''Tratayenia'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

megaraptora Megaraptora is a clade of carnivorous Tetanurae, tetanuran theropod dinosaurs with controversial relations to other theropods. Its Derived (phylogenetics), derived members, the Megaraptoridae are noted for their elongated hand claws and proporti ...

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s known from remains found in the

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. The ...

-age

Bajo de la Carpa Formation The Bajo de la Carpa Formation is a geologic formation of the Neuquén Basin that crops out in northern Patagonia, in the provinces of Río Negro and Neuquén, Argentina. It is the oldest of two formations belonging to the Río Colorado Subgroup ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. The type and only species, ''Tratayenia rosalesi'', was described in March 2018. ''Tratayenia'' can be distinguished from other megaraptorans on the basis of three

autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

(unique derived features) of the front portion of each dorsal vertebra, as well as a single autapomorphy of the sacrum. ''Tratayenia'' is one of the youngest known genera of megaraptorans, having lived only about 83 million years ago.

Discovery and naming

The holotype consists of a well-preserved partial skeleton, MUCPv 1162, which includes several articulated portions of the

backbone The backbone is the vertebral column of a vertebrate. Arts, entertainment, and media Film * ''Backbone'' (1923 film), a 1923 lost silent film starring Alfred Lunt * ''Backbone'' (1975 film), a 1975 Yugoslavian drama directed by Vlatko Gilić M ...

. One portion of the skeleton is a string of five dorsal

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

e, likely the seventh to eleventh dorsals. The largest articulated portion of the skeleton is a string of vertebrae including the last two dorsals as well as the five sacrals and much of the right ilium. Other preserved bones include two partial dorsal

rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...

s and fragments of the pubis and

ischium The ischium () form ...

. This skeleton was first discovered in 2006 at a

fossil site by

Universidad Nacional del Comahue The National University of Comahue ( es, Universidad Nacional del Comahue, UNCNavarro, Fernando A. ''. Tremédica, Asociación Internacional de Traductores y Redactores de Medicina y Ciencias Afines/UNCoPortal de Prensa de la Uncoma, Universidad ...

technician Diego Rosales. Shortly thereafter it was excavated by UNC paleontologist Juan D. Porfifi. Porfiri and his colleagues published a preliminary report on the new dinosaur in a 2008 abstract, and suggested that it may have been a relative of

Carcharodontosauridae Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...

. In 2018, the new taxon was described with the generic name ''Tratayenia'', named after Tratayén, the fossil site at which it was excavated. The specific name ''Tratayenia rosalesi'' honors Diego Rosales.

Description

''Tratayenia'' was a medium-sized megaraptoran, growing up to long. It was closely related to genera such as ''

Megaraptor ''Megaraptor'' () is a genus of large theropod dinosaur that lived in the ages of the Late Cretaceous. Its fossils have been discovered in the Patagonian Portezuelo Formation of Argentina, South America. Initially thought to have been a giant dr ...

'', ''

Australovenator ''Australovenator'' (meaning "southern hunter") is a genus of megaraptoran theropod dinosaur from Cenomanian (Late Cretaceous)-age Winton Formation (dated to 95 million years ago) of Australia. It is known from partial cranial and postcranial rem ...

'', and ''

Murusraptor ''Murusraptor'' ("wall thief") is a genus of carnivorous megaraptoran theropod dinosaur from the Sierra Barrosa Formation, part of the Neuquén Group of Patagonia, in Argentina, South America. It is known from a single specimen that consists of ...

''. Like most other

ns, it probably had large claws on its hands for use in hunting prey. Analysis of the Baja de la Carpa indicates that ''Tratayenia'' may have been geologically one of the youngest megaraptorans yet discovered. ''Tratayenia'' is also the largest-bodied carnivorous animal named from the Bajo de la Carpa Formation, reinforcing the hypothesis that megaraptorids were apex predators in southern South America from the

Turonian The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by t ...

through the

or early

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

, following the extinction of

carcharodontosaurids Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...

