I know it has been a while since I last posted a blog but life has been busy, with a fossil festival in Lyme, a thesis to write and a beer festival thrown into the middle. Apologies for the absence but luckily for you, here I am with another installment.
A new specimen of a Triassic ichthyosaur has been discovered in South China. This alone is not huge news as lots of new Triassic specimens are coming out of China. However, this particular specimen is a lot more interesting than that. This is a mostly complete specimen of Phalarodon atavus (Fig. 1).
Fig. 1: Remains of the ichthyosaur and interpretive drawing from Liu et. al. 2013.
Although useful information can be gathered from the skull alone, this is typically just about the genus and species to which the animal belongs while teeth can provide some information about diet The fact that this specimen is nearly complete provides a lot more information than just cranial elements. The size of the organism can be shown, the paddles are preserved, as are the vertebrae. As a result of all this, information can be gleaned about the swimming style and abilities of the animal.
So, lets talk swimming styles. The typical body shape of an ichthyosaur is what’s known as ‘Thunniform’ body shape. This is the typical semi-lunate (crescent) tail shape and a ‘stiff’ body, such as in Tuna and Sharks and the like. This body shape and swimming style is ideally suited to pursuit predators and sustained swimming. This type of body plan is not thought to have evolved until the late Triassic. It is currently thought that earlier ichthyosaurs would have a more ‘reptilian’ body plan and would swim by moving the whole body side to side like a typical crocodile swimming motion.
However, in the new specimen the centra (vertebrae) are quite long and high, similar to some sharks today. This suggests a ‘rigid’ body as seen in the thunniform ichthyosaurs, potentially allowing this ichthyosaur to have a sustained swimming ability. Furthermore, the teeth of this specimen are relatively well preserved. They are quite small and bluntly pointed with no cutting edges. There are however longitudinal ridges along the crown of the tooth. The blunt points suggest a more ‘crushing’ type feeding strategy but the longitudinal ridges suggest at least some ability to hold onto a prey item. Therefore, it is most likely that this ichthyosaur would favour prey items with a relatively soft outer body, such as belemnites or fish with very few scales and would forage for them. The rigid body, allowing sustained swimming, would suit a wide-ranging forager and seems plausible for this specimen
I am sure you are all overwhelmed and very excited with all the information and stuff that’s been said so far in this blog but get this, there’s more! This particular species of ichthyosaur is only known from Muschelkalk Basin in Germany, and due to an assumed inability for sustained swimming as well as geographic barriers, that it was endemic (limited to one area).
Fig. 2: Global palaeogeographical reconstruction showing the distribution of Phalarodon atavus from Liu et. al. 2013
The new material from China suggests that this is not the case and the geographical distribution was much larger than previously thought (Fig. 2). Again, this supports the idea of a sustained swimming style, made possible by a rigid body and potentially, a tail beginning to resemble the classic crescent shape. It’s a fun time to be into ichthyosaurs.
As always, thanks for reading. I hope you enjoyed it. Feel free to leave feedback, good or bad.
Liu, J., Motani, R., Jiang, D-Y., Hu, S-X., Aitchison, J. C., Rieppel, O., Benton, M. J., Zhang, Q. Y. & Zhou, C. 2013. The first specimen of the middle Triassic Phalarodon atavus (Ichthyosauria: Mixosauridae) from south China, showing post-cranial anatomy and pero-Tethyan distribution. Palaeontology. pp. 1-18 DOI: 10.1111/pala.12021