Taxon exclusion mars 2020 study of evolutionary innovation in reptiles

Simões et al. 2020 present
their vision of phenotypic diversity in reptiles (Fig. 1).

Unfortunately they do so
without knowing the last common ancestor of reptiles (Silvanerpeton) and the basal dichotomy of reptiles, both of which lead to a complete misunderstanding of the main branches in the phylogeny of reptiles. That lack of taxa led to a shuffling of the two major clades in the LRT, the new Archosauromorpha and the new Lepidosauromorpha.

For instance,
Simões et al. have no idea that ‘Diapsida’ is an invalid clade, unless restricted to only Archosauromorpha. Lepidosauriformes are the lepidosaur branch of the former ‘Diapsida’. Their figure 3 cladogram of the Lepidosauria omits Tritosauria and flips the order, nesting Iguania as a derived clade, rather than the basal clade it is in the LRT.

The large reptile tree (LRT) with 1746+ taxa remains the overlooked standard by which all smaller studies can be measured for no other reason that it includes more taxa. In the LRT phylogenetic miniaturization occurred at the genesis of many evolutionary novelties. This factor was overlooked in Simões et al. 2020 due to taxon exclusion.

Figure 1. Cladogram from Simoes et al. 2020 suffering from so much taxon exclusion that Archosauromorpha are shuffled within Lepidosauromorpha.

Figure 1. Cladogram from Simoes et al. 2020 suffering from so much taxon exclusion that Archosauromorpha are shuffled within Lepidosauromorpha.

The Simões et al. plan:
“Here, we explore megaevolutionary dynamics on phenotypic and molecular evolution during two fundamental periods of reptile evolution: (i) the origin and early diversification of the major lineages of diapsid reptiles (lizards, snakes, tuataras, turtles, archosaurs, marine reptiles, among others) during the Permian and Triassic periods, and (ii) the origin and evolution of lepidosaurs (lizards, snakes and tuataras) from the Jurassic to the present.”

Lacking pertinent taxa, Simões et al. mistakenly place turtles in diapsids and do not include pterosaurs, rhynchosaurs and tanystropheids in lepidosaurs.

Simões et al. conclude:
“Collectively, our findings suggest a considerably more complex scenario concerning the evolution of reptiles in deep time than previously thought.”

Without a proper phylogenetic context
anything this study presents is suspect or invalid from the get-go. Bring back your math, your charts, your statistics after you have a wide gamut, comprehensive cladogram with proper outgroup taxa, a working last common ancestor and valid branching thereafter, as in the LRT.

Colleagues:
add more taxa. That will expand, clarify and validate your cladograms.


References
Simões TR, Vernygora O, Caldwell MW and Pierce SE 2020. Megaevolutionary dynamics and the timing of evolutionary innovation in reptiles. Nature 11:3322  https://doi.org/10.1038/s41467-020-17190-9 http://www.nature.com/naturecommunications

Simões et al. 2020 fail to understand ‘diapsids’ due to taxon exclusion

Simões et al. 2020 brings us their study
on the rates of evolutionary change in reptiles with a diapsid skull architecture.

From the abstract:
“The origin of phenotypic diversity among higher clades is one of the most fundamental topics in evolutionary biology. However, due to methodological challenges, few studies have assessed rates of evolution and phenotypic disparity across broad scales of time to understand the evolutionary dynamics behind the origin and early evolution of new clades. Here, we provide a total-evidence dating approach to this problem in diapsid reptiles. We find major chronological gaps between periods of high evolutionary rates (phenotypic and molecular) and expansion in phenotypic disparity in reptile evolution. Importantly, many instances of accelerated phenotypic evolution are detected at the origin of major clades and body plans, but not concurrent with previously proposed periods of adaptive radiation. Furthermore, strongly heterogenic rates of evolution mark the acquisition of similarly adapted functional types, and the origin of snakes is marked by the highest rates of phenotypic evolution in diapsid history.”

This study suffers from taxon exclusion
By adding taxa the first dichotomy of the Reptilia (Amniota is a junior synonym) splits taxa closer to lepidosaurs (Lepidosauromorpha) from those closer to archosaurs (Archosauromorpha, including Synapsida). Thus members of the traditional clade ‘Diapsida’ are convergent. Other than through the last common ancestor of all Reptiles, Silvanerpeton in the Viséan, archosaurs are not related to lepidosaurs. The present paper by Simões et al. 2020 fails to recover this topology due to taxon exclusion. Without a valid phylogenetic context, the results are likewise hobbled.


