SVP abstracts 11: Palacrodon returns as a drepanosauromorph?

Jenkins et al. 2020 review
“the phylogenetic placement of an enigmatic reptile from the Early Triassic Transantarctic Mountains.” This reptile has gone through some name changes, but the large reptile tree (LRT, 1751+ taxa) nested it in 2016 with similar, big-eyed, basal placodonts like Palatodonta and Pappochelys (Fig. 1). Co-authors Jenkins and Lewis (2016) nested it with rhynchocephalians, but limited their taxon list to rhynchocephalians and procolophonids. There is no indication that they included basal placodonts in 2020.

Originally
(Broom 1906) considered what little is known of Palacrodon browni (= Fremouwsaurus geludens; Early Triassic; Fig. 1) a member of the Rhynchocephalia.

Figure 1. A comparison of basal placodonts to scale (and Paraplacodus reduced to one-third shows how Fremouwsaurus (Palacrodon) is transitional between the small spike-tooth ancestors like Palatodonta and Pappochelys and the pavement toothed Paraplacodus.

Figure 1. A comparison of basal placodonts to scale (and Paraplacodus reduced to one-third shows how Fremouwsaurus (Palacrodon) is transitional between the small spike-tooth ancestors like Palatodonta and Pappochelys and the pavement toothed Paraplacodus.

From the Jenkins et al. 2020 abstract:
“The phylogenetic placement of Palacrodon has been contentious since its initial description, with workers naming it as either a rhynchocephalian, lizard, procolophonid, eosuchian, or archosauromorph.”

Taxon inclusion nests it with basal placodonts.

“The uncertainty surrounding the phylogenetic affinity of Palacrodon in large part stems from the fact that nearly all the specimens found are teeth and fragmentary portions of tooth-bearing bone. Palacrodon bears characteristic labio-lingually elongate, molariform, cuspidate teeth reminiscent of herbivorous reptiles like extinct trilophosaurs and polyglyphanodonts and modern shell-crushing lizards.”

“Because previous workers lacked any other skeletal material, Palacrodon has never been placed within a phylogeny.”

Never? The LRT placed it in 2016,

“Though its phylogenetic affinity is uncertain, Palacrodon is a cosmopolitan genus spanning most of the Triassic, with specimens found in the Early Triassic of Antarctica, Early-Middle Triassic of South Africa, and the Late Triassic of Arizona. The only specimen of Palacrodon possessing more than dentition is from the Early Triassic lower Fremouw Formation of Antarctica (specimen number BP/1/5296). That formation is the sedimentary sequence immediately preceding the Permian-Triassic mass extinction boundary in the Transantarctic Mountains and represents the only known Early Triassic paleopolar deposit with abundant tetrapod material. The Antarctic specimen of Palacrodon was described from the impression of a latex peel as a partial small skull belonging to an unknown diapsid reptile initially named Fremouwsaurus geludens, which was later synonymized with Palacrodon.”

“We CT scanned the Antarctic specimen and found that previously undescribed skeletal elements are preserved in BP/1/5296. These include limb bones, ribs, phalanges, caudal vertebrae, ankle bones, and an ilium. Of the cranial elements, portions of the right maxilla, lacrimal, prefrontal, jugal, postorbital, ectopterygoid, and dentary are preserved. Both parsimony and Bayesian analyses found Palacrodon to be a stem saurian with close affinities to drepanosauromorphs.”

See figure 2 for known drepanosaurs (all Late Triassic) and their ancestor, Jesairosaurus (Early to Middle Triassic) in the LRT.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

From the Jenkins et al. 2020 abstract:
“This finding suggests that Palacrodon is the earliest known drepanosaur, extending the temporal range of the clade by nearly 20 million years. Palacrodon is also the only known drepanosauromorph from the southern hemisphere. Further analysis of these new skeletal elements will now allow a more thorough understanding of the behavior and niche of Palacrodon and primitive drepanosuars generally.”

Excluding far fewer taxa, in the large reptile tree (LRT, 1749+ taxa) moving Palacrodon from the base of the Placodontia to the base of the Drepanosauromorpha adds 8 steps based on very few skull traits. Of course the post-crania could change things, but usually taxon exclusion changes things more.

Figure 2. The head of Palacrodon and the headless body of the Majiashanosaurus compared.

Figure 2. The head of Palacrodon and the headless body of the Majiashanosaurus compared.

References
Broom R 1906. On a new South African Triassic rhynchocephalian. Transactions of the Philosophical Society of South Africa 16:379-380.
Gow CE 1992. An enigmatic new reptile from the Lower Triassic Fremouw Formation of Antarctica. Palaeontologia Africana 29:21-23.
Gow CE 1999. The Triassic reptile Palacrodon brown Broom, synonymy and a new specimen.
Jenkins K, Lewis P, Choiniere J and Bhullar B-A 2020. The phylogenetic placement of an enigmatic reptile from the Early Triassic Transantarctic Mountains. SVP abstracts 2020.
Jenkins KM and Lewis PJ. 2016. Triassic lepidosaur from southern Gondwana. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Neenan JM, Li C, Rieppel O, Bernardini F, Tuniz C, Muscio G and Scheyer TG 2014. Unique method of tooth replacement in durophagous placodont marine reptiles, with new data on the dentition of Chinese taxa. Journal of Anatomy 224(5):603-613.

https://pterosaurheresies.wordpress.com/2016/10/30/is-palacrodon-a-rhynchocephalian-svp-abstract-2016/

 

SVP abstracts – Drepanosaurs are not ‘highly enigmatic’

Britt et al. 2019 bring us a new look
at a 3D drepanosaur.

From the abstract:
“With a bird-like head, mole-like arms, and a “claw” at the end of the tail, derived drepanosaurs (lizard-sized neodiapsids) are highly enigmatic.” 

Not so. The large reptile tree (LRT, 1594 taxa, subset Fig. 2) documents exactly what they are. Paleontologists should stop using the word ‘enigmatic’ when what they really are saying is ‘we haven’t put in the effort.’ And that means the very little effort needed to click on www.ReptileEvolution.com where all candidates for drepanosaur ancestry are considered and tested.

