Abstract
Several skulls of the ornithischian dinosaur Lesothosaurus diagnosticus (Lower Jurassic, southern Africa) are known, but all are either incomplete, deformed, or incompletely prepared. This has hampered attempts to provide a comprehensive description of skull osteology in this crucial early dinosaurian taxon. Using visualization software, computed tomographic scans of the Lesothosaurus syntypes were digitally segmented to remove matrix, and identify and separate individual cranial and mandibular bones, revealing new anatomical details such as sutural morphology and the presence of several previously undescribed elements. Together with visual inspection of exposed skull bones, these CT data enable a complete description of skull anatomy in this taxon. Comparisons with our new data suggest that two specimens previously identified as Lesothosaurus sp. (MNHN LES 17 and MNHN LES 18) probably represent additional individuals of Lesothosaurus diagnosticus.
Highlights
Cranial and lower jaw material is preserved for at least four additional heterodontosaurid taxa from the Early Jurassic of South Africa (Haughton, 1924; Thulborn, 1974; Hopson, 1975; Porro et al, 2011; Sereno, 2012) and one undescribed specimen from the Early Jurassic of western North America (Attridge, Crompton & Jenkins, 1985; Sereno, 1986). Despite their early occurrence and basal position within ornithischian phylogeny (Butler, Upchurch & Norman, 2008), most Early Jurassic heterodontosaurids exhibit cranial and dental specializations atypical of primitive ornithischians, including: a strongly heterodont dentition; closely-packed, chisel-shaped maxillary and dentary ‘cheek’ teeth; heavy tooth wear; a strongly developed coronoid process of the lower jaw; a strongly depressed jaw joint; and extensive fusion of cranial sutures (e.g., Norman et al, 2011; Sereno, 2012)
The cranium of NHMUK PV RU B23 is tallest just behind the orbit; the skull roof is gently rounded in lateral profile and the snout tapers smoothly to the premaxillae; there is no break in slope along the snout anterior to the orbits as occurs in Heterodontosaurus (SAM-PK-K1332; Norman et al, 2011; Sereno, 2012)
Digital preparation has clarified the cranial anatomy of Lesothosaurus diagnosticus as well as revealing new features, allowing fresh comparisons with two additional ornithischian specimens from the Upper Elliot Formation of Lesotho (MNHN LES 17 and MNHN LES 18)
Summary
Ornithischian dinosaurs underwent major taxonomic and ecological radiations during the Jurassic (Sereno, 1997; Butler, Upchurch & Norman, 2008) resulting in diverse craniodental morphologies and, presumably, disparate feeding strategies (e.g., Weishampel & Norman, 1989; Norman & Weishampel, 1991; Sereno, 1997; Barrett, 2014; Mallon & Anderson, 2014). Cranial and lower jaw material is preserved for at least four additional heterodontosaurid taxa from the Early Jurassic of South Africa (Haughton, 1924; Thulborn, 1974; Hopson, 1975; Porro et al, 2011; Sereno, 2012) and one undescribed specimen from the Early Jurassic of western North America (Attridge, Crompton & Jenkins, 1985; Sereno, 1986). The skull of Heterodontosaurus is probably not representative of skull morphology in the earliest ornithischians
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