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

A new giant titanosaur sauropod from the Upper Cretaceous of Argentina

Image credit: Jose Luis Carballido/CTyS-UNLaM/AFP

Since the discovery of dinosaur remains in the Neuquen basin in 1882, Argentina has gained the title of Land of the Giants. The tittle was reinforced by the discoveries of titanosaurs like Argentinosaurus, Dreadnoughtus, Notocolossus, Puertasaurus, and Patagotitan. The study of this diverse group of sauropod dinosaurs embrace an extensive list of important contributions, which started with Richard Lydekker’s pioneering work on Patagonian dinosaurs. 

Titanosauria is a diverse clade of sauropod dinosaurs represented by nearly 80 genera described worldwide. The group includes the smallest (e.g. Rinconsaurus, and Saltasaurus; with estimated body masses of approximately 6 tonnes) and largest sauropods known to date. The Argentinean record of titanosaurs is particularly abundant with almost 50% of the total world record. For years, Argentinosaurus huinculensis was considered the largest dinosaur that ever walked the Earth. The tittle is now in possession of Patagotitan mayorum, discovered in 2010. The first estimations of Patagotitan body mass suggested that it weigh around 70 tons and reached 40 metres (131 feet) long. But a new study published in 2020 indicates that the body mass of Patagotitan ranges between 42–71 tons, with a mean value of 57 tons.

 

Figure 2. Caudal sequence of MOZ-Pv 1221 and detail of caudal vertebrae 3, 4, 11 and posterior element. From Otero et al., 2021

A new specimen from the Candeleros Formation (98 Ma) of Neuquén Province probably exceeds Patagotitan in size. This new giant titanosaur sauropod was discovered in 2012 and is the second taxon from Candeleros Formation, in addition to Andesaurus. The new specimen, identified as MOZ-Pv 1221, includes a sequence of anterior and middle caudal vertebrae, consisting of the first 20 mostly articulated caudal vertebrae and haemal arches plus isolated posterior caudals, pelvis and other appendicular elements. The preserved caudal sequence corresponds to approximately the anterior half of the tail. The neural spines of the anterior caudal vertebrae in MOZ-Pv 1221 are transversely wider than anteroposteriorly long.

Compared to other giant titanosaurs, the recovered appendicular bones of MOZ-Pv 1221 are larger than any known titanosaur described to date. The maximum dorsoventral height at the proximal section of the scapula is 17% higher than in Patagotitan, 26% higher than in Dreadnoughtus, and 130% higher than in Mendozasaurus. The maximum proximo distal length of the pubis of MOZ-Pv 1221 is 166 cm, which is 10% longer than in Patagotitan, 18% longer than in Dreadnoughtus, and 21% longer than in Futalognkosaurus. Although it is not currently possible to estimate the body mass of MOZ-Pv 1221 because of the fragmentary nature of this specimen, it is clear that this new titanosaur partially recovered from the Candeleros Formation can be considered one of the largest titanosaurs that ever walked the Earth.

 

References:

Otero A, Carballido JL, Salgado L, Canudo JI, Garrido AC (2021), Report of a giant titanosaur sauropod from the Upper Cretaceous of Neuquén Province, Argentina, Cretaceous Research https://doi.org/10.1016/j.cretres.2021.104754

Carballido JL, Pol D, Otero A, Cerda IA, Salgado L, Garrido AC, Ramezani J, Cúneo NR, Krause JM. 2017 A new giant titanosaur sheds light on body mass evolution among sauropod dinosaurs. Proc. R. Soc. B 284: 20171219.
DOI: 10.1098/rspb.2017.1219

Otero, A., J. L. Carballido, A. Pérez Moreno. 2020. The appendicular osteology of Patagotitan mayorum (Dinosauria, Sauropoda). Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2020.1793158

Benson, R. B. J., Campione, N. E., Carrano, M. T., Mannion, P. D., Sullivan, C., Upchurch, P., & Evans, D. C. (2014). Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biology, 12(5), http://doi.org/10.1371/journal.pbio.1001853.

