Torvosaurus

Reconstructed T. tanneri skull, Museo Capellini of Bologna, Italy

Fossilized remains of Torvosaurus have been found in North America, Portugal, Germany, and possibly in England, Spain, Tanzania, and Uruguay. The first discovered remains referable to Torvosaurus were discovered in 1899 by Elmer Riggs in the "Freeze-out Hills" of southeastern Wyoming, 18 kilometers (11 mi) northwest of Medicine Bow. The material consisted of part of the left foot and right hand and they were taken to the Field Museum of Natural History in Chicago, where they were stored until being re-discovered around 2010. The specimen was assigned to Torvosaurus tanneri after being described in 2014.[4]

More remains of a large theropod that is now believed to have been Torvosaurus were discovered in the Tendaguru Formation of Tanzania and was named "Megalosaurus" ingens by Werner Janensch in 1920, based on the specimen MB R 1050, a 12-centimeter (4.7 in) long tooth from German East Africa (now Tanzania).[5] It was eventually reclassified as a probable member of Carcharodontosauridae before being reclassified as a probable member of the Torvosaurus genus in 2020.[6] Although it was only referred to as Torvosaurus sp., one commentator has noted it could potentially be called Torvosaurus ingens.[7][8] Soto et al. described teeth of a member of the genus Torvosaurus from the Tacuarembó Formation of Uruguay. The authors noted that some of the specimens of “Megalosaurus” ingens figured by Werner Janensch share the features of the Uruguayan material and stated that the materials from Tanzania and Uruguay may represent the same taxon, due to geographical proximity, but ultimately concluded that, based on only teeth, they do not share any derived characteristics to distinguish them from the described species of the genus, T. tanneri and T. gurneyi.[6][9] However, Rauhut et al. consider the teeth to be undiagnostic, being coherent in size and shape with a variety of other theropods (including carcharodontosaurids), thus considering their attribution to the genus to be problematic.[1]

In 1971, Vivian Jones of Delta, Colorado, in the Calico Gulch Quarry in Moffat County, discovered a single gigantic thumb claw of a theropod. This was shown to James Alvin Jensen, a collector who was working for Brigham Young University. In an effort to discover comparable fossils, Vivian's husband Daniel Eddie Jones directed Jensen to the Dry Mesa Quarry, where abundant gigantic theropod bones, together with Supersaurus remains, proved present in rocks of the Morrison Formation. From 1972 onward, the site was excavated by Jensen and Kenneth Stadtman. The type species Torvosaurus tanneri was named and described in 1979 by Peter Malcolm Galton and Jensen.[10] The genus name Torvosaurus derives from the Latin word torvus, meaning "savage", and the Greek word sauros (σαυρος), meaning "lizard".[11] The specific name tanneri comes from the, first counselor in the First Presidency of the Church of Jesus Christ of Latter-day Saints, Nathan Eldon Tanner.

In 1985, Jensen could report a considerable amount of additional material, among it being the first skull elements.[12] The fossils from Colorado were further described by Brooks Britt in 1991.[13] The holotype, BYU 2002, originally consisted of upper and lower arm bones. The paratypes included some back bones, hip bones, and hand bones.[10] When the material described in 1985 is added, the main missing elements are the shoulder girdle and the thighbone.[13] The original thumb claw, specimen BYUVP 2020, was only provisionally referred, as it had been found in a site 195 kilometers (121 mi) away from the Dry Mesa Quarry.[10] The holotype and paratypes represented at least three individuals, these being two adults and a juvenile.[13] In 1991, Britt concluded that there was no proof that the front limbs of the holotype were associated and chose the left humerus as the lectotype.[13] Several single bones and teeth found in other American sites have been referred to Torvosaurus.[13]