Dorsal vertebrae

The dorsal

e were tall and narrow, with large pits known as pleurocoels on the side of their centra (spool-shaped main portion). These features are common in the vertebrae of large carnivorous theropods. Some of the vertebrae had fragments of bone in the pleurocoels, which were likely remnants of thin bony walls known as septa which divided the pits. Septa are also known in other megaraptorans and carcharodontosaurids. The neural arches of the vertebrae are taller and narrower in ''Tratayenia'' than in most other theropods. The tubular transverse processes (rib facets) project upwards and to the side. A large and deep excavation is located directly below each transverse process, bounded from the front and rear by thin laminae (ridges). The front edge is formed by the paradiapophyseal lamina and the rear edge is formed by the posterior centrodiapophyseal lamina. These features are also known in the megaraptoran ''Murusraptor''. The

prezygapophyses The articular processes or zygapophyses (Greek language, Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "-physis, process") of a vertebra are projections of the vertebra that serve the purpose of fitting ...

(front vertebral joint plates) are rectangular when see from the side, with the front and lower edges converging at nearly a right angle. This is an

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

(unique adaptation) of ''Tratayenia''. A ridge known as a prezygodiapophyseal lamina connects the prezygapophyses to the transverse processes. Another autapomorphy of ''Tratayenia'' is that the prezygodiapophyseal lamina is parallel to the paradiapophyseal lamina. Other theropods either have a weakly developed (or absent) paradiapophyseal lamina, or one which is angled relative to the prezygodiapophyseal lamina. The front edge of each vertebra has a third autapomorphy, related to two pairs of laminae (four total) connecting the prezygapophyses to the neural spines. At the base of the neural spines, the two laminae comprising each pair are very close together. But as the laminae get closer to the prezygapophyses, they diverge into a shape akin to an inverted Y. There are two of these inverted Y-like structures visible from the front, for both the left and right sides of a vertebra. The postzygapophyses (rear vertebral joint plates) are more typical in shape, and the rear edge of each vertebra has a small, blade-like

hyposphene The hyposphene-hypantrum articulation is an accessory joint found in the vertebrae of several fossil reptiles of the group Archosauromorpha. It consists of a process on the backside of the vertebrae, the hyposphene, that fits in a depression in the ...

which splits into three ridges from below. The neural spines are tall and rectangular when seen from the side, and uniformly thin when seen from the front. Most are completely vertically, but one of the dorsal vertebrae preserved near the hip slightly inclines forward as in various allosauroids. Preserved rib fragments are curved and hollow. They connected to the vertebrae by means of two distinct

condyles A condyle (;Entry "condyle"
in

Sacrum and hip

''Tratayenia'' has five

sacral Sacral may refer to: *Sacred, associated with divinity and considered worthy of spiritual respect or devotion *Of the sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spi ...

(hip) vertebrae, as is the norm for theropods. They are very similar to the dorsal vertebrae in various aspects, such as the presence of large pleurocoels, tall and narrow centra, and laminae-bound excavations below the transverse processes. However, they only have a single autapomorphy: the anteroposterior (front-to-back) width of the neural spine increases drastically in the second to fifth sacral vertebrae compared to the first vertebra. In fact, the fifth sacral's neural spine is twice as long anteroposteriorly than that of the first. This trait has also been observed in ''

Tyrannosaurus ''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...

