer than the frontals.” Actually the nasals are subequal to the frontals. You can measure them yourself.

Bever et al. report a “moderately sized suborbital fenestra,” but I did not see any space between the ectopteryoid and palatine, only between the palatine and anterior pterygoid. In any case, the palate of Eunotosaurus does not resemble the palate of basal turtles.

Bever et al. report, “A lower temporal arcade is not present, leaving the cheek open ventrally.” Actually the adult jugal has a very tiny quadratojugal process. In the juvenile (Figs. 4, 5) the jugal has a large process that invades the lateral temporal fenestra, as in Acleistorhinus and Deloryhnchus, the verified sisters of Eunotosaurus. We just looked at that new process here.

Bever et al report, “The roof of the adductor chamber in a juvenile skull is marked by a distinct upper temporal fenestra (on both sides.” 

Actually there are several new fenestra in the juvenile skull (Fig. 4). And where is the supratemporal? On the left, the supratemporal appears to be crushed down into, rather than arching over the other temporal bones. On the right (Fig. 5) the supratemporal appears to have shifted medially. Now it looks like an unintended bump. So these purported ‘upper temporal fenestra’ were not really present in vivo. Furthermore, there are no genuine diapsids that nest close to Eunotosaurus in the large reptile  tree.

In the Bever et al. phylogenetic studies 
(Fig. 3) Eunotosaurus nests between basal Sauropterygia + Acerosodontosaurus and the turtles, Proganochelys + Odontochelys. Many suprageneric taxa were used, so there were many opportunites to cherry pick traits to fit a preconceived idea. That does not happen in the large reptile tree where every taxon is represented by a specimen or species. The large reptile tree is still fully resolved, and breaks down into fully resolved subsets.

Bever et al. report, “The adductor chamber (in Eunotosaurus)  is closed posteriorly by what appears to be an expanded tabular, though this bony plate may represent a posterolateral flange of the parietal. The putative tabular fills a space corresponding to what would otherwise be a moderately sized post-temporal fenestra.” That is a tabular.

Bever et al write, “The presence of a lower temporal fenestra in Eunotosaurus supports the hypothesis that the characteristically closed cheek of modern turtles is a secondary condition that evolved through expansion of the jugal, quadratojugal, and squamosal.”

 

Actually
the lower (lateral) temporal fenestra in Eunotosaurus is homologous with that of Acleistorhinus and kin. Turtle ancestors never had a lateral temporal fenestra according to the large reptile tree, but came closest with bolosaurs.

Eunotosaurus is not a good turtle ancestor.
Better ones are to be found. Unfortunately, the best turtle ancestors, Stephanospondylus, Arganaceras, Sclerosaurus, Meiolania and Elginia are not represented in the Bever et al. taxon list. Once again, taxon exclusion raises its ugly head.

Removal
of Acleistorhinus and Delorhynchus from the large reptile tree nests Eunotosaurus with its other sisters, Feeserpeton and Australothyris. One look, or deep study, and you’ll see why. Removal of those taxa nests Eunotosaurus between cousins Milleretta and the casesauria. Removal of those taxa nests Eunotosaurus with second cousins, Limnoscelis, Orobates and kin. Still no change in tree topology. Removal of these taxa finally nests Eunotosaurus between Stephanospondylus and Bashkyroleter, each at the base of their own clades with a slight change in tree topology. Still Eunotosaurus does not nest with turtles, Ascerosodontosaurus or basal sauropterygians.

At least some of the problem
with the Bever et al. report rests with their use of prior phylogenetic analyses, and/or accepting the results of those analyses without their own critical analysis of recovered sister taxa. For instance, the swimming  Claudiosaurus and they gliding Kuehneosauridae appear as sister taxa, while Claudiosaurus and another similar swimmer, Hovasaurus, do not. Those are problems. Nesting Diadectomorpha outside the Amniota is a problem.. Nesting bulky Rhynchosaurs as relatives of gliding Kuehneosaurs is also a problem. None of these problems exist in the large reptile tree, where all sister taxa look alike and display gradual accumulations of derived traits. Perhaps Bever et al. should have created their own matrix from scratch, as in the large reptile tree.

Bever et al. write: “Although it is the case that neither our parsimony nor Bayesian analyses recover the dominant molecular solution of a unique turtle–archosaur relationship, both approaches do agree that turtles arose somewhere within the greater diapsid radiation.”

