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.

Advertisements

Murusraptor barrosaensis, a new species in the megaraptorid clade.

Body reconstruction of Murusraptor barrosaensis (From Coria et al., 2016)

Body reconstruction of Murusraptor barrosaensis (From Coria et al., 2016)

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 Megaraptor, Orkoraptor and Aerosteon, 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 (Novas et al, 2013). The enigmatic nature of this group has been a matter of discussion since the description of the first megaraptoran, Megaraptor namunhaiquii. For years, Megaraptor has been alternatively interpreted as belonging to different theropod lineages: as basal coelurosaurians (Novas,1998), basal tetanurans (Calvo et al.,2004; Smith et al., 2008), and allosauroids closely related with carcharodontosaurids (Smith et al., 2007; Benson et al., 2010; Carrano et al., 2012). The main reason for so many different interpretations is the incomplete nature of most available megaraptorid skeletons and the little information about their cranial anatomy.

Murusraptor barrosaensis, from the Upper Cretaceous of Neuquén Province, Argentina, belongs to a Patagonian radiation of megaraptorids together with Aerosteon, Megaraptor and Orkoraptor. Murusraptor, meaning “Wall Raptor”, was discovered in a canyon wall in 2001 during an expedition to Sierra Barrosa in northwestern Patagonia. The holotype specimen includes much of the skull, axial skeleton, pelvis and tibia. The braincase is intact and most of the sutures are still visible, indicating that this was not a fully mature animal.

Different appendicular elements of Murusraptor in their original burial positions (From Coria et al., 2016)

Different appendicular elements of Murusraptor in their original burial positions (From Coria et al., 2016)

Murusraptor barrosaensis is unique in having anterodorsal process of lacrimal longer than height of preorbital process; sacral ribs hollow and tubelike; short ischia distally flattened and slightly expanded dorsoventrally.

Murusraptor shares with all Megaraptoridae two unambiguous synapomorphies: teeth with no enamel wrinkles (interpreted as a reversion to primitive condition in Theropoda); and anterior caudal vertebrae with neural arch bearing prominent centrodiapophysial laminae that define a deep infradiapophysial fossa. Murusraptor also exhibits some characters that are interpreted as convergencies of this taxon with non-tyrannosauroid theropods, including lacrimal with a small pneumatic recess; and a highly pneumatic braincase (Coria et al., 2016)

References:

Rodolfo A. Coria, Philip J. Currie. A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia. PLOS ONE, 2016; 11 (7): e0157973 DOI: 10.1371/journal.pone.0157973

Porfiri, J. D., Novas, F. E., Calvo, J. O., Agnolín, F. L., Ezcurra, M. D. & Cerda, I. A. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research 51: 35-55.

 

Introducing Gualicho.

Gualicho shinyae, at the Centro Cultural de la Ciencia.

Gualicho shinyae, at the Centro Cultural de la Ciencia.

The Cretaceous beds of Patagonia have yielded the most comprehensive record of Cretaceous theropods from Gondwana and includes at least five main theropod lineages: Abelisauroidea, Carcharodontosauridae, Megaraptora, Alvarezsauridae, and Unenlagiidae. The best represented theropod clades in the Late Cretaceous terrestrial strata of the Neuquén Basin are the Abelisauroidea and the Carcharodontosauridae. The  Abelisauroidea has been divided in two main branches: the Noasauridae which includes the small-sized abelisauroids, and the Abelisauridae which comprises medium to large-sized animals, like the popular Carnotaurus sastrei. The group exhibits strongly reduced forelimbs and hands, stout hindlimbs, with a proportionally robust and short femur and tibia.  The Carcharodontosauridae includes the largest land predators in the early and middle Cretaceous of Gondwana, like the popular, Giganotosaurus carolinii. The group evolved large skulls surpassing the length of the largest skull of Tyrannosaurus rex.  Another common trait is the fusion of cranial bones. Gualicho shinyae gen. et sp. nov, a partially articulated mid-sized theropod (about 7.6m long and 450kg in weight) represents a new tetanuran theropod taxon from the Huincul Formation.

Articulated right foot of the holotype of Gualicho shinyae during excavation (from Apesteguía et al., 2016)

Articulated right foot of the holotype of Gualicho shinyae during excavation (from Apesteguía et al., 2016)

The new specimen exhibits a new and unusual combination of characters observed in various remotely related clades including ceratosaurs, tyrannosaurids, and megaraptorans. The didactyl manus with a semilunate distal carpal are indicative of derived tetanuran affinities, while the expanded posterior margin of the metatarsal III proximal articulation, are shared with ceratosaurs. The reduced forelimbs with didactyl manus are similar to those of the tyrannosaurids. However, in tyrannosaurids, the carpal elements are reduced and proximodistally flattened, whereas in Gualicho the semilunate and scapholunare carpals retain a more complex shape typical of the carpal elements of most non-coelurosaurian tetanurans. In addition, the manus of Gualicho differs from tyrannosaurids in having a proportionately more robust metacarpal I with a rectangular, rather than triangular, proximal articulation in end view (Apesteguía et al., 2016).

Left humerus of the of the holotype specimen of Gualicho shinyae (MPCN PV 0001) in (A) anterior, (B) posterior, (C) proximal, and (D) distal views. Abbreviations: dpc, deltopectoral crest; ics, intercondylar sulcus; it, internal tuberosity; msh, scar for insertion of m. scapulohumeralis (From Apesteguía et al., 2016).

Left humerus of the of the holotype specimen of Gualicho shinyae (MPCN PV 0001) in (A) anterior, (B) posterior, (C) proximal, and (D) distal views. Abbreviations: dpc, deltopectoral crest; ics, intercondylar sulcus; it, internal tuberosity; msh, scar for insertion of m. scapulohumeralis (From Apesteguía et al., 2016).

Gualicho shares several derived characters with the African theropod Deltadromeus, including reduced distal humeral articulations, and an expanded lobe bearing a medial trough on the proximocaudal aspect of the fibula. The faunal resemblances between strata in the Neuquén and San Jorge Basins of Patagonia and North African Cenomanian beds are intriguing, but difficult to interpret due to a lack of well sampled, age equivalent strata elsewhere.

Gualicho was discovered on a paleontological expedition led by Sebastian Apesteguía in 2007. The name derived from the Gennaken (Northern Tehuelche languaje) watsiltsüm, an old goddess now considered a source of misfortune. The name was chosen to reflect the difficult circumstances surrounding the discovery and study of the specimen. The specific name honors Ms. Akiko Shinya, Chief Fossil Preparator at the Field Museum.

References:

Apesteguía S, Smith ND, Juárez Valieri R, Makovicky PJ (2016) An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina. PLoS ONE 11(7): e0157793. doi: 10.1371/journal.pone.0157793