Maxillae of T. gurneyi and T. tanneri compared

In 1992, fossils of a large theropod found at Como Bluff in Wyoming contained skull, shoulder girdle, pelvic, and rib elements. They were named by Robert T. Bakker et al. as the species Edmarka rex. Bakker et al were impressed with the size of Edmarka, noting that it "would rival T. rex in total length," and viewing this approximate size as "a natural ceiling for dinosaurian meat-eaters."[14] This was often considered a junior synonym of Torvosaurus,[15] but a detailed analysis has not been carried out yet.[16] The same site has rendered comparable remains for which the nomen nudum Brontoraptor has been used.[17][18] Most researchers now regard both specimens as belonging to Torvosaurus tanneri.[2] However, Edmarka rex and Brontoraptor require reclassification to determine whether or not they actually belong to T. tanneri, as all the specimens described prior to their discovery indicate that they reached their adult size and both incomplete specimens lack detailed osteological descriptions.[19]

In 2012, a still undescribed, 55% complete specimen was discovered in Colorado in the Skull Creek Quarry, which is an exposure of the Morrison Formation. The specimen, nicknamed "Elvis", included the pelvic, spine, and hind limb bones, a complete, associated backbone, as well as cranial elements. It is the most complete specimen of Torvosaurus found to date.[20] A mounted skeleton of the specimen, with missing parts reconstructed with casts from other Torvosaurus specimens, is currently on display in the Museum of Natural History & Science in Cincinnati.[20][21]

In 2000, material from Portugal was referred to a Torvosaurus sp. by Octávio Mateus and Miguel Telles Antunes.[22] In 2006, fossils from the Portuguese Lourinhã Formation were referred to Torvosaurus tanneri.[3] In 2012, however, Matthew Carrano et al. concluded that this material could not be more precisely determined than a Torvosaurus sp.[23] In 2013 and 2014, eggs with and without embryos were reported from Portugal and referred to Torvosaurus.[24][25] The species from Portugal was named T. gurneyi in honor of James Gurney in 2014, the creator of the Dinotopia series of books. It is the largest named theropod known from Europe, although an isolated anterior caudal vertebra from the Vega Formation in Spain, which may belong to Torvosaurus or a closely related taxon, is about 15% larger than the one found on T. gurneyi.[2][26] Furthermore, remains of a large spinosaurid from the Vectis Formation in the Isle of Wight include vertebrae of size comparable to those of Spinosaurus, indicating an animal exceeding 10 m in length, making it the largest reported European theropod.[27][28] It was the morphological distinctiveness of the holotype maxilla ML1100 that led to the naming of the Portuguese species.[2] In 2017, a set of Portuguese cranial material assigned to Torvosaurus was described, including a specimen interpreted as belonging to the same individual as the holotype of Torvosaurus gurneyi.[29]

In 2020, Soto et al. described FC-DPV 2971, a tooth from Uruguay, as belonging to a new unnamed species of Torvosaurus.[6] They also assigned Megalosaurus/Ceratosaurus ingens (specimen MB R 1050) from Tanzania to Torvosaurus.[6] Also in 2020, a fragmentary maxilla referable to Torvosaurus was described from the middle Callovian Ornatenton Formation of Germany. This is the oldest record of the genus and suggests that megalosaurines originated in Europe, or at least that Europe was a biogeographical turntable for them from the Middle to the early Late Jurassic. Other possible Torvosaurus instances in Europe include fragmentary remains from the Kimmeridge Clay of England that possibly belong to the genus.[1] These consist of a tibia (OUMNH J.29886) and a maxilla fragment that were collected separately from each other.[23]

Restoration of T. tanneri

Torvosaurus was a very large and robust predatory dinosaur, with an estimated maximum body length of 10–11 meters (33–36 ft) and mass of 4–5 metric tons (4.4–5.5 short tons) for the Portuguese species T. gurneyi,[2][3] making T. gurneyi among the largest terrestrial carnivores of the Jurassic. Claims have been made indicating even larger sizes for the American species T. tanneri up to 12 m (39 ft) in length and more than 4 t (4.4 short tons) based on incomplete remains of Edmarka rex and Brontoraptor.[30][16][31] However, these claims regarding T. tanneri are likely erroneous, as the discovered remains of T. tanneri indicate that they reached adult size at 9 meters (30 ft) in length and approximately 2 metric tons (2.2 short tons) in body mass.[13][32][33][34] Furthermore, Edmarka rex and Brontoraptor lack detailed analyses to verify whether or not they actually belong to T. tanneri.[19][16]

