New paper, old Chanaresuchus: traditional taxon exclusion issues

A new look at the holotype of Chanaresuchus
by Trotteyn and Ezcurra 2020 provides crisp color photos of the holotype material from several angles, in white light and after µCT scanning.

Unfortunately their small focused cladogram
is a little too small and a little too focused for their taxon list. It might seem large because it includes 115 active taxa from a list of 151 total taxa from (Ezcurra 2016), but, as before, it omits several taxa that would move the thalattosaur, Vancleavea, and the pterosaur, Dimorphodon, out of Archosauromorpha (along with other lepidosaurs like Macrocnemus and Tanystropheus.

Earlier we looked at the many problems in Ezcurra 2016. The largest problem: Ezcurra did not and still does not understand that traditional diapsid taxa are diphyletic and convergent, with some among the Lepidosauria and others starting with Petrolacosaurus and kin within the Archosauromorpha. The Viséan last common ancestor of all reptiles is their last common ancestor.

Earlier we looked at a similar taxon list by Nesbitt 2011 in a 7-part series and demonstrated dozens of scoring errors. After corrections the tree topology came to match the large reptile tree (LRT, 1698+ taxa).

Figure 1. 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.

From the Trotteyn and Ezcurra 2020 abstract:
“Proterochampsids are one of the several diapsid groups that originated, flourished and became extinct during the Triassic Period. Here we redescribe, figure and compare in detail the holotype of one of these rhadinosuchine species, Chanaresuchus bonapartei from the Chañares Formation. Our new cladistic analyses find stronger support than previous studies for the monophyly of Rhadinosuchinae and the clades that include Doswelliidae + Proterochampsidae and Tropidosuchus + Rhadinosuchinae. Doswelliids are recovered within Proterochampsidae, as the sister taxon to the genus Proterochampsa, in some analyses under implied weights.”

If you find any taxa
in figures 1 and 2 missing from the above list (hint: there are several), those are the taxa Trotteyn and Ezcurra need to add to their next look at proterochampsids.

Figure 2. Cladogram of basal archosauriforms. Note the putative basalmost archosauriform, Teyujagua (Pinheiro et al 2016) nests deep within the proterosuchids. The 6047 specimen that Ewer referred to Euparkeria nests as the basalmost euarchosauriform now.

References
Ezcurra MD 2016. The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, 4, e1778. doi:10. 7717/peerj.1778
Trotteyn MJ and Ezcurra MD 2020. Redescription of the holotype of Chanaresuchus bonapartei Romer, 1971 (Archosauriformes: Proterochampsidae) from the Upper Triassic rocks of the Chañares Formation of north-western Argentina.
Journal of Systematic Palaeontology (advance online publication)
doi: https://doi.org/10.1080/14772019.2020.1768167
https://www.tandfonline.com/doi/full/10.1080/14772019.2020.1768167

https://pterosaurheresies.wordpress.com/2016/04/29/basal-archosauromorpha-paper-ezcurra-2016/

What is Polymorphodon adorfi?

Sues et al. 2020 bring us a new Middle Triassic German diapsid,
Polymorphodon adorfi (Fig. 1; SMNS 91343, SMNS 91400) with a large toothy premaxilla and a hint of an antorbital fenestra.

Figure 1. Skull elements of Polymorphodon. Consider the possibility that the quadrate had an anterior lean, as in figure 2,, elongating the postorbital region of the skull.

At first glance Polymorphodon looks a lot like
Archosaurus (Fig. 2; Late Permian, eastern Europe), a taxon not yet tested in the LRT due to a paucity of material.

Figure 2. Archosaurus is not in the LRT, but shares several traits with Polymorphodon.

From the Sues et al. abstract
“Skeletal remains of a small reptile with a distinctive dentition from the Lower Keuper (Erfurt Formation; Middle Triassic, Ladinian) of the Schumann quarry near Eschenau, in the municipality of Vellberg in Baden-WÃrttemberg, Germany, represent a new taxon of non-archosaurian archosauriforms, Polymorphodon adorfi.”