No one knows
why turtle DNA is close to archosaur DNA. It is not supported by morphology.

Bever et al. write: “Singular expression of a lower temporal fenestra once unambiguously diagnosed mammals and their stem lineage, but is now recognized in a number of phylogenetically disparate ‘anapsid’ parareptiles, and may represent the ancestral

condition for the amniote crown. That is a false statement. The ancestral condition in basal amniotes was anapsid. Such a statement by Bever et al. is one based on hope, not observation.

Bever et al. write: “This observed pattern of concentrated homoplasy near the evolutionary origin of a character state is congruent with the concept of a protracted zone of variability that may commonly confound attempts to resolve the early history of clades and character systems” \This is observed only in bad cladograms. There is no such thing as a “protracted zone of variability.” At least I haven’t seen one. How would you measure it?

Bever et al. write, “The amniote upper temporal fenestra has enjoyed a famously uncomplicated history, being a nearly consistent fixture of the diapsid body plan since its first appearance in the Carboniferous.”  This is another false statement, according to the large reptile tree. The so-called Diapsida had two origins. Bever et al are working with outmoded data and small taxon sets.

Bever et al. write, “The combined morphologies expressed in the juvenile and adult specimens of Eunotosaurus provide not only the earliest direct evidence of an upper
temporal fenestra in a putative stem turtle, but the first evidence for how that fenestra may have closed before the origin of the turtle crown clade.” Except the juvenile does not have an upper temporal fenestra (careful examination reveals otherwise) and so it cannot close at this point. Bever et al did not examine the specimen carefully enough to find the taphonomically displaced supratemporals. Turtle embryos do not recapitulate this change during ontogeny. No sister taxa have an upper temporal fenestra. This is just a unique fossil that has successfully tempted a set of paleontologists into accepting its illusion, just like the pterosaur, Sordes and the thalattosaur, Vancleavea. 

Bever et al write: “The role of the supratemporal is an aspect of the Eunotosaurus model of temporal closure that would not have been predicted based on earlier studies.” No shit, Sherlock. “An anteriorly expanded supratemporal that develops late in postnatal development to cover the upper temporal fenestra must currently be considered an autapomorphy of Eunotosaurus.” Be wary of autapomorphies. Evolution does not create many of those.

Morevover, what is wrong with the logic here?
According to Bever et al. the giant supratemporal closed off the upper temporal fenestra in Eunotosaurus, but the supratemporal is a tiny bone at the back of the skull in Proganochelys. The several misidentifications in Proganochelys are noted above.

Bever et al. answer this logic conundrum with,
“but it is important to stress that an expanded supratemporal is not a necessary component of an evolutionary model of fenestral closure in turtles that has Eunotosaurus as a central figure. For example, an analogous secondary expansion of the supratemporal partially or completely covers the upper temporal fenestra of the marine thalattosaurs.” This is false. The upper temporal fenestra in thalattosaurs is not reduced by expansion of the supratemporal, which remains small and not involved. Rather the upper temporal fenestra in thalattosaurs is reduced to a slit or less by the straightening (loss of curvature) of the parietal and postorbital rims.

Bever et al. further speculate, “Moreover, the construction of the modern turtle skull played out over a time span of tens of millions of years, and it is well attested that dermal bones in
major vertebrate lineages can shift back and forth considerably relative to the underlying tissues on these timescales.” As you have seen so far, Bever et al. have no idea how the turtle skull evolved, based on evidence from the large reptile tree. They have not included the correct ancestral taxa, but have pulled similar taxa from other clades. They are working in a hopeful vacuum of outmoded analyses, small taxon lists and incorrect bone identities.

Bever et al. conclude, “It is thus evident that the turtle skull, like the turtle postcranium,
underwent profound modifications during its history that similarly obscured anatomical evidence for phylogenetic affinities by the time the crown-group condition was reached.” This is, as you know by now, a conclusion based on mistake after mistake.

Finally,
let us remind ourselves that turtles developed their own method for creating space for larger temporal adductors. It seems illogical that they would first lose this space by early closure of the upper temporal fenestra only to reacquire additional space by anterior expansion of the posttemporal fenestra and subsequent skull emargination.

