Abelisaurid Theropods Research Articles

An Early Cretaceous theropod dinosaur from Brazil sheds light on the cranial evolution of the Abelisauridae

Abelisaurid theropods dominated the predator role across Gondwana during the Late Cretaceous. They are characterized by highly reduced forelimbs and one of the most specialized cranial morphologies among carnivorous dinosaurs, exemplified by a broad skull, short rostrum, high occipital region, and highly kinetic intramandibular joint, suggestive of a specialized feeding strategy. Late Cretaceous abelisaurids are known from some remarkably complete taxa with well-preserved skulls. However, little is known about the pattern of character transformation that led to their highly modified condition because there are no well-preserved abelisaurids before the Late Cretaceous. Here we report a basal abelisaurid from the Early Cretaceous of Brazil that preserves a complete skull and reveals an early stage in the cranial evolution of the group. It lacks the specialized temporal and mandibular features characteristic of derived abelisaurids, including the kinetic intramandibular joint and knob-like dorsal projection of the parietals.

Cenomanian vertebrates from Algora (central Spain): New data on the establishment of the European Upper Cretaceous continental faunas

The palaeontological area of Algora (Guadalajara Province, central Spain) provides the largest concentration of vertebrate macroremains for the Cenomanian of south-western Europe. The available faunal list for Algora, based on the analysis of scarce remains collected in geological surveys carried out more than thirty years ago, was never updated. Therefore, and despite the great potential of this site to reveal novel information about the composition of the vertebrate fauna from the base of the Upper Cretaceous in the continent, the previous determination of many of the taxa recognized there is identified here as inaccurate or erroneous (e.g., the identification of two actinopterygian fishes, a single crocodyliform, the helochelydrid turtle Helochelys danubina and carcharodontosaurid dinosaurs). Recent fieldwork campaigns have provided numerous remains, including those of clades poorly represented so far, as well as others hitherto unknown at this site. The new faunal list proposed here included the lepisosteoid Obaichthys africanus, the helochelydrid aff. Plastremys lata, the pleurodiran Algorachelus peregrina, an indeterminate elasmosaurid, a non-eusuchian neosuchian and a eusuchian crocodyliform, a likely abelisaurid theropod and a lithostrotian sauropod. The study of these taxa provides new information about the palaeobiogeography and temporal distributions of some lineages, and increases knowledge about the poorly-known transition between the Lower and the Upper Cretaceous faunas in Europe. This faunal replacement, in which several well-represented lineages in the uppermost Cretaceous were established, is recognized as strongly conditioned by climate changes that took place between the end of the Early Cretaceous and the beginning of the Late Cretaceous.

Paleopathology in a nearly complete skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae)

Research in the Upper Cretaceous (Maastrichtian) Maevarano Formation of northwestern Madagascar has yielded numerous individuals of the abelisaurid theropod Majungasaurus crenatissimus. The number of individuals and quality of preservation allow for a detailed assessment of pathology in this species. A previous survey of Majungasaurus material collected prior to 2005 indicated assorted types of potential infectious and traumatic etiologies. Ongoing research on materials recovered since 2005 provide many additional opportunities to better characterize the anatomy and paleopathology in Majungasaurus. In particular, an almost complete skeleton of a single individual (FMNH PR 2836) preserves evidence of pre-mortem pathologies on multiple bones, including elements of the face and lower jaw, vertebrae, forelimb, ribs and gastralia. Analyses of the pathologies suggest infection of the jugal and quadratojugal, healed fractures and hypertrophic bone growth on several dorsal ribs and a gastralium, septic arthritis in the left forelimb, and evidence of healed/partially healed tooth marks on one cervical vertebra. The injuries appear to be the result of multiple non-fatal events experienced during the life of the individual, rather than a single traumatic incident. Our survey of Majungasaurus indicates most well preserved individuals lack observable pathology, whereas select individuals possess multiple pathologies, a general pattern also noted in other large, nonavian theropods. Such a pattern may result from a snowball effect wherein one injury or infection increases the likelihood of additional maladies due to functional impairment or a compromised immune system in an individual once an initial injury has occurred.

