The base of the new Lepidosauriformes illustrated to scale

Short one today, 
told mostly in pictures (Figs. 1, 2). Click here or see below for more data and taxon links.

These are the taxa from which all later lepidosaurs
arose and diversified. Thus, these are the ancestors of snakes, pterosaurs, ‘rib’ gliders and rhynchosaurs at their genesis and basal diversification.

Proximal outgroups
in the large reptile tree (subset Fig. 2) include Owenetta, Barasaurus and other small, low, wide owenettid lepidosauromorphs lacking an upper temporal fenestra.

Figure 1. Taxa at the base of the Lepidosauria include Paliguana, Tridentinosaurus, Lanthanolania, Lacertulus, Gephyrosaurus, Megachirella, Lacertulus and Palaegama. See figure 2 for a subset of the LRT.

Basal lepidosauriformes are rare.
For tens of millions of years, between the the first and last days of the Triassic, these are just about all we have in the sparse fossil record at the genesis of new Lepidosauriformes (= Paliguana + Sophineta, their last common ancestor and all descendants). Paliguana is a late survivor of that earlier genesis.

Figure 2. Subset of the LRT focusing on basal Lepidosauria. Taxa in colored blocks are shown to scale in figure 1. Note: the chronology is not reflected in the phylogeny due to the rarity of fossil specimens.

Chronology does not always mirror phylogeny.
And that’s okay.

For instance:
It’s okay that Archaeopteryx was found in Late Jurassic strata and one of its its putative ancestor, Velociraptor, was found in Late Cretaceous strata. You might remember when a bunch of paleontologists waved their hands over that matter, then later blushed and said, “Never mind.” In like manner, it’s okay that Paliguana was found in younger strata than its phylogenetic descendants.

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References
http://reptileevolution.com/owenetta.htm
http://reptileevolution.com/paliguana.htm
http://reptileevolution.com/lacertulus.htm

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

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

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

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

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

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

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

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

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

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

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

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

wiki/Youngina

Bolosaurid thecodont tooth implantation

Snyder et al. 2020 report,
“Analysis of the specialized dentition of the bolosaurid parareptiles Bolosaurus from North America and Belebey from Russia, utilizing a combination of histological and tomographic data, reveals unusual patterns of tooth development and replacement. The data confirm that bolosaurid teeth have thecodont implantation with deep roots, the oldest known such example among amniotes,”

Bolosaurus is known from the Early Permian. The oldest amniote, Silvanerpeton, from the Viséan (Early Carboniferous) needs to be examined for tooth implantation before making this statement.

“and independently evolved among much younger archosauromorphs (including dinosaurs and crocodilians) and among synapsids (including mammals).”

In the large reptile tree (LRT, 1690+ taxa) synapsids and dinosaurs are both archosauromorphs. Given that the last common ancestor of all amniotes may also have had thecodont tooth implantation, this is not confirmed as ‘independently evolved.’ 

Co-author Reisz still believes in the invalid clade Parareptilia and is not aware of the basal dichotomy splitting Reptilia (Amniota is a junior synonym) between Archosauromorpha and Lepidosauromorpha.

Figure 1. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Snyder et al. report,
“Finally, the nearly complete Eudibamus cursoris (Berman, 2000) of Germany represents the only other known taxon within the group.”

In the LRT Eudibamus is an unrelated diapsid (Fig. 1). Adding taxa reveals this interrelationships. In the LRT bolosaurids are sisters to diadectids, all derived from Milleretta and more ancestral taxa. None of these are bipedal with a parasagittal gait.

Snyder et al. report,
“Uninterrupted marginal tooth rows in the fossil record of Paleozoic tetrapods are rare, usually associated with unusual attachment and replacement cycles, such as in captorhinids.”

In the LRT bolosaurids and Milleretta are derived from captorhinids. I can’t find any examples in the LRT of interrupted marginal tooth rows in taxa surrounding bolosaurids.

Snyder et al. report,
“The level of heterodonty in bolosaurids is also remarkable, with mesial incisiform teeth transitioning to large, transversely bulbous cheek teeth distally along the tooth row. Tooth cusps slope posteriorly and have a conical apex that is more obvious in the larger, posterior teeth.”

Perhaps not so remarkable. Sister taxa, like Diadectes, have long, flat-tipped ‘incisors’ and short conical ‘molars’. Out-group Limnoscelis likewise has long anterior teeth and short posterior teeth. Other outgroups (captorhinids, Colobomycter, Tetraceratops, etc. are likewise heterodont.

