Ichthyovenator: The Sail-Backed Fish Hunter of Laos

Spinosaurus was one of my favorite childhood dinosaurs. The carnivore’s enigmatic sail was certainly eye-catching, and that immense billboard set the predator apart from the other huge theropods. But the Spinosaurus I grew up with isn’t around anymore. The creature I knew was based on a partial skeleton discovered by German paleontologist Ernst Stromer in 1912, but was destroyed by an Allied bombing raid during World War II. With only photographs left, paleontologists and artists filled in the missing parts of the spinosaur’s anatomy on the basis of other large, carnivorous dinosaurs. The end result was something like an Allosaurus with a sail.

The blunt-skulled Spinosaurus faded away as paleontologists found new specimens of closely related dinosaurs. The long-snouted Baryonx, discovered in England in 1983, showed that spinosaurs had huge hand claws, crocodile-like skulls. And despite the group’s name, some lacked sails. With this new search image in place, paleontologists began to turn up multiple new spinosaurs from Africa, South America, Australia and now southeast Asia.

Earlier this week, paleontologist Ronan Allain and co-authors described the partial skeleton of a new spinosaur in the journal Naturwissenschaften. The dinosaur, named Ichthyovenator laosensis, appears to be the first definite spinosaur known from Asia. (A few probable spinosaur teeth have been uncovered, hinting that there are skeletons still waiting to be found.) Exactly how long ago this dinosaur roamed Laos is unclear. While Ichthyovenator was discovered in Early Cretaceous rock, the deposits could be anywhere from about 125 to 112 million years old.

If the reconstruction presented by Allain and colleagues is correct, Ichthyovenator was an unusual spinosaur. In other sail-backed forms, such as Spinosaurus and Suchomimus, the great ornament is created by neural spines that rise to a peak and gradually slope downwards. But Icthyovenator might have had a more wavy sail that dipped downwards at the hips before briefly rising again, creating the appearance of two smaller sails.

We still don’t know why spinosaurs had sails to start with, so why Ichthyovenator displayed a different arrangement is doubly perplexing. And equally frustrating is the fact that the skull of Ichthyovenator remains unknown. More than anything else, the distinctive skulls of these dinosaurs set them apart from other theropods, but no skull bones or even teeth were found with this dinosaur. This makes the name Ichthyovenator—”fish hunter”—a hypothesis that has yet to be confirmed by additional evidence. Spinosaurs have often been cast as specialized fish hunters that may have hunted along prehistoric rivers and lakes. Ichthyovenator is expected to have shared this way of life, but we as yet know little of this dinosaur’s biology.

Reference:

Allain, R., Xaisanavong, T., Richir, P., & Khentavong, B. (2012). The first definitive Asian spinosaurid (Dinosauria: Theropoda) from the early cretaceous of Laos Naturwissenschaften DOI: 10.1007/s00114-012-0911-7

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Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.