That’s a wee bit general. Let’s see if the large reptile tree (LRT, 1698+ taxa; subset Fig. 5) can nest it more precisely.

The Sues et al. abstract continues:
“It is diagnosed by various craniodental autapomorphies, including mesial and distal carinae of labiolingually flattened maxillary and dentary tooth crowns with large, somewhat hook-shaped denticles aligned at distinct angle to apicobasal axis of tooth crown; premaxilla with long, leaf-shaped posterodorsal process that is slightly longer than body of element; presence of prominent lateral fossa on premaxilla anteroventral to external narial fenestra; premaxilla with five gently recurved, conical teeth; medial surface of maxilla with distinct ledge above the interdental plates; and maxilla and dentary with distinctly heterodont dentition”

The Sues et al. diagnosis is focusing on the dentition, plus the premaxilla and maxilla. Again, not much to work with, even though quite distinctive.

The Sues et al. abstract continues:
“Phylogenetic analysis recovered Polymorphodon adorfi in a position crownward of Erythrosuchus africanus but in an unresolved polytomy with derived non-archosaurian archosauriforms such as Proterochampsidae and Euparkeria capensis and with Archosauria.”

The first red flag: Proterochampsidae is not related to Euparkeria in the LRT. Simply add taxa to fix this.

The Sues et al. abstract continues:
“The maxillary and dentary teeth of Polymorphodon adorfi differ from those of other non-archosaurian archosauriforms and indicate a different, possibly omnivorous diet, suggesting that these reptiles were more diverse in terms of feeding habits than previously assumed.”

This abstract plus Wikipedia information plus results from the LRT indicate taxon exclusion is the issue here.

In the LRT (subset Fig. 5, not yet updated)
Polymorphodon nests at the base of the Pararchosauriformes, basal to all the many included proterosuchids, choristoderes, phytosaurs and proterochampsids in that order (Fig. 5). In the LRT the clade Pararchosauriformes is a sister to the clade Euarchosauriformes, which begins with two specimens of Euparkeria and ends with crocs, dinos and birds. All these are derived from the UC 1528 specimen of Youngoiides (Fig. 3), the most derived of the various non-archosauriform younginids.

Figure 3. Cladogram on the Polymorphodon Wikipedia page based on Ezcurra 2016. Note the lack of taxa preceding the taxon “Proterosuchidae”, which is where the LRT nests Polymorphodon.

So, yes, taxon exclusion is the problem
with the Sues et al. 2020 cladogram based on the Ezcurra 2016 cladogram, which suffered from taxon exclusion, as detailed here four years ago.

Polymorphodon is a late survivor
of a Late Permian radiation and is a key taxon with many pararchosauriform descendants. This hypothesis of relationships was overlooked by the original authors due to taxon exclusion.

Figure 4. Updated image of various proterosuchids and their kin within the LRT clade, Pararchosauriformes. When you see them all together it is easier to appreciate the similarities and slight differences that are gradual accumulations in derived taxa.

I still have not seen the Sues et al. 2020 PDF.
When it arrives (see below) we’ll see if it includes Youngoides, Archosaurus and many of the pertinent taxa in figure 4. Since they are using Ezcurra 2016 the odds are reduced. For now the nesting of Polymorphodon in the LRT is more certain and more stem-ward than originally proposed (Fig. 3).

Figure 5. Cladogram of basal archosauriforms from 2016. Polymorphodon nests basal to Proterosuchus BPI 1 4016, awaiting an update soon.

Adding taxa solves so many problems.
Not sure why academics are hesitating to do what needs to be done. Sure it’s hard work, but it only has to be done once.

Via email
Hans Sues indicated that a PDF of the paper will be ready within a week due to some publisher issues linking the supplemental information. We may explore this taxon again if that data provides information not available from present sources. For now, only a little data from a new taxon was enough to nest it with confidence, so long as taxon exclusion is minimized, as it is in the LRT. This helpful online resource is free for all to use.