But logic is not a factor here.
This is evolution. Phylogenetic analysis, as recovered in the large reptile tree, provides the story of how the turtle got its skull… and shell… and all of its other accessories.

And if the juvenile Eunotosaurus did have missing supratemporals creating quasi and temporary upper temporal fenestrae, like the fontanelle in the baby human skull, then the diapsid status of turtles is still not verified. Turtles have no diapsid relatives when enough pertinent taxa are included in analysis.

References
Bever GS, Lyson TR, Field DJ and Bhular B-A S 2015. Evolutionary origin of the turtle skull. Nature published online Sept 02. 2015.

A new jugal for Acleistorhinus

Earlier work by yours truly
on Acleistorhinus relied on drawings of the specimen (Fig. 3). Here (Fig. 1) a DGS tracing (colorizing skull bones) of photos from the original paper (Daly 1969) reveals a slightly new interpretation of the skull, and the jugal in particular.

Figure 1. Acleistorhinus skull with bones colorized (on left) along with reconstructions in dorsal and lateral view (on right). Note the distinct jugal restored here with two posterior processes arising from the postorbital process, as in Delorhynchus. Click to enlarge. Note the holes in several skull bones. The middle posterior process of the jugal is broken in situ and overlying the lower posterior process. Essentially both Delorhynchus and Acleistorhinus had dual lateral temporal fenestrae.

Acleistorhinus pteroticus (Daly 1969) Early Permian, ~3.5 cm skull length was consiered by DeBraga (2001, 2003) and DeBraga Reisz (1996) to be a Parareptile related to Lanthanosuchus, which is a clear mismatch. Daly (1969) considered Acleistorhinus a procolophonid. Here, in the large reptile tree, Acleistorhinus is derived from a sister to the RC14 specimen of Milleretta, is a sister to Delorhynchus (below; Reisz, Macdougall  and Modesto 2014) and phylogenetically precedes the turtle-like (but not related) Eunotosaurus (Fig. 2).

Figure 2. Acleistorhinus compared to sister taxa, Delorhynchus and Eunotosaurus.

The middle posterior process of the jugal in Acleistorhinus
is broken in situ and overlying the lower posterior process. Essentially both Delorhynchus and Acleistorhinus had dual lateral temporal fenestrae.

Since both Eunotosaurus and Milleretta 
had expanded ribs, it is likely that Acleistorhinus did so too. We do not know the post-crania at present.

Figure 3. The earlier attempt at reconstructing the skull of Acleistorhinus based on drawings in DeBraga and Reisz 1996. The interpretation of the temple region changes the most between this version and figure 1. No other taxa have such a temporal region, but the new interpretation resembles that of Delorhynchus. 

The new data
on Acleistorhinus did not change its placement in the large reptile tree. I did not have access to any of the specimens listed above. Even so, the new data further unites two taxa, Delorhynchus and Acleistorhinus, that had been earlier united by a suite of traits. Colorizing the bones greatly helps produce the reconstruction.

References
Daly E 1969. A new procolophonoid reptile from the Lower Permian of Oklahoma. Journal of Paleontology 43: 676-687.
DeBraga M 2001. The postcranial anatomy of Procolophon (Parareptilia: Procolophonidae) and its implications for the origin of turtles. PhD thesis, University of Toronto.
DeBragra M 2003. The postcranial skeleton, phylogenetic position and probable lifestyle of the Early Triassic reptile Procolophon trigoniceps. Canadian Journal of Earth Sciences 40: 527-556.
DeBraga M and Reisz RR 1996. The Early Permian reptile Acleistorhinus pteroticus and its phylogenetic position. Journal of Vertebrate Paleontology 16(3): 384–395.
Reisz RR, Macdougall MJ and Modesto S 2014. A new species of the parareptile genus Delorhynchus, based on articulated skeletal remains from Richards Spur, Lower Permian of Oklahoma. Journal of Vertebrate Paleontology 34:1033–1043.

wiki/Acleistorhinus

Turtles: still not related to Eunotosaurus, a turtle-mimic

Bever et al. (2014) report that Eunotosaurus (Fig. 1) is a turtle ancestor. This has been falsified in phylogenetic analysis (and see below). We learned earlier that Eunotosaurus is a turtle-mimic that actually nests with Acleisotorhinus, leaving no known descendants. Phylogenetic turtle ancestors include Stephanospondylus (Fig. 2), which does not have temporal fenestration. However, bolosaurids (Bolosaurus and Belebey), taxa known only from skulls, are also close to the base of this lineage and do have lateral temporal fenestra.

