Teraterpeton news – SVP abstract 2016

To start with
in the large reptile tree the genus Teraterpeton (Fig. 1) nests as a sister to Diandongosuchus at the base of the Phytosauria.

Figure 1. Diandongosuchus (above) compared to Teraterpeton (below). Note the similar scapula shapes and the way the posterior dorsal ribs terminate in a line. Both lack the flaring cheeks of parasuchians and Youngina. Teraterpeton, with so few teeth, could well have been a plant eater or anything but a carnivore. Hopefully we'll find more of this genus someday.

Figure 1. Diandongosuchus (above) compared to Teraterpeton (below). Note the similar scapula shapes and the way the posterior dorsal ribs terminate in a line. Both lack the flaring cheeks of parasuchians and Youngina. Teraterpeton, with so few teeth, could well have been a plant eater or anything but a carnivore. Hopefully we’ll find more of this genus someday.

From the Pritchard and Sues 2016 abstract (abridged)
Teraterpeton hrynewichorum, from the Upper Triassic (Carnian) Wolfville Formation of Nova Scotia, is one of the more unusual early archosauromorphs, with an elongate edentulous snout, transversely broadened and cusped teeth, and a closed lateral temporal fenestra. Initial phylogenetic analyses recovered this species as the sister taxon to Trilophosaurus spp. (1). New material of Teraterpeton includes the first-known complete pelvic girdle and hind limbs and the proximal portion of the tail. These bones differ radically from those in Trilophosaurus, and present a striking mosaic of anatomical features for an early saurian (2). The ilium has an elongate, dorsoventrally tall anterior process similar to that of hyperodapedontine rhynchosaurs. (3) The pelvis has a well-developed thyroid fenestra, a feature shared by Tanystropheidae, Kuehneosauridae, and Lepidosauria. (4) The calcaneum is ventrally concave, as in Azendohsaurus. (5) The fifth metatarsal is proximodistally short, comparable to the condition in Tanystropheidae. (6) Much as in the manus, the pedal unguals of Teraterpeton are transversely flattened and dorsoventrally deep. Phylogenetic analysis of 57 taxa (7) of Permo-Triassic diapsids and 315 characters supports the placement of Teraterpeton as the sister-taxon of Trilophosaurus in a clade that also includes Azendohsauridae and, rather unexpectedly, Kuehneosauridae.(8) In the current phylogeny, the aforementioned amalgam of characters in Teraterpeton were all acquired independently from the other saurian lineages. We partitioned the dataset based on anatomical region to examine metrics of homoplasy across early Sauria. The CI of the partitions are not markedly different, but the RI of the pelvic girdle and hindlimb partitions are markedly higher than the others. Although the characters in the hindquarters partitions underwent a similar number of homoplastic changes, a higher proportion of them contribute to the overall structure of this phylogenetic reconstruction. The mosaic condition in Teraterpeton underscores the importance of thorough taxon sampling for understanding the dynamics of character change in Triassic reptiles and the use of apomorphies in identifying fragmentary fossils.”

Figure 2. Paleorhinus also has a tall ilium with an anterior process like that of rhynchosaurs, AND it is closely related to Teraterpeton in the LRT.

Figure 2. Paleorhinus also has a tall ilium with an anterior process like that of rhynchosaurs, AND it is closely related to Teraterpeton in the LRT. The ventral pelvis is unknown but no phytosaur or any basal archosauriform has a thyroid fenestra, but then none of these are toothless, like Teraterpeton.