---

References
Sues H-D, Schoch RR, Sobral G and Irmis RB 2020. A new archosauriform reptile with distinctive teeth from the Middle Triassic (Ladinian) of Germany. Journal of Vertebrate Paleontology Article: e1764968 (advance online publication)
doi: https://doi.org/10.1080/02724634.2020.1764968
https://www.tandfonline.com/doi/abs/10.1080/02724634.2020.1764968Â

wiki/Polymorphodon

Lagerpeton: not the first of its kind, but the last of its kind

Quick note
I updated the reconstruction and nesting of Colobomycter, which you can see here.

Traditional paleontologists
consider Lagerpeton (Fig. 1, Romer 1971) a basal dinosauromorph, thus the first of its kind (ancestral to dinosaurs).

In contrast
Lagerpeton nests as a terminal taxon in the large reptile tree, leaving no known descendants. Here (Fig. 1) convergent evolution has created a bipedal chanaresuchid, derived from Tropidosuchus that has similar pedal proportions to the second specimen attributed to Tropidosuchus.

Figure 1. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

According to
Wikipedia, seven fossil specimens have so far been attributed to L. chanarensis. They don’t add up to much more than a hind limb and pelvic girdle.

1. UPLR 06 (holotype) – articulated right hindlimb
2. PVL 4619 – articulated pelvis with sacrum, partial right and complete left hindlimbs
3. PVL 4625 – left pelvis with left femur and articulated vertebral column (dorsal, sacral and anterior caudal vertebrae
4. PVL 5000 – proximal end of left femur
5. MCZ 4121 – complete left, and partial right, femur.

Brusatte et al.
found Early Triassic footprints they attributed to lagosuchids. In reality the ichnites were closer to Rotodactylus tracks, which match the feet of fenestrasaurs, like Cosesaurus through pterosaurs.

In the large reptile tree
archosauriformes split at their origin, shortly after Youngina (AMNH 5561) and Youngoides (UC 1528) into two clades. The larger specimens start with Proterosuchus and radiate into choristoderes, parasuchians, doswellians and chanaresuchians terminating with Lagerpeton and its sister, Tropidosuchus (Fig. 1). The other branch starts with Euparkeria and extends to crocs, dinos and birds.

So,
Lagerpeton is not a close relative of dinosaurs, but convergent in several regards. The odd feet and pelves give them away as distinctly different from dinosaurs. Even so paleontologists continue clinging to this hypothesis. Better dino ancestors can be found here.

References
Arcucci A 1986. New materials and reinterpretation of Lagerpeton chanarensis Romer (Thecodontia, Lagerpetonidae nov.) from the Middle Triassic of La Rioja, Argentina. Ameghiniana 23(3-4):233-242. online pdf
Brusatte SL, Niedźwiedzki G, Butler RJ 2011. “Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic.”. Proceedings of the Royal Society B: Biological Sciences 278 (1708): 1107–1113. doi:10.1098/rspb.2010.1746. PMC 3049033. PMID 20926435.
Romer AS 1971 The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria, n. 378, p. 1-10.
Sereno PC and Arcucci AB 1993. Dinosaurian precursors from the Middle Triassic of Argentina: Lagerpeton chanarensis. Journal of Vertebrate Paleontology, 13, 385–399.

wiki/Lagerpeton

Teraterpeton nests with Trilophosaurus

Updated January 06, 2019
with new data in the form of photos leading to a new nesting of Teraterpeton with Trilophosaurus, despite the many differences (Fig. 1).

Figure 1. Skulls of Teraterpeton and Trilophosaurus compared.

The enigmatic Teraterpeton (Fig. 1), originally (Sues 2003) considered a relative of Trilophosaurus largely due to its toothless beak and lack of a lateral temporal fenestra. Now that nesting is confirmed.

Figure 2. Teraterpeton skull. Note the confluent naris and antorbital fenestra.