“Multiple 3D skeletons of a new drepanosaur taxon from Utah provides insights into this clade, previously known from flattened skeletons and isolated 3D elements.”

Always good to have, but 2D specimens are still diagnostic, like a photo, rather than a sculpture. You don’t need as many characters as possible to make a taxonomic determination. What you need is a surfeit of taxa.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Figure 1. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale. Drepanosaurs nest at the base of the Lepidoauria. Pink bone is a sesamoid, not an ulna.

The rest of the abstract
describes the drepanosaur as a scratch-digger with an elongate naris and a hook tail capable of striking a tripod pose. They do not consider the ancestry or clade to which drepanosaurs belong, but consider them common and worldwide in distribution during the Late Triassic.

Figure 1. Subset of the LRT focusing on the Lepidosauria. Now the drepanosaur clade lumps with the rhynchocephalians in the crown group. Extant lepidosaurs are in gray.

Figure 1. Subset of the LRT focusing on the Lepidosauria. Now the drepanosaur clade lumps with the rhynchocephalians in the crown group. Extant lepidosaurs are in gray.

The title of this abstract 
may be the longest one I have ever read. See below.


References
Britt B et al. 2019. Still stranger things: MicroCT imaging of 3D drepanosaur skulls and skeletons (Saints & Sinners quarrry, Late Triassic, Eolian/Interdunal nugget formation) reveals bizarre and novel morphologies including a beak combined with transversely wide teeth, sauropod-like pneumatic dorsal vertebrae, a chevron that articulates with the pelvis and tripodal adaptations. Journal of Vertebrate Paleontology abstracts.

Where would drepanosaurs nest, if Jesairosaurus was not known?

We’re getting back
to an older series today as we ‘play’ with the large reptile tree (1262 taxa, LRT) by cherry-deleting taxa.

Drepanosauromorpha are so distinct from other reptiles
that experts have been hard at work trying to figure out what they are—without success or consensus. There are so many competing ideas (which means none are convincing) that I’m going to refer you to the Wikipedia page on Drepanosauridae that lists and discusses them all with citations. The latest work (Pritchard and Nesbitt 2017) recovered a very basal diapsid nesting, but they did not realize that lepidosaur ‘diapsids’ were not related to archosaur ‘diapsids’, due to taxon exclusion at the genesis of reptiles.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Unfortunately,
all prior workers omitted or overlooked the widely tested closest relatives, Jesairosaurus (Jalil 1997, Fig. 1) followed by the basal lepidosauriformes, Tridentinosaurus, Lanthanolania, Sophineta and Palaegama (Fig. 1) in the LRT, which tests all prior sister candidates Megachirella (Fig. 2), at the base of the Rhynchocephalia (Fig. 3), is also closely related in the LRT. So, once again, taxon exclusion is the problem in all prior studies. Jesairosaurus was documented as the last common ancestor of drepanosauromorpha here in October 2012. This is not one of those “obvious as soon as you realize it” nestings. You really do need the wide gamut testing of the LRT to eliminate all other candidates.

FIgure 2. Megachirella (Renesto and Posenato 2003) is a sister to the BSRUG diapsid.

FIgure 2. Megachirella (Renesto and Posenato 2003) is a sister to the BSRUG diapsid.

So let’s play the game of taxon exclusion…

If Jesairosaurus and all Archosauromorpha are deleted,
the remaining drepanosauromorphs do not shift to another node within the Lepidosauromorpha.

If Jesairosaurus and Hypuronector and all Archosauromorpha are deleted,
the remaining drepanosauromorphs do not shift to another node, and nest with basalmost Sphenodontia, like the BSRUG 29950-12 specimen related to Megachirella and Pleurosaurus.

If Lepidosauromorpha and Diapsida are deleted,
Jesairosaurus and the drepanosauromorphs nest with the herbivorous synapsids, Suminia and Dicynodon.

If Lepidosauromorpha and Diapsida are deleted,
Megalancosaurus alone nests between the herbivorous synapsids Venjukovia + Tiarajudens and Suminia Dicynodon.

Figure 3. Subset of the LRT focusing on basal lepidosauriformes and Jesairosaurus at the base of the Jesairosauria.

Figure 3. Subset of the LRT focusing on basal lepidosauriformes and Jesairosaurus at the base of the Jesairosauria. Several new clades are named here.

If only Diapsida is tested,
Jesairosaurus and the remaining drepanosauromorphs nest as a clade between the sauropterygians and mesosaurs + thalattosaurs + ichthyosaurs.

If only Diapsida is tested,
Megalancosaurus alone nests between the sauropterygians and mesosaurs + thalattosaurs + ichthyosaurs.

Nomenclature and some suggestions:

  1. JesairosauriaJesairosaurus, Megachirella, their last common ancestor all descendants. More taxa reveal this phylogenetic pattern that has, so far, escaped the notice of professional paleontologists.
  2. RhynchocephaliaGephyrosaurus, Megachirella, their last common ancestor all descendants.
  3. Sphenodontia —  Sphenodon, Ankylosphenodon, their last common ancestor all descendants.
  4. TransphenodontiaTrilophosoaurus, Mesosuchus, their last common ancestor all descendants. These taxa bridge the gap between sphenodonts and rhynchosaurs and include the latter. More taxa reveal this phylogenetic pattern that has, so far, escaped the notice of professional paleontologists.
  5. RhynchosauriaRhynchosaurus, Hyperodapedon, their last common ancestor all descendants.
  6. PseudoribiaCoelurosauravus, Icarosaurus, their last common ancestor all descendants. These so-called ‘rib-gliders’ actually use elongate dermal ossifications to extend their gliding membranes. More taxa and a closer examination of Icarosaurus and kin reveal this clade that has, so far, escaped the notice of professional paleontologists.

The related taxa shown
in figure 3 as a subset of the large reptile tree come together by way of taxon inclusion. Prior workers missed these relationships by excluding taxa. Rhynchosaurs were once considered Rhynchocephalians, but recently that has not been accepted based on the invalidated hypothesis that rhynchosaurs were archosauriformes.

