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

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

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

 

Introducing Asteriornis maastrichtensis

 

Three-dimensional image of the skull of Asteriornis maastrichtensis.
Image credit: Daniel J. Field, University of Cambridge

The earliest diversification of extant birds (Neornithes) occurred during the Cretaceous period. After the mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary, the Neoaves, the most diverse avian clade, suffered a rapid global expansion and radiation. A genome-scale molecular phylogeny indicates that nearly all modern ordinal lineages were formed within 15 million years after the extinction, suggesting a particularly rapid period of both genetic evolution and the formation of new species. Today, with more than 10500 living species, birds are the most species-rich class of tetrapod vertebrates. The description of a new neornithine from the Late Cretaceous of Belgium shed new light on the evolution of birds.

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. The new specimen, dated between 66.8 and 66.7 million years ago, was collected in 2000 by Maarten van Dinther. 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).

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

Asteriornis exhibits caudally pointed nasals that overlie the frontals and meet at the midline of the skull, and a slightly rounded, unhooked tip of the premaxilla. The new specimen 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.

 

References:

Field, D.J., Benito, J., Chen, A. et al. Late Cretaceous neornithine from Europe illuminates the origins of crown birds. Nature 579, 397–401 (2020). https://doi.org/10.1038/s41586-020-2096-0

A Short History of the Early Female Geoscientists from Argentina

Mathilde Dolgopol de Saez. Image credit: Asociación Paleontológica Argentina (A.P.A.)

Women have played various and extensive roles in the history of geology. Unfortunately, their contribution has not been widely recognised by the public or academic researchers. In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. Early female scientists were often born into influential families, like Grace Milne, the eldest child of Louis Falconer and sister of the eminent botanist and palaeontologist, Hugh Falconer; or Mary Lyell, the daughter of the geologist Leonard Horner. They collected fossils and mineral specimens, and were allowed to attend scientific lectures, but they were barred from membership in scientific societies. Thanks to the pioneer work of these women, the 20th century saw the slow but firm advance of women from the periphery of science towards the center of it.

Edelmira Inés Mórtola (1894-1973)

In Argentina, during the 1870s, public schools were organized and expanded for the training of teachers in different cities of the country. North American teachers were hired, some of whom promoted among their students the interest in pursuing university studies. Cecilia Grierson (1859-1934) was the first woman to earn a PhD in Medicine and Surgery in 1889. She was an important reference for other women, collaborating in the women’s movement in the early twentieth century.

The first papers in natural sciences signed by women were published around 1910. Edelmira Inés Mórtola was the first woman to earn her Ph. D in geology in Argentina, in 1921. She was also the first woman to work for the Dirección General de Minas, Geología, e Hidrología (DGMGH) in 1919. She focus on teaching and was an inspiring figure for young women. In 1924, she was appointed Professor at the Universidad de Buenos Aires (UBA). The Museum of Mineralogy “Dr. E. Mórtola “, that she helped to organize, honors her extraordinary career. She died on May 28, 1973.

Noemí Violeta Cattoi. Image credit: Asociación Paleontológica Argentina (A.P.A.)

Mathilde Dolgopol de Saez was born on March 6, 1901. She was one of the first female paleontologist from Argentina (graduated in 1927), along with Ana Cortelezzi (1928?), Dolores López Aranguren (1930), Andreína Bocchino de Ringuelet (1930?) y Enriqueta Vinacci Thul (1930). Unfortunately, only her thesis and the one of López Aranguren were formally published. The mayor part of her research was focused on fossil fish and birds. She died on June 27, 1957.

Noemí Violeta Cattoi was born in Buenos Aires on December 23, 1911. She received her PhD degree in Natural Science at the University of Buenos Aires, but before her graduation she was trained at the Museo Argentino de Ciencias Naturales. She was head of Paleozoology at the Museum, and adjunt professor at the Museo de la Plata. Her research was mainly focused on extinct birds and mammals from South America. She was also one of the founding member of the Asociación Paleontológica Argentina (A.P.A), along with María Bonetti de Stipanicic, Andreína B. de Ringuelet, Elsa F. de Alvarez and Hildebranda A. Castellaro. Noemí Cattoi died on January 29, 1965.

