Cladogram quirk and basalmost Euarchosauriformes

Updated July 31, 2020
with so many additional taxa, the LRT is no longer completely resolved. Many headless taxa nest with skull only taxa, which leads to loss of resolution. The LRT is built taxon upon taxon, day by day. Updated data on Browniella and Euparkeria are provided along with an updated subset of the LRT. The new data moved Browniella closer to Osmolskina.


I’ve claimed on several occasions 
that my cladogram was fully resolved and all of its subsets were also fully resolved. While that is typically true, everyone prefers a cladogram with more strength, where the taxa are lumped and separated by at least three points in Bootstrap Analysis. When that happens the Bootstrap tree will also be completely resolved (= all scores 50-100).

I found a quirk
And as I write this I am going to figure out why this happened and wonder if it can be repaired. Typically a bad score or several bad scores are responsible for any lack of resolution. Not sure if that’s the case this time.

Follow me
as I describe the setup and the problem. I’m looking to apply Bootstrap scores to members of the basal Archosauriformes with the addition of Teyujagua, a proterosuchid we looked at earlier.

  1. A heuristic search algorithm using PAUP of the entire cladogram: fully resolved. 
  2. The same deleting all anamniotes and lepidosaurormorpha — the new Archosauromorpha (Eldeceeon and all derived taxa) remains: fully resolved.
  3. The same deleting all basal archosauromorphs and synapsids: the protodiapsida (Myceteosaurus and all derived taxa) remains: fully resolved.
  4. The same deleting all basal protodiapsids and basal diapsids: the new younginiforms  (Spinoaequalis and all derived taxa) remains: fully resolved.
  5. The same deleting all aquatic younginiforms: the terrestrial younginiforms: Spinoaequalis + the SAM K7710 specimen(s) of Youngina and all derived taxa) remains: fully resolved.
  6. Now, working backwards: The same deleting all dinosaurs: 6 trees retained. Loss of resolution in the Protodinosauria. Several incomplete taxa based on drawings there. We’ll reexamine that clade in a later post.
  7. The same adding Herrerasaurus: fully resolved. A more complete data specimen solves the problem in #6.
  8. The same deleting all archosaurs: fully resolved.
  9. The same deleting the protoarchosaurs (the Gracilisuchus clade): fully resolved.
  10. The same deleting all the poposaurs: fully resolved.
  11. The same deleting all the Arizonasaurus/Ticinosuchus/Aetosaurus clade: fully resolved. 
  12. The same deleting all remaining Rauisuchia (Vjushkovia through Postosuchus): fully resolved.
  13. The same deleting all erythrosuchidae and ornithosuchidae: 2 trees retained. Loss of resolution at the Euparkeria node.
  14. The same adding Garjainia: fully resolved. 
  15. The same deleting all Choristodera: fully resolved.
  16. The same deleting all Chanaresuchidae and Parasuchia: fully resolved.
  17. At this point with a single tree scoring 447, I attempted a Bootstrap analysis. Basically all that is left here are the basal terrestrial younginiforms including several Youngina and Youngoides specimens, protorosaurs and basal archosauriforms up to and including all tested proterosuchids + Euparkeria, Osmolskina and Garjainia. Here  the small Proterosuchus skull (BPI/1/4016) and Elaphrosaurus rubidgei (RC59) are apparently mucking up the works, even though they do not nest together otherwise.
  18. The same adding Diandongosuchus, a basal parasuchian: fully resolved.
  19. At this point with a single tree scoring 488, warrants another Bootstrap analysis. Again Elaphrosuchus scores insufficiently distinct from several other included taxa to lack a score of 50+ across four other clades. And a very low score of 51 separates Elaphrosuchus from the BPI/1/4016 specimen of Proterosuchus. Both are skull only taxa and both have a certain amount of damage.
  20. The same deleting the new taxon, Teyujagua: Bootstrap scores all above 50. So that addition caused problems.