Among the differentiating features originally recognized between T. gurneyi and T. tanneri are the number of teeth, alongside the size and shape of the mouth. While the upper jaw of T. tanneri has more than 11 teeth, that of T. gurneyi has less.[2] However, later examination of a new right maxilla, probably belonging to the same individual as the holotype of T. gurneyi, has determined that, while the two species can be distinguished based on the morphology of the maxillary medial wall and interdental plates, the supposedly lower number of maxillary teeth in the Portuguese form may be an artifact of preservation, since it is not possible to know the exact number of teeth in the complete maxilla at the moment.[29]

The material from Germany is further distinguished by the other two species by a temporal difference of c. 10 Ma and a few morphological differences which indicate that it was the third species outside a sister taxon relationship between T. tanneri and T. gurneyi. The material is only 10% smaller than the maxilla of T. tanneri, although the ontogenetic stage of the specimen is unknown. This indicates that derived megalosaurines were already among the largest terrestrial predators of the late Middle Jurassic, with only a moderate increase in size in the genus by the Late Jurassic.[1]

Skeletal restoration showing the size of T. gurneyi, known remains highlighted

Torvosaurus had an elongated, narrow snout, with a kink in its profile just above the large nostrils. The frontmost snout bone, the premaxilla, bore three rather flat teeth oriented somewhat outwards with the front edge of the teeth crown overlapping the outer side of the rear edge of the preceding crown. The maxilla was tall and bore at least eleven rather long teeth. The antorbital fenestra was relatively short. The lacrimal bone had a distinctive lacrimal horn on top. Its lower end was broad in side view. The eye socket was tall with a pointed lower end. The jugal was long and transversely thin. The lower front side of the quadrate bone was hollowed out by a tear-shaped depression, the contact surface with the quadratojugal. Both the neck vertebrae and the front dorsal vertebrae had relatively flexible ball-in-socket joints. The balls on the front side of the vertebral centra had a wide rim, a condition by Britt likened to a Derby hat. The tail base was stiffened in the vertical plane by high and in side view wide neural spines. The whole of the arm was very strong, but somewhat short. Whether the thumb claw was especially enlarged is uncertain. In the pelvis, the ilium resembled that of Megalosaurus and had a tall, short, front blade and a longer pointed rear blade. The pelvis as a whole was massively built, with the bone skirts between the pubic bones and the ischia contacting each other and forming a vaulted closed underside.[13]

Torvosaurus sp. in Japan

When first described in 1979 by Galton and Jensen,[10] Torvosaurus was classified as a megalosaurid, which is the current consensus.[15] It was later assigned to Carnosauria by Ralph Molnar et al. in 1990,[35] then to a basal position in Spinosauroidea by Oliver Walter Mischa Rauhut in 2003,[36] and to a very basal position in Tetanurae by Thomas Holtz in 1994.[37] All these assignments are not supported by present phylogenetic analysis.[15] In 1985, Jensen assigned Torvosaurus to a family of its own, Torvosauridae.[12] Despite support for this concept by Paul Sereno[38] and Mateus,[3] it seems redundant because Torvosaurus is closely related to, and perhaps the sister species of, the earlier Megalosaurus within Megalosaurinae.[15] However, Torvosauridae may be used as an alternative name for Megalosauridae if Megalosaurus is considered an indeterminable nomen dubium.[39] Though a close relative of Megalosaurus, Torvosaurus is seemingly more advanced, or apomorphic. Torvosaurus's larger clade, Megalosauridae, is most commonly held as a basal branch of Tetanurae, considered to be less derived than carnosaurs or coelurosaurs and likely related to the spinosaurids.[15]

