Megalosauridae

Body size '', among the largest megalosaurids Like other tetanurans, megalosaurids are carnivorous theropods characterized by large size and bipedalism. Specifically, megalosaurids exhibit especially giant size, with some members of the family weighing more than one tonne. Over time, there is evidence of size increase within the family. Basal megalosaurids from the Early Jurassic had smaller body size than those appearing in the late Middle Jurassic. Due to this size increase over time, Megalosauridae appear to follow a size increase pattern similar to that of other giant sized theropods like Spinosauridae. This pattern follows Cope's rule, the postulation by paleontologist Edward Cope about evolutionary increase in body size. Anatomical characteristics , Torvosaurus, Afrovenator, Megalosaurus, Eustreptospondylus'' One unambiguous synapomorphy of Megalosauridae is a lower and longer skull with a length to height ratio of 3:1. In addition, the typical skull roof tends to be much less ornamented than that of other tetanurans, and crests or horns are either very small or absent entirely. Megalosaurids also have femoral heads with an orientation 45 degrees between anteromedial and fully medial. Megalosauridae are also defined by the following unique unambiguous synapomorphies: ==Classification==

Historical classification From the family's inception, many specimens found in the field have been wrongly classified as megalosaurids. For example, most large carnivores found for about a century after the naming of Megalosaurus bucklandii were placed in Megalosauridae. Megalosaurus was the first paleontological finding of its kind when William Buckland discovered a giant femur and named it in 1824, predating even the term Dinosauria. As early paleontologists and researchers found more dinosaur bones in the surrounding area, they attributed them all to M. bucklandii since it was the only named and described dinosaur at this point in history. Therefore, the species was initially described and classified by a mass of possibly unrelated characteristics. Today, it is accepted that megalosaurids existed at least as a group of basal tetanurans, due to the fact that they have more derived taxa than ceratosaurs }} '', a typical megalosaurine Then, in 2012, Carrano, Benson, and Sampson did a much larger analysis of tetanurans and defined Megalosauria more broadly as the clade containing Megalosaurus, Spinosaurus, and all its descendants. In other words, Megalosauria is the group that contains the two families Megalosauridae and its close relative Spinosauridae. Within this new cladogram, Megalosauridae was given a new subfamily Afrovenatorinae, which included all megalosaurids more closely related to Afrovenator than Megalosaurus. Carrano, Benson, and Sampson also included various megalosaurids that had previously been excluded from cladograms in their 2012 study, such as Duriavenator and Wiehenvenator in Megalosaurinae and Magnosaurus, Leshansaurus, and Piveteausaurus in Afrovenatorinae. However, subsequent analyses have placed Sciurumimus as a basal coelurosaur, and several supposed megalosauroid synapomorphies reported in the original description are shared with basal coelurosaurs. In 2016, Wiehenvenator was found by phylogenetic analysis to be in the Megalosauridae as a sister taxon to Torvosaurus. The following is a cladogram based on the phylogenetic analysis conducted by Rauhut et al., showing the relationships of Wiehenvenator. }} In 2019, Rauhut and Pol described Asfaltovenator vialidadi, a basal allosauroid displaying a mosaic of primitive and derived features seen within Tetanurae. Their phylogenetic analysis found traditional Megalosauroidea to represent a basal grade of carnosaurs, paraphyletic with respect to Allosauroidea. This would render Megalosauridae a family of carnosaurs. }} ==Palaeoecology==

Megalosaurids have been suggested to be predators or scavengers inhabiting coastal environments. Middle Jurassic-era tracks believed to have left by megalosaurids have been found at Vale de Meios in Portugal. During the middle Jurassic, this site would have been a tidal flat exposed at low tide on the edge of a lagoon. Unlike most coastal tracks, which are parallel to the coastline and probably left by migrating animals, the Vale de Meios tracks were perpendicular to the coast, with the vast majority oriented towards the lagoon. This indicates that the megalosaurids which would have left these tracks approached the tidal flat once the tide retreated. This indicates that megalosaurids could have scavenged for the carcasses of marine creatures left by the receding tides. Another possibility is that megalosaurids were piscivorous, approaching the coast to hunt for fish. Spinosaurids, which were close relatives of megalosaurids, had numerous adaptations for piscivory and semiaquatic life, so such a lifestyle is supported by phylogenetic data. Shark teeth, cartilage fragments, and gastroliths have been documented as stomach contents in Poekilopleuron. Both this genus and Dubreuillosaurus were discovered in sediments also preserving mangrove roots, providing further evidence for a coastal habitat. Nevertheless, this does not rule out the possibility that megalosaurids also fed on terrestrial prey. Palaeogeography before the split into Gondwana and Laurasia Species included in Megalosauridae have been found on every modern continent, split relatively equally between sites on the Gondwana and Laurasia supercontinents. Paleogeography findings show that Megalosauridae was mainly restricted to the Middle to Late Jurassic, suggesting they went extinct at the Jurassic-Cretaceous boundary 145 million years ago. The global radiation of these carnivorous theropods occurred in two steps. First, radiation occurred during Pangaea's breakup during the Early Jurassic, about 200 million years ago. When the Tethys Sea emerged between the supercontinent, megalosauroids radiated to the two-halves of Pangaea. The second step of radiation occurred during the Middle and Late Jurassic, 174 to 145 million years ago, in allosauroids and coelurosaurs. Megalosauridae appears to have gone extinct at the end of this time period. Megalosaurid remains have been found in various areas of the world throughout history. For example, Megalosauridae contains the most primitive theropod embryo ever found, from Early Tithonian Portugal 152 million years ago (mya). In addition, various megalosaurid fossil discoveries have been dated to Bajocian-Callovian England and France 168 to 163 mya, Middle Jurassic Africa about 170 mya, Late Jurassic China 163 to 145 mya, and Tithonian North America about 150 mya. Most recently, megalosaurids have been found in the Tiourarén Formation in Niger, proving again that these basal tetanurans have experienced global radiation. Teeth from the Late Jurassic aged Tacuarembó Formation of Uruguay and the Tendaguru Formation of Tanzania indicate the presence of a large megalosaurine, likely Torvosaurus. ==References==