I‘m excited to welcome a guest contributor to Max’s Blogo-saurus today, Oliver Dong! Oliver is a 4th year student at the University of Toronto and a fellow paleo-nerd. Today’s article has been adapted from a Herpetology (EEB384) assignment that he recently completed at the UofT. Over to you Oliver!
What could make a lineage of massive hypercarnivores even more frightening?
Venom, perhaps?
Mosasaurs are one of the most iconic lineages of prehistoric marine reptiles. Featured in media such as Prehistoric Planet and Jurassic World, mosasaurs have been given their fair share of the spotlight in recent years. While even the largest mosasaurs did not approach the blue-whale-surpassing leviathans depicted in Jurassic World, they did have other spectacular features, such as the highly controversial possibility of venom.
First proposed by paleontologist Darren Naish in 2009, the venom theory has not yet been researched in-depth by paleontologists. However, enough work has been done to shed light on what could be a fascinating aspect of mosasaur ecology. This article will discuss the evidence that supports this theory with some speculation regarding its plausibility.
To determine the credibility of this theory, we need to start with the mosasaur’s modern relatives: the squamates, or lizards and snakes. The use of venom as a feeding mechanism has long been a controversial topic for non-serpent squamates. Barring the family Helodermatidae (Gila monsters and kin), venom has only recently been recently found in monitor lizards and, to a much lesser extent, iguanas. Along with snakes, these animals form a larger clade known as Toxicofera, which groups all lineages of venomous reptiles.
While debate exists as to whether mosasaurs are more closely related to snakes or monitor lizards, it’s clear that they fall within the Toxicofera clade[v]. The defining feature, or synapomorphy, of Toxicofera are several common venom proteins that assist in incapacitating prey[i]. These proteins were present in the common ancestor of the lineage and have become inherited by all extant members of Toxicofera, which means that we can assume mosasaurs likely would have possessed them too. However, Toxicofera is a controversial clade that some scientists dispute, and without any direct evidence of venom proteins in mosasaurs, we cannot prove this assumption.
Even if we assumed the validity of Toxicofera, using the evolutionary relationships of mosasaurs alone cannot be used to prove the presence of venom. Many non-venomous members of Toxicofera have retained venom proteins, including herbivorous iguanas[i]. While mosasaurs may have retained venom proteins, they may have lost the ability to produce venom capable of inflicting damage.
If mosasaurs did retain the ability to produce venom, the real question is whether they used it effectively while hunting. Using venom in an aquatic environment would have required direct injection into its prey through fangs. No mosasaurs have been found with such fangs, most notably the hollow fangs associated with venomous reptiles such as snakes.
Alternatively, some mosasaurs (such as the genus Platecarpus) exhibit a dental structure known as plicidentine, in which dentine infoldings can be found at the base of the tooth pulp cavity and run along the tooth’s axis[iii]. These infoldings cause external grooving, which could have aided mosasaurs with injecting venom. While the effect of this would have likely been minor, plicidentine infolding in some venomous snakes has produced deadly fangs that allow the venom to be channelled below the skin of their victims[iv].
Another characteristic that could hint towards venom is the presence of tooth serrations. Komodo Dragons, a giant species of monitor lizard from Indonesia, are closely related to mosasaurs and could provide an insightful analog. Instead of hollow fangs, Komodo Dragons possess serrated teeth that create gashes when gripping meat, and it is through these wounds that venom can effectively act upon prey [ii]. However, serrations are not exclusively an adaptation for venom transfer; many non-venomous reptiles (including theropod dinosaurs) have this feature, and, in the absence of other traits that suggest the presence of venom, this point remains unconfirmed [vii].
However, new evidence was presented regarding mosasaur skull morphology at the 82nd Annual Meeting of the Society of Vertebrate Paleontology that strengthens the venom hypothesis. An abstract by Sharpe et al. (2022) found that the mobile nature of the lower jaw in mosasaurs could indicate alternative feeding mechanisms such as venom and constriction. They also discovered that mosasaur bite force and bite force distribution were similar to extant venomous lizards, meaning their bite force was weak relative to size. While this could indicate that they preyed on smaller organisms (a concept known as microphagy), we know this to be untrue for multiple mosasaur species[vi]. Sharpe et al. argue that having a weaker bite force would have led mosasaurs to use the assistance of venom to prey on large animals. To date, this may be the best evidence of venom being a meaningful tool for predation in mosasaurs, but more research is required to say for certain.