Reference:.

Rafael Herbst, Luisa M. Anzótegui, Las mujeres en la paleontología argentina, Revista del Museo de La Plata (2016) Volumen 1, Número Especial: 130-13 DOI:https://doi.org/10.24215/25456377e024

GARCIA, Susana V.. Ni solas ni resignadas: la participación femenina en las actividades científico-académicas de la Argentina en los inicios del siglo XX. Cad. Pagu [online]. 2006, n.27, pp.133-172 https://doi.org/10.1590/S0104-83332006000200007.

Link: https://www.apaleontologica.org.ar/

Soft-tissue evidence in a Jurassic ichthyosaur.

Plesiosaurus battling Temnodontosaurus (Oligostinus), front piece the Book of the Great Sea-Dragons by Thomas Hawkins.

In 1811, in Lyme Regis, one of the richest fossil locations in England and part of a geological formation known as the Blue Lias, Mary Anning and her brother Joseph unearthed the skull of an enigmatic ‘sea monster’. A year later, Mary uncovered the torso of the same specimen. The Annings sold the fossil to the Lord of the Manor of Colway, Mr. Henry Henley, for £23. The specimen was described by Sir Everard Home in 1814. Although no name was proposed for the fossil, Home concluded that it represented a transitional form between fish and crocodiles. Later, in 1819, the skeleton was purchased by Karl Dietrich Eberhard Koenig of the British Museum of London who suggested the name Ichthyosaur (“fish lizard”) in 1817.

Ichthyosaurs are extinct marine reptiles that first diversified near the end of the Early Triassic and remained one of the main predators in the Mesozoic ocean until their disappearance near the Cenomanian-Turonian boundary, 30 million years before the end-Cretaceous mass extinction. They had the largest eyes of all vertebrates, sometimes exceeding 25 cm in maximum diameter. They also have one of the earliest records of live-birth in amniotes.

 

Stenopterygius specimen from the Holzmaden quarry. Credit: Johan Lindgren

Stephen Jay Gould said that the ichthyosaur was his favourite example of convergent evolution: “Consider my candidate for the most astounding convergence of all: the ichthyosaur. This sea-going reptile with terrestrial ancestors converged so strongly on fishes that it actually evolved a dorsal fin and tail in just the right place and with just the right hydrological design. These structures are all the more remarkable because they evolved from nothing— the ancestral terrestrial reptile had no hump on its back or blade on its tail to serve as a precursor.”

During the Norian, the evolution of ichthyosaurs took a major turn, with the appearance of the clade Parvipelvia (ichthyosaurs with a small pelvic girdle). They were notably similar in appearance to extant pelagic cruisers such as odontocete whales. An exquisitely fossilized parvipelvian Stenopterygius from the Early Jurassic (Toarcian) of the Holzmaden quarry in southern Germany, indicates that their resemblance with dolphin and whales is more than skin deep.

Structure and chemistry of MH 432 blubber. From Lindgren et. al. 2018.

The specimen (MH 432; Urweltmuseum Hauff, Holzmaden, Germany) reveals endogenous cellular, sub-cellular and biomolecular constituents within relict skin and subcutaneous tissue. The external surface of the body is smooth, and was presumably comparable in life to the skin of extant cetaceans. The histological and microscopic examination of the fossil, evinced a multi-layered subsurface architecture. The approximately 100-μm-thick epidermis retains cell-like structures that are likely to represent preserved melanophores. The subcutaneous layer is over 500 μm thick, and comprises a glossy black material superimposed over a fibrous mat. The anatomical localization, chemical composition and fabric of the subcutaneous material is interpreted as fossilized blubber, a hallmark of warm-blooded marine amniotes.

