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

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

 

 

The Antorbital Fenestra of Drepanosaurs

The drepanosaurs are a rag-tag clade of slow-moving arboreal tritosaur lizards derived from Jesairosaurus in the large reptile tree. Drepanosaurs include Hypuronector, Vallesaurus, Megalancosaurus and Drepanosaurus in order of greater derivation.

The skull of Vallesaurus in situ.

Figure 1. The skull of Vallesaurus in situ. Difficult to interpret, to be sure, but I don’t see any large maxillary plates here. Perhaps palatal elements, though.

There has been some debate as to whether or not drepanosaurs had an antorbital fenestra. If so, this would have been the fifth (or perhaps the fourth since this clade is very close to Langobardisaurus and Cosesaurus) origin of the antorbital fenestra. Unfortunately only two drepanosaurs include skulls, Vallesaurus and Megalancosaurus. Here we’ll trace and reconstruct both. It’s no easy task.

The skull of Vallesaurus as interpreted by Renesto

Figure 2. The skull of Vallesaurus as interpreted by Renesto (2006). He found no evidence of an antorbital fenestra. The stem-like nasal and lacrimal are both present here. The question is, what, if anything, filled the space between them? Was it folded and flattened palatal bones? Renesto did not note any palatal elements here, yet they must have been present.

The palatal elements of Jesairosaurus,

Figure 3. The palatal elements of Jesairosaurus, the outgroup for the drepanosaurs. Fairly solid-looking. This contrasts with the lighter airier palates of fenestrasaurs and Megalancosaurus.

The palate
When skulls are crushed in lateral view, something has to happen to the transverse palatal elements. Typically they flip up or down, like playing cards, presenting their broadest surface to the matrix plane. It is difficult to discern the shape of the palatal elements in Vallesaurus, but if they were more solid, like the elements in Jesairosaurus, then this may account for the bone that Renesto found behind and through the rostrum (= antorbital fenestra).

In the more derived drepanosaur, Megalancosaurus (fig. 8) these solid elements were reduced to more gracile elements.

Figure 4. Interpretation of the skull elements of Vallesaurus. Note the slender ascending process of the maxilla in green.

Figure 4. Interpretation of the skull (sans palatal) elements of Vallesaurus. Note the slender ascending process of the maxilla in green and the slender lacrimal stem in magenta.

Interpretation of the skull of Vallesaurus based on figure 4.

Figure 5. Interpretation of the skull of Vallesaurus based on figure 4.

Vallesaurus
Talk about difficult skulls to trace (Figs. 1, 4), reconstruct and restore (Fig. 5)!! And remember, if we are looking at a light and airy skull, we’re looking through a light and airy skull to the right side elements obscured by intervening palatal elements. I did not attempt to outline the palatal elements in Vallesaurus, but considering the size of the eyes, the palate had to be nearly as wide as the height of the skull, as in Megalancosaurus.

Both part and counterpart of Megalancosaurus superimposed.

Figure 6. Both part and counterpart of Megalancosaurus superimposed using Photoshop.

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. The slender ascending process of the left maxilla is convincing evidence for an antorbital fenestra in Megalancosaurus. The huge size of the naris is further evidence for skull lightening as a selective influence.

Megalancosaurus
The skull of Megalancosaurus was split in two, the part and counterpart (Figs. 6, 7). Reassembling them with software helps to realign the two crushed halves together for interpretation of the elements. What I see there is a slender ascending process of the maxilla. That can only occur if there is an antorbital fenestra. If that bone is another bone, then this will have to be reconsidered. At this point an antorbital fenestra seems likely. And I’m open to new data if anyone out there has some.

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.

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

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
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.
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.
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.
Wild R 1990. Ein Flugsaurierrest (Reptilia, Pterosauria) aus der Unterkreide (Hauterive) von Hannover (Niedersachsen). Neues Jahrbuch für Geologie und Paläontologie. Abhandlung 181,241–254.

wiki/Vallesaurus
wiki/Megalancosaurus

Jesairosaurus and the origin of drepanosaurs

Updated November 29, 2015 with new data and a new nesting for Jesairosaurus and the drepanosaurs. 