In the discussion section, Snyder et al. report, 
“One comparable taxon are the diadectids. Dentitions in both diadectids and bolosaurids show heterodonty, thecodont implantation, as well as evidence of occlusal wear. The molariform cheek teeth of Diadectes are mediolaterally expanded compared to the more teardrop-shaped of bolosaurids, but like bolosaurids, they also frequently possess numerous replacement pits along the length of their jaws, suggesting a similar origin of tooth buds in both taxa.”

An inadequate taxon list prevented Snyder et al. from realizing the close relationship of diadectids and bolosaurids, as recovered several years ago in the LRT. Phonodus (Early Triassic) is also a bolosaurid in the LRT, unacknowledged by Snyder et al.

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References
Snyder AJ, LeBlanc ARH, Jun C, Bevitt JJ and Reisz RR 2020. Thecodont tooth attachment and replacement in bolosaurid parareptiles. PeerJ 8:e9168
doi: Âhttps://doi.org/10.7717/peerj.9168 – https://peerj.com/articles/9168/

SVP 2018: Large biped in the Permian

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

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

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

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

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

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

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

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

Not even an elevated Dimetrodon made these Dimetropus tracks

Matching tracks to trackmakers
can only ever be a semi-rewarding experience. Estimates and exclusions can be advanced. Exact matches are harder to come by. This is due to both the vagaries and varieties of sequential footprints in mud or sand, and to the rarity of having skeletal data that matches.

Figure 1. Dimetrodon adult, juvenile, skull, manus, pes. Note the asymmetry of the fingers and toes. Dimetropus tracks were named for this taxon.

Which brings us to Dimetropus
Traditionally Early Permian Dimetropus tracks (Fig. 2–8; Romer and Price 1940) have been matched to the coeval pelycosaur, Dimetrodon (Fig. 1)—but only by narrowing the gauge of the Dimetrodon feet and elevating the belly off the surface, as Hunt and Lucas 1998 showed.

Today we’ll take a look at some other solutions
not involving Dimetrodon doing high-rise pushups. Several distinctly different tracks have fallen into the Dimetropus wastebasket. Let’s look at three ichnospecimens.

Traditionally, and according to Wikipedia,
citing Hunt and Lucas 1998: “Trackways called Dimetropus (“Dimetrodon foot”) that match the foot configuration of large sphenacodontids show animals walking with their limbs brought under the body for a narrow, semi-erect gait without tail or belly drag marks. Such clear evidence for a more efficient upright posture suggests that important details about the anatomy and locomotion of Sphenacodon and Dimetrodon may not be fully understood.” Hunt and Lucas blamed traditional reconstructions of Dimetrodon for the mismatch. Instead they should have looked at other candidate trackmakers from the Early Permian. Note the asymmetric manus and pes of Dimetrodon (Fig. 1). Those don’t match the tracks no matter how high the belly is above the substrate. Dimetrodon is just fine the way it is.

Figure 2. Early Permian Dimetropus tracks matched to Middle Triassic Sclerosaurus, one of the few turtle-lineage pareiasaurs for which hands and feet are known.

A better match
can be made to the Middle Triassic pre-softshell turtle pareiasaur, Sclerosaurus (Fig. 2). Note the symmetric manus and pes like those of living turtles (Fig. 3) and the Dimetropus specimen in figure 2.

Figure 3. Snapping turtle tracks in mud. Note the relatively narrow gauge and symmetric imprints like those of Dimetropus.

Living turtle tracks
like those of the snapping turtle, Macrochelys (Fig. 3) are also symmetrical and surprisingly narrow gauge. Let’s not forget, Dimetropus tracks occur in Early Permian sediments, predating the earliest fossil turtles, like Proganochelys, first appearing in the Late Triassic. Let’s also not forget, in the large reptile tree (LRT, subset Fig. 7) Proganochelys is not the most basal turtle and valid predecessors (not eunotosaurs) had similar hands and feet.

FIgure 4. Dimetropus tracks compared to a large Dimetrodon matched to finger and toe tips. Hand too wide. Compared to a small Dimetrodon. Hand too small. Compared to a normal size Hipposaurus, good match even if not all the digits are known.

A second set of Dimetropus tracks
(Fig. 4, right), have distinctive heels behind symmetric + asymmetric imprints. A large Dimetrodon could not have made these tracks because they are too narrow. A small Dimetrodon had extremities that were too small, as the animated GIF shows.

FIgure 5. Hipposaurus compared Dimetropus. The overall and leg length is right, as are many of the digits. Unfortunately the medial digits are too short in Hipposaurus. Hipposaurus has a narrower gauge and lifted its belly of the ground, as did the Dimetropus trackmaker.

