Introducing Llukalkan aliocranianus

Photograph of the materials in the field. Image credit: Federico Gianechini

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by Jose Bonaparte with the description of  Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Tralkasaurus cuyi and Viavenator exxoni. Llukalkan aliocranianus, a new furileusaurian abelisaurid from the Bajo de la Carpa Formation (Santonian) in northwestern Patagonia, is an important addition to the knowledge of abelisaurid diversity.

 

Reconstruction of the complete skull and mandible of Llukalkan aliocranianus. Scale bar: 5 cm. From Gianechini et al., 2021

The new specimen was found near the site where the remains of Viavenator exxoni were recovered at La Invernada fossil area, 50 km southwest of Rincón de los Sauces city, Neuquén province, Argentina. This site has provided a valuable theropod record. Other taxa discovered at La Invernada include the titanosaurian sauropods Bonitasaura salgadoi, Traukutitan eocaudata, and Rinconsaurus caudamirus, pterosaurs, multiple crocodyliforms, snakes, and turtles.

The holotype (MAU-Pv-LI-581) is an incomplete but partially articulated skull with a complete braincase. The generic name derived from the word Llukalkan, “one who scares or causes fear” in Mapudungun language. The specific name aliocranianus means “different skull” in Latin.  Llukalkan exhibits some similarities with Viavenator, that include: elongate and robust olfactory tracts; large and horizontally oriented olfactory bulbs; cerebral hemispheres clearly delimited in lateral view; a tongue-shaped floccular process of cerebellum posteriorly projected and reaching the level of the posterior semicircular canal; and elongate and ventrally projected passage for the rostral middle cerebral vein. Additionally, Llukalkan has a small pneumatic recess caudal to the columellar recess, which is identified as a poorly developed caudal tympanic recess. This taxon also presents a T-shaped lacrimal with jugal ramus lacking a suborbital process, that differs significantly from the lacrimal of other abelisaurids.

 

References:

Federico A. Gianechini, Ariel H. Méndez, Leonardo S. Filippi, Ariana Paulina-Carabajal, Rubén D. Juárez-Valieri & Alberto C. Garrido (2021): A New Furileusaurian Abelisauridfrom La Invernada (Upper Cretaceous, Santonian, Bajo De La Carpa Formation), NorthernPatagonia, Argentina, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2020.1877151

Meet Niebla antiqua

Silhouette of Niebla antiqua showing the preserved bones in white. Scale bar: 0.5 meters. From Aranciaga et al., 2020.

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by Jose Bonaparte with the description of  Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Tralkasaurus cuyi and Viavenator exxoni.  Niebla antiqua, a new specimen from the Late Cretaceous of Río Negro province, is an important addition to the knowledge of abelisaurid diversity.

Niebla antiqua is much smaller than other abelisaurids like Carnotaurus and Abelisaurus, with only 4–4.5 metres (13–15 ft) long. It was found near Matadero Hill, located within the Arriagada Farm, at 70 km south from General Roca city, Río Negro province, Argentina. The generic name derived from the Spanish word for “mist”, referring to the foggy days during the excavation of the specimen. The specific name “antiqua”, comes from the Latin “old” and makes reference to the age of the specimen.

 

Digital reconstruction of the braincase of Niebla antiqua in right lateral (A), dorsal (B), and posterior (C) views. From Aranciaga et al., 2020

Digital reconstruction of the braincase of Niebla antiqua in right lateral (A), dorsal (B), and posterior (C) views. From Aranciaga et al., 2020

 

The holotype (MPCN-PV-796) is represented by a nearly complete braincase, incomplete left dentary, isolated teeth, relatively complete scapulocoracoid, dorsal ribs and incomplete vertebrae. The braincase of Niebla is exquisitely preserved, allowing the recognition of most cranial nerves and vascular foramina. The cranial endocast has a total length of 144 mm and has an approximate volume of 64.2 cm3. The scapulocoracoid is notably similar to that of Carnotaurus with a narrow and elongate scapular blade, a glenoid surface posteriorly oriented, and a dorsoventrally expanded and wide coraco-scapular plate. Paleohistological analysis indicates that despite of its relatively small size, the holotypic specimen represents a somatically mature individual.