Gregarious behaviour among non-avian theropods inferred from trackways: A case study from the Cretaceous (Cenomanian) Candeleros Formation of Patagonia, Argentina

Gregarious behaviour among dinosaurs has been inferred from several lines of evidence (monospecific bonebeds, skeletal morphology, phylogenetic inferences, comparison with modern ecosystems and parallel trackways with particular characteristics), but is relatively poorly documented for non-avian theropods. Here, we report five parallel theropod trackways of large track size (average length of 28 cm) in the Cretaceous (Cenomanian) Candeleros Formation from northwestern Patagonia, Argentina. The tracks are provisionally assigned to aff. Asianopodus pulvinicalx and considering the autopod morphology of the theropod taxa documented in the Candeleros Formation, abelisaurid theropods are suggested as trackmakers. The trackways possess similar stride, speed estimation, direction and preservational features, and track show uniform depth and do not overlap. Physical barriers (i.e., large fluvial channels or perennial lake) that could influence the direction of the theropod trackmaker gaits were not recognized in the section. Taking into account these considerations, a gregarious behaviour for the abelisaurid theropod trackmakers is proposed. The tracks are preserved as shallow undertracks in a medium-grained sandstone bed deposited in a floodplain setting. The tracking surface is interpreted as the overlaying layer of muddy-siltstone. The occurrence of swelling clays and microbial mats in the track-bearing level could have contributed to the substrate stabilization and their role in the preservation is discussed.

Taxonomic identification of isolated theropod teeth: The case of the shed tooth crown associated with Aerosteon (Theropoda: Megaraptora) and the dentition of Abelisauridae

Shed teeth are usually the most abundant theropod material on a dinosaur fossil site and are constantly reported in the literature. Although new quantitative techniques have emerged to identify isolated theropod teeth with better accuracy, they remain difficult to assign to a certain family-level or genus-level taxon because of the presence of rampant homoplasy in their morphology and the lack of thorough descriptions. Here we test three methods to investigate the phylogenetic position of a tooth previously considered to be part of the holotype of the megaraptoran Aerosteon riocoloradensis (MCNA-PV-3137): a cladistic analysis performed on a dentition-based data matrix scored across 105 theropod species and using a backbone topology as constraint, as well as discriminant and cluster analyses conducted on a dataset of non-avian theropod crown measurements. Even though the cladistic technique appears to be the most reliable method to investigate the phylogenetic affinities of theropod teeth, we recommend using the three techniques conjointly to corroborate the identification of isolated dental material. The results of the cladistic and discriminant analyses support the assignment of the tooth associated with MCNA-PV-3137 to an abelisaurid theropod. It should therefore be excluded from the holotype of Aerosteon. A thorough description of the dental anatomy of Abelisauridae is also provided. The current study is the first to evaluate different methodological tools to identify isolated theropod teeth. With the added detailed description of the dental anatomy of Abelisauridae, it will also assist future authors to investigate the systematic palaeontology of isolated theropod teeth with more confidence.

An abelisaurid (Dinosauria: Theropoda) ilium from the Upper Cretaceous (Cenomanian) of the Kem Kem beds, Morocco.

Abelisaurid theropods first appear in the fossil record in the early Jurassic and survived at least until the end of the Mesozoic. They were known to have dominated South America, India and Madagascar but were not so abundant in North America or Asia. Much less is known about their presence in Africa, although there has been several recent discoveries of abelisaurid material in Morocco. Here we add a partially preserved ilium to a growing body of evidence that suggests abelisaurs might also have dominated Africa.

Cretaceous-Paleogene Transition of Reptilian Tetrapods across Deccan Volcanism in India

Eruptions of lava flows of Deccan large igneous province straddled the Cretaceous-Palaeogene boundary (K-Pg). Sediments associated at different stratigraphic levels within the lava piles of Deccan volcanic sequences (DVS) are mainly terrestrial. We studied the sediments of Eastern and Central Deccan Volcanic Province, and the Malwa Plateau for tracking changes in reptilian tetrapods across the volcanism. The reptiles are mainly represented by abelisaurid-titanosaurid dinosaurs, Alethinophidia madtsoiia snakes, Notosuchian crocodylomorph Simosuchus, bothremydid Kurmademydinae turtles and Anguimorph and Scincomorphs lizards. The evidences suggest that the non-avian dinosaurs were adversely affected by the arrival of the first volcanic flows locally in the province either within C30N or C29R Maastrichtian. The abelisaurid theropods became extinct whereas a single or two species of titanosauriforme dinosaurs survived but eventually became extinct at least 350 ky before the K-Pg boundary with increasing volcanism. The madtsooid snakes and crocodylimorphs were also adversely affected with decline in their diversity and abundance, whereas the Bothremydid turtles survived the initial onslaught of Deccan volcanism and continued across the K-Pg boundary.