Are there scoring errors here? 
Or do these taxa converge? Or do two sisters lack any data points in common? Let’s find out by taking a closer look at the offending parties.

[About a day or two elapses at this point in the narrative]

Scoring errors
There were many errors around these nodes, hopefully all are now repaired. I reexamined several drawings, photos and tracings. Unfortunately fossil bones don’t come with overlying colors, so they have to be interpreted.

I also added a taxon
(Figs, 1, 2). It turned out to be a key transitional taxon. Score corrections and the new taxon boosted 5/6 of the Bootstrap scores.

Figure 1. The SAM 4967a specimen attributed to Euparkeria. Images from Sookias et al. 2020 with colors and reconstruction added here.

Figure 1. The SAM 4967a specimen attributed to Euparkeria. Images from Sookias et al. 2020 with colors and reconstruction added here.

Adding the ‘other Euparkeria‘: SAM PK K6047A
While reexamining the images of the Euparkeria holotype in Ewer 1967, I compared the rostrum that has a naris (SAM PK K6047A) with the classic holotype (SAM PK K 5867) that lacks a naris (Fig. 1). The fossils did not match. The dimensions were off (orbit vs antorbital fenestra, etc.) and the teeth were different in length. Ewer provides two images of the 6047 specimen, lacking data for the middle rostrum between the pix. The tracing (Fig. 1) recovers a basal euarchosauriform with a longer rostrum and narrower orbit, more like that of its phylogenetic predecessor, the BPI/1/4016 specimen of Proterosuchus (Fig. 3). This taxon ties Euparkeria more closely (more gradual transition in traits) to Proterosuchus (Figs. 2, 3).

There is also a SAM PK K6047B specimen
and it has been named Browniella africana by Broom (1913) I have not seen it. I do not know if it resembles or was found with the 6047A specimen. Most workers consider this taxon a junior synonym of Euparkeria.

Sookias and Butler 2013
reviewed the Euparkeriidae, but did not mention the 6047A or B specimens, except, perhaps as two of the eleven specimens that comprise their hypodigm. They defined the clade in this fashion: “Euparkeriidae Huene 1920. Stem-based definition –the most inclusive clade containing Euparkeria capensis Broom 1913a but not Crocodylus niloticus Laurenti 1768 or Passer domesticus Linnaeus 1758. (new).” I have not tested all the taxa listed by Sookias and Butler, but their definition seems to be overly broad.

Figure 1. Subset of the LRT focusing on Archosauriformes. Clade colors match figure 2 overlay.

Figure 1. Subset of the LRT focusing on Archosauriformes. Clade colors match figure 2 overlay.

What do we learn here?

  1. Incomplete taxa can cause loss of resolution, as everyone knows. The addition of a more complete cousin can provide the remedy.
  2. Scoring errors also lead to loss of resolution.
  3. There is only one tree, the tree of Nature, that we are trying to model here. So there IS a correct solution to this problem.
  4. Adding taxa almost always provides traits that make phylogenetic transitions more gradual. The only exceptions are terminal taxa, those that lack descendants.
  5. Known proterosuchids still do not represent ontogenetic (maturation) stages. They are phylogenetically distinct taxa that lead to more derived clades (Figs. 2,3).
  6. There is still no evidence for the sisterhood of Euparkeria with the verified sisters Turfanosuchus and Gracilisuchus  (Sookias and Butler 2013, Butler et al. 2014).
  7. Phylogenetic miniaturization preceded and was part of the basal archosauriform radiation.
  8. It is important for professionals not to assume that different specimens represent a single species. Minor differences might turn out to be key traits as demonstrated here.
Figure 3. Click to enlarge. 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.

Figure 3. Click to enlarge. 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. In the white zone are specimens considered proterosuchids.

Finally: the value of a large gamut cladogram
becomes more valuable with every added taxon. More gradual transitions become apparent and bias is further minimized.