 

References:

Lindgren, J., Sjövall, P., Thiel, V., Zheng, W., Ito, S., Wakamatsu, K., … Schweitzer, M. H. (2018). Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur. Nature. doi:10.1038/s41586-018-0775-x

Motani, R. (2005). EVOLUTION OF FISH-SHAPED REPTILES (REPTILIA: ICHTHYOPTERYGIA) IN THEIR PHYSICAL ENVIRONMENTS AND CONSTRAINTS. Annual Review of Earth and Planetary Sciences, 33(1), 395–420. doi:10.1146/annurev.earth.33.092203.1227

Introducing Jinguofortis perplexus.

Photograph of main slab of J. perplexus (Credit: Wang et al., 2018)

Birds originated from a theropod lineage more than 150 million years ago. By the Early Cretaceous, they diversified, evolving into a number of groups of varying anatomy and ecology. In recent years, several discovered fossils of theropods and early birds have filled the morphological, functional, and temporal gaps along the line to modern birds. Most of these fossils are from the Jehol Biota of northeastern China, dated between approximately 130.7 and 120 million years ago. The Jehol Biota provides an incredibly detailed picture of early birds, including Jeholornis, slightly more derived than Archaeopteryx, that lived with Sapeornis, Confuciusornis, and the earliest members of Enantiornithes and Ornithuromorpha. The clade Ornithothoraces (characterized by a keeled sternum, elongate coracoid, narrow furcula, and reduced hand) along with Jeholornithiformes, Confuciusornithiformes and Sapeornithiformes, form the clade Pygostylia. Basal members of this clade are essential to understand the evolution of the modern avian bauplan. The trait that gives the group its name is the presence of a pygostyle, a set of fused vertebrae at the end of the tail.

Jinguofortis perplexus gen. et sp. nov., from the Early Cretaceous of China, exhibits a mosaic combination of plesiomorphic nonavian theropod features like a fused scapulocoracoid and more derived traits, including the earliest evidence of reduction in manual digits among birds. The generic name is derived from “jinguo” (Mandarin), referring to female warrior, and “fortis” for brave (Latin). The specific name is derived from Latin “perplexus,” and highlights the combination of plesiomorphic and derived features present in the holotype specimen.

Holotype of J. perplexus. (Scale bar, 5 cm.) From Wang et al., 2018.

The holotype (IVPP V24194) was collected near the village of Shixia, Hebei Province, China. Biostratigraphic correlation confirms that the fossil-bearing horizon belongs to the Lower Cretaceous Dabeigou Formation of the Jehol Biota (127 ± 1.1 Ma). The holotype of Jinguofortis is subadult or adult given the bone histology, the presence of a fused carpometacarpus, tarsometatarsus, and pygostyle. The body mass estimated is 250.2 g, the wing span is 69.7 cm, with a wing area of 730 cm2.

Jinguofortis exhibits the following features: dentary with at least six closely packed teeth; scapula and coracoid fused into a scapulocoracoid in the adult; sternum ossified; deltopectoral crest of humerus large and not perforated; minor metacarpal strongly bowed caudally; minor digit reduced with manual phalangeal formula of 2–3-2; metatarsals III and IV subequal in distal extent; pedal phalanx II-2 with prominent heel proximally; and forelimb 1.15 times longer than hindlimb. The highly vascularized fibro-lamellar bone tissue indicates that Jinguofortis grew rapidly in early development, but the growth rate had slowed substantially by the time of death. The histology of Jinguofortis is comparable to that of Chongmingia and Confuciusornis, suggesting a similar growth pattern shared among these basal pygostylians. The phylogenetic analysis recovered Jinguofortis as the sister to Chongmingia. The clade uniting these two specimens is Jinguofortisidae, and constitutes the second most basal pygostylian lineage.

Forelimb of Jinguofortis. (A) Photograph. (B) Line drawing. (Scale bar, 1 cm.) From Wang et al., 2018.

Early avian flight clearly underwent a series of evolutionary experiments, as demonstrated by the diverse combination of plesiomorphic and derived features found among early extinct birds. The most striking primitive feature present in the flight apparatus of Jinguofortis is the fused scapulocoracoid, present predominantly in nonavian theropods. The convergently evolved scapulocoracoid in jinguornithids and confuciusornithiforms suggests that these basal clades likely reacquired a similar level of osteogenesis (or gene expression) present in their nonavian theropod ancestors.

