What made those Early Triassic tracks?

Mujal et al. 2017
reported on an Early Triassic tracksite dominated by what they considered to be ‘archosauromorph’ trackmakers (Fig. 1), akin to coeval Euparkeria (Fig. 2).

Figure 1. Early Triassic tracks from Mujal et al. 2017 compared to Didelphis, the extant Virginia opossum to scale. I don’t see any lateral expansion due to a hooked metatarsal (as in Fig. 2) here.

Unfortunately, the track in question
identified as Prorotodactylus mesaxonichnus IPS-93867 had three long slender digits (2–4), about the same length, #2 a stitch shorter. #1 and #5 much shorter. The width is about 2 cm. The pes is much larger than the manus. All in all, it is close to the shape and size of Didelphis, the extant, but very ancient Virginia opossum (Fig. 1). Originally the track was assigned to a taxon near Euparkeria, and it’s a pretty good match, but there is no indication of a hooked metatarsal 5 and digit 3 is often the longest (BUT see below).

Figure 2. Euparkeria pes.

Figure 2. Euparkeria pes is similar in size and configuration to the Early Triassic trackmaker. Note the hooked lateral metatarsal (#5) and digit #3 the longest.

Among archosauriformes
in proterosuchids and Garjainia pedal digit 4 is the longest. Some chorisoderes retain this pattern. In some 3 and 4 are the longest. In Champsosaurus 3 is the longest. Similar patterns are found in phytosaurs. In basal proterochampsids digit 3 is the longest. In derived proterochampsids like Tropidosuchus and Lagerpeton digit 4 is not slender and it is the longest in the series. None are matches for the

Among euarchosauriformes
In Euparkeria, as in most euarchosauriformes, digit 3 is longer than 2 and 4 and much longer than 1 and 5. In erythrosuchids pedal digits 2 and 3 are slightly longer than 4, but all are short and large. Ornithosuchus has long toes and short fingers, but it is a much larger taxon. Pedal digit 3 is still the longest. Same with Qianosuchus and Ticinosuchus.

Among basal diapsids and enaliosaurs
the pes is typically asymmetric with digit 4 or digits 3 and 4 the longest. The same with lepidosaurs. Basal lepidosauromorphs have short digits.

Basal synapsids are no match, either.
because they, too, have asymmetric feet. That changes with therapsids, but most have short toes, similar sized manus and pes and are Permian in age. That changes with the pre-mammals, the tritylodontids, like Spinolestes, which extend into the Cretaceous. The only problem with many of the trackmakers with symmetrical pedes, they all had narrow-gauge trackways – distinct from the Early Triassic trackways, which are quite wide-gauge. We can’t discuss mammals, because they only developed in the Late Triassic, at the earliest.

There’s one more factor
To me it looks like the tracksite toes are webbed. If the trackmaker was mostly aquatic, it was more likely to have sprawling hind limbs.

So, in summary
the best match in terms of size, relative size, age, morphology and such… appear to be aquatic Early Triassic tritylodontids… or tiny unknown archosauromorphs somewhere between Proterosuchus and Euparkeria. That hypothetical taxon would have had a pes transitional between the long digit 4 of Proterosuchus and the long digit 3 of Euparkeria. I really could not find a better match for this tracksite maker. I could not nail it down with available candidates.

References
Mujal E, Fortuny J, Bolet A, Oms O, López JA 2017. An archosauromorph dominated ichnoassemblage in fluvial settings from the late Early Triassic of the Catalan Pyrenees (NE Iberian Peninsula). PLoS ONE 12(4): e0174693. https://doi.org/10.1371/journal.pone.0174693

Telocrater: a sister to Yarasuchus, not the earliest bird-line archosaur.

Unfortunately
another paper that was improperly vetted (refereed). I heard about this one on NPR when co-author Richard Butler was interviewed by the BBC.

Nesbitt et al. 2017
report: The relationship between dinosaurs and other reptiles is well established (1–4,) but the sequence of acquisition of dinosaurian features has been obscured by the scarcity of fossils with transitional morphologies.”

We’re in trouble from the opening salvo.
The large reptile tree (LRT) does not recover the same tree topology as these authors hypothesize (Fig. 1). And the sequence of dinosaurian features is not obscured in the LRT. There are plenty of fossils with transitional morphologies. Unfortunately, these authors either chose to ignore them or scored them haphazardly. Based on the theory that evolution happens with small changes the Nesbitt et al. tree topology (Fig. 1) is completely bonkers, adding unrelated taxa while excluding pertinent sisters to Teleocrater (here labeled under its new clade, Aphanosauria).

Figure 1. Aphanosauria according to Nesbitt et al. 2017. Two of these clades are unrelated to archosaurs. Marasuchus IS a dinosaur. Silesaurus is a poposaur more distantly related to dinos than crocs.

Figure 1. Aphanosauria according to Nesbitt et al. 2017. Two of these clades are unrelated to archosaurs. Marasuchus IS a dinosaur. Silesaurus is a poposaur more distantly related to dinos than crocs. Where are the crocs? 

