First dinosaur remains from Ireland

Abstract

Several specimens from the Lias Group (Lower Jurassic) of Northern Ireland have been suspected as dinosaurian in origin. Bone histology and morphology demonstrates that two of these, both from the same locality in Co. Antrim, demonstrably are from dinosaurs. We interpret one as the proximal end of the left femur of a basal thyreophoran ornithischian, and tentatively assign it to cf. Scelidosaurus. The other is the proximal part of the left tibia of an indeterminate neotheropod, perhaps a member of the averostran-line similar to Sarcosaurus, or a megalosauroid. These are the first dinosaur remains reported from anywhere in Ireland and some of the most westerly in Europe, and they are among only a small number of dinosaurs known from the Hettangian Stage. Two additional specimens are no longer considered to be from dinosaurs. We interpret one as a surangular or mandible fragment from a large marine reptile, perhaps an ichthyosaur or pliosaur; the other is a polygonal fragment of Paleocene basalt.

Introduction

Although dramatic finds from North America, Asia and elsewhere have dominated the literature for decades, Britain remains one of the richest areas in the world in terms of documented dinosaur diversity. Important faunas have been recovered from the Upper Triassic (e.g. Benton et al., 2000; Whiteside et al., 2016), the Jurassic of south central and eastern England (Benton and Spencer, 1995) and especially the Lower Cretaceous of the Isle of Wight and the Weald (Martill and Naish, 2001), but elsewhere in the UK dinosaur remains are less abundant. Footprints and skeletal remains have been discovered in the Jurassic of Yorkshire (Whyte et al., 2010), in northern England; from the Late Triassic and Early Jurassic of south Wales (Benton and Spencer, 1995; Yates, 2003; Martill et al., 2016); and the Jurassic of both western and eastern Scotland (Andrews and Hudson, 1984; Benton et al., 1995; Clark, 2018; dePolo et al., 2018; Young et al., 2018). However, no dinosaur remains have hitherto been recorded from the island of Ireland.

Some might attribute the apparent absence of dinosaur remains from Ireland to the activities of St Patrick, whose apparent success in casting out snakes is well known, but there is a more mundane explanation. The sparsity of dinosaur remains in Britain beyond southern England directly reflects the geology of these regions. Suitable Mesozoic rocks are poorly represented in northern and western Britain where most rocks are too old to contain dinosaur remains, and this is true too across large areas of Ireland. Outside of Northern Ireland there are just a few, largely concealed, patches of Mesozoic (Fig. 1) inluding Triassic clastics in the Kingscourt Inlier (Simms, 2009) and possibly in the South Wexford Outlier (Clayton et al., 1986); Jurassic clastics at Cloyne, near Cork (Higgs and Beese, 1986), Piltown, near Carrick-on-Suir (Higgs and Jones, 2000), and beneath Dublin Bay; and a small patch of Upper Cretaceous Chalk at Ballydeenlea in Co. Kerry (Walsh, 1966).

Substantial Mesozoic basins are present in the north-east (Larne-Lough Neagh Basin) and north-west (Foyle-Rathlin Basin) of Northern Ireland (Raine et al., 2019) but they are mostly concealed beneath younger rocks and exposure is confined largely to a narrow strip around the margins of the Paleocene basalt plateau (Fig. 1). Triassic, Jurassic and Cretaceous strata are all represented (Fig. 2) but there is a gap, representing at least 100 million years, between the youngest preserved Jurassic strata (early Pliensbachian) and oldest preserved Cretaceous (early Cenomanian). In places pre-Cenomanian erosion of earlier Mesozoic strata has removed the Jurassic entirely and Cretaceous strata rest directly upon Triassic or even older rocks.

Unfortunately, despite being of the right age to contain dinosaurs these Mesozoic strata are developed in facies that do not favour the preservation of terrestrial vertebrates. The Jurassic and Cretaceous strata here are entirely of open marine facies in which dinosaur fossils are unlikely to be common, while the Upper Triassic succession is largely non-marine and developed in red-bed facies of the Mercia Mudstone Group (Milroy et al., 2019) in which fossils of any kind are rarely preserved. In short, Ireland’s rocks are either of the wrong age or of the wrong type to contain dinosaur fossils.

Palaeogeographic reconstructions (Cope et al., 1992) suggest that at times during the Mesozoic dinosaurs could have walked on dry land across parts of what is now Ireland. However, if any rocks were deposited here at these times they were either removed long ago by erosion, along with any dinosaur remains that they might contain, or they were deposited in environments distant from dinosaur habitats. Finding an Irish dinosaur might seem a hopeless task but, nonetheless, several potential candidates have been identified and are described for the first time here.