 

References:

Wang, M., Stidham, T. A., & Zhou, Z. (2018). A new clade of basal Early Cretaceous pygostylian birds and developmental plasticity of the avian shoulder girdle. Proceedings of the National Academy of Sciences, 201812176. doi:10.1073/pnas.1812176115

A very short history of Dinosaurs.

Evolutionary relationships of dinosaurs. From Benton 2018.

On 20 February 1824, William Buckland published the first report of a large carnivore animal: the Megalosaurus. The description was based on specimens in the Ashmolean Museum, in the collection of Gideon Algernon Mantell of Lewes in Sussex, and a sacrum donated by Henry Warburton (1784–1858). One year later, the Iguanodon entered in the books of History followed by the description of Hylaeosaurus in 1833. After examined the anatomy of these three genera, Richard Owen erected the clade Dinosauria in 1842.

Dinosaurs likely originated in the Early to Middle Triassic. The closest evolutionary relatives of dinosaurs include flying pterosaurs and herbivorous silesaurids. Early ecological divergences in dinosaur evolution are signaled by disparity in dental morphology, which indicates carnivory in early theropods, herbivory in ornithischians, and omnivory in sauropodomorph (subsequently sauropodomorphs underwent a transition to herbivory).

Eoraptor lunensis, outcropping from the soil. Valle de la Luna (Moon Valley), Parque Provincial Ischigualasto, Provincia de San Juan, Argentina.

The oldest dinosaurs remains are from the late Carnian (230 Ma) of the lower Ischigualasto Formation in northwestern Argentina. Similarly, the Santa Maria and Caturrita formations in southern Brazil preserve basal dinosauromorphs, basal saurischians, and early sauropodomorphs. In North America, the oldest dated occurrences of vertebrate assemblages with dinosaurs are from the Chinle Formation. Two further early dinosaur-bearing formations, are the lower (and upper) Maleri Formation of India and the Pebbly Arkose Formation of Zimbabwe. These skeletal records of early dinosaurs document a time when they were not numerically abundant, and they were still of modest size.

During the Late Triassic period numerous extinctions, diversifications and faunal radiations changed the ecosystems dynamics throughout the world. Nevertheless, dinosaurs exhibited high rates of survival. According to the competitive model, the success of dinosaurs was explained in terms of their upright posture, predatory skills, or warm-bloodedness. In the opportunistic model, dinosaurs emerged in the late Carnian or early Norian, and then diversified explosively. The current model contains some aspects of both the classic competition model and the opportunistic model. In this model, the crurotarsan-dominated faunas were replaced by a gradual process probably accelerated by the ecological perturbation of the CPE (Carnian Pluvial Episode).

Ingentia prima outcropping from the soil.

In the Jurassic and Cretaceous dinosaurs achieved enormous disparity. Sauropodomorphs achieved a worldwide distribution and become more graviportal and increased their body size. Gigantism in this group has been proposed as the result of a complex interplay of anatomical, physiological and reproductive intrinsic traits. For example, the upright position of the limbs has been highlighted as a major feature of the sauropodomorph bauplan considered an adaptation to gigantism. However, the discovery of Ingentia prima, from the Late Triassic of Argentina, indicates that this feature was not strictly necessary for the acquisition of gigantic body size.

Ornithischian were primitively bipedal, but reverted to quadrupedality on at least three occasions: in Ceratopsia, Thyreophora and Hadrosauriformes. The presence of early armored dinosaurs (thyreophorans) in North America, Asia, and Europe, but their absent from the southern African record, suggests some degree of provinciality in early ornithischian faunas.