Top fossil discoveries of 2020

Reconstruction of Bagualia alba. Credit: Jorge Gonzalez

2020 started with massive wildfires, locusts devouring crops across East Africa and the coronavirus outbreak. By early March, the World Health Organization (WHO) declared the coronavirus, SARS-CoV-2, to be a pandemic and recommend “surveillance to find, isolate, test and treat every case, to break the chains of transmission.”

The climate crisis escalated. Mega-fires were exacerbated by drought, and anthropogenic climate change. In September, the Arctic sea ice shrank to its second-lowest extent in more than 40 years. Meanwhile fossil explorations were put on hiatus because of the pandemic. We also lost two great paleontologists: Jose Bonaparte and Jenny Clack. But 2020 hasn’t been all bad. Cool new papers about fossil biosignatures, mass extinctions, the tetrapod transition to land (co-authored by Jenny Clack), the evolution of the avian brain, the first well-documented case of bone cancer in a non-avian dinosaur, the nature of the first dinosaur eggs, and perfectly preserved remains of an Ice Age cave bear, shapped a remarkable year in paleontology. Among the most striking fossil discoveries are:

  • Wulong bohaiensis, the dancing dragon

Wulong bohaiensis. From Poust et al., 2020

This small, feathered dromaeosaurid theropod lived in the Early Cretaceous (Aptian) of China, and was discovered by a farmer more than a decade ago. The holotype (D2933) is a complete articulated skeleton (only some ribs are missing) and exhibits special preservation of keratinous structures. Wulong is distinguished by the following autapomorphic features: long jugal process of quadratojugal, cranially inclined pneumatic foramina on the cranial half of dorsal centra, transverse processes of proximal caudals significantly longer than width of centrum, presence of 30 caudal vertebrae producing a proportionally long tail, distally located and large posterior process of the ischium, and large size of supracoracoid fenestra (>15% of total area). The holotype has several gross osteological markers of immaturity like the unfused dorsal and sacral vertebrae, but mature feathers are present across the entire body of Wulong.

  • Tralkasaurus cuyi

Photo: AFP/MUSEO ARGENTINO DE CIENCIAS NATURALES

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. 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. 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.

  • Asteriornis maastrichtensis

Artist’s reconstruction of Asteriornis maastrichtensis. Illustration: Phillip Krzeminski

Asteriornis maastrichtensis is a small member of the clade Pangalloanserae, the group that includes Galliformes and Anseriformes, with an estimated body weight of about 400 grams. The holotype (NHMM, 2013 008) includes a nearly complete, articulated skull with mandibles, and associated postcranial remains preserved in four blocks. It was collected in 2000 by Maarten van Dinther. The new specimen, dated between 66.8 and 66.7 million years ago, reveals a previously undocumented combination of ‘galliform’ and ‘anseriform’ features that emphasizes the modular nature of the skull and bill of crown birds. The narrow and elongate hindlimbs and provenance from nearshore marine sediments suggest that Asteriornis might have had a shorebird-like ecology. The generic name is derived from the name of the Asteria, the Greek goddess of falling stars, and the Greek word ornis for bird. The specific name maastrichtensis honors the provenance of the holotype, the Maastricht Formation (the type locality of the Late Cretaceous Maastrichtian stage).

  • Overoraptor chimentoi

Silhouette of Overoraptor chimentoigen. et sp. nov. (MPCA-Pv805) showing selected skeletal elements. From Motta et al., 2020.

Overoraptor was a gracile theropod that reached about 1.3 m in total length. The name derived from the Spanish word “overo”, meaning piebald, in reference to the coloration of the fossil bones (a pattern of light and dark spots), and the word “raptor” from the Latin for thief. The species name honors Dr. Roberto Nicolás Chimento, who discovered the specimen. The holotype (MPCA-Pv 805) and paratype (MPCA-Pv 818) specimens of O. chimentoi were found in a quarry in association with disarticulated crocodilian and turtle bones. The new taxon comes from the Huincul Formation. The new taxon comes from the Huincul Formation. The unusual combination of a plesiomorphic hindlimb with features that are correlated with cursorial habits, and the more derived forelimb with features that show some adaptations related to active flight, placed Overoraptor, together with Rahonavis in a clade that is sister to Avialae.