Fortunately,
we also have Middle Permian basal therapsid, Hipposaurus (Figs. 4, 5), a close relative of the last common ancestor of all pelycosaurs (see Haptodus and Pantelosaurus; Fig. 6). No doubt Hipposaurus elevated its torso on a narrow gauge track, with manus tracks slightly wider than pedal traces, as in Dimetropus. Both the carpus and tarsus are elongate, matching Dimetropus tracks.

Unfortunately,
we don’t have all the phalanges for the Hipposaurus manus and pes (Fig. 4). Drag marks can lengthen a digit trace. Flexing a claw into the substrate can shorten a digit trace. It is also important to note that during the last moment of the manus propulsion phase, the medial and lateral metacarpals can rotate axially, creating the impression of an ‘opposable thumb’ in the substrate. Note that no two ichnites are identical, despite being made one after another by the same animal.

Figure 6. Closeup of Hipposaurus manus and pes compared to random Dimetropus manus and pes tracks. Note, some digits remain unknown. Some digits might create drag marks. Others may dig in a claw or two apparently shortening the digit imprint.

At present
a more primitive sister to Hipposaurus is the best match for the Hunt et al. 1995 Dimetropus tracks and the Early Permian timing is right.

FIgure 7. Subset of the LRT focusing on Hipposaurus and its relatives, color coded to time. Hipposaurus is nearly Early Permian and probably had its genesis in the Early Permian.

In the popular press
NewScientist.com reported, “We’ve drawn iconic sail-wearing Dimetrodon wrong for 100 years. Some palaeontologists did offer an explanation – that Dimetrodon thrashed its spine from side to side so much as it walked that it could leave narrow sets of footprints despite having sprawled legs.” That hypothesis, based on omitting pertinent taxa, is no longer necessary or valid.

Abbott, Sues and Lockwood 2017 reported the limbs of Dimetrodon were morphologically closest to those of the extant Caiman, which sits on its belly, but also rises when it walks.

It is unfortunate that no prior workers considered Hipposaurus, a nearly coeval taxon with Dimetropus having matching slender digits, long legs, an erect carriage, and just about the right digit proportions.

A third ichnotaxon,
Dimetropus osageorum (Sacchi et al. 2014), was considered a possible caseid, rather than a sphenacodontid, but caseids have more asymmetric digits (= a shorter digit 2). Unfortunately, taxon exclusion also hampered the Sacchi et al. study. They did not consider Early Permian stephanospondylids, Late Permian pareiasaurs in the turtle lineage and Triassic turtles. No skeletal taxon is a perfect match for this ichnotaxon, but the Late Cretaceous turtle, Mongolochelys, is close  (Fig. 8). It took some 200 million years after the trackmaker of Dimetropus for the lateral pedal digits to shrink, but everything else is a pretty good match.

Figure 8. Dimetropus oageorum from Sacchi et al. 2014 matched to Mongolochelys, a Late Cretaceous turtle. Only pareiasaurs and turtles, among basal taxa, have such a long manual and pedal digit 2. The reduction of pedal digits 4 and 5 are derived in this late surviving basal turtle.

Also compare the hands and feet
of Early Permian Dimetropus osageorum (Fig. 8) to the Middle Triassic Sclerosaurus (Fig. 2). Dimetropus is solid evidence that turtle-ancestor pareiasaurs were present in the Early Permian (see Stephanospondylus, an Early Permian turtle and pareiasaur ancestor).

Saachi et al. conclude, “At the same time, the process of attributing ichnotaxa, on the basis of well preserved tracks and by comparison with known skeletal remains, is validated.”  True. Unfortunately all prior workers overlooked a wider gamut of skeletal taxa to compare with their ichnotaxon in their search for a ‘best match.’ Perhaps they felt restricted by time (Early Permian). As the above notes demonstrate, that is not a good excuse.

