Monday, 25 February 2013

N is for Nichollssaura

This week for the Albertan dinosaurian alphabet, we bring you 'N is for Nichollssaura'. The first thing to point out, is that Nichollssaura is not a dinosaur, but a marine reptile called a plesiosaur. I was struggling to find a dinosaur genus that started with the letter 'N' from Alberta (there are none that I could find), and a Twitter follower (thanks Dan!) suggested Nichollssaura. Although not a dinosaur, it is a very well preserved fossil found in Alberta. 

Although Alberta is better known for dinosaur and terrestrial fossils, there are actually a large number of marine fossils found as it was once covered by a large body of water called the Western Interior Seaway. It stretched from the Arctic Ocean to the north, all the way down through the Northwest Territories, Alberta, and western US, down to the Gulf of Mexico. It existed during much of the Cretaceous, and is the reason why Alberta is full of marine fossils. Large marine reptiles like plesiosaurs, pliosaurs, and mosasaurs were common fauna during this time, and can be found often in marine deposits in Alberta from this time. The dinosaurs in Alberta are of ages younger than the seaway, in the very Late Cretaceous. 
Image showing the extent of the Western Interior Seaway (from the USGS)
Now this is where our feature animal Nichollssaura comes in. Nichollssaura had a typical plesiosaurian shape, with a long neck and small head, that lived approximately 110 million years ago. The only known fossil was found in a Syncrude Mine near Fort McMurray, when a large electric shovel knocked off part of the skeleton in 1994. Fortunately, the worker recognised that there was a fossil, stopped digging, and notified the correct people who were able to excavate the fossil. It was first named 'Nichollsia' in honour of Elizabeth "Betsy" Nicholls, former curator of marine reptiles at the Royal Alberta Museum of Palaeontology [1]. However, 'Nichollsia' was preoccupied by a crustacean, and so was renamed Nichollssaura [2]. The single specimen is nearly complete, and was a juvenile or young adult, as seen from the lack of fusion in the vertebrae. It was 2.6 m long and had four flipper-like limbs used for propelling it through the water. The discovery of Nichollssaura filled a 40 million year gap in plesiosaur diversity in the Early Cretaceous. Before this find, there was a huge gap with no plesiosaurs, and this helped us to better understand plesiosaur evolution. This nearly complete, extremely well preserved fossil has revealed a wealth of morphological information on plesiosaurs of this age. 
Artists impression of Nichollssaura by ArthurWeasley
Next week, we'll move on to 'O' with a fairly well-known theropod dinosaur. 

1. Druckenmiller, P.S., and Russell, A.P. 2008. Skeletal anatomy of an exceptionally complete specimen of a new genus of plesiosaur from the Early Cretaceous (Early Albian) of northeastern Alberta, Canada. Palaeontographica Abteilung A 283: 1-33.
2. Druckenmiller, P.S., and Russell, A.P. 2009. The new plesiosaurian genus Nichollssaura from Alberta, Canada: replacement name for the preoccupied genus Nichollsia. Journal of Vertebrate Paleontology 29: 276.

Monday, 18 February 2013

M is for Mojoceratops

Moving on to the letter 'M', we welcome another ceratopsian (horned) dinosaur to our Alberta dinosaurian alphabet with Mojoceratops

