January 30, 2012
How an Ankylosaur Went Out to Sea
About 110 million years ago, an ankylosaur settled on the bottom of a Cretaceous sea. This was no place for a dinosaur. No dinosaurs were adapted to a marine lifestyle, and the heavily armored ankylosaurs were probably the least suited to paddling around in the water. Yet, almost a year ago, shovel operator Shawn Funk found an ankylosaur in the marine, Early Cretaceous sediments at a Suncor mine in northern Alberta. How did the dinosaur get there?
Donald Henderson, curator of dinosaurs at the Royal Tyrrell Museum, explained how this dinosaur died, was preserved and was discovered in a recent lecture for the Royal Tyrrell Museum Speaker Series. Almost everything about the discovery was lucky. The dinosaur just happened to settle in a place where sediment quickly covered its body; the carcass was not torn apart by scavengers; the shovel operator who stumbled across the ankylosaur recognized that he found something potentially significant and the discovery of the dinosaur in the mine meant that paleontologists had lots of heavy machinery on hand to help excavate the skeleton.
But the strangest aspect of the find is the ecological context of the dinosaur. This ankylosaur must have lived along the coastline of the great Western Interior Seaway which once split North America into two. But that was many, many miles away from where the skeleton was found. Exactly how the dinosaur died is unknown, but as Henderson notes, the carcass undoubtedly floated upside-down through the sea. The gases from decomposition gave the body enough buoyancy to travel—what paleontologists commonly refer to as a “bloat and float” scenario.
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I love that they put the lecture up in this way! More museum need to do that! In that vein, check out the New Zealand talk by Craig Dylke.
This ankylosaur reminds me of Nothronychus graffami. It too was found tens of miles out at sea from the nearest land and yet, like the ankylosaur, it was fairly complete. Too bad Aletopelta ( http://accpaleo.wordpress.com/2010/04/07/critters-abroad-aletopelta/ ) wasn’t as lucky. Just the hip region was preserved, but i can’t complain too much since he is an endemic California dinosaur.
This also reminds me of the Niobarasaurus material collected from Smoky Hill Chalk (obviously marine) in Kansas. There is a rather infamous (to KU grad students) display in the museum on campus proposing that ankylosaurs were marine or at least lived in near shore environments.
http://www.oceansofkansas.com/Dinosaur.html
This is like the ankylosaur in the San Diego Natural History Museum, found in the Pt. Loma Formation (Aletopelta): http://www.sdnhm.org/archive/exhibits/mystery/fg_ankylosaur.html
Of course Scelidosaurus was a victim of bloat and float too, being found in marine deposits at Lyme Regis. Perhaps thyreophorans were particularly vulnerable to being swept out to sea for some reason.
Our still-fuzzy-on-the-details Alaskan hadrosaur, Lizzie, was also found in marine sediments.
One of Jack Horner’s earliest papers (1979 – J. Paleo) summarizes dinosaur fossils from the Bearpaw Shale of Montana (Maastrichtian, offshore marine), and at the time it turned out that there were more ankylosaurid skeletons known marine deposits than from terrestrial deposits, surprisingly enough.
There are a surprising number of dinosaurs found in marine sediments in North America; in fact, according to Schwimmer (1997), all east coast dinosaurs are from marine sediments and thus examples of bloat and float (or perhaps only maastrichtian dinosaurs).
Aletopelta is perhaps one of the more interesting cases, because it’s encrusted with oysters and has some weird taphonomic damage to the hindlimb bones.
An alternative taphonomic explanation (and possibly more likely) is that these ankylosaurids were hanging out near rivers, and their carcasses being dumped out by rivers; I’ve never bought the coastal hypothesis, simply because most carcasses that end up near the coast tend to float towards the beach (and not in the opposite direction, against the waves). Granted there are variations (rip currents, etc.) but I feel that washing terrestrial vertebrates out to sea is more common via rivers.
@ Boessse: I’ve heard that too.I remember hearing somewhere that the teeth of ankylosaurs would have been more suited to munching the soft vegetation found in riparian habitats.
And forget, the two most complete dinosaurs in California (a pair of Saurolophus skeletons collected by Chester Stock) were found in the marine sediments of the Panoche Hills in Fresno County.