Is a Fossil Trackway Proof of Pack Hunting in “Raptors”?
For many years scientists have speculated that the speedy, carnivorous raptors (more appropriately termed dromaeosaurs), such as Velociraptor and Deinonychus were pack hunters. Movies such as “Jurassic Park” popularised theories about these animals, making them out to be vicious, ruthless, yet intelligent killers.
Hollywood’s depiction of these swift hunters stretched the truth to say the least, the likes of Velociraptor became a man-sized predator when in truth it stood about 1 metre tall. Even the sickle shaped foot claw on the second toe was blown out of proportion to some extent. Movie directors wanted to show this claw as a razor sharp scythe capable of tearing victims to pieces, recent studies indicate that in Velociraptor’s case the claw (which barely exceeded 9 cm in length was not a terrible slashing weapon. It may have had a sharp point and been an effective “grappling hook” to help the animal jump onto and stay on its larger victims.
However, the dromaeosaurs did come in different sizes, although the basic body plan – swift biped with a stiffened tail to assist with balance and sharp turns, remains the same of the genera associated with this family. Dinosaurs such as Utahraptor represent very large and formidable beasts.
Now evidence to back up how raptors have been depicted in the movies has emerged from China. A recently excavated fossil trackway shows six dromaeosaurs tracks, all moving in the same direction. If the tracks were made at the same time (and there is some palaeontological data to suggest this), then could this be a pack of raptors out on patrol?
A joint international team drawn from the University of Chicago and the Qingdao Institute of Marine Geology have uncovered a series of footprints that capture the moment when six equally sized dromaeosaurs walked side by side next to some flowing water, possibly a stream or small river.
The fossil site is in the Shandong Province of eastern China and the sediments have been dated to between 120 -100 million years ago, placing the footprints in the Cretaceous period. This is the first fossil evidence palaeontologists have of possible pack behaviour in these animals. Ripple marks also preserved in the rock strata indicate that the trackways were covered shortly after they were made, thus strengthening the hypothesis that this evidence represents a group moving together.
This site has already provided a number of sets of dinosaur prints, providing a great deal of material for ichnologists (the term used to describe scientists who specialise in studying trackways). The report on the evidence for dromaeosaur pack hunting plus some additional information on the trackways of a smaller dromaeosaur found nearby have been published in the European scientific journal “Naturwissenschaften”.
The picture on the left shows one of the trackways left by the larger dromaeosaur. The line drawing on the top right depicts a single footprint (made by the left foot). The picture on the bottom right with the 5cm scale bar is a picture of a footprint made by a smaller dromaeosaur at the same site (left foot).
In the trackways, two clear toe prints can be seen. The third toe print (actually representing the second digit on the foot) is only partial, indicating that this toe, the one with the sickle claw was held off the ground. Scientists had suspected that the sickle claw was raised off the ground, examination of the joints in the second toe bones indicated that this was probably the case. These beautifully preserved tracks confirm the theories, that indeed the sickle toe was carried off the ground.
The larger tracks contain foot prints about 28 cm long and 12 cm wide, these indicate the presence of larger dromaeosaurs in this area, possibly about the size of Deinonychus from North America. Ironically, these tracks may represent an animal about as big as the over-sized Velociraptors as seen in the movie “Jurassic Park”. The second set of tracks represent a much smaller raptor, possibly the same size of a Velociraptor (1 metre tall at the hips).
Although it is not possible to identify the species that made these tracks, the larger trackway provides the first evidence of the presence of big dromaeosaurs in China. Ichnologists have named the bigger dromaeosaur Dromaeopodus shandongensis. The name means “swift footed from Shandong Province”. The smaller tracks have been ascribed to a new genus of raptor called Velociraptorichnus.
The parallel trackways do not demonstrate pack behaviour, nor can we assume that these animals adopted any sophisticated group hunting strategies like packs of mammals, such as wolves or lions. However, this is the first evidence of potential social groups in dromaeosaurs, plus proof that the second toe was held off the ground – just like in the movies.
Films depict the raptors as deadly, pack predators using cunning to outwit their victims. Is this too the stuff of fiction or will we find evidence to support this theory as well?
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