"Oxalaia" or Spinosaurus quilombensis?

[Yutyrannus]

A journal I wrote on deviantART about my theories on "Oxalaia" quilombensis:

Oxalaia quilombensis is a spinosaurine spinosaurid that was discovered in 2004 and named in 2011, known only from a premaxilla, MN 6119-V, and an isolated fragment of the left maxilla. It is thought to have lived ~98 MYA in what is now Brazil. Oxalaia was the eighth officially named species of theropod from Brazil and is currently the largest. However, it is very likely that this same dinosaur was named much earlier, in 1915 by German paleontologist Ernst Freiherr Stromer von Reichenbach. Stromer discovered many animals on his expedition to the Bahariya Oasis in Egypt, but one is much more important to the story of Oxalaia: a theropod that Stromer named Spinosaurus aegyptiacus, a dinosaur that remained a mystery for over 100 years, which may well be a senior synonym of Oxalaia.

Stromer initially thought that Spinosaurus looked somewhat similar to Allosaurus with a sail on its back, but later discoveries, such as MSNM V4047, would show that its skull looked more like that of a crocodilian than that of a carnosaur. It would not be until 2014 that the mystery of Spinosaurus was finally solved, revealing it to be an aquatic animal with very reduced hind limbs and an unusually long body. These discoveries also revealed something else: the likelihood of Oxalaia quilombensis being a species of Spinosaurus, rather than a distinct genus as suggested by Kellner et al.

The skull fragments known for Oxalaia bear a striking similarity to the skull of Spinosaurus aegyptiacus and are clearly different from the skull of the other Brazilian spinosaur, Irritator challengeri. On top of this, the discoveries made by Nizar Ibrahim indicate that Spinosaurus aegyptiacus spent much more time in the water than on land, and that it was an efficient swimmer. At the time Spinosaurus and Oxalaia are thought to have lived, Brazil and North Africa were not particularly far apart, and a few million years earlier were connected. This suggests that Spinosaurus could've swam from North Africa to Brazil and that Oxalaia is really a species of Spinosaurus, possibly even S. aegyptiacus.

When comparing the known elements of O. quilombensis to the skull of S. aegyptiacus, it becomes apparent that the two are almost identical. The only obvious difference is that the premaxilla of Oxalaia is more rounded at the tip than that of S. aegyptiacus. Many of the tooth sockets even match up. As for the fragment of the maxilla, the top actually matches up almost perfectly with the nostril placement of S. aegyptiacus. Another interesting fact is that the ichthyofauna of the Alcântara Formation, where Oxalaia was discovered, is incredibly similar to that of the Kem Kem Beds, where Spinosaurus aegyptiacus is known to have lived at about the same time.

Based on this evidence, it is extremely likely that Oxalaia quilombensis is really Spinosaurus quilombensis, or perhaps even Spinosaurus aegyptiacus. Which it really is cannot be proven without more fossils of "Oxalaia", but what can be proven now is that it is not a distinct genus from Spinosaurus. There is virtually no difference between the two and if S. aegyptiacus was really as aquatic as suggested by Nizar Ibrahim, it could well have migrated across the sea to Brazil. What would be very interesting to discover is exactly how the native fauna of Brazil was affected by the appearance of this new species, and how successful this population of Spinosaurus was in Brazil. This, we may never know.

[Newt]

Interesting speculation. How wide was the (proto) Atlantic at that time?

[Yutyrannus]

Thanks!

Here's a map from the time:

[DinoLord]

Very interesting theory, though I don't really know enough about spinosaurs to chime in.

[stargatedalek]

I brought this up on another forum and received a very great response, I was thinking you guys would like to see

personally I'm skeptical of oxalaia's validity as a genus

which brings up another point of speculation, could oxalaia be a species of spinosaurus?
I think it is extremely likely that oxalaia quilombensis is really spinosaurus quilombensis, or perhaps even spinosaurus aegyptiacus

heres what we have of oxalia overlaying what we have from spinosaurus

*snip*

-only obvious difference is that the premaxilla of oxalaia is more rounded at the tip
-for the fragment of the maxilla, the top actually matches up almost perfectly with the nostril placement of spinosaurus


and heres a little perspective on just how close Africa and Brazil were at the time

*snip*

-if spinosaurus was really as aquatic as suggested by Nizar Ibrahim, it could well have migrated across the sea to Brazil
-the ichthyofauna of the Alcântara Formation, where oxalaia was discovered, is incredibly similar to that of the Kem Kem Beds

This genuinely would not surprise me.

