High-latitude neonate and perinate ornithopods from the mid-Cretaceous of southeastern Australia

Justin L Kitchener,Phil R Bell,Nicolás E Campione,Elizabeth T Smith

doi:10.1038/s41598-019-56069-8

Justin L Kitchener, Phil R Bell + Show 2 more

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https://doi.org/10.1038/s41598-019-56069-8

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Abstract

Dinosaurs were remarkably climate-tolerant, thriving from equatorial to polar latitudes. High-paleolatitude eggshells and hatchling material from the Northern Hemisphere confirms that hadrosaurid ornithopods reproduced in polar regions. Similar examples are lacking from Gondwanan landmasses. Here we describe two non-iguanodontian ornithopod femora from the Griman Creek Formation (Cenomanian) in New South Wales, Australia. These incomplete proximal femora represent the first perinatal ornithopods described from Australia, supplementing neonatal and slightly older ‘yearling’ specimens from the Aptian–Albian Eumeralla and Wonthaggi formations in Victoria. While pseudomorphic preservation obviates histological examination, anatomical and size comparisons with Victorian specimens, which underwent previous histological work, support perinatal interpretations for the Griman Creek Formation femora. Estimated femoral lengths (37 mm and 45 mm) and body masses (113–191 g and 140–236 g), together with the limited development of features in the smallest femur, suggest a possible embryonic state. Low body masses (<1 kg for ‘yearlings’ and ~20 kg at maturity) would have precluded small ornithopods from long-distance migration, even as adults, in the Griman Creek, Eumeralla, and Wonthaggi formations. Consequently, these specimens support high-latitudinal breeding in a non-iguanodontian ornithopod in eastern Gondwana during the early Late Cretaceous.

Highlights

The discovery of dinosaurs at high paleolatitudes (>60° North or South) prompts considerable discussion on the coping mechanisms needed to accommodate the associated seasonality[1,2,3,4,5,6]
Histological analysis is obviated by the pseudomorphic opalization of some fossils from the Griman Creek Formation[22], gross anatomical comparisons with the histologically sampled specimens from the Eumeralla and Wonthaggi formations[25,26] indicate that the GCF specimens represent perinate individuals
Work on the ornithopod femora from the Eumeralla and Wonthaggi formations indicated as many as four morphotypes[23], this was later revised to two[24]

Summary

Introduction

The discovery of dinosaurs at high paleolatitudes (>60° North or South) prompts considerable discussion on the coping mechanisms needed to accommodate the associated seasonality[1,2,3,4,5,6]. The high-paleolatitude (~60–70°S) mid-Cretaceous Australian dinosaur faunas of the Griman Creek, Eumeralla, and Wonthaggi formations preserve a diverse array of small-bodied, bipedal www.nature.com/scientificreports non-iguanodontian ornithopods[9,12,22,23,24] The diversity of these animals suggests that they were well suited to the high-latitude conditions[23,24], their breeding habits remain unknown, due to the absence of appropriate material. Histological analysis is obviated by the pseudomorphic opalization of some fossils from the Griman Creek Formation (opalised fossils typically do not preserve bone microstructure)[22], gross anatomical comparisons with the histologically sampled specimens from the Eumeralla and Wonthaggi formations[25,26] indicate that the GCF specimens represent perinate (around the point of hatching) individuals Together, these specimens constitute the first evidence of perinatal dinosaurs from Australia and, more broadly, the first insights into the high-latitude breeding preferences of non-iguanodontian ornithopods in Gondwana. The significance of hatchling dinosaurs in Australia is discussed within the context of adaptations to high-latitude environments[2,7,19,27]

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