References
Abbott CP, Sues H-D and Lockwood R 2017. The Dimetrodon dilemma: reassessing posture in sphenacodonts. GSA annual meeting in Seattle, WA USA 2017. DOI: 10.1130/abs/2017AM-307190
Hunt AP and Lucas SG 1998. Vertebrate tracks and the myth of the belly-dragging, tail-dragging tetrapods of the Late Paleozoic. Bulletin New Mexico Museum of Natural History and Science. 271: 67–69.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Romano M, Citton P and Nicosia U 2015. Corroborating trackmaker identification through footprint functional analysis: the case study of Ichniotherium and Dimetropus. Lethaia https://doi.org/10.1111/let.12136
Romer AS and Price LI 1940. Review of the Pelycosauria: Geological Society of America, Special Paper 28:538pp
Sacchi E, Cifelli R, Citton P, Nicosia U and Romano M 2014. Dimetropus osageorum n. isp. from the Early Permian of Oklahoma (USA): A trace and its trackmaker. Ichnos 21(3):175–192. https://doi.org/10.1080/10420940.2014.933070

Rough chronology of basal tetrapods and basal reptiles

Today we’ll look at WHEN
we find fossils of basal tetrapods and basal reptiles. According to the large reptile tree (959 taxa, LRT, subset shown in Fig. 1), oftentimes we find late survivors of earlier radiations in higher strata. The origin of Reptilia (amphibian-like amniotes) extends back to the Devonian and Early Carboniferous now, not the Late Carboniferous as Wikipedia reports and as the Tree of Life project reports.

Figure 1. Color coded chronology of basal tetrapods and reptiles.We’re lucky to know these few taxa out of a time span of several tens of millions of years. Click to enlarge.

The Late Devonian 390–360 mya
Here we find late survivors of an earlier radiation: Cheirolepis, a basal member of the Actinopterygii (ray-fin fish) together with Eusthenopteron and other members of the Sarcopterygii (lobe-fin fish). Coeval are basal tetrapods, like Acanthostega and basal reptiles, like Tulerpeton. These last two launch the radiations we find in the next period. The presence of Tulerpeton in the Late Devonian tells us that basal Seymouriamorpha and Reptilomorpha are waiting to be found in Devonian strata. We’ve already found basal Whatcheeriidae in the Late Devonian taxa Ichthyostega and Ventastega.

Early Carboniferous 360–322 mya
Here we find the first radiations of basal reptilomorphs, basal reptiles, basal temnospondyls,  basal lepospondyls and microsaurs, lacking only basal seymouriamorphs unless Eucritta is counted among them. It nests outside that clade in the LRT.

Late Carboniferous 322–300 mya
Here we find more temnospondyls, lepospondyls and phylogenetically miniaturized archosauromorphs, likely avoiding the larger predators and/or finding new niches. Note the first prodiapsids, like Erpetonyx and Archaeovenator, appear in this period, indicating that predecessor taxa like Protorothyris and Vaughnictis had an older, Late Carboniferous, origin. Not shown are the large basal lepidosauromorphs, Limnoscelis and Eocasea and the small archosauromorphs, Petrolacosaurus and Spinoaequalis.

Early Permian 300–280 mya
Here we find the first fossil Seymouriamorpha and the last of the lepospondyls other than those that give rise to extant amphibians, like Rana, the frog. Here are further radiations of basal Lepidosauromorpha, basal Archosauromorpha (including small prodiapsids), along with the first radiations of large synapsids.

Late Permian 280–252 mya
Here we find the next radiation of large and small synapsids, the last seymouriamorphs, and derived taxa not shown in the present LRT subset.

Early/Mid Triassic 252 mya–235 mya
Among the remaining basal taxa few have their origins here other than therapsids close to mammals. Afterwards, the last few basal taxa  listed here, principally among the Synapsida, occur later in the Late Triassic, the Jurassic and into the Recent. Other taxa are listed at the LRT.

What you should glean from this graphic
Taxa are found in only the few strata where fossilization occurred. So fossils are incredibly rare and somewhat randomly discovered. The origin of a taxa must often be inferred from phylogenetic bracketing. And that’s okay. This chart acts like a BINGO card, nesting known taxa while leaving spaces for taxa we all hope will someday fill out our card.

 

 

Tridentinosaurus antiquus: a glider ancestor, not a protorosaur

I had never heard of this one before. 
Evidently this Early Permian reptile is famous for being fossilized between volcanic layers and for preserving more skin than bone. Using DGS I was able to tease out some of the bone (Fig. 1) and nest Tridentinosaurus not with the protorosaurs, as Leonardi (1959) proposed, but with basal lepidosauriforms. Tridentinosaurus nests in the large reptile tree as an Early Permian descendant of the late-surviving Palaegama and an ancestor to the Late Permian ‘rib’ glider, Coelurosauravus and the Late Triassic ‘rib’ glider, Icarosaurus along with other glider clade members.

Figure 1. Tridentinosaurus at 26.5 cm long is an Early Permian ancestor to Late Permian Coelurosauravus and Late Triassic Icarosaurus. Here two images taken in different light conditions were superimposed, then traced. An arboreal lifestyle is suspected here, based on the long limbs and toes.