Notes

  1. Teraterpeton (Sues 2003) was described 9 years before Diandongosuchus (Li et al. 2012).
  2. Seems like Prtichard and Sues do not reject the Trilophosaurus relationship.
  3. A related basal phytosaur, Paleorhinus (Fig. 2) also has a rhynchosaur-like ilium.
  4. No related taxa among basal archosauriforms have a thyroid fenestra. No trilophosaurids or rhynchosaurs have a thyroid fenestra. Other than Amotosaurus, no tanystropheids have a thyroid fenestra. Rather a separate pubis and ischium are not joined ventrally.
  5. I don’t see any other examples of ventrally concave calcaneal tubers in candidate taxa, nor is this apparent in the Nesbitt et al. 2015 reconstruction of Azendohsaurus.
  6. No candidate taxa have a metatarsal 5 as short as the one in Tanystropheus.
  7. We don’t know if Diandongosuchus or phytosaurs were included.
  8. They may have just metaphorically ‘shot themselves in the foot’ as kuehneosaurids are unrelated to any previously mentioned candidate taxa. They are the arboreal gliding reptiles. This throws doubt on any and all of their scoring and results.
  9. None of the candidate taxa listed by Pritchard and Sues have an antorbital fenestra or a long narrow snout with a very short cranial/temporal region like Teraterpeton has (Fig. 1). This brevity of the temporal region is what closed off the lateral temporal fenestra found in LRT sister taxa.

References
Pritchard AC, Sues H-D 2016. Mosaic evolution of the early saurian post cranium revealed by the postcranial skeleton of Teraterpeton hrynewichorum (Archosauromorpha, Late Triassic). Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.

Trialestes rises again!!

Lecuona et al. 2016
redescribe in greater detail Trialestes (Reig 1963; Figs. 1, 2), more than 50 years after its original discovery and publication. Glad to see this! Data used to nest Trialestes in the LRT as the proximal outgroup for the Dinosauria consisted of a few old drawings (Fig. 1), nothing more. The new data do not move the nesting much.

Figure 1. Tracings from old drawings are the data used to create this reconstruction of Trialestes, which nested it basal to the Dinosauria.

Figure 1. Tracings from old drawings are the data used to create this reconstruction of Trialestes, which nested it basal to the Dinosauria. New data from Lecuona et al. 2016 greatly reduce the guesswork here. 

From the Lecuona et al. abstract:
“Here, we describe in detail all the material assignable to the species and test its phylogenetic relationships using a comprehensive data matrix focused on early archosaurs. We support the referral of PVL 3889 to Trialestes and reject the presence of a mesotarsal ankle joint in this specimen. We recovered Trialestes within Crocodylomorpha, closer to Crocodyliformes than Pseudhesperosuchus, Hesperosuchus, Dromicosuchus and Sphenosuchus. Therefore, Trialestes represents the most completely known of the earliest non-crocodyliform crocodylomorph taxa known to date.”

They report, “In contrast, Reig’s third taxon, ‘Triassolestes’ romeri has received relatively little attention. In his original publication, Reig (1963) interpreted this taxon as a theropod dinosaur of the family Podokesauridae, a group now considered roughly equivalent to Coelophysoidea (Holtz 1994). Because of this interpretation, Reig considered only part of PVL 2561 as the holotype of the dinosaur ‘Triassolestes’, including an incomplete cranium and mandible, four cervical vertebrae, and 16 caudal vertebrae. Other postcranial remains associated with PVL 2561 were excluded from this genus, including a scapula, humerus, ulna, radius, carpus and proximal metacarpus, which were interpreted by Reig (1963, p. 15) as crocodilian elements because of the presence of an elongated radiale and ulnare.”

FIgure 2. Assembly of the many Trialestes parts featured in Lecuona et al. 2016.  This is an odd combination of robust cervicals and gracile limbs and girdles.

FIgure 2. Assembly of the many Trialestes parts featured in Lecuona et al. 2016. This is an odd combination of robust cervicals and gracile limbs and girdles.

Those proximal wrist elements
(radiale and ulnare) are never elongated in dinosaurs, but they are elongated in dinosaur ancestors like Trialestes. The name ‘Triassolestes’ was preoccupied by an Australian Triassic dragonfly, hence the change we know today.

Lecuona et al. continue: “Clark (in Benton & Clark 1988, fig. 8.6) hypothesized Trialestes as the sister taxon of Crocodylomorpha, but expressed some caution given the structure of the ankle and the poor knowledge of the specimens.”

