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

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

The fossil history of the Christmas tree

Queen Victoria, Prince Albert, and their family around a Christmas tree. From the Illustrated London News (1848)

The Christmas tree is one of the most iconic tradition of modern culture. But long before the advent of Christiany, Egyptians, Celts and Vikings used evergreen plants and trees to celebrate the winter solstice. During Saturnalia, held between 17 and 25 December, Romans also decorated their homes and temples with evergreen boughs. In the 16th century, Germans started the Christmas tree tradition as we now know it. They carried the custom to Britain, though it wasn’t until 1846 that the fir tree became a worldwide custom, after Queen Victoria and her husband, Prince Albert, were sketched in the Illustrated London News standing with their children around a Christmas tree. 

Conifers are cone-bearing seed plants that originated in the Northern Hemisphere during the Middle Pennsylvanian, approximately 310 million years ago. During the LateTriassic and Early Jurassic, the group experienced a considerable diversification that resulted in the divergence of several modern families. Conifers range from small wiry shrubs to giant trees: Sequoiadendron giganteum reachs almost 100 m high, while Microcachrys tetragona from Tasmania has about few centimeters high. The group declined in diversity and abundance after the rise of angiosperms, and many taxa now have very restricted geographic distributions. Conifers also have the longest living non-clonal terrestrial organisms on Earth, with some examples of Pinus longaeva exceeding 4,600 years of age.

Pityostrobus pluriresinosa. From Smith et al., 2016.

Modern Christmas trees belong to a family called Pinaceae, the most species-rich clade of living conifers. The other conifer families include Cupressaceae, Araucariaceae, Podocarpaceae, Cephalotaxaceae, Taxaceae and most recently, the monotypic family Sciadopityacea. Numerous fossils, which include a number of anatomically preserved ovulate cones with many systematically informative characters, documeted the evolutionary history of Pinaceae.

Leaves and ovulate cones are widely variable and help to highlight the Cretaceous radiation of the family. Preserved fossil pinaceous ovulate cones include Pseudoaraucaria, Pityostrobus, Obirastrobus and Eathiestrobus. The estimated age for the initial crown split in Pinaceae between abietoids and pinoids is in the Early Jurassic, ~188 mya. Recent phylogenetic analyses suggest that the earliest- known member of the Pinaceae, Eathiestrobus mackenziei may be more closely related to Pinus than to other extant lineages; while various species of the widespread Cretaceous form genus Pityostrobus are stem members of both extant abietoids and pinoids.

 

 

 

References:

Leslie, A. B., Beaulieu, J., Holman, G., Campbell, C. S., Mei, W., Raubeson, L. R., & Mathews, S. (2018). An overview of extant conifer evolution from the perspective of the fossil record. American Journal of Botany. doi:10.1002/ajb2.1143 

 

Smith, S. Y., Stockey, R. A., Rothwell, G. W., & Little, S. A. (2016). A new species of Pityostrobus (Pinaceae) from the Cretaceous of California: moving towards understanding the Cretaceous radiation of Pinaceae. Journal of Systematic Palaeontology, 15(1), 69–81. doi:10.1080/14772019.2016.1143885 

 

 

 

On the origin of Pterosaurs

The recently discovered and selected bones characterizing the lagerpetid body plan. From Ezcurra et al., 2020

In 1784, Cosimo Alessandro Collini, a former secretary of Voltaire and curator of the natural history cabinet of Karl Theodor, Elector of Palatinate and Bavaria, published the first scientific description of a pterosaur. The specimen came from one of the main sources of such fossils, the Late Jurassic lithographic limestones of northern Bavaria, and Collini, after much deliberation, interpreted it as the skeleton of an unknown marine creature. In 1801, on the basis of Collini’s description, George Cuvier identified the mysterious animal as a flying reptile. He later coined the name “Ptero-Dactyle”. This discovery marked the beginning of pterosaur research.

Pterodactylus antiquus, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA (From Wikipedia Commons)

Pterosaurs were the first flying vertebrates. Their reign extended to every continent and achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 200 species recognized so far. During their 149 million year history, the evolution of pterosaurs resulted in a variety of eco-morphological adaptations, as evidenced by differences in skull shape, dentition, neck length, tail length and wing span. The oldest-known pterosaurs appear in the fossil record about 219 million years ago. Most Triassic pterosaurs are small but already had a highly specialized body plan linked to their ability to fly: shoulder girdle with strongly posteroventrally enlarged coracoid braced with the sternum and laterally facing glenoid fossa; forelimb with pteroid bone and hypertrophied fourth digit supporting a membranous wing; and pelvic girdle with prepubic bone and strongly developed preacetabular process.

Due to the fragile nature of their skeletons and the absence of fossils with transitional morphologies, the origin of pterosaurs is one of the most elusive questions in vertebrate paleontology. They have been hypothesized to be the close relatives of a wide variety of reptilian clades. Now, a new study published in Nature indicates that lagerpetids are the sister group 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. Previous studies of lagerpetid anatomy was mostly limited to vertebrae, hindlimbs and a few cranial bones, but new fossil discoveries over the past few years have greatly increased the understanding of this group. 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.

