Introducing Llukalkan aliocranianus

Photograph of the materials in the field. Image credit: Federico Gianechini

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by Jose Bonaparte with the description of  Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Tralkasaurus cuyi and Viavenator exxoni. Llukalkan aliocranianus, a new furileusaurian abelisaurid from the Bajo de la Carpa Formation (Santonian) in northwestern Patagonia, is an important addition to the knowledge of abelisaurid diversity.

 

Reconstruction of the complete skull and mandible of Llukalkan aliocranianus. Scale bar: 5 cm. From Gianechini et al., 2021

The new specimen was found near the site where the remains of Viavenator exxoni were recovered at La Invernada fossil area, 50 km southwest of Rincón de los Sauces city, Neuquén province, Argentina. This site has provided a valuable theropod record. Other taxa discovered at La Invernada include the titanosaurian sauropods Bonitasaura salgadoi, Traukutitan eocaudata, and Rinconsaurus caudamirus, pterosaurs, multiple crocodyliforms, snakes, and turtles.

The holotype (MAU-Pv-LI-581) is an incomplete but partially articulated skull with a complete braincase. The generic name derived from the word Llukalkan, “one who scares or causes fear” in Mapudungun language. The specific name aliocranianus means “different skull” in Latin.  Llukalkan exhibits some similarities with Viavenator, that include: elongate and robust olfactory tracts; large and horizontally oriented olfactory bulbs; cerebral hemispheres clearly delimited in lateral view; a tongue-shaped floccular process of cerebellum posteriorly projected and reaching the level of the posterior semicircular canal; and elongate and ventrally projected passage for the rostral middle cerebral vein. Additionally, Llukalkan has a small pneumatic recess caudal to the columellar recess, which is identified as a poorly developed caudal tympanic recess. This taxon also presents a T-shaped lacrimal with jugal ramus lacking a suborbital process, that differs significantly from the lacrimal of other abelisaurids.

 

References:

Federico A. Gianechini, Ariel H. Méndez, Leonardo S. Filippi, Ariana Paulina-Carabajal, Rubén D. Juárez-Valieri & Alberto C. Garrido (2021): A New Furileusaurian Abelisauridfrom La Invernada (Upper Cretaceous, Santonian, Bajo De La Carpa Formation), NorthernPatagonia, Argentina, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2020.1877151

Introducing Ninjatitan zapatai, the earliest known titanosaur

Anterior caudal vertebra of Ninjatitan zapatai. Scale bar equals 10 cm. From Gallina et al., 2021

Titanosauria is the most diverse sauropod clade represented by nearly 80 genera described worldwide, the vast majority of which were recovered from Upper Cretaceous sediments of Argentina. It has been suggested that the titanosaurian origin took place around 135 million years ago in South America. The study of this diverse group of large, long-necked, herbivorous dinosaurs embrace an extensive list of important contributions, which started with Richard Lydekker’s pioneering work on Patagonian dinosaurs.

The discovery of Ninjatitan zapatai, a new specimen from the Lower Cretaceous Bajada Colorada Formation (Berriasian–Valanginian) of north Patagonia, supports the hypothesis that the group was already established in the Southern Hemisphere and reinforces the idea of a Gondwanan origin for Titanosauria. Ninjatitan lived 140 million years ago and reached 20 meters in length (65 feet). The firs remains were discovered in 2014 by technician Jonatan Aroca. The holotype (MMCh-Pv228) includes an incomplete anterior–middle dorsal vertebra, a middle dorsal centrum, and anterior caudal centra with the base of neural arches preserved, a complete left scapula, a fragmentary distal femur, and a nearly complete left fibula of a single individual. The generic name honors the Argentine paleontologist Sebastián “Ninja” Apesteguía. The species name refers to Mr. Rogelio “Mupi” Zapata, in recognition for his work as a technician of the Museo Municipal Ernesto Bachman.

Left scapula of Ninjatitan zapatai. Scale bar equals 10 cm. From Gallina et al., 2021.

Despite the fragmentary nature of the new taxon, three derived characters of Ninjatitan support its possition within the clade Titanosauria: 1) presence of procoelous anterior caudal centra; 2) pneumatized neural arch of anterior caudal vertebrae; and 3) position of the acromial process near the glenoid level. The position of Ninjatitan, as a basal titanosaur, extends the origin of this clade by at least 10 Myr.

The Berriasian–Valanginian Bajada Colorada Formation of Neuquén Province, Patagonia Argentina, has provided novel information in the last years that helps to elucidate the evolutionary history of different sauropod lineages. The first sauropod taxon recognized from this unit was the diplodocid Leinkupal laticauda. The second taxon is the recently described dicraeosaurid Bajadasaurus pronuspinax.

References:

Pablo Ariel Gallina, Juan Ignacio Canale, & José Luis Carballido (2021).The earliest known titanosaur sauropod dinosaur. Ameghiniana58(1), 35–51 http://dx.doi.org/10.5710/AMGH.20.08.2020.3376

Sander PM, Christian A, Clauss M, et al. Biology of the sauropod dinosaurs: the evolution of gigantism. Biol Rev Camb Philos Soc. 2011;86(1):117-155. doi:10.1111/j.1469-185X.2010.00137.x

The Middle Eocene Climatic Optimum and the Patagonian floras.