 

References:

Aranciaga Rolando, M., Cerroni, M. A., Garcia Marsà, J. A., Agnolín, F. l., Motta, M. J., Rozadilla, S., Brisson Eglí, Federico., Novas, F. E. (2020). A new medium-sized abelisaurid (Theropoda, Dinosauria) from the late cretaceous (Maastrichtian) Allen Formation of Northern Patagonia, Argentina. Journal of South American Earth Sciences, 102915. doi:10.1016/j.jsames.2020.102915

The skull of Carnotaurus

Carnotaurus sastrei. Credit: Gabriel Lio.

The iconic Carnotaurus sastrei was collected in the lower section of La Colonia Formation, Chubut Province, Argentina, by an expedition led by Argentinian paleontologist José Bonaparte. In 1985, Bonaparte published a note presenting Carnotaurus sastrei as a new genus and species and briefly describing the skull and lower jaw. The skull is almost complete (the only missing parts correspond to portions of the left epipterygoid, the right posterolateral area of the parietal and most of teeth crowns) and is exceptionally well preserved measuring 60 cm from the tip of the premaxillae to the distal tip of the paroccipital process. The most distinctive features of Carnotaurus are the two robust conical horns that extend from the frontals. The horns are dorsoventrally compressed, and 146 mm long on both sides. The dorsal surface of each horn is ornamented with a series of longitudinal grooves. A new study by Mauricio Cerroni, Fernando Novas, and Juan Canale provides some new potential autapomorphies diagnostic of Carnotaurus, such as nasolacrimal conduct with an accessory canal, ventral excavation on the quadrate and lateral fossa of the pterygoid.

Skull and neck of Carnotaurus sastrei

The skull of abelisaurids is characterized by having a short and deep cranium at the level of the snout, antorbital fenestra with reduced antorbital fossa, frontals strongly thickened and ornamented conforming well-developed cornual structures, and expanded parietal crest with a tall parietal eminence. The nasal bones of a Carnotaurus are extensively sculptured by highly projected rugosities. Previous studies showed the presence of a row of foramina probably neurovascular, along the dorsal nasal surface, a condition also shared with Rugops and Skorpiovenator. Although in Carnotaurus these foramina are much smaller in diameter.

The horns are predominantly solid and CT scans analyses reveals the presence of a small pneumatic recess on each frontal horn. Those small pneumatic recesses in the frontal horns of Carnotaurus adds new information about the variability of the pneumatic traits on the frontal bones in non-avian theropods. Due to the nature of the horns, the thickness of the skull roof, and the robust neck (with a possible well developed epaxial musculature), it was suggested that Carnotaurus would have the potential to use the horns for some kind of agonistic behaviour. The CT scans also revealed several pneumatic cavities (e.g. promaxillary and lacrimal recesses) much less developed than in Majungasaurus, the only other abelisaurid in which these structures were extensively analysed. The ossification of hyoid apparatus (including basihyal), is one the most complex and outstanding features of Carnotaurus because this element would have remained cartilaginous in most theropods.

 

References:

M.A. Cerroni , J. I. Canale & F. E. Novas (2020): The skull of Carnotaurus sastrei Bonaparte 1985 revisited: insights from craniofacial bones, palate and lower jaw, Historical Biology, DOI: 10.1080/08912963.2020.1802445

Cerroni, M.A., Paulina Carabajal, A., Novel information on the endocranial morphology of the abelisaurid theropod Carnotaurus sastrei .C .R. Palevol (2019), https://doi.org/10.1016/j.crpv.2019.09.005

 

The skull of Skorpiovenator bustingorryi

Skorpiovenator, from the late Cretaceous of Argentina. Museo Municipal Ernesto Bachmann