Tridentinosaurus antiquus (Early Permian, Dal Piaz 1932, Leonardi 1959, 26.5cm long; Museum of Paleontology of the University of Padua 26567). Ronchi et al. described the specimen as “a beautiful but biochronologically useless specimen of which only the out−line of the soft tissues is well preserved.” The volcanic sediments in Sardinia occur in Cisuralian / Sakmarian deposits 291 million years old.

Although known for more than 50 years, 
and with quite a story to tell, this genus was not famous enough to merit its own Wikipedia page when I wrote this. Based on phylogenetic bracketing, the tail may have been twice as long originally.

Most prior workers do not nest 
Coelurosauravus and kin with Kuehneosaurus and kin (including Xianglong from the Cretaceous. Here they do nest together and Tridentinosaurus provides clues to the clade’s arboreal origin. Apparently this is a novel hypothesis, a by-product of having so many (694) taxa in the large reptile tree (subset Fig. 2).

Figure 2. Subset of the large reptile tree showing the nesting of Tridentinosaurus at the base of the gliders, close to the drepanosaurs.

References
Dal Piaz Gb. 1932 (1931). Scoperta degli avanzi di un rettile (lacertide) nei tufi compresi entro i porfidi quarziferi permiani del Trentino. Atti Soc. Ital. Progr. Scienze, XX Riunione, v. 2, pp. 280-281. [The discovery of the remains of a reptile (lacertide) in tuffs including within the Permian quartz porphyry of Trentino.]
Leonardi P 1959. Tridentinosaurus antiquus Gb. Dal Piaz, rettile protorosauro permiano del Trentino orientale. Memorie di Scienze Geologiche 21: 3–15.
Ronchi, A., Sacchi, E., Romano, M., and Nicosia, U. 2011. A huge caseid pelycosaur from north−western Sardinia and its bearing on European Permian stratigraphy and palaeobiogeography. Acta Palaeontologica Polonica 56 (4): 723–738.

Burnetia sutures revealed with DGS (Digital Graphic Segregation)

Sorry to be away for awhile.
I was updating the basal synapsid portion of the large reptile tree at ReptileEvolution.com. Still working on the website as of this writing, but the tree is more robust with a few added taxa. Notably Nikkasaurus and Niaftasuchus have been removed from the Synapsida. The former is now a basal prodiapsid nesting with Mycterosaurus. The latter now nests as another prodiapsid with Mesenosaurus.

Now that all the hard work is done,
let’s take a fresh look at the basal therapsid, Burnetia (Fig. 1), the most derived member of the Burnetiidae. Sutures delineate bones and in order to correctly score the bones you have to see the sutures. And they have to closely resemble those of clade members (Fig. 2). See what you think of these. And note that those who had the fossil in their hands and presumably under the microscope were not able to provide the sutures shown here, gleaned from published photographs.

A Burnetiidae therapsid, Burnetia skull in four views. 1. the original published drawing (Broom 1923); 2. an updated published drawing (Rubidge and Sidor 2002); neither of which are able to indicate sutures; and 3) a DGS tracing with sutures indicated. Finally I add the mandible of Proburnetia as a stand-in for the missing mandible. Only a few paleontologists colorize bones. It’s the best way to show where the sutures are.

Burnetia mirabilia
(Broom 1923, Rubidge and Sidor 2002; BMNH R5397; Late Permian) had a flat, wide skull with exceptional skull ornamentation. The squamosal cheeks flared widely. The teeth are very small. Derived from a sister to Proburnetia.

Derived from a sister to Hipposaurus,
the Burnetidae were basal therapsids from the Middle to Late Permian that evolved bizarre skull ornamentation. Rubidge and Sidor (2002) report, “The systematic position of the Burnetiidae has been unsure largely because of a poor understanding of the cranial morphology of these two enigmatic skulls. In the past they have been considered gorgonopsians (Boonstra, 1934; Haughton and Brink, 1955; Sigogneau, 1970), dinocephalians (von Huene, 1956), and more recently, biarmosuchians (Hopson and Barghusen, 1986; Sigogneau-Russell, 1989). Like Gorgonopsids, this clade has anterior facing nares and a proparietal by convergence.”

We’ll take a look at the other members of this clade later.
But for now here’s the data for the taxa (Fig. 2). Lemurosaurus and Proburnetia appear to have antorbital fenestrae/foraminae and the lacrimal overlaps the jugal. Note the gradual reduction of the teeth in this clade and the gradual widening of the back of the skull. The supratemporals are supposed to be missing from al therapsids, but I found they are missing from all therapsids more derived than this clade.