Teraterpeton is so weird,
t is no wonder it has remained an enigma for so long. Nesting such enigmas is exactly what the large reptile tree (not updated yet) is for. Earlier Teraterpeton nested with Tropidosuchus in the large reptile tree, but a mismatch that needed repairing.

Teraterpeton hrynewichorum (Sues 2003) Late Triassic, ~215 mya, was described as euryapsid (lacking a lateral temporal fenestra) and possibly related to the rhynchocephalian, Trilophosaurus on that basis, but with a stretched out rostrum and far fewer, smaller teeth. The lateral temporal fenestra has been shortened so much that the lateral temporal fenestra has closed up. So, it’s still a diapsid morphology. The teeth had the multiple cusps of a plant eater. The pedal(?) unguals are robust, but note the disparate sizes.

References
Sues H-D 2003. An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia. Canadian. Journal of Earth Science 40(4): 635-649.

 

A new Doswellia snout!~!

Traditional paleontologists are still a little off about Doswellia (Fig. 1). It is a strange one with transverse and square ribs, a horizontal ilium, and a low wide skull that fills in a former lateral temporal fenestra. Unfortunately the rostrum has not been known for the last 30 years. Neither have the feet.

Even so, the large reptile tree firmly nested Doswellia at the base of the Choristodera, derived from Youngoides (RC91) and more distantly related to taxa at the base of the Parasuchia and Proterochampsia, all members of the Pararchosauriformes.

Figure 1. Doswellia in several views from Weems (1980). Missing pieces from 1980 are in black.

News about the rostrum!
Thankfully Heckert et al. (2012) discovered some of the last missing pieces, the premaxilla and maxilla of Doswellia (Fig. 2). Unfortunately they could not bring more focus to relationships, but repeated Dilkes and Sues (2009) assessment that Doswellia was close to proterochampsids, again ignoring the Choristodera and younginoids.

Figure 2. The newfound elements of Doswellia found by Heckert et al. (2012). The naris is dorsal. A tiny antorbital fenestra is present. The ventral maxilla is wavy. The premaxilla is deeper anteriorly and tips downward.

So what’s new?
The maxilla has teeth of several sizes and the ventral margin is wavy, not straight as in sister taxa.

There is an antorbital fenestra, small, and without much of a fossa. This follows the pattern seen in some (but certainly not all) Youngina and proterochampsids, and not seen  in the Choristodera.

The naris is dorsal in position, but still at the jaw tips. This is totally in line with the entire clade, which, other than Champsosaurus, all have dorsal nares. The premaxilla is also deeper anteriorly, downturned at the tip, as in several sisters.

The teeth are stout cones ideal for capturing prey.

This is a welcome discovery by Heckert et al. (2012) and fills a minor gap with real data. Glad to see it. Thanks to Dr. Heckert for sending the pdf.

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
Dilkes D and Sues H-D 2009. Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology 29(1):58-79.
Heckert AB, Lucas SG and Spielmann JA 2012. A new species of the enigmatic archosauromorph Doswellia from the Upper Triassic Bluewater Creek Formation, New Mexico, USA”. Palaeontology (Blackwell Publishing Ltd) 55 (6): 1333––1348. 
Weems RE 1980. An unusual newly discovered archosaur from the Upper Triassic of Virginia, U.S.A. Transactions of the American Philosophical Society, New Series 70(7):1-53

wiki/Doswellia

Strange Bedfellows – Nesbitt (2011) – part 3 – Euparkeria

Sometimes we miss the big picture. 
Here then, for your approval and disapproval are comparisons between closest kin found by the Nesbitt (2011) tree versus those found by the large reptile tree. We started at the base with Mesosuchus. Yesterday we looked at Vancleavea. Today we look at Euparkeria, surrounded by Tropidosuchus + Chanaresuchus on primitive side and the phytosauria led by Parasuchus on the derived side (Fig. 1).

Figure 1. The nesting of Euparkeria in Nesbitt (2011) surrounded by Tropidosuchus + Chanaresuchus and the Phytosauria, including Parasuchus.

