Abstract
Pliosaurids were a long-lived and cosmopolitan group of marine predators that spanned 110 million years and occupied the upper tiers of marine ecosystems from the Middle Jurassic until the early Late Cretaceous. A well-preserved giant pliosaurid skull from the Late Jurassic Kimmeridge Clay Formation of Dorset, United Kingdom, represents a new species, Pliosaurus kevani. This specimen is described in detail, and the taxonomy and systematics of Late Jurassic pliosaurids is revised. We name two additional new species, Pliosaurus carpenteri and Pliosaurus westburyensis, based on previously described relatively complete, well-preserved remains. Most or all Late Jurassic pliosaurids represent a globally distributed monophyletic group (the genus Pliosaurus, excluding ‘Pliosaurus’ andrewsi). Despite its high species diversity, and geographically widespread, temporally extensive occurrence, Pliosaurus shows relatively less morphological and ecological variation than is seen in earlier, multi-genus pliosaurid assemblages such as that of the Middle Jurassic Oxford Clay Formation. It also shows less ecological variation than the pliosaurid-like Cretaceous clade Polycotylidae. Species of Pliosaurus had robust skulls, large body sizes (with skull lengths of 1.7–2.1 metres), and trihedral or subtrihedral teeth suggesting macropredaceous habits. Our data support a trend of decreasing length of the mandibular symphysis through Late Jurassic time, as previously suggested. This may be correlated with increasing adaptation to feeding on large prey. Maximum body size of pliosaurids increased from their first appearance in the Early Jurassic until the Early Cretaceous (skull lengths up to 2360 mm). However, some reduction occurred before their final extinction in the early Late Cretaceous (skull lengths up to 1750 mm).
Highlights
Pliosaurids were Mesozoic ocean predators, some of which achieved giant sizes .12 metres long [1,2,3]. They had a global distribution and spanned c. 110 million years, from the Early Jurassic until the early Late Cretaceous (e.g., [4,5,6,7,8,9,10,11,12,13,14]). Their fossils are best known from the Late Jurassic Oxford and Kimmeridge Clay formations of England (e.g., [15,16,17])
The latest pliosaurids are from the early Late Cretaceous [14], [27], and they may have been made extinct by the appearance of large-bodied mosasauroids as competitors in the Middle Turonian [14]
The matrix was modified by the addition of five operational taxonomic units representing pliosaurid specimens from the Kimmeridge Clay Formation
Summary
Pliosaurids were Mesozoic ocean predators, some of which achieved giant sizes .12 metres long [1,2,3]. Pliosaurid evolution shows a transition from plesiomorphic, intermediate body proportions and a small skull in the earliest Early Jurassic taxa [13], [19] to Middle Jurassic taxa with ‘pliosauromorph’ body proportions and piscivorous (gracile, longirostine skulls, many slender teeth) or macropredaceous habits (robust longirostrine or brevirostrine skulls with robust teeth) (e.g., [20,21,22,23,24,25]). These Middle Jurassic and younger taxa belong to an recognisable clade called Thalassophonea [26]. The latest pliosaurids are from the early Late Cretaceous [14], [27], and they may have been made extinct by the appearance of large-bodied mosasauroids as competitors in the Middle Turonian [14]
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