STL Science Center

STL Science Center

30 June 2015

Confounding Arguments

Just prior to the release of Jurassic Park as a movie, but after its publication as a novel, there was a renewed interest in Procompsognathus. Whether this arose from the book and movie or simply because the fossil was looked at with new eyes, two papers reviewed the material that was attributed to the holotype and one nearly declassified the animal. That paper, a 1992 study published in the Journal of Vertebrate Paleontology, was written by Paul Sereno and Rupert Wild. Their findings declared that Procompsognathus was in fact a fossil chimera composed of theropod post cranial skeleton and crocodylomorph cranial elements (and a forelimb for good measure). Other papers since that time, see Fabien Knoll, have asserted that parts of the postcranial skeleton are not portions of Procompsognathus and this should not be a surprise anyway. The holotype is based on a three part slab fossil which could have easily been "contaminated" with other species. There is no insinuation in any papers that the chimera was purposefully assembled, but evidence supporting non-Procompsognathus material in the fossil is important to spread apart from the material that does belong to the dinosaur. To that end, in 1993, Sankar Chatterjee, after more fossil preparation work, set about refuting Sereno and Wild's 1992 paper (the abstract for this work can be found here). Chatterjee asserted that the skull was not that of a crocodylomorph, but of a basal theropod. It appears that all sources since those two have agreed that Procompsognathus is, as the 1990 version of The Dinosauria states, "a problematic theropod". That version of the publication actually considered Procompsognathus a nomen dubium based on confounding and insufficient evidence. The agreement on the general basal position of the skull has been further agreed upon, I think we can say this satisfactorily, as being close to Coelophysis and Segisaurus halli in the tree. Paul's 2010 Princeton Field Guide states that Procompsognathus is a misleading name as the dinosaur is not related to Compsognathus very closely at all; so much for the comparisons in body shape presented here the past few days! However, we can still use those comparisons as both genera and Coelophysis (to which we know Procompsognathus is related) have basic small theropod body plans and would have had similarities in diet and sometimes in locomotion, though the typical unknowns (e.g. behaviors and mannerisms affecting locomotion and life history) must still be observed as unknown whenever discussing dinosaurs.
Model is ©Steve Baldock, photo posted by Amos Wolfe

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