Skorpiovenator bustingorryi. Museo Municipal Ernesto Bachmann

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by Jose Bonaparte with the description of Abelisaurus comahuensis. The group exhibits strongly reduced forelimbs and hands, stout hindlimbs, with a proportionally robust and short femur and tibia. The skull of abelisaurids is characterized by having a short and deep cranium at the level of the snout, antorbital fenestra with reduced antorbital fossa, frontals strongly thickened and ornamented conforming well-developed cornual structures, expanded parietal crest with a tall parietal eminence. The nasal bones of abelisaurids are distinctive on having two distinct patterns: Abelisaurus, Carnotaurus, and Majungasaurus have nasals transversely convex and extensively sculptured by highly projected rugosities, while Skorpiovenator and Rugops have nasals posteriorly expanded, with lateral and tall bony crests, which give the nasals a transversally concave profile, and conspicuous foramina over the dorsal surface.

Skull of Skorpiovenator (MMCH-PV 48). (scales bar: 5 cm)

Skull of Skorpiovenator bustingorry (MMCH-PV 48). (scale bar: 5 cm)

Skorpiovenator bustingorry is a derived abelisaurid known from a single and nearly complete skeleton (MMCh-PV 48) recovered from rocks of the famous Huincul Formation (Late Cenomanian–Early Turonian). The skull of Skorpiovenator is strongly ornamented with ridges, furrows and tubercles. Unlike other abelisaurids, in Skorpiovenator both nasals are completely unfused. But the most striking feature is an outstanding series of three large foramina in the skull roof of Skorpiovenator that appear to be an extension of the foramina row from the nasals. This feature likely represent an autapomorphy of Skorpiovenator. CT scans made on the skull of Skorpiovenator and Carnotaurus revealed an internal system of canals linked to the dorsal nasal foramina, which likely represent a correlate for a neurovascular complex. This neurovascular system was probably related to the lateral nasal vessels and perhaps innervated by the trigeminal nerve as in extant archosaurs. The biological significance of such neurovascular system could be linked to a zone of thermal exchange, which may help avoid overheat of encephalic tissues.

References:

Cerroni, M. A., Canale, J. I., Novas, F. E., & Paulina-Carabajal, A. (2020). An exceptional neurovascular system in abelisaurid theropod skull: New evidence from Skorpiovenator bustingorryi. Journal of Anatomy. doi:10.1111/joa.13258

Introducing Tralkasaurus cuyi, the thunder lizard.

Photo: AFP/MUSEO ARGENTINO DE CIENCIAS NATURALES

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by the legendary paleontologist Jose Bonaparte with the description of  Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Eoabelisaurus mefi and Viavenator exxoni.

Abelisauroids were traditionally divided into two main clades: large-sized Abelisauridae, and small-sized Noasauridae. Although represented by relatively well-known skeletons, the phylogenetic relationships within abelisaurids remain debated. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous. Now, a new abelisaurid from the upper section of the Huincul Formation (Cenomanian-Turonian) at the Violante Farm fossil site, Río Negro province, northern Patagonia, Argentina, is an important addition to the knowledge of abelisaurid diversity.

Map of El Cuy region showing the Violante farm fossil site. From Cerroni et al., 2020.

The holotype MPCA-Pv 815 is represented by an incomplete specimen including a right maxilla, distorted and incomplete dorsal, sacral and caudal vertebrae, cervical ribs, and pubis. Tralkasaurus is a medium-sized abelisaurid, much smaller than large abelisaurids as Abelisaurus and Carnotaurus. The name derived from Tralka, thunder in Mapudungun language, and saurus, lizard in Ancient Greek. The specific name “cuyi” derived from the El Cuy, the geographical area at Rio Negro province, Argentina, where the fossil was found.

This four-meter-long (13-foot-long) theropod exhibits a unique combination of traits, including deeply incised and curved neurovascular grooves at the lateral maxillary body that originate at the ventral margin of the antorbital fossa, and shows an extensive antorbital fossa over the maxillary body that is ventrally delimited by a well-marked longitudinal ridge that runs from the promaxillary fenestra level towards the rear of the maxilla.
Because body mass is usually indicative of an ecological niche, the new taxon probably occupied a different ecological niche within the predatory guild.

