Taurovenator

Taurovenator Temporal range: Late Cretaceous, (Cenomanian), ~95–93.9  Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Reconstruction of the head of Taurovenator violantei
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	† Carcharodontosauridae
Tribe:	† Giganotosaurini
Genus:	† Taurovenator Motta et al., 2016
Type species
†Taurovenator violantei Motta et al., 2016

Taurovenator ("bull hunter") is a genus of large carcharodontosaurid theropod that lived in what is now Argentina during the Cenomanian age of the Late Cretaceous around 95 to 93.9 million years ago. Initially only known from a single postorbital skull bone described from the Huincul Formation, Taurovenator violantei was named in 2016 by Argentine paleontologist Matias Motta and a group of colleagues. Debate came about over the validity of the genus and species, with some paleontologists arguing that Taurovenator was synonymous with the earlier-named carcharodontosaurid Mapusaurus . This was until a 2024 study referred a well-preserved partial skull and incomplete skeleton to Taurovenator.

Discovery and naming

Initial discovery and description

In 2005, a right postorbital of a theropod dinosaur was unearthed by Argentine paleontologist Matias Motta from a section of sandstone strata deriving from the lower member of the Huincul Formation, dating to the Cenomanian stage of the Late Cretaceous (95-93.9 million years old). ^[1] The strata located on the Violante Farm, a farm located in Rio Negro Province, Argentina. This fossil was found in the vicinity of the megaraptoran Aoniraptor, several abelisauroids, and a possible unenlagiine paravian. ^[2] The fossils recovered were then transported to the Museo Provincial "Carlos Ameghino", with the isolated postorbital deposited under catalogue number MPCA-Pv 803. ^[2] This postorbital remained undescribed until in 2016, when Matias Motta and colleagues described the postorbital as the holotype (name-bearing specimen) of a new genus and species of carcharodontosaurid dinosaur, Taurovenator violantei. Taurovenator was then the second carcharodontosaurid described from the Huincul Formation, with Mapusaurus named in 2006 based on several incomplete skeletons. ^{[3] [4]} The generic name Taurovenator means "bull hunter", derived from the Latin roots taurus "bull" and venor "hunter" whereas the specific name is in honor of Violante Farm where the postorbital was unearthed. ^{[2] [1]}

Validity debate and additional specimen

Taurovenator went largely unnoticed due to its fragmentary nature, ^{[5] [1]} with Coria et al. (2019) suggesting that Taurovenator is synonymous with Mapusaurus, considering both of its original autapomorphies as shared with Mapusaurus and also pointing out that both taxa shared a curved lateral margin of the palpebral. ^[6] Additionally, the authors considered that there was a high likelihood of them being coeval, ^[6] however, Taurovenator is actually from the lower unit of the Huincul Formation, while Mapusaurus is from the upper unit of the formation. ^[1] Researcher Mickey Mortimer also believed that Taurovenator was synonymous with Mapusaurus due to the lack of sufficient material and diagnostic traits for the genus. ^[7] In 2022, another carcharodontosaurid from the Huincul Formation, Meraxes, was named on the basis of a well-preserved skull and partial skeleton from the same strata as Taurovenator. In their description of Meraxes, the authors stated that Taurovenator lacks sufficient diagnostic characters and may be coeval with Meraxes. ^{[5] [1]}

Notably in the same site on Violante Farm as the Taurovenator holotype, an associated skeleton (MPCA-Pv 803) including a partial skull and posterior (back portion) mandible, incomplete cervical (neck vertebrae) series, fragments of dorsal (back) vertebrae, several ribs, two partial forelimbs, a femur (thighbone), a partial pes (foot), gastralia, and a caudal vertebra was unearthed along with the Taurovenator holotype in 2005 but were regarded as belonging to an indeterminate carcharodontosaurid in the 2016 description of Taurovenator. Additionally, the material of MPCA-Pv 803 had not been completely collected, prepared, or made available for study, delaying its description. ^{[2] [1]} These fossils were also spread out over a sizeable area and intermingled with bones of an indeterminate sauropod. In 2024, this specimen was described and, despite not overlapping in material with the holotype, was referred to Taurovenator. This was done for several reasons: the holotype fits perfectly with MPCA-Pv 803 suggesting they may be from the same individual, the close proximity to the holotype (the specimen was found 800 metres (870 yd) away from the holotype's dig site, and the fossils are congruent in size. In an analysis of the strata from which the holotype was discovered, the 2024 study noted that the Huincul Formation is separated into two distinct sequences; a lower section of thin, multicolored sandstones and an upper section of thick conglomeratic sediments. Mapusaurus derives from the upper sequence of the formation, whereas Meraxes and Taurovenator are exclusive to the lower rock layers. Meraxes, however, was collected in strata close to the Candeleros-Huincul Formation boundary, whereas Taurovenator's specimens were found over 30 meters above the Candeleros-Huincul Formation limit. It is for these reasons that the three carcharodontosaurids found at Huincul were potentially not coeval, supporting the argument for Taurovenator's validity. Additionally, the holotype preserve features of the Giganotosaurini, further supporting its referral to Taurovenator. A new host of diagnostic traits were found on the bones of MPCA-Pv 803, properly demonstrating its distinctiveness from Mapusaurus and Meraxes. ^[1]

Description

Taurovenator life reconstruction, compared to a person.