Invalidated or modified nomenclature:

  1. Allokotosauria — While protorosaurs, including Pamelaria, are basal members of the new Archosauromorpha, Trilophosaurus and Azendohsaurus are members of the new Lepidosauromorpha.
  2. Diapsida — The LRT documents two unrelated clades evolving diapsid skull architecture. In the LRT only archosauromorph diapsids are considered Diapsida. More taxa reveal this pattern that has, so far, escaped the notice of professional paleontologists.

I hope readers enjoy and learn from these daily blogs.
If you disagree with any of the results, I encourage you to run your own tests with similar taxon lists, then let us all know if you confirm or refute the LRT results. Don’t be like those who just hurl adjectives at the work done here. Keep up your professional demeanor and attitude and be prepared to accept new discoveries if they cannot be refuted. The strength of the LRT is that is covers all available candidates and minimizes taxon exclusion problems that plague smaller prior studies.

References
Jalil N-E 1997. A new prolacertiform diapsid from the Triassic of North Africa and the interrelationships of the Prolacertiformes. Journal of Vertebrate Paleontology 17(3), 506-525.
Pritchard AC and Nesbitt SJ 2017. A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida. Royal Society Open Science DOI: 10.1098/rsos.170499

wiki/Jesairosaurus
wiki/Drepanosaur
wiki/Allokotosauria

Avicranium: a 3D drepanosaur skull

Pritchard and Nesbitt 2017
bring us a new Late Triassic drepanosaur, Avicranium renestoiAMNH FARB 30834, based on CT scanning a crushed skull and reconstructing it digitally (Fig. 1). I added a little distance between the anterior and posterior elements in order to get a rounder orbit. I also restored the missing ascending process of the premaxilla and nasal.

Figure 1. Avicranium from Pritchard and Nesbitt 2017, in situ, original reconstruction and revised with rostral restoration.

Figure 1. Avicranium from Pritchard and Nesbitt 2017, in situ, original reconstruction and revised with rostral restoration in accord with the plesiomorphic drepanosaur, Vallesaurus. Distinct from Vallesaurus, Avicranium has a concave maxilla and lacks teeth. That long convex squamosal is unique.

The new reconstructed skull
looks like a little oviraptorid (Fig. 2)— strictly by convergence.

Figure 3. Khaan, an oviraptorid that nests with Limusaurus in the large reptile tree AND the repaired Cau, Brougham and Naish tree.

Figure 2. Khaan, an oviraptorid, has a skull similar to that of Avicranium.

The closest sister taxon of Avicranium
in the large reptile tree (LRT, 1087 taxa) is the drepanosaur, Vallesaurus based on the skull alone. Pritchard and Nesbitt nested Avicranium as a drepanosaur based on the cervical vertebrae (Fig. 1) and noticed ‘striking similarities’ to birds. The difference includes the crooked jaw line, perhaps related to the absence of teeth in Avicranium.

Figure 2. Vallesaurus is a sister to Avicranium in the LRT.

Figure 2. Vallesaurus is a sister to Avicranium in the LRT.

Pritchard and Nesbitt nested
drepanosaurs uncertainly, reporting “A phylogenetic analysis of Permo-Triassic diapsids supports the hypothesis that drepanosaurs are an archaic lineage that originated in the Permian, far removed from crown group Reptilia.” They did not realize their clade ‘Diapsida’ was actually diphyletic, with lepidosauriformes arising convergently with archosauriformes. The authors did not include taxa that nested basal to drepanosaurs in the LRT including Jesairosaurus, Palaegama and Saurosternon even those these have been on the Internet for several years. In fact, their figure 4 cladogram shows no outgroups for the Drepanosauromorpha, a very dangerous phylogenetic proposition. By contrast the LRT provides certain and verified outgroups back to Devonian tetrapods.

Figure 4. Subset of the LRT focusing on drepanosaurs and Avicranium.

Figure 4. Subset of the LRT focusing on drepanosaurs and Avicranium.

So once again taxon exclusion obscures relationships.
All Pritchard and Nesbitt had to do was to go online for some taxonomic suggestions and their unsolved problem would have been quickly remedied using their own character list. Are paleo-workers trying to avoid taxa offered for testing by the LRT? It would seem so given the present circumstances. Would it tear down the walls if someone knowingly confirmed the present hypothesis of interrelationships?

Well, that’s not going to happen,
except, as we’ve seen, without citation.

References
Pritchard AC and Nesbitt SJ 2017. A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida. Royal Society Open Science DOI: 10.1098/rsos.170499

wiki/Avicranium

Wrist supination/pronation in Megalancosaurus?

Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

Figure 8. Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

One of the weirdest of the weird
Megalancosaurus has been studied and published previously (see refs below). A recent addition (Castiello et al. 2016) adds fused clavicles, a saddle-shaped glenoid, a tight connection between the radius and ulna that hindered pronation/suppination (but see below) and hypothetical forelimb muscles to our knowledge of this basal lepidosauriform.

Unfortunately 
the authors only go as far as labeling this taxon a drepanosaur and a drepanosauromorph without further identifying the larger and even larger clades these taxa nest within.

News

  1. “unlike those of other drepanosauromorphs [the clavicles] are fused together and possess a small median process caudally directed so that the whole structure looks similar to the furcula of theropod dinosaurs, especially oviraptorids.”
  2. “The scapular blade reaches the modified, expanded neural spines of the third and fourth dorsal vertebra so that the pectoral girdle formed a solid ring, which would have been very rigid.”
  3. “the glenoid fossa has a saddle-shaped structure and lies on the coracoid”
  4. “paired sternal plates are fused to the coracoids forming a craniocaudally elongate coracosternal complex.”
  5. “the coracosternal complex was more vertically oriented than in previous reconstructions” but as figured for Drepanosaurus and Megalancosaurus (Fig. 1) at ReptileEvolution.com.
  6. Rather than a separate olecranon sesamoid (Figs. 1, 2) that Megalancosaurus and all of its sisters share, the authors report on, “the elongate olecranon process of the ulna.”
  7. Rather than recognizing a bone break in the ulna (Fig. 2), the authors report, “a small notch is present on the medial margin of the ulna distal to the articular surface for the humerus. This notch houses the medial corner of the proximal head of the radius, suggesting that in life, the two bones were firmly connected together at their proximal end, preventing pronation and supination of the forearm.” No other sister taxa or tetrapods have such an ulna notch. Note, the notch is not present in figure 2, but the sesamoid is pretty broken up. These bones are hollow, fragile and crushed. Be careful how you interpret them. Earlier we saw another misinterpretation of a drepanosaur forelimb.
  8. When the authors present a hypothetical forelimb myology they do not present a pertinent actual forelimb myology (Fig. 3) for comparison. Such a comparison helps assure the reader that the myology for Megalancosaurus has not been invented and follows actual patterns and sizes.
Megalacosaurus elbow

Figure x. The break and the broken pieces of the Megalancosaurus ulna are reidentified here. The sesamoid is prominent and crescent-shaped as in Drepanosaurus.