References
Simões TR, Vernygora O, Caldwell MW and Pierce SE 2020. Megaevolutionary dynamics and the timing of evolutionary innovation in reptiles. Nature Communications 11: 3322.

http://reptileevolution.com/reptile-tree.htm

Here’s a project ripe for a PhD dissertation: Youngina and kin

Summary for those in a hurry:
Specimens nesting at the base of the marine and terrestrial younginiforms need a good review, as in a doctoral dissertation. Many of the specimens below have not been described and the collection has not been tested in a phylogenetic analysis, except here in the LRT. And let’s not forget headless Galesphyris (Fig. 4), the last common ancestor of this monophyletic clade of (at present) wastebasket “young-” younginids (Youngina, Youngolepis and Youngoides) needs to be part of the picture. The Late Carboniferous diapsid, Spinoaequalis (Fig. 2), is the outgroup taxon in the LRT.

A new ‘Youngina’ specimen came to my attention
(Fig. 1) published in Sues 2019. Unfortunately no museum number was provided. Pending acquisition of that number, the new specimen was added to the large reptile tree (LRT, 1694+ taxa) just to see where the new one would nest among the many Youngina, Youngoides and Youngolepis specimens (Figs. 2, 3) already in the LRT. Scale bars indicate it’s a big one.

Figure 1. Unidentified specimen attributed by Sues 2019 to Youngina capensis. Here it nests with the much smaller BPI 375 specimen basal to protosaurs.

Figure 1. Unidentified specimen attributed by Sues 2019 to Youngina capensis. Here it nests to scale with the much smaller BPI 375 specimen basal to protosaurs, like the AMNH 9520 specimen assigned to Prolacerta.

Relatively few workers
have published on the Youngina, Younginoides and Youngolepis specimens. That is unexpected considering the key position in the LRT of these largely ignored taxa at the bases of several major clades.

Figure 1. Terrestrial Yonginiformes + Galesphyrus representing the marine clade, all to scale except the toned area containing protorosaurs, which have their own scale.

Figure 2. Terrestrial Yonginiformes + Galesphyrus representing the marine clade, all to scale except the toned area containing protorosaurs, which have their own scale.

One traditional Youngina specimen, 
short-legged BPI 3859, does not nest with the terrestrial taxa in the LRT, despite the many similarities.

Figure 3. The odd one out, the BPI 3859 specimen assigned to Youngina does not nest with the others, but with marine taxa.

Figure 3. The odd one out, the BPI 3859 specimen assigned to Youngina does not nest with the others, but with marine taxa.

However,
if headless Galesphyris turns out to be a junior synonym of Youngina, then the genus would be monophyletic across tested taxa. Let’s leave open that possibility. Otherwise, let’s rename them all appropriately.

Figure 4. If Galesphyrus was Youngina, the genus would be monophyletic.

Figure 4. If Galesphyrus was Youngina, the genus would be monophyletic.

At nine cm in length, the skull of the new specimen
is the largest skull assigned to the genus Youngina. Like the smaller BPI 375 specimen, it nests basal to protorosaurs in the LRT. Other specimens nest basal to Archosauriformes. As noted above, the BPI 3859 specimen nests basal to Claudiosaurus in the LRT along with other marine younginiformes, including plesiosaurs, mesosaurs and ichthyosaurs.


References
Broom R 1914. A new thecodont reptile. Proceedings of the Zoological Society of London, 1914:1072-1077.
Broom R and Robinson JT 1948. Some new fossil reptiles from the Karroo beds of South Africa: Proceedings of the Zoological Society of London, series B, v. 118, p. 392-407.
Gardner NM, Holliday CM and O’Keefe FR 2010. The braincase of Youngina capensis (Reptilia, Diapsida): New insights from high-resolution CT scanning of the holotype. Paleonotologica Electronica 13(3).
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Olson EC 1936. Notes on the skull of Youngina capensis Broom. Journal of Geology, 44 (4): 523-533.
Olson EC and Broom R 1937. New genera and species of tetrapods from the Karroo Beds of South Africa. Journal of Paleontology 11(7):613-619.
Smith, RMH and Evans SE 1996. New material of Youngina: evidence of juvenile aggregation in Permian diapsid reptiles. Palaeontology, 39 (2):289–303.
Sues HD 2019. The Rise of Reptiles: 320 Million Years of Evolution.
Johns Hopkins University Press, Baltimore. xiii + 385 p.; ill.; index.
ISBN: 9781421428673 (hc); 9781421428680 (eb).

wiki/Youngina

SVP 2018: Large biped in the Permian

Shelton, Wings, Martens, Sumida and Berman 2018 report,
from the same quarry that produced bipedal Eudibamus, comes a MUCH larger taxon most closely comparable to Eudibamus (Fig. 1) with long bones 10 to 24 cm in length. They report, “Given this evidence, we hypothesize that either there was an additional bipedal species that existed sypatrically with E. cursori, or these bone casts represent a later ontogenetic stage of Eudibamus with the type specimen being a juvenile.”