“Novas (1989) recognized that the referred specimen PVL 2559 contained elements belonging to two individuals of different sizes (Reig 1963, fig. 4b part.) and assigned both of them to Herrerasauridae indet. (Novas 1989, 1993); presently, they can only be assigned to an indeterminate saurischian dinosaur.”

“Clark et al. (2000) questioned the referral of PVL 3889 to Trialestes romeri, suggesting that this specimen was more likely assignable to a basal dinosaur. Nevertheless, these authors could not reject the alternative explanation that PVL 2561 and PVL 3889 belong to one taxon with a combination of crocodylomorph and dinosaurian character states.”

“In addition, Trialestes has not been included in a quantitative phylogenetic analysis so far and, thus its affinities remain untested using modern methodologies.”

Well, the large reptile tree did that several years ago. But let’s keep an open mind moving forward.

Under materials and methods, Lecuona et al report,
“Herein we study the two specimens assigned to Trialestes romeri, the holotype PVL 2561 and PVL 3889; we exclude PVL 2559 because we agree with previous authors that it represents an indeterminate saurischian.”

Unfortunately
Lecuona et al. based their analysis on a cladogram originated by Nesbitt (2011) which had several problems listed here. They also included data from Butler et al. (2014) and added Carnufex, a related taxon.

The Trialestes fossils have a pristine beauty. The authors did not create a reconstruction, so I attempt one here (Fig. 2).

A little background data
Trialestes romeri (Bonaparte 1982)= Triassolestes (Reig, 1963/Tillyard, 1918) Carnian, Late Triassic ~235 mya is known from scattered parts. Clark, Sues and Berman (2000) redescribed the known parts and admitted the possibility that this taxon combined dinosaurian and crocodylomorph characters. As it nests here, Trialestes was derived from a sister to Carnufex. This clade phylogenetically preceded Herrerasaurus and the Dinosauria. We looked at this heretical relationship several years ago here.

Distinct from Pseudhesperosuchus,
the skull of Trialestes had a larger antorbital fenestra and a deeper rostrum. The mandibular fenestrae (yes, there are two!) were smaller.

The vertebral centra had excavated lateral surfaces, for bird-like air sacs. The radius was longer than the humerus, a character otherwise known only in dinosaurs. The radiale was smaller than the ulnare, matching the radius and ulna. The fingers were tiny.

The pelvis was semi-perforated, as in basal dinosaurs, with a well-developed supraacetabular crest. The dorsal pelvis was straight, as in Gracilisuchus. The femoral head was not inturned, suggesting a variable posture, promoted by that really long forearm. The ankle joint had a crocodile normal configuration and a functionally pentadactyl pes. Most crocs lose pedal digit 5, but not those basal to dinos, like PVL4597.

References
Bonaparte JF 1982. Classification of the Thecodontia. Geobios Mem. Spec. 6, 99-112
Clark JM, Sues H-D and Berman DS 2000. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20(4):683-704.
deFranca MAG, Bittencourt JdS and Langer MC 2013. Reavaliação taxonomica de Barberenasuchus brasiliensis (Archosauriformes), Ladiniado do Rio Grande do Sul (Zona-Assembleia de Dinodontosaurus). Palaenotogia em Destaque Edição Especial Octubro 2013: 230.|
Irmis RB, Nesbitt SJ and Sues H-D 2013. Early Crocodylomorpha. Pp. 275–302 in Nesbitt, Desojo and Irmis (eds). Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. The Geological Society of London. doi:10.1144/SP379.24.
Kischlat EE 2000. Tecodôncios: a aurora dos arcossáurios no Triássico. Pp. 273–316 in Holz and De Ros (eds.). Paleontologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS.
Lecuona A, Ezcurra MD and Irmis RB 2016. Revision of the early crocodylomorph Trialestes romeri (Archosauria, Suchia) from the lower Upper Triassic Ischigualasto Formation of Argentina: one of the oldest-known crocodylomorphs. Papers in Palaeontology (advance online publication). DOI: 10.1002/spp2.1056
Nesbitt S 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

Reig, OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.

Riff D et al. 2012. Crocodilomorfos: a maior diversidade de répteis fósseis do Brasil. TERRÆ 9: 12-40, 2012.

