Paleontologists in New Zealand have discovered a partial skeleton of platypterygiid ichthyosaur dating to the Cretaceous period.
A pair of Platypterygius sp. Image credit: Dmitry Bogdanov / CC BY 3.0.
“Ichthyosaurs were a clade of secondarily aquatic marine reptiles that inhabited the seas for much of the Mesozoic Era, first appearing in the Early Triassic before their ultimate extinction at the Cenomanian-Turonian boundary,” said University of Canterbury paleontologist George Young and his colleagues.
“Cretaceous ichthyosaurs were once thought of as a group with low diversity and disparity resulting from a long-term decline since the Jurassic.”
“However, recent work has produced a growing body of evidence that Cretaceous ichthyosaurs were much more diverse than previously thought.”
“Ichthyosaur fossils were first recorded in New Zealand by von Haast in 1861 from Mt Potts in the central South Island,” they added.
“Over the subsequent 150 years, fossil material of ichthyosaurs has been recovered from the Triassic, Jurassic, and Cretaceous.”
The new New Zealand ichthyosaur was found in the Coverham area at the northern end of the Waiau Toa/Clarence valley.
The specimen is a disarticulated partial skeleton preserved within a concretion.
It dates back 98 million years ago to the Cretaceous period — approximately 4 million years before the final extinction of the ichthyosaurs.
“The material derives from a concretion that was found in situ within the Swale Siltstone Member of the Split Rock Formation, a siliciclastic unit deposited during the Cenomanian age and found throughout southern Marlborough and northernmost Canterbury in the New Zealand’s South Island,” the paleontologists said.
“All of New Zealand’s previously described Cretaceous ichthyosaur material comes from the North Island.”
The specimen is the most completely preserved individual ichthyosaur known from New Zealand.
It possesses a well-preserved pelvis and hindfin which have added to the known dataset of these elements which are so rarely preserved in Cretaceous species.
“Whilst the specimen is too fragmentary to formally name, this taxon shows an extreme reduction of the basioccipital extracondylar area, a scapula with a prominent acromion process and a strap-like scapula shaft, as well as a complete left pelvic girdle with an elongated depression on the anteroproximal face of the ischiopubis,” the researchers said.
They suggest that it is a late branching member of the platypterygiid ichthyosaurs, closely related to an Eastern Gondwanan species called Platypterygius australis and to many European Cretaceous ichthyosaurs.
However, it appears to be unrelated to the Cretaceous ichthyosaurs of Western Gondwana, suggesting potential regionalism amongst the Gondwanan Cretaceous ichthyosaur populations.
“The new New Zealand ichthyosaur adds to the known diversity of Gondwanan Cretaceous ichthyosaurs and may suggest a regionalized rather than cosmopolitan distribution of ichthyosaur populations around the margin of Cretaceous Gondwana,” the scientists conlcuded.
The findings appear in the Journal of Vertebrate Paleontology.
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George R.A. Young et al. A platypterygiid ichthyosaur from the Cenomanian of central New Zealand. Journal of Vertebrate Paleontology, published online October 30, 2024; doi: 10.1080/02724634.2024.2408391