Nesbitt et al. report:
“H
ere we describe one of the stratigraphically lowest and phylogenetically earliest members of the avian stem lineage (Avemetatarsalia), Teleocrater rhadinus gen. et sp. nov., from the Middle Triassic epoch.” There is no such thing as an avian stem lineage. Avemetarsalia includes pterosaurs and dinosaurs, so it is a junior synonym for Reptilia in the LRT. The closest ancestors to dinosaurs were bipedal basal crocodylomorphs in the LRT. I don’t see them in figure 1. 
Telocrater holotype.
NHMUK (N
atural History Museum, London, UK) PV 
R6795, a disassociated skeleton of one individual, including: cervical, trunk, and caudal vertebrae, partial pectoral and pelvic girdles, partial forelimb and hind limbs. 
Referred material.
Elements f
ound near the holotype, but from other 
individuals, which represent most of the skeleton and that are derived from a paucispecific bone bed containing at least three individuals.
Figure 2. The chimaera created by several specimens attributed to Telocrater. Even if all these piece do fit together like Nesbitt et al. indicate, Telocrater is closer to Yarasuchus and Ticinosuchus than it is to the last common ancestor of Archosauria.

Figure 2. The chimaera created by several specimens attributed to Telocrater. Even if all these piece do fit together like Nesbitt et al. indicate, Telocrater is closer to Yarasuchus and Ticinosuchus than it is to the last common ancestor of Archosauria. See figure 3.

The specimens that produced this reconstruction (Fig. 2)
are all associated. So there is great confidence that all of the bones are conspecific. The problem, once again, is taxon exclusion, and maybe a large dose of bad scoring (see below)

Figure 3. Telocrater to scale compared with likely sister taxa among the Ticinosuchidae in the LRT. Note the resemblance of the Telocerater maxilla to that of these sister taxa.

Figure 3. Telocrater to scale compared with likely sister taxa among the Ticinosuchidae in the LRT. Note the resemblance of the Telocerater maxilla to that of these sister taxa.

Oddly
the authors report that “Osteoderms are not preserved and were probably absent.” And yet their reconstruction (Fig. 2) has osteoderms in the black outline. What bias is present here?

Oddly
the authors report, Our phylogenetic analyses recovered Teleocrater in a clade containing Yarasuchus, Dongusuchus and Spondylosoma.” And yet they did not include Yarasuchus in their phylogenetic figure (Fig. 1). The latter two are know from scraps. Yarasuchus (Fig. 3) is much more complete. 

Problems with the Nesbitt et al. 2017 cladogram

  1. The outgroup for Prolacerta + Archosauriformes (Proterosuchus) is the unrelated lepidosaur, Mesosuchus.
  2. The unrelated thalattosaur, Vancleavea, nests between Erythrosuchus and the unrelated chanaresuchid, Tropidosuchus. None of these taxa even look alike!
  3. The Yarasuchus clade, and before it the Parasuchus clade gives rise to the pterosaurs DimorphodonEudimorphodon and another chanaresuchid, Lagerpeton, both purportedly in the lineage of dinosaurs. These are all actors pretending to be relatives. How is this possible that Nesbitt et al, and the referees and editors at Nature are not raising objections to this? This is total madness at the highest levels.

Need I go on???
Why is Telocrater big news? Because the authors positioned it as an ancestor to dinosaurs. It may be, but it is buried deep, deep, deep in the lineage. Why was the relationship with Yarasuchus buried? You know why… it’s not as ‘sexy’ to the press.

Nesbitt et al. report,Aphanosauria…is the sister taxon of Ornithodira (pterosaurs and birds) and shortens the ghost lineage inferred at the base of Avemetatarsalia.” Surprised to see they didn’t say, ‘pterosaurs and Tyrannosaurus rex.’ 

Folks, it’s all showmanship.
I’m sure the authors have all toasted their new paper in Nature by now. I hate seeing the subject of evolution twisted, torn and laid bare like this.

The real importance of Telocrater
is its basal position in a clade I earlier called Ticinosuchidae, arising from basal rauisuchians, like Vjushkovia, giving rise to a wide variety of taxa like Aetosaurus and Arizonasaurus) while also giving rise to Decuriasuchus, which gave rise to poposaurs, like Turfanosuchus, and archosaurs, thus ultimately including dinosaurs.

References
Nesbitt SJ et al. (10 co-authors) 2017. The earliest bird-line archosaurs and the assemblof the dinosaur body plan. Nature doi:10.1038/nature22037. (online pdf)

1. Benton, M. J. & Clark, J. M. in The Phylogeny and Classification of the Tetrapods.
Volume 1: Amphibians, Reptiles, Birds. Systematics Association Special Volume
35A (ed. Benton, M. J.) 295–338 (Clarendon, 1988).
2. Gauthier, J. Saurischian monophyly and the origin of birds. Mem. Calif. Acad.
Sci. 8, 1–55 (1986).
3. Sereno, P. C. Basal archosaurs: phylogenetic relationships and functional
implications. Soc. Vertebr. Paleontol. Mem. 2, 1–53 (1991).
4. Sereno, P. C. The evolution of dinosaurs. Science 284, 2137–2147 (1999).

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.