‘Origin of Dinosaurs’ video. 

wiki/Trialestes

New paper on stem archosauromorpha: Foth et al. 2016

When Foth et al. 2016 report,
“Here, we analyse the cranial disparity of late Permian to Early Jurassic archosauromorphs and make comparisons between non-archosaurian archosauromorphs and archosaurs (including Pseudosuchia and Ornithodira) on the basis of two-dimensional geometric morphometrics.” we are immediately ready for a bogus report based on the antiquated inclusion of the clades listed above.

Foth et al. 2016 set up their study
based on traditional phylogenies, not the large reptile tree [my comments follow]:

  1. “Living birds and crocodylians, as well as their extinct relatives including pterosaurs and non-avian dinosaurs, comprise the extraordinarily diverse and successful crown clade Archosauria.” [pterosaurs are lepidosaurs]
  2. “non-archosaurian archosauromorphs (i.e. taxa on the stem lineage leading towards archosaurs) formed a species rich component of Triassic ecosystems (>90 valid species) and achieved high morphological diversity, including highly specialized herbivores (Azendohsaurus, rhynchosaurs), large apex predators (erythrosuchids), marine predators with extremely elongated necks (tanystropheids), armoured crocodile-like forms (dosewellids, proterochampsids ), and possibly even turtles).” [Azendosaurus, rhynchosaurs, tanystropheids and turtles are all lepidosauromorphs].

The Foth et al. cladogram includes the following taxa
that have nesting problems:

  1. Tanystropheidae [should be in Tritosauria, Lepidosauria]
  2. Allokotosauria (a new paraphyletic ‘clade’ by Nesbitt et al. 2015 nesting between Protorosaurus and Prolacerta) – Pamelaria [Protorosauria], Azendohsaurus, Trilophosaurus [Rhynchocephalia] Teraterpeton [this is actually an archosauriform sister to Diandongosuchus.]
  3. Rhynchosauria [should be in Rhynchocephalia, Lepidosauria]
  4. Pterosauria [should be in Tritosauria, Lepidosauria]
  5. and the archosauriforms could use a lot of work! It’s all mixed up in there.

The rest of the paper
discusses the large amount of  cranial disparity in this clade. No wonder there is so much cranial disparity, they have thrown in so many unrelated taxa!!! As a referee I would have sent this manuscript back to the authors. The sister taxa do not demonstrate a gradual accumulation of character traits. They really need to expand their taxon list. They are missing SO many transitional taxa.

By contrast
there is not so much cranial disparity in the archosauriform subset of the LRT because they are more closely related to each other. In fact, the differences between sisters have been minimalized by taxon inclusion, creating the microevolution between taxa that even Creationists support.

References
Foth C, Ezcurra MD, Sookias RB, Brusatte SL and Butler RJ 2016. Unappreciated diversification of stem archosaurs during the Middle Triassic predated the dominance of dinosaurs. BMC Evolutionary Biology, 2016, Volume 16, Number 1, Page 1 online here.

Nesbitt SJ, Flynn JJ, Pritchard AC, Parrish MJ, Ranivoharimanana L and Wyss AR 2015. Postcranial osteology of Azendohsaurus madagaskarensis (?Middle to Upper Triassic, Isalo Group, Madagascar) and its systematic position among stem archosaur reptiles. Bulletin of the American Museum of Natural History. 398: 1–126.

Is this the footprint of Arizonasaurus?

Figure 1. Synaptichnium MNA V3425. Arrow points to direction of movement and aligns with sagittal plane. PILs and pads added.

Figure 1. Synaptichnium MNA V3425. Arrow points to direction of movement and aligns with sagittal plane. PILs and pads added. The pink manus track is another specimen.

The middle Triassic Moenkopi formation
in Arizona has provided a rich trove of fossils. An excellent footprint (MNA V3425, Fig. 1) was recently published online here and attributed to Arizonasaurus, a likely bipedal carnivorous archosauriform (Fig. 2). Arizonasaurus was derived from basal Rauisuchia, like Vjushkovia, and is most closely related to Yarasuchus and Qianosuchus according to the large reptile tree.