Archaeopteryx lithographica, specimen displayed at the Museum für Naturkunde in Berlin. (From Wikimedia Commons)

Theropod dinosaurs also increased their diversity and exhibit a greater range of morphological disparity. The group underwent multiple parallel increases in brain size. The volumetric expansion of the avian endocranium began relatively early in theropod evolution. For instance, the endocranium of Archaeopteryx lithographica is volumetrically intermediate between those of more basal theropods and crown birds. The digital brain cast of Archaeopteryx also present an indentation that could be from the wulst, a neurological structure present in living birds used in information processing and motor control with two primary inputs: somatosensory and visual. The extensive skeletal pneumaticity in theropods such as Majungasaurus demonstrates that a complex air-sac system and birdlike respiration evolved in birds’ theropod ancestors. Anatomical features like aspects of egg shape, ornamentation, microstructure, and porosity of living birds trace their origin to the maniraptoran theropods, such as oviraptorosaurs and troodontids. In addition, some preserving brooding postures, are known for four oviraptorosaurs, two troodontids, a dromaeosaur, and one basal bird providing clear evidence for parental care of eggs.

Nonavian dinosaurs disappeared more or less abruptly at the end of the Cretaceous (66 mya). Birds, the only living dinosaurs, with more than 10,500 living species are the most species-rich class of tetrapod vertebrates.

 

References:

Benson, R. B. J. (2018). Dinosaur Macroevolution and Macroecology. Annual Review of Ecology, Evolution, and Systematics, 49(1).  doi:10.1146/annurev-ecolsys-110617-062231

Michael J. Benton et al. The Carnian Pluvial Episode and the origin of dinosaurs, Journal of the Geological Society (2018). DOI: 10.1144/jgs2018-049

Xing Xu, Zhonghe Zhou, Robert Dudley, Susan Mackem, Cheng-Ming Chuong, Gregory M. Erickson, David J. Varricchio, An integrative approach to understanding bird origins, Science, Vol. 346 no. 6215, DOI: 10.1126/science.1253293.

 

Introducing Caelestiventus hanseni.

A 3D printed model of Caelestiventus skull.

Pterosaurs were the first flying vertebrates appearing initially in Late Triassic. The group achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 200 species recognized so far. From the Late Triassic to the end of the Cretaceous, 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. Because of the fragile nature of their skeletons the fossil record of pterosaurs is strongly biased towards marine and lacustrine depositional environments. Therefore, Triassic pterosaurs are extraordinarily rare and consists of fewer than 30 specimens, including single bones. With the single exception of Arcticodactylus cromptonellus from fluvial deposits in Greenland, the other specimens are known from marine strata in the Alps.

Pterosaurs have been divided into two major groups: “rhamphorhynchoids” and “pterodactyloids”. Rhamphorhynchoids are characterized by a long tail, and short neck and metacarpus. Pterodactyloids have a much larger body size range, an elongated neck and metacarpus, and a relatively short tail.

a, Schematic silhouette of a dimorphodontid pterosaur in dorsal view. b, Preserved skull and mandible elements of C. hanseni. From Brooks B. Britt et al., 2018.

Caelestiventus hanseni, from the Upper Triassic of North America, is the oldest pterosaur ever discovered, and it predates all known desert pterosaurs by more than 65 million years. The generic name comes from the Latin language: caelestis, ‘heavenly or divine’, and ventus, ‘wind’. The species name, ‘hanseni’, honors Robin L. Hansen, a geologist, who facilitated work at the Saints & Sinners Quarry.

The holotype, BYU 20707, includes the left maxilla fused with the jugal, the right maxilla, the right nasal, the fused frontoparietals, the right and left mandibular rami, the right terminal wing phalanx and three fragments of indeterminate bones. The maxilla, jugal, frontoparietal, and mandibular rami of the specimen are pneumatic. The unfused skull and mandibular elements suggest that BYU 20707 was skeletally immature or had indeterminate growth. Based on the relationship between the length of the terminal wing phalanges and wing span in other non-pterodactyloid pterosaurs the new taxon would have a wing span greater than 1.5 m.

