Torvosaurus

Reconstructed T. tanneri skull, Museo Capellini of Bologna

Fossilized remains of Torvosaurus have been found in North America and Portugal. In 1971, Vivian Jones, of Delta, Colorado (USA), 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 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.[2] The genus name Torvosaurus derives from the Latin word torvus, meaning "savage", and the Greek word sauros (σαυρος), meaning "lizard".[3] The specific name tanneri, is named after 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 the first skull elements.[4] The fossils from Colorado were further described by Brooks Britt in 1991.[5] The holotype BYU 2002 originally consisted of upper arm bones (humeri) and lower arm bones (radii and ulnae). The paratypes included some back bones, hip bones, and hand bones.[2] When the material described in 1985 is added, the main missing elements are the shoulder girdle and the thighbone.[5] 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.[2] The holotype and paratypes represented at least three individuals: two adults and a juvenile.[5] 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.[5] Several single bones and teeth found in other American sites have been referred to Torvosaurus.[5]

Maxillae of T. gurneyi and T. tanneri compared

In 1992, fossils of a large theropod found at Como Bluff in Wyoming, containing skull, shoulder girdle, pelvis and rib elements, 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."[6] This was often considered a junior synonym of Torvosaurus.[7] The same site has rendered comparable remains for which the nomen nudum Brontoraptor has been used.[8][9] Most researchers now regard both specimens as belonging to Torvosaurus tanneri.[1]

In 2000, material from Portugal was referred to a Torvosaurus sp. by Octávio Mateus and Miguel Telles Antunes.[10] In 2006 fossils from the Portuguese Lourinhã Formation were referred to Torvosaurus tanneri.[11] In 2012, however, Matthew Carrano e.a. concluded that this material could not be more precisely determined than a Torvosaurus sp.[7] In 2013 eggs and embryos were reported from Portugal, referred to Torvosaurus.[12] 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 theropod known from Europe.[1] It was the morphological distinctiveness of the holotype maxilla ML1100 that led to the naming of the Portuguese species.[1]

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.[13]

Restoration of T. tanneri

Torvosaurus was a very large predator, with an estimated maximum body length of 10 meters (33 ft) and mass of 3.6–4.5 metric tons (4.0–5.0 short tons) for both T. tanneri and T. gurneyi,[1][2][14] making Torvosaurus among the largest land carnivores of the Jurassic. Thomas Holtz estimated it at 12 meters (39 feet).[15] Claims have been made indicating even larger sizes. The synonymous Edmarka rex was named thus because it was assumed to rival Tyrannosaurus rex in length. Likewise "Brontoraptor" was supposed to be a torvosaur of gigantic size.[16] The T. gurneyi specimens from Portugal initially prompted larger size estimates to be made. In 2006 a lower end of a thighbone, specimen ML 632, was referred to Torvosaurus sp. and later to T. gurneyi. This specimen was initially stated to indicate a length of 11 meters (36 ft). Applying the extrapolation method of J.F. Anderson, correlating mammal weights to their femur circumference, resulted in a weight of 1,930 kilograms (4,250 lb). However, revised estimates performed in 2014 suggested a slightly smaller total body size for this specimen, of about 10 meters (33 ft).[1] Among the differentiating features between T. gurneyi and T. tanneri are the number of teeth and 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.[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 upper arm was robust; the lower arm robust but 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.[5]

Torvosaurus sp. in Japan

When first described in 1979 by Galton and Jensen,[2] Torvosaurus was classified as a megalosaurid, which is the current consensus.[7] It was later assigned to Carnosauria by Ralph Molnar et al. in 1990,[17] and to a basal position in Spinosauroidea by Oliver Walter Mischa Rauhut in 2003,[18] and to a very basal position in the Tetanurae by Thomas Holtz in 1994;[19] all these assignments are not supported by present phylogenetic analysis.[7] In 1985, Jensen assigned Torvosaurus a family of its own, the Torvosauridae.[4] Despite support for this concept by Paul Sereno[20] and Mateus,[11] it seems redundant as Torvosaurus is closely related to, and perhaps the sister species of, the earlier Megalosaurus within a Megalosaurinae.[7] However, Torvosauridae may be used as an alternative name for Megalosauridae if Megalosaurus is considered an indeterminable nomen dubium.[21] Though a close relative of Megalosaurus, Torvosaurus is seemingly more advanced or apomorphic. Torvosaurus's larger clade, the Megalosauridae, is most commonly held as a basal branch of the Tetanurae, and considered less derived than carnosaurs or coelurosaurs, and likely related to the spinosaurids.[7]

The following is a cladogram based on the phylogenetic analysis conducted by Carrano, Benson & Sampson (2012), showing the relationships of Torvosaurus:[7]

Distinguishing anatomical features

Caudal vertebra of T. gurneyi

According to Carrano et al. (2012), Torvosaurus can be distinguished based on the following characteristics:[22]

• 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 are expanded, forming enlarged, deep openings
• the puboischiadic plate is 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, the Carnosauria having independently evolved from carnivorous Prosauropoda)[2]
• a distal expansion of the ischium shaft with a prominent lateral midline crest and an oval 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)[23]

• Largest Predatory Dinosaur in Europe Found at nationalgeographic