Figure 1. Eunotosaurus and its sister taxa, Acleistorhinus and Milleretta RC14.

From the Bever et al. abstract: “The reptile skull is an increasingly utilized model for understanding the evolution and development of vertebrate adaptation. Turtles are an important yet enigmatic piece of this puzzle. The earliest uncontroversial stem turtles exhibit a fully anapsid skull with an adductor chamber concealed by bone. If this lack of fenestration reflects conservation of the ancestral condition, then turtles are an extant remnant of an early reptile radiation that excludes the other living forms. If turtles are nested within crown Diapsida, then their anapsid skull is a secondary configuration built on a diapsid structural plan. No direct paleontological evidence yet exists for this reversal, a situation that epitomizes a general lack of consilience between the fossil record and the molecular signature of living taxa and one that obfuscates attempts to synthesize broad evolutionary patterns across Reptilia.

“Eunotosaurus africanus is a 260 Ma fossil reptile whose status as an early stem turtle continues to be strengthened by new cranial and postcranial synapomorphies. Here we use computed tomography (CT) to study the temporal region of Eunotosaurus and to formulate a model for the origin of the anapsid and diapsid skulls of modern amniotes. Expression of a lower temporal fenestra (LTF) supports the hypothesis that the closed cheek of modern turtles is secondary (1). The ventrally unbounded nature of the LTF places Eunotosaurus at odds with parareptiles (2), but also with pandiapsids where an unbounded LTF is known only in conjunction with the more conservative upper temporal fenestra (UTF) (3). The region housing the diapsid UTF is overlain by an elongate supratemporal in Eunotosaurus. In contrast to the plesiomorphic condition, digitally removing the supratemporal reveals a moderate-sized opening circumscribed by the same elements that define the UTF (4). Additional evidence that this covering is secondary is drawn from the observation that in Eunotosaurus the supratemporal overlaps the postorbital, whereas plesiomorphically these two elements are abutting or the postorbital overlaps the supratemporal. We propose (5) Eunotosaurus captures an early step in the evolution of the anapsid turtle skull in which the UTF was secondarily covered by the supratemporal before being obliterated through expansion of neighboring dermal elements (6). The recognition of such a critical transitional form facilitates the articulation of meaningful transformational and functional models that can be tested with future paleontological discoveries and rapidly emerging developmental data.”

1). Pure speculation when done without phylogenetic analysis.

2). The post-crania of Eunotosaurus is clearly derived, so the skull is also, reduced from the ‘synapsid’ grade skull found in the following (non-synapsid) millerettids: Acleistorhinus, Feeserpeton, Australothyris, Oedaleops, Eothyris, Ennatosaurus, Casea and Cotylorhynchus, taxa closer to Eunotosaurus than Eunotosaurus is to turtles.

3). Like Owenetta and basal lepidosauriforms like Paliguana, Gephyrostegus and the rib-gliders, like Icarosaurus, all clearly distinct from turtles.

4). The same could be said of any of the taxa in (2).

5). “Propose” is another word for “speculate without evidence.” For this idea to have weight, they should “show” or “demonstrate,” but they cannot do this phylogenetically if they include bolosaurids and Stephanospondylus.

6). Except in basal turtles the supratemporal is a long bone rimming the posterior cranium, as in related pareiasaurs, bolosaurids and Stephanospondylus.

Figure 2. Click to enlarge. Stephanospondylus based on parts found in Stappenbeck 1905. Several elements are re-identified here. Note the large costal plates on the ribs, as in Odontochelys. The pubis apparently connected to a ventral plastron, not preserved. The interclavicle was likely incorporated into the plastron.

Turtles are so firmly nested in their present tree topology that you can remove (as I did) Stephanospondylus, all four pareiasaurs, and both bolosaurids and the tree topology does not change. I even deleted the Macroleter clade. Turtles still don’t nest with Eunotosaurus. This has been known online for the last three years.

References
Bever GS, Lyson T and Bhullar B-A 2014. Fossil evidence for a diapsid origin of the anapsid turtle skull. SVP 2014 Abstracts pg. 91

Delorhynchus – getting closer to Eunotosaurus

A recent paper by Reisz et al. (2014) presented a large portion of the anterior skeleton of a specimen previously known from smaller scraps.

