First trace and body fossil evidence of a burrowing, denning dinosaur

Abstract

A fossil discovery in the mid-Cretaceous Blackleaf Formation of southwest Montana, USA, has yielded the first trace and body fossil evidence of burrowing behaviour in a dinosaur. Skeletal remains of an adult and two juveniles of Oryctodromeus cubicularis gen. et sp. nov. a new species of hypsilophodont-grade dinosaur, were found in the expanded distal chamber of a sediment-filled burrow. Correspondence between burrow and adult dimensions supports Oryctodromeus as the burrow maker. Additionally, Oryctodromeus exhibits features of the snout, shoulder girdle and pelvis consistent with digging habits while retaining cursorial hindlimb proportions. Association of adult and young within a terminal chamber provides definitive evidence of extensive parental care in the Dinosauria. As with modern vertebrate cursors that dig, burrowing in Oryctodromeus may have been an important adaptation for the rearing of young. Burrowing also represents a mechanism by which small dinosaurs may have exploited the extreme environments of polar latitudes, deserts and high mountain areas. The ability among dinosaurs to find or make shelter may contradict some scenarios of the Cretaceous-Paleogene impact event. Burrowing habits expand the known range of nonavian dinosaur behaviours and suggest that the cursorial ancestry of dinosaurs did not fully preclude the evolution of different functional regimes, such as fossoriality.

The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia

“…The Paw Paw formation was deposited during the Late Albian (e.g., Lee, 1996), thus being similar in age to the Dakota, Wayan, Blackleaf, and Willow Tank Formations (e.g., Liggett, 2005;Varricchio et al, 2007;Bonde et al, 2012;Ullman et al, 2012;Krumenacker et al, 2017). Like these other formations, the Paw Paw evinces that nodosaurids continued being widespread across North America during the Albian.…”

“…Albian Dinosaur Faunas. The Dakota Formation is late Albian to early Cenomanian in age (e.g., Joeckel et al, 2004;Koch, 2007) and was compared with the similarly-aged Wayan, Blackleaf, and Willow Tank formations of the western United States (Varricchio et al, 2007;Bonde et al, 2012;Ullman et al, 2012;Krumenacker et al, 2017). The Wayan Formation of Idaho was found to be deposited between 101.8 and 95.5 Ma by Krumenacker (2010), who reviewed the formation's stratigraphy.…”

“…The Wayan Formation of Idaho was found to be deposited between 101.8 and 95.5 Ma by Krumenacker (2010), who reviewed the formation's stratigraphy. The Willow Tank Formation has been found to be between 98.5 and 98.1 million years old (e.g., Fleck, 1970;Troyer et al, 2006;Bonde et al, 2012), and the Blackleaf Formation has been dated to the late Albian and early Cenomanian (e.g., Dorr, 1985;Varricchio et al, 2007;Ullman et al, 2012). All of these western formations have been considered as overlapping in age (e.g., Bonde et al, 2012; figure 2 in Krumenacker et al, 2017).…”

“…Although the Paluxy is middle Albian in age (112.2-106 Ma) (Jacobs and Winkler, 1998;D'Emic, 2013) and the Dakota, Wayan, Blackleaf and Willow Tank formations were deposited in the late Albian to early Cenomanian (e.g., Liggett, 2005;Varricchio et al, 2007;Bonde et al, 2012;Krumenacker et al, 2017), the scarcity of dinosaurbearing deposits from this time in North America and the relatively well-documented state of the Paluxy Formation fauna warranted statistical comparison between it and the faunas of the other aforementioned sedimentary units. Genus level similarity for both indices used was 0.0 between the Paluxy and all other formations, whereas family-level comparisons resulted in low Simpson similarity index and Jaccard coefficient values between the Paluxy fauna and those of all other formations save for the Dakota (Tables 7-10 of Appendix 1).…”

“…It is notable that the Raritan shares with the Mussentuchit, Wayan, and Blackleaf formations tyrannosauroid dinosaurs (e.g., Baird, 1989;Kirkland et al, 1998;Varricchio et al, 2007;Ullman et al, 2012;Zanno and Mackovicky, 2013). The size of the Raritan facies tyrannosauroid is relatively large compared to Cenomanian North American tyrannosauroids (pers.…”