The braincase of Daspletosaurus.

Daspletosaurus torosus, holotype CMN 8506, Canadian Museum of Nature, Ottawa. From Wikepedia Commons

In 1970, Dale Russell described Daspletosaurus torosus. For decades, this specimen was regarded as the “prototypical” Campanian tyrannosaurine. It was discovered in 1921 by Charles Mortram Sternberg, who thought it was a new species of Gorgosaurus. But Daspletosaurus was heavier and more powerfully built than Gorgosaurus, and specilized in feeding on ceratopsians. A new study by a team of scientists from Canada and Argentina provides the first detailed study of the braincase of Daspletosaurus. The holotype of Daspletosaurus torosus (CMN 8506) from the Oldman Formation of Dinosaur Provincial Park, southern Alberta, includes a complete braincase. TMP 2001.36.1 (Daspletosaurus sp.) is a nearly complete skull and skeleton of an ontogenetically mature individual from the Oldman Formation. Both specimens were used to digitally reconstruct the brain, inner ear, and the braincase of Daspletosaurus and revealed extensive morphological variations. 

Cast of the skull of Daspletosaurus torosus in the Canadian Museum of Nature’s collections.

Our knowledge of dinosaurian braincases and the structure of their endocranial cavities has a surprisingly long history. The first well-preserved braincase (NHMUK R2501) was found almost 150 years ago in the Isle of Wight and was described as probably belonging to Iguanodon. In 1897, Charles William Andrews – using the same specimen – suggested that dinosaurian brains, and in particular their lobes and surface convolutions, were not closely pressed against the cranial wall. Almost sixty years later, John Ostrom published a study on the anatomy of the hadrosaurian dinosaurs of North America and reinforced the general opinion that they had brains that were not packed tightly within the braincase. In 1970, Dale Russell was the first to recognize taxonomic significance in the variation of the braincase morphology among tyrannosaurids.

The braincase of Daspletosaurus sp. (TMP 2001.36.1). From Carabajal et al., 2021

The new study reveals a set of characters useful to distinguish the genus Daspletosaurus from other tyrannosaurids: a deep midbrain flexure, the presence of an anterodorsal chamber of the basisphenoid recess, and the presence of a prohypophyseal sinus of the anterior tympanic recess at large body size Among the variations that potentially distinguish TMP 2001.36.1 from Daspletosaurus torosus are the short, vertical lagena, and the paired sinuses on the lateral wall of the basisphenoid recess (unique among tyrannosaurids), the entirely pneumatized paroccipital process (shared with Gorgosaurus), the well-developed crista tuberalis, and the curved ala basisphenoidalis. Additionally, the bottlenecked olfactory tract in TMP 2001.36.1 occurs mainly in smaller tyrannosaurids.

 

 

References:

Ariana Paulina Carabajal, Philip J. Currie, Thomas W. Dudgeon, Hans C.E. Larsson, and Tetsuto Miyashita. Two braincases of Daspletosaurus (Theropoda: Tyrannosauridae): anatomy and comparison. Canadian Journal of Earth Sciences. DOI: 10.1139/cjes-2020-0185

Russell, D.A. 1970. Tyrannosaurs from the Late Cretaceous of Western Canada. National Museum of Natural Sciences Publications in Palaeontology, 1: 1–32. DOI: 10.5281/zenodo.1040973

Introducing Ypupiara lopai

Restoration of two individuals of Ypupiara lopai. Credit: Guilherme Gehr

The iconic Velociraptor mongoliensis, described by Osborn in 1924, belongs to the Dromaeosauridae, a family of highly derived small to mid-sized theropod dinosaurs closely related to birds. Their fossils have been found in North America, Europe, Africa, Asia, South America and Antarctica. The group is characterized by the presence of long, three-fingered forelimbs that ended in sharp, trenchant claws, and a tail stiffened by the elongated prezygapophyses. In Gondwana, the clade Unenlagiinae is a diversification of dromaeosaurids. The group includes Buitreraptor and Austroraptor from Argentina. Ypupiara lopai from the Maastrichtian of the Bauru Group is the first unenlagiine dromaeosaurid species from Brazil.

The holotype (DGM 921-R) includes a partial preantorbital portion of a right maxillary, with three teeth in loci, and a partial posterior portion of a right dentary. The generic name means ‘the one who lives in the water’, an allusion to a Tupian myth about an aquatic creature. The specific name honors Alberto Lopa, the holotype’s discoverer. Ypupiara was found between the 40s and 60s in Peirópolis, near Uberaba, and placed in storage at the National Museum of Brazil. Unfortunately, the fossil was lost when the museum was consumed by a fire on 2 September 2018, but photographs of the specimen survived.

Right maxilla of DGM 921-R with details of teeth. Scale bar: 10 mm. From Brum et al., 2021.

Ypupiara is characterized by the morphology of the maxilla that exhibits a restrict number of neurovascular foramina on lateral surface, rectangular and anteroposteriorly expanded interdental plate, and teeth widely spaced and labiolingually compressed. Based on the ratio between the labiolingual and mediodistal diameters of the teeth more than 3/5, Ypupiara was classified as a sister-group of A. cabazai. It was suggested that unenlagiines consumed fish at least as part of their diet and potentially as the main source of food at least in Austroraptor due to its conidont dentition.

 

References:

Brum, Arthur Souza, Pêgas, Rodrigo Vargas, Bandeira, Kamila Luisa Nogueira, Souza, Lucy Gomes de, Campos, Diogenes de Almeida, & Kellner, Alexander Wilhelm Armin. (2021). A new Unenlagiinae (Theropoda: Dromaeosauridae) from the Late Cretaceous of Brazil. https://doi.org/10.1002/spp2.1375

Gianechini, Federico A and S. Apesteguía. (2011) “Unenlagiinae revisited: dromaeosaurid theropods from South America.” Anais da Academia Brasileira de Ciencias 83 1: 163-95 .