‘The Incredible Ichthyosaurus,’ video lecture by Dr. Dean Lomax

Ichthyosaur expert, Dr. Dean Lomax, brings up the question
in this video, “What is an ichthyosaur?”

The problem is,
Dr. Lomax tells us only what ichthyosaurs are not. He has fun reporting that ichthyosaurs are not swimming dinosaurs.

Here
in the large reptile tree (LRT, 1326), which tests all candidate taxa, ichthyosaurs nest with thalattosaurs + mesosaurs, derived from basal sauropterygians. All are derived from marine younginiforms in the Permian. These are derived from Late Carboniferous diapsids arising from the pro-diapsid clade within the new Archosauromorpha.

Still not recognized by Dr. Lomax
Wumengosaurus (Fig. 2) is a late surviving (in the Middle Triassic) basalmost ichthyosaur. We first looked at this nesting of Wumengosaurus here in 2011.

Figure 3. Basal ichthyosauria to scale. Here Wumengosaurus, Thaisaurus, Mikadocephalus and a specimen attributed to Shastasaurus are illustrated. Note the phylogenetic miniaturization shown by Thaisaurus, a trait often seen at the origin of major clades.

Figure 3. Basal ichthyosauria to scale. Here Wumengosaurus, Thaisaurus, Mikadocephalus and a specimen attributed to Shastasaurus are illustrated. Note the phylogenetic miniaturization shown by Thaisaurus, a trait often seen at the origin of major clades.

Three years later,
Chen et al.. 2014 suggested Wumengosaurus might be related to basal ichthyosaurs and hupehsuchids. So, once again, you heard it here first… but I’m not giving Chen et al. much credit because their cladogram excludes so many taxa that, as a result, it recovers a  bogus mix of archosauromorph and lepidosauromorph taxa (Fig. 4).

Figure 4. Cladogram from Chen et al. 2014 showing Wumengosaurus nesting with hupesuchids and ichthyosaurs and nearby: thalattosaurs. Here mesosaurs are hidden somewhere within 'Parareptilia' along with pareiasaurs and other distinct clades. Red and green colors applied here to show the mix of Lepidosauromorph and Archosauromorph taxa (in the LRT) making this a small inclusion list cladogram of limited utility and several major errors.

Figure 4. Cladogram from Chen et al. 2014 showing Wumengosaurus nesting with hupesuchids and ichthyosaurs and nearby: thalattosaurs. Here mesosaurs are hidden somewhere within ‘Parareptilia’ along with pareiasaurs and other distinct clades. Red and green colors applied here to show the mix of Lepidosauromorph and Archosauromorph taxa (in the LRT) making this a small inclusion list cladogram of limited utility and several major errors.

Dr. Lomax also asks,
“What is Ichthyosaurus (and the various species within this genus)?” In this portion of the video, Dr. Lomax is extremely informative, showing distinctions made with skeletons—not with teeth, which can vary within one set of jaws.

Figure 3. Various ichthyosaur skulls attributed to Ichthyosaurus

Figure 3. Various ichthyosaur skulls attributed to Ichthyosaurus

References
Chen X-H, Motani R, Long C, Jiang D-Y and Rieppel O 2014. “The enigmatic marine reptile Nanchangosaurus from the Lower Triassic of Hubei, China and the phylogenetic affinities of Hupehsuchia”PLoS ONE9 (7): e102361. online here

 

https://pterosaurheresies.wordpress.com/2011/08/27/the-origin-and-evolution-of-ichthyosaurs/

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