Crushed hollow bones
are sometimes difficult to interpret, as we’ve seen before.

Elbow sesamoid in another specimen of Megalancosaurus, MPUM 8437.

Figure 2. Elbow sesamoid in another specimen of Megalancosaurus, MPUM 8437.

The authors provided a hypothetical myology
which they phylogenetically bracketed by lepidosaurs and crocodilians (which means what??) based on prior pterosaur forelimb myology as imagined by Bennett (2003, 2008). Pterosaurs are unrelated to drepanosaurs. The Bennett pterosaur myology had problems because it located extensors and flexors anterior and posterior to the fore arm, rather than dorsal and ventral (palmar) as in Sphenodon (Fig. 3) the closest living taxon to drepanosaurs AND pterosaurs.

Sphenodon hand muscles

Figure 3 Sphenodon hand muscles. Click to enlarge. These were not referenced in the Castiello et al. study.

It would have been appropriate

  1. to show that the fingers of Megalancosaurus had more phalanges (Fig. 4), as seen in sister taxa and as I see them in Megalancosaurus itself.
  2. to show two versions of the manus, with spread metacarpals (as presented) and another with more closely appressed metacarpals, as in sister taxa, Hypuronector, Vallesaurus, and Drepanosaurus (Fig. 4).
  3. to take a closer look at that ulna notch, knowing that such a notch mechanically weakens the cylinder, is produced by broken bone, and is not repeated in other drepanosaurs.
  4. to take a closer look at that olecranon ‘process’ because sister taxa all have a large sesamoid.
  5. to phylogenetically nest drepanosaurs in order to provide the most accurate myology analogy possible.
The sister taxa of Drepanosaurus

Figure 4. Click to enlarge. The sister taxa of Drepanosaurus all had an olecranon sesamoid. Drepanosaurus simply had a larger one.

The above data
has been online for the past six years. Plenty of time to consider it. No need to cite it.

Pronation/supination
Arboreal taxa in general and distant drepanosauromroph sisters (Palaegama and Jesairosaurus) are able to axially rotate the forearm by at least some degree. Like the human forearm, the radius and ulna in these taxa are separated by a long oval space that enables the radius to axially rotate on the ulna.

By contrast 
the radius and ulna of Hypuronector are appressed (Fig. 4), restricting pronation/ supination. Vallesaurus may have been similar, but taphonomic disarticulation makes it difficult to tell. The forearm was relatively shorter than the humerus. Drepanosaurus had a similar short forearm, but also had a giant elbow sesamoid that essentially extended the humerus, separated the proximal radius and ulna, as in birds, but shifted the radius to the sesamoid, deleting the parallelogram effect — AND likely reducing pronation and supination.

Unlike its sisters, but like humans,
the radius and ulna of Megalancosaurus were slender, elongate and separated by an interosseus space. I don’t see any reason to suggest that pronation and supination were restricted to 0º here, but not nearly to the extent found in humans (Homo), about 180º. The radius in Megalancosaurus still appears to articulate with the humerus and if re-inflated from its crushed state, might be a cylinder with a circular proximal articulation, enabling pronation and supination.

References
Bennett SC 2003. Morphological evolution of the pectoral girdle of pterosaurs: myology and function. In: Buffetaut E, Mazin J-M, editors. Evolution and palaeobiology of pterosaurs. Geol Soc Spec Publ. 217. London (UK): Geological Society of London. p. 191–215.
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. In: Buffetaut E, Hone DWE, editors. Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. München: Zitteliana. B28. p. 127–141.
Calzavara M, Muscio G and Wild R 1980. Megalancosaurus preonensis n. gen. n. sp., a new reptile from the Norian of Friuli. Gortania 2: 59-64.
Castiello M, Renesto S and Bennett SC 2016. The role of the forelimb in prey capture in the Late Triassic reptile Megalancosaurus (Diapsida, Drepanosauromorpha). Historical Biology DOI: 10.1080/08912963.2015.1107552
Feduccia A and Wild R 1993. Birdlike characters in the Triassic archosaur Megalancosaurus. Natur Wissenschaften 80:564–566.
Geist NR and Feduccia A 2000. Gravity-defying Behaviors: Identifying Models for Protoaves. American Zoologist 4):664-675. online pdf
Renesto S 1994. Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of Northern Italy. Journal of Vertebrate Paleontology 14(1):38-52.
Renesto S 2000. Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of Northern Italy. Rivista Italiana di Paleontologia e Stratigrafia 106: 157–179.

wiki/Megalancosaurus

Perpetuating the Drepanosaurus elbow myth: Pritchard et al. 2016

First of all
it’s always good to see fresh, exciting material coming out of the Triassic. In this case a 3D preservation of a new type of Drepanosaurus forelimb (Figs. 1-3). but this time retaining only two fingers and digit 2 is quite robust. This specimen GR 737 deserves a new genus, but it was recognized by Pritchard et al. as conspecific with the holotype MCSNB 5728.

Figure 1. Italian Drepanosaurus at left, compared to the New Mexico drepanosaur at right. Original and corrected identifications are shown at 5 second intervals.

Figure 1. Italian Drepanosaurus at left, compared to the New Mexico drepanosaur at right. Original and corrected identifications are shown at 2 second intervals.