A new Abelisauridae (Dinosauria: Theropoda) from São José do Rio Preto Formation, Upper Cretaceous of Brazil and comments on the Bauru Group fauna

ABSTRACT Abelisaurid theropods are well-know from the Cretaceous of several parts of the Southern Hemisphere, including South America, Madagascar, and Africa, but also in India and Europe. Abelisaurids are high-diverse among other theropods with several cervicocephalic specializations reaching medium/large sizes. In the present contribution, we describe a new abelisaurid (Thanos simonattoi, gen. et sp. nov.) from the São José do Rio Preto Formation, Bauru Group, Brazil (Upper Cretaceous). Thanos differs from other theropods by having a well-developed keel becoming wider and deeper posteriorly on the ventral surface; two lateral small foramina separated by a relative wide wall on each lateral surface of the centrum, and well-developed and deep prezygapophyseal spinodiapophyseal fossae. The closed sutures between the axis and odontoid suggest that Thanos had reached a subadult/adult stage before death. Thanos is phylogenetically related to Brachyrostra abelisaurid. The keel on the ventral axial centrum in abelisauroids is here interpreted as a homoplastic condition that became more pronounced towards the phylogeny. The presence of well-developed keel in Thanos suggests that this taxon could be more derived than other abelisaurids. Finally, even though abelisaurids could reach large sizes, Thanos shared the environment with a larger theropod that was probably close to Megaraptora.

The oldest abelisaurid record from Brazil and the palaeobiogeographic significance of mid-Cretaceous dinosaur assemblages from northern South America

Knowledge on the faunal record from the mid-Cretaceous of northern South America has come mainly from the Araripe Basin, northeastern Brazil. However, the Cenomanian Alcântara Formation of the São Luís-Grajaú Basin has recently increased in paleontological importance. Regarding their non-avian dinosaur diversity, the formation has yielded body and trace fossils of spinosaurid, carcharodontosaurid, noasaurid, and maniraptoran theropods, rebbachisaurid and titanosaur sauropods, and possible ornithopods. Here, we report the first unequivocal record of an abelisaurid theropod from the Alcântara Formation, consisting of two shed tooth crowns from the Baronesa Beach locality. They are the oldest occurrence of Abelisauridae from Brazil. With this new record, the non-avian dinosaur assemblage from the Alcântara Formation is most similar to that of the Kem Kem Beds, as suggested by previous works and supported here by similarity analyses of mid-Cretaceous dinosaur-bearing units. Our results also indicate a faunal heterogeneity within northern South America, previously overlooked by studies of this whole landmass as a single sampling unit. We also suggest future approaches treat the dinosaur assemblage from each fossil site or formation as a particular sample unit instead of combining geographically and temporally distinct records.

New brachyrostran remains (Theropoda, Abelisauridae) from La Invernada fossil site (Bajo de la Carpa Formation, Upper Cretaceous), northern Patagonia, Argentina

Several remains of an abelisaurid theropod including a nearly complete sacral complex articulated with both ilia, the distal boot of the pubes, the furcula, teeth, and fragments of transverse processes of caudal vertebrae was discovered in the La Invernada fossil site, northern Patagonia from the Bajo de la Carpa Formation (Santonian). The sacrum exhibit features typical of abelisauroids as narrowing of the middle sacral centra, fused neural spines forming a continuous sheet and ventral bow of the sacrum, in lateral view. The furcula represents de first mention of this bone for a South American abelisaurid. The morphology observed in the transverse processes with distal end projected forward and sagittal ridge on the ventral surface allows its taxonomic assignment to the clade Brachyrostra.