References
Broom R 1913. On the South-African Pseudosuchian Euparkeria and Allied Genera. Proceedings of the Zoological Society of London 83: 619–633.
Butler RJ, Sullivan C, Ezcurra MD, Liu J, Lecuona A and Sookias RB (2014). New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and the biogeography of the archosaur radiation. BMC Evolutionary Biology 14:1-16.
Ewer RF 1965. The Anatomy of the Thecodont Reptile Euparkeria capensis Broom Philosophical Transactions of the Royal Society London B 248 379-435.
doi: 10.1098/rstb.1965.0003
Sookias RB and Butler RJ 2013. Euparkeriidae. Geological Society, London, Special Publications published online January 24, 2013 as doi: 10.1144/SP379.6

 

 

 

Teyujagua: Not “transitional between archosauriforms and more primitive reptiles”

A new paper by Pinheiro et al. 2016
reports that the small skull (UNIPAMPA 653) of a new genus, Teyujagua paradoxa (Figs. 1, 2), is “transitional in morphology between archosauriforms and more primitive reptiles. This skull reveals for the first time the mosaic assembly of key features of the archosauriform skull, including the antorbital and mandibular fenestrae, serrated teeth, and closed lower temporal bar. Phylogenetic analysis recovers Teyujagua as the sister taxon to Archosauriformes…”

Well, that might be true if
you restrict the taxon list to the few (44) taxa employed by Pinheiro et al.

But when you expand the taxon list
to the size of the large reptile tree (660+ taxa) where we already have a long list of Youngina, Youngoides (Fig. 1) and Youngopsis sisters to Archosauriformes, then Teyujagua nests as a phylogenetically miniaturized sister to the NMQR 1484/C specimen attributed to Chasmatosaurus alexandri (Fig. 1). Like another phylogenetically miniaturized descendant of chasmatosaurs, Elachistosuchus huenei MB.R. 4520 and BPI 2871 (Figs. 3, 4), Teyujagua also turned its once large antorbital fenestra into a vestige (Figs. 1, 2).

Figure 1. Teyujagua compared to sister taxa, including Youngoides, Proterosuchus and Chasmatosaurus. Teyujagua is a phylogenetic miniature in which the antorbital fenestra became a vestige.

Figure 1. Teyujagua compared to sister taxa, including Youngoides, Proterosuchus and Chasmatosaurus. Teyujagua is a phylogenetic miniature in which the antorbital fenestra became a vestige. Note the posterior jugal, which may or may not have supported a now missing quadratojugal anterior process.

I can see why the authors got so excited about their discovery.
The Teyjjagua skull looks like a little Chasmatosaurus skull without the antorbital fenestra. That’s because it IS one. In their own words, “This skull represents a previously unknown species that is the sister taxon to Archosauriformes and which fills a major morphological gap in understanding of early archosauriform evolution.”

Unfortunately, the authors were dealing with an antiquated cladogram
in which Youngina is basal to lizards and archosaurs… among many, many other atrocities.  They report, “Our novel cladistic analysis recovered two most parsimonious trees with 872 steps. The strict consensus of these topologies positions Teyujagua as the sister taxon of Archosauriformes, a position previously occupied by the Lower Triassic Prolacerta.”

So this is where it really pays off
to use several specimens from the Youngina grade and several specimens from the Proterosuchus grade along with 660+ opportunity taxa to nest with.

Figure 2. The rostrum of Teyujagua with the vestigial antoribital fenestra circled here. You can see how the maxilla grew over the opening. Once again, this is data that should have been announced from firsthand observation by PhD level paleontologists, not from a casual observer of photographic data.

Figure 2. The rostrum of Teyujagua with the vestigial antoribital fenestra circled here. You can see how the maxilla grew over the opening. Once again, this is data that should have been announced from firsthand observation by PhD level paleontologists, not from a casual observer of photographic data.