The following is a cladogram based on the phylogenetic analysis conducted by Carrano, Benson, and Sampson (2012) showing the relationships of Torvosaurus:[15]

Distinguishing anatomical features

Caudal vertebra of T. gurneyi

According to Carrano et al. (2012), Torvosaurus can be distinguished based on the following characteristics:[40]

• The presence of a very shallow maxillary fossa (it lacks a fenestra maxillaris piercing the bone wall)
• The presence of fused interdental plates
• The pneumatic fossae in the posterior dorsal and the anterior caudal vertebrae centra being expanded to form enlarged, deep openings
• The puboischiadic plate being highly ossified (the paired bony plates of both sides connect and close off the entire underside of the pelvis, a very basal trait that Galton & Jensen saw as an indication that Theropoda was polyphyletic, with Carnosauria having independently evolved from carnivorous Prosauropoda)[10]
• A distal expansion of the ischium shaft with a prominent lateral midline crest and an ovalur outline when examined in lateral view
• The cervical vertebrae are opisthocoelous with a pronounced flat rim around the anterior ball (according to Rauhut, 2000)
• A transverse fenestra is situated in the neural arch of the dorsal vertebrae in front of the hyposphene (according to Rauhut, 2000)[41]

Teeth of Torvosaurus gurneyi.

The study of fossilized embryos of Torvosaurus provides researchers with information about the transformation of the embryo over time, the different developmental pathways present in dinosaur lineages, dinosaur reproductive behavior, and dinosaur parental care.[42][43][44] In 2013, Araújo et al. announced the discovery of specimen ML1188, a clutch of crushed dinosaur eggs and embryonic material attributed to Torvosaurus.[45] This discovery further supports the hypothesis that large theropods were oviparous, meaning that they laid eggs and hence that embryonic development occurred outside the body of female dinosaurs. This discovery was made in 2005 by the Dutch amateur fossil-hunter Aart Walen at the Lourinhã Formation in Western Portugal in fluvial overbank sediments that are considered to be from the Tithonian age of the Jurassic, approximately 152 to 145 million years ago. This discovery is paleontologically significant for a number of reasons: (a) these are the most primitive dinosaur embryos known; (b) these are the only basal theropod embryos known; (c) fossilized eggs and embryos are rarely found together; (d) it represents the first evidence of a one-layered eggshell for theropod dinosaurs; and (e) it allows researchers to link a new eggshell morphology to the osteology of a particular group of theropod dinosaurs.[24] The specimen is housed at the Museu da Lourinhã in Portugal. As the eggs were abandoned due to unknown circumstances, it is not known if Torvosaurus provided parental care to its eggs and young or abandoned them shortly after laying.[46] However, the eggshells are highly porous, allowing efficient gaseous exchange between the external and internal media, thus indicating the eggs were buried for incubation within substrate in a manner similar to modern seaturtles. This is also corroborated by the undisturbed taphonomic setting and low-energy geological context.[24]

All documented Torvosaurus specimens from the Morrison Formation are from similarly sized, likely adult individuals and the lack of immature individuals may be explained by many factors, none of which are mutually exclusive. For one thing, the formation is known to preserve large vertebrates better than smaller ones. Immature individuals may also have occupied a different ecological niche from adults in habitats where their remains were likely to preserve as fossils and they may have been the prey of choice of larger predators as well. Torvosaurus may also have experienced Type B1 population survivorship, as has been found in other dinosaurs, with mortality increasing after sexual maturity was achieved, leading to an abundance of mature individuals in the fossil record. A final possibility is that immature Torvosaurus remains could be misidentified due to having different proportions compared to the very large and robust adults.[4]

• Largest Predatory Dinosaur in Europe Found at nationalgeographic