  • The Spinosaurus tail

Reconstructed skeleton and caudal series of Spinosaurus aegyptiacus. From Ibrahim et al., 2020.

Spinosaurus aegyptiacus is one of the most famous dinosaur of all time. It was discovered by German paleontologist and aristocrat Ernst Freiherr Stromer von Reichenbach in 1911. Almost a century later, a partial skeleton of a subadult individual of S. aegyptiacus was discovered in the Cretaceous Kem Kem beds of south-eastern Morocco. At the time of deposition, this part of Morocco was located on the southern margin of the Tethys Ocean and it was characterized by an extensive fluvial plain dominated by northward flowing rivers and terminating in broad deltaic systems on Tethys’ southern shores. The neotype of S. aegyptiacus preserves portions of the skull, axial column, pelvic girdle, and limbs. An international team led by Nizar Ibrahim published the first description of the fossil in 2014 and suggested that Spinosaurus may have been specialised to spend a considerable portion of their lives in water.

 

  • Kongonaphon kely.

Reconstruction of Kongonaphon kely. Credit: Alex Boersma

Kongonaphon kely, from the Middle to Late Triassic of Madagascar, is close to the ancestry of dinosaurs and pterosaurs. Discovered in 1998, the holotype (UA 10618) is a partial skeleton composed of a right maxilla, distal portion of the humerus, right femur, proximal portions of the right and left tibia, and indeterminate skeletal fragments. The most striking feature of Kongonaphon is its extraordinarily small size (estimated height,∼10 cm).

 

  • Niebla antiqua

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

Niebla antiqua, a new specimen from the Late Cretaceous of Río Negro province, is an important addition to the knowledge of abelisaurid diversity. This new taxon 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 braincase of Niebla is exquisitely preserved, allowing the recognition of most cranial nerves and vascular foramina.

  • Oksoko avarsan

The skull of Oksoko avarsan in lateral view. From Funston et al., 2020.

Oksoko avarsan is a small oviraptorosaur, with a large, toothless beak and only two fingers on each forearm. The generic name is derived from the word Oksoko, one of the names of the triple-headed eagle in Altaic mythology. The specific name is derived from the Mongolian word avarsan, meaning rescued, because the holotype was rescued from poachers and smugglers in 2006. Preserved in an assemblage of four individuals, the holotype, MPC-D 102/110.a, is a nearly complete juvenile skeleton missing only the distal half of the tail. The excellent preservation of this assemblage provides strong evidence of gregarious behaviour.

 

  • Bagualia alba

Bagualia alba. From Pol et al., 2020

Bagualia alba, recovered from the base of the Cañadón Asfalto Formation, lived 179 million years ago and is the oldest known eusauropod. Discovered in 2007 by an international team of researchers led by Argentinean paleontologist Diego Pol, the holotype of Bagualia alba (MPEF PV 3301) consists of a posterior half of a skull found in articulation with seven cervical vertebrae. It was found in close association with multiple cranial and postcranial remains belonging to at least three individuals. Body mass estimated suggests that Bagualia weighted 10 tons, approximately the size of two African elephants. The teeth have a D-shaped cross section, apical denticles, and buccal and lingual grooves. But the most striking feature of Bagualia is the enamel layer which is extremely thick, seven times that of other pre-volcanic herbivores, and is heavily wrinkled on its outer surface.

  • The origin of Pterosaurs

A partial skeleton of Lagerpeton (Image Credit: Virginia Tech/Sterling Nesbitt)

Lagerpetids are small to medium-sized (less than 1 m long), cursorial, non-volant reptiles from Middle–Upper Triassic of Argentina, Brazil, Madagascar, and North America. Based on the anatomical information from Lagerpeton chanarensis (from the Chañares formation, Argentina), Ixalerpeton polesinensis (from the Santa Maria Formation, Brazil), Kongonaphon kely (from Morondava Basin, Madagascar), and Dromomeron spp. (from North America), an international team lead by Martin Ezcurra from the Museo Argentino de Ciencias Naturales in Buenos Aires, Argentina, elucidated their relationship to pterosaurs. The recognition of this group as the sister taxon to pterosaurs provides clues to study the origin of Pterosauria, its specialized body plan and flying abilities.

