Ichthyovenator is a genus of spinosaurid dinosaur that lived in what is now Laos, sometime between 120 and 113 million years ago, during the Aptian stage of the Early Cretaceous period. It is known from fossils collected from the Grès supérieurs Formation of the Savannakhet Basin, the first of which were found in 2010, consisting of a partial skeleton without the skull or limbs. This specimen became the holotype of the new genus and species Ichthyovenator laosensis, and was described by palaeontologist Ronan Allain and colleagues in 2012. The generic name, meaning "fish hunter", refers to its assumed piscivorous lifestyle, while the specific name alludes to the country of Laos. In 2014, it was announced that more remains from the dig site had been recovered; these fossils included teeth, more vertebrae (backbones) and a pubic bone from the same individual. The holotype specimen is estimated to have been between 8.5 to 10.5 metres (28 to 34 feet) long and to have weighed 2.4 tonnes (2.6 short tons; 2.4 long tons). Ichthyovenator's teeth were straight and conical, and its neck resembled that of the closely related genus Sigilmassasaurus (which may be synonymous with Spinosaurus). Like others in its family, Ichthyovenator had tall neural spines that formed a sail on its back. Unlike other known spinosaurids, Ichthyovenator's sail had a sinusoidal (wave-like) shape that curved downwards over the hips and divided into two separate sails. The pelvic girdle was reduced; the ilium—the uppermost body of the pelvis—was proportionately longer than both the pubis and ischium than in other known theropod dinosaurs. Ichthyovenator was initially thought to belong to the subfamily Baryonychinae but more recent analyses place it as a primitive member of the Spinosaurinae. As a spinosaur, Ichthyovenator would have had a long, shallow snout and robust forelimbs. Its diet likely mainly consisted of aquatic prey, hence its etymology. Spinosaurids are also known to have eaten small dinosaurs and pterosaurs in addition to fish. Ichthyovenator's conspicuous sail might have been used for sexual display or species recognition. Fossil evidence suggests spinosaurids, especially spinosaurines, were adapted for semiaquatic lifestyles. The vertebral spines of Ichthyovenator's tail were unusually tall, suggesting—as in today's crocodilians—the tail may have aided in swimming. Ichthyovenator lived alongside sauropod and ornithopod dinosaurs, as well as bivalves, fish and turtles.
Discovery and naming
The first fossils of Ichthyovenator were found in 2010 at Ban Kalum in the Grès supérieurs Formation of the Savannakhet Basin in Savannakhet Province, Laos. These fossilized bones were recovered from a red sandstone layer within a surface area of less than 2 square metres (22 sq ft). Designated under the specimen numbers MDS BK10-01 to 15, they consist of a partly articulated, well-preserved skeleton lacking the skull and limbs, and including the third-to-last dorsal (back) vertebra, the neural spine of the last dorsal vertebra, five partial sacral (hip) vertebrae, the first two caudal (tail) vertebrae, both ilia (main hip bones), a right pubis (pubic bone), both ischia (lower and rearmost hip bones) and a posterior dorsal rib. The twelfth dorsal spine is bent sideways when viewed front-to-back due to taphonomic distortion. The centra (vertebral bodies) of the sacrals are largely incomplete due to erosion, but preserved all of their accompanying spines with their upper edges intact. At the time of Ichthyovenator's description, excavations at the site were still ongoing.
After undergoing preparation in 2011, the skeleton was used as the basis, or holotype, for the type species Ichthyovenator laosensis, which was named and described in 2012 by palaeontologists Ronan Allain, Tiengkham Xeisanavong, Philippe Richir, and Bounsou Khentavong. The generic name is derived from the Old Greek word ἰχθύς (ichthys), "fish", and the Latin word venator, "hunter", in reference to its likely piscivorous (fish-eating) lifestyle. The specific name refers to its provenance from Laos. Ichthyovenator is the third named spinosaurid dinosaur from Asia after the Thai genus Siamosaurus in 1986 and the Chinese species "Sinopliosaurus" fusuiensis in 2009. The latter may represent the same animal as Siamosaurus. In 2014, Allain published a conference paper on Ichthyovenator; the abstract indicated additional remains from the original individual had been found after excavations continued in 2012. These remains include three teeth, the left pubis, and many vertebrae, including a nearly complete neck, the first dorsal vertebra, and seven more caudal vertebrae. Some of these additional vertebrae were compared with those of other spinosaurids in a 2015 paper by German palaeontologist Serjoscha Evers and colleagues, in which they noted similarities with the vertebrae of the African spinosaurid Sigilmassasaurus.
Description
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