Mojoceratops has an interesting history, and invokes discussion of a common problem in palaeontology that we deal with constantly. As is often the case, Mojoceratops is known from partial remains, and in this case, it is known from several skull pieces, representing nearly an entire skull. First, Lambe found a partial skull, which he called "Eoceratops canadensis" in 1915 [1]. Unfortunately, this was based on a skull with no descriptive characters, and furthermore, is a juvenile. A few years later, Brown found another partial skull and named it "Chasmosaurus kaiseni", again from partial remains with few descriptive characters (albeit more than E. canadensis[2]. Even more difficult, a further specimen was named "Chasmosaurus canadensis". This specimen is the type specimen, of the species Mojoceratops perifania named by Nick Longrich in 2010, along with the previously mentioned specimens and other new specimens [3]. You might think the name is a bit funny, and you would be right. First of all, genus and species names are almost always derived from Latin or Greek, and 'mojo' is neither: it's derived from "20th century African-American English" [3]. Furthermore, it means just what you think it means. Longrich describes a mojo as "a magic charm or talisman often used to attract members of the opposite sex", referring to its large frill that may have been used in courtship. He distinguishes it from Chasmosaurus because it lacks a forward-curving process on the frill and reduced postorbital horns found in Chasmosaurus. Currently recognised specimens come mainly from southern Alberta in the Dinosaur Park Formation, while some may be found in southern Saskatchewan as well. The fossils come from the Late Cretaceous, about 75 million years ago. 
Artists impression of Mojoceratops perifania by Nobu Tamura. Note the large frill and orbital horns.
The complicated history of Mojoceratops makes it a somewhat controversial taxon. It does seem to be recognised as separate from Chasmosaurus, because it lacks specific features found in Chasmosaurus (like the curved processes and short orbital horns). However, the rules of zoological nomenclature are clear: the name that was first given to an animal takes precedent over any other name given to it, unless there is a valid reason not to. In the case of "Eoceratops canadensis", its non-descriptive and juvenile nature provide a good reason NOT to use this as a name. Moving to "Chasmosaurus kaiseni" provides us with another challenge. It is recognisably different from Chasmosaurus, and therefore should be given a new generic (as in the first name in species). Normally in these cases, a new generic name is erected, while the specific epithet ("kaiseni") is kept, to recognise the original name. However, Longrich chose to erect both a new generic and specific name. In one study, they refer to it as Mojoceratops kaiseni, recognising the original specific name [4]. This is often a problem in palaeontology, especially when looking at fossils that were found in the early 1900's. Making this species even more controversial, a recent study questioned its distinctiveness from Chasmosaurus [4]

In general, it's a bit of a mess, but it is currently recognised as a valid taxon. Hopefully this has given you a bit of insight into the complicated nature of naming fossils, and the struggles that follow.  Next week we'll carry on with the letter 'N', with an armoured dinosaur! 

Other 'M' dinosaurs found in Alberta:
Monoclonius (also a controversial ceratopsian)
Montanaceratops - a ceratopsian 

1 Lambe, L. 1915. On Eotriceratops canadensis, gen. nov., with remarks on other genera of Cretaceous horned dinosaurs. Canada Geological Survey, Museum Bulletin 12: 1-49.
2 Brown, B. 1933. A new longhorned Belly River ceratopsian. American Museum Novitates 669: 1-3.
3 Longrich, N.R. 2010. Mojoceratops perifania, a new chasmosaurine ceratopsid from the late Campanian of western Canada. Journal of Paleontology 84: 681-694.
4. Mallon, J.C., et al. 2011. Variation in the skull of Anchiceratops (Dinosauria, Ceratopsidae) from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta

Monday, 11 February 2013

L is for Lambeosaurus

Next up in our Albertan dinosaurian alphabet is 'L is for Lambeosaurus'. Lambeosaurus is another duck-billed dinosaur, or hadrosaur, from southern Alberta. Unlike last week's hadrosaur Kritosaurus, Lambeosaurus is known from many fossils and is very well known. 

