An 80-million-year-old fossilized braincase from an enantiornithine bird

MPM-334-1 is a diminutive basicranium of a skeletally mature enantiornithine bird. From Chiappe et al., 2022.

Birds are extraordinarily intelligent and they can rival mammals in terms of relative brain size and behavioural complexity. The clade originated from a theropod lineage more than 150 million years ago. By the Early Cretaceous, they diversified, evolving into a number of groups of varying anatomy and ecology. Recent studies have shown that corvids and some parrots are capable of cognitive achievement comparable to those of great apes. They manufacture and use tools, solve puzzles, and plan for future needs. Futhermore, they share with humans and a few other animal groups a rare capacity for vocal learning.

Over the last decades, several discovered fossils of theropods and early birds have enriched our knowledge of the evolution of the avian skull. Now, the discovery of an exceptionally well preserved braincase from an Upper Cretaceous (~80 Ma) enantiornithine bonebed in southeastern Brazil shed light on the early evolution of the avian braincase, brain and inner ear.

Enantiornithine braincase MPM-334-1 from the Late Cretaceous of southeastern Brazil; (a) Ventral view, (b) dorsal view. From Chiappe et al., 2022

Enantiornithes are the most diverse group of Mesozoic birds. The clade shows a mosaic of characters, reflecting their intermediate phylogenetic position between the basal-pygostylians and modern bird, and their remains, ranging from the size of hummingbirds to turkeys, have been collected on every continent except Antarctica. MPM-334-1 (Museu de Paleontologia de Marília, São Paulo State) is a diminutive basicranium of a skeletally mature enantiornithine bird. The endocast comprises impressions from the external surfaces of most of the medulla, parts of the cerebellum, and the ventral portion of the optic tectum.

MPM-334-1 displays a mosaic combination of plesiomorphic dinosaurian traits and a set of endocranial transformations: a flexed brain that are remarkably similar to those of extant birds, a ventralized foramen magnum and ‘crown-like’ endosseous labyrinth. The new study lead by Luis Chiappe, suggest a more complex scenario for the evolution of the avian skull and central nervous system than had previously been understood, with key features of the modern avian endocranium evolving much earlier than what was formerly thought. 

 

References:

Chiappe LM, Navalón G,Martinelli AG, Nava W, Field DJ. 2022 Fossil basicranium clarifies the origin of theavian central nervous system and inner ear. Proc. R. Soc. B289: 20221398. https://doi.org/10.1098/rspb.2022.1398

Chiappe, L. M., Ji, S. & Ji, Q. Juvenile birds from the Early Cretaceous of China: implications for enantiornithine ontogeny. Am. Mus. Novit. 3594, 1–46 (2007).

Introducing Elemgasem nubilus

Elemgasem nubilus. Image credit: Abel Germán Montes

Abelisauroidea is the best known carnivorous dinosaur group from Gondwana. The clade was erected by the legendary paleontologist Jose Bonaparte with the description of Abelisaurus Comahuensis. These ceratosaurian theropods are medium to large, robust animals, such as the Carnotaurus and the Majungasaurus of Madagascar. The group exhibits short, round snouts; thickened teeth; short, stocky arms; and highly reduced forearms. 

The Cretaceous beds of Patagonia holds an extraordinary record of abelisaurids, although there is a paucity during the whole Coniacian.  This lack of specimens during this interval is a worldwide phenomenon. Thus, the Late Cretaceous record of abelisaurids is represented by two intervals: the Cenomanian–Turonian, with taxa from Argentina, Africa and Madagascar, and the Santonian–Maastrichtian, with taxa from Argentina, Brazil, Africa, Madagascar and India. Elemgasem nubilus, from the Portezuelo Formation of Argentina, is the first abelisaurid from the Turonian–Coniacian interval. The new specimen increases the diversity of this clade at a time of significant turnover in the tetrapod fauna of South America, marked by global climate change, and mass extinction events recorded worldwide in the marine realm.

Femur histology of Elemgasem nubilus. From Baiano et al., 2022.

The holotype (MCF-PVPH-380), discovered in 2002, includes several axial and appendicular elements, and exhibits the following features: a marked rugosity on the lateral surface of the fibula, a high lateral surface and a high proximolateral wall of the calcaneum, as well as posterior caudal centra with oval articular surfaces and a groove on the ventral surface. Osteohistological analysis of the femur and phalanx III-2 indicates that this new specimen was at least 8 year old and had achieved sexual maturity but was still growing.

Elemgasem measured about 4 meters (13 feet) long. The genus name refers to the Tehuelche god Elemgasem, the ‘owner’ of the animals and founder of the northern Tehuelche people. The specific name nubilus comes from the Latin ‘foggy days’ in reference to the climatic conditions during the palaeontological expedition when this specimen was discovered.

Location map and geological strata from which the specimen Elemgasem nubilus MCF-PVPH-380 holotype was recovered. From Baiano et al., 2022.

In the Late Cretaceous Abelisauridae splits in the clade Majungasaurinae and and the clade Brachyrostra. Post-Coniacian brachyrostrans constitute a natural group, Furileusauria. Phylogenetic analysis recovered Elemgasem as an unstable taxon, occupying all possible positions within Furileusauria, or as a sister taxon of this clade. 

Elemgasem nubilus lived about 90 million years ago in one of the most phylogenetically diverse fauna from the middle Late Cretaceous of South America, which includes crocodiles, pterosaurs, ornithopods, and four distinct lineages of tetanuran theropods, such as Megaraptor, the alvarezsaurid Patagonykus, the dromaeosaurids Neuquenraptor, Pamparaptor and Unenlagia, and an indeterminate neornithine. 

 

 

References:

Mattia A. Baiano, Diego Pol, Flavio Bellardini, Guillermo J. Windholz, Ignacio A. Cerda, Alberto C. Garrido & Rodolfo A. Coria Elemgasem nubilus: a new brachyrostran abelisaurid (Theropoda, Ceratosauria) from the Portezuelo Formation (Upper Cretaceous) of Patagonia, Argentina (2022). https://doi.org/10.1002/spp2.1462