Currently, not enough evidence exists to ascertain the presence of venom feeding in mosasaurs. Nonetheless, it’s a fun topic to speculate about given its connections to the phylogeny and morphology of Toxicofera. Plus, it makes for an even scarier movie monster, though they didn’t need venom for that! I think it’s possible that venom was not omnipresent in mosasaurs, but may have been restricted to a few lineages that evolved it independently.
Perhaps we will find a mosasaur with definitive morphological characteristics that indicate venom. After all, venom has appeared multiple times in Toxicofera, meaning that mosasaurs may have had the genetic potential to produce it. Coupled with the diversity and success of mosasaurs, it doesn’t seem that far-fetched to imagine venomous species. But who knows; only time will tell.
Until then, we’ll have to withstand the outlandishly large (and non-venomous) mosasaurs of Jurassic World…
Side note: I’d like to thank Max for featuring me on his blog. It was an honour for him to showcase my writing and you may see more articles from me in the future.
Thank you for reading today’s article! If learning about (potentially) venomous prehistoric reptiles is something you’re interested in, then I suggest you read about some (potentially) venomous dinosaurs, here at Max’s Blogosaurus!
We do not take credit for any images found in this article. All images belong to their respective creators, with the header image coming courtesy of Phuonglam11, found here
References:
[i] Fry BG, Vidal N, Norman JA, Vonk FJ, Schieb H, Ramjan SFR, Kuruppu S, Fung K, Hedges SB, Richardson MK, Hodgson WC, Ignjatovic V, Summerhayes R, Kochva E. 2006. Early evolution of the venom system in lizards and snakes. Nature 439: 584–588.
[ii] Fry BG, Wroe S, Teeuwisse W, van Osch MJ, Moreno K, Ingle J, McHenry C, Ferrara T, Clausen P, Scheib H, Winter KL, Greisman L, Roelants K, van der Weerd L, Clemente CJ, Giannakis E, Hodgson WC, Luz S, Martelli P, Krishnasamy K, Kochva E, Kwok HF, Scanlon D, Karas J, Citron DM, Goldstein EJ, McNaughtan JE, Norman JA. 2009. A central role for venom in predation by Varanus Komodoensis (Komodo Dragon) and the extinct giant Varnus (Megalania) priscus. Proc Natl Acad Sci U S A 106(22):8969-74.
[iii] Maxwell EE, Caldwell MW, Lamoureux DO. 2011. The structure and phylogenetic distribution of amniote plicidentine. J Vertebr Paleontol 31(3): 553-56.
[iv] Palci A, LeBlanc ARH, Panagiotopoulou O, Cleuren SGC, Mehari AH, Hutchinson MN, Evans AR., Caldwell MW, Lee MSY. 2021. Plicidentine and the repeated origins of snake venom fangs. Proc. R. Soc. B. 288(1956): 20211391
[v] Reeder, TW, Townsend, T, Mulcahy, DG, Noonan, BP, Wood PL Jr, Sites JW Jr, Wiens JJ. 2015. Integrated analyses resolve conflicts over squamate reptile phylogeny and reveal unexpected placements for fossil taxa. PLoS One 10(3): e0118199.
[vi] Sharpe, HS, Powers, MJ, Zietlow, AR, Evans, DC. Venom-assisted feeding in mosasaurs implied by comparative mandibular biomechanics[abstract]. In: 82nd Annual Meeting of the Society of Vertebrate Paleontology; 2022 Nov 2-5; Toronto, Ontario; 317.
[vii] Yi, HY, Norell, MA. 2013. New materials of Estesia mongoliensis (Squamata: Anguimorpha) and the evolution of venom grooves in lizards. Am Mus Novit 3767: 1-31.
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