Figure 2. Arizonasaurus. Not sure which of the two mandibles is correct here, so both are presented. Note, neither manus nor pes is preserved in the specimen.

Figure 2. Arizonasaurus. Not sure which of the two mandibles is correct here, so both are presented. Note, neither manus nor pes is preserved in the specimen.

According to the online article,
“Paleontologist Christa Sadler has written a book, “Dawn of the Dinosaurs,” about the archosaurs of the Middle and Late Triassic in the region. Unusually detailed footprints of the large reptile, or something like it, are preserved in a slab of Moenkopi sandstone in the collections repository at the Museum of Northern Arizona, where Sadler has studied. MNA  [Museum of Northern Arizona] Colbert Collections Curator of Vertebrate Paleontology David Gillette, Ph.D., says the footprints were discovered in Wupatki National Monument in 1973.”

Figure 3. Manus impression of man v3245. Note the heavy scales here.

Figure 3. Manus impression of man v3245. Note the heavy scales here.

The LRT currently doesn’t include ichnites (footprints)
but let’s see what happens this time, since the track is so precisely imprinted. Unfortunately, Arizonasaurus does not preserve the manus or the pes (Fig. 1). Nevertheless, out of 801 candidate taxa, MNA 3425 nests with a sister to Arizonasaurus, Decuriasuchus, and is similar to the pes of other Arizonasaurus sisters, Qianosuchus and Nandasuchus, all Middle Triassic taxa. So, phylogenetic bracketing works, at least to this extent. And it just shows you don’t need a long list of character traits to successfully nest some taxa.

Figure 3. Scaly palms of two crocodilians. Digit 1 is on the left in both specimens.

Figure 4. Scaly palms of two crocodilians. Digit 1 is on the left in both specimens.

Notes on the scaly palm of MNA V3425
Dinosaur footprints do not have large scale impressions. By contrast, croc hands and feet do have large scales (Fig 3). The sisters to Arizonasaurus, Qianosuchus and Yarasuchus, both have short limbs, a long rostrum and a general crocodile-like build. Likewise Decuriasuchus was long-bodied, quadrupedal with a large foot and a presumably small hand (not preserved). In similar fashion, Arizonasaurus likely also had a large foot and small hand based on its pectoral and pelvic girdles and femur (Fig. 2), but was a likely biped.

Figure 5. Decuriasuchus does not preserve the manus, but it was probably small based on the forelimb.

Figure 5. Decuriasuchus does not preserve the manus, but it was probably small based on the forelimb.

Belated apologies
to those who tried [or continue to try] to access www.reptileevolution.com yesterday and today. Eviidently the server is down, wherever it is. I can’t access it either to make updates and repairs. Hopefully the RepEvo website will be restored soon. :  )

 

The Archosauria according to the U of Maryland website

The University of Maryland website on the Rise of the Dinosauria includes the following cladogram (Fig. 1) which pretty much follows paleo traditions. Note the proximal position of pterosaurs to ‘Dinosauromorpha’ and the distant position of crocodylomorphs, which makes room for many intervening taxa to be considered archosaurs (= birds + crocs).

Figure 1. The Archosauria according to the University of Maryland. Here pterosaurs are close to dinosaurs.

Figure 1. The Archosauria according to the University of Maryland. Here pterosaurs are close to dinosaurs. Click to enlarge.

By contrast
in the large reptile tree, pterosaurs nest far from dinosaurs and crocs nest alongside them. So there are no intervening taxa between dinosaurs and crocs (Fig. 2). And there are no odd nesting partners here, like pterosaurs nesting with taxa with small hands and tiny fingers and no toe 5, etc. etc

Figure 2. Same cladogram rearranged to more closely match the large reptile tree. Note how, even at this scale, the gradual evolution of dinosaur traits is not interrupted by the odd morphology of pterosaurs. And how the basal bipedal crocs nest close to the basal bipedal dinos. Click to enlarge. 

