Introducing Tratayenia rosalesi

A speculative reconstruction of Tratayenia rosalesi. From Porfiri et al., 2018.

Patagonia has yielded the most comprehensive fossil record of Cretaceous theropods from Gondwana, including Megaraptora, a clade of medium-sized and highly pneumatized theropods represented by Fukuiraptor, Aerosteon, Australovenator, Megaraptor, Murusraptor, and Orkoraptor, and characterized by the formidable development of their manual claws on digits I and II and the transversely compressed and ventrally sharp ungual of the first manual digit. The enigmatic nature of this group has been a matter of discussion since the description of the first megaraptoran, Megaraptor namunhaiquii in 1990s . 

The phylogenetic position of Megaraptora is still controversial. But despite the lack of consensus, megaraptorans themselves remain a well-supported, monophyletic clade. Now, a new megaraptoran theropod dinosaur from the Upper Cretaceous of the Neuquén Group, sheds light on on these enigmatic predators.

Fossilized vertebrae and right hip bone of Tratayenia rosalesi. From Porfiri et al., 2018.

Tratayenia rosalesi is the first megaraptoran theropod described from the Santonian Bajo de la Carpa Formation of the Neuquén Group. The genus name is for Tratayén, the locality where the holotype was collected. The specific name honors Diego Rosales, who discovered the specimen in 2006.
The holotypic specimen (MUCPv 1162) consists of a well-preserved, mostly articulated series of dorsal and sacral vertebrae, two partial dorsal ribs, the right ilium, pubis and ischium fragments. Tratayenia is the first megaraptoran that unequivocally preserves the complete sequence of sacral vertebrae. The dorsal and sacral centra and neural arches of Tratayenia are unfused, suggesting that the specimen was a subadult at the time of death.

The elevated pneumaticity and morphological resemblance of the axial and pelvic elements of Tratayenia with Aerosteon riocoloradensis and Murusraptor barrosaensis suggests a particularly close relationships between these three taxa. Tratayenia is also the largest carnivorous taxon known from Bajo de la Carpa Formation, reinforcing the hypothesis that megaraptorids were apex predators in South America from the Turonian through the Santonian or early Campanian, following the extinction of carcharodontosaurids.

 

References:

Porfiri, J.D., Juárez Valieri, Rubé.D., Santos, D.D.D., Lamanna, M.C., A new megaraptoran theropod dinosaur from the Upper Cretaceous Bajo de la Carpa Formation of northwestern Patagonia, Cretaceous Research (2018), doi: 10.1016/j.cretres.2018.03.014.

Novas, F.E., 1998. Megaraptor namunhuaiquii gen. et. sp. nov., a large-clawed, Late Cretaceous Theropod from Argentina. Journal of Vertebrate Paleontology 18, 4-9.

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Introducing Corythoraptor jacobsi.

The cranial casque of Corythoraptor jacobsi and recent cassowaries (From Lü et al., 2017)

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. They have only been found in Asia and North America and include animals like Protarcheoepteryx, Caudipteryx, Microvenator, Avimimus, Anzu, and Citipati. 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 Ganzhou area in the Jiangxi Province, in southern China, is one of the most productive oviraptorosaurian regions of the world. Six oviraptorosaurian dinosaurs have been named from Ganzhou: Banji long, Jiangxisaurus ganzhouensis, Nankangia jiangxiensis, Ganzhousaurus nankangensis, Huanansaurus ganzhouensis, and Tongtianlong limosus.  

The holotype of Corythoraptor jacobsi gen. et sp. nov. (From Lü et al., 2017)

The new oviraptorid dinosaur unearthed from the Upper Cretaceous deposits of Ganzhou, was named Corythoraptor jacobsi. The generic name Corythoraptor refers to a raptor bearing a “cassowary-like crest” on its head. The holotype (JPM-2015-001), an almost complete skeleton with the skull and lower jaw, probably corresponds to a young adult that was approaching a stationary stage of development. The anterodorsal part of the crest is missing, but apparently the highest point of the crest would project far above the orbit. The internal structure of the crest is similar to the casque of Casuarius unappendiculatus. The extensive cranial casque was probably composed of the skull roofing bones: nasals, frontals and parietals. The inner structure consists of randomly branching, sparse, trabeculae of variable thickness ranging from 0.3 to 1.2 mm, which implies that the inner core was light, fragile, and not suitable for percussive behavior including intraspecific combat.

Corythoraptor jacobsi forms one clade with Huanansaurus ganzhouensis, but both mainly differs in the skull morphology and the structure of the cervical vertebrae

 

References:

Lü, J., Li, G., Kundrát, M., Lee, Y., Sun, Z., Kobayashi, Y., Shen, C., Teng, F., Liu, H. 2017. High diversity of the Ganzhou oviraptorid fauna increased by a new “cassowary-like” crested species. Scientific Reports. doi: 10.1038/s41598-017-05016-6