Here (Fig. 2) are the selected Nesbitt (2011) sisters for visual comparison. They don’t look like sisters to me with their disparate shapes and proportions.

Figure 2. Surrounding Euparkeria in the Nesbitt (2011) tree are Tropidosuchus and Parasuchus, as shown here. The first and third have dorsal nares and a long narrow rostrum, among other traits. Euparkeria does not. If >I< were to propose these three as closest kin, I would have been laughed out of the city. Tropidosuchus is relatively close to Parasuchus in the large reptile tree, but several taxa, including Chanaresuchus and both the large and small Proterochampsa intervene.

Euparkeria does not fit here.
While Tropidosuchus and Parasuchus do share a suite of characters (dorsal naris, long narrow rostrum among them), several intervening taxa, like Chanaresuchus and Proterochampsa are missing here. Even with this distance, Euparkeria shares very little with these two and belongs with erythrosuchids and primitive rauisuchians. Here they are (Fig. 3), as promised yesterday.

Figure 3. Here Euparkeria nests between Garjainia, a basal erythrosuchid, and Ornithosuchus following the nestings recovered by the large reptile tree. All three share a suite of traits that do not include a long narrow rostrum and a dorsal naris, among other traits. Overall and in most details, these three look alike. Here, oddly enough, the much larger taxon has the juvenile trait of a larger skull and shorter tail!!

Euparkeria fits better here.
Matching the Nesbitt (2011) tree, Euparkeria nested with the Garjainia (and Erythrosuchus) and Ornithosuchus in the large reptile tree (Fig. 3). Being surrounded by two pararchosauriforms (Fig. 2) is quite odd. They share very few traits not more closely shared by other taxa.  This should have raised red flags and should have been cause for concern regarding the scoring of Nesbitt’s (2011) characters, no matter how many he used. In real evolution, sister taxa should look alike (Fig. 3) with slight variation. In real evolution, one should be able to trace a gradual accumulation of character traits, as we do with fossil hominids. The rules don’t change with reptiles. You need to take the shortest path, the one with the fewest changes, to nest sister taxa. One look at these results brings immediate understanding that there’s something wrong in the Nesbitt (2011) matrix that produces such strange bedfellows.

Figure 4. Youngina BPI 2871 and its descendants, according to the large reptile tree, the choristodere Cteniogenys and the chanaresuchid, Gualosuchus.

Choristodera and the Chanaresuchidae
While Tropidosuchus is on our minds… previously overlooked, the choristoderes were descendants of Youngina and a basal taxon produced parasuchians and chanaresuchians, according to the results recovered from the large reptile tree. Comparing the the choristodere, Cteniogenys, with the chanaresuchid, Gualosuchus, is instructive. The former lacks an antorbital fenestra, but it developed independently in the common ancestor of parasuchia and chanaresuchidae,  the BPI 2871 specimen of Youngina, a taxon not far from Gualosuchus.

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
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

Strange Bedfellows – Nesbitt (2011) – part 2 – Vancleavea

Sometimes we miss the big picture. 
Here then, for your approval and disapproval are comparisons between closest kin found by the Nesbitt (2011) tree versus those found by the large reptile tree. Yesterday we started at the base (Fig. 1) and the ill-advised inclusion of Mesosuchus. Today we reexamine the mistaken inclusion of Vancleavea (we did this several months ago, but differently).

Figure 1. The base of the Nesbitt (2011) tree with featured taxa in yellow.

Nesbitt (2011) included the new Triassic reptile, Vancleavea, in his list of Archosauriform taxa. It nested between Erythrosuchus and Tropidosuchus + Chanaresuchus (Figs. 1, 2). Since evolution works in minute steps, you may rightly ask, what’s wrong with this picture?

Figure 2. Closest known taxa recovered by the Nesbitt (2011) study. Here Vancleavea nested between Erythrosuchus and Tropidosuchus.

For comparison
The much larger and more inclusive large reptile tree, recovered Vancleavea with the thalattosaurs, Helveticosaurus and Askeptosaurus (Fig. 3). Nesbitt’s 2011 study did not include these sisters.