Time-calibrated reduced strict consensus tree focused on Pterosauria and Lagerpetidae. From Ezcurra et al., 2020.

The team found at least 33 skeletal traits suggesting an evolutionary link between lagerpetids and pterosaurs. The anterior region of the lagerpetid dentary is ventrally curved similar to those of the early pterosaurs like Austriadactylus. Lagerpetids and pterosaurs also share a unique inner ear morphology among archosaurs, characterized by taller than anteroposteriorly long semicircular canals. The semicircular canals detect head movements and a larger radius increases the sense of equilibrium. The cranial endocasts of D. gregorii and Ixalerpeton reveal strongly developed cerebellar floccular lobes, which resemble the even more developed floccular lobes of pterosaurs. 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 in Pterosaurs has been hypothesized to be important for information processing related to flight.

Lagerpetids and pterosaurs also share similarities in hand, leg, ankle and pelvic bones. For example pelvic girdles of Lagerpeton and Ixalerpeton have a long pubo-ischiadic contact that extends ventrally up to the level of the anterovental margin of the pubis, as is the case in several early pterosaurs.

 

References:

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

Halloween special VIII: The Great Dying

“Out of the Aeons” is a short story by H. P. Lovecraft and Hazel Heald. The story introduces the powerful Ghatanothoa, a Great Old One and the first-born of Cthulhu, brought to Earth from the planet Yuggoth by the Mi-go, an anciente alien race, who built a colossal fortress atop the Mount Yaddith-Gho, and sealed Ghatanothoa inside the mountain. Those who worship this entity hold the god responsible for earthquaques and other natural disasters. Like Groth himself, Ghatanothoa is the harbinger of death.

The fossil record indicates that more than 95% of all species that ever lived are now extinct. Occasionally, extinction events reach a global scale with many species of all ecological types dying out in a near geological instant. These mass extinctions were originally identified in the marine fossil record and have been interpreted as a result of catastrophic events or major environmental changes that occurred too rapidly for organisms to adapt.

Global paleogeographic map for the Permian-Triassic transition showing the location of the Siberian Traps Large Igneous Province. From Vajda et al., 2019

During the last 540 million years five mass extinction events shaped the history of the Earth. The end-Permian extinction (PTB) is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis occurred 252 million years ago (Ma), and is linked to the emplacement of the large igneous province of the Siberian Traps. A new study published early this month in the journal Nature Geoscience is the first to conclusively reconstruct the entire cascade of events that lead to the PTB mass extinction.

The team lead by Hana Jurikova used the boron isotope of well preserved shells of brachiopods and paired with carbon and oxygen isotope data, generating a new record of ocean pH for the Permian/Triassic boundary. These findings indicate that the PTB mass extinction was triggered by a multimillennial-scale voluminous injection of carbon to the atmosphere by the emplacement of Siberian Traps sill intrusions. Massive volcanic eruptions with lava flows, released large quantities of sulphur dioxide, carbon dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere. The CO2 greenhouse effect resulted in strong heating and acidification of the surface ocean, which prompted the initial disappearance of all reef-building taxa. Acid rain likely had an impact on freshwater ecosystems and may have triggered forest dieback. 

 

References:

Hana Jurikova et al, Permian–Triassic mass extinction pulses driven by major marine carbon cycle perturbations, Nature Geoscience (2020). DOI: 10.1038/s41561-020-00646-4

V. Vajda et al. (2020), End-Permian (252Mya) deforestation, wildfires and flooding—An ancient biotic crisis with lessons for the present, Earth and Planetary Science Letters 529 (2020) 115875 https://doi.org/10.1016/j.epsl.2019.115875

H. P. Lovecraft & Hazel Heald, “Out of the Aeons”, Weird Tales magazine, 1935

 

Introducing Oksoko avarsan

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  Holotype block of Oksoko avarsan MPC-D 102/110. From Funston et al., 2020

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 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 early eukaryote fossil record

Some examples of fossils of early eukaryotes. From Porter, 2020.

The origin of the eukaryotic cell is one of the major evolutionary events in the history of life on our planet. However, the mosaicism of the eukaryotic genome is challenging. Bacteria, Archaea, and Eukarya share common ancestry but they have very distinctive features. The eukaryotic cell differs by its much simpler prokaryote relatives, by possessing not only a nucleus, but also a complex cytoskeleton, a sophisticated endomembrane system, and mitochondria, the last of these, the result of an ancient endosymbiosis with a proteobacterium. Recently, the discovery in deep marine sediment of the Asgard archaea, a group closely related to eukaryotes, could lead us to unravel the origin of eukaryotes.

