Bipedal archosaur locomotion: Bates and Schachner 2011

Bates and Schachner 2011
report on bipedal archosaur locomotion with an emphasis on the basal poposaur, Poposaurus (Fig. 1).

Figure 1. Poposaurus skeleton and skull. Proportions indicate bipedal configuration.

Figure 1. Poposaurus skeleton and skull. Proportions indicate bipedal configuration.

Unfortunately,
Poposaurus
 and the Poposauridae (Fig. 2) nest just outside the Archosauria in the LRT (Fig. x). The basal croc, Pseudhesperosuchus, and the basal dinosaur, Herrerasaurus (Fig. 3), are valid candidates IF you want to stick to present definitions for the Archosauria.

Figure 1. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

Figure 2. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

We need a new name
for the unnamed clade Poposauria + Archosauria: Huperarchosauria (“more than Archosauria”). By just changing the title of Bates and Schachner 2011 to “Disparity and convergence in bipedal huperarchosaur locomotion,” the use of Poposaurus (Fig. 1) as an example becomes valid.

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

Figure 3. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

From the introduction:
“The clade Archosauria contains a staggering level of morphological, functional and ecological diversity that includes living birds and crocodilians, in addition to an array of enigmatic extinct forms such as dinosaurs and pterosaurs.”

Not pterosaurs. Those have nested apart from archosaurs for the last 20 years (Peters, 2000–2011). Over and over taxon exclusion prevents Bates and Schachner 2011 from understanding the phylogenetic context of their subject matter. For a more complete understanding of archosaur interrelations see the large reptile tree (LRT, 1734+ taxa; subset Fig. x).

Pterosaur and related fenestrasaur bipedalism, based on sprawling lepidosaur hind limbs, was not part of the Bates and Schachner study. Rather they concentrated on the erect hind limb bones and hypothetical muscles in Poposaurus and similar dinosaurs and birds.

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

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

Add taxa to discover 
all the clade members within the Archosauria (= birds + crocs, their last common ancestor and all descendants). In the LRT Archosauria includes crocs + dinosaurs and nothing more. Poposaurs are the proximal outgroup. Pterosaur nest elsewhere, within Lepidosauria, far from these archosauriform taxa.


Addendum:
There were 10x more views of the recent post on bat origins than the next most popular blogpost this week. I hope these ‘bat’ blogposts help us all understand the transition of arboreal mammals to flapping flight.


References
Bates KT and Schachner ER 2011. Disparity and convergence in bipedal archosaur locomotion. Journal of The Royal Society Interface 9(71):1339–1353.
Farlow JO, Schachner ER, Sarrazin JC, Klein H and Currie PJ 2014.Pedal Proportions of Poposaurus gracilis: Convergence and Divergence in the Feet of Archosaurs. The Anatomical Record. DOI 10.1002/ar.22863
Gauthier JA, Nesbitt SJ, Schachner ER, Bever GS and Joyce WG 2011.
 The bipedal stem crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion. Bulletin of the Peabody Museum of Natural History 52:107-126.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.
Peters D 2000b. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605

 

https://pterosaurheresies.wordpress.com/2011/07/16/what-exactly-is-a-pterosaur-part-3-of-3/

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