FIgure 1. Eudibamus scaled to femoral (=long bone) lengths of 10 and 24 cm. This makes the giant eudibamid either half a meter or a meter in snout-vent length.

FIgure 1. Eudibamus scaled to femoral (= long bone) lengths of 10 and 24 cm. This makes the giant eudibamid either half a meter or a meter in snout-vent length.

None of the present sisters
to Eudibamus (Fig. 2) in the LRT approach the size of the new bone cast specimen.

Figure 1. Basal diasids and proto-diapsids. Largely ignored these putative synapsids actually split from other synapsids while retaining the temporal fenestra trait that serves as the basis for the addition of upper temporal fenestra in diapsids. Included here are Protorothyris, Archaeovenator, Mycterosaurus, Heleosaurus, Mesenosaurus, Broomia, Milleropsis, Eudibamus, Petrolacosaurus, Spinoaequalis, and Tangasaurus.

Figure 2. Basal diasids and proto-diapsids. Largely ignored these putative synapsids actually split from other synapsids while retaining the temporal fenestra trait that serves as the basis for the addition of upper temporal fenestra in diapsids. Included here are Protorothyris, Archaeovenator, Mycterosaurus, Heleosaurus, Mesenosaurus, Broomia, Milleropsis, Eudibamus, Petrolacosaurus, Spinoaequalis, and Tangasaurus.

The authors continue to hold to their original hypothesis
that Eudibamus is a bolosaurid (Fig. 3). In the large reptile tree (LRT, 1313 taxa) bolosaurids nest with diadectids and procolophonids. Eudibamus nests with basalmost diapsids (Fig. 3).

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

It will be interesting to see
what this new Early Permian taxon looks like when it becomes available. Right now it is an outlier.

References
Shelton CD, Wings O, Martens T, Sumida SS and Berman DS 2018. Evidence of a large bipedal tetrapod from the Early Permian Tambach Formation preserved as natural bone casts discovered at the Bromacher quarry (Thuringia, Germany). SVP abstracts.

The Early Permian Ascendonanus assemblage

There are five specimens from the same pit
that were assigned to the varanid taxon Ascendonanus. Spindler et al. 2018 thought they were all conspecific.

Given their distinct proportions
(Fig. 1) and the phylogenetic differences recovered in 2 of the 5 so far (earlier one nested as a basal iguanid), we’re going to need some new generic names for at least one of the referred specimens. The others have not yet been tested in the large reptile tree (LRT, 1179 taxa).

The holotype
remains Ascendonanus, but here it’s no longer a varanopid synapsid. Here it nests as a derived prodiapsid and the basalmost tested diapsid (Fig. 2), a little younger than the oldest diapsid, Petrolacosaurus.

Figure 1. The five specimens from the Ascendonanus quarry, all to the same scale. Most images from Spindler et al. 2018. Some have skulls 3x the occiput/acetabulum length. Others as much as 5x, the first hint that these taxa are no conspecific.

Figure 1. The five specimens from the Ascendonanus quarry, all to the same scale, counter plate flipped in every specimen. Most images from Spindler et al. 2018. Some have skulls 3x the occiput/acetabulum length. Others as much as 5x, the first hint that these taxa are no conspecific.

Some of these specimens
(Fig. 1) have an occiput/acetabulum length distinct from the others, ranging from 3x to 5x the skull length, the first clue to their distinct morphologies.

Figure 2. The Prodiapsida now include the holotypes of Ascendonanus and Anningia.

Figure 2. The Prodiapsida now include the holotypes of Ascendonanus and Anningia. Remember, the Diapsida does not include any Lepidosauriforms, which nest elsewhere.

Spindler et al. 2018
did not include several taxa typically included in pelycosaur studies and should not have included any caseasaurs, despite their traditional inclusion. Spindler et al. did not include any diapsids nor did they understand the role of the former varanopids now nesting as ancestors to the Diapsida (sans Lepidosauriformes).

Figure 3. Cladogram from Spindler et al. 2018. Colors refer to clades in the LRT.

Figure 3. Cladogram from Spindler et al. 2018. Colors refer to clades in the LRT.

The holotype 0924 specimen has more of a varanopid skull
than the 1045 specimen we looked at earlier. Prodiapsid sisters include varanopids ancestral to synapsids. Prodiapsids, as their name suggests, are late-surviving ancestors to diapsids like the coeval Araeoscelis (Early Permian) and the earlier Spinoaequalis (Late Carboniferous).

