Introducing Overoraptor, a new theropod dinosaur from the Upper Cretaceous of Patagonia

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

The fossil record of basal paravians in Gondwana is restricted to a relatively small number of taxa. South American paravians are included within the clade Unenlagiidae. Overoraptor chimentoi, a new specimen paravian from Cenomanian-Turonian beds of Patagonia differs morphologically from unenlagiids and other non-avialan paravians. The new taxon comes from the Huincul Formation. This geological unit has yielded remains of different theropod clades including several abelisaurid theropods like Skorpiovenator, Tralkasaurus and Ilokelesia.

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.

Comparative image of the right scapulacoracoid of Bambiraptor, Buitreraptor, Overoraptor, and Archaeopteryx in lateral view. Image not to scale. From Motta et al., 2020.

Overoraptor exhibits the following features: posterior caudal centra with a complex system of lateral longitudinal ridges concavities (also present in Buitreraptor and Rahonavis); the scapula is proximally stout; the glenoid fossa is cup-shaped (also observed in Archaeopteryx and Jeholornis, but is absent in unenlagiids); the ulna is robust, and the posterior margin of the ulna is longitudinally convex so that the ulna is bowed as in most basal paravian; the radial process of Overoraptor has a saddle-shaped radial cotyle proximally (a condition also present in modern birds and some basal paravians as Bambiraptor); metacarpal I with extensive medioventral crest; metatarsal II with longitudinal lateroventral crest on distal half, ending distally in a posterior tubercle; absence of a distal ginglymoid articular surface on metatarsal III; and the foot exhibits the characteristic raptorial digit II. The unusual combination of a plesiomorphic hindlimb, with features that are correlated with cursorial habits (the characteristic raptorial digit II, unfused metatarsals, and poorly curved ungual phalanx I); 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.



Motta, M.J., Agnolín, F., Brissón Egli, F. et al. New theropod dinosaur from the Upper Cretaceous of Patagonia sheds light on the paravian radiation in Gondwana. Sci Nat 107, 24 (2020).

Florentino Ameghino, the father of Argentinian paleontology.

Portrait of Florentino Ameghino (1854-1911) by Luis De Servi (1863-1945).

Portrait of Florentino Ameghino (1854-1911) by Luis De Servi (1863-1945).

Florentino Ameghino was born on September 19, 1854. He came from a family of Italian immigrants who settled in 1854 in the town of Lujan, Buenos Aires, Argentina, where the extraction and exportation of fossils were a lucrative activity. The first well known fossil from South America, Megatherium americanum, was recovered by Fray Manuel Torres in this place and later described by George Cuvier in 1796. Fossil collectors and museum commissioners visited the Lujan area pursuing the colossal fossil bones. Darwin himself described the small city in his famous Notebook: “The houses at Luxan are all of one ground-floor, except that of the Cabildo, on the east side of the plaza, which has rooms above. They are all built with sun-burnt bricks, called adobes, not white-washed. The church is a small plain building, with a little turret, and a cupola top.”

Despite being a self-taught naturalist, Ameghino became an international authority in the field of paleontology of vertebrates, geology, and archeology. He was portrayed by his biographers as the incarnation of materialism, leftist culture and national genius. Throughout his scientific career, Ameghino was seconded by his younger brother Carlos Ameghino (1865–1936), who was a “travelling naturalist” for the Museo de La Plata. During his trips, he gathered a remarkable collection of fossil mammals, later described by Florentino.

Ameghino ́s house at Las Heras 466. (ca. 1920). From Ludueña, 2011.

Thanks to the financial support obtained by members of the Genovese community in Argentina, Ameghino traveled to Paris in 1878 and presented his archaeological and paleontological collections at the Paris Anthropological Exhibition. He studied with various French experts, including Paul Gervais and Gabriel de Mortillet, and sold part of his collection to the North American paleontologist Edward Drinker Cope. In 1879, he married Léontine Poirier. She became an important part of Ameghino’s scientific career helping him with his writings, their bookstore, and hosting her husband’s visitors in their home in La Plata. In 1880, Ameghino published La antigüedad del Hombre en el Plata (Man’s Antiquity in the la Plata Basin). He and Léontine stayed in France until 1881.

