Fossil Predators of the Wapiti Formation

The late Cretaceous rock unit exposed throughout much of northwestern Alberta is known as the Wapiti Formation, named by George Dawson for the river along which many of its outcroppings can be found. The Wapiti Formation overlaps in age with other rock units from the southern parts of the province, namely the Dinosaur Park, Bearpaw, and Horseshoe Canyon Formations. However, while these southern formations have been extensively researched for over a hundred years, the Wapiti Formation has been largely ignored by professionals until fairly recently. Lacking vast swaths of badlands where fossils can be found with relative ease, Alberta’s northwest is mostly covered by dense forests and farmlands, which means getting to exposures and looking for fossils usually isn’t easy.

This isn’t to say that there aren’t fossils here worth looking for. Quite the opposite in fact- with many of the dinosaur-rich zones of the Wapiti equivalent in age to the marine Bearpaw Formation further south, northwestern Alberta contains a unique and mysterious period of dinosaur evolution in North America.

So what’s in the rocks up here? Well, it’s mostly the same types of creatures you’ll find in similar aged rocks elsewhere in the province. But the species themselves are different, and many seem to be endemic to this region alone. As for plant eaters, there’s obviously the famous bonebeds of the battering ram-faced ceratopsian Pachyrhinosaurus. Duck-billed hadrosaurs also abound in the Wapiti Formation, but so far only one species has been identified (stay tuned though- this may not be the case for long). A wonderful specimen of the well-known hadrosaur Edmontosaurus regalis was found west of Grande Prairie with skin impressions from the head and neck, including a fleshy crest on the head- a first for this common dinosaur. Remains of the big armored ankylosaurs are comparatively rare, but from footprints and a few teeth we know they were here.

As for the remains of predatory dinosaurs, they’re also tantalizingly scant. It might be surprising to know that many of our big herbivore bonebeds also preserve tyrannosaur teeth, shed from the jaws of the animals as they fed at the sites. This is as frustrating to palaeontologists as it is exciting. We don’t have good tyrannosaur bones from the Wapiti yet, and you can’t determine a tyrannosaur species from teeth alone. The famous tyrant Albertosaurus is a reasonable candidate for the dominant predator of the Wapiti Formation due to similarity in age to fossils from this species further south. However, this is a guess at best for now, and we don’t know yet exactly what type of tyrant carnivore prowled Alberta’s northwest.

Gorgosaurus

The tyrannosaur Gorgosaurus, a close relative of Albertosaurus.

While small predatory dinosaurs in Alberta are known from fewer complete skeletons than big ones, there are just enough remains known from the Wapiti Formation to give a name to a small, snappy predator. Amongst the jumble of Pachyrhinosaurs fossils from Pipestone Creek has also been found bits and pieces of small dromaeosaur (known to most people as ‘raptors’). This turkey-sized feathered predator, dubbed Boreonykus by palaeontologists in 2015, is known from tantalizingly few fossils- some claw bones, shed teeth, and a single skull bone. This however was just enough to give scientists some picture of what Boreonykus was, and it seems as though it may have been very closely related to Velociraptor. The teeth of troodontids, the owl-eyed and big-brained cousins to the dromaeosaurs (and birds), pop up here and there as well. Though troodontids had pretty distinctive teeth, like tyrannosaurs they’re hard of not impossible to tell apart beyond the family level, and troodontid bone fossils are notoriously rare anywhere.

Boreonykus

The holotype of Boreonykus, an isolated frontal bone.

All predatory dinosaurs belong to the group known as the theropods. However, to paleontologists some of the most interesting theropods are ones that evolved from carnivorous ancestors but went on to eat plants. Plant-eating theropods tended to have toothless beaks, birdlike bodies, and all around were pretty strange. Examples of these include the ornithomimids, which looked and behaved almost identically to the modern ostrich. There was also the bizarre, crested oviraptorosaurs, something like a cross between a cassowary and a turkey. The faintest traces of these dinosaurs, mainly footprints and a few isolated bones, are known from the Wapiti Formation, and their presence in similar ecosystems throughout the province means there’s probably more of them out there waiting to be found.

Diversity

A selection of dinosaurs known from the Wapiti Formation- by Nicholas Carter.

by Nicholas Carter


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