References:

Poust, AW; Gao, C; Varricchio, DJ; Wu, J; Zhang, F (2020). “A new microraptorine theropod from the Jehol Biota and growth in early dromaeosaurids”. The Anatomical Record. American Association for Anatomy. doi:10.1002/ar.24343

Ibrahim, N., Maganuco, S., Dal Sasso, C. et al. Tail-propelled aquatic locomotion in a theropod dinosaur. Nature (2020). https://doi.org/10.1038/s41586-020-2190-3

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

Gregory F. Funston; Tsogtbaatar Chinzorig; Khishigjav Tsogtbaatar; Yoshitsugu Kobayashi; Corwin Sullivan; Philip J. Currie (2020). «A new two-fingered dinosaur sheds light on the radiation of Oviraptorosauria». Royal Society Open Science, doi:10.1098/rsos.201184

Pol D., Ramezani J., Gomez K., Carballido J. L., Carabajal A. Paulina, Rauhut O. W. M., Escapa I. H. and Cúneo N. R., (2020) Extinction of herbivorous dinosaurs linked to Early Jurassic global warming eventProc. R. Soc. B.28720202310 http://doi.org/10.1098/rspb.2020.2310

 

Ezcurra, M.D., Nesbitt, S.J., Bronzati, M. et al. Enigmatic dinosaur precursors bridge the gap to the origin of Pterosauria. Nature (2020). https://doi.org/10.1038/s41586-020-3011-4

Introducing Bagualia alba, the oldest known eusauropod.

Bagualia alba. From Pol et al., 2020

During the Early Jurassic the southwestern margin of Gondwana was affected by a voluminous magmatic episod related to the emplacement of t heKaroo-Ferrar-Chon Aike Large Igneous Provinces (LIPs). That pulse of volcanism led to global warming, with at least four times the present level of atmospheric CO2, and ocean acidification that resulted in a mass extinction of marine invertebrates and turnover among groups of marine plankton. The period is also characterized by a floristic turnover and the diversification of the conifers, especially modern families, with small coriaceous leaves. Biostratigraphic and high-precision geochronologic results indicate that a major faunal turnover of the sauropodomorph dinosaurs took place in the Early Jurassic, which led to the rise of the eusauropods. Cañadón Asfalto Basin (part of the Chon Aike Igneous Province of Patagonia) in the Chubut Province of Argentina preserves an extraordinary record of Jurassic fauna and flora that marks key events in the evolution of Mesozoic life. The recently described Bagualia alba, recovered from the base of the Cañadón Asfalto Formation, lived 179 million years ago and is the oldest known eusauropod. The name of the new specimen refers to Cañadón Bagual, the site where the fossil was found, and alba (dawn, in Spanish), for its early age.

Reconstruction of Bagualia alba. Credit: Jorge Gonzalez

Discovered in 2007 by an international team of researchers led by Argentinean paleontologist Diego Pol, the holotype of Bagualia alba (MPEF PV 3301) consists of a posterior half of a skull found in articulation with seven cervical vertebrae. It was found in close association with multiple cranial and postcranial remains belonging to at least three individuals. Body mass estimated suggests that Bagualia weighted 10 tons, approximately the size of two African elephants. Among the characters that distinguish Bagualia from other early sauropods area pointed process on the anteroventral end of the premaxilla and anterodorsal end of the dentary; orbital margin of the frontal with a close V-shape pointed medially that results in a short contribution to the orbit; supratemporal fenestra about as anteroposteriorly long as lateromedially wide; and strongly marked proatlantal facets on the laterodorsal margin of the foramen magnum. The teeth have a D-shaped cross section, apical denticles, and buccal and lingual grooves. But the most striking feature of Bagualia is the enamel layer which is extremely thick, seven times that of other pre-volcanic herbivores, and is heavily wrinkled on its outer surface.

