Theropod

How theropod dinosaur skulls experience stress and strain during the application of adductor muscle loads provides a unique insight into their feeding behaviour and principles of skeletal construction and scaling. Of particular interest are unusual cranial morphologies, such as those seen in the spinosaurid theropods, Baryonyx walkeri, Suchomimus tenerensis, Irritator challengeri and Spinosaurus aegyptiacus. This study uses the engineering technique finite element analysis to reconstruct feeding-related stress and strain in the skulls of seven theropod dinosaurs: five non-neotetanurans (Afrovenator, Dubreuillosaurus, Monolophosaurus, Spinosaurus and Suchomimus) and two basal neotetanurans (Acrocanthosaurus, and Carcharodontosaurus). Two-dimensional finite element models are created, and simulated adductor muscle loads are applied in proportion to the lateral surface area of the skull, thereby removing the influence of size and testing the efficiency of shape at resisting relative loads. Results show a significant size-related trend, with large taxa experiencing greater stresses than smaller taxa. Whilst Suchomimus scales with other theropods, Spinosaurus is a notable outlier and experiences much higher magnitudes of cranial stress than would be predicted. It may be that when realistic loading parameters are considered, larger theropods mitigate potential cranial weakness through concomitnat scaling of adductor muscle and bite force or through modifications to feeding ecology, especially in taxa such as Spinosaurus. Give the 2D nature of these models, results and interpretations should be treated with caution, and are best considered predictors of biomechanical performance and feeding ecology, to be tested in the future with more appropriate 3D finite element models.

Most dinosaurian material discovered on the Korean Peninsula remains undescribed and poorly documented. The specimen DGBU-78 is a well-preserved, non-avian theropod femur found in the Hayang Group of the Gyeongsang Supergroup in Korea. A phylogenetic analysis based on femoral characters suggests that it belongs to non-avian Maniraptora more derived than Oviraptorosauria. This specimen possesses a crest-like fourth trochanter, which is similar to those in dromaeosaurids such as Adasaurus mongoliensis and Velociraptor mongoliensis, suggesting a possible close phylogenetic relationship to these taxa. Non-avian maniraptorans including dromaeosaurids have been found in roughly contemporaneous deposits in China and Japan. Therefore, the discovery of the present material in the Korean Peninsula provides further supporting evidence for possible faunal exchange within East Asia during the Early Cretaceous.

Background: Troodontids are a predominantly small-bodied group of feathered theropod dinosaurs notable for their close evolutionary relationship with Avialae. Despite a diverse Asian representation with remarkable growth in recent years, the North American record of the clade remains poor, with only one controversial species—Troodon formosus—presently known from substantial skeletal remains.

Methodology/Principal Findings: Here we report a gracile new troodontid theropod—Talos sampsoni gen. et sp. nov.— from the Upper Cretaceous Kaiparowits Formation, Utah, USA, representing one of the most complete troodontid skeletons described from North America to date. Histological assessment of the holotype specimen indicates that the adult body size of Talos was notably smaller than that of the contemporary genus Troodon. Phylogenetic analysis recovers Talos as a member of a derived, latest Cretaceous subclade, minimally containing Troodon, Saurornithoides, and Zanabazar. MicroCT scans reveal extreme pathological remodeling on pedal phalanx II-1 of the holotype specimen likely resulting from physical trauma and subsequent infectious processes.

Conclusion/Significance: Talos sampsoni adds to the singularity of the Kaiparowits Formation dinosaur fauna, which is represented by at least 10 previously unrecognized species including the recently named ceratopsids Utahceratops and Kosmoceratops, the hadrosaurine Gryposaurus monumentensis, the tyrannosaurid Teratophoneus, and the oviraptorosaurian Hagryphus. The presence of a distinct troodontid taxon in the Kaiparowits Formation supports the hypothesis that late Campanian dinosaurs of the Western Interior Basin exhibited restricted geographic ranges and suggests that the taxonomic diversity of Late Cretaceous troodontids from North America is currently underestimated. An apparent traumatic injury to the foot of Talos with evidence of subsequent healing sheds new light on the paleobiology of deinonychosaurians by bolstering functional interpretations of prey grappling and/or intraspecific combat for the second pedal digit, and supporting trackway evidence indicating a minimal role in weight bearing.

An isolated theropod tooth from the Early Cretaceous Sebayashi Formation is described. It is almost identical to those of the possible spinosauridtheropod Siamosaurus from the Early Cretaceous Sao Khua Formation of Thailand and it is tentatively referred to the Spinosauridae. The tooth represents the second dinosaur species to be identified from the Sebayashi Formation and the second report of the family Spinosauridae in Asia.