In 1884, Ameghino published Filogenia, his most important theoretical work which evidenced that Ameghino was a true Darwinist. The book was shaped by Haeckel’s reconstruction of the human ancestral tree, and Gabriel de Mortillet’s ideas. A year later, Ameghino was appointed professor of zoology at Universidad de Córdoba a position that he quit for the vice-directorship of the recently founded Museo de La Plata.

Photo from the Archives of the Museo de La Plata. Although it has no references, it is thought to portray Carlos and Florentino during the latter’s only visit to Patagonia. From Sergio F. Vizcaíno, 2011.

Between the 1880s and 1890s, Ameghino’s descriptions revolutionized scientific opinion regarding primitive mammals. He began corresponding with Hermann von Ihering, a German scientist who had settled in São Paulo, Brazil. They both studied the Tertiary geological formations in South America and elaborated the idea that all mammals had originated in Patagonia and then moved to Africa through the continental bridges connecting the ancient continents. This partnership was internationally known as Ameghino, von Ihering & Co. At the time, Ameghino had alredy published his monograph Contribución al conocimiento de los mamíferos fósiles de la República Argentina. The work was praised by Karl von Zittel in his History of Geology and Paleontology of 1899, who remarked that “the most important paleontological event of the last two decades of the nineteenth century has been the disclosure made by Florentino Ameghino of a rich Mammalian fauna in the Tertiary rocks of Patagonia.”

In 1887, Ameghino described a large, toothless jaw from the Miocene of the Province of Santa Cruz, naming it Phorusrhacos longissimus and assigning it to a new family of edentulous mammals. He used this finding as a critical evidence for his contention that modern mammalian lineages originated in Argentina and later spread across the globe. At that time, Ameghino and Francisco P. Moreno, Director of the Museo de la Plata, were in the middle of a bitter dispute. The feud between the two men was in many aspects similar to the well-known feud between E.D. Cope and O.C. Marsh, which took place in the United States at roughly the same time. Four years later, Moreno and Alcides Mercerat recognized for the first time that the mandible described by Ameghino was really that of a bird.

Images of the type specimen of the Santacrucian sloth
Proschismotherium oppositum Ameghino, 1902. From Vizcaino et al., 2017-

Ameghino resigned from his position at the Museo de La Plata in 1888, and Moreno denied him access to the paleontological collection. From that moment, and until became head of the Museo Argentino de Ciencias Naturales in Buenos Aires in 1902, the Ameghino brothers continued with their palaeontological exploration, without any permanent official support, but they managed to get the funds to run their paleontological investigations as a private enterprise. Karl von Zittel, subsidized their explorations, receiving in exchange fossils for the collection of the Munich University. Meanwhile Moreno, in order to gain priority over his rivals, published a series of brief reports about the new palaeontological discoveries made by his field researchers.

In 1895, the critical financial situation forced Florentino Ameghino to sell his fossil bird collection, in order to support his further work in Patagonia. The collection was purchased by the London Museum by the sum of 350 £ in 1896. When Florentino became director of the Museo Nacional de Buenos Aires in 1902 the selling of fossils ceased, and he started making claims for the return of the museum’s collections. He also proposed for the most remarkable specimens of Patagonian and Pampean fossil faunas to be cast and stored in Buenos Aires and La Plata museums to be used in Argentinean schools. The same casts were sent to Museums all over the world and in exchange, Ameghino received casts of the oldest fossil mammals from Africa and the Northern Hemisphere to compare with the Patagonian faunas. It was a clever way to prevent the sale of the original fossils.

Florentino Ameghino in his archaeological deposit, 1902. Archivo General de la Nación Argentina. Inventario 4738.

Florencio Ameghino died on August 6, 1911. After his death, he became a national icon for his role in creating national science and culture. The Ameghino collection is still today the reference collection of the entire Cenozoic Era biostratigraphic system for the South American continent. The Florentino Ameghino Partido, situated in the north-west of Buenos Aires Province, was named after him, as well as various educational institutions across the country, libraries and museums, squares, schools, parks and other locations. The Ameghino Crater, located to the north of the Sinus Successus on the Moon, is also named in his honor. A very rare privilege for a paleontologist.