 

Figure 3. The closest kin of Vancleavea recovered by the large reptile tree. Askeptosaurus, Vancleavea and Helveticosaurus, all thalattosaurs unrelated to archosauriforms.

Tropidosuchus and Chanaresuchus

The large reptile tree also recovered Tropidosuchus with Chanaresuchus (matching Nesbitt 2011) and Lagerpeton (Fig. 4), which nests closer to dinos in the Nesbitt (2011) tree. That’s pretty far from Erythrosuchus. So the three putative sisters found by Nesbitt (2011) are all strange bedfellows.

Figure 4. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton. Note the distinct sizes, the shape of the pelvis nd the evolution of the foot.

Erythrosuchus
I’ll show pix of erythrosuchids and kin in a blog or two.

Remember
Fewer anatomical differences signal a closer relationship. Conversely, that means sister taxa share are a larger suite of traits. Our trees should recover sisters with a large suite of traits. By not including thalattosaurs, Vancleavea was inappropriately nested with archosauriforms by Nesbitt (2011).

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
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

What About That Hooked Snout on Basal Archosauriformes?

They’re stunning and a little off-putting, those strange, hook-snouted, basal archosauriforms like Proterosuchus and Archosaurus. Yes, this otherwise obscure specimen lent its name to that famous clade).

Figure 1. Basal euarchosauriformes with hooked snouts, overhanging the dentary and sometimes with posteriorly-oriented premaxillary teeth.

Origins
The origin of the hooked premaxilla may go back as far as Orovenator in which the premaxilla tilted down and extended only slightly beyond the dentary. This same degree of down tilt can be seen in Prolacerta and Protorosaurus, sisters to the ancestors of the archosauriforms.

Next we come to two taxa without a premaxilla preserved, Youngina BPI 3859 and Youngoides UC1528. And yet, considering the break and the tip of the dentary, there had to be a small or large premaxilla overhanging as shown in Figure 1. The BPI specimen nested at the base of all archosauriformes and otherwise resembled Proterosuchus.

Not in Pararchosauriforms
None of the basal pararchosauriformes had a hooked premaxilla, although Cerritosaurus and Chanaresuchus developed a minor one later by convergence.

Euarchosauriform Patterns
All of the basal euarchosauriformes had an enhanced hooked premaxilla. The premaxilla was smaller in Proterosuchus, much larger in Archosaurus. In the former the tip above the teeth was so curved over it was visible ventrally, but not in Archosaurus. Likewise in Fugusuchus the tip of the premaxilla was not visible ventrally.

The premaxilla was much deeper beneath the naris in Gargainia, giving it a shark-like appearance. The other erythrosuchids did not have such a hooked premaxilla. In Euparkeria and Vjushkovia the premaxilla did not descend.

In Ornithosuchus and Riojasuchus the premaxilla continued to descend, but with fewer teeth and a toothless notch anterior to the maxilla.

That’s the pattern. The hooked premaxilla developed, had its heyday, then disappeared.

Why Hook the Premaxilla?
Good question. Modern analogs are not readily apparent other than, perhaps the hooked beak of certain raptorial birds and turtles known to rip flesh from their prey.  With no dentary teeth to oppose the premaxillary teeth one wonders if the hooked premaxilla might have acted like a scoop or scraper. If a fish was caught at the apex of the hook and at the tip of the dentary, there was no escape. These Komodo Dragon-sized reptiles may have lain in wait underwater in shallows for prey to come close for a drink, much like alligators do. In such a case a hooked premaxilla may have indeed worked like a hook to collar wading prey and drag them underwater.

Baby and juvenile proterosuchids are not known, so a growth series showing any sort of enlargement of the hook during maturity has not been demonstrated.