Diagnosis (from the paper)
“Archosauromorph with the following unique character combination: confluent, dorsally positioned external nares; maxilla participating in orbital margin; antorbital fenestra absent; trapezoidal infra temporal fenestra with incomplete lower temporal bar; teeth serrated on distal margins; surangular bearing a lateral shelf; external mandibular fenestrae present and positioned beneath the orbits when the lower jaw is in occlusion (autapomorphic for Teyujagua).”

Comments on the diagnosis
The NMQR 1484/C specimen of Chasmatosaurus (Fig. 1) is pretty well preserved except for the premaxilla/narial region. Given the morphology of the Teyujagua rostrum, the NMQR specimen likely shares the trait of a dorsal naris, perhaps with a slender ascending process of the premaxila, which might be lost in both specimens. The maxilla actually does not appear to reach the orbit. The antorbital fenestra remains present as a closed over vestige. The lower temporal bar might be incomplete, but just as likely the anterior process of the quadratojugal might be taphonomically missing, as in the NMQR specimen (Fig. 1). Other proterosuchids have similar tooth serrations. The mandibular fenestra is further forward, but the posterior mandible is also deeper. The specimen is indeed distinct enough to merit a unique generic name, as is the case with several of the Chasmatosaurus/Proterosuchus specimens, which do NOT represent a growth series.

Phylogenetic miniaturization
has reduced the antorbital fenestra in BPI 2871 and Elachistosuchu, which nest at the base of the Choristodera. Both nest as descendants of larger Chasmatosaurus specimens in the large reptile tree.

Figure 1. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Figure 3. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Not mentioned by the authors
The miniaturized skull of Teyujagua has fewer teeth than in sister or ancestors, but matching the condition in Euparkeria (Fig. 1), a related taxon only one node away at the base of a sister clade.

Rostral area of BPI 2871, formerly considered a younginid and here nesting at the base of the Choristodera.

Figure 4. Rostral area of BPI 2871, formerly considered a younginid and here nesting at the base of the Choristodera as a descendant of Chasmatosaurus.

If you don’t remember
this earlier post (2011), Youngoides (UC1528, Fig. 5) had the genesis of an antorbital fenestra. It is the current proximal sister to the Archosauriformes in the large reptile tree.

Figure 1. GIF movie tracing the antorbital fenestra with fossa and surround bones of the FMNH UC 1528 specimen of Youngoides romeri. This is one of the earliest and most primitive appearances of the archosauriform antorbital fenestra, previously overlooked.

Figure 5. GIF movie tracing the antorbital fenestra with fossa and surround bones of the FMNH UC 1528 specimen of Youngoides romeri. This is one of the earliest and most primitive appearances of the archosauriform antorbital fenestra, previously overlooked.

In summary, the authors report
“Teyujagua presents an unexpected combination of basal archosauromorph and typical archosauriform features. For example, Teyujagua resembles basal archosauromorphs in lacking an antorbital fenestra and retaining open lower temporal bars1. However, Teyujagua possesses external mandibular fenestrae and serrated teeth, features previously considered unique to Archosauriformes.”

Unfortunately, the authors appear to forget
that the antorbital fenestra can phylogenetically disappear and Chasmatosaurus demonstrates that the quadratojugal can wither phylogenetically or taphonomically disappear. It is a fragile bone.

References
Pinheiro FL, França MAG, Lacerda MB, Butler RJ and Schultz CL 2016. An exceptional fossil skull from South America and the origins of the archosauriform radiation. Nature Scientific Reports 6:22817 DOI: 10.1038/srep22817.

Evolution basics – starring Jon Stewart and Babe Ruth

Evolution does not work in mysterious ways.
The basics (small variations leading over dozens of generations to larger changes) are simple:

GIF movie 1. Skull width as a variable demonstrated by Babe Ruth and John Stewart in this animated GIF file.

GIF movie 1. Skull width as a variable demonstrated by Babe Ruth and John Stewart in this animated GIF file.