Ameghino, F. 1889. Contribución al conocimiento de los mamíferos fósiles de la República Argentina. Actas de la Academia Nacional de Ciencias en Córdoba 6: 1-1028.

Podgorny, I. (2016). The Daily Press Fashions a Heroic Intellectual: The Making of Florentino Ameghino in Late Nineteenth-Century Argentina. Centaurus, 58(3), 166–184. doi:10.1111/1600-0498.12125

Ludueña, E. 2011. La Casa era de los Ameghino. Monumento Histórico Nacional. La Graphica, Luján, 176 pp.

Sergio F. Vizcaíno, Gerardo De Iuliis, Paul D. Brinkman, Richard F. Kay, and Daniel L. Brinkman (2017). On an album of photographs recording fossils in the “Old collections” of the Museo de la Plata and Ameghino’s private collection at the beginning of the XXTH century. Publicación Electrónica de la Asociación Paleontológica Argentina 17 (1): 14–23.
Vizcaíno, Sergio Fabián; Cartas para Florentino desde la Patagonia: Crónica de la correspondencia édita entre los hermanos Ameghino (1887-1902); Asociación Paleontológica Argentina; Publicación Especial – Asociación Paleontológica Argentina; 12; 1; 12-2011; 51-67

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. This gigantic theropod possessed highly derived cranial and vertebral features sufficiently distinct for it to be designated as the nominal genus of the clade Spinosauridae. Unfortunatelly, the holotype of Spinosaurus aegyptiacus was destroyed after a British Royal Air Force raid bombed the museum and incinerated its collections. Only two photographs of the holotype of Spinosaurus aegyptiacus were recovered in the archives of the Paläontologische Museum in June 2000, after they were donated to the museum by Ernst Stromer’s son, Wolfgang Stromer, in 1995. These photographs provide additional insight into the anatomy of the holotype specimen of the animal.

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.


Selected caudal vertebrae and chevrons of Spinosaurus. From Ibrahim et al., 2020.

Spinosaurus clearly show some adaptations to a partially or predominantly piscivorous diet (because of their morphological convergence with those of crocodilians and other fish-eating reptiles, isolated spinosaurid teeth have frequently been misinterpreted). Furthermore, the presence of a short, robust femur with hypertrophied flexor attachment and the low, flat-bottomed pedal claws are consistent with aquatic foot-propelled locomotion. Now, the description of a nearly complete and partially articulated tail of S. aegyptiacus reinforces the hypothesis that this giant theropod spent plenty of time underwater.

Proximal and distal elements of the tail are complete and preserved in three dimensions, indicating a minimal taphonomic distortion. The preserved tail is approximately 400 cm long. The zygapophyses are significantly less developed than in most tetanurans, hinting at a different functional capacity for the tail in this taxon. The neural arches are also distinctive elements of the Spinosaurus tail, while the morphology of the neural spines shows considerable variation. The elongate neural and haemal arches result in a tail shape that is markedly vertically expanded and has an extensive lateral surface area. The highly specialized morphology of the Spinosaurus tail allowed it to function as a propulsive structure for aquatic locomotion. The anterior positioning of the center of mass within the ribcage may have also enhanced balance during aquatic movement. The model proposed by Ibrahim indicates that Spinosaurus tail shape was capable of generating more than 8 times the thrust of the tail shapes of other theropods, and achieved 2.6 times the efficiency.




Ibrahim, N., Maganuco, S., Dal Sasso, C. et al. Tail-propelled aquatic locomotion in a theropod dinosaur. Nature (2020).

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

HONE, D. W. E. and HOLTZ, T. R. (2017), A Century of Spinosaurs – A Review and Revision of the Spinosauridae with Comments on Their Ecology. Acta Geologica Sinica, 91: 1120–1132. doi: 10.1111/1755-6724.13328