Previously (Renesto 1994)
identified the large bone at the elbow of Drepanosaurus as a displaced and flattened ulna while the ulnare and intermedium evidently fused and took the place and shape of the cylindrical, but proximally concave ulna. That interpretation was dismissed with evidence five years ago here by showing that the purported elbow bone was in reality an olecranon sesamoid, similar to that found in sisters Megalancosaurus (Fig. 4 in yellow) and Vallesaurus (Fig. 5). The new specimen does nothing to change that and has a long list of reconstruction and identification problems here solved by DGS (digital graphic segregation) using a computer monitor as a microscope having not seen the actual specimen firsthand.

Figure 2. Hayden Quarry drepanosaur as originally presented by Pritchard et al. 2016. No other tetrapod ever had such an arrangement of bones.

Figure 2. Hayden Quarry drepanosaur as originally presented by Pritchard et al. 2016. No other tetrapod ever had such an arrangement of bones. Compare to figure 3 where the ulna is in its usual position and shape. Also, note the lack of detail presented here despite firsthand access. Finally, note that most scale bars do not scale with one another, nor with the reconstruction. These problems are repaired in figure 3.

Unfortunately
Pritchard et al. 2016 followed the earlier Renesto mistake. Occam’s razor is once again ignored in favor of bizarre morphologies never before seen. The ulna always has been a cylindrical bone parallel to the radius. The elbow sesamoid is a flattened plate. Moreover, Pritchard et al. were unable to see the fused sutures between the metacarpals and phalanges (Fig. 3) in their specimen. They did not realize that when cylindrical bones, like the ulna, are crushed and scattered they need to be put back together before you add them to a reconstruction (Fig. 3). Massive bones, like digit 2, are never backed up by gracile and perforated never-before-seen structures as Pritchard et al. reconstructed. Finally, bones Pritchard et al. identified as the intermedium and ulnare in Megalancosaurus are actually the intermediaum and pisiform (Fig. 4) based on taxa close to megalancosaurs preserving a complete carpus.

Figure 3. The Hayden Quarry drepanosaur as interpreted here with scale bars all to the same scale and the ulna in its usual place with an olecranon sesamoid at the elbow. Note DGS was able to tease out the former metacarpals and carpals here.

Figure 3. The Hayden Quarry drepanosaur as interpreted here with scale bars all to the same scale and the ulna in its usual place with an olecranon sesamoid at the elbow. Note DGS was able to tease out the former metacarpals and carpals here.

From the Pritchard et al. abstract:
“Along with the crushed type specimen from Italy, these specimens have a flattened, crescent-shaped ulna with a long axis perpendicular to that of the radius and hyperelongate, shaft-like carpal bones contacting the ulna that are proximodistally longer than the radius.”

Figure 4. Carpus of Megalancosaurus in situ, in vivo and compared to a relatively close outgroup taxon that preserves carpal elements, Daedalosaurus, a kuehneosaur.

Figure 4. Carpus of Megalancosaurus in situ, in vivo and compared to a relatively close outgroup taxon that preserves carpal elements, Daedalosaurus, a kuehneosaur. Note that bones Pritchard et al. identified as intermedium and ulnare are actually the intermediaum and pisiform. Here the megalancosaur ulnare continue to be located proximal to distal carpals 4 and 5. The medial carpal enlarges to replace the dislocated and elongated intermedium, parallel to an equally elongated pisiform. Finally, note that the artist of Daedalosaurus misidentifies distal carpals 1 and 5. Carpal 1, proximal to the thumb, should always be on the radius side.

Unfortunately
the keywords ‘sesamoid‘ and ‘olecranon‘ do not appear in this paper. So the authors did not test alternate identities that were presented online 5 years agoDrepanosaurus is a highly derived drepanosaur and the elbow bone in question is quite large. It is reasonable to look for smaller versions of this olecranon sesamoid in more primitive taxa. And when you look for them, you find them in Megalancosaurus (Fig. 5) and Vallesaurus (Fig. 6).

The elbow of Megalancosaurus.

Figure 5. The elbow of Megalancosaurus. The perfect alignment of the olecranon sesamoid with the ulna masked the separation of these two bones, which are often fused in taxa with an olecranon process, like the kuehneosaur, Daedalosaurus. Note the ulna no longer articulates with the humerus as in Drepanosaurus.

Figure 6. Vallesaurus forelimb as drawn by Renesto and Binellit 2006.

Figure 6. Vallesaurus forelimb as drawn by Renesto and Binellit 2006.

Pritchard et al. 
rely on the interpretation of the apparent elongation of the intermedium and ulnare (a misidentified pisiform) in Megalancosaurus as their transitional stage enabling the three-part forelimb in the Hayden Quarry drepanosaur. The more primitive Hypuronector has an unossified carpus. The more derived Vallesaurus has a poorly ossified carpus and a small elbow sesamoid. The more derived Megalancosaurus has a larger olecranon sesamoid and a more completely ossified carpus (Fig. 4). Not mentioned by the authors, the pes (foot) of Megalancosaurus has an identical elongation of the calcaneum and astragalus (Fig. 7).

Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

Figure 7. Megalancosaurus showing the elongation of the astragalus and calcaneum in the pes.

Unfortunately, Pritchard et al. have no clue as to what drepanosaurs are.
They report, “Drepanosaurus is a member of Drepanosauromorpha, a group of Triassic reptiles with lizard-like body proportions and elongate, slender digits likely adapted for specialized grasping.” By contrast the large reptile tree nests them as basal Lepidosauriformes, sisters to Jesairosaurus and this clade is a sister to the gliding kuehneosaurs and their immediate arboreal ancestors.

And finally, the link to supplementary material in the paper: http://dx.doi.org/10.1016/j.cub.2016.07.084 is broken and does not connect with it. There are several high-impact, new generation PhDs authoring this paper. Let’s hope next time they test alternate identities, conduct a proper phylogenetic analysis and produce more precise reconstructions.

