Monday, 8 April 2013

T is for Troodon

Last week in our Albertan dinosaurian alphabet we talked about the hadrosaur Saurolophus, and now we're going to talk about a well known theropod in ' T is for Troodon'. 

Troodon is a genus of theropod dinosaur from the Late Cretaceous (about 75 million years ago) of North America, with fossils being found as far north as Alaska and as far south as New Mexico. The name means 'wounding-tooth' in reference to the small, pointed, serrated teeth that are characteristic of this dinosaur. As a carnivore, it may have used these serrations much in the same way that you would use a steak knife to cut through meat. However, these teeth are also similar to herbivorous dinosaurs like Stegoceras and lizards, suggesting it may have been an omnivore. In fact their teeth were so similar to pachycephalosaur teeth that for a long time, the pachycephalosaurs were known as troodontids until Canadian palaeontologist Charles Sternberg noted their differences and named the group Pachycephalosauridae in 1945 [1]. Troodon was a relatively small theropod, reaching 2.5 m in length and stood less than a metre tall. It may have weighed as much as 50 kg. It had a large sickle-shaped claw on each foot that it was able to retract and raise while running, and was likely a fast runner. The eyes of Troodon were quite large compared to other dinosaurs, which may mean it was nocturnal, and they pointed forwards, which likely gave it binocular vision and depth perception. It also had the largest brain to body size ratio of any other dinosaur, suggesting it was a more intelligent dinosaur.
Image of Troodon formosus teeth from The Childrens Museum of Indianapolis
The genus was first named from a single tooth from southern Alberta, which is problematic when trying to determine the rest of the animal, as teeth can sometimes be very similar between genera and species. Again, we can highlight the difficulty in naming species from fossils. The first non-tooth remains were named in 1932, but placed in a separate genus (Stenonychosaurus), and a more complete specimen found in 1969 was as well. However, Philip Currie united Troodon, 'Stenonychosaurus' and 'Pectinodon' under the genus Troodon, suggesting they are all the same genus [2]. Of course, as is the story with many dinosaurs, this has been questioned and reviewed since. A more recent study suggests that what we now think of as Troodon formosus is most likely not a single species, or even a single genus especially since many of these identifications are based on single teeth [3]. They also note that since the holotype is based on a single tooth, the name Troodon may be a nomen dubium, which literally means 'dubious name'. Obviously significant work is required to determine what is going on in the complicated history of Troodon

Egg nests of Troodon formosus have been found in Montana that have revealed many aspects about the reproduction of Troodon. They laid eggs two at a time, over the period of a day or so, and incubated the eggs by covering them with their body or with soil [4]. Eggs are found roughly in pairs, suggesting they had two functioning oviducts, and appear to have a reproductive system that is intermediate between crocodiles and birds, as we would expect. Furthermore, their eggs were also intermediate in size between crocodiles and birds. The nests were dish-shaped, 100 cm in diameter, and had 16-24 eggs. 

That's it for Troodon. You can see a feathered Troodon at Jurassic Forest, and remember that we will be opening in less than 3 weeks! Another interesting fact about Troodon: it is Phil Currie's favourite dinosaur! Next week we'll be talking about the only 'U' dinosaur from Alberta, a ceratopsian. 

Other 'T' dinosaurs from Alberta:

1. Sternberg, C.M. 1945. Pachycephalosauridae proposed for dome-headed dinosaurs, Stegoceras lambei, n. sp., described. Journal of Paleontology 19: 534-538
2. Currie, P.J. 1987. Bird-like characteristics of the jaws and teeth of troodontid theropods (Dinosauria, Saurischia). Journal of Vertebrate Paleontology 7: 72-81.
3. Zanno, L.E. et al. 2011. A new troodontid theropod, Talos sampsoni gen. et sp. nov., from the Upper Cretaceous Western Interior Basin of North America. PLoS ONE 6: e24487. doi:10.1371/journal.pone.0024487
4. Varricchio, D.J.  et al. 1997. Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits. Nature 385: 247-250.

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