Megalosauroidia, as defined by Carrano, Benson and Sampson (2012) is the sister-group to Avetherapoda, which includes both carnosaurs and coelurosaurs. I've already talked a great deal about both the carnosaurs, and one branch of the coelurosaurs (the tyrannosauroids.) Of course, the coelurosaurs also give us, for instance, the oviraptors, the "raptors" (dromeosaurs), the ostrich-dinosaurs (ornithomimosaurs), the therizonsaurs, the compsognathids, and of course, the birds themselves. There are several posts worth of exploration within coelurosauria, but I'm not feeling very inclined to do it, because I think many of those animals are weird and less interesting to me personally than some other dinosaur groups.
I'll do the megalosaurs, and maybe the ceratosaurs (someday), including abelisaurs, and I'll be done with meat-eaters. I may yet explore some of the plant-eating lineages, like the ceratopsians or the sauropods, but we'll see.
The megalosauroids consist, at a high level, of three groups: the piatnitzkysaurs, the spinosaurs, and the megalosaurs proper (which also has the spin-off group of afrovenators.) The earliest known examples come from the Middle Jurassic, and this seems to be their period of greatest diversity. Their larger and more famous examples include Late Jurassic forms (like Torvosaurus), but the spinosaur radiation is more of a "mid" Cretaceous phenomena. (Keep in mind, there is no official Middle Cretaceous; just Early and Late. "Mid" Cretaceous is therefore a convenient informality.)
The Piatitzkysaur family is united by five synapomorphies, and is usually the "first" encountered on the megalosaur family tree. It consists of only three animals; two Middle Jurassic therapods from South America and Marshosaurus bicentesimus from the Cleveland-Lloyd quarry of Utah.
If you recall, Cleveland-Lloyd is from the Brushy Basin member, and is therefore the later part of the Morrison. There were other large megalosaurs in the Morrison; mainly Torvosaurus, but Marshosaurus was a more modestly sized animal, maybe the size of a grizzly. Known from not a lot of remains, and have some tail fragments from Colorado provisionally referred to it as well, we don't know a lot about Marshosaurus. It would have been, curiously about the same size as the holotype of Ceratosaurus, but a large individual of the latter was also found in the Cleveland-Lloyd. Altogether, there seem to be more predators in the Morrison than we'd expect, and exactly how they evaded competing directly with each other is unclear—but the Morrison area was large and spread over many millions of years; maybe they didn't all exist in the same time and place at the same time as much as it seems that they did.
Leaving the piatnitzkysaurs and entering megalosauria proper, before we get to any of the groupings within it, we have to deal with Streptospondylus altdorfensis, a French animal of (again) medium size, known from some vertebrae and limb elements. Although it was one of the very first dinosaurs identified, it was actually known and misidentified as crocodylian for quite some time prior to that. The remains are too fragmentary for a really confident placement of its relation to the rest of its family. It was found in rocks that are about 161 million years old, and like many megalosaurs known from fragmentary remains, has bounced all over the therapod family tree for many years, and has seen a bizarre split into numerous proposed species, almost all of which are dubious. Although within Megalosauria, it is not within Megalosauridae, which means that it's not really all that closely related to Eustreptospondylus oxoniensis, which is within the Megalosauridae proper. Eustreptospondylus is sometimes placed within its own subfamily. Like everyone else in the family we've looked at so far, it was about 20 feet long and maybe half a ton in weight. Also from the Middle Jurassic around 162 million years ago, it is one of the most complete largish therapods discovered in Europe, and certainly that was true when it was unearthed in 1870.
Europe during this period was an East Indies-style archipelago, with relatively large islands, but nowhere near the landmass of a continent, because high sea levels flooded much of the epicontinental areas with shallow, tropical seas. It makes an appearance in Walking With Dinosaurs which, although pretty dates, is probably more or less accurate enough.
It's funny that the megalosaurs have been an infamous trashcan taxon for decades when in reality not a ton is known about megalosaurs, because they've been found most frequently in formations that are poorly known, or they've been relatively rare in the formations in which they are found. There are really on three genuine megalosaurs, by which I mean members of the Megalosaurinae subfamily. The most primitive and oldest is Duriavenator hesperis from 170 million years ago in England; one of the earliest of all tetanuran therapods, actually. Of course, it was originally referred as a new species of Megalosaurus itself, but it's fairly closely related, at least. Known only from some jaw fragments, it was... probably about the same 20-25 foot or so size as everything else we've looked at so far. Very little is known about it or its environment, except that it had more teeth in its jaws than Megalosaurus itself.
Which, after all that, only has one valid species left after all, Megalosaurus bucklandii. From the same time period, the Bathonian of about 166 million years ago, in Oxford. Amusingly, its famous for having the knob end of a leg bone named Scrotum humanum, the first scientifically named dinosaur remains, although they were assumed to have been the fossilized testicles of a giant at the time. Although among the largest animals known of those we've reviewed so far, it still wasn't all that big; less than 25 feet long—this seems to have been an upper limit for Middle Jurassic finds so far. A hip and sacrum is known, some leg bones and plenty of vertebrae, and some jaw bones, but nothing like a complete skeleton has ever emerged, and its exact proportions and details remain fairly speculative. A bit of skull (although no nose elements) suggests that it might have been an unusually large-headed therapod.
Megalosaurus lived alongside primitive cetiosaur-grade sauropods (including Cetiosaurus itself), some other smaller therapods and primitive ornithopods. By inference, some stegosaurs are believed to have lived in its habitat as well, and it's believed to be the apex predator of its ecosystem. As described elsewhere, including earlier in this post, it is part of the island Europe environment.
The final megalosaur (before I do afrovenators and spinosaurs tomorrow) is Torvosaurus, which comes in two species, tanneri from the late and northern Morrison and gurneyi from Portugal. There may be another specimen (or closely related animal) found in Germany as well, and as at least a few already collected but not prepared or properly described bones lurking in museums have been referred to it, there may yet be more to come that's already been unearthed.
Torvosaurus, compared to, say, Allosaurus, which appeared in the same time and place (more or less) seems to have been quite large; from nearly 35 feet long to nearly 40—possibly—with a heavy body, kinda short legs, and a long snout. It is presumed that Torvosaurus (and Ceratosaurus) may have preferred the more thickly vegetated gallery forests, and the allosaurs may have preferred the drier plains, but this is an inference based on pretty circumstantial evidence.
Tomorrow (or Monday) I'll turn to the spinosaurs and afrovenators. In general, the megalosaurs have not been among my favorite predators (which are the predictable tyrannosaurs and the less predictable carnosaurs) but the last two; particularly Torvosaurus is a kind of favorite of sorts of mine. As a contemporary of Allosaurus and the possible king of my favorite dinosaur faunal assemblage from the Morrison, I've got to give Torvosaurus his due. I'm also a bit fascinated by Megalosaurus himself and his environment. I've long been interested in the immediate predecessors of my Morrison-aspect faunas (and by Morrison aspect faunas, I mean Lourinha and Tendaguru too); i.e., where did they come from, and what were the more primitive Middle Jurassic faunas that led to them come from and what did they look like? In general, the early Jurassic is very poorly known and the Middle Jurassic could use a lot more exploration. It's a bit of a blank spot on our paleontology map that I'd love to see filled.
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