Cranial anatomy, palaeoneurology, palaeobiology and stratigraphic age of the large-bodied ornithopod, Muttaburrasaurus langdoni Bartholomai and Molnar, 1981, from the mid-Cretaceous of Australia
The holotype of Muttaburrasaurus langdoni Bartholomai & Molnar, 1981, a large-bodied ornithopod from the mid-Cretaceous of Australia, consists of an almost complete skull and partial postcranium, and is among the most skeletally complete ornithopods from Gondwana. The taxon was defined by a dorsally inflated muzzle, thought to be formed by the nasals, enlarged mandibular adductor musculature and cheek teeth thought to have a uniquely en masse eruption pattern. The rostrum, however, was unknown. The original description of the holotype skull was superficial, which has confounded numerous attempts to resolve the phylogenetic relationships of the taxon. Recently, the holotype quarry was reworked and new craniodental materials were collected. In addition, previously undescribed materials of the holotype skull are now identified. Here, using CT imagery, we extensively revise the craniodental osteology of Muttaburrasaurus langdoni and describe its palaeoneurology. From detrital zircons, we date the holotype locality in the Cenomanian at 96.3 ± 8.6 Ma. The premaxillary ramus of the holotype, now discovered, has five well-developed teeth, as in early diverging ornithischians. Modified premaxillary processes exclude the nasals from the nares, convergent with lambeosaurines, and novel paired ossifications, termed prenasals, form the roof and internal septa of the muzzle. Superior airway chambers in the muzzle, descending turbinate support ridges and highly enlarged olfactory bulbs, suggest heightened olfactory acuity. As in other megahervorous vertebrates, wide monocular vision potentially aided predator detection and conspecific interaction, such as herding behaviour. Stereoscopic vision in the narrow binocular field potentially assisted target selection, obstacle avoidance and distance timing during locomotion. Low frequency hearing (<1 kHz) could have aided communication in open and closed habitats and under low light conditions. Proportions of the semicircular canals suggest a facultative biped. Cognition appears comparable to non-hadrosaurid iguanodontians. The narrow premaxilla is consistent with selective browsing and caniniform premaxillary dentition potentially aided access to nutritious plant food items encased in cones and possibly invertebrates. The cheek teeth erupted in a wave-like pattern, as in other ornithischians and were configured for grinding mastication. Nasal salt glands were possibly developed, suggesting a diet that included excess salt ingestion. Our findings shed new light on the behavioural and sensory palaeobiology of Muttaburrasaurus. We anticipate future phylogenetic analyses of Muttaburrasaurus will be better informed from the anatomical information provided herein.
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