You heard it here first: Lagerpeton is NOT a dinosauromorph

Thanks to Dr. Max Langer
for sending this abstract.

Five years after
Lagerpeton was removed from the Dinosauromorpha online here, Novas and Agnolin 2016 follow suit by nesting Lagerpeton with Tropidosuchus, among the Proterochampsidae.

This is confirmation of methodology
and the value of a large gamut analysis in reducing a priori bias and the influence of paradigm. You don’t have to see the fossil firsthand to make a contribution to paleontology. The Science is in the testing of heretical hypotheses. The Pseudoscience is in the critical blackwashing of results without testing.

Not sure how the critics will take this news.
I know they hate it every time testing reveals something that is not in their paradigm.

From the Novas and Agnolin 2016? abstract
“The relationships of basal ornithodirans [1] constitute a hotly debated topic of vertebrate evolution. Among one of the most important basal ornithodirans is the enigmatic Lagerpeton chanarensis, coming from the Middle Triassic Los Chañares Formation, Talampaya National Park, La Rioja Province, Argentina. With the aim to evaluate the phylogenetic position of this taxon, a detailed comparison with other Triassic archosauriforms was conducted. Surprinsingly, extensive similarities between Lagerpeton and proterochampsids, particularly Tropidosuchus, were found. Because of that, an integrative phylogenetic analysis including Lagerpeton and several archosauriform clades was constructed. The analysis resulted in the recognition of Lagerpeton as a basal archosaurifom nested within Proterochampsidae, and nearly related to the genus
Tropidosuchus.

“Lagerpeton resembles proterochampsids in several derived features, including 1) proximal pubis with robust ambiens process; 2) lateral margin of pubis sigmoid in anterior view; 3) acetabulum cup-like and ellipsoidal shaped; 4) transverse processes on caudal vertebrae long and narrow; 5) femoral 4th trochanter proximodistally expanded; 6) caudal surface of distal tibia with a middle tubercle surrounded by two shallow concavities; 7) astragalus with anteromedial corner acute; and 8) metatarsal II tranversely thick. Furthermore, Lagerpeton and Tropidosuchus share elongate and compact metatarsus with metatarsal V reduced and devoid of phalanges, and with articular surface for distal tarsal 4 subparallel to the longitudinal axis of shaft, and metatarsal IV longer than III. In spite of the similarities noted above, Lagerpeton differs from proterochampsids and resembles dinosauriforms in having a well-defined and proximally convex femoral head, and absence of osteoderms.

“Previous authoritative papers by J. Bonaparte and P. Sereno and A. Arcucci have illustrated the hindlimbs of Lagerpeton as vertically positioned. However, manual articulation of the femoral head within the deep and elliptical-shaped acetabulum avoids a parasagittal position of the entire hindlimb. On the contrary, the most unforced position of the hindlimbs in Lagerpeton depicts its femora in a sprawling posture. In this position, distal femoral condyles orientate almost ventrally to articulate with tibia and fibula. In lateral view, the articulated hindlimb is oblique, being subhorizontally oriented. In these respects, Lagerpeton resembles basal archosauriforms, including proterochampsids, but differs from the parasagittal posture of ornithodirans.

“The exclusion of Lagerpeton from the dinosaur lineage results in the removal of the clade Dinosauromorpha, [2, 3] which was originally conceived to encompass Lagerpeton plus Dinosauriformes. The recognition of Lagerpeton as a derived proterochampsian widens the morphological radiation that this clade of basal archosauriforms manifested during mid-Triassic times.”

Notes

  1. Ornithodira is still an invalid clade encompassing pterosaurs and dinosaurs and their kin, which, in the LRT, encompasses all Reptilia.
  2. We may want to resurrect a clade name for the archosaur outgroups to the Dinosauria listed here and discussed and illustrated here and here.
  3. Dinosauromorpha was also removed here five years ago.

References
Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios”. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

Lagerpeton: foot configurations modeled in cardboard

Earlier discussions about the pes of Lagerpeton and the ichnite it would have produced inspired these tests. Here a cardboard model of the Lagerpeton pes has been raised to low (Fig. 1) and high (Fig. 2) digitigrade configurations.