Spore-pollen species from the Eocene of southern South America. From Fernandez et al., 2021

The geological records show that large and rapid global warming events occurred repeatedly during the course of Earth history. Ecological models can predict how biodiversity is affected by those events, but only the fossil record provides empirical evidence about the impact of rising temperatures and atmospheric CO2 on species diversity.

The Middle Eocene Climatic Optimum (MECO, ~40 Ma) was a transient period of global warming that interrupted the general cooling trend initiated at the end of the early Eocene climate optimum (EECO, ~49 Ma). The MECO is related to major oceanographic and climatic changes in the Neo-Tethys and also in other oceanic basins, and lasted about 500–600 Kyr. The MECO altered the pelagic ecosystem with repercussions on the food web structure. The lack of nutrients in the surface waters led to a significant decrease in planktonic foraminiferal accumulation rates, while autotroph nannoplankton accumulation rates remained stable.

Relative frequency of the most common plant groups across the MECO and Late Eocene. From Fernández et al., 2021

The MECO also influenced terrestrial biotas. A new study quantify the response of the floras of southern Patagonia to this warming event. The samples were collected from the Río Turbio Formation in southern Patagonia. The terrestrial palynological assemblage revealed a clear inverse relationship between the abundance of ferns and angiosperms. At the beginning of the MECO, ferns highly increase in abundance (with Cyatheaceae, Dicksoniaceae, and Osmundaceae as the most frequent families), while the abundance of angiosperms decreases dramatically. Podocarpaceae also increases from ~5 % to ~20%. At the core of MECO, ferns drop to a minimum, and angiosperms become dominant. Finally, at the end of the MECO ferns rise again to maximum values and angiosperms decrease.

Palynological analysis also revealed that floras in southern Patagonia were in average ~40% more diverse during the MECO than pre-MECO and post-MECO intervals. The penetration of neotropical migrant species to the highest latitudes along with the persistence of southern Gondwanan natives may have triggered the gradual increasing diversity that can be observed across the MECO.

 

References:

Fernández, D.A., Palazzesi, L., González Estebenet, M.S. et al. Impact of mid Eocene greenhouse warming on America’s southernmost floras. Commun Biol 4, 176 (2021). https://doi.org/10.1038/s42003-021-01701-5

Giorgioni, M., Jovane, L., Rego, E.S. et al. Carbon cycle instability and orbital forcing during the Middle Eocene Climatic Optimum. Sci Rep 9, 9357 (2019). https://doi.org/10.1038/s41598-019-45763-

Sonal Khanolkar, Pratul Kumar Saraswati & Karyne Rogers (2017) Ecology of foraminifera during the middle Eocene climatic optimum in Kutch, India, Geodinamica Acta, 29:2,181-193, DOI: 10.1080/09853111.2017.130084

 

Introducing Bagualia alba, the oldest known eusauropod.

Bagualia alba. From Pol et al., 2020

During the Early Jurassic the southwestern margin of Gondwana was affected by a voluminous magmatic episod related to the emplacement of t heKaroo-Ferrar-Chon Aike Large Igneous Provinces (LIPs). That pulse of volcanism led to global warming, with at least four times the present level of atmospheric CO2, and ocean acidification that resulted in a mass extinction of marine invertebrates and turnover among groups of marine plankton. The period is also characterized by a floristic turnover and the diversification of the conifers, especially modern families, with small coriaceous leaves. Biostratigraphic and high-precision geochronologic results indicate that a major faunal turnover of the sauropodomorph dinosaurs took place in the Early Jurassic, which led to the rise of the eusauropods. Cañadón Asfalto Basin (part of the Chon Aike Igneous Province of Patagonia) in the Chubut Province of Argentina preserves an extraordinary record of Jurassic fauna and flora that marks key events in the evolution of Mesozoic life. The recently described Bagualia alba, recovered from the base of the Cañadón Asfalto Formation, lived 179 million years ago and is the oldest known eusauropod. The name of the new specimen refers to Cañadón Bagual, the site where the fossil was found, and alba (dawn, in Spanish), for its early age.

Reconstruction of Bagualia alba. Credit: Jorge Gonzalez

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. Among the characters that distinguish Bagualia from other early sauropods area pointed process on the anteroventral end of the premaxilla and anterodorsal end of the dentary; orbital margin of the frontal with a close V-shape pointed medially that results in a short contribution to the orbit; supratemporal fenestra about as anteroposteriorly long as lateromedially wide; and strongly marked proatlantal facets on the laterodorsal margin of the foramen magnum. 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.