The clade Burnetiidae/Ictidorhinidae to scale includes Ictidorhinus, Herpetoskylax, Lemurosaurus, Proburnetia and Burnetia, and a few others not shown. The bones were colorized using Photoshop in a method known as DGS or digital graphic segregation. Note the lacrimal overlapping the jugal. The pre parietal (anterior to the parietal foramen) once nested these taxa with gorgonopsids. Some antorbital fenestrae/foramina are present.

References
Broom 1923. On the structure of the skull in the carnivorous dinocephalian reptiles. Proceedings of the Zoological Society of London 2:661–684.
Rubidge BS and Sidor CA 2002. On the crnial morphology of the basal therapsids Burnetia and Proburnetia (Therapsida: Burnetiidae). Journal of Vertebrate Paleontology 22(2):257–267.

Surviving the Permian-Triassic boundary

For those of you
who typically ignore the letters to the editor, this is one exchange that you might find interesting.

Earlier Bill Erickson asked me 
“So, why, in your opinion, did diapsid reptiles suddenly — and I do mean suddenly — become so dominant beginning in or about Carnian time, and remain dominant thereafter throughout the Mesozoic, after millions of years of synapsid dominance beforehand in the mid-to-late Paleozoic and early Triassic?”

I answered
-Why- questions are very tough in Science, Bill. I don’t know the answer to your question. I don’t have an opinion either.

B. Erickson replied
“David – I’d agree for the most part, but I do think Peter Ward made a good case [in his book Gorgon.] that synapsids had a less efficient respiratory system than many archosaurs, and that lower atmospheric oxygen was a major driver in the end-Permian extinction. Of course, some synapsids, especially cynodonts, were diverse in early Triassic, and that’s another story.”

To which I replied
Bill, I have heard of Ward’s hypothesis and it makes a certain sense. Let me toss this off-the-cuff idea at you.

Synapsids, to my knowledge, survived the Permian extinction event by burrowing, or perhaps there was a part of the world they found refuge in. If the former, whether in dirt or leaf litter, both niches seem to support small to tiny tetrapods. See Pachygenelus, Megazostrodon and Hadrocodium for examples. [Well, those are all bad examples as they are all Early Jurassic, but consider the small earliest Triassic cyndont, Thrinaxodon (Fig. 1).]

Figure 1. Thrinaxodon, a burrowing synapsid from the Early Triassic was similar in size and proportion to the Late Permian ancestor of all archosauriformes, Youngoides (Fig. 2). These similar basal taxa were the genesis for all later mammals, dinosaurs and birds.

On the diapsid/archosauriform side, the likely aquatic proterosuchids cross the Permo-Triassic boundary, then give rise to all the familiar archosauriformes. In the water niche larger tetrapods, like crocs, are supported. As Malcolm Gladwell documented so well [in his book Outliers], an initial minor advantage can accelerate or become emphasized over time.

So, again guessing here, the largely nocturnal denizens of the burrows and leaf litter apparently played to their environment and stayed small yielding the otherwise unoccupied largely diurnal aquatic-grading-to-terrestrial taxa the larger size as they played to their niche. Maybe the diapsids just got to the outdoors/daylight niche first.

Figure 2. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa. Youngoides and the earliest proterosuchids were Late Permian. Others were Early Triassic and later.

Along the same lines, the lepidosaur diapsids stayed relatively small and unobtrusive except for the Late Triassic sea-going tanystropheids and Late Cretaceous sea-going mosasaurs, perhaps following the same niche rules and regs as above. Pterosaur lepidosaurs also experienced much greater size in the Late Cretaceous.

Just a thought/opinion supported by what I can recall at the moment. Let me know your thoughts if you’d like to continue this thought journey. [END]

And then beyond that exchange…
I note that EarlyTriassic synapsid taxon list also includes the large dicynodont, Kanneymeira and a number of small therocephalians. Burrowing taxa are pre adapted to a nocturnal existence. The big dicynodont must have survived in some sort to refuge niche.

The standard story
includes the notion that dinosaurs and other archosauriform predators were snapping up every little synapsid they saw, so the survivors became invisible by becoming nocturnal and or really tiny… and that probably continued throughout the Mesozoic, with both clades improving generation after generation.

Figure 3. Basal archosauriforms from the Early Triassic,  including Euparkeria, Proterosuchus and Garjainia.