Figure 3. The Ascendonanus holotype skull as originally traced and as traced here.

Figure 3. The Ascendonanus holotype skull as originally traced and as traced here. Whether an upper temporal fenestra was present (as shown in the color tracing), or not (as shown in the drawings, makes no difference as this taxon nests at the transition. 

Not sure yet
where the other three specimens assigned to Ascendonanus nest. Enough muck stirred for the moment.

References
Rößler R, Zierold T, Feng Z, Kretzschmar R, Merbitz M, Annacker V and Schneider JW 2012. A snapshot of an early Permian ecosystem preserved by explosive volcanism:
New results from the Chemnitz Petrified Forest, Germany. PALAIOS, 2012, v. 27, p. 814–834.
Spindler F, Werneburg R, Schneider JW, Luthardt L, Annacker V and Räler R 2018. First arboreal ‘pelycosaurs’ (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany, with a review of varanopid phylogeny. DOI: https://doi.org/10.1007/s12542-018-0405-9

SVP abstracts 2017: Eudibamus forelimb description

Sumida et al. 2017 bring us new information
on the pectoral region of Eudibamus, (Figs. 1,2) an early likely biped in the sprawling manner of the unrelated extant iguanian lizards, Chlamydosaurus and Basiliscus by convergence.

Unfortunately,
Sumida et al. continue to cling to the invalidated tradition that Eudibamus is a bolosaurid, largely based on convergent tooth shapes and taxon exclusion in their analyses.

Figure 1. Basal diasids and proto-diapsids. Largely ignored these putative synapsids actually split from other synapsids while retaining the temporal fenestra trait that serves as the basis for the addition of upper temporal fenestra in diapsids. Included here are Protorothyris, Archaeovenator, Mycterosaurus, Heleosaurus, Mesenosaurus, Broomia, Milleropsis, Eudibamus, Petrolacosaurus, Spinoaequalis, and Tangasaurus.

Figure 1. Basal diasids and proto-diapsids. Largely ignored these putative synapsids actually split from other synapsids while retaining the temporal fenestra trait that serves as the basis for the addition of upper temporal fenestra in diapsids. Included here are Protorothyris, Archaeovenator, Mycterosaurus, Heleosaurus, Mesenosaurus, Broomia, Milleropsis, Eudibamus, Petrolacosaurus, Spinoaequalis, and Tangasaurus.

From the Sumida et al. abstract
Eudibamus cursoris, a bolosaurid parareptile, from the Early Permian Tambach Formation (approximately 290 mybp), Thüringer Wald (Thuringian Forest), of central Germany, has been interpreted as the earliest known facultative biped. This was initially proposed based on the postcranial limb proportions in the type specimen (MNG [Museum der Natur, Gotha, Germany] 8852), but the forelimb itself has never been formally described. A nearly complete left, and partial right forelimb are preserved in the type specimen. The forelimb is less than 60% the length of the hindlimb. Only a thin, blade-like scapula is visible. Brachial, antebrachial, and manual elements are slender and elongate compared to those of other basal amniotes. The humerus has two well developed distal condyles with terminally facing articular facets. Delto-pectoral attachments were along a narrow ridge. The radius and ulna are nearly subequal in length. Conspicuously, the ulna lacks a well developed olecranon process. Carpals are proximodistally elongate compared to other basal amniotes. The intermedium and lateral centrale and the radiale and medial centrale articulate end-to-end, and their combined lengths equal that of the ulnare; the intermedium and radiale, and the medial and lateral centralia are equal in length. Four distal carpals are visible, it is unclear whether whether the fifth is truly absent or simply unossified. The distal carpal associated with digit two is reduced to a tiny pebble of bone, whereas that associated with digit four is largest and somewhat wedge shaped. Four metacarpals, likely equivalent to digits two-five, are present. The proximal portion of metacarpal two is present but length of the entire element cannot be determined. No elements of digit one can be seen, though its absence could be an artifact of preservation; however, the presence of only four distal carpals suggests Eudibamus may have had only four manual digits. Three phalanges are preserved in digits three and four. Both come to blunt tips and neither exhibits a significantly elongate penultimate element. The overall limb proportions seen in Eudibamus could suggest facultative bipedality or vertical clinging and leaping. However, vertical clingers and leapers normally have at least one is proportionately elongate manual digit and well-developed manual claws. Neither phalangeal proportions, nor the two well-developed terminal phalanges show such adaptations in Eudibamus and its interpretation as a facultative biped remains the most plausible interpretation of its postcranial anatomy.”

