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

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