The twist brought to you by
the large reptile tree is the outgroup for the Archosauriforms, Youngoides, is a small, Thrinaxodon-sized terrestrial younginiform diapsid (Fig. 1). Perhaps an early affinity for rivers and lakes was the key to survival among proterosuchid archosauriforms when the P-Tr problems escalated. But also note that the small ancestors to dinosaurs, the euparkeriids, (Fig. 3) ALSO survived the P-Tr boundary as small terrestrial forms alongside the much larger terrestrial erythrosuchids, otherwise known as giant younginids.

Maybe we’ll never know…
but it’s interesting to put at least some of the puzzle pieces together.

 

 

The Protorosaurus Wastebasket

Back in  2009
Gottmann-Quesada and Sanders produced the first comprehensive study of Protorosaurus (Meyer 1832, Tatarian, Late Permian) in over a hundred years. Protorosaurus was one of the first fossil reptiles ever described (Spener 1710). According to Gottmann-Quesada and Sanders, “large numbers” of Protorosaurus specimens have been added to collections, Only one (Fig. 6), they say, preserves a complete skull.

Unfortunately 
Gottmann-Quesada and Sanders lumped several disparate genera under the genus Protorosaurus. Evidently the genus Protorosaurus has become a phylogenetic ‘wastebasket’ for a variety of protorosaurs and other reptiles in the Late Permian.

Figure 1. The lectotype of Protorosaurus identified by Gottmann and Sanders. See below for a reconstruction and comparisons.

Unfortunately
Gottmann-Quesada and Sanders consider Diapsida the ancestral clade for Archosauromorpha and Lepidosauromorpha. The large reptile tree (now 614 taxa) does not support that old paradigm. Their analysis is based on the data set of Dilkes (1998) “because he was the first to propose a paraphyletic Prolacertiformes.” Unfortunately for Gottmann-Quesada and Sanders the Dilkes study focuses on the basal rhynchosaur, Mesosuchus, a taxon completely unrelated to Protorosaurus in the large reptile tree. The Gottmann and Sanders tree is similar to that of Nesbitt et al. (2015) we just looked at with regard to Azendohsaurus.

Relying on someone else’s tree
has become more and more of a headache for paleontologists who keep chasing their tails with untenable and falsified cladograms.

Figure 2. Results of the most inclusive phylogenetic analysis of early archosauromorphs by Gottman-Queseda and Sanders. Note the separation of Protorosaurus and Prolacerta, the nesting of Protorosaurus with Megalancosaurus and the use of suprageneric taxa. This tree suffers greatly from too few specific taxa. Pamelaria is misspelled Palmeria, the least of the many problems with this tree.

In contrast,
the large reptile tree finds that Archosauromorpha and Lepidosauromorpha are basal reptile clades (with Gephyrostegus bohemicus of the Westphalian) nesting as a closest known sister to that as yet unknown, but close to Eldeceeon, a Viséan ancestor. The Diapsida, therefore, turns out to be diphyletic with lepidosaurs on one branch and archosaurs on the other, related to each other only through G. bohemicus.

Figure 3. The Protorosauria. nests two Prolacerta specimens and three Protorosaurus specimens, along with a scattering of others. Click to enlarge.

Getting back to Protorosaurs (taxa nesting with Protorosaurus)
they nest basal to the archosauriformes and both are derived from terrestrial younginiformes. Former  protorosaurs, like Macrocnemus and Tanystropheus now nest within the Lepidosauria between Rhynchocephalia and Squamata. This new paradigm has to start sinking in and permeating the paleo world.

Gottmann-Quesada and Sanders used
144 characters, 15 hand-picked terminal ungroup taxa, two hand-picked outgroup taxa. Bootstrap and Bremer values were considered “low.”

That compares to
228 characters and 610 taxa in the completely resolved large reptile tree with generally high to very high Bootstrap values throughout. All subsets remain fully resolved. That means deletion of taxa do not affect the remaining tree topology in the large reptile tree. And all derived taxa are preceded by series of taxa with gradually accumulating character traits — unlike other traditional trees, like the Dilkes/Gottman-Quesada and Sanders tree

Figure 4. Two taxa assigned to Protorosaurus by Gottmann-Quesada and Sanders. The lower one is the new electrotype (Fig. 1). The upper one nests closer to Pamelaria and is clearly not congeneric. See how reconstructions help? Some of this is not immediately apparent in the fossils themselves.

The Gottmann-Quesada and Sanders analysis (Fig. 2) 
nested Protorosaurus with the drepanosaurid Megalancosauru and away from Prolacerta. That should have been noticed as a red flag. One can only wonder how poorly these taxa were scored for such nestings to happen.

