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.

[1] 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.

They also bore robust front tubercles (processes for skeletal muscle attachment) and lacked interzygapophyseal laminae (bony plates), which resulted in their spinopre- and spinopostzygapophyseal fossae (depressions) having open undersides.

The first dorsal vertebra had extensive transverse processes (wing-like projections that articulate with the ribs), as well as deep excavations at the front and back of its base that were filled by air sacs in life.

The parapophyses (processes that articulated with the capitulum of the ribs) increased in height from the rear cervicals to the first dorsal; its underside remained in contact with the front lower edge of the centrum.

Ichthyovenator's mid-cervical vertebrae had elongate, somewhat wider-than-tall centra that became progressively shorter towards the rear of the neck, as well as well-developed keels on their bottom surfaces, traits that were shared with the spinosaurids Baryonyx, Suchomimus, Sigilmassasaurus,[6] and Vallibonavenatrix.

[9] In 2012, Ichthyovenator's describers established the unique derived traits of the genus: its dorsal and sacral sinusoidal sail; the thirteenth dorsal neural spine being 410% the length of the centrum, and its distinct, finger-shaped process on its front upper corner; the broad, expanded tips of the third and fourth sacral spines; the first caudal vertebra's deep prezygapophyseal and centrodiapophyseal fossae and S-shaped transverse processes in top view; and the higher ratio of length between the ilium and the accompanying pubis than in any other known theropod.

Allain and colleagues also identified some anatomical features that are unique among other known tetanuran theropods, including the rearmost dorsal ribs articulating with the sternal complex, the pubis's main body having obturator and pubic openings, and the ischium having a foramen on its upper end and a shaft that was flattened sideways.

[1] Though prior spinosaurids had been named from the continent—including Siamosaurus from Thailand's Barremian Sao Khua Formation and "Sinopliosaurus" fusuiensis from China's Aptian Xinlong Formation—the authors noted that palaeontologists have debated the validity of these taxa because they are only confidently known from isolated teeth.

[11] In addition to tooth fossils, a spinosaurid skeleton that possibly belongs to Siamosaurus was excavated from the Thai Khok Kruat Formation in 2004[12] and was identified as a definite spinosaur in a 2008 conference abstract by Angela Milner and colleagues, eight years prior to Ichthyovenator's description.

[13] In 2012, Allain and colleagues assigned Ichthyovenator to the Spinosauridae; more precisely to the subfamily Baryonychinae in a basal position as the sister taxon of a clade formed by Baryonyx and Suchomimus.

[5] In a 2015 phylogenetic analysis by Evers and colleagues, they suggested the apparent presence of both baryonychine and spinosaurine characteristics in Ichthyovenator means the distinction between the two subfamilies may not be as clear as previously thought.

[6] In 2017, American palaeontologist Mickey Mortimer informally hypothesized Ichthyovenator may have been a sail-backed carcharodontosaurid dinosaur closely related to Concavenator, rather than a spinosaurid.

[14] A 2017 analysis by Sales and Schultz questioned Baryonychinae's validity, citing the morphology of Brazilian spinosaurids Irritator and Angaturama, and suggesting they may have been transitionary forms between the earlier baryonychines and the later spinosaurines.

[11] Ichthyovenator's spinosaurine classification was supported by Thomas Arden and colleagues in 2018, who resolved it as a basal member of the group due to its tall dorsal sail.

This type of jaw and tooth morphology, which is also observed in today's gharials and other fish-eating predators, has led many palaeontologists to believe spinosaurids were largely piscivorous (as implied by Ichthyovenator's name).

[1] In a 2013 blog post, Darren Naish considered the latter function unlikely, favouring the hypothesis of sexual selection for Ichthyovenator's sail because it appears to have evolved on its own, without very close relatives.

[23] Spinosaurids appear to have had semiaquatic lifestyles, spending much of their time near or in water, which has been inferred by the high density of their limb bones that would have made them less buoyant, and the oxygen isotope ratios of their teeth being closer to those of remains from aquatic animals like turtles, crocodilians, and hippopotamuses than those of other, more terrestrial theropods.

[15] A similar, though more extreme, shrinkage of the pelvic girdle and elongation of the tail's neural spines, creating a paddle-like structure, was observed in Spinosaurus, which appears to have been more aquatic than any other known non-avian (or non-bird) dinosaur.

[26] Ichthyovenator is known from the Barremian to Cenomanian Grès supérieurs Formation, and was found in a layer probably dating to the Aptian stage of the Early Cretaceous period between 125 and 113 million years ago.

[1][28] Fossils of non-dinosaurian fauna are represented by ray-finned fish like Lanxangichthys[27] and Lepidotes, as well as turtles including Shachemys, Xinjiangchelys, and an indeterminate carettochelyid and trionychid.

It may also be possible spinosaurids already had a cosmopolitan distribution before the Middle Cretaceous preceding the breakup of Laurasia from Gondwana, but the authors noted more evidence is needed to test this hypothesis.

[31] In 2012, Allain and colleagues suggested such a global distribution may have occurred earlier across Pangaea before the Late Jurassic, even if Asia was the first landmass to be separated during the breakup of the supercontinent.

[1] In 2019, Elisabete Malafaia and colleagues