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quinta-feira, 1 de outubro de 2015

[Paleontology • 2015]  

Ugrunaaluk kuukpikensis • A New Arctic Hadrosaurid from the Prince Creek Formation (lower Maastrichtian) of northern Alaska

Ugrunaaluk kuukpikensis
Mori, Druckenmiller & Erickson, 2015
The Liscomb bonebed in the Price Creek Formation of northern Alaska has produced thousands of individual bones of a saurolophine hadrosaurid similar to Edmontosaurus; however, the specific identity of this taxon has been unclear, in part because the vast majority of the remains represent immature individuals. In this study, we address the taxonomic status of the Alaskan material through a comparative and quantitative morphological analysis of juvenile as well several near adult-sized specimens with particular reference to the two known species of Edmontosaurus, as well as a cladistic analysis using two different matrices for Hadrosauroidea. In the comparative morphological analysis, we introduce a quantitative method using bivariate plots to address ontogenetic variation. Our comparative anatomical analysis reveals that the Alaskan saurolophine possesses a unique suite of characters that distinguishes it from Edmontosaurus, including a premaxillary circumnarial ridge that projects posterolaterally without a premaxillary vestibular promontory, a shallow groove lateral to the posterodorsal premaxillary foramen, a relatively narrow jugal process of the postorbital lacking a postorbital pocket, a relatively tall maxilla, a relatively gracile jugal, a more strongly angled posterior margin of the anterior process of the jugal, wide lateral exposure of the quadratojugal, and a short symphyseal process of the dentary. The cladistic analyses consistently recover the Alaskan saurolophine as the sister taxon to Edmontosaurus annectens + Edmontosaurus regalis. This phylogenetic assessment is robust even when accounting for ontogenetically variable characters. Based on these results, we erect a new taxon, Ugrunaaluk kuukpikensis gen. et sp. nov. that contributes to growing evidence for a distinct, early Maastrichtian Arctic dinosaur community that existed at the northernmost extent of Laramidia during the Late Cretaceous.

Key words: Dinosauria, Hadrosauridae, Saurolophinae, Edmontosaurini, Ugrunaaluk, Edmontosaurus, ontogeny, Cretaceous, Prince Creek Formation, Arctic.
 Ugrunaaluk kuukpikensis illustrates a scene from ancient Alaska during the Cretaceous Period.
illustration: James Havens
Fig. 4. Cranial reconstruction of Ugrunaaluk kuukpikensis gen. et sp. nov. from the early Maastrichtian Prince Creek Formation in left lateral view.
Systematic Paleontology

Ornithischia Seeley, 1887
Ornithopoda Marsh, 1881
Hadrosauridae Cope, 1869
Saurolophinae Brown, 1914 sensu Prieto-Márquez, 2010a
Edmontosaurini Brett-Surman, 1989
Genus Ugrunaaluk nov.
urn:lsid:zoobank.org:act:8B8256BA-F280-4460-B0F0-31762267586E
Etymology: Transliterated from the Alaskan Iñupiaq noun ugruŋnaq, referring to a grazing animal with a long set of grinding teeth, and the adjective -aluk, old. Literally, “ancient grazer”. Intended pronunciation: “oo-GREW-nah-luk”. The name honors the Alaskan Native Iñupiaq culture from the area where the type material was discovered.
Type species: Ugrunaaluk kuukpikensis sp. nov., monotypic
urn:lsid:zoobank.org:act:1CAF186F-11A2-4A9E-A8F9-C3789B97459F 
Figs. 4–10. 

Etymology: The specific name is derived from the Iñupiaq word kuukpik, which refers to the Colville River, Alaska, USA along which the type material was found.

Type locality: Liscomb bonebed, along the Colville River, northern Alaska, USA. The exact location is on file with the Bureau of Land Management Arctic Field Office.

Type horizon: Upper portion of the Prince Creek Formation, lower Maastrichtian (Upper Cretaceous).
Fig. 2. Temporal distribution of Edmontosaurus species and the Prince Creek Formation taxon in the Late Cretaceous.

Conclusions
In this study, we; (i) identify and name a new taxon of saurolophine hadrosaurid, Ugrunaaluk kuukpikensis gen. et sp. nov. from the Prince Creek Formation of Alaska; (ii) demonstrate that skeletally immature specimens can be reliably used in addressing taxonomic problems within
Hadrosauridae based on a detailed understanding of the growth patterns of closely related taxa; and (iii) show that Ugrunaaluk kuukpikensis gen. et sp. nov. does not represent a juvenile form of either recognized species of Edmontosaurus. Further morphological description of the new Alaskan taxon and greater clarification of its differences from Edmontosaurus will require discovery of adult material from the Prince Creek Formation and/or description of other juvenile specimens from E. regalis and E. annectens.

The establishment of a new species of hadrosaurid, Ugrunaaluk kuukpikensis gen. et sp. nov. further clarifies the faunal composition of the Prince Creek Formation and contributes to a growing body of evidence that the paleo-Arctic hosted a distinct and endemic polar, early Maastrichtian dinosaurian fauna. Ongoing field work in the formation and taxonomic clarifications of existing material will help to further establish the faunal composition of the unit and add critical new data to test hypotheses of dinosaur provinciality in Laramidia during the latest Cretaceous.
Hirotsugu Mori, Patrick S. Druckenmiller, and Gregory M. Erickson. 2015. A New Arctic Hadrosaurid from the Prince Creek Formation (lower Maastrichtian) of northern Alaska. Acta Palaeontologica Polonica. in press.  doi: 10.4202/app.00152.2015
  
Alaskan duck-billed dinosaur find spurs physiological mystery http://www.slashgear.com/alaskan-duck-billed-dinosaur-find-spurs-physiological-mystery-22405828/ via @slashgear
Newly discovered hadrosaur dino was one serious, cold-winter survivor

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