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British Dorset (Jurassic Bathonian) dromaeosaurid dinosaur fossil teeth

WILLS, Simon
Smallbodied theropod taxa are known from isolated teeth and fragmentary remains occurringthroughout the British Bathonian. The exception is the tyrannosaurid Proceratosaurusbradleyi which comprises a partial skull, mandibles, hyoid and cervical ribfragments. Small isolated teeth occur at a number of microsites in southernEngland. The sites usually represent small ponds, channel fills or swampsformed on low-lying exposed limestone platforms. Some 200 kg of sediment fromthe Forest Marble Formation (Middle Jurassic, Bathonian) microsite of WattonCliff, Dorset was analysed for microvertebrate remains. The microsite is a channeldeposit cutting through a nearshore bioclastic limestone. Sixteen smalltheropod teeth, including four complete crowns, were recovered during thisprocess. The majority of the teeth are fragmentary and show evidence ofextensive abrasion. In addition to the theropod teeth, the microvertebratefauna comprises a mixture of both terrestrial and non-terrestrial taxa includingmammals, ornithischian dinosaurs, amphibians, crocodiles, sharks and fish. The teethwere scanned using a micro-CT. Each stack of CT data was processed to produce 3Dmodels representing individual teeth. Standard measurements (crown width and height,basal width and denticle counts) were taken directly from the 3D models and addedto a database containing > 3500 tooth measurements obtained from thepublished literature. The dataset is dominated by small bodied North Americantheropod taxa (dromaeosaurs and troodontids) with the addition of some datafrom non coleurosaurian theropods. Principle component analysis anddiscriminant function analysis were used to test the similarity of the Wattonteeth with known clades, allowing the referral of the Watton teeth to theDromaeosauridae. This pushes back the origin of dromaeosaurids from the Kimmeridgianto the Bathonian, supporting previous suggestions that the clade was present inthe Middle Jurassic, and adding to the hypothesis that the coelurosaur radiationoccurred earlier than the current body fossil record supports.