Baby tylosaurine skull from Kansas

[The Amateur Paleontologist]

Hey everyone

I just got news of a recently described set of juvenile Tylosaurus cranial remains! This cranial material is from the Santonian Smoky Hill Chalk Member (part of the Niobrara Fm.) of western Kansas. What's really exciting is that this specimen (FHSM VP-14845) originated from a neonate (newborn) individual, which can reveal numerous details about mosasaur growth and ontogeny. I've attached the paper below:

 

Konishi, T., P. Jimenez-Huidobro, and M. W. Caldwell. 2018. The smallest-known neonate individual of Tylosaurus (Mosasauridae, Tylosaurinae) sheds new light on the tylosaurine rostrum and heterochrony. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1510835.

Abstract: 

We here report on the smallest-known, neonate-sized Tylosaurus specimen, FHSM VP-14845, recovered from the lower Santonian portion of the Niobrara Chalk exposed in Kansas, U.S.A. Lacking any associated adult-sized material, FHSM VP-14845 comprises fragmentary and associated cranial bones, here considered to represent a single neo- natal individual with an estimated skull length of 30 cm. Despite its small size, a suite of cranial characters diagnoses FHSM VP-14845 as a species of Tylosaurus, including the elongate basisphenoid morphology. At the same time, FHSM VP-14845 unexpectedly lacks a conical predental rostrum on the premaxilla, generally regarded as diagnostic of this genus. Further, the first and the second premaxillary teeth are closely spaced, with the second set positioned posterolateral to the first, contributing to the overall shortness of the dentigerous premaxilla. Because a conical predental rostrum is already present in ontogenetically young specimens of T. nepaeolicus and T. proriger with respective skull lengths of approxi- mately 40 and 60 cm, formation of such a rostrum must have taken place very early in postnatal ontogeny. Our recognition of a neonate-sized Tylosaurus specimen without an elongate predental rostrum of the premaxilla suggests hypermorphosis as a likely heterochronic process behind the evolution of this iconic tylosaurine feature.

 

 

Partial pterygoids of the newborn Tylosaurus. Taken from fig. 4 of Konishi et al. (2018)

 

Here's the paper - hope you'll enjoy it!

Juvenile tylosaur skull.pdf

 

-Christian