Several years ago we looked at Vancleavea campi (Figs. 1,2 ), a Triassic aquatic reptile described by Nesbitt, et al. 2008 as an archosauriform nesting with Erythrosuchus, Euparkeria, Turfanosuchus and Doswellia (according to Wikipedia, based on published work listed above). Unfortunately, Vancleavea shares few traits with these archosauriforms. It has no antorbital fenestra, no upper temporal fenestra and no mandibular fenestra.
Figure 1. Vancleavea surrounded by purported sister taxa as figured by Nesbitt and Wikipedia. None of these taxa share more traits with Vancleavea than does Helveticosaurus, a taxon ignored since it was proposed here.
Not yet tested in academic publications,
the thalattosaur, Helveticosaurus, shares more traits with Vancleavea than 569 other tested taxa in the large reptile tree.
Figure 2. Vancleavea with its sister, Helveticosaurus.
This counter argument
was made more than 4 years ago. To date no one else has supported or refuted the argument. Nevertheless, in the last four years Vancleavea has appeared in several cladograms without Helveticosaurus. Unfortunately this demonstrates that paleontologists are really not interested in its correct nesting node, but would rather just add new taxa to existing flawed analyses and cladograms. Testing prior work is not their strong suite. Discovery is.
Vancleavea campi (Nesbitt et al. 2009) Late Triassic,~210 mya, ~1.2 meters in length, was originally considered a very weird archosauriform close to Doswellia, Turfanosuchus, Chanaresuchus and Erythrosuchus, but that’s because the authors did not compare it to Helveticosaurus with which Vanclevea shares more traits. It turns out that Vanclevea was a not-so-weird thalattosaur and a prime example of what happens when the gamut of the inclusion set is decided prior to the analysis. Vancleavea was the last in its lineage. Unlike other thalattosauriforms, Vancleavea was armored with a variety of ossified scales covering the body.
There must be dozens
of Vancleavea-like thalattosaurs yet to be discovered, judging by the variation present between it and Helveticosaurus. Even so, after adding hundreds of taxa to the large reptile tree, these two still nest together.
Not the only time a taxon’s correct nesting ignored.
These taxa are also traditionally incorrectly nested based on the results of the large reptile tree.
- Turtles
- Pterosaurs
- Fenestrasauria and Tritosauria
- Snakes
- Caseasauria
- Mesosauria
- Poposauria
- Rhynchosauria
- Synapsida
- Chilesaurus and Daemonosaurus
- Gephyrostegus
- Procolophon
- Cartorhynchus
- Youngina and Youngoides
- Xianglong
- Tetraceratops
- Eudibamus
- Doswellia
- Revuletosaurus
- Scleromochlus
- Pseudhesperosuchus
- Marasuchus
- Lagerpeton
- Teraterpeton
- Ticinosuchus
- and whatever else I’ve forgotten to list here
References
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.
Parker WG and Barton B 2008. New information on the Upper Triassic archosauriform Vancleavea campi based on new material from the Chinle Formation of Arizona. Palaeontologia Electronica 11 (3): 20p.