Figure 1. Click to enlarge. Eudibamus in situ (above), traced (middle) and reconstructed (below). The revised skull retains a large orbit and has a shorter rostrum.

Figure 1. Click to enlarge. Eudibamus in situ (above), traced (middle) and reconstructed (below). The revised skull retains a large orbit and has a shorter rostrum.

First of all,
Parareptilia has been invalidated as a monophyletic clade since 2012. 

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Since 2011
Eudibamus has nested with other slender, speedy, basalmost archoauromorph diapsids (Araeoscelis, Petrolacosaurus and kin) (Fig. 1) in the large reptile tree, far from the squat, slow, bolosaurids, like Bolosaurus and Belebey that nest with diadectids and pareiasaurs.

Let’s look again
at the pectoral region and forelimb of Eudibamus as listed by Sumida et al. above. Note how many of these traits are also present in basal archosauromorph diapsid taxa and their outgroups shown in figure 1 above. Bolosaurids, by contrast, are known chiefly by skull material, so direct comparisons to forelimbs cannot be made.

Imagine the co-authors, grad students 
who disagree with Dr. Sumida on the phylogenetic position of Eudibamus, perhaps after testing a larger gamut of taxa or by reading this blog. All co-authors sign that they agree with what is in the abstract. This is how paleontology puts on blinders, clings to traditions and generally avoids rocking the hypotheses of senior professors.

Fortunately
non-academic renegades and independent researchers have no such restrictions, but are free to explore and experiment.

References
Sumida SS et al. 2017. Structure of the pectoral limb of the early Permian bolosaurid reptile Eudibamus cursors: further evidence supporting it as the earliest known facultative biped. SVP abstracts 2017.

Sumida 2009 Ted Talk video
What is Eudibamus?

Go back far enough in dinosaur ancestry and you come to: Heleosaurus

With our never-ending fascination with dinosaurs
it’s interesting to list some of the taxa in their deep, deep!, deep!! ancestry. One such ancestor is Heleosaurus (Fig. 1; Broom 1907; Middle Permian ~270 mya, ~30 cm snout to vent length), the first known basal prodiapsid, the clade the includes diapsids (sans lepidosaurs, which are unrelated but share the same skull topology by convergence).

Figure 1. Heleosaurus is closer to the main lineage of dinosaurs. It retained canine fangs.

Figure 1. Heleosaurus is close to the main lineage of dinosaurs. It retained canine fangs. Note the squamosal distinct from the quadratojugal, as in Nikkasaurus. Also note the continuing lacrimal contact with the naris, as in Protorothyris.

But first
I want to discuss a derived Heleosaurus cousin, Nikkasaurus (Ivahnenko 2000; Fig. 2), also one of the most basal prodiapsids.

It is only by coincidence
that Ivahnenko labeled Nikkasaurus one of his ‘Dinomorpha,’ a clade name ignored by other authors. Wikipedia considers Nikkasaurus one of the Therapsida and possibly a relic of a more ancient stage of therapsid development. Like Heleosaurus, Nikkasaurus had a single synapsid-like lateral temporal fenestra. Only their nesting outside of that clade and basal to the clade Diapsida in the LRT tell us what they really are. Most of the time, as you know, we can tell what a taxon is simply by looking at it. In this case, as in only a few others, we cannot do so readily.

Figure 1. Nikkasaurus, one of the most primitive prodiapsids, direct but ancient ancestors of dinosaurs.

Figure 2. Nikkasaurus, one of the most primitive prodiapsids, direct but ancient ancestors of dinosaurs.

Nikkasaurus tatarinovi (Ivahnenko 2000) Middle Permian was a tiny basal prodiapsid with a large orbit. It retained a large quadratojugal. The fossil is missing the squamosal. Others mistakenly considered the quadratojugal the squamosal, as in therapsids. That’s an easy mistake to make. Compare this bone to the QJ in Heleosaurus (Fig. 1), another prodiapsid. Nikkasaurus has small sharp teeth and no canine fang. Nikkasaurus is a sister to Mycterosaurus. They both share a large orbit and fairly long snout. What appears to be a retroarticular process may be something else awaiting inspection in the actual fossil. Based on all other data points, I don’t trust that post-dentary data. It doesn’t match the in situ figure.

Distinct from other prodiapsids,
the Nikkasaurus, Mycerosaurus and Mesenosaurus maxilla extended dorsally, overlapping the lacrimal and contacting the nasal, as it does in Dimetrodon and basal therapsids like Hipposaurus and Stenocybus. This trait tends to be homoplastic / convergent in all derived taxa, but the timing differs in separate clades.

Figure 1. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it.