References
Colbert EH and Olsen PE 2001. A New and Unusual Aquatic Reptile from the Lockatong Formation of New Jersey (Late Triassic, Newark Supergroup) American Museum Novitates, 3334: 15pp.
Olsen PE 1979. 
A new aquatic eosuchian from the Newark Supergroup LateTriassic-Early Jurassic) of North Carolina and Virginia. Postilla 176: 1-14.
Pinna G 1980. 
Drepanosaurus unguicaudatus, nuovo genere e nuova specie di Lepidosauro del trias alpino. atti Soc. It. Sc.Nat. 121:181-192.
Pinna G 1986. 
On Drepanosaurus unguicaudatus, an upper Triassic lepidosaurian from the Italian Alps. Journal of Paleontology 50(5):1127-1132.
Pritchard AC, Turner AH, Irmis RB, Nesbitt SJ and Smith ND 2016. Extreme Modification of the Tetrapod Forelimb in a Triassic Diapsid Reptile. Current Biology, 2016 DOI: 10.1016/j.cub.2016.07.084 online here
Renesto S 1994. Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of Northern Italy. J. Vertebr. Paleontol. 14, 38–52.
Renesto S 1994. The shoulder girdle and anterior limb of Drepanosaurus unguicaudatus (Reptilia, Neodiapsida) from the upper Triassic (Norian of Northern Italy. Zoological Journal of the Linnean Society 111(3):247-264 December
Renesto S and Binelli G 2006. ’Vallesaurus Cenensis“’ Wild, 1991, A Drepanosurid (Reptilia, Diapsida): From the Late Triassic of Northern Italy”, Rivista Italiana di Paleontologia e Stratigrafia 112: 77–94, Milano.
Renesto S, Spielmann JA, Lucas SG and Spagnoli GT 2010. The taxonomy and paleobiology of the Late Triassic (Carnian-Norian: Adamanian-Apachean) drepnosaurs (Diapsida: Archosauromorpha: Drepanosauromorpha): Bulletin 46. Bull. NM Museum of Natural History 46, 1–81.

Earlier rebuttals
December 2011 rebuttal
January 2016 rebuttal

Publicity
livescience.com
www.nhregister.com
www.bbc.com
www.sciencedaily.com

The hand and super-claw of Drepanosaurus

When Drepanosaurus (Pinna 1980, Figs. 1-3) was first discovered and described, this oddity, metaphorically from the land of Dr. Seuss, presented several never-before-seen morphologies including a hooked tail, humped shoulder, a giant olecranon sesamoid (earlier misidentified as a displaced ulna) and an odd hand with a super-claw on finger two — all on one headless body.

Figure 1. Drepanosaurus featuring fused finger phalanges and a super claw -- among several other odd traits.

Figure 1. Drepanosaurus featuring fused finger phalanges and a super claw — among several other odd traits. This image is updated from a prior attempt. Note: the tips of manual unguals 2-4 are aligned.

After fielding a question,
I told a reader that I would take another look at the Drepanosaurus hand. I’m glad I did. The prior tracing was not based on DGS techniques or high resolution images. This one (Figs. 1-3) is. Earlier I mistakenly reconstructed ungual 2 extending beyond the others. Now I find that the middle three unguals terminated at about the same line (Fig. 3).

Figure 1. Drepanosaurus hand with DGS (digital graphic segregation) techniques used to separate the fingers and discover the vestigial joints in the fused digits. The size and proportions of ungual 1 are guesstimated based on very vague outlines impressed from below on ungual 2. On digit 4 (gold on gold) the original tracing appears to have missed the penultimate phalanx (n dark gold).

Figure 2. In situ tracing using DGS (Photoshop layers) to segregate fingers from one another. The outline of digit 1 (purple) is tentative, based on general patterns and very slight impressions in ungual 2.

Yes
several of the phalanges are apparently fused together. Nevertheless their former joints are still visible and are traced here. The penultimate phalanges are very short, the opposite of most arboreal lizards. The cervicals are also quite short, the opposite of other drepanosaurs.

Why did the phalanges fuse?
Perhaps because that big claw prevented the typical flexion function among phalanx sets. Ungual 2 is so big that several former PILs (now fused phalanges) ran through it.

Figure 2. GIF animation of Drepanosaurus fingers reconstructed and imagined in dorsal view. Metacarpal outlines may not be reconstructed in dorsal view. They are typically arranged with mc4 the longest.

Figure 2. GIF animation of Drepanosaurus fingers reconstructed and imagined in dorsal view from data in figure 2. Metacarpal outlines may not be reconstructed in dorsal view. They are typically arranged with mc4 the longest.

Function?
Like almost all digits, the acted together for grasping. The large size of ungual 2 simply made up for the relative brevity of metacarpal 2 and the proximal phalanges, traits that are plesiomorphic for reptiles. That the extensor surface of the ungual is much larger than the flexor surface suggests that the claws were often held retracted, like cat claws. So these were more like paws, the tendril like arboreal lizard toes. Others have considered drepanosaurs slow movers. I agree.

Unlike earlier chameleon-like hypotheses
for Megalancosaurus, the manual digits of Drepanosaurus appear to have swung through parallel arcs, as in most tetrapods.

In situ
the tall narrow claws lie on their sides, as is typical of ungual preservation in crushed fossils. In figure 3, I imagined them in dorsal view, which is the typical presentation of a manus for other tetrapods. Atypically the ungual extends proximally over the penultimate phalanges in dorsal view. So the transparent colors help to visualize this. One can only imagine the size of the extensor tendons on those hands. The flexors were strong too. Don’t let one of these climb on your arm or hand. You might not ever be able to shake it off.

Phylogeny
Wikipedia reports that Drepanosaurus nests within the Protorosauria, a terrestrial clade or small to large archosauromorphs. In counterpoint, and with actual phylogenetic testing (not tradition), the large reptile tree nests Drepanosaurus and the drepanosaurs with Jesairosaurus and the Keuhneosaurs at the base of the Lepidosauriformes. This clade was arboreal.

