I is for Irenesauripus and Ichnofossils!

This week we are going to do something a little bit different for the Alberta Dinosaurian Alphabet. This week, we have 'I is for Irenesauripus, and ichnofossils!

Irenesauripus is a type of ichnogenus, also known as a trace fossil or ichnofossil. Specifically, it is a kind of dinosaur footprint from the Cretaceous of North America. It was first discovered in the 1930's in Peace River, British Columbia, but has since been recorded in Alberta, the Yukon, and Texas. Albertan Irenesauripus tracks are typically found in the area of Grand Cache. These fossils are all three-toed and found in trackways. They represent an animal that walked on two legs (bipedal), walked on its toes (digits) rather than flat-footed, and had widely spaced impressions of the toes. They have evenly distributed weight, and show evidence of claws on each toe. In the original description, it was described as a theropod, and several studies have since agreed [1-3] while one has even gone further in declaring it a member of the Megalosauroidea [4]. These prints represent large theropods, as they are typically 28-40 cm in length. 

Example of Irenesauripus from Richard McCrea

As mentioned before, 'I' is also for ichnofossils, and ichnology. Ichnology is the study of trace fossils, which includes anything other than actual remains of animals, but rather they show behaviour. These include trackways or footprints, burrows, or even coprolites (fossilised feces). The great thing about trace fossils is that they can give us direct evidence of behaviour, which traditional fossils (like bones) typically do not. For example, a large number of trackways showing several different kinds of tracks can show a herbivore being attacked by carnivores. Or, a number of tracks from the same type of animal can show that they travelled in a herd or pack. Fossilised burrows can show us how an extinct animal made its burrow and how it lived. Unfortunately, more often than not, it is very difficult to associate a trace fossil with a specific animal. We can make assumptions based on the size of fossil and the animals that we know were around at the right time, but there is often no way we know for sure what animal made the tracks. This is why trace fossils are called ichnospecies rather than species, because they do not necessarily represent an entirely new species. Irenesauripus was a theropodian ichnogenus that would have represented a large theropod because of the size of print as well as stride (about 1 m in length). 

That's it for this week. Hopefully we introduced you to another side of palaeontology that you may not have thought about before, as well as a new area in Alberta where dinosaur fossils can be found! Stay tuned for 'J' next week, which unfortunately will be from outside of Alberta. 

Other 'I' dinosaurs from Alberta:
Ichthyornis - a bird (remember, birds technically are dinosaurs!)

References:
1. Kuhn, O. 1963. Pars 101. Ichnia Tetrapodorum. In F. Westphal (ed.), Fossilium Catalogus. I: Animalia. Ysel Press, Deventer, Netherlands. 176 pages
2. M. G. Lockley. 1992. Cretaceous dinosaur-dominated footprints assemblages: their stratigraphic and palaeoecological potential. In N.J. Mateer & P.-J. Chen (eds.) Aspects of Cretaceous Geology. China Ocean Press, Beijing, 269-282.
3. Gangloff, R. A., et al. 2004. An early Late Cretaceous dinosaur tracksite in central Yukon Territory, Canada. Ichnos 11: 299-309.
4. Haubold, H. 1971. In O. Kuhn (ed.) Handbuch der Palaeoherpetologie. Part 18. Ichnia Amphibiorum et Reptiliorum Fossilium. Gistav Fischer Verlag, Stuttgart. 1-124.