Figure 2. Same cladogram rearranged to more closely match the large reptile tree. Note how, even at this scale, the gradual evolution of dinosaur traits is not interrupted by the odd morphology of pterosaurs. And how the basal bipedal crocs nest close to the basal bipedal dinos. This tree is missing SO many taxa, it puts the reader into the position of having to believe the relationships, not observe them. Click to enlarge.

There is a clinging to tradition at the U of Maryland
that needs to be revisited. If students need to regurgitate these antiquated hypotheses in order to get a good grade, then what does that teach them at the university level?

Take a look at those key traits (in red) above (Fig. 1).

  1. Elongate pubes and ischia: also found in basal bipedal crocs and prodinosaurs, like the PVL 4597 specimen. Also in poposaurs, like Poposaurus an Turfanosuchus.
  2. Parasagittal stance and hinge-like ankle joint: also found basal bipedal crocs, like Scleromochlus and Terrestrisuchus. Sure pterosaurs have such a stance and ankle, but so do fenestrasaurs (tritosaur lepidosaurs) like Sharovipteryx.
  3. Ellongate tibiae and metatarsi; loss of bony armor: again, basal bipedal crocs and fenestrasaurs.
  4. The lower traits are synapomorphies.

Students,
put your thinking caps on. Ask the hard questions. Do the experiments yourself. This is Science. Don’t be satisfied with answers that don’t make sense and can’t be validated up and down the entire cladogram.

The large reptile tree does not use suprageneric taxa, as shown above. Only species- and specimen-based taxa are included there. All taxa demonstrate a gradual accumulation of derived traits. All subsets retain the tree topology. The tree has grown from 200+ taxa to 674 taxa with the same 228 characters lumping and splitting them to full resolution.

Plus pterosaurs and plus basal therapsids drive this taxon list into the 900s.

 

 

Basal Archosauromorpha paper – Ezcurra 2016

Another paper repeating the ‘sins’ of the past,
based on an incomplete taxon inclusion list (that also includes taxa that should not be included). And a huge amount of otherwise excellent work! It proves once again that first hand access to specimens and an overly large character list will not bring full resolution to a small taxon list cobbled together by tradition, rather than testing.

I envy, am proud of and have to feel sorry for 
Martin Ezcurra (2016). He went around the world gathering data, obviously took a huge amount of time studying the specimens and writing this paper, but he’s stuck with that less than adequate traditional taxon list rather than the testing offered by the wide gamut taxon list (large reptile tree) in ReptileEvolution.com. He’s using 96 taxa (vs. 674 at ReptileEvolution.com). He’s using 600 characters. That should be more than enough, and it is more than enough (less than half that number will do), but more taxa is really what Ezcurra needs.

Just a few notes
Ezcurra wrote: “Jesairosaurus lehmani was described in detail by Jalil (1997). Despite its short neck, this species has been considered since its original description as a member of “Prolacertiformes.” Nevertheless, the phylogenetic position of this species has not been further tested in more recent quantitative analyses.” Yes it has, Here Jesairosaurus nests with drepanosaurs at the base of the Lepidosauriformes, not with Macrocnemus, as shown by Ezcurra (Fig. 1). Drepanosaurs were excluded by Ezcurra.

Figure 1. Ezcurra 2016 tree of basal archosauromorphs. He has basically repeated the mistakes of Nesbitt 2011 here.

Figure 1. Ezcurra 2016 tree of basal archosauromorphs. He has basically repeated the mistakes of Nesbitt 2011 here. Colors denote taxa that lie outside the gamut of the Archosauriformes + Protorosauria under study here.

Ezcurra is still including the thalattosaur, Vancleavea which nests with Doswellia in the Ezcurra tree. It just doesn’t belong in a study on archosauriforms.

He still holds to the tradition of a monophyletic Diapsida proven invalid here.