Figure 2. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it. Note the posterior mandible mismatch in the purported retroarticular process. I suspect the process is not there.

And finally we come back to Heleosaurus.
Slightly closer to the lineage of dinosaurs is the slightly more basal prodiapsid, Heleosaurus (Fig. 2), which retained canine fangs, had a more typical posterior mandible and retained a lacrimal / naris contact. This naris trait was retained by Petrolacosaurus, Eudibamus, Spinoaequalis and other basal diapsids (archosauromorpha with both upper and lateral temporal fenestra ). The maxilla did not rise again to cut off lacrimal contact with the naris in the ancestry of dinosaurs until the small Youngina specimens huddled together, SAM K 7710 and every more derived taxon thereafter, up to and including dinos.

References
Broom R 1907. On some new fossil reptiles from the Karroo beds of Victoria West, South Africa. Transactions of the South African Philosophical Society 18:31–42.
Ivahnenko MF 2000. 
Cranial morphology and evolution of Permian Dinomorpha (Eotherapsida) of eastern Europe. Paleontological Journal 42(9):859-995. DOI: 10.1134/S0031030108090013

Eudibamus skull revisited

Unfortunately,
requests for hi-rez images of the skull of Eudibamus (Berman et al. 2000) have gone unanswered.

Fortunately,
an image from a Stuart Sumida lab pdf file (Fig. 1) provides the best image I’ve seen so far. Even so, it could be better.

Figure 1. GIF movie of the skull of Eudibamus along with a DGS interpretation of the elements. A reconstruction (Fig. 2) appears to 'make sense" but I'd still like to see better resolution.

Figure 1. GIF movie of the skull of Eudibamus along with the original (line art) interpretation and a DGS interpretation of the elements. Where are the teeth in the line art? They are not indicated. A reconstruction based on the DGS tracings (Fig. 2) appears to ‘make sense” but I’d still like to see better resolution. The presumed mandible here does not have the appearance of the rest of the bones. The mandible is based on a possible impression that looks like it has teeth. These could be pick marks. Black lines in the color tracing appear to represent palatal elements that basically match those of Petrolacosaurus.

Eudibamus is still considered a bolosaurid
(Fig. 2) in traditional paleontology, but it nests with basal diapsids, like Petrolacosaurus, in the large reptile tree. We looked at Eudibamus earlier here, here and here.

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

This skull remains confusing.
This is only an attempt at understanding it. Higher resolution and color would be helpful. The original authors did not publish a skull reconstruction, nor did they label individual skull bones. I wonder if they were just as confused, even with the skull in front of them.

 Eudibamus reconstruted.

Figure 3. Eudibamus reconstructed. This will probably not be the last such attempt. But I think it is the most accurate so far.

References
Berman, DS, Reisz RR, Scott D, Henrici AC, Sumida SS and Martens T 2000. Early Permian bipedal reptile. Science 290: 969-972.

The Marine (Aquatic) Younginiformes

Whenever one thinks of marine reptiles,
the giant mosasaurs, ichthyosaurs and plesiosaurs immediately come to mind. Dig a little deeper and the placodonts, mesosaurs and thalattosaurs pop up. Basal to all these taxa are the pachypleurosaurs. Basal to the pachypleurosaurs are the marine younginiformes (Fig. 1), beginning with Galesphyrus. The odd saurosphargids are newcomers to this list (Fig. 2) nesting between basal younginiforms and pachypleurosaurs.

Yesterday we looked at the outgroup taxon to the younginiformes, Spinoaequalis. Today we’ll discuss the basal marine younginiformes beginning with Galesphyrus (Fig. 1).

Figure 3. Spinoaequalis and descendant marine younginiformes.

Figure 3. Spinoaequalis and descendant marine younginiformes. These give rise to plesiosaurs, placodonts, mesosaurs, ichthyosaurs and thalattosuchians. Click to enlarge. Note hoe hew taxa adequately preserve the skull. The flattening of the pectoral girdle is notable here.

1. Galesphyrus (Carroll 1976; Late Permian ~260 mya) This headless articulated partial skeleton had no obvious aquatic adaptations, other than, perhaps, those big, broad feet (and also note that wider tarsus and more widely separated tibia and fibula). The hourglass-shaped proximal carpal is a trait shared with basal diapsids, like AraeoscelisGalesphyrus had more robust limbs and relatively larger feet than Spinoaequalis. Most of the tail is unknown.

2. Youngina capensis? BPI 3859 (Broom 1922; Late Permian ~260 mya). The genus Youngina was once considered basal to both lepidosaurs and archosaurs. The BPI 3859 specimen does not nest with the holotype. So the BPI 3859 specimen is not a Youngina. The BPI 3859 specimen has a taller scapula than Galesphyrus. Few other traits are preserved in common.