In Patagonia, prior to the Toarcian palaeoenvironmental crisis the plant assemblage consisted of sphenophytes, dipteridacean ferns, conifers, seed ferns, Bennetitales and cycads. This diversity is indicative of more humid conditions. By contrast, the less diverse palynologycal assemblage postdating the volcanic event is indicative of seasonally dry and warm conditions, and are largely dominated by the conifers Araucariaceae, Cheirolepidiaceae and Cupressaceae. These large conifers with coriaceous leaves as the dominant trees likely acted as a strongly selective regime favouring the survival and success of eusauropods, which had powerful jaws and an oversized gut. Conversely, the disappearance of many elements of the diverse pre-Toarcian flora could have influenced the extinction of the diverse lineages of smaller non-sauropods, which lacked adaptations to high-fibre herbivory as their gracile skulls and mandibles were less mechanically efficient and their teeth were small, with thin enamel (less than 200 μm) and lacked tooth–tooth occlusion.

 

 

References:

Pol D., Ramezani J., Gomez K., Carballido J. L., Carabajal A. Paulina, Rauhut O. W. M., Escapa I. H. and Cúneo N. R., (2020) Extinction of herbivorous dinosaurs linked to Early Jurassic global warming eventProc. R. Soc. B.28720202310 http://doi.org/10.1098/rspb.2020.2310
 
Cúneo, R., Ramezani, J., Scasso, R., Pol, D., Escapa, I., Zavattieri, A. M., & Bowring, S. A. (2013). High-precision U–Pb geochronology and a new chronostratigraphy for the Cañadón Asfalto Basin, Chubut, central Patagonia: Implications for terrestrial faunal and floral evolution in Jurassic. Gondwana Research, 24(3-4), 1267–1275. doi:10.1016/j.gr.2013.01.010 

The endocranial anatomy of Buriolestes

The skull of Buriolestes shultzi. From Müller et al., 2018

The Santa Maria Formation in southern Brazil, comprises a succession of Middle to Late Triassic sedimentary rocks that have been long renowned for their rich tetrapod fossils including one of the oldest (and the best preserved) associations of dinosaur and dinosaur precursor. Buriolestes shultzi, discovered in 2009 and described in 2016, is one of the earliest member of Sauropodomorpha, the group known for giant quadrupedal and herbivorous forms.

Buriolestes lived in what’s now Brazil about 230 million years ago. The holotype (ULBRA-PVT280) includes a partial skull, few pre-sacral, three sacral, and 42 tail vertebrae, left scapula and forelimb lacking most of the manus, paired iliaand ischia, partial left pubis, and nearly complete left hind limb. More remains of Buriolestes were discovered between 2015 and 2018. One of thoses new specimens (CAPPA/UFSM 0035) is a nearly complete and articulated skeleton. More important, the skull is almost entirely preserved, including both lower jaws.

Bones of the skull roof of CAPPA/UFSM 0035. Frontals in (a) dorsal and (b) ventral views. Parietals in (c) dorsal and (d) ventral views. From Müller et al., 2020

The estimated body mass for this new specimen was 4.50 kg. The endocast of Buriolestes exhibits an elongated olfactory tract, differing from the short tract observed in later forms, combined to a relatively small pituitary gland. The CT scans show a well‐developed flocculus of the cerebellum, with this structure projecting into the space between the semicircular canal. The flocculus plays a key a role in coordinate eye movements, and tends to be enlarged in taxa that rely on quick movements of the head and the body. This condition is also observed in another of the earliest sauropodomorphs, Saturnalia. Additionally, the dentary traits are compatible with a faunivorous diet suggesting that early members of the Sauropodomorpha were likely predators.

 

References:

Müller, Rodrigo T.; Ferreira, José D.; Pretto, Flávio A.; Bronzati, Mario; Kerber, Leonardo (2020). “The endocranial anatomy of Buriolestes schultzi (Dinosauria: Saurischia) and the early evolution of brain tissues in sauropodomorph dinosaurs”. Journal of Anatomy. doi:10.1111/joa.13350

Müller, Rodrigo T.; Langer, Max C.; Bronzati, Mario; Pacheco, Cristian P.; Cabreira, Sérgio F.; Dias-Da-Silva, Sérgio (2018). “Early evolution of sauropodomorphs: anatomy and phylogenetic relationships of a remarkably well-preserved dinosaur from the Upper Triassic of southern Brazil”. Zoological Journal of the Linnean Society. 184 (4): 1187–1248. doi:10.1093/zoolinnean/zly009