The term ‘FECA’, the first eukaryotic common ancestor, is often used to refer to the initial lineage of total group eukaryotes, just after its split from its closest living relative. By contrast, ther term ‘LECA’, the last eukaryotic common ancestor, refers to the ancestor only of extant eukaryotes (all known ones) plus extinct post-LECA lineages. Eukaryogenesis is the interval between FECA and LECA, when the characters that define the crown group evolved. LECA is generally believed to have lived during the Mesoproterozoic era, about 1.6 to 1 billion years ago, or possibly somewhat earlier. The age of FECA is even more uncertain. Based on the earliest widely acceptable eukaryote fossils, FECA had arrived some time before 1.9 Ga. Some models suggest a younger age for LECA. Hence, Mesoproterozoic rocks dominantly preserve stem group eukaryotes.

The Asgard archaea and the origin of eukaryotes. Credit: Nature Publishing Group.

To understand the paths from FECA to LECA, it is necessary to identify eukaryote characters correctly in the deep fossil record. Therefore, the key to reconstructing the origin of eukaryotes lies in the integration of modern cell biology, molecular phylogeny, and the fossil record.

So, how do we recognize ancient fossils as eukaryotic? Size is a relevant parameter. On average, eukaryotic cells are substantially larger than those of prokaryotes, with diameters ranging from 10 to 100 μm. Another feature widespread among all eukaryotic supergroups is the formation of resistant-walled structures known as cysts. These forms are recognized in the fossil record by the presence of openings, spines or complex ornamentation. Some prokaryotes can be large too, and they can have processes and preservable walls. But none of them present these three characters at the same time. By contrast, eukaryotes exhibit these features in combination. Shuiyousphaeridium, one of the oldest evidence of eukaryotes, is a large, spiny, ornamented, organic walled microfossil found in latest Paleoproterozoic rocks. This form is an extinct genus of acritarch discovered in 1993.

Shuiyousphaeridium macroreticulatum from the Mesoproterozoic Ruyang Group, China. From Knoll et al., 2006.

Acritarchs are a heterogeneous and polyphyletic group of organic-walled microfossils of unknown affinity, consisting of a central cavity enclosed by a wall of single or multiple layers, with a great variability of shapes and ornamentations. The wall is made by sporopollenine or a very similar compound and the size range is about 5 to 200 micrometers. The acritarchs were dominant forms of eukaryotic phytoplankton during the NeoProterozoic and the Paleozoic. These forms diversified markedly, in parallel with the Cambrian and Ordovician radiations of marine invertebrates.

The term was first introduced by Evitt in 1963 and means “undecided origin” (from the Greek akritos = undecided, and arche = origin”), and replaced the older group “hystricosphaerid”. Based on their morphology, acritarchs are divided in nine groups: sphaeromorph, acanthomorphs, polygonomorphs, netromorphs, diacromorphs, prismatomorphs, oomorphs, herkomorphs, and pteromorphs.

Diagram showing the different group of Acritarchs. Imagen from UCL.

The iconic Grypania spiralis has been questioned as eukaryotic. This coiled ribbon-like impression, was first discovered in the Greyson Shale and Chamberlain Shale of the Mesoproterozoic Ravalli Group, in Montana, western USA. An alternative interpretation suggest that Grypania was a giant cyanobacterium.

The Tirohan Dolomite of the Lower Vindhyan (~1.6 Ga) in central India contains well-preserved fossils interpreted as probable crown-group rhodophytes (red algae). Rafatazmia chitrakootensis, is a nonbranching filamentous alga, 58–175 μm in width, and has uniserial rows of large cells. Ramathallus lobatus,  is a lobate sessile alga with pseudoparenchymatous thallus. Both represent crown-group multicellular rhodophytes, or a very ancient side branch.

Microscope images of the fossil Bangiomorpha pubescens. Credit: Nick Butterfield/University of Cambridge.

One of the oldest multicellular organisms is Bangiomorpha pubescens. This extraordinary fossil provides the earliest unambiguous record of photosynthetic eukaryotic life. The individual filaments of the fossil are up to 2 mm long, and are composed of a single series of cells, or of several series running side by side, or a combination of the two, as in modern Bangia. The age of its first appearance was ~ 1.047 Ga. Other early multicellular eukaryotes include Palaeastrum, and Proterocladus. Those much younger fossils appeared only 800 million years ago.

While some questions still remains unanswered, the continued studies of the fossil record and biomarker assemblages may allow us to identify the environmental conditions that allowed the appearance of complex life.

References:

Porter SM. (2020) Insights into eukaryogenesis from the fossil record. Interface Focus 10: 20190105. http://dx.doi.org/10.1098/rsfs.2019.0105

Bengtson S, Sallstedt T, Belivanova V, Whitehouse M (2017) Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae. PLoS Biol 15(3): e2000735. doi:10.1371/journal.pbio.2000735

Knoll AH. (2014) Paleobiological perspectives on early eukaryotic evolution. Cold Spring Harb. Perspect. Biol. 6, 1-14. doi:10.1101/cshperspect.a016121

Yonas I. Tekle, Laura Wegener Parfrey, Laura A. Katz, (2009) Molecular Data Are Transforming Hypotheses on the Origin and Diversification of Eukaryotes, BioScience(2009),59(6):471 http://dx.doi.org/10.1525/bio.2009.59.6.5