Lagerpeton model pes raised to a low digitigrade configuration in which pedal digit 2 would have impressed in line with the metacarpophalangeal joints of 3 and 4.

Figure 1. Lagerpeton model right pes raised to a low digitigrade configuration in which pedal digit 2 would have impressed in line with the metacarpophalangeal joints of 3 and 4. Digit 4 completely impresses and digit 3 is slightly raised proximally.

Lagerpeton raised to a high digitigrade configuration. Here only two digits would have impressed with raised proximal phalanges.

Figure 2. Lagerpeton raised to a high digitigrade configuration. Here only two digits would have impressed with raised proximal phalanges. Either both of these configurations were part of the step cycle or just this one was. We have no Lagerpeton ichnites at present. Rotodactylus and Prorotodactylus ichnites impress five digits. These one likely impressed just two.

Niedwickski et al. (2013) in their quest for a trackmaker to fit Rotodactylus published this image of Lagerpeton, which is an obvious mismatch that doesn't even have a pedal digit 5. Plenty of other taxa are better matches (Figs. 3,4) but those weren't published, tested or promoted.

Figure 3. Click to enlarge. Niedwickski et al. (2013) in their quest for a trackmaker to fit Rotodactylus published this image of Lagerpeton, which is an obvious mismatch that doesn’t even have a pedal digit 5. Plenty of other taxa are better matches (Figs. 3,4) but those weren’t published, tested or promoted.

These models emphasize the impossibility that anything like Lagerpeton could have produced Prorotodactylus or Rotodactylus ichnites (contra Brusatte et al. 2013). Better matches can be found in Cosesaurus, Tanystropheus and kin as shown earlier.

The Ascending Process
On dinosaurs the ascending process of the astragalus is in front of the ankle. It advances upwards and ultimately covers the lower tibia.

By contrast, in Lagerpeton the ascending process is in back. This is a key difference that goes unrecognized by those who promote a dinosauromorph nesting for Lagerpeton. A small posterior ascending process can also be found in the chanaresuchid, Tropidosuchus.

Cardboard models
In the absence of 3D and wire modeling (which I used for Pteranodon), cardboard feet make quick models for difficult subjects. I’ve used them earlier (Peters 2000, 2011) to model various pterosaur feet. Here (Figs. 1, 2)  the model pes of Lagerpeton can be raised or lowered to test a variety of possible configurations. You can even split the metatarsals if appropriate. That enables one to arc the metatarsals, like teepee tent poles. In every configuration the PILs (parallel interphalangeal lines) can be drawn on the base/substrate. Those that are the most continuous typically reflect the actual pedal configuration. Here (Fig. 1) the more upright two-digit implant configuration, produces an ostrich-like pes with PILs at right angles to the proposed direction of movement, reflecting that stage in the step-cycle. My guess is this is the more likely candidate.

The evolution of a longer pedal digit 4 in chanaresuchids
In ancestral quadrupedal taxa, like Chanaresuchus (Fig. 3) and Tropidosuchus (Fig. 4) pedal digit 4 is so slender as to appear vestigial.

Chanaresuchus a quadrupedal ancestor to Tropidosuchus and Lagerpeton and the third taxon.

Figure 4. Chanaresuchus a quadrupedal ancestor to Tropidosuchus and Lagerpeton and the third Tropidosuchus-like taxon.

In derived taxa, like the other purported Tropidosuchus (Fig. 5), the pes does not appear to be so derived.

Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions.

Figure 5. Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions. This is reptile evolution at work.

This apparent reversal to a more primitive condition appears to coincide with the reduction of the forelimb, and, in Lagerpeton to the elongation of the hind limb relative to the size of the pelvis.

Figure 3. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

Figure 6 The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the larger and taller Lagerpeton.

Besides, the foot mismatch, Lagerpeton is a pretty large animal, at least twice the size of Tropidosuchus and a maginitude larger than the Rotodactylus trackmaker.

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
Brusatte SL, Niedz´wiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B, 278, 1107–1113.
Niedzwiedzki G, Brusatte SL and Butler RJ 2013. Prorotodactylus and Rotodactylus tracks: an ichnological record of dinosauromorphs from the Early–Middle Triassic of Poland. Geological Society, London, Special Publications, first published April 23, 2013. doi 10.1144/SP379.12.

wiki/Lagerpeton

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.