Ezcurra is still including pterosaurs in an archosauriform study
Proterochampsia (now including Vancleavea) is still recovered by Ezcurra as the proximal outgroup. Phytosauria and Lagerpeton are sister taxa. How is this possible? What characters do they share? They certainly don’t look alike. He notes Peters (2000) then writes, “The phylogenetic analysis conducted here [Ezcurra 2016] constitutes the best data matrix compiled so far to test the position of pterosaurs within Archosauromorpha because of the broad sample of Permo-Triassic species, including the undoubted pterosaur Dimorphodon macronyx.”  Martin, but you’re not looking, really looking at your results. Your proximal outgroup should look kind of like a pterosaur. Right?

Ezcurra notes that 33 extra steps
are needed to place Dimorphodon with Tanystropheidae and 19 synapomorphies support the Ornithodira. That might be true in his study. Hard to imagine how that is possible though. I will try to plow through his 600 characters to figure it out.  Convergence is rampant in the Reptilia. More synapomorphies support pterosaurs outside the Ornithodira when pertinent taxa are not excluded (see below).

Ezcurra writes, “Future analyses focused on testing the higher-level phylogenetic relationships of pterosaurs should also incorporate a broader sample of early pterosaurs and some enigmatic diapsids that were found as more closely related to pterosaurs than to other archosauromorphs by Peters (2000) and are not included in the current taxonomic sample (i.e., Langobardisaurus pandolfi, Cosesaurus aviceps, Sharovipteryx mirabilis and Longisquama insignis). However, it seems extremely unlikely that the addition of these enigmatic diapsids, which are unambiguously considered to not be members of Archosauriformes (e.g., Peters, 2000Senter, 2004), will affect the higher-level phylogenetic position of pterosaurs.”

In Science, the word ‘seems” and “extremely unlikely” need to be tested, especially when Langobardisaurus, for instance, shares so many traits with Tanystropheus and Macrocnemus. And especially when they have been tested sixteen years ago (Peters 2000). The word “enigmatic” is inappropriate here, unless Ezcurra just preferred to avoid them and stay with the traditional nod and move on.

Many good color photos of specimens here.
Precise descriptions. Like Nesbitt (2011) he’s just not playing with a full deck — of taxa.

Ezcurra’s tree
had 1.8 million+ possible MPTs. The large reptile tree was fully resolved with a single tree and high Bootstrap values. His analysis 3 recovered 40 MPTs by dropping largely incomplete taxa. That’s often a good idea. No reconstructions were offered, except for some skulls. No gradual accumulations of derived traits for odd partners like pterosaurs, Vancleavea, Doswellia, etc. Many purported sisters do not look alike.

Still not sure how
these trees don’t nest Tropidosuchus and Lagerpeton together. They are virtually identical.

Figure 2. Ezcurra tree with Bremer supports AFTER pruning incomplete taxa.

Figure 2. Ezcurra tree with Bremer supports AFTER pruning incomplete taxa. Many oddly paired sisters still show up here.

Ezcurra comments on Choristodera
“The problematic phylogenetic position of choristoderans may be a result of an unsampled early evolutionary history. The phylogenetic position of choristoderans is also ambiguously resolved in this analysis, but is constrained to the base of either Lepidosauromorpha or Archosauromorpha.” Actually the early history is sampled (here), just not included in this analysis.

Ezcurra has to be feeling pretty confident.
He writes, “Much of the general topology of the phylogenetic trees recovered in this analysis agrees with that found by several previous workers (e.g., Sereno, 1991Dilkes, 1998Gottmann-Quesada & Sander, 2009Ezcurra, Lecuona & Martinelli, 2010Nesbitt, 2011Ezcurra, Scheyer & Butler, 2014).”

I’d feel more confident
if all sister taxa looked alike and a gradual accumulation of traits could be traced for every taxon. Ezcurra needs more taxa to weed out the problems here. This study carries with it the sins of past studies.

PS
I was unable to open the Ezcurra data files on either Mesquite or MacClade.

References
Ezcurra MD 016.The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriformsPeerJ 4:e1778https://doi.org/10.7717/peerj.1778
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352:1–292 DOI 10.1206/352.1.
Peters D 2000. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106:293-336

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. 

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.

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.

erythrosuchid

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.