3. Acerosodontosaurus piveteaui (Currie 1980; Bickelmann, Müller and Reisz 2009; Late Permian ~260 mya). Acerosodontosaurus descended from a sister to Galesphyrus was a sister to the BPI 3859 specimen attributed to Youngina (see below) and phylogenetically preceded Hovasaurus, Claudiosaurus and Thadeosaurus and Tangasaurus.

4. Thadeosaurus colcanapi (Carroll 1981; Late Permian, ~260 mya), nests between Acerosodontosaurus and ClaudiosaurusTangasaurus and Hovasaurus are sister taxa. The scapula and coracoid were fused only in adults. Many specimens are known including several juveniles. None preserve the skull very well. A juvenile skull gives provides the most data.

5. Hovasaurus boulei (Piveteau 1926, Currie 1981; Late Permian to Early Triassic ~250mya ) was originally considered a tangasaurid. Here Hovasaurus nests as a sister to Tangasaurus and Thadeosaurus. Distinct from Thadeosaurus, the cervicals were more robust. The torso was shorter and deeper with longer dorsal ribs. The presacral number was 26. Accessory articulations were present on the vertebra. The tail had higher neural spines and deeper chevrons. The chevrons were broader distally. The scapulocoracoid was larger and the scapula was part of the chest shield. The metarsals were shorter. Pedal digit 5 was longer relative to digit 4.This genus is known from several specimens varying in size. Gravel was found in the belly of several specimens, likely used for ballast or digestion.

6. Tangasaurus mennelli (Haughton 1924; Late Permian) was known from only two specimens collected in 1922. Later, Currie (1982) reported over 300 partial specimens were attributed to Tangasaurus, but reattributed most of them elsewhere. Haughton (1924) described a long, powerful, flattened tail and presumed an aquatic existence. The great size of the transverse processes at the base of the tail are notable. So is their anterior curvature. These reflect the size of the caudofemoralis muscles driving the large hind limbs. Note the large coracoid, central sternum, short ribs, massive humerus (especialy distally) and high caudal spines creating a sculling tail ideal for swimming.

7. Claudiosaurus germaini (Carroll 1981; Late Permian ~260 mya) was originally described as a close relative of Thadeosaurus, and indeed it is. Claudiosaurus also nests with Adelosaurus and Atopodentatus. The skulls of predecesor taxa, like Hovasaurus, are poorly known, so distinct from Spinoaequalis, the reduced skull of Claudiosaurus had a premaxilla enlarged to a third or more of the rostral length. The premaxilla ascending process split the nasals. The naris is elongated horizontally  perhaps just contacting the lacrimal. The jugal was gracile. The supratemporal was a small oval.  A quadratojugal was present contacting both the jugal and the squamosal + quadrate, but other workers have not recognized that loose bone as the quadratojugal. A retroarticular process was present. The number of cervicals increased to at least nine and they decreased in size cranially. The posterior cervicals were as tall as the little skull. The cervical neural spines were taller than each centrum. Intercentra were absent. The pre sacral number of vertebrae dropped to 24.  Metacarpals 3 and 4 were subequal.

8. Adelosaurus huxleyi (Hancock and Howse 1870, Evans 1988) was originally considered to be a small and distinct species of Protorosaurus. Here, derived from a sister to Claudiosaurus, Adelosaurus was basal to, Atopodentatus and the rest of the marine younginiformes and enaliosaurs. Smaller than Claudiosaurus, Adelosaurus had more robust ribs. The humerus did not have an expanded distal end. The hind limb was more gracile. The proximal metatarsals were all subequal in width, except perhaps, metatarsal 5. Adelosaurus was one of the most terrestrial of the known enaliosaurs, showing few aquatic characters, but the disc-like shape of the scapulocoracoid is a trait that was retained. Evans (1988) considered the incomplete ossification of joint surfaces as evidence for immaturity or an aquatic lifestyle. Most taxa around this node have been considered immature for the same reasons.

Figure 3. Basal marine younginiformes, including Galesphyrus, Tangasaurus, Claudiosaurus and others. This is a subset of the large reptile tree.

Figure 3. Basal marine younginiformes, including Galesphyrus, Tangasaurus, Claudiosaurus and others. This is a subset of the large reptile tree. Spinoaequalis is also basal to the terrestrial younginiformes. 

In future posts
we’ll look at the terrestrial younginiformes that ultimately gave rise to the Archosauriformes. New data has clarified relationships at those nodes (Fig. 2).