Doswellia in several views

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.

The newfound elements of Doswellia found by Heckert et al. (2012).

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

A New Proterochampsa? This Time with Postcrania!

For several decades all we knew of Proterochampsa barrionuevoia (Reig 1959) consisted of several skulls and cervical vertebrae. The rest of the postcranium remained unknown until now. A new report by Trotteyn (2011) reveals much of the missing post-crania. PVSJ 606 was at least twice as large as the holotype (Fig. 1). It was found in the Ischigualisto Formation of the Late Triassic.

A new specimen (PVSJ 606) attributed to Proterochampsa by Trotteyn (2011)

Figure 1. A new specimen (PVSJ 606) attributed to Proterochampsa by Trotteyn (2011). Lateral view from Trotteyn (2011). Dorsal view after tracing the skull image in Trotteyn (2011).

Proterochampsa nodosa
A third specimen and a separate species, P. nodosa, I have not seen yet. The abstract distinguishes the two species, “..snout becoming narrow anteriorly in a less gradual manner than in P. nodosa, lower occiput, nares lanceolate with narrow anterior and posterior ends, and frontal less irregular that in P. nodosa.”

Proterochampsa? dorsal view.

Figure 2. Bone identification in a dorsal view of the skull PVSJ 606.

Comparisons
Due to the compressed skull of PVSJ 606 and its attribution, I expected the post-crania to be likewise compressed with short legs, perhaps most similar to basal parasuchians, like Parasuchus. As it turns out, the post-crania more closely resembled that of Chanaresuchus.

The Pararchosauriformes.

Figure 3. The Pararchosauriformes. Click to see entire tree. Note the nesting of the new specimen attributed to Proterochampsa as a sister to the holotype, but at the base of the chanaresuchids.

Description
The skull of PVSJ 606 (Fig. 2) was relatively enormous! It was as long as the presacral vertebral column. The various fenestrae were relatively smaller. The premaxilla was shorter and the post-orbital area was more robust. The premaxilla was not squared off. Do these differences, plus the major size difference mean the new specimen is a new species? Unfortunately Trotteyn (2011) completely ignored comparisons to the holotype skull, focusing all her efforts on a description of the post-crania alone.

The cervicals and caudals were more gracile in PVSJ 606 than in sister taxa. This seems improbable considering the size of the skull, but true. The torso was rather short and the legs were rather long.

Ecology and Behavior
No one has figured out the ecology and behavior of Proterochampsa or this specimen. Not sure what to make of it yet. It’s a bizarre creature!

Analysis
Trotteyn (2011) did not published a cladistic analysis having opted instead to synonymize the new specimen with the holotype of Proterochampsa. Under cladistic analysis PVSJ 606 nested as a sister to Proterochampsa (Fig. 3) at the base of the Cerritosaurus clade that also includes Chanaresuchus. So, PVSJ 606 is likely not congeneric or conspecific with Proterochampsa. It takes 8 extra steps to create a sisterhood with the holotype.

pes of Proterochampsa

Figure 4. DGS reveals two other digits and metatarsal 5 not described in the pes of Proterochampsa hidden among the skull bones. See Figure 1 for a reconstruction.

The Pes
Only two toes (including their metatarsals) were described by Trotteyn (2011). Examination of the photograph (Fig. 2) appears to show two more toes plus metatarsal 5 on the skull, which is somewhat fragmented, but largely intact. The  reconstructed elements create what appears to be a valid pes with continuous PILs (Fig. 1). Are these interpretations valid or not? Send data! We’ll figure this out. I’m only working from published photos in black and white.

An Ancestral Sister to Pterosaurs and Dinosaurs?
A recent report on archosaur relations (Brusatte et al. 2010) placed Proterochampsa at the base of the clade that produced dinosaurs and pterosaurs. Ridiculous for dozens of reasons, yet this was one of many such studies with similar results. Unsupportable and illogical results such as these are a direct result of inappropriate exclusions and inclusions in the taxon list resulting in “by default” nestings.