The authors of Wikipedia
have no idea what drepanosaurs are other than reptiles. In the large reptile tree drepanosaurs were descended from Jesairosaurus and, more primitively, the basal tritosaur lepidosauriform, Palaegama. Here we’ll start with Palaegama (Fig. 1)the father of all drepanosaurs and kuehneosaurs.

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

Figure 1 Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Palaegama is a basal lizard-like lepidosauriform that shared few obvious traits with the highly derived drepanosaurs. It does not take a transitional taxon, like Jesairosaurus (Fig. 1) to make the case for a relationship here because deletion does nothing to tree topology.

Now we narrow our focus
to Jesairosaurus, the father of all drepanosaurs (Fig. 2). Essentially Jesairosaurus was a long torso palaegamid lepidosauriform. The skulls are readily comparable. The limbs are shorter in the derived taxon.

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

Figure 2. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Jesairosaurus lehmani (Jalil 1997) Early to Middle Triassic ~240 mya was originally described as a prolacertiform and thus related to Prolacerta. All shared traits are by convergence here. By virtue of its nesting, Jesairosaurus is also basal to the kuiehneosaurs, like Coelurosauravus (Fig.  3).

 

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

Figure 3. Jesarosaurus to scale with sisters Palaegama and Coelurosauravus.

With its bigger torso and smaller limbs,
Jesairosaurus was not a speedster. This was the first step in the evolution of the slow-moving, arboreal drepanosaurs. The high scapula of drepanosaurs finds an origin in Jesairosaurus.

It is unfortunate
that the hind feet and tail are not known for Jesairosaurus, because both of these body parts underwent a great transformation in early drepanosaurs.

As in Palaegama, the pelvis of Jesairosaurus was relatively tiny and included an anterior process of the ilium that developed further in drepanosaurs. While  Palaegama employed its expanded ilium to sprint, drepanosaurs were not sprinters, but arboreal climbers and clingers, like modern day chamaeleons.

 

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.

wiki/Prolacertiformes

Where is the Ulna on Drepanosaurus?

Drepanosaurus.

Figure 1. The unusual lepidosaur, Drepanosaurus with forelimb and elbow elements re-identfied. The carpals were poorly ossified.

Drepanosaurus unguicaudatus (Pinna 1980, 1986) Norian, Late Triassic ~210 mya was originally considered an unusual lizard. It had a fused astragalus/calcaneum and sprawling limbs.

Drepanosaurus was the first, and one of the most unusual, of all the drepanosaurs, those hook-tailed, bird-headed, arboreal, chamaeleon-like reptiles of the Triassic.

Renesto’s Reinvestigation of Pinna’s Misidentifications
In 1994 Dr. Silvio Renesto reexamined the skeleton of Drepanosaurus and clarified certain earlier errors (Fig. 2). Those plate-like bones at the elbows were originally identified as coracoids by Pinna — because they looked like coracoids. Renesto (1994) tentatively considered them ulnae.

The forelimbs of Drepanosaurus.

Figure 2. The forelimbs of Drepanosaurus. Left: According to Pinna (1986). Right: Re-identified by Renesto (1994).

Pinna (1986) considered the ulna-like bones the ulna + radius. Renesto (1994) considered them the ulnare + intermedium, essentially wrist bones replacing the ulna.

Pinna (1986) considered the medial forearm bone the scapula. Renesto (1994) identified it as the radius.

Pinna (1986) considered the tall narrow bone the interclavicle. Renesto (1994) identified it as the scapula. Pinna (1986) considered the bone between the humeri a clavicle). Renesto (1994) reidentified it as a coracoid.

Renesto (1994) correctly identified many of the strange bones of Drepanosaurus, but the result created a most unusual three-part (rather than two-part) forearm in which the tubular ulna became a plate-like disc at the elbow and the tiny disc-like ulnare became elongated and tube-like. Very unusual, but this identification was widely accepted.