References
Pinna G 1980. Drepanosaurus unguicaudatus, nuovo genere e nuova specie di Lepidosauro del trias alpino. atti Soc. It. Sc.Nat. 121:181-192.
Pinna G 1986. On Drepanosaurus unguicaudatus, an upper Triassic lepidosaurian from the Italian Alps. Journal of Paleontology 50(5):1127-1132.
Renesto S 1994. The shoulder girdle and anterior limb of Drepanosaurus unguicaudatus (Reptilia, Neodiapsida) from the upper Triassic (Norian of Northern Italy. Zoological Journal of the Linnean Society 111(3):247-264

wiki/Drepanosaurus

 

Jesairosaurus and the drepanosaurs leave the Tritosauria :-(

My earlier reconstruction
of the basal lepidosauriform, Jesairosaurus (Fig. 1; contra Jalil 1997, not a protorosaur/prolacertiform) included several errors based on attempting to create a chimaera of several specimens of various sizes based on scale bars. In this case, scale bars should not have been used. Rather fore and hind parts had to be scaled to common elements, like dorsal vertebrae, as shown below (Fig. 2). I think this version more accurately reflects the in vivo specimen, despite its chimeric origins. All of the partial skeletons assigned to this genus were discovered at the same Early to Middle Triassic sandstone site and two were touching one another. A larger skull, ZAR 7, shows the variation in size from the skull to shoulders remains of the ZAR 6 specimen.

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1997). The wide and flat ribs are interesting traits for a likely arboreal reptile.

Mother of all drepanosaurs
The Drepanosauria is an odd clade of slow-moving arboreal reptiles that includes Hypuronector, Vallesaurus, Megalancosaurus and Drepanosaurus (Figs. 2, 3). Jesairosaurus was not a drepanosaur, but nested basal to this clade before the present revisions. It remains basal to the Drepanosauria now with revisions.

The revised reconstruction of Jesairosaurus 
shifts this clade away from Huehuecuetzpalli, Macrocnemus and the rest of the Tritosauria. Now Jesairosaurus and the drepanosaurs nests between Saurosternon, Palaegama and the so-called “rib” gliders, beginning with Coelurosauravus.

A short history of Jesairosaurus
Shortly after their discovery Lehman 1971 referred the several hematite encrusted specimens to the Procolophonida. Further preparation showed that they were referable to the Diapsida, according to Jalil (1990) and the, more specifically, to the Prolacertiformes (Jalil 1997) as a sister to Malerisaurus with Prolacerta as a common ancestral sister. Jalil did not include the closest sisters of Jesairosaurus as revealed by the present analysis.

With a much larger list of taxa,
the large reptile tree nests Malerisaurus between the Antarctica specimen assigned to Prolacerta (AMNH 9520) and the holotype of Prolacerta. Jesairosaurus, as mentioned above, nests with the basal lepidosauriformes. Any traits shared with protorosaurs are by convergence. Deletion of Jesairosaurus does not affect the nesting of the Drepanosauria as basal lepidosauriformes.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Arboreal
This new nesting shifts drepanosaurs closer to kuehneosaurs (Figs. 3, 4), another notably arboreal clade.

Figure 3. The new nesting for Jesairosaurus and the drepanosaurs as sisters to the Kuehneosaurs, several nodes away from Huehuecuetzpalli and the tritosaurs.

Figure 3. The new nesting for Jesairosaurus and the drepanosaurs as sisters to the Kuehneosaurs, several nodes away from Huehuecuetzpalli and the tritosaurs.

Certainly
there will someday be more taxa to fill in the current large morphological gaps in and around Jesairosaurus, but here’s what we have at present (Fig. 3) with regard to the origin of the so-called “rib” gliders (actually dermal rods, not ribs, as shown by Coelurosauravus) and the origin of the drepanosaurs.

Figure 4. Jesarosaurus to scale with sisters Palaegama and Coelurosauravus.

Figure 4. Jesairosaurus to scale with sisters Palaegama and Coelurosauravus.

The shifting of a clade
like Jesairosaurus + Drepanosauria occurred due to inaccurate reconstructions used for data. Science builds on earlier errors and inaccuracies. I let the computer figure out where taxa nest in a cladogram of 606 possible nesting sites, minimizing the negative effects of bias and tradition.

It’s sad
to see the drepanosaurs leaving the Tritosauria as it contains several oddly Dr. Seuss-ian variations on the tritosaur theme.

Also note the nesting
of the basal Rhynchocephalians, Megachirella and Pleurosaurus, between the palaegamids and the tritosaurs (Fig. 4). In the course of this study, both also received updates to their skull reconstructions. The former was difficult to interpret without knowing where it nested. What appeared to be an odd sort of a squamosal in Megachirella now appears to be a pair of displaced pleurosaur-like premaxillae. For Pleurosaurus I should not have trusted a prior line drawing by another worker. Here I used DGS to create what appears to be a more accurate skull without so many apparent autapomorphies.

References
Jalil N 1990. Sur deux cranes de petits Sauria (Amniota, Diapsida) du Trias moyen d’ Algerie. Comptes Rendus de I’ Academic des Sciences, Paris 311 :73 1- 736.
Jalil N-E 1997. A new prolacertiform diapsid from the Triassic of North Africa and the interrelationships of the Prolacertiformes. Journal of Vertebrate Paleontology 17(3), 506-525.
Lehman JP 1971. Nouveaux vertebres du Trias de la Serie de Zarzai’tine. Annales de Paleontologic (Vertebres) 57 :71-93.

 

 

Drepanosaur skull: Pritchard and Nesbitt 2014 JVP abstracts

Megalancosaurus including the palate, the only palate ever figured for a drepanosaur.

Figure 1. Megalancosaurus including the palate, the only palate ever figured for a drepanosaur. This is not the specimen described by Pritchard and Nesbitt 2014.

Pritchard and Nesbitt (2014) present new skull data based on a 3D drepanosaur skull (posterior elements only) from the Triassic of Arizona. Comments follow.