 

References:

Cerroni, M.A., Motta, M.J., Agnolín, F.L., Aranciaga Rolando, A.M., Brissón Egli, F., & Novas, F.E. (2019). A new abelisaurid from the Huincul Formation (Cenomanian-Turonian; Upper Cretaceous) of Río Negro province, Argentina. Journal of South American Earth Sciences https://www.sciencedirect.com/science/article/abs/pii/S0895981119304766

A Brief Introduction to the Osteology of Viavenator exxoni

Viavenator exxoni, Museo Municipal Argentino Urquiza

The Abelisauridae is the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The group was erected by Jose Bonaparte with the description of  Abelisaurus comahuensis, and includes: Carnotaurus sastrei, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Eoabelisaurus and Viavenator exxoni

The holotype of Viavenator exxoni (MAU-Pv-LI-530) was found in the outcrops of the Bajo de la Carpa Formation (Santonian, Upper Cretaceous), northwestern Patagonia, Argentina. Viavenator series of autapomorphies are: transversely compressed parietal depressions on both sides of the supraoccipital crest; ventral edges of the paraoccipital processes located above the level of the dorsal edge of the occipital condyle; basioccipital-opisthotic complex about two and a half times the width and almost twice the height of the occipital condyle, in posterior view; well-developed crest below the occipital condyle; deeply excavated and sub-circular basisphenoidal recess; basipterygoid processes horizontally placed with respect to the cranial roof and located slightly dorsally to the basal tubera; mid and posterior cervical centra with slightly convex lateral and ventral surfaces; presence of an interspinous accessory articular system in middle and posterior dorsal vertebrae; presence of a pair of pneumatic foramina within the prespinal fossa in anterior caudal vertebrae; distal end of the scapular blade posteriorly curved.

Figure 1. Rendering of the type braincase of Viavenator exxoni (MAU-Pv-LI-530) in dorsal (A,B), and right lateral (C,D) view. Adapted from Carabajal y Filippi, 2017.

Viavenator presents highly-derived postcranial characters, and a relatively plesiomorphic skull in comparison with Carnotaurus and Aucasaurus. Cranial elements of this specimen include the complete neurocranium: frontals, parietals, sphenethmoids, orbitosphenoids, laterosphenoids, prootics, opisthotics, supraoccipital, exoccipitals, basioccipital, parasphenoids and basisphenoids. The plesiomorphic traits of the skull of Viavenator are mainly related with the anatomy of frontals, wich lack osseous prominences such as domes or horns. The dorsal surface of the frontals exhibits an ornamentation that consists of pits and sinuous furrows and ridges, although it is not well-preserved. The  exoccipitals form the lateral and possibly the laterodorsal margins of the foramen magnum, as apparently occurs in Carnotaurus. 

Vertebrae of Viavenator exxoni. Scale bar: 5 cm. From Filippi et al., 2017),

The postcranial skeleton of Viavenator is represented by eight cervical vertebrae (the atlas; seven dorsal vertebrate, four of them articulated; twelve caudal vertebrae); ribs; gastralias; one chevron; scapulocoracoid; ischium foot; and fibulae. The atlas is similar to that of Carnotaurus, though less robust and anteroposteriorly shorter; and there  are not observed prezygapophyseal facets in the neurapophyses, so it is inferred that the proatlas was absent, as also occurs in Carnotaurus and Majungasaurus. The shape of the epipophyses of the cervical region, which are
characterized by anterior and posterior projections, is shared by Viavenator and Carnotaurus, but it is not present in pre-Santonian forms such as Ilokelesia and Skorpiovenator. The derived vertebral characters of Viavenator are linked with an increase in the structural rigidity of the vertebral column, and with an increase in the cursorial abilities of these abelisaurids. This combination of plesiomorphic and derived traits suggests that Viavenator is a transitional form.

 

References:

Filippi, L.S., Méndez, A.H., Gianechini, F.A., Juárez Valieri, Rubé.D., Garrido, A.C., Osteology of Viavenator exxoni (Abelisauridae; Furileusauria) from the Bajo de la Carpa Formation, NW Patagonia, Argentina, Cretaceous Research (2017), doi: 10.1016/j.cretres.2017.07.019.

