Dolichorhynchops

Dolichorhynchops is a polycotylid plesiosaurian reptile from the Late Cretaceous of the United States of America and Canada. It was named in 1902 by Samuel Wendell Williston. It was one of the more bizzare plesiosaurs to exist, having evolved a body plan similar to pliosauroids such as Liopleurodon.

## Physiology

Like all plesiosaurs, Dolichorhynchops had a bulky body, 4 flippers, and a short tail. However, its neck was shorter than that of most other closely-related plesiosaur families, and its head was long and bore a slender snout and a mouth filled with sharp, interlocking teeth; as well as this, its tail lacked a fin.[1] Its body would have been covered in scaly skin.

## Diet

Dolichorhynchops as a predator, preying on fish, cephalopods, and diving birds. The many teeth in its mouth were long and sharp, were used to get a hold of slippery prey.

## Ecology

While Dolichorhynchops would have mainly used its slender snout and interlocking teeth to snag fish and other small, minimally-defended aquatic prey, it would have occasionally preyed on diving birds, as toothmarks on a healed Hesperornis leg with growth marks indicate a failed attack on a juvenile that would soon grow to adulthood;[2] Dolichorhynchops itself would have fallen prey to larger predators like the mosasaur Tylosaurus, as stomach contents of the latter would prove.[3] In all, Dolichorhynchops would have filled an ecospace similar to that of a dolphin or an ichthyosaur, being a fast-swimming, fully aquatic tertiary consumer within its ecosystem. Occasionally, Dolichorhynchops would have swallowed stones to grind down its food, similarly to other plesiosaurs - however, it would have swallowed smaller, lighter stones, as opposed to larger elasmosaurids like Elasmosaurus and Styxosaurus, which would have swallowed larger, heavier stones.[4] Dolichorhynchops infants demonstrated a growth rate so rapid that they would come out of their mother's womb at 40% their body length; however, at that point in life, they would have compromised swimming abilities due to their weakly-built bone cortices, so while they still would have experienced rapid growth, it would have been focused on thickening those cortices, making parts of their limbs slightly thicker compared to those in adults.[5]

## In popular culture

Dolichorhynchops was featured in the 2007 documentary film *Sea Monsters: A Prehistoric Adventure*, where a female named Dolly is the protagonist. Dolly travels across the Western Interior Seaway - the seaway that covered much of North America during the Cretaceous - with her family. Her life is fraught with turmoil, as her mother is killed by a Cretoxyrhina, with her brother later meeting his fate in the jaws of a Tylosaurus - however, she herself manages to live to adulthood (she would even survive a Squalicorax attack as an infant, although mainly because a Tylosaurus would ambush the shark) and have young of her own, eventually dying of natural causes.

## References

1. Frey, E., Mulder, E. W. A., Stinnesbeck, W., Rivera-Sylva, H. E., Manuel Padilla-Gutiérrez, J., & Homero González-González, A. (2017). A new polycotylid plesiosaur with extensive soft tissue preservation from the early Late Cretaceous of northeast Mexico. La Sociedad Geológica Mexicana, 69(1), 87–134. https://doi.org/10.2307/26461888
2. Martin, L. D., Rothschild, B. M., & Burnham, D. A. (2016). Hesperornis escapes plesiosaur attack. Cretaceous Research, 63, 23–27. https://doi.org/10.1016/j.cretres.2016.02.005
3. Everhart, M. J. (2004). Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas. https://www.researchgate.net/publication/284484258
4. Schmeisser, R. L., & Gillette, D. D. (2009). Unusual occurrence of gastroliths in a polycotylid plesiosaur from the upper cretaceous tropic shale, Southern Utah. Palaios, 24(7), 453–459. https://doi.org/10.2110/palo.2008.p08-085r
5. O’Keefe, F. R., Sander, P. M., Wintrich, T., & Werning, S. (2019). Ontogeny of polycotylid long bone microanatomy and histology. Integrative Organismal Biology, 1(1), 1–26. https://doi.org/10.1093/iob/oby007