Cartorhynchus: not an ichthyosaur, not amphibious and not a sucker

Earlier (in early November 2014) we looked at the new discovery of Motani et al. (2014), Cartorhynchus (Fig. 1), which they recovered as an ichthyosaur ancestor, amphibious and a suction feeder. The paper was officially released by Nature (Motani et al. 2015) recently, hence the redux here.

Unfortunately
Like the Holy Roman Empire, Cartorhynchus is neither an ichthyosaur, amphibious nor a suction feeder.

Figure 1. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

Figure 1. Although the pectoral girdle was preserved just behind the skull, in all sister taxa there are about 19 cervicals and 19 dorsals. Plus the pectoral girdle itself is very wide, better suited to the widest ribs. Perhaps Cartorhynchus had a longer neck than commonly assumed.

Not an ichthyosaur
1. The large reptile tree, now up to 484 taxa, nests Cartorhynchus as a basal sauropterygian, between Pachypleurosaurus and Qianxisaurus. That’s why Cartorhynchus has a short snout, like its sisters, unlike the long snout in Wumengosaurus, hupehsuchids and ichthyosaurs. A large suite of traits separates Cartorhynchus from ichthyosaurs. Shifting Cartorhynchus to the base of the ichthyosaurs adds 33 steps.

Not amphibious
2. That tiny neck, tiny cervical ribs and giant head (Fig. 1) strongly indicate that life above the water would be very difficult indeed. Then there’s a lack of ossified phalanges as the limbs turn into rather soft flippers. Then there’s the shortening of the limb bones and a lack of elbows and knees. Ironically, Cartorhynchus was less amphibious than its sister taxa, Pachypleurosaurus and Qianxisaurus. Then there’s the flat ventral surface, perfect for bottom dwelling underwater. Nothing but [a] drag on land.

Not a suction feeder
3.  Suction feeders, like seahorses, can have a tiny mouth, unable to open much. On the other hand, the mata mata turtle does not have a tiny mouth, but it does have a long neck and a strong hyoid apparatus, which quickly expands the neck creating the suction of water that impels prey back to the throat. Suction feeders also tend to lose their teeth. Cartorhynchus, but contrast, has a wide gape and large teeth, despite its pincer like premaxilla. The high coronoid process and large temporal fenestra indicate large jaw muscles were present, perfect for biting, unnecessary for suction feeding. There is no great hyoid apparatus here and no long neck for the water to rush into.

References
Motani R et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature doi:10.1038/nature13866
Motani R, Jiang D-Y, Chen G-B, Tintori A, Rieppel O, Ji C & Huang J-D 2015. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature 517: 485–488. doi:10.1038/nature13866

http://www.nature.com/
wiki/Cartorhynchus

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