Leonardo S. Filippi, Ariel H. Méndez, Rubén D. Juárez Valieri and Alberto C. Garrido (2016). «A new brachyrostran with hypertrophied axial structures reveals an unexpected radiation of latest Cretaceous abelisaurids». Cretaceous Research 61: 209-219. doi:10.1016/j.cretres.2015.12.018

Paulina-Carabajal, A., Filippi, L., 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, Cretaceous Research (2017), doi: 10.1016/j.cretres.2017.06.013

 

A brief introduction to the Carnotaurus family tree.

 

Skull and neck of Carnotaurus sastrei

Skull and neck of Carnotaurus sastrei (From Novas et al., 2013)

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The oldest records of abelisauroid theropods are from the Early Jurassic. These ceratosaurian theropods exhibit spectacular cranial ornamentation in the form of horns and spikes; and strongly reduced forelimbs and hands. The group was erected by Jose Bonaparte with the description of  Abelisaurus Comahuensis. Although represented by relatively well-known skeletons, the phylogenetic relationships within abelisaurids remain debated. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous, from Cenomanian (Ilokelesia, Xenotarsosaurus, and Ekrixinatosaurus) to Campanian–Maastrichtian (Abelisaurus, Carnotaurus, Aucasaurus, and Noasaurus).

Abelisauroidea has been divided into two main branches: the Noasauridae and the Abelisauridae. The Noasauridae are known from Cretaceous beds in northern Argentina, Madagascar, India, and Niger. They are small and slender with sizes that range from 1 to 3 metres in length. The best-preserved and most complete noasaurid is Masiakasaurus knopfleri from the Maastrichtian of Madagascar. The Abelisaurids 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.

Masiakasaurus on display at the Royal Ontario Museum.

Masiakasaurus on display at the Royal Ontario Museum.

Carnotaurus sastrei is the most advanced member of Abelisauridae. It was collected in the lower section of La Colonia Formation, Chubut Province, Argentina, by an expedition led by Argentinian paleontologist José Bonaparte. In 1985, Bonaparte published a note presenting Carnotaurus sastrei as a new genus and species and briefly describing the skull and lower jaw. The skull of Carnotaurus is complete, measuring 60 cm from the tip of the premaxillae to the distal tip of the paroccipital process. The most distinctive features of Carnotaurus are the two robust conical horns that extend from the frontals. The horns are dorsoventrally compressed, and 146 mm long on both sides. The dorsal surface of each horn is ornamented with a series of longitudinal grooves. Because relatively few abelisaurid braincases are known, the description of the Carnotaurus braincase is important for understanding the variability of this structure within the clade (Carabajal 2011). C. sastrei would have had a comparatively weak muscle-driven bite.

The forelimbs of Carnotaurus show an extreme reduction, proportionally greater than the reduction observed in tyrannosaurids, although the radius, ulna and humerus are very robust. The hand has four digits, including a large, conical-shaped metacarpal IV lacking an articulation for a phalanx.

 

References:

Novas, F.E., et al., Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia, Cretaceous Research (2013), http://dx.doi.org/10.1016/j.cretres.2013.04.001

Bonaparte, José F.; Novas, Fernando E.; Coria, Rodolfo A. (1990). “Carnotaurus sastrei Bonaparte, the horned, lightly built carnosaur from the Middle Cretaceous of Patagonia”, Contributions in Science (Natural History Museum of Los Angeles County) 416.

Mazzetta, Gerardo V.; Fariña, Richard A.; Vizcaíno, Sergio F. (1998). “On the palaeobiology of the South American horned theropod Carnotaurus sastrei Bonaparte”, Gaia 15: 185–192.

Ruiz, Javier; Torices, Angélica; Serrano, Humberto; López, Valle (2011). “The hand structure of Carnotaurus sastrei (Theropoda, Abelisauridae): implications for hand diversity and evolution in abelisaurids”. Palaeontology 54 (6): 1271–1277.