  1. wider / narrower (skull, body, feet, etc.)
  2. taller-larger / smaller-shorter
  3. longer (more ribs) / shorter (fewer ribs)
  4. longer limbs / shorter limbs
  5. larger skull / smaller skull
  6. longer preorbital region / longer postorbital region
  7. longer neck / shorter neck
  8. sharp claws / rounded claws
  9. etc. / etc.

At left 
are extinct baseball star, Babe Ruth, and extant comedian/commentator, Jon Stewart, graphically demonstrating #1 on the above list, wider / narrower in the skull shape. Both are male members of the species Homo sapiens.

Other traits
one can add to this list include various perforations or fenestrae (which have several and often convergent origins and disappearances:

  1. fenestra between the naris and orbit (antorbital fenestra)
  2. fossa surrounding antorbital fenestra
  3. one or more fenestrae between the orbit and occiput
  4. fenestra in the mandible
  5. occipital fenestrae expand over braincase
  6. acetabulum perforated or not

And once fenestrae are formed:

  1. Loss of lower temporal arch
  2. Loss of upper temporal arch
  3. Loss of both

Then add
the size and shape of various bones and their processes compared to other bones and you have yourself a long character list. Enough of these (150+) provide a good matrix of characters and character states that can produce the menagerie of reptiles found in the large reptile tree, now numbering 566 taxa for 228 characters.

The wider / narrower and smaller / larger dichotomies 
can also be seen in the variety of specimens attributed to Proterosuchus and Chasmatosaurus (Fig. 2, Broom 1903). Some paleontologists (Welman 1998, Ezcurra  and Butler 2015) consider these taxa congeneric. They think this variety constitutes an ontogenetic series. On the other hand, the large reptile tree recovered these taxa in distinct nodes and clades. Narrower-skulled forms nest together. So do wider-skulled forms and they lead to other even more distinct taxa, including some once again tiny forms. The tall-skulled proterosuchids do not lead to more derived taxa.

Figure 3. The many faces of Proterosuchus to scale and in phylogenetic order, among with their closest known relatives. Note the phylogenetic miniaturization, reduction of the drooping premaxilla and loss of the antorbital fenestra after the TM 201 specimen of Chasmatosaurus. Click to enlarge.

Figure 2. The many faces of Proterosuchus to scale and in phylogenetic order, among with their closest known relatives. Note the phylogenetic miniaturization, reduction of the drooping premaxilla and loss of the antorbital fenestra after the TM 201 specimen of Chasmatosaurus. Click to enlarge.

The smallest taxon
shown here (Fig. 2), Youngoides romeri, leads to euparkeriids and then to a long list of archosauriforms including dinosaurs, crocs and birds. This last common ancestor of proterosuchids and euparkeriids (all archosauriforms) also had a small antorbital fenestra.

Have a great weekend!
Keep those cards and letters coming.

References
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Ezcurra MD and Butler RJ 2015. Post-hatchling cranial ontogeny in the Early Triassic diapsid reptile Proterosuchus fergusi. Journal of Anatomy. Article first published online: 24 APR 2015. DOI: 10.1111/joa.12300
Welman J 1998. The taxonomy of the South African proterosuchids (Reptilia, Archosauromorpha). Journal of Vertebrate Paleontology 18 (2): 340–347.

The many faces of Proterosuchus: not a growth series

Recent papers by Ezcurra and Butler (2015) and Welman (1998) purported to show a growth series in Proterosuchus (Fig. 1; Broom 1903) using a number of small to large skulls. Anyone can see why these authors thought these two skulls could be samples from a growth series. But is that what these skulls truly represent? After all, the only way to become a giant proterosuchid is to evolve over hundreds of generations from an original pair of small proterosuchids (Figs. 2, 3). 

Figure 1. Two proterosuchid skulls which Ezcurra and Butler report represent a juvenile and adult. That hypothesis is not supported by phylogenetic analysis.