Taurovenator is a very large carcharodontosaurid. It had an estimated body mass of 5,728 kg (12,628 lb), 5.728 metric tons (6.314 short tons), based on a formula that utilizes the circumference of the femur to predict body mass. For reference, this is smaller than Giganotosaurus 6,349 kilograms (13,997 lb), but larger than Meraxes and Mapusaurus,4,263 kilograms (9,398 lb) and 4,343 kilograms (9,575 lb), respectively). ^{[1] [8]} This puts Taurovenator among the largest theropod dinosaurs known and therefore one of the biggest terrestrial carnivores known to science, though still smaller than genera like Tyrannosaurus and Spinosaurus . ^{[9] [10] [11] [12]}

Skull

The skull of Taurovenator is known from the holotype postorbital in addition to the cranial and mandibular elements of MPCA-Pv 803 which include: both jugals (cheekbones), left quadrate (skull bone articulating with the lower jaw), left palatine (main palate bone), right ectopterygoid (smaller palate bone), both surangulars and angulars (back of lower jaw bones), prearticulars (rearmost lower jaw bone), left articular (lower jaw bone articulating with the skull), right ceratohyal (throat bone), and three isolated teeth. The maximum length of the skull of MPCA-Pv 803 was estimated to be around 135 centimetres (4.43 ft) based on the more complete skulls of relatives like Meraxes. The postorbital is strongly rugose and projected out like a horn, markedly different from the orbital bosses of other carcharodontosaurids. Both Motta et al., 2016 and Rolando et al., 2024 consider this a unique trait, ^{[2] [1]} but its sister taxon Meraxes too has a postorbital that was described as laterally projecting out like a horn. ^[5] The 2024 description of MPCA-Pv 803 however argued that this horn-like projection is distinct from that of Meraxes, with the projection measuring 3–4 centimetres (1.2–1.6 in) in height and 2–3 centimetres (0.79–1.18 in) in diameter. In addition, there is a deep fossa (depression in bone) and excavation on the ventral surface of the postorbital. Though the excavations are observable in the postorbitals of Mapusaurus, Meraxes, and other carcharodontosaurids, they all do not preserve the unique fossa found on the Taurovenator holotype. The jugal is long and sub-triangular in shape with a slightly posteromedially (backwards) pointed postorbital ramus . Its lateral (exposed side) surface is rugose with a thick shelf, a condition similarily observed in South American carcharodontosaurids like Tyrannotitan and Meraxes but absent from the jugals of other allosauroids. The anterior (front) process of the jugal is compressed and bears an ovular pneumatic foramen (pits in bone for air sac systems) on its articulating (contacting) surface with the lacrimal . The quadrate of MPCA-PV 803 is distinctly stout, triangular in lateral view, bearing a large, anteriorly projected pterygoid flange as in related genera. The pterygoid fossa is wide, subdivided by a crest, and lacks pneumaticity as in contemporary carcharodontosaurids of its time. In contrast the palatine of Taurovenator is tetraradiate with an anteriorly expanded vomeropterygoid process (expansion), a short and sub-triangular pterygoid process, a narrow jugal process, and an elongated maxillary process. The ectopterygoid is C-shaped from dorsoventral (top and bottom) views with a pneumatic recess on its medial surface, a trait in other tetanurans. A distinguishing feature of Taurovenator's pterygoid is the thin, long jugal process which is longer than those of Meraxes and Giganotosaurus. As for the mandible, only the posterior portion is known from Taurovenator. It preserves a robust and dorsoventrally (top-down) high morphology, akin to the mandibles of Acrocanthosaurus, Tyrannosaurus, and other tyrannosauroids. Two teeth are preserved from Taurovenator, both of which are large, around 4 centimetres (1.6 in) in length. The margins of these teeth are convex and straight, with chisel-like denticles which number around 8.5 per 5 millimetres (0.20 in) at the mid-crown and 11 per 5 millimetres (0.20 in) at the base. Their blood grooves are well developed and their enamel wrinkles are notably deep, ^[1] a distinct characteristic of carcharodontosaurid teeth. ^{[13] [14]}

