A little Triassic Ichthyosaur: Phalarodon

Figure 1. Phalarodon, a little mid Triassic ichthyosaur. Note the deep depression in the dorsal skull.

Figure 1. Phalarodon, a little mid Triassic ichthyosaur. Note the deep depression in the dorsal skull. Bones in situ and restored here to in vivo positions and skull bones colorized. Note the actual size is not much larger than shown here. 

From the Liu et al. 2013 abstract:
Phalarodon atavus from the Germanic Muschelkalk Basin was previously represented only by cranial elements.Here we report a nearly complete and articulated specimen of P. atavus from the Middle Triassic Luoping Biota, Yunnan, South China. This is the first specimen of P. atavus from outside the Germanic Basin. This discovery demonstrates a peri-Tethyan distribution of P. atavus. The new specimen is also the first one preserving the postcranial anatomy of this species, providing the opportunity to evaluate its sustained swimming ability. Inferences made on its functional morphology suggest that this species was probably adapted for active foraging. Tooth crown morphology suggests that P. atavus may have preferred externally soft prey.”

The mixosaurian body plan is recognized as an evolutionary intermediate between the basal stem plan represented by Early Triassic forms and the parvipelvian plan of largely post-Triassic ichthyosaurs. Size-independent criteria indicate this specimen (LPV 30872) is a subadult. It is a tiny ichthyosaur, not much larger than the image shown above.

Sinosaurosphargis is from the same equatorial deposits. The Germanic deposits were also equatorial at the other end of the Tethys Ocean bounded on all sides by continents and peninsulas.

Giant Cymbospondylus (Fig. 2) also nests with Mixosaurus and Phalarodon. Note the share trait of side-by-side dips in the cranium with the upper temporal fenestra as “drains” in these basins, areas that probably housed jaw muscles.

Figure 1. Cymbospondylus overall in situ.

Figure 2. Cymbospondylus overall in situ.

References
Liu J et al 2013. The first specimen of the Middle Triassic Phalarodon atavus (Ichthyosauria: Mixosauridae) from South China, showing postcranial anatomy and per–Tethyan distribution. Palaeontology  56:849-866.

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