Figure 1. Two proterosuchid skulls which Ezcurra and Butler report represent a juvenile and adult. That hypothesis is not supported by phylogenetic analysis. Compare these images to RC96 and RC59 in figure 3.

Unfortunately,
Ezcurra and Butler did not perform the required phylogenetic analysis of the several specimens of Proterosuchus. Instead, like Bennett (1995) did with Rhamphorhynchus, Ezcurra and Butler assumed a single species of Proterosuchus was present with differences attributed to ontogeny. The smaller Proterosuchus skulls, Ezcurra and Butler reported, were juveniles. They reported the shape of the skulls changed during ontogeny, becoming taller and relatively narrower with ages. They did not consider the possibility of ‘Cope’s Rule’ or the process of evolution in the creation of a large Proterosuchus.

As with Rhamphorhynchus, the large reptile tree found the morphological differences in Proterosuchus/Chasmatosaurus were all due to phylogeny (evolution), not ontogeny. Basal Proterosuchus specimens more closely resembled outgroup Youngina specimens. Derived Proterosuchus specimens more closely resembled more derived genera (Fig. 3, like Diandongosuchus and Doswellia

Figure 2. The origin and evolution of Proterosuchus based on skulls. On the left to scale. On the right to the same length.

Figure 2. The origin and evolution of Proterosuchus based on skulls. On the left to scale. On the right to the same length. What you’re seeing here is the evolutionary steps taken to produce the large RC96 skull. You have to start somewhere, and here you can start with the AMNH 5561 specimen of Youngina.

Bottom line:
Despite their size differences, all of the Proterosuchus skulls in figures 1-3 are adults, or at least they can be scored as adults.

Figure 3. The many faces of Proterosuchus to scale and in phylogenetic order, among with their closest known relatives. Note the phylogenetic miniaturization, reduction of the drooping premaxilla and loss of the antorbital fenestra after the TM 201 specimen of Chasmatosaurus. Click to enlarge.

Figure 3. The many faces of Proterosuchus to scale and in phylogenetic order, among with their closest known relatives. Note the phylogenetic enlargement, phylogenetic miniaturization, reduction of the drooping premaxilla and loss of the antorbital fenestra after the TM 201 specimen of Chasmatosaurus. Click to enlarge. Yes there are two choristoderes related to the tiny BPI 2871 specimen wrongly attributed to Youngina. Moving the BPI 2871 closer to Youngina and the Choristodera adds 30 steps, so it appears that the antorbital fenestra disappeared in this lineage.

I’m not sure if we know
what a juvenile Proterosuchus specimen looks like. I don’t think we’ve found one yet. My guess is it will look like and phylogenetically nest with a specific adult, only smaller, as in pterosaurs and other reptile taxa. To that point, the smallest putative Proterosuchus specimen shown here (Fig. 3), RC 59, (formerly considered Elaphrosaurus), phylogenetically nests as a derived proterosuchian. At it nests with an even smaller little archosauriform, BPI 2871, formerly referred to Youngina. So the littlest Proterosuchus is not a juvenile, as imagined by Ezcurra and Butler. Rather RC 59 is going through phylogenetic miniaturization and it is not done shrinking.

By the way we can be pretty confident about these nestings because the taxon list has grown to 540+ taxa.

You might find this fascinating..
Everyone who sees a Proterosuchus skull must think, “That odd premaxilla drooping snout…that has to belong to a terminal taxon. What could possibly evolve from that?” Well, apparently the answer is: “a long list of taxa,” which you already know and we’ll meet in future blog posts. Some hints as to the identify of those taxa are in figure 3 and at reptileevolution.com. That premaxilla doesn’t stay so long and droopy in descendant taxa, perhaps due to neotony.

And one more thing…
The skulls of Proterosuchus and Chasmatosaurus are not shaped differently because they were crushed during burial in different directions. No, what you see is what you get. And it all appears to fit together in the tree of life — without any a priori assumptions as to relative ontogenetic age.