Cabreira et al., A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet, Current Biology (2016), http://dx.doi.org/10.1016/j.cub.2016.09.040

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

Introducing Oksoko avarsan

Oviraptorosaurs are a well-defined group of coelurosaurian dinosaurs characterized by short, deep skulls with toothless jaws, pneumatized caudal vertebrae, anteriorly concave pubic shafts, and posteriorly curved ischia. The most basal forms were small, similar to a chicken or a turkey, and like extant birds, they had pennaceous feathers. Their fossil record span much of the Cretaceous of Asia and North America. The most famous dinosaur of this group, Oviraptor, was discovered in 1923 by Roy Chapman Andrews in Mongolia, associated with a nest of what was thought to be Protoceratops eggs. The misconception persisted until 1990s when it was revealed that the eggs actually belonged to Oviraptor, not Protoceratops. Since then, more skeletons of Oviraptor and other oviraptorids like Citipati and Nemegtomaia have been found brooding over their eggs.

The Nemegt Basin in the Gobi Desert holds an extraordinary record of members of all three Late Cretaceous families of oviraptorosaurs: avimimids, caenagnathids,and oviraptorids. Oksoko avarsan is a newly described small oviraptorosaur, with a large, toothless beak and only two fingers on each forearm. The generic name is derived from the word Oksoko, one of the names of the triple-headed eagle in Altaic mythology. The specific name is derived from the Mongolian word avarsan, meaning rescued, because the holotype was rescued from poachers and smugglers in 2006.

The skull of Oksoko avarsan in lateral view. From Funston et al., 2020.

Preserved in an assemblage of four individuals, the holotype, MPC-D 102/110.a, is a nearly complete juvenile skeleton missing only the distal half of the tail. The excellent preservation of this assemblage provides strong evidence of gregarious behaviour.

The new taxon exhibits the following features: a dome-shaped cranial crest composed of the nasals and frontals, with a small contribution from the posteroventrally inclined parietals, nasal recesses housed in a depression; postorbital with dorsally directed frontal process; cervical vertebrae with large epipophyses; accessory ridge of brevis fossa of ilium, anteriorly curving pubis; and large proximodorsal process of distal tarsal IV. But the most striking feature of Oksoko is the functionally didactyl manus. This is the first evidence of digit loss in oviraptors. Maximum-likelihood reconstruction reveals a trend towards forelimb and digit reduction in oviraptorosaurs. This variation in forelimb length and morphology variation may have facilitated the radiation of the clade in the Late Cretaceous.

 

 

References:

Gregory F. Funston; Tsogtbaatar Chinzorig; Khishigjav Tsogtbaatar; Yoshitsugu Kobayashi; Corwin Sullivan; Philip J. Currie (2020). «A new two-fingered dinosaur sheds light on the radiation of Oviraptorosauria». Royal Society Open Science, doi:10.1098/rsos.201184

Funston, G. F., Mendonca, S. E., Currie, P. J., & Barsbold, R. (2018). Oviraptorosaur anatomy, diversity and ecology in the Nemegt Basin. Palaeogeography, Palaeoclimatology, Palaeoecology, 494, 101–120. doi:10.1016/j.palaeo.2

The nature of the first dinosaur eggs

Protoceratops embryos in a curled position. Credit: M. Ellison/American Museum of Natural History

The evolution of the cleidoic egg was an important milestone in the history of the vertebrates, an innovation that enabled amniotes to colonize land. The complex structure the cleidoic egg added extramembryonic membranes (the chorion and the ammnion) and a shell that provides protection for the developing embryo while being permeable enough to allow for the exchange of carbon dioxide and oxygen. The shell may be either leathery or calcified. Early amniotes and more primitive tetrapods laid soft eggshells. Lizards, snakes, and pterosaurs, also laid soft eggs. Modern crocodilians and birds lay hard-shelled eggs. This feature has been interpreted as a key factor in their survival through the Cretaceous–Palaeogene extinction (approximately 66 million years ago).