Reassessment of a fragmentary maxilla attributed to Carcharodontosauridae from Presidente Prudente Formation, Brazil

Carcharodontosauridae and Abelisauridae are two coexisting clades of theropod dinosaurs from the Cretaceous of Africa, South America and possibly Europe. The oldest and most recent carcharodontosaurid remains are from the Kimmeridgian-Tithonian of Africa and Turonian of South America, respectively. Recently, a fragmented maxilla bearing a single in-situ tooth (UFRJ-DG409-R) from the Maastrichtian of Brazil has been interpreted as belonging to a carcharodontosaurid. We here reassessed the phylogenetic distribution of these material using morphological, morphometric and phylogenetic analyses. If the morphology of the tooth is shared with carcharodontosaurids and abelisaurids, the morphometric analyses found the crown in the same morphospace as abelisaurids, and the phylogenetic analysis performed on a dentition-based datamatrix retrieved it among Abelisauridae. The maxilla also shares features with both groups, yet the horizontal striations on the paradental plates of UFRJ-DG409-R support abelisaurid affinities. Our data strongly suggest that these specimens belong to abelisaurid theropods, supporting the fact that carcharodontosaurids were likely extinct from Coniacian.

Neuroanatomy of the abelisaurid theropod Viavenator: The most complete reconstruction of a cranial endocast and inner ear for a South American representative of the clade

The type braincase of Viavenator exxoni (MAU-Pv-LI-530) was recovered complete and isolated from most of the other skull bones. Although the braincase is crossed by numerous fractures, using CT scans allowed the generation of 3D renderings of the endocranial cavity enclosing the brain, cranial nerves, and blood vessels, as well as the labyrinth of the inner ear. Within the abelisaurids, the only taxon with a complete braincase and known endocranial morphology is Majungasaurus crenatissimus, from Madagascar. In turn, in Argentina, partial endocranial morphology is known for another two Cretaceous forms: Abelisaurus comahuensis and Aucasaurus garridoi. Here, we present the most complete reconstruction of the neuroanatomy for a representative of the clade in South America. These findings add knowledge to the field of theropod paleoneuroanatomy in general, and abelisaurid diversity in particular. Comparisons of Viavenator with other abelisaurids indicate greater similarity with Aucasaurus than with Majungasaurus, suggesting that South American forms shared the same neurosensorial capabilities, which include larger flocculus of the cerebellum and larger olfactory ratios than the form from Madagascar.

Revised morphology of Pycnonemosaurus nevesi Kellner & Campos, 2002 (Theropoda: Abelisauridae) and its phylogenetic relationships.

Abelisaurid theropods were most abundant in the Gondwana during the Cretaceous Period. Pycnonemosaurus nevesi Kellner & Campos, 2002 was the first abelisaurid dinosaur described from the Bauru Group (Brazil, Upper Cretaceous). Nevertheless, its initial description was based on the comparison of a restricted number of remains with other abelisaurids. In this paper, I present a new description of the morphology of Pycnonemosaurus nevesi, including three new caudal transverse processes and a discussion of several new characteristics based on perspectives derived from recently described abelisauroids. Pycnonemosaurus nevesi differs from other abelisaurids based on the following features: a pubis with a small rounded foot and a ventrally-bowed anterior distal end; posterior caudal vertebrae with a hook-shaped transverse process that has an anterodistal expansion that is short and bowed; a strong and massive tibia with a well-developed lateral malleolus that is ventrally expanded. The unfused sutures represent signs of skeletal immaturity, but the specific ontogenetic stage is still uncertain. The current phylogenetic analysis suggests strongly relationship within Pycnonemosaurus and the most-derived abelisaurids (e.g Carnotaurus and Aucasaurus).

An abelisaurid from the latest Cretaceous (late Maastrichtian) of Morocco, North Africa

