Spinosaurids Success As Specialized Theropods

Suchomimus_skeleton-gil3ggu5a5.jpgSuchomimus skeleton, showcasing the narrow, elongated rostrum and large arms typical of Spinosauridae. Image by Belinda Hankins Miller (via Flickr) [CC by 2.0] via Wikimedia Commons.

Specialized theropods such as spinosaurids (Spinosaurus, Baryonyx, etc.) are known from the fossil record from the Bajocian; about 170.3 ma. to 168.3 ma., to the Cenomanian (100.5 to 93.9 ma.). While this does suggest that conditions were particularly favorable for piscivorous predators, it must not go unnoticed. Ostafrikasaurus crassisseratus, from the Upper Tithonian (circa 149 to 145 ma.) of the Tendaguru and it’s descendants seemed to have gradually grew in specialization in an environment that was splitting.

Differences from other Megalosaurids

Most spinosaurids have the appearance as if you pasted a crocodile skull onto an average theropod’s body. Other members of Megalosauria are considerably different than their spinosaurid relative, as even the closest relative of Spinosauridae, Torvosaurus spp. is considerably different. Megalosaurids look like a carcharodontosaurid that has a flatter skull, and megalosaurids presumably get no bigger than 12 meters, while spinosaurids could reach 16.5 meters.



In several papers from 1998 to 2011 (many will be cited here), paleontologists such as Paul Sereno, C. E. Larsson, etc. noted how spinosaurid builds from the EK to the LK were much different from even other megalosauroids. Some examples include:

  • A coracoid with the shape of a hook (which joins the scapula to the front base of the sternum)
  • Nares behind the pre maxilla
  • An elongated (secondary) palate
  • Terminal rosette (possessing large teeth at the front of the jaws)
  • (Mostly) conical teeth, with little to no serrations.

The teeth of spinosaurs heavily resemble modern day crocodilians, which suggest that the teeth would function to pierce a small area of skin, and then would apply a massive amount of pressure.

This was instrumental for spinosaurids success as piscivores, as these types of teeth were evolved for killing fish. The way how these needle like teeth work is simple, theropods with teeth meant for crushing or slicing, like tyrannosauridae or carcharodontosauridae, could catch fish, but the fish would squirm, trying to get back into water. The teeth of spinosaurids would hold the fish in place, while the arms would likely help hold the fish, while other theropods would lose grip of the fish.

From an earlier blog of mine

Skull Functions

Based on comparisons to crocodilians and other fauna, it is often stated that spinosaurids were piscivorous predators. Rayfield et al.(2007) compared the compressed, long skull of the baronychinae Baryonyx walkeri to gharials and alligators; which the former has a long, tubular skull while the latter has a flat, wide skull. However gharials are not a good comparison to spinosaurids as the crocodilian has a very narrow skull, while the Australian freshwater crocodile, Crocodylus johnstoni, has a similar skull to spinosaurids was an opportunistic predator. This suggests that the spinosaurids were mainly piscivorous, but they still killed other prey and scavenged.

Cuff and Rayfield (2013) challenged the idea of spinosaurid and gharial skulls being similar, with considerably different conclusions than the previous paper. Their paper found that the skull of Baryonyx was better built for more tension within the compressions of the skull than a gharial, but less than the saltwater crocodile, Crocodylus porosus.

In a recent paper in 2017, C.L Schultz and M.A.F Sales found that Spinosaurus aegyptiacus led a more piscivorous lifestyle than other spinosaurids due to the size and position of the nares on the skull.


In a 2010 paper; “Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods” Amiot and co. concluded that due to the Oxygen isotope levels in spinosaurids were closer to turtles and crocodilians. They concluded that spinosaurids would have spent most of their lives within water similarly to crocodilians and hippopotamuses. They concluded that spinosaurids would have removed direct competition from theropods within the area due to the difference in location and diet.


Spinosaurids were able to survive so long due to their environment being favorable during the Mid Jurassic to the beginning of the Late Cretaceous. Their diet of mainly iron rich fish likely allowed them to not need to eat as often as other theropods. Were it not for the Cenomanian-Turonian Event it is very likely that spinosaurids would have persisted to the Campanian, where they would meet their (hypothetical) doom if they persisted post the C-T Event.


March 12, 2018

- Holden Williams

So... what do you think? Please leave me a comment.


  • Vale: Could you maybe discuss how the differences between Spinosaurids and other Megalosaurids would have benefited the spinosaurs?
  • Suchosaurine: I’ll edit that.
  • Vale: Thanks

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