Monday, 25 March 2013

R is for Richardoestesia

Last week, we discussed the giant pterosaur, Quetzalcoatlus. This week, we're back to dinosaurs from Alberta, with 'R is for Richardoestesia', which is the only dinosaur from Alberta that starts with 'R'.

Richardoestesia was a medium-sized theropod that lived mainly in the Late Cretaceous (76-75 million years ago) of North America. The holotype, a pair of lower jaws, was found by well known Canadian palaeontologist Charles Sternberg in Dinosaur Provincial Park in 1917. However, it remained un-named until 1924, when Charles Gilmore named a new genus Chirostenotes, and referred the jaws to this new genus. However, the rest of the skeleton of Chirostenotes was obviously from an oviraptorsaur, and this jaw was not, again leaving these jaws nameless. In 1990, Phil Currie and two colleagues named a new species Richardoestesia gilmorei, with these jaws as the holotype. The genus name comes from Richard Estes, to honour his significant research in small vertebrates in the Cretaceous, while the specific epithet honours Charles Gilmore, for his attempt to name it in 1924. These jaws are long and slender, with relatively small, finely serrated teeth having a whopping 5-6 denticles per mm. This high density of serrations is what distinguishes Richardoestesia from other genera. Although the holotype is actually represented by immature teeth, there are many, many mature shed teeth from older individuals in the fossil record [1]
Photo showing the serrations and examples of teeth from Richardoestesia gilmorei (left) and R. isosceles (right) from Larson and Currie [1]. Scale bar = 1mm.
Unfortunately, because Richardoestesia is known primarily from teeth, there is very little known about this dinosaur. Based on the size of the teeth, it is estimated to be a medium-sized theropod, around 100 kg. The teeth also tell us that it was a coelurosaur (which is a very broad group of dinosaurs), and that it was a carnivore based on the serrations. In fact, it was possibly a piscivore (fish-eater), at least this has been suggested for R. isosceles [2]. While Richardoestesia-like teeth have been reported from several other formations, a recent study has suggested that many of these teeth are significantly different from each other (7 different morphotypes), and that they may represent different species [1]. This study suggests that R. gilmorei is only definitely known from the Dinosaur Park Formation, and that it is distinctly different from  R. isosceles. This study was actually very important as it suggested that the number of small theropod dinosaurs in the Late Cretaceous of North America had been greatly underestimated. Previously, the lack of small-sized theropods was not fully understood as other contemporaneous ecosystems had several, while North America did not. While others tried to explain this lack, Larson and Currie looked at over 1100 fossil teeth from this area and suggested that it is possible to separate out species just from teeth, which brought the number of possible small theropod species in western North America to 23. 

Although there wasn't a lot to say about Richardoestesia as an animal, I hope this gave a bit of an insight into some of the challenges that palaeontologists face when it comes to fossils. I also hope that it revealed some of the painstaking methods that some palaeontologists go through to find information. 1100 dinosaur teeth! Wow!

Next week we'll be talking about another dinosaur from Alberta, but I haven't decided which one yet. Hadrosaur or theropod? Let me know which one I should do! 

1. Larson, D.W., and Currie, P.J. 2013. Multivariate analyses of small theropod dinosaur teeth and implications for paleoecological turnover through time. PLoS ONE 8: e54329. doi:10.1371/journal.pone.0054329
2. Sankey, J.T. 2001. Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas. Journal of Paleontology 75: 208-215.

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