Postcrania

Distinctively, Taurovenator's neck vertebrae bore prominent neural spines with flange-like dorsal tips. As a result, the neural spines of cervical vertebrae C3-C6 are "imbricated", ie interlocking with each other. The authors describing this morphology termed this unusual structure a "cervical complex", and likened them to overlapping roof tiles. A similar, though less extreme condition is also known in the C3-C5 of the more basal carcharodontosaurid Acrocanthosaurus . ^{[1] [15]} Available information of Giganotosaurus and Mapusaurus further suggests that this "cervical complex" is a unique synapomorphy of the group. The presence of the cervical complex would have likely restricted the range of movement of the cervical vertebrae. On the other hand, the skull of Taurovenator and other carcharodontosaurids had a ball-shaped occipital condyle similar to that seen in the skulls of ceratopsian dinosaurs. This could have allowed a large range of rotational movement between the skull and the first cervical vertebra. Furthermore, the cervical complex of Taurovenator could have similar functional implications to those of the syncervical vertebrae (ie fused C1-C3 vertebrae) of ceratopsians, strengthening the anterior region of the neck, and increasing the surface area for epaxial cervico-cranial muscles. ^[1]

Only remains of two dorsal vertebrae are known. One is composed of a centrum, but the other is composed of a very tall, 52 cm high neural arch. ^[1]

Taurovenator had proportionately the smallest arms of all known allosauroids. The nearly completely preserved arms were reduced to a greater degree than even in other carcharodontosaurids, being proportionately smaller than that of taxa such as Meraxes , particularly where the forearm is concerned. Despite such limb reduction, the forearms were robust, and the digits had a great degree of flexibility. Nonetheless like other giganotosaurines, the forelimbs were likely incapable of a wide range of movement. ^[1]

Taurovenator also shares with Meraxes an enlarged ungual claw on the second toe, approximately 20% longer than the equivalent phalanx of the third toe and more laterally compressed. ^[1]

Classification

Motta et al. (2016) suggested that Taurovenator occupied a derived position within Carcharodontosauridae, comparing it to Giganotosaurus, Carcharodontosaurus and Mapusaurus in particular. ^[2] Coria et al. (2019) suggested that Taurovenator is synonymous with Mapusaurus, considering both of its original autapomorphies as shared with Mapusaurus and also pointing out that both taxa shared a curved lateral margin of the palpebral. ^[6] Additionally, the authors considered that there was a high likelihood of them being coeval, ^[6] however, Taurovenator is actually from the lower unit of the Huincul Formation, while Mapusaurus is from the upper unit of the formation. ^[1] Rolando et al. (2024) reaffirmed Taurovenator's validity, considering the autapomorphies preserved on the holotype as more strongly developed in Taurovenator than any other carcharodontosaurid, while also considering the supposedly diagnostic curved margin of the palpebral as a more widely distributed feature in Carcharodontosauridae. ^[1]

In order to test the systematics of Taurovenator with the information supplemented by the new specimen, the study used the phylogenetic dataset used in the description of Meraxes, with some additional data. The results of their phylogenetic analysis are shown in a cladogram below: ^{[1] [5]}

Carcharodontosauridae	Neovenator Eocarcharia Lajasvenator Acrocanthosaurus Carcharodontosaurinae Lusovenator Shaochilong Carcharodontosaurus saharicus Carcharodontosaurus iguidensis Giganotosaurini Tyrannotitan Giganotosaurus Mapusaurus Meraxes Taurovenator

Paleoenvironment

Several dinosaurs from the Huincul Formation (Taurovenator not figured)

The fossil remains of Taurovenator were recovered from the Huincul Formation, which is known for a large assemblage of dinosaurian taxa. Two other giant carcharodontosaurids were discovered from the formation as well, Mapusaurus and Meraxes , though all being found in different layers it is unlikely they are coeval (contemporaneous with each other). ^[1] Other theropods include the paravian Overoraptor , the elaphrosaurine Huinculsaurus , the abelisaurs Skorpiovenator , Tralkasaurus , and Ilokelesia , and the megaraptoran Aoniraptor . ^{[16] [17]} Sauropods are the dominant herbivores of the area and are represented by the rebbachisaurid sauropods Cathartesaura and Limaysaurus along with the titanosaurs including the famous Argentinosaurus , Choconsaurus , and Chucarosaurus . ^{[18] [19] [20]} Ornithischians are rarer fossil-wise, but are represented by indeterminate iguanodonts and the elasmarian Chakisaurus . ^[21]

See also

• 2016 in paleontology

References

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