November 1, 2012
If an Allosaurus fell in the Jurassic, would it leave a trace fossil? We know that resting dinosaurs can leave body impressions behind, as shown by a theropod trace found in St. George, Utah, but what if a dinosaur lost its footing and fell over onto a mudflat or sand dune? Such events surely must have happened. The question is whether the embarrassing moments ever became set in stone.
A trace fossil would be the obvious mode of preservation for a dinosaur fall. A messy footprint, recording the slip, paired with a body impression would be a gorgeous snapshot of a dinosaur’s tumble. Sadly, no one has yet found such a fossil, but paleontologists have identified a more subtle clue of a dinosaur fall. In 2007, paleontologist Oliver Wings and colleagues described a Middle Jurassic dinosaur tracksite described in China. Among the dozens of tracks was what appeared to be a slip footprint–parallel grooves made when the dinosaur’s foot slipped backward or foreword over the wet mud of the ancient environment.
But tracks and other impressions may not be the only way dinosaur falls might be recorded. When I brought up the idea of a fossilized dinosaur tumble on Twitter yesterday, Sam Barnett brought up Allosaurus gastralia, or rib-like belly bones, that showed signs of fracture due to a fall. I hadn’t heard of these specimens before, so I checked a review of theropod pathologies published by Ralph Molnar in 2001. The broken bones got a nod, with a reference to a more thicker biography of dinosaur injuries called Dinosores published two years before by Darren Tanke and Bruce Rothschild. I kept pulling at the thread, hoping to find something more.
A 1998 New Scientist story by Jeff Hecht called “The deadly dinos that took a dive” outlined the idea. In a preview of research he was getting ready to show off at that year’s DinoFest symposium in Philadelphia, Rothschild mentioned that an Allosaurus specimen showed “exactly the pattern of fractures that would be caused by a belly flop onto hard ground while running.” But I wanted to know more. What, exactly, was it about the breaks that indicated a clumsy fall?
Unfortunately, I wasn’t able to find any more detailed information. I don’t have any doubt that Allosaurus and other dinosaurs suffered fractures from falls. That’s an inevitable interaction between biology, geology and physics when you have animals walking and running around the Mesozoic. The trick is connecting the pathology with the cause. Still, I have to wonder if virtual models that estimate bone stress–such as the finite element analysis models used in bite mechanics studies–might help paleontologists investigate what happened to dinosaurs when they fell. If paleontologists can trip up a virtual Allosaurus and investigate how those computerized bones respond to the stress of a fall, maybe researchers can predict where breaks might occur and compare the models to the fossil record. For now, though, we can do little more than imagine an Allosaurus falling face-first on a mudflat, shaking itself off, and ignoring the pain in its ribs as it tromped off.
[Hat-tip to Heinrich Mallison for pointing me to the trackway study, on which he was one of the coauthors.]
Claessens, L. 2004. Dinosaur gastralia; origin, morphology, and function. Journal of Vertebrate Paleontology 24, 1. 89-106
Molnar, R. 2001. Theropod paleopathology: A literature survey. pp 337-363 in Tanke, D. and Carpenter, K. eds. Mesozoic Vertebrate Life. Bloomington: Indiana University Press.
Rothschild, B., Tanke, D. 2005. Theropod paleopathology: state of the art review. pp 351-365 in Carpenter, K. ed. The Carnivorous Dinosaurs. Bloomington: Indiana University Press.
Tanke, D., Rothschild, B. 2002. DINOSORES: An annotated bibliography of dinosaur paleopathology and related topics—1838–2001. New Mexico Museum of Natural History and Science. Bulletin, 20.
Wings, O., Schellhorn, R., Mallison, H., Thuy, B., Wu, W., Sun, G. 2007. The first dinosaur tracksite from Xinjiang, NW China (Middle Jurassic Sanjianfang Formation, Turpan Basin) – a preliminary report. Global Geology 10, 2. 113-129
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