The Alcantara formation is bizarre, even by Brazilian standards. The species are more similar to North African fauna than they are to other areas of South America. And this genuinely shouldn't make sense given that they were an ocean apart, and have been separated by the formation of the Atlantic Ocean for about 15 million years give or take. Even about 120 million years ago, back in Suchomimus's day, there woulda still been a bigass rift valley dividing the continents.

So in my mind, that leaves us with 3 options:

1) Spinosaurus for reasons unknown, managed to cross the early Atlantic in enough numbers to establish a new population in South America. I find this concept the least likely because its a freshwater/estuarine animal from North Africa, while the closest part of Africa to South America was around Central Africa, so that's a lot of coastline to assume Spinosaurus covered in its early days. And then crossing deep ocean in itself is a difficult feat for any animal that's only semi aquatic.

2) The common ancestor between Spinosaurus and Oxalaia was already widespread across both continents 120 million years ago. A bit more likely than the first option. The presence of not just spinosaurines on both continents, but entire ecosystems, suggests that at some point, both landmasses shared a more extensive ecosystem in its past which then was split by the atlantic. This seems perfectly reasonable at an ecological scale.

3) I think this one's the most likely - since spinosaurines like Irritator were already well established in Brazil about 12 million years before Oxaiala or Spinosaurus's time, it's likely that Oxalaia was more related to Irritator than to Spinosaurus with Oxalaia's size being the result of convergent evolution. This keeps Oxalaia's genus intact and has important implications on Spinosaurus itself.

Given that all known spinosaurids in South America are spinosaurines, while Europe and Africa (and maybe Asia too) had baryonychines AND spinosaurines, it could be that rather than Oxalaia having African origins, Spinosaurus's ancestors originated in South America and crossed over to North Africa before the formation of the Atlantic Ocean. Given that South America and Africa were indeed connected, and spinosaurids may have dated back into the Jurassic, it wouldn't surprise me if both clades evolved in different parts of gondwana before the split, stranding baryoncyhines in Africa and Europe, and spinosaurines generally in South America, with some that managed to get a bit of a hold on North Africa before the split was complete.

But this is all me speculating and talking out of my ass. All I know is that it's extremely unlikely that Kem Kem's entire ecosystem crossed the Atlantic to Alcantara or vice versa after the two continents split. They shared similar FRESHWATER species, semiaquatic theropods and even abelisaurids and sauropods. If Spinosaurus crossed over, how does one attempt to explain the other Alcantara species? More likely that regardless of Oxalaia's placement in the Spinosaurine family tree, both Kem Kem and Alcantara were connected for some time, and their ancestors frolicked between the two continents over one extensive swamp.

Side note of all this, all the South American spinosaurids of Brazil, while covering a very BIG time period, were actually rather close to each other grographically (Alcantara and Santana formations were separated by 12 million years, but were technically no further apart than T. rex's northern range geographically). Oddly enough, these areas were clustered around the part of South America that woulda lined up nicely with Niger (Suchomimus territory back when the two continents were still connected).

Also, for temporal span reference of well known/reasonably understood spinosaurids:
Baryonyx - Wealden Group, UK - 125Ma
Suchomimus - Elrhaz Formation, Niger - 120Ma
Ichthyovenator - Gres superieurs Formation, Laos - 113Ma
Irritator - Santana Formation, Brazil - 100Ma
Oxalaia - Alcantara Formation, Brazil - 98Ma
Stromer's Spinosaurus - Bahariya Formation, Egypt - 97Ma
Sereno's Spinosaurus - Kem Kem Beds, Morocco - 95Ma

As I was typing this up, I realised that Oxalaia outdated Spinosaurus by a million years as far as we know. So given the current data, IT would have had to cross over TO Africa for Oxalaia and Spinosaurus to be synonymous genera. But more likely was that both clades of spinosaurid were widespread before the two continents split, and that Oxalaia was more related to Irritator-like animals rather than Spinosaurus (makes sense since Irritator for the longest of time was used to fill in gaps of Spinosaurus's skull, and many parts still are).

Yeah so, food for thought.

[Yutyrannus]

Interesting. I used to think that Oxalaia and Irritator were very close relatives too, but recently I noticed that there are more similarities between Spinosaurus and Oxalaia than between Oxalaia and Irritator. Also, soon I will post part two of this focusing on the geography at the time and slightly earlier, as well as my average size estimates for the two based on the proportions of Ibrahim's Spinosaurus.