Anguimorph lizards (Squamata, Anguimorpha) from the Middle and Late Eocene of the Hampshire Basin of southern England

Abstract

The Hampshire Basin in southern England is the only sequence virtually spanning the Eocene-Oligocene boundary in western Europe. It has provided an opportunity to observe changes in populations across the Grande Coupure event, as an overturn in the squamate assemblage of continental Europe has also been noted. Five Tertiary formations have yielded lizard material: Creechbarrow Limestone, Barton Clay, Headon Hill, Bembridge Limestone and Bouldnor Formation. These formations span the period from the late Middle Eocene to the earliest Oligocene. Localities in the Hampshire Basin represent a depositional environment with an increasing tendency towards lacustrine and riparian influences in later horizons. The anguimorph fauna includes one new anguine, Headonhillia parva gen. et sp. nov., diagnosed by: (1) small size, (2) large parietal area levis, and (3) short parietal crista postfovealis. Another anguine, Ophisaurus sp., is identified on the basis of the morphology of the parietal. Three further morphotypes of anguines have been distinguished based on dentary, vertebrae and osteoderm specimens. Two types of indeterminate Anguidae are distinguished on the basis of maxillae and dentaries and three morphotypes of indeterminate Anguidae on the basis of vertebrae. Glyptosaurines have been identified in three members on the basis of osteoderms. ‘Necrosaurs’ have also been identified from the Hampshire Basin: two types, distinguished on the basis of dentary material and osteoderms, are identified as indeterminate ‘necrosaurs’. One type of indeterminate Varanoidea is distinguished on the basis of dentaries. The presence of anguids in the Hampshire Basin is well documented, and they appear to form a consistently diverse assemblage throughout the sequence. Anguine osteoderms are present in both pre- and post-Grande Coupure material. Pre-Grande Coupure vertebrae and osteoderms are similar in size to those of adult Recent anguine Pseudopus apodus, although many of the Hampshire Basin anguines, including Headonhillia parva, represent the smallest anguines known to date.