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