From the abstract:
“Drepanosaurs are an enigmatic clade of Late Triassic diapsids from Europe and North
America with superficially chameleon-like bauplans. The phylogenetic position of the
group among diapsids is contentious. (1) Most hypotheses suggest that drepanosaurs are
basal archosauromorphs closely related to ‘protorosaurs’ (e.g., Protorosaurus,
Tanystropheus). (2) Other phylogenies place drepanosaurs as non-saurian diapsids,
suggesting a substantially older origin for the lineage. Clarifying the phylogenetic
position of drepanosaurs is important to understanding the degree of taxonomic
diversification among diapsids prior to the Permo-Triassic Extinction (PTE).
The poor quality of the drepanosaur fossil record has hampered an understanding of
their position. (3) Nearly all drepanosaur skeletal material is badly distorted (4), and all
described skulls are crushed such that phylogenetically important characters are
obscured. (5) A new drepanosaur specimen from the Late Triassic Coelophysis Quarry of
New Mexico includes a partial, three-dimensionally preserved skull. The postorbital
region of the skull, atlas-axis complex, and anterior cervical vertebrae are preserved in
near-articulation. (6) 3D reconstruction of micro computed tomography (CT) data allows the first detailed description of most drepanosaur skull bones. Many are surprisingly
plesiomorphic (e.g., squamosal with massive descending process, quadrate lacking
posterior concavity, occipital condyle with notochordal pit), sharing more in common
with non-saurian diapsids than early archosauromorphs. (7).

A phylogenetic analysis of 300 characters and 40 early diapsids supports the
hypothesis that drepanosaurs fall outside of Sauria. (8). This suggests a very long ghost
lineage (~35 million years), extending well into the Late Permian. The results of this
phylogeny suggest that both drepanosaurs and a number of early saurian lineages must 
have originated by the Late Permian. Although the fossil record suggests an enormous
morphological diversification among saurians following the PTE, a great deal of
taxonomic diversification among diapsids must also have occurred prior to the extinction.”

(1) not at all contentious. Drepanosaurs are derived from Jesairosaurus in the Tritosauria. This has been known for several years.

(2) Protorosaurus and Tanystropheus are not related to one another. This has been known for many years.

(3) Repeating a false allegation.

(4) crushed flat, but not otherwise distorted (see Fig. 2).

(5) Not so, IMHO.  Use DGS to retrieve data. Works every time.

(6) good news, but the key traits are found in the preorbital region. The big question is: did they have an antorbital fenestra? I see one on several specimens.

(7) These traits were first identified in Megalancosaurus. The occiput data is news. Non-saurian diapsids could include sauropterygians, ichthyosaurians, rib gliders and basal younginiforms according to traditional trees, which are outdated at best. Saurians include lepidosaurs and archosaurs. In this regard, drepanosaurs are saurians, tritosaur lepidosaurs.

(8) 40 is way too few taxa if you don’t know where drepanosaurs nest, especially if Jesairosaurus and Huehuecuetzpalli are excluded (I haven’t seen the inclusion set). Using 420 taxa drepanosaurs firmly nest within the Tritosauria and Lepidosauria, thus within the traditional definition of Sauria, which is a junior synonym of Amniota/Reptilia. Actually there is no long ghost lineage. Drepanosaurs originated in the Triassic following Jesairosaurus in the Early to Middle Triassic.

This is my take (Figs. 1, 2) on the skull of the drepanosaur Megalancosaurus. Note the occiput is not exposed in this 2D crushed specimen. It’s a fragile construction with a large naris, an antorbital fenestra, large orbit, diapsid temporal architecture (like that of a pterosaur) and a Y-shaped hyoid.

Interpretation of figure 6, the skull of Megalancosaurus.

Figure 7. Interpretation of figure 6, the skull of Megalancosaurus. Struts of bone surround antorbital fenestra here.

References
Pritchard A and Nesbiitt S 2014. The cranial morphology of drepanosaurs and the PermoTriassic diversification of diapsid reptiles. JVP abstracts 2014.

A closer look at Jesairosaurus

Updated November 29, 2015 with a new reconstruction and nesting for Jesairosaurus.

Earlier we looked at Jesairosaurus (Jalil 1991) and the origin of the Drepanosauridae. Today we’ll take a closer look at Jesairosaurus.

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Jesairosaurus was originally considered a procolophonid, then a prolacertiform
Sure it has a long neck, but in phylogenetic analysis, it doesn’t nest with Prolacerta or Marlerisaurus, but after the basal lepidosauriform Palaegama and prior to drepanosaurs and kuehneosaurs. Note the dorsal nares and large orbit. There’s a very tall scapula here, a precursor to the tall stem in drepanosaurs.

Distinct from most lepidosauriforms,
Jesairosaurus has fairly large thecodont teeth. Gastralia appear here for the first and last time in this lineage. The ventral pelvis isn’t fused, but the thyroid fenestra is gone.

Like most lepidosauriforms,
the scapulocoracoid was not fenestrated. And there’s a nice ossified sternum there.

On a side note…
As you know, I’m always attempting to improve the data here. Several months ago I mentioned to a detractor that most prior workers reported  forelimbs present in Sharovipteryx. Only Unwin et al. (2000) thought they were buried in the matrix. My detractor claimed the opposite, that I was the only one to see forelimbs. No word yet on this issue. Still waiting.

Another detractor claimed I had seen soft tissue on a Bavarian museum fossil pterosaur. When I asked which specimen, he refused to provide the number.

In a third case I asked to see a closeup of a pterosaur mandible tip that had been published. I wondered if the sharp tip might be a tooth, as it is in other sharp mandible pterosaurs. The offer was refused with the phrase, “trust us, it’s not there.” I replied “trust” is antithetical to Science. No reply and no closeup yet.

So, is it so hard to provide a museum number? A closeup of a photograph? Or a reply to a note on forelimbs? Should we trust other scientists? Or should we test and confirm or refute? There may be cooperation among other paleontologists. Or maybe they’re all very protective of their data. Evidently I also have a very bad reputation, and that may be the reason for the lack of cooperation. These things happen when paradigms are broken.

References
Jalil N-E 1997. A new prolacertiform diapsid from the Triassic of North Africa and the interrelationships of the Prolacertiformes. Journal of Vertebrate Paleontology 17(3), 506-525.
Unwin DM, Alifanov VR and Benton MJ 2000. Enigmatic small reptiles from the Middle-Late Triassic of Kyrgyzstan. In: Benton M.J., Shishkin M.A. & Unwin D.M. (Eds) The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge U. Press: 177-186.

wiki/Prolacertiformes