'' and an unnamed megaraptoran sacrum (SNMS 58023) from the

Romualdo Member The Romualdo Formation is a geologic Konservat-Lagerstätte in northeastern Brazil's Araripe Basin where the states of Pernambuco, Piauí and Ceará come together. The geological formation, previously designated as the Romualdo Member of the Sa ...

of the

Santana Formation The Santana Group is a geologic group, formerly included as the middle part of the Araripe Group, in the Araripe Basin of northeastern Brazil. The group comprises the Crato, Ipubi and Romualdo Formations and is dated to the Aptian to Albian stag ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, so its status as an autapomorphy of ''Tratayenia'' is not concrete. Some of the sacral vertebrae have neural spines which are fused together, and the last three curve backwards. The fourth sacral has a shape similar to those of the Santana Formation sacrum. The ilium (upper blade of the hip) was heavily pneumatized, meaning that it was filled with air pockets. Pneumatization of the ilium is most common in megaraptorans among theropods, as seen in taxa such as ''

Aerosteon ''Aerosteon'' is a genus of megaraptoran dinosaur from the Late Cretaceous period of Argentina. Its remains were discovered in 1996 in the Anacleto Formation, which is from the late Campanian. The type and only known species is ''A. riocolorade ...

'' and ''Murusraptor''. The outer surface of the ilium is perforated by several pneumatic pores, similar to that of ''Aerosteon'', but the upper edge of the bone is straight, in contrast with the curved ilium of ''Aerosteon''. A bone identified as the pubic boot (expanded tip of the pubis) has been found in the holotype, as well as fragments of the

ischium The ischium () form ...

, which has the form of a long, thin shaft covered in grooves.

Classification

Megaraptorans have very controversial relations to other theropods. The first mainstream hypothesis is that they are

carnosaurs Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gi ...

, distantly related to ''

Allosaurus ''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...

'' and more closely related to ''

Neovenator ''Neovenator'' (nee-o-ven-a-tor meaning "new hunter") is a genus of carcharodontosaurian theropod dinosaur. It is known from several skeletons found in the Early Cretaceous (Barremian~130-125 million years ago) Wessex Formation on the south coa ...

'' and

. The second popular hypothesis considers them to be basal

tyrannosauroids Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent be ...

, part of the

coelurosaur Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrann ...

lineage which includes the crested proceratosaurids as well as the famous

tyrannosaurids Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family (biology), family of coelurosaurian Theropoda, theropod dinosaurs that comprises two subfamilies containing up to thirteen genus, genera, including the eponymous ''Tyrannos ...

such as ''

''. A third hypothesis also considers them to be coelurosaurs, but outside Tyrannosauroidea and basal to practically all other groups of Coelurosauria. Porfiri ''et al''.'s description of ''Tratayenia'' prefers this third hypothesis. The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

below follows the strict consensus (average result) of the 12 most

parsimonious Occam's razor, Ockham's razor, or Ocham's razor ( la, novacula Occami), also known as the principle of parsimony or the law of parsimony ( la, lex parsimoniae), is the problem-solving principle that "entities should not be multiplied beyond neces ...

trees (the simplest evolutionary paths, in terms of the total amount of sampled features evolved or lost between sampled

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

) found by Porfiri ''et al.'' (2018)'s phylogenetic analysis. Although the results are different, the methodology analysis was practically identical to that of Apesteguia ''et al''. (2016), only differing in the fact that it incorporated ''Tratayenia'' and ''Murusraptor'', two megaraptorans not sampled in the analysis of Apesteguia ''et al''.

Paleoecology

''Tratayenia'' lived in the

alongside many

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

s and

turtles Turtles are an order (biology), order of reptiles known as Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) an ...

, the

snake Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...

species '' Dinilysia patagonica'', many

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

such as ''

Patagopteryx deferrariisi ''Patagopteryx'' is an extinct monotypic genus of patagopterygiforms that lived during the Late Cretaceous, around 80 mya, in what is now the Sierra Barrosa in northwestern Patagonia, Argentina. About the size of a chicken, it is the earliest ...

'', a diverse amount of

crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cro ...

s and many

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

such as '' Viavenator exxoni'' and '' Traukutitan eocaudata''.

References

{{Taxonbar, from=Q50821199 Late Cretaceous dinosaurs of South America Megaraptorans Fossil taxa described in 2018