The many faces of Proterosuchus and Chasmatosaurus
have been perplexing, but phylogenetic analysis puts everything in order. Let’s get this problem behind us. Please encourage paleontologists to run all their taxa through analysis before assuming any are juveniles.

References
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Ezcurra MD and Butler RJ 2015. Post-hatchling cranial ontogeny in the Early Triassic diapsid reptile Proterosuchus fergusi. Journal of Anatomy. Article first published online: 24 APR 2015. DOI: 10.1111/joa.12300
Welman J 1998. The taxonomy of the South African proterosuchids (Reptilia, Archosauromorpha). Journal of Vertebrate Paleontology 18 (2): 340–347.

 

The Proterosuchus holotype – restoration and imagination

Several skulls and skeletons have been attributed to Proterosuchus, the basalmost archosauriform. Unfortunately the holotype is the worst of the lot.

Figure 1. Top and bottom images from Ezcurra et al. 2014. Middle with missing pieces imagined and restored based on other specimens.

Figure 1. Top and bottom images of Proterosuchus holotype from Ezcurra and Butler 2014. Middle with missing pieces imagined and restored based on other specimens. As you can see, the bones and impressions of bones are very difficult to see. Colorizing the bones, as I do in DGS, is an amazing way to present what those two observed in the fossil.

A recent paper by Ezcurra and Butler 2014 explores the many skulls of Proterosuchus.

From the abstract
“Based upon a comprehensive re-examination of all known specimens, as well as examination of other proterosuchid taxa in collections worldwide, we conclude that the holotype of Proterosuchus fergusi (Fig. 1) is undiagnostic… As a result, we recognize a minimum of four archosauriform species following the Permo-Triassic mass extinction in South Africa. Our results suggest a greater species richness of earliest Triassic archosauriforms than previously appreciated, but that archosauriform morphological disparity remained low and did not expand until the late Early Triassic – early Mid-Triassic.”

This skull, IMHO, cannot be used in phylogenetic analysis, and it hasn’t been used in that way. However, add a few other taxa identified by museum numbers and you’re good to go.

References
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Ezcurra, MD and Butler RJ. 2014. Taxonomy of the proterosuchid archosauriforms (Diapsida: Archosauromorpha) from the earliest Triassic of South Africa, and implications for the early archosauriform radiation. Palaeontology. (advance online publication)
DOI: 10.1111/pala.12130 http://onlinelibrary.wiley.com/doi/10.1111/pala.12130/abstract
Ezcurra MD, Butler RJ and Gower D 2013. ‘Proterosuchia’: the orign and early history of Archosauriformes. Pp. 9–33 in S. J. Nesbitt, J. B. Desojo, R. B. Irmis (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and Their Kin. Geological Society, London, Special Publications 379.
Welman J 1998. The taxonomy of South African proterosuchids (Reptilia, Archosauromorpha). Journal of Vertebrate Paleontology 18:340–347.
Welman J and Flemming  AF 1993. Statistical analysis of the skulls of Triassic proterosuchids (Reptilia, Archosauromorpha) from South Africa. Palaeontologia africana 30:113–123.

wiki/Proterosuchus

 

What is Tasmaniosaurus?

Updated September 20, 2014 with a new reconstruction and nesting for this taxon.

Revised skull reconstruction of Tasmaniosaurus nesting at the base of the Erythrosuchia.

Revised skull reconstruction of Tasmaniosaurus nesting at the base of the Erythrosuchia.

Ezcurra 2014 considered the tiny Early Triassic archosauriform Tasmaniosaurus traissicus (Camp and Banks 1978) a tiny proterosuchid, following the original assessment.

Previous authors thought the maxilla was exposed in lateral view. If so, it has a maxillary fossa. Ezcurra thought the maxilla was exposed in medial view. Proterosuchids do not have a maxillary fossa. If the premaxilla was not downturned, Tasmaniosaurus is anything but a proterosuchid. If the maxilla is exposed in lateral view, Tasmaniosaurus is anything but a proterosuchid.