The holotype specimen of Dimorphodon macronyx found by Mary Anning in 1828 (From Wikimedia Commons)

Caelestiventus hanseni is placed as sister taxon to Dimorphodon macronyx. Both share the following derived features: a ventral blade along the dentary that forms a rostral keel and becomes a flange distally; a diastema between the second large mandibular tooth and the following smaller teeth; the overall morphology of the maxilla; the shape of the external naris and antorbital fenestra; the external naris by far the largest skull opening; the orbit smaller than the antorbital fenestra; and teeth with bicuspid apices. But despite their morphological similarity, C. hanseni and D. macronyx lived in very different environments. Dimorphodon, discovered by Mary Anning, was an island dweller in a humid climate and was preserved in the marine Blue Lias of southern England.

The significance of C. hanseni lies in its exceptional state of preservation, and its close phylogenetic relationship with Dimorphodon macronyx, indicating that dimorphodontids originated by the Late Triassic and survived the end-Triassic extinction event.

 

References:

Brooks B. Britt et al. Caelestiventus hanseni gen. et sp. nov. extends the desert-dwelling pterosaur record back 65 million years, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0627-y

Ingentia prima, the first giant

Skeletal anatomy of Ingentia prima (From Apaldetti et al., 2018)

During the Late Triassic period numerous extinctions, diversifications and faunal radiations changed the ecosystem dynamics throughout the world. Followed the extinction of rhynchosaurs in most, or all, parts of the world, there was a burst of dinosaurian diversity in the late Carnian, represented by the upper Ischigualasto Formation and coeval units, with mostly carnivorous small- to medium-sized dinosaurs. Then, the long span of the early Norian, from 228.5–218 Ma, during which dicynodonts and sauropodomorph dinosaurs were the major herbivores.

Sauropods evolved from small, gracile, bipedal forms, and it was long thought that acquisition of giant body size in this clade occurred during the Jurassic and was linked to several skeletal modifications. Ingentia prima — literally the “first giant” in Latin — from the Late Triassic of Argentina shed new lights on the origin of gigantism in this group. The holotype, PVSJ 1086, composed of six articulated posterior cervical vertebrae, glenoid region of right scapula and right forelimb lacking all phalanges, has been recovered from the southern outcrops of the Quebrada del Barro Formation, northwestern Argentina. Discovered in 2015 by Diego Abelín and a team led by Cecilia Apaldetti of CONICET-Universidad Nacional de San Juan, Argentina, this new fossil weighed up to 11 tons and measured up to 32 feet (10 meters) long.

Bones of Ingentia prima (Image credit: Cecilia Apaldetti, CONICET-Universidad Nacional de San Juan, Argentina)

Ingentia was unearthed with three new specimens of Lessemsaurus sauropoides. The four dinosaurs belongs to the clade Lessemsauridae, that differs from all other Sauropodomorpha dinosaurs in possessing robust scapulae with dorsal and ventral ends equally expanded; slit-shaped neural canal of posterior dorsal vertebrae; anterior dorsal neural spines transversely expanded towards the dorsal end; a minimum transverse shaft width of the first metacarpal greater than twice the minimum transverse shaft of the second metacarpal; and bone growth characterized by the presence of thick zones of highly vascularized fibrolamellar bone, within a cyclical growth pattern.

The age of the oldest lessemsaurid (mid-Norian) indicates the appearance of an early trend towards large body size at least 15 Myr earlier than previously thought. For a long time, gigantism in eusauropods has been proposed as the result of a complex interplay of anatomical, physiological and reproductive intrinsic traits. For example, the upright position of the limbs has been highlighted as a major feature of the sauropodomorph bauplan considered an adaptation to gigantism. However Lessemsaurids lacked the purported adaptations related to a fully erect forelimb and the marked modifications of the hindlimb lever arms in eusauropods, showing that these features were not strictly necessary for the acquisition of gigantic body size. Another feature interpreted as a key acquisition was the elongated neck. However, lessemsaurids also lacked an elongated neck as they had proportionately short cervical vertebrae, indicating that the neck elongation was not a prerequisite for achieving body sizes comparable to those of basal eusauropods or gravisaurians.

 

References:

Cecilia Apaldetti, Ricardo N. Martínez, Ignacio A. Cerda, Diego Pol and Oscar Alcober (2018). An early trend towards gigantism in Triassic sauropodomorph dinosaurs. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-018-0599-y