References
Bickelmann C, Müller J and Reisz RR 2009. The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of “younginiform” reptiles. Canadian Journal of Earth Sciences 46:651-661.
Broom, R. 1922. An imperfect skeleton of Youngina capensis, Broom, in the collecton of the Transvaal Museum. Annals of the Transvaal Museum 8:273–277.
Carroll RL 1976. Galesphyrus capensis, a younginid eosuchian from South Africa. Annals of the South African Museum 72(4):59-68.
Carroll RL 1981. Plesiosaur ancestors from the Upper Permian of Madagascar. Philosophical Transactions of the Royal Society London B 293: 315-383.
Currie PJ 1980. A new younginid (Reptilia: Eosuchia) from the Upper Permian of Madagascar. Canadian Journal of Earth Sciences 17(4):500-51.
Currie PJ 1981. Hovasaurus bolei, an aquatic eosuchian from the Upper Permian of Madagascar. Palaeontologica Africana, 24: 99-163.
Evans 1988. The Upper Permian reptile Adelosaurus from Durham. Palaeontology 31(4): 957-964. online pdf
Gardner NM, Holliday CM and O’Keefe FR 2010. The braincase of Youngina capensis (Reptilia, Diapsida): New insights from high-resolution CT scanning of the holotype. Paleonotologica Electronica 13(3).
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Hancock A and Howse R 1870. On Protorosaurus speneri von Meyer, and a new species, Protorosaurus huxleyi, from the Marl Slate of Middridge, Durham. Quarterly Journal of the geological Society of London 26, 565-572.
Olsen EC 1936. Notes on the skull of Youngina capensis Broom. Journal of Geology, 44 (4): 523-533.
Piveteau, J. 1926. Paleontologie de Madagascar XIII. Amphibiens et reptiles permiens. Annls  Paleont. 15: 53-180.

Thadeosaurus renested

Earlier Thadeosaurus (Carroll 1981, Figs. 1-3) nested close to protorosaurs in the large reptile tree (still needs to be updated), as a sister to Tangasaurus at the base of the Enaliosauria. Another look at Currie’s (1984) tracings (Fig. 3), rather than Carroll’s 1981, 1993 reconstruction (Fig. 1), inspired a new reconstruction (Fig. 2) and nested it within the Enaliosauria, on the other side of Tangasaurus, between Thadeosaurus and Acerosodontosaurus. So this new nesting shifts Thadeosaurus a few nodes. Thadeosaurus usually nests with tangasaurs. So everyone is in agreement here.

Figure 1. Original reconstruction of Thadeosaurus from Carroll 1981, 1993.

Figure 1. Original reconstruction of Thadeosaurus from Carroll 1981, 1993. I didn’t find the fused scapulocoracoid. All the specimens separated these elements, but they were all subadults to juveniles. The new reconstruction found more variability in the vertebra and a shallower torso.

At this grade, these basal enaliosaurs show no obvious aquatic adaptations. Rather, Thadeosaurus appears to have been a long-legged sprinter. The skull remains very much like those of basal diapsids. No special features there.

Figure 1. Thadeosaurus reconstructed from bits and pieces over large and small specimens scaled up to the large specimen. Only one of the smallest juveniles preserves any skull bones.

Figure 2. Thadeosaurus reconstructed from bits and pieces over large and small specimens scaled up to the large specimen. Only one of the smallest juveniles preserves any skull bones. Are those sternal plates or posterior coracoids? You have to know the phylogenetic nesting to be sure.

Sometimes you just have to employ more than one specimen to create a chimaera. In this case, Thadeosaurus was reconstructed from several specimens of various sizes (Fig. 3). Hopefully these are all congeneric and conspecific specimens, as reported by Currie (1984). I didn’t see any red flags here. Nothing about the reconstruction is at odds with Currie’s observations.

Figure 2. The various specimens in various sizes, all to scale attributed to Thadeosaurus. If the largest specimen did not have a bone, it was scaled up from the smaller specimens.

Figure 3. The various specimens in various sizes, all to scale attributed to Thadeosaurus. If the largest specimen did not have a bone, it was scaled up from the smaller specimens.

When genera look so much alike, as basal enaliosaurs do, it is paramount to get the details right. Try to get back to the original material. If not, try to get back to the in situ tracing. If not, use the reconstruction and hope it is accurate.

References
Carroll RL 1981. Plesiosaur ancestors from the Upper Permian of Madagascar. Philosophical Transactions of the Royal Society London B 293: 315-383
Currie PJ 1984. Ontogenetic changes in the eosuchian reptile Thadeosaurus. Journal of Vertebrate Paleontology 4(1 ): 68-84.

wiki/Thadeosaurus