Lambeosaurus was first named in 1923, despite some poorly preserved fossils being found and described about 20 years earlier by well-known Canadian palaeontologist Lawrence Lambe, which is where the name comes from. In fact, the type species is called Lambeosaurus lambei, with both the genus and specific epithet honouring for Lambe. It lived during the Late Cretaceous, about 75 million years ago. To repeat what I've said many times before about hadrosaurs, like others, it was capable of walking on two or four legs, or as we say, it was a 'facultative biped', which means it was capable of either. It was also a herbivore, and used its large 'battery' of teeth to grind down tough vegetation, and had a cheek-like structure that allowed it to chew its food. Another similarity to other hadrosaurs that I haven't mentioned previously is that it had 'ossified tendons' in its tail, which means the tendons were strengthened to keep the tail stiff. Lambeosaurus is also the type species for the group of hadrosaurs that typically have large, hollow cranial crests (the Lambeosaurinae), and it is no exception. These crests have a nasal cavity that runs through it, making it hollow, and was likely used to make noise for species recognition or social uses [1]. This is also supported by the fact that the crests are only present in adult individuals, and are not found in juveniles. 
Artists impression of Lambeosaurus magnicristatus showing the large cranial crest
Currently, only two species of Lambeosaurus are recognised, and they have only been found in Alberta. They are differentiated primarily by their crest. L. magnicristatus, as seen above, has an expanded blade-like crest, like a pompadour, while L. lambei has a thinner blade, and is described as a hatchet-like crest (as seen below). Lambeosaurus was about 9 metres in length, and 4 metres tall when standing on all fours. At one point, there were many species recognised, and several other species of smaller hadrosaurs were thought to be separate species. However, a re-evaluation of the groups showed that the smaller ones were actually juvenile Lambeosaurus, while other differences between species were thought to be sexual dimorphism [2,3]
Artists impression of possible growth stages and male/female variation within Lambeosaurus. Image by Nobu Tamura 
Both currently recognised species of Lambeosaurus are found in the Dinosaur Park Formation of southern Alberta. Other dinosaurs that live in this formation include ceratopsians (e.g. Centrosaurus and Styracosaurus, hadrosaurs (e.g. Corythosaurus and Parasaurolophus) and the theropod Gorgosaurus. This rock formation represents a highly diverse, and very well documented Late Cretaceous ecosystem, thought to be from a low-lying area with swamps, rivers, an floodplains [4]

That's it for Lambeosaurus! Next week, we'll talk about a ceratopsian dinosaur from southern Alberta. 

Other dinosaurs from Alberta that start with 'L':

1. Horner, J. R. et al. 2004. Hadrosauridae. In: Weishampel, D.B., Dodson, P., and Osmolska, H. (eds) The Dinosauria (2nd edition). Berkeley: University of California Press pp. 438-463.
2. Dodson, P. 1975. Taxonomic implications of relative growth in lambeosaurine dinosaurs. Systematic Zoology 24: 37-54.
3. Horner, J.R. 1979. Upper Cretaceous dinosaurs from the Bearpaw Shale (marine) of south-central Montana with a checklist of Upper Cretaceous dinosaur remains from marine sediments in North America. Journal of Paleontology 53: 566-577.
4. Eberth, D.A. The geology. Dinosaur Provincial Park. Indiana University Press, Bloomington (2005): 54-82.

Monday, 4 February 2013

K is for Kritosaurus

This week, we're back to dinosaurs from Alberta, with 'K is for Kritosaurus'. Kritosaurus was a hadrosaur (duck-billed) dinosaur from the Late Cretaceous (about 73 million years ago) of North America, including southern Alberta, New Mexico, and Texas. It is recognised by a crest in front of its eyes, but the exact form of this crest is unknown. It was similar to other hadrosaurs in size, at about 8 m long, walked on two or four legs, and like all hadrosaurs, it was a herbivore. It used its large battery of flat teeth to grind down tough plant material. The teeth were constantly replaced, unlike mammals which have only two sets of teeth. Unfortunately, its known from very partial remains, which has made its taxonomic affinities debatable. In the past, Kritosaurus has been synonymised with Gryposaurus and Hadrosaurus, but is currently considered to be a valid genus. 
Kritosaurus by Nobu Tamura
Kritosaurus was first discovered in the US, in a formation alongside other dinosaurs like the hadrosaur Parasaurolophus, the ceratopsian Pentaceratops, and theropod Saurornitholestes. The nasal crest may have been used for social displays. 

Kritosaurus is actually the only dinosaur that starts with 'K'  from Alberta. Next week, we'll talk about another hadrosaur (I know, there's a lot of hadrosaurs from Alberta!) with a neat crest.