During the latest Cretaceous, distinct dinosaur faunas were found in Laurasia and Gondwana. Tyrannosaurids, hadrosaurids, and ceratopsians dominated in North America and Asia, while abelisaurids and titanosaurians dominated in South America, India, and Madagascar. Little is known about dinosaur faunas from the latest Cretaceous of Africa, however. Here, a new abelisaurid theropod, Chenanisaurus barbaricus, is described from the upper Maastrichtian phosphates of the Ouled Abdoun Basin in Morocco, North Africa on the basis of a partial dentary and isolated teeth. Chenanisaurus is both one of the largest abelisaurids, and one of the youngest known African dinosaurs. Along with previously reported titanosaurian remains, Chenanisaurus documents the persistence of a classic Gondwanan abelisaurid-titanosaurian fauna in mainland Africa until just prior to the end-Cretaceous mass extinction. The animal is unusual both in terms of its large size and the unusually short and robust jaw. Although it resembles South American carnotaurines in having a deep, bowed mandible, phylogenetic analysis suggests that Chenanisaurus may represent a lineage of abelisaurids that is distinct from those previously described from the latest Cretaceous of South America, Indo-Madagascar, and Europe, consistent with the hypothesis that the fragmentation of Gondwana led to the evolution of endemic dinosaur faunas during the Late Cretaceous.

Small-sized abelisaurid (Theropoda: Ceratosauria) remains from the Upper Cretaceous of northwest Patagonia, Argentina

A new abelisaurid theropod from the Cenomanian of Candeleros Formation (Neuquén Province, NW Patagonia, Argentina) is described. It includes an isolated frontal, partial pelvis, two fused sacral centra, femoral shaft, rib fragments, partial metatarsal II and shaft of metatarsal III. A paleohistological analysis shows that MMCh-PV 69 was somatically mature at time of death. The prevalence of relatively ordered intrinsic fibers in the primary bone indicates a relatively lower growth rate of MMCh-PV 69 compared with other abelisauroids, such as Aucasaurus garridoi. Phylogenetic analysis found MMCh-PV 69 as a basal abelisaurid, sister group of the node formed by Majungasaurinae and Brachyrostra. We estimated the body mass of MMCh-PV 69 in 240 kg, which makes it one of the smallest abelisaurids recorded. This new form adds to the extensive theropod fauna of the Candeleros Formation, probably the most diverse association of meat-eating dinosaurs recorded in a Cretaceous Formation from South America.

Ontogenetic changes in the craniomandibular skeleton of abelisaurid dinosaur Majungasaurus crenatissimus from the Late Cretaceous of Madagascar

Abelisaurid theropods were one of the most diverse groups of predatory dinosaurs in Gondwana during the Cretaceous. The group is characterized by a tall, wide skull and robust cervical region. This morphology is thought to have facilitated specialized feeding behaviors such as prolonged contact with prey. The Late Cretaceous abelisaurid Majungasaurus crenatissimus typifies this abelisaurid cranial morphotype. Recent fossil discoveries of this species include a partial growth series that allows for the first time an investigation of ontogenetic variation in cranial morphology in a representative abelisaurid. Herein we examine growth trajectories in the shape of individual cranial bones and articulated skulls of Majungasaurus using geometric morphometrics. Several major changes in skull shape were observed through ontogeny, including an increase in the height of the jugal, postorbital, and quadratojugal, an increase in the extent of the contacts between bones, and a decrease in the circumference of the orbi...

Late Cretaceous reptilian biota of the La Colonia Formation, central Patagonia, Argentina: Occurrences, preservation and paleoenvironments

Cropping out on the southeastern margin of the Somún Curá Plateau, the La Colonia Formation (Campanian–Maastrichtian) has yielded, over the last several decades, a varied fossil tetrapod fauna (mammals, ophidians, turtles, dinosaurs, plesiosaurs, anurans). For this study several field trips were carried out specifically to recover reptile remains. Three sections, located on the southeastern slope of the Sierra de La Colonia and in the vicinity of Cerro Bayo, Chubut Province (Argentina), were selected for particular attention. The prospected sections are composed of massive, laminated or heterolithic siltstones and claystones, with scarce and thin intercalations of massive, heterolithic o cross-bedded fine sandstones and of fossiliferous conglomerates. The most abundantly recovered reptiles are terrestrial and freshwater turtles, followed by plesiosaurs and dinosaurs. Among the chelonians, more than 16 specimens of Patagoniaemys gasparinae (Meiolaniformes), three specimens of Yaminuechelys aff. Y. gasparinii (Chelidae), and the remains of a new genus of Chelidae were identified. Among the dinosaurs, theropod metatarsal fragments, an incomplete abelisaurid theropod skeleton, sauropod vertebrae, ankylosaur osteoderms and appendicular fragments of hadrosaurs were found. Among the plesiosaurs there are several well preserved elasmosaurids (including two with associated gastroliths) and a polycotylid (Sulcusuchus erraini). Except for the plesiosaurs, all the reptiles are terrestrial or freshwater taxa. However, analysis of the elasmosaurids indicates they are adult specimens of small body size, which could be related to forms that lived in restricted aquatic environments. Likewise, the polycotylid possesses deep rostral and mandibular grooves, and a conspicuous vascularization and/or innervation, that is consistent with the presence of some associated special sensory structures similar to those known in some cetaceans that inhabit modern rivers and estuaries. Sedimentological analysis suggests that deposition would have been mostly in low-energy restricted environments, like muddy plains, marshes and ponds cut by meandering channels, probably in the central mixed-energy zone within an estuary. This interpretation is consistent with the habitat inferred for the recovered reptiles, as well as with associated foraminifers and with the probable origin of gastroliths found associate with the plesiosaurs.

