Saturday, 3 October 2015

Ugrunaaluk kuukpikensis: A new species of Hadrosaurid Dinosaur from the End Cretaceous of Alaska.

The Prince Creek Formation of Northern Alaska is noted for the production of numerous End Cretaceous Dinosaurs, with at least thirteen different species thought to have been present. One of the most numerous of these is a Hadrosuarid Dinosaur, known from thousands of dis-articulated bones known from a single horizon, the Liscomb Bonebed. These bones appear to have come from an animal similar to the widespread and numerous Late Cretaceous genus Edmontosaurus, and have often been referred to as Edmontosaurus sp. or even Edmontosaurus regalis (one of two described species in the genus), although recent studies have cast doubts upon this designation. The Liscomb Bonebed material has proved difficult to analyse taxonomically, as it appears to come almost entirely from juvenile animals, and most Dinosaur species are identified using characteristics seen in adult animals.

In a paper published in the journal Acta Palaeontologica Polonica on 22 September 2015, Hirotsugu Mori of the Department of Geosciences at the University of Alaska Fairbanks, the University of Alaska Museum and the Saikai City Board of Education, Patrick Druckenmiller of the University of Alaska Museum and the Department of Geosciences at the University of Alaska Fairbanks and Gregory Erickson of the Departmentof Biological Science at Florida State University re-examine the Liscomb Bonebed material and formally describe it as a new species.

As noted before, almost all the Liscomb Bonebed material is attributed to juvenile animals, whereas almost all Dinosaur species are described from adult specimens, making direct comparisons difficult. However the Liscomb Bonebed clearly shows closer affinities to the Late Cretaceous Hadrosaur Edmontosaurus than to any other Dinosaur, and Edmontosaurus is one of the most common known Cretaceous Dinosaurs, with a large number of specimens described from across western Canada and the western United States. This enabled Mori et al. to study the ontogeny of Edmontosaurus, and document the way in which its bones grew and changed as it got older, from which they conclude that the Liscomb Bonebed material represents a new species of Hadrosaur, less closely related to the two species of Edmontosaurus than they are to one-another, but more closely related to these two species than to their three closest known relatives to date, Shantungosaurus, Kerberosaurus and Kundurosaurus, all of which are known from northeastern Asia. This new species is named Ugrunaaluk kuukpikensis, where 'Ugrunaaluk' means 'ancient grazing animal' in the Alaskan Iñupiaq language, spoken in the area where the material was found, and 'kuukpikensis' means 'from Kuukpik', the Iñupiaq name for the River Colville, besides which the Liscomb Bonebed outcrops.

Cranial reconstruction of Ugrunaaluk kuukpikensis from the early Maastrichtian Prince Creek Formation in left lateral view. Photograph (A) and bone interpretation (B). Mori et al. (2015).

The fauna of the Prince Creek Formation is of particular interest to palaeontologists studying the Late Cretaceous of North America, as it produces the most northerly known material from the island of Laramidia, which comprises much of the western United States and Canada, and which was cut off from the rest of North America by the Western Interior Seaway, an intracontinental sea created by the high sea levels associate with the warm Cretaceous climate. The climate in which the Prince Creek Formation was laid down is interpreted as having been very cool by Late Cretaceous standards, with a mean annual temperature of 5–6 °C, and a distinct cold season, which probably did not produce permanent winter-long freezing, but certainly would have had cold periods with sub-zero temperatures. These deposits have produced a wide variety of Dinosaur species (including at least one Bird) as well as a range of Mammals, but have produced no members of unequivocally cold-blooded groups such as Crocodilians, Champsosaurs (an extinct group of Crocodile-like Diapsid Reptiles), Choristodires (also Crocodile-like Diapsid Reptiles), Squamates (Snakes and Lizards) or Turtles.


Study area in northern Alaska, USA (A) and location of the Liscomb bonebed (B). (C) Paleogeographic reconstruction of North America at 70 Ma; the box indicates the approximate position of Alaska at that time. Mori et al. (2015).

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