This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Museum fossil halls can be overwhelming. There’s so much to see. Towering skeletons, bones behind glass, dozens of text placards, and looping multimedia displays, all competing with each other for awe and attention. It’s easy to breeze through lest you become fossilized in the hall yourself. But take your time and secrets may jump out at you. One of my favorites is in hidden in an upstairs alcove at the Natural History Museum of Los Angeles’ Dinosaur Hall. It’s a curiously-placed shark tooth.
The tooth isn’t by itself. The Cretaceous fossil is nestled against the neck vertebrae of a Pteranodon - one of the most charismatic of the flying pterosaurs - known to experts as LACM 50926. Even if you know what you're looking for, it can take a moment for it to pop out from the osteological background. But it’s there, the triangular, serrated profile the remnant of a large shark called Cretoxyrhina mantelli that used to swim a warm seaway divided North American in two circa 75 million years ago.
This fossil, paleontologists Dave Hone, Mark Witton, and Michael Habib note in a study of the fossil, is an association. It puts Pteranodon and Cretoxyrhina in the same place at the same time, the fossils buried way back in the Late Cretaceous. And it's a rare one. Of over a thousand Pteranodon fossils collected so far, only seven have been found with signs of interactions with sharks. The question is what kind of interaction brought this Cretoxyrhina tooth to come to rest against the neck bone of the Pteranodon.
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The Pteranodon bones don’t show bite marks - as other fossils chomped on by Cretoxyrhina do - and the tooth tip isn’t jammed into the bone. All the same, Hone and colleagues write, there is an “intimate association of the fossils” in which the tooth is “wedged” beneath part of the Pteranodon vertebra. It seems unlikely that the tooth became firmly nestled in this spot by chance, and so it may be evidence of the shark biting the pterosaur.
The shark could have scavenged on the Pteranodon after the flying archosaur died, its carcass perhaps floating on the surface or settling on the bottom. Then again, Pteranodon is thought to have been a fish-eating species that was able to launch from the water as some modern seabirds do. Perhaps one such Pteranodon was in repose, bobbing along, when assaulted from below by Cretoxyrhina. It’s a scene both alien and familiar, an interaction played out tens of millions of years before tiger sharks and young albatrosses would play out the same violent dance. Seek out the display, if you have the chance. It's an opportunity to look, and wonder, about what a now-static monument might tell us about ancient life.
Top image by Mark Witton, from Hone et al 2018.