Early Reptile Convergence Among Planteaters
Captorhinids, like Labidosaurus, developed a very similar premaxilla by convergence. This is a character derived from the earliest of all reptiles, Cephalerpeton, in which the anteriomedial premaxillary teeth were longer than the lateral ones, emphasizing the appearance of the hook, reaching an acme in Limnoscelis. Many of these were plant eaters. Such a hook may have been useful in gathering food or may have served as their only defense, inflicting a sharp bite in an oncoming predator.  On the other branch of basal Reptilia, the early insectivorous archosauromorphs did not have a descending premaxilla.

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.
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.
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
wiki/Sarmatosuchus

Introducing the Pararchosauriformes

Traditional studies (eg. Nesbitt 2011) nest all Archosauriformes in a ladder of taxa that  includes a major split between the so-called “Pseudosuchia” (aetosaurs, poposaurs, rauisuchids, crocodylomorphs and several individual genera) and the so-called “Avemetatarsalia” (pterosaurs and dinosauriforms).

Figure 5. The Pararchosauriformes. Lagerpeton is the most derived taxon.

The present large heretical study, that includes many times more taxa, recovers a major split at the grade of Youngina and Youngoides. One branch includes the taller, narrower skull forms descending from sisters to Proterosuchus. The other branch includes the wider, lower skull forms that include choristoderes, phytosaurs and chanaresuchids along with related taxa.

Taxon Exclusion is the Problem 
Traditional studies do not include dozens of key taxa due to a priori exclusion policies based on tradition and prejudice. The present heretical study minimizes those prejudices by including specimens from every corner of the reptile family tree.

Figure 1. The Pararchosauriformes. Only the larger taxa are visible here.

It All Begins with Youngoides
Youngina and Youngoides (Fig. 2) have been recognized for decades as basal taxa to the Archosauriformes. That’s absolutely correct. What hasn’t been recognized is that the variety in Youngina is real. The skulls look crushed and distorted, but some really are taller than wide or wider than tall. Basically, that’s what sets euarchosauriforms (Proterosuchus and descendants) apart from pararchosauriforms (choristoderes and desendants). The nares drift dorsally. The rostrum becomes elongated. The orbits either are or are not elevated above the rostrum. After those basal traits, evolution produced bipeds, croc-like forms and pachypleurosaur-like forms, along with at least one plant-eater in both branches of the Archosauriformes.

Figure 3. Several choristoderes (in white), their predecessor and sisters (in yellow).

Choristodera
Basal pararchosauriforms, like Doswellia and the Choristodera (Fig. 2), did not have an antorbital fenestra. These enlarged descendants of Youngoides elongated the snout and moved the naris dorsally.  Lazarussuchus lost the lateral temporal fenestra and further elongated the pre-narial premaxilla.

Proterochampsa
Currently known from a single published skull and an unpublished post-crania, Proterochampsa (Figs. 1, 2) is the most basal pararchosaur to sport an antorbital fenestra and no fossa surrounded it. This flat-skulled form was probably aquatic and short-legged like its sisters.

Phytosuchia/Parasuchia
The croc-like phytosaurs are a distinct clade sharing a long list of character traits. Even basal taxa have a longer rostrum than Proterochampsa.

Chanaresuchidae
Chanaresuchus and Tropidosuchus comprise the Chanaresuchidae, a clade of increasingly terrestrial forms culminating in the biped, Lagerpeton, a taxon commonly and mistakenly associated with dinosaurs by traditional workers.

Strangely, members of the Phytosauria and Chanaresuchidae have nested in traditional studies with pterosaurs, but this is patently ridiculous, a result of improper taxon inclusion and exclusion as demonstrated by the results of the large study.

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
Broom R 1914. A new thecodont reptile. Proceedings of the Zoological Society of London, 1914:1072-1077.
Gardner NM, Holliday CM and O’Keefe FR 2010. The braincase of Youngina capensis(Reptilia, Diapsida): New insights from high-resolution CT scanning of the holotype. Paleonotologica Electronica 13(3):online PDF
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Olsen EC 1936. Notes on the skull of Youngina capensis Broom. Journal of Geology, 44 (4): 523-533.