June 2, 2013 | 9
You liked the photo of the brilliant Angaturama skeletal mount, right? Photographed at the Museu Nacional, Rio de Janeiro, the mount shows Angaturama limai – a spinosaurine spinosaurid – carrying the skeleton of an anhanguerid pterosaur. Here are some more views of the same display…
The behavioural interaction you see here was not just invented in whimsical fashion. Rather, it reflects an actual fossil discovery: Buffetaut et al. (2004) described the neck section from an anhangeurid-style pterosaur from Brazil with obvious spinosaurid bite damage. In fact, a spinosaurid tooth was still embedded in one of the neck vertebrae. Of course, we have no way of knowing whether the spinosaurid was consuming an entire carcass or just chewing on a detached neck, nor do we know whether the spinosaurid was scavenging, or whether it hunted and killed the pterosaur itself. All of these possibilities are on the cards.
Angaturama is from the Albian Romualdo Formation (part of the Santana Group: the stratigraphic terminology of these units is complex and I’m keen to avoid discussing it here) and was originally named for a section of laterally compressed rostrum that preserves evidence for a low sagittal crest (Kellner & Campos 1996).
Just a month or so earlier, Martill et al. (1996) described another Romualdo Formation spinosaurid: based on a near-complete skull that lacks its snout-tip, they named it Irritator challengeri. That paper (it misidentified Irritator as a maniraptoran coelurosaur) cannot (chooses words carefully) be regarded as an especially valuable contribution to the dinosaur literature, and a more reliable description was later produced by Sues et al. (2002). Therein, it was argued that Angaturama is most likely a junior synonym of Irritator, and I agree that this is most likely to be correct (see also Charig & Milner 1997, Sereno et al. 1998). However, our Brazilian colleagues have argued that the two should be maintained as distinct taxa and additional spinosaurid remains described from the Romualdo Formation – they include a near-complete pelvis, a partial hand and various vertebrae (some of these specimens are on display at the Museu Nacional) - are implied to belong to Angaturama. Some of these elements are clearly incorporated into the mounted skeleton shown above.
Moving on, Angaturama/Irritator isn’t the only Brazilian spinosaurid on display at the Museu Nacional…
This is the holotype of Oxalaia quilombensis, another spinosaurid named for a snout-tip! It’s much younger than Angaturama and Irritator since it comes from the Cenomanian Alcântara Formation (Kellner et al. 2011). It also must have been much larger (the estimated skull length is 1.3 m) and its snout shape is very different: the premaxillary bones form a wider, more rounded snout-tip and a sagittal crest is absent. Overall, Oxalaia seems to have been very similar to the classic African spinosaurid Spinosaurus, meaning that Cretaceous Brazil was home to both giant, Spinosaurus-like forms as well as the more peculiar, narrow-snouted Irritator- or Angaturama-type forms. Like Spinosaurus, Oxalaia would have been very large: Kellner et al. (2011) suggested a total length of 12-14 m.
Some of the taxa mentioned here have been discussed on Tet Zoo before. Check out the links for more. While in Rio, it was a privilege to see these remarkable fossils: I got to see them while at the 2013 International Symposium on Pterosaurs.
Refs – -
Buffetaut, E., Martill, D. & Escuillié, F. 2004. Pterosaurs as part of a spinosaur diet. Nature 430, 33.
Charig, A. G. & Milner, A. C. 1997. Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. Bulletin of the Natural History Museum 53, 11-70.
Kellner, A. W. A., de Azevedo, S. A. K., Machado, E. B., de Carvalho, L. B. & Henriques, D. D. R. 2011. A new dinosaur (Theropoda, Spinosauridae) from the Cretaceous (Cenomanian) Alcântara Formation, Cajual Island, Brazil. Anais de Academia Brasileira de Ciências 83, 99-108.
- . & Campos, D. de A. 1996. First Early Cretaceous theropod dinosaur from Brazil with comments on Spinosauridae. Neues Jahrbuch fur Geologie und Paläontologie, Abhandlungen 199, 151-166.
Martill, D. M. , Cruickshank, A. R. I., Frey, E., Small, P. G. & Clarke, M. 1996. A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil. Journal of the Geological Society, London 153, 5-8.
Sereno, P. C., Beck, A. L., Dutheil, D. B., Gado, B., Larsson, H. C. E., Lyon, G. H., Marcot, J. D., Rauhut, O. W. M., Sadleir, R. W., Sidor, C. A., Varricchio, D. D., Wilson, G. P. & Wilson, J. A. 1998. A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids. Science 282, 1298-1302.
Sues., H.-D., Frey, E., Martill, D. M. & Scott, D. M. 2002. Irritator challangeri, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil. Journal of Vertebrate Paleontology 22, 535-547.