The large reptile tree nested Protorosaurus with Prolacerta and other protorosaurs.
Which analysis would you have more confidence in?

Figure 5. The putative Protorosaurus juvenile (in situ) is actually a large Permian Homoeosaurus.

A juvenile Protorosaurus?
Gottmann-Quesada and Sanders considered the Late Permian reptile IPB R 535 (Institut für Paläontologie, Unversität, Bonn) the first and only juvenile Protorosaurus.  I added it to the large reptile tree and recovered it rather securely as a large Homoeosaurus, a long-lived taxon otherwise known from Jurassic strata. This specimen adds to the small but growing number of known Permian lepidosaurs,

Figure 6. The WMsN-P47 specimen assigned to Protosaurus, but is closer to Pamelaria. The scapulocoracoid is not fused, as proven by one scapula flipped so that the dorsal rim is in contact with its corticoid. I’ve always wondered about that inconsistency. A hi-rez image and DGS solved that problem.

The WMsN-P47 specimen that Gottmann-Quesada and Sanders assigned to Protorosaurus (Fig. 4) is actually closer to Pamelaria (see figure 7) in the large reptile tree. This specimen is too distinct to be lumped with Protorosaurus.

Gottmann-Quesada and Sanders reported
that Protorosaurus has seven cervicals. I found evidence for eight without seeing the fossil first hand. DGS techniques enable the identification and reconstruction of skull elements in the pre-Pamelaria specimen (Fig. 6) previously considered too difficult to attempt.

Figure 7. Several protorosaurs to scale including Pamelaria, Protorosaurus, Prolacerta, Malerisaurus, Boreopricea and Jaxtasuchus. Click to enlarge.

It is unfortunate
that Gottmann-Quesada and Sanders lumped all of their Protorosaurus specimens together when there is clearly a diversity of morphologies and sizes here. They did not feel the need to perform a phylogenetic analysis on the individual specimens or to create more than a single skull reconstruction (Fig. 8).

And I apologize
for earlier reconstructions created out of more than one specimen. I should never have created chimaeras. They really mess up phylogenetic analyses.

Figure 8. GIF animation of the NMK S 180 specimen assigned to Protorosaurus by Gottmann and Sanders. I was able to tease out certain palatal bones ignored by them. Reconstruction by Gottman and Sanders.

Gottmann-Quesada and Sanders mention Peters (2000)
due to that paper adding pterosaurs to the list of then considered prolacertiformes (later corrected in Peters 2007). They report, “this analysis suffers from over interpretation of poorly preserved fossils.” This is more professional BS. Either one look or rigorous examination of the fossils studied in Peters (2000) reveals that all include soft tissue and preserve every bone in articulation, which is the definition of “exquisitely preserved.”

I can only imagine
that, like Hone and Benton (2007, 2009) Gottmann-Quesada and Sanders felt the need to cite relevant literature, but shuddered at the prospect of actually dealing with non-traditional results. To their point on interpretation, mistakes were made in Peters (2000), some from under-interpretation and some from naiveté. That is why I submitted corrections (which were rejected), including Peters 2007 (which was published as an abstract). ReptileEvolution.com/cosesaurus.htm and links therein publicly repair the errors found in Peters (2000).

Gottmann-Quesada and Sanders report
the only trait uniting the Prolacertiformes [protorosaurs] are the elongated mid-cervical vertebrae. Unfortunately this trait also appears in several other clades within the Reptilia. The large reptile tree likewise did not find a single common character in the protosaurs. As in so many other clades it is the suite of traits that lump and separate them.

References
Gottmann-Quesada A and Sander PM 2009. A redescription of the early archosauromorph Protorosaurus speneri Meyer, 1832, and its phylogenetic relationships. Palaeontographica Abt. a 287: 123-220.
Meyer H von 1832. Palaeologica zur Geschichte der Erde und ihrer Geschöpfe. Verlag Siegmund Schmerber, Frankfurt a.M. 560 pp.
Peters D 2000. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27.
Seeley K 1888. Research on the structure, organisation and classification of the fossil Reptilia 1. On the Protorosaurus speneri (von Meyer). Philosophical Transactions of the Royal Society, London B 178, 187–213.
Spener CM 1710. Disquisitio de crocodilo in lapide scissilli expresso, aliisque Lithozois. Misc. Berol. ad increment. sci., ex scr. Soc. Regiae Sci. exhibits ed. IL92-110.