The caudal vertebrae are very long, longer than 3x their width, very un-proterosuchid like. Seven in a row have no neutrals spines.

The interclavicle of Tasmaniosaurus is T-shaped with a very long and slender posterior process. Among archosauriforms, only Euparkeria has a T-shaped interclavicle. Many are I-shaped.

The femur and tibia/fibula are short and robust, so no possible biped here and the Early Triassic is a little too early for bipeds.

Tasmaniosaurus is tiny. About the size of Youngina and Euparkeria, much smaller than any known proterosuchid or erythrosuchid.

In phylogenetic analysis (not updated online yet), Tasmaniosaurus nests at the base of the Erythrosuchidae, as a sister taxon to Fugusuchus + Revueltosaurus. So, another miniaturized taxon nests basal to a large clade.

References
Camp CL, Banks MR 1978. A proterosuchian reptile from the Early Triassic of Tasmania. Alcheringa 2: 143–158.
Ezcurra MD. 2014. The Osteology of the Basal Archosauromorph Tasmaniosaurus triassicus from the Lower Triassic of Tasmania, Australia. PLoS ONE 9(1):e86864. doi:10.1371/journal.pone.0086864

Synaptichnium and Proterosuchus

Synaptichnium (Nopcsa 1923, Fig. 1) is a fairly large quadrupedal, semi-plantigrade ichnotaxon of the Early to Middle Triassic in which pedal digit 4 remains longer than digit 3, which is atypical for derived archosauriforms. Here (Fig. 1) the pes of Proterosuchus, a basal archosauriform with pedal digit 4 longer than 3, was slightly modified to fit the ichnite. This is appropriate because other less completely known proterosuchids, like Archosaurus and Sarmatosuchus are known. The manus of Proterosuchus is poorly known, but when matched to the impression of Synaptichnium, our guesses become more precise in that now we can model digit 4 shorter than digit 3 despite a lack of bone data. Similar data mining from ichnites occured in Erythrosuchus matched to Isochirotherium ichnites.

Synaptichnium

Figure 1. Synaptichnium compared to a slightly altered pes of Proterosuchus. Note a reduction of one phalanx in pedal digit 4 to match one less pad in the ichnite.

Comparisons to Prolacerta
Prolacerta is a predecessor taxon to Proterosuchus. The manus of Prolacerta is more clompletely known and it has a digit 4 longer than 3. To my knowledge, successor taxa to Proterosuchus do not  preserve a manus until one gets to Ticinosuchus, which also has a manual digit 4 shorter than 3.

Prolacerta.

Figure 2. Prolacerta. Note the relative lengths of the manual and pedal lateral digits. Click for more info.

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

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

References
Avanzini M and Mietto P 2008. The occurrence of the vertebrate ichnogenus Synaptichnium in the Anisian (Middle Triassic) of Southern Alps. Studi Trent. Sci. Nat., Acta Geol., 83 (2008): 259-265. online pdf
Broom R. 1903. On a new reptile (Proterosuchus fergusi) from the Karroo beds of Tarkastad, South Africa. Annals of the South African Museum 4: 159–164.
Gower DJ and Sennikov AG 1997. Sarmatosuchus and the Early History of the Archosauria. Journal of Vertebrate Paleontology 17(1):60-73.
Nopcsa F 1923. Die Familien der Reptilien. Fortschritte der Geologie und Paläontologie der Rheinlande und Westfalens. 210 pp.
Sennikov AG 1994. Pervyj srednetriansovyj proteroscchid iz Vostochnoy Evropy. Doklady Akademii Nauk 336:359-661.
Tatarinov LP 1960. Otkrytie pseudozhukhii v verkhnei permi SSSR: Paleontologischeskii Zhurnal, 1960, n. 4, p. 74-80.

wiki/Proterosuchus