The fore limb of Hypuronector

Figure 3. The fore limb of Hypuronector (from Colbert and Olsen 2001). Here the humerus is much more robust than the ulna and radius. Around the elbow there are a number of ossified elements and breaks, so the positive identification of the separate olecranon ossification, as found in sister taxa, is more difficult to ascertain.

The Evidence from Sister Taxa
Curious about the homologies of the large plate-like “elbow” bone, I looked at sister taxa recovered by the large reptile tree (Vallesaurus, Huehuecuetzpalli and Cosesaurus) to see what clues they might offer. Notably, all had an olecranon sesamoid, a distinct and separate elbow bone (Fig. 3) that typically would have been fused to the ulna, as in Sphenodon (Fig. 3).

Thus, if homologous, the bone identified as the “coracoid” by Pinna (1986) and the tentative “ulna” by Renesto (1994) was actually a greatly enlarged olecranon sesamoid that articulated with the humerus, radius and ulna. In turn, that makes the tube-like “ulnare + intermedium” tentatively identified by Renesto (1994) the ulna, located parallel to the radius as in all other tetrapods. The actual ulnare + intermedium is a small wrist bone, essentially the only bones that were ossified in the wrist.

megalancosaur elbows and wrists

Figure 3. Click to enlarge. Most sister taxa of Drepanosaurus had an olecranon sesamoid. Drepanosaurus simply had a larger one. See the Megalancosaurus olecranon below.

So what looks like the ulna is the ulna. What looks like the wrist bones are wrist bones. The big elbow bone is an elbow bone (the olecranon sesamoid). All that makes more sense, yet takes away none of the wonder from this incredible arboreal reptile.

The huge olecranon sesamoid anchored a huge muscle to drive digit 2. The ulna was “dished out” to make more room for this forearm/finger muscle complex.

The elbow of Megalancosaurus.

Figure 5. The elbow of Megalancosaurus. (UPDATED BELOW) The perfect alignment of the olecranon sesamoid with the ulna masked the separation of these two bones. Note the ulna no longer articulates with the humerus as in Drepanosaurus. Here the DGS (digital graphic segregation using Photoshop) method uncovered an overlooked trait. Personal communication from S. Renesto identifies this intriguing break as a taphonomic artifact. More on this later as the details emerge!

An Olecranon Sesamoid in Megalancosaurus
The olecranon bone was overlooked in Megalancosaurus, probably due to its perfect alignment with the ulna. Larger than in outgroup taxa, the olecranon bone separated the humerus from the ulna as in its sister taxon, Drepanosaurus.

Megalacosaurus elbow

Figure 6. The break and the broken pieces of the Megalancosaurus ulna are reidentified here. The sesamoid is prominent and crescent-shaped as in Drepanosaurus. Note that the broken part of the ulna would have stood straight up from the matrix if similar to that of Drepanosaurus, hence its destruction during crushing.

A New Interpretation of the Sesamoid in Megalancosaurus
Here the various broken pieces of the ulna are reidentified using DGS (digital graphic segregation). The results are more similar to the situation in Drepanosaurus.

A Lepidosaur?
Renesto (1994) considered the taxonomic assignment of Drepanosaurus “quite difficult,” and labeled it a Neodiapsid (all diapsids other than Araeoscelidae under the old paradigm). “Neodiapsida” is here considered a diphyletic taxon since lepidosaurs and archosaurs nest on separate reptile branches. Therefore this clade label has lost its utility.

An Atypical Tritosaur with a Fused Ankle
As Pinna (1980) surmised, Drepanosaurus indeed nested with the lepidosaurs, but it did not nest with either the Iguania or the Scleroglossa. Here Drepanosaurus nested within the Tritosauria, a third clade of squamates. And yes, the fusion of the astragalus and calcaneum came about by convergence with other members of the Lepidosauria.

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

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

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.
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
wiki/Hypuronector