In Patagonia, prior to the Toarcian palaeoenvironmental crisis the plant assemblage consisted of sphenophytes, dipteridacean ferns, conifers, seed ferns, Bennetitales and cycads. This diversity is indicative of more humid conditions. By contrast, the less diverse palynologycal assemblage postdating the volcanic event is indicative of seasonally dry and warm conditions, and are largely dominated by the conifers Araucariaceae, Cheirolepidiaceae and Cupressaceae. These large conifers with coriaceous leaves as the dominant trees likely acted as a strongly selective regime favouring the survival and success of eusauropods, which had powerful jaws and an oversized gut. Conversely, the disappearance of many elements of the diverse pre-Toarcian flora could have influenced the extinction of the diverse lineages of smaller non-sauropods, which lacked adaptations to high-fibre herbivory as their gracile skulls and mandibles were less mechanically efficient and their teeth were small, with thin enamel (less than 200 μm) and lacked tooth–tooth occlusion.

 

 

References:

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
 
Cúneo, R., Ramezani, J., Scasso, R., Pol, D., Escapa, I., Zavattieri, A. M., & Bowring, S. A. (2013). High-precision U–Pb geochronology and a new chronostratigraphy for the Cañadón Asfalto Basin, Chubut, central Patagonia: Implications for terrestrial faunal and floral evolution in Jurassic. Gondwana Research, 24(3-4), 1267–1275. doi:10.1016/j.gr.2013.01.010 

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.

 

References:

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). https://doi.org/10.1007/s00114-020-01682-1

Introducing Tralkasaurus cuyi, the thunder lizard.

Photo: AFP/MUSEO ARGENTINO DE CIENCIAS NATURALES

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by the legendary paleontologist Jose Bonaparte with the description of  Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Eoabelisaurus mefi and Viavenator exxoni.

Abelisauroids were traditionally divided into two main clades: large-sized Abelisauridae, and small-sized Noasauridae. Although represented by relatively well-known skeletons, the phylogenetic relationships within abelisaurids remain debated. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous. Now, a new abelisaurid from the upper section of the Huincul Formation (Cenomanian-Turonian) at the Violante Farm fossil site, Río Negro province, northern Patagonia, Argentina, is an important addition to the knowledge of abelisaurid diversity.

Map of El Cuy region showing the Violante farm fossil site. From Cerroni et al., 2020.

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. 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.

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.
Because body mass is usually indicative of an ecological niche, the new taxon probably occupied a different ecological niche within the predatory guild.

 

References:

Cerroni, M.A., Motta, M.J., Agnolín, F.L., Aranciaga Rolando, A.M., Brissón Egli, F., & Novas, F.E. (2019). A new abelisaurid from the Huincul Formation (Cenomanian-Turonian; Upper Cretaceous) of Río Negro province, Argentina. Journal of South American Earth Sciences https://www.sciencedirect.com/science/article/abs/pii/S0895981119304766

Introducing Lajasvenator

Preserved elements of Lajasvenator ascheriae. From Coria et al., 2019

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. Most discoveries come from continental units of ages ranging from Barremian to Maastrichtian. The lowest levels of the Cretaceous are well exposed in the marine and terrestrial deposits of the Mulichinco and Bajada Colorada formations.
The Carcharodontosauridae includes the largest land predators in the early and middle Cretaceous of Gondwana, like the popular Giganotosaurus carolinii, and in some way, they were considered as ecological equivalents to the Laurasian tyrannosauroids. The group evolved large skulls surpassing the length of the largest skull of Tyrannosaurus rex; and some derivaded forms had heavily sculptured facial bones. Another common trait is the fusion of cranial bones. Lajasvenator ascheriae, a new specimen from the Valanginian Mulichinco Formation, represents the oldest Cretaceous carcharodontosaurid from South America. The name derived from the Lajas, the city near where the specimen was found; and venator, a Latin word for hunter. The specific name honors Susana Ascheri, owner of the land where the fossil was discovered.

The holotype (MLL-PV-005) of this medium-sized theropod is an incomplete but partially articulated skeleton that includes a partial skull, partially articulated presacral vertebral series, four articulated caudal vertebra and fragments of the pelvic girdle. A second specimen (MLL-PV-Pv-007) includes the anterior ends of both dentaries, a quadratojugal, and fragments of cervical vertebrae, ribs and a possible tarsal bone. The holotype of Lajasvenator was collected in 2010 during fieldwork at Pilmatué. The second specimen was recovered in 2012.

Lajasvenator exhibits anterior projections on cervical prezygapophyses, lip-like crests on the lateral surfaces of cervical postzygapophyses, and bilobed anterior processes on cervical ribs. The phylogenetic analysis indicates that Lajasvenator is clearly nested in a basal position within Carcharodontosauridae.

References:

Coria, R.A., Currie, Currie, P.J., Ortega, F., Baiano, M.A., An Early Cretaceous, medium-sized carcharodontosaurid theropod (Dinosauria, Saurischia) from the Mulichinco Formation (upper Valanginian), Neuquén Province, Patagonia, Argentina, Cretaceous Research (2019) https://doi.org/10.1016/j.cretres.2019.104319
Novas, F.E., et al., Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia, Cretaceous Research (2013), http://dx.doi.org/10.1016/j.cretres.2013.04.001

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.

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