Paleontological studies of this critical event have been greatly hampered by the poor early record of fossil eggs. Eggs from ornithopods, sauropodomorphs, titanosaurs and tetanuran have been reliably identified but most of these fossils are from the Cretaceous period. The bias in the egg fossil record cannot be explained solely by preferential preservation of certain nesting sites, as previously hypothesized. A new study by an international team of scientists lead by Mark Norell found that hard-shelled eggs evolved at least three times independently in dinosaurs.

Egg assigned to the basal sauropodomorph Mussaurus. Credit: Diego Pol

The first description of dinosaur eggshells was made in 1859 by Jean-Jacques Pouech, a Catholic priest and amateur naturalist. Although he did not identify the eggshell as dinosaurian, but from a gigantic bird. The egg architecture of non-avian dinosaurs, crocodilian, extant birds, and turtles, is the same: an innermost shell membrane, a biomineralized protein matrix (both arranged in multiple layers), and an outer cuticle. The new study analyzed eggs from two very different non-avian dinosaurs: Protoceratops, a small plant-eater, and Mussaurus, a long-necked herbivore.

The Protoceratops specimen, from the the Ukhaa Tolgod locality (Campanian/Upper Cretaceous) in Mongolia, comprises a clutch of at least 12 eggs and embryos. The researchers found the presence of a diffuse black and white egg-shaped halo. Raman spectroscopy revealed the presence of protein fossilization products (PFPs) and phosphate (the white layer) in the Protoceratops eggshell. Additionally, they found that the PFPs in the Protoceratops eggshells contain relatively high amounts of S-heterocycles, which are characteristic of eggshell-derived organic matter.

Simplified phylogeny showing the evolution of eggshell in Archosauria. From Norell et al., 2020

Mussaurus patagonicus was originally described from several well-preserved post-hatchling specimens associated with egg remains found at Laguna Colorada Formation (Late Triassic/Early Jurassic) in Argentina. The histological evaluation of the Mussaurus eggshells revealed a dark brown, semi-transparent, apparently multilayered carbonaceous film, comparable to the Protoceratops soft eggshell.

The discovery of the soft nature of Protoceratops and Mussaurus eggs provides direct evidence for the independent evolution of calcified eggs in dinosaurs. This finding is supported by the recent description of several reproductives traits in theropod dinosaurs that differs considerably from that of derived ornithischians and sauropods, and may have played a key part in the Cretaceous–Palaeogene survival and radiation of modern birds.

References:

Norell, M.A., Wiemann, J., Fabbri, M. et al. The first dinosaur egg was soft. Nature (2020). https://doi.org/10.1038/s41586-020-2412-8

Neuroanatomy of Irritator challengeri

Reconstructed mount of Irritator challengeri.

The Spinosauridae is a specialized group of large tetanuran theropods known from the Berriasian to the Cenomanian of Africa, South America, Europe and Asia, characterised by a long, narrow skull, robust forelimbs with a hooked thumb claw, and tall neural spines forming a dorsal sail. The ecology of the group has been debated since the original discovery of Spinosaurus aegyptiacus in 1911. The recient description of a nearly complete and partially articulated tail of S. aegyptiacus reinforces the hypothesis that this giant theropod spent plenty of time underwater.

The holotype of Irritator challengeri (SMNS 58022; Staatliches Museum für Naturkunde Stuttgart, Stuttgart, Germany) from the Romualdo Member of the Santana Formation (Lower Cretaceous) in northeastern Brazil represents one of the few preserved spinosaurid braincases and can provide insights into neuroanatomical structures that might be expected to reflect the ecological affinities of the group.

3D renderings of the holotype fossil of Irritator challengeri (SMNS 58022) in right lateral view. From Schade et al., 2020

The skull of Irritator is remarkably narrow, especially in the region of the elongated snout. The braincase is short anteroposteriorly but deep dorsoventrally, extending ventrally far below the occipital condyle. The cranial endocast of Irritator shows weakly demarcated brain regions, elongate olfactory tracts and pronounced cranial flexures that are consistent with the inferred phylogenetic position of spinosaurids as basal tetanurans. Irritator also exhibits enlarged floccular recesses, which is an unusual feature for basal tetanurans. The flocculus of the cerebellum plays a role in coordinate eye movements, and tends to be enlarged in taxa that rely on quick movements of the head and the body. Within non-avian theropod dinosaurs, large floccular recesses are common among coelurosaurs. Additionally, lateral semicircular canal orientation suggests a downward inclined snout posture, which enables unobstructed, stereoscopic forward vision, important for distance perception and thus precise snatching movements of the snout.

