Although it was one of the first dinosaurs to be scientifically described during the early 19th century, the theropod Megalosaurus remains one of the most enigmatic (and problematic) large dinosaurs known. Even though an entire family, the Megalosauridae (established by Huxley in 1869), bears the name of this famous dinosaur, the group has come to be seen as a taxonomic wastebasket with no real meaning. Indeed, a new paper in the journal Palaeontology advocates dropping the family, at least until better material can be found from Megalosaurus.
According to the new paper by Benson, Barrett, Powell, and Norman, the only fossil material that we can truly say represents Megalosaurus is the lower jaw (dentary) that allowed William Buckland to identify the dinosaur as an immense carnivore, not unlike a giant terrestrial crocodile. The rest of the material, even the fossil femur tip described by Robert Plot in his Natural History of Oxfordshire, cannot be attributed to Megalosaurus with any degree of certainty, at least not until a more complete skeleton is found for comparison. This means that previous analysis going back to the earliest days of paleontology were essentially working with a fossil chimera; many parts of the post-cranial skeleton attributed to Megalosaurus may have belonged to other species of theropods.
The recognized lack of Megalosaurus material creates a bit of a problem, then. The dentary, which is distinct enough to continue to bear the name Megalosaurus bucklandii (not M. bucklandi or M. conybeari), cannot be compared with material from other theropods as the dentary is often missing from species that may be closely related. According to the authors of the paper, the family Megalosauridae should be discontinued as Megalosaurus cannot be effectively compared with other genera placed within the family, and the status of the family representing basal members of the Spinosauroidea (Megalosauridae + Spinosauridae) isn’t upheld.
If paleontologists accept the recommendations of the authors there could be quite a bit of taxonomic reshuffling. Only Megalosaurus could be said to be a “megalosaurid,” and the rest of the genera associated with it (i.e. Afrovenator, Torvosaurus, Eustreptospondylus, Piatnitzkysaurus, Poekilopleuron, and Dubreuillosaurus) will require re-analysis. Perhaps a more complete skeleton of Megalosaurus will someday be found to help resolve some of these issues, but for now one of the cornerstones of paleontology will remain mysterious.
BENSON, R.B., BARRETT, P.M., POWELL, H.P., NORMAN, D.B. (2008). THE TAXONOMIC STATUS OF MEGALOSAURUS BUCKLANDII (DINOSAURIA, THEROPODA) FROM THE MIDDLE JURASSIC OF OXFORDSHIRE, UK. Palaeontology, 51(2), 419-424. DOI: 10.1111/j.1475-4983.2008.00751.x