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
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Reig OA 1959
 Primeros datos descriptivos sobre nuevos Reptiles Arcosaurios del Triasico de Ischigualsto (San Juan, Argentina): Revista de la Asociacion Geologica Argentina, tomo 13, n. 4, p. 257-270.
Trotteyn MJ 2011. Material postcraneano de Proterochampsa barrionuevoi Reig, 1959 (Diapsida: Archosauriformes) del Triásico Superior del centro-oeste de Argentina. Ameghiniana 48:424-446.

wiki/Proterochampsa

Cerritosaurus – A Key Overlooked Taxon in the Pararchosauriformes

Cerritosaurus binsfeldi,

Figure 1. Cerritosaurus binsfeldi, Late Triassic, known only from a skull. Such a taxon was basal to Chanaresuchus and the chanaresuchids. It also would have been morphologically close to the ancestor of the phytosaurs (parasuchians) and not far from Proterochampsa given its resemblance to the RC 91 specimen of Youngoides.

Where are the Phytosaur and Chanaresuchid Ancestors?
There has been relatively little interest in finding ancestral taxa to the phytosaurs and chanaresuchids. Prior efforts have recovered questionable candidates. Nesbitt’s (2011) tome on archosaurs recovered Euparkeria nesting at the base of the Phytosauria.  He also recovered Vancleavea nesting at the base of the Proterochampsia (= Tropidosuchus + Chanaresuchus). Erythrosuchus nested basal to all the above taxa.

These Nestings Raise Red Flags
Phytosaurs and chanaresuchids were flat-headed archosauriformes with skulls wider than tall and nares located dorsally on the skull. The orbits were located high on the skull. The rostrum was narrow in dorsal view and the “cheeks” flared widely. The antorbital fenestra was small. By contrast the skulls of VancleaveaEuparkeria and Erythrosuchus were taller than wide, with narrow cheeks, lateral nares and the latter two had a large antorbital fenestra. Vancleavea did not have an antorbital, mandibular or upper temporal fenestra because indeed it was not related to archosaurs. Vancleavea was a thalattosaur as reported earlier. Nesbitt (2011) did not include other thalattosaurs in his analysis, so Vancleavea nested by default within the Archosauriformes. The large reptile study solves that shortcoming.

Cerritosaurus binsfeldi (Price 1946, Fig. 1) Late Triassic, ~210 mya, nests here between the Parasuchia and the base of the Chanaresuchidae within the Pararchosauriformes. Nesbitt (2011) briefly mentioned Cerritosaurus as a member of the Proterochampsia [a paraphyletic taxon]. With its short snout and generally primitive characters Cerritosaurus likely also resembled the common ancestor of the Choristodera, Parasuchia and Proterochampsa. It was also not far from the RC 91 specimen of Youngoides (Fig. 1).

Distinct from RC91Cerritosaurus had a skull with a downturned rostrum. The skull was box-like with distinct rims both anterior and posterior to the orbits. The nares opened dorsally. An antorbital fenestra appeared with a deep fossa. The dorsal squamosal flared posteriorly. The mandibular fenestra was enlarged. The retroarticular process ascended. The teeth were extremely long, which is an autapomorphy.

With its wide flat skull, dorsal nares and elevated orbits Cerritosaurus provides a nearly ideal transitional taxon linking the RC91 specimen of Youngoides to basal phytosaurs and chanaresuchids. It is certainly a superior candidate compared to the taller narrow skulls of Euparkeria and Erythrosuchus. Exclusion of Cerritosaurus by Nesbitt (2011) and others before him impaired those earlier studies.

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
Bonaparte JF 1971Cerritosaurus binsfeldi Price, tipo de uma nova família de tecodontes (Pseudosuchia-Proterochampsia). Anais da Academia Brasileira de Ciências, 43(Supl.): 417-422.
Kischlat E-E and Schultz CL 1999. Phylogenetic analysis of Proterochampsia (Thecodontia: Archosauriformes): Ameghiniana, v. 36, p. 13R.
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.
Price LI 1946. Sôbre um novo pseudosuquio do Triássico superior do Rio Grande do Sul: Boletim da Divisão de Geologia e Paleontologia, DNPM, v. 120, p. 7-38.

wiki/Cerritosaurus