An articulated pectoral girdle and forelimb of the abelisaurid theropod Majungasaurus crenatissimus from the Late Cretaceous of Madagascar

ABSTRACT Abelisaurid theropods are common members of Cretaceous Gondwanan faunas and are characterized by a bizarre, highly reduced forelimb. Unfortunately, forelimb elements are rarely preserved and thus the basic structure of the abelisaurid forelimb remains poorly understood. Until recently, the Upper Cretaceous Maevarano Formation of northwestern Madagascar has produced numerous exceptional specimens of the abelisaurid theropod Majungasaurus crenatissimus but comparatively little forelimb material. A recently discovered articulated skeleton of Majungasaurus preserves a virtually complete pectoral girdle and forelimb, which, along with additional isolated forelimb elements, affords important new insights into the structure of these elements. New specimens of the scapulocoracoid and humerus allow more detailed description of their morphology, and antebrachial and manual elements are described for the first time. The radius and ulna are approximately one-quarter the length of the humerus and both have expanded proximal and distal articular surfaces relative to their narrow diaphyses. The manus consists of four digits, each composed of a short metacarpal and one (digits I and IV) or two (digits II and III) phalanges. No ossified carpals are present. The proportions of the brachium and antebrachium are stout, more similar to the condition in Carnotaurus than in Aucasaurus. We reinterpret manual digit identities in Aucasaurus and Carnotaurus based on new information provided by the manus of Majungasaurus. Overall, the morphology of the forelimb in Majungasaurus reveals that abelisaurids share an extremely reduced, unique morphology that is dissimilar to the more typical theropod condition seen in other ceratosaurs.

El Museo Argentino de Ciencias Naturales y su colección de dinosaurios

The Museo Argentino de Ciencias Naturales and its collection of dinosaurs. The dinosaur specimens housed in the paleontological collections of the Museo Argentino de Ciencias Naturales have undoubtedly international significance. In addition some have historical value, like Antarctosaurus wichmannianus Huene, 1929, one of the first sauropods in being collected in South America; others are unique in its type, as Amargasaurus cazaui Salgado & Bonaparte, 1991, a dicraeosaurid sauropod of elongated cervical neural spines, and Carnotaurus sastrei Bonaparte, 1985, an abelisaurid theropod with strong frontal horns. The first dinosaur bones incorporated to the collections of the MACN were gathered by Carlos Ameghino, just before his brother Florentino occupied the charge of Director of the Museum. Dinosaur discoveries intensified notably with the arrival to the Museum of Jose Bonaparte, at the end of the decade of 1970. Besides Amargasaurus and Carnotaurus, Bonaparte collected remains of Jurassic dinosaurs, like the sauropod Patagosaurus fariasi Bonaparte, 1986a and the theropod Piatnitzkysaurus floresi Bonaparte, 1986b, which, at their time, formed part of the first association of Jurassic dinosaurs recorded in South America.

NEW ABELISAURID MATERIAL FROM THE UPPER CRETACEOUS (CENOMANIAN) OF MOROCCO

Fragmentary cranial bones of dinosaur origin have been recently recovered from the Kem Kem beds (Upper Cretaceous, Cenomanian) of Morocco. They include two incompletely preserved maxillary bones evidencing diagnostic features of abelisaurid theropods. These new finds provide further evidence of Abelisauridae in the Late Cretaceous of Morocco.