 

References:

Schade, M., Rauhut, O.W.M. & Evers, S.W. Neuroanatomy of the spinosaurid Irritator challengeri (Dinosauria: Theropoda) indicates potential adaptations for piscivory. Sci Rep 10, 9259 (2020). https://doi.org/10.1038/s41598-020-66261-w

Ibrahim, N., Maganuco, S., Dal Sasso, C. et al. Tail-propelled aquatic locomotion in a theropod dinosaur. Nature (2020). https://doi.org/10.1038/s41586-020-2190-3

Sues, H., Frey, E., Martill, D., Scott, D. 2002. Irritator challengeri, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil. Journal of Vertebrate Paleontology. 22, 3: 535-547 https://doi.org/10.1671/0272-4634(2002)022[0535:ICASDT]2.0.CO;2

Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., Zouhri, S., Myhrvold, N., Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 345(6204), 1613–1616. doi:10.1126/science.1258750 

The growth of Tyrannosaurus rex

Tyrannosaurus rex ontogram. From Carr 2020.

Tyrannosaurus rex is the most iconic dinosaur of all timeIt was discovered in the Hell Creek Formation by Barnum Brown in 1902, and later described  by Henry Fairfield Osborn in 1905. Osborn actually named two large Hell Creek tyrannosaurids, T. rex and Dynamosaurus imperiosus. He later realized that Dynamosaurus imperiosus and Tyrannosaurus rex were synonymous, but Tyrannosaurus has priority, as it preceded Dynamosaurus in the description (Osborn, 1906). Over he past 20 years, morphological, histological and functional studies expanded our knowledge of the T. rex and its closest relatives.

Much attention has focused on how T. rex achieved such massive size and how their skeletons changed during the transition from embryo to adult. Previous studies estimate that during its growth cycle, T. rex grew at almost 2.5 kilograms per day for about 14 years. This extraordinary rapid growth rate sets T. rex apart from other tyrannosaur species like Albertosaurus and Gorgosaurus.

 

Skulls of the basal tyrannosauroids Guanlong (A), Dilong (B); Skulls of juvenile (C) and adult (D)Tyrannosaurus. All scale bars equal 10 cm. (Adapted from Brusatte et. al., 2010)

A new study by Thomas Carr reconstructs the growth series of T. rex. using an ontogram, the ontogenetic equivalent of cladogram, that shows the distinctives growth stages. The ontogram is composed of 21 growth stages. The growth series of T. rex was recovered using cladistic analysis based on an expanded dataset that includes chronological age, size, and size-independent cranial and postcranial characters. Five growth categories (juvenile, subadult, young adult, adult, senescent adult) were diagnosed based on histology, synontomorphies (the equivalent of a synapomorphy), and, in part, size and mass.

Tyrannosaurids are united by a conservative pattern of growth in which the skulls of juveniles were entirely reshaped during ontogeny. The sequence has been reconstructed by cladistic analysis. During the growth of an individual species, the skull and the jaws deepened, pneumatic bones inflated, the ornamented structures enlarged and coarsened, the sutural surfaces deepened and became more rugose, and the teeth became larger and thicker. In the post-cranial skeleton the most notably change is the shortned of the forearm. The new study shows that the number of growth changes generally decreases during adulthood. Additionally, changes to the pectoral girdle and pes are dominant early in ontogeny. Similarily, the transition from a long and low skull to a stout and deep skull occurred rapidly within a 2-year time span.

 

References:

Carr TD. 2020. A high-resolution growth series of Tyrannosaurus rex obtained from multiple lines of evidence. PeerJ 8:e9192 https://doi.org/10.7717/peerj.9192

Brusatte SL, Norell MA, Carr TD, Erickson GM, Hutchinson JR, et al. (2010) Tyrannosaur paleobiology: new research on ancient exemplar organisms. Science 329: 1481–1485. doi: 10.1126/science.1193304