The theropod that wasn't: an ornithopod tracksite from the Helvetiafjellet Formation (Lower Cretaceous) of Boltodden, Svalbard

Jørn H Hurum,Snorre Olaussen,Hans A Nakrem,Patrick S Druckenmiller,Øyvind Hammer

doi:10.1144/sp434.10

Abstract

Abstract We re-examine a Lower Cretaceous dinosaur tracksite at Boltodden in the Kvalvågen area, on the east coast of Spitsbergen, Svalbard. The tracks are preserved in the Helvetiafjellet Formation (Barremian). A sedimentological characterization of the site indicates that the tracks formed on a beach/margin of a lake or interdistributary bay, and were preserved by flooding. In addition to the two imprints already known from the site, we describe at least 34 additional, previously unrecognized pes and manus prints, including one trackway. Two pes morphotypes and one manus morphotype are recognized. Given the range of morphological variation and the presence of manus tracks, we reinterpret all the prints as being from an ornithopod rather than a theropod, as previously described. We assign the smaller (morphotype A, pes; morphotype B, manus) to Caririchnium billsarjeanti . The larger (morphotype C, pes) track is assigned to Caririchnium sp., differing in size and interdigital angle from the two described ichnospecies C . burreyi and C . billsarjeanti . The occurrence of a quadrupedal, small to medium-sized ornithopod in Svalbard is puzzling, considering the current palaeogeographical reconstructions and that such dinosaur tracks have mainly been described from Europe but not North America.

Highlights

In 1976, two tracks were discovered in eastern Spitsbergen in the Helvetiafjellet Formation at Boltodden in the Kvalvagen area (Fig. 1), which were described as belonging to a medium-sized theropod by Edwards et al (1978)
The occurrence of a quadrupedal, small to medium-sized ornithopod in Svalbard is puzzling, considering the current palaeogeographical reconstructions and that such dinosaur tracks have mainly been described from Europe but not North America
Four ichnospecies of Caririchnium are known (Dıaz-Martınez et al 2015): C. magnificum is found in Berrasian –Albianaged deposits of Brazil and Spain; C. kortmeyeri is only known from the Aptian –Albian of Canada; C. billsarjeanti is from the Aptian of Switzerland; and C. lotus is known from the Barremian–Albian of China and Spain

Summary

Introduction

In 1976, two tracks were discovered in eastern Spitsbergen in the Helvetiafjellet Formation at Boltodden in the Kvalvagen area (Fig. 1), which were described as belonging to a medium-sized theropod by Edwards et al (1978). The Triassic –Lower Cretaceous basin fill in Svalbard and the western platform areas were deposited in a subsiding epicontinental sag basin (Steel & Worsley 1984; Faleide et al 2008; Worsley 2008; Midtkandal & Nystuen 2009; Glørstad-Clark et al 2010). The overlying Helvetiafjellet Formation, in which the dinosaur tracks are found, is a sandstone-dominated Barremian–early Aptian unit, up to 155 m thick. It was deposited in fluvial, deltaic, tidal and paralic environments

Methods

Discussion

Conclusion