Figure 1. Delorhynchus compared to its closest sisters, Acleistorhinus and Eunotosaurus to scale.

Delorhynchus cifelli (Reisz et al. 2014, Fig. 1) is an Early Permian terrestrial reptile from Oklahoma. Derived from a sister to Acleistorhinus, Delorhynchus was basal to Eunotosaurus and was larger than both. The jugal had two posterior processes. The squamosal is largely unknown. No expanded ribs were found with this specimen.

Reisz et al. nested Delorhynchus with Lanthanosuchus and Acleistorhinus, but Lanthanosuchus nests with Macroleter in the large reptile tree here as we discussed earlier here.

References
Reisz RR, Macdougall MJ and Modesto S 2014. A new species of the parareptile genus Delorhynchus, based on articulated skeletal remains from Richards Spur, Lower Permian of Oklahoma. Journal of Vertebrate Paleontology 34:1033–1043.

Eunotosaurus news – svp abstracts 2013

From the abstract:
Bever and Lyson 2013 wrote: “The reemergence of the Middle Permian amniote Eunotosaurus africanus as a potential early stem turtle is based on a number of striking postcranial synapomorphies, many of which are related directly to the evolutionary origin of the iconic turtle shell. Our data reveal a cranial morphology characterized by a large number of plesiomorphic features that suggest Eunotosaurus lies near the base of Panreptilia and outside the early radiation of pandiapsid forms. A good example is the large supratemporal bone that sweeps forward to broadly contact the postorbital – a character essentially unknown in Pandiapsida. The cranial characters of Eunotosaurus that are derived within Panreptilia are variously shared with an interesting taxonomic mix of turtles, parareptiles, and relatively derived diapsids (crownward stem diapsids and crown diapsids). One character that exemplifies this distribution is the slender, vertically oriented quadratojugal. This is a feature present in the early stem turtle Proganochelys quenstedti, a handful of parareptile forms, and as a derived character within Panarchosauria. Almost none of these derived features are shared with those taxa more nearly contemporaneous with Eunotosaurus and that constitute the early portions of the diapsid stem. Eunotosaurus also shares a number of characters with Proganochelys that are not established as present in other parareptiles. Examples include ossification of the anterolateral wall of the braincase and presence of a tall quadrate process of the pterygoid. We articulate and compare the models of cranial evolution as dictated by the currently competing hypotheses for the origin of turtles. The cranial evidence supporting a close relationship between Eunotosaurus and turtles amplifies the apparent conflict between the seemingly plesiomorphic morphology of the turtle stem and the seemingly derived molecular signature of the turtle crown.”

Figure 1. Skull of Eunotosaurus compared to Odontochelys, Proganochelys, Milleretta and Stephanospondylus. The odd bedfellow here in Eunotosaurus, which retains the lateral temporal fenestra of its Milleretta (RC14) and Acleistorhinus (Fig. 2) sister/ancestors.

Earlier we tested Eunotosaurus with 350 reptiles and recovered it as a sister to Acleistorhinus, not turtles. Earlier we tested turtles with 350 reptiles and recovered the stem turtle, Proganochelys with Stephanospondylus far from Eunotosaurus. Even Odontochelys, previously considered a turtle sister, instead nested with the RC 70 specimen of Milleretta.

So that means we have three different convergent origins for turtle-like morphologies. Only one, Stephanospondylus, is the real deal. My guess is Bever and Lyson have not tested it in their “currently competing hypotheses.” They are also stuck with old pseudo clades, like Parareptilia, that lose their utility when the gamut of included taxa is increased here.

Figure 2. Acleistorhinus is a sister to Milleretta (RC14) and Eunotosaurus. Lanthanosuchus, previously considered close to Acleistorhinus, is more closely related to Romeriscus and Macroleter, all three of the flathead variety.

As you can see from the above illustrations, Acleistorhinus is the closest sister to Eunotosaurus. And Stephanospondylus is the closest known sister to turtles. More details are available by clicking the taxon links above.

References
Bever G and Lyson T 2013. Cranial evolution and the origin of turtles: insights from Eunotosaurus africanus. Journal of Vertebrate Paleontology abstracts 2013.