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Friday, 8 February 2013

Ornithocheirus and Anhanguera: 4 m wingspans are rubbish

It's been a bit pterosaur-light around these parts since I opened the blog in November, with dinosaurs dominating most posts. This week, to start setting things right, we're returning to the warm, leathery-winged bosom of pterosaurs, with a painting from 2010 showing two of the most famous ornithocheirid pterosaurs, Anhanguera santanae (on the left) and Ornithocheirus mesembrinus (right). These Brazilian pterosaurs are both from the Lower Cretaceous Santana Formation, a fossil site renowned for its excellent, three-dimensionally preserved vertebrate fossils. Pterosaurs are the most common tetrapods in this unit, and ornithocheirids are a well known component of that fauna. In fact, they're probably the most extensively documented pterosaurs from the Santana, in part because of the thorough and beautifully illustrated descriptions by Peter Wellnhofer, including those for specimens of Ornithocheirus and Anhanguera (Wellnhofer 1987; 1991). 
Cock of the slight awkward walk: Ornithocheirus. mesembrinus out for a  stroll, possibly trying to accentuate it's bottom. Perhaps it works out. 
Ornithocheirids are unusually proportioned pterosaurs, bearing extremely robust and long wings, enormous heads but tiny bodies and legs. Only other ornithocheiroids, particularly members of Pteranodontia and (to a lesser extent) Istiodactylidae can boast similar proportions. These forms are considered closely related by some (e.g. Unwin 2003), suggesting that their unusual bauplan developed only once, and was taken to extremes by members of Ornithocheiridae and Pteranodontia. In all likelihood, this evolutionary emphasis on increasing the size of the wings and head reflects adaptations for long soaring flight over seas and oceans, while retaining long jaws to grab pelagic prey. This group of ocean-soaring pterosaurs also includes Nyctosaurus, which may be one of the most effective soaring animals to have ever lived. Nyctosaurus also achieves the accolade of being the cover star of my book, which I'm sure it would be much more excited about. 
Two cowardly Anhanguera santanae, being cowardly.
 The painting here shows a few ornithocheirids striding around, an activity that probably wasn't their favourite pastime. Their short trunk skeletons and hindlimbs make for very disproportionate frames, and their forelimbs are probably at the limit of being useful in terrestrial locomotion, beyond simply preventing them from falling over. The pair of Anhanguera on the left are clearly somewhat wary of the larger Ornithocheirus, but it's worth mentioning that they're hardly small. The wingspan of A. santanae is estimated at 4.15 m, which is fairly middling for a Cretaceous pterosaur, but dwarfs the largest flying animals we have today with their piddling 3 m wingspans. Ornithocheirus mesembrinus, by contrast, is one of the largest ornithocheiroids known with an estimated wingspan of 6 m (this, of course, contradicts what Kenneth Branagh told us in Walking with Dinosaurs, but evidence for Ornithocheirus, or any ornithocheirid for that matter, spanning 10 m has yet to be presented). The only ornithocheirid that may have intimidated O. mesembrinus was Coloborhynchus capito, which may have spanned up to 7.25 m (Martill and Unwin 2012), gigantic proportions comparable to those of the largest Pteranodon. Accordingly, when Ornithocheirus wanted to walk or fly somewhere, Anhanguera moved out of its way. 

And that will have to do today, I'm afraid. I've already gone on too long, and I'm much too busy to say anything about other things that are relevant here: colour choices, ornithocheirid rostral structure, ornithocheirid taxonomy and many other things. Perhaps another time, then. 

References

  • Martill, D. M. and Unwin, D. M. 2012. The world’s largest toothed pterosaur, NHMUK R481, an incomplete rostrum of Coloborhynchus capito (Seeley, 1870) from the Cambridge Greensand of England. Cretaceous Research. 
  • Wellnhofer, P. 1987. New crested pterosaurs from the Lower Cretaceous of Brazil. Mitteilungen der Bayerischen Staatsammlung für Paläontologie und Historische Geologie, 27, 175-186.
  • Wellnhofer, P. 1991. Weitere pterosaurierfunde aus der Santana-Formation (Apt) der Chapada do Araripe, Brasilien (Translated title: Additional pterosaur remains from the Santana Formation (Aptian) of the Chapada do Araripe, Brazil).  Palaeontographica Abt. A, 215, 43-101.

1 comment:

  1. I strongly disagree with "I've already gone on too long," as I think you've got enough to say about pterosaurs to fill a book.

    Love the pics. Though they are very different animals, I've got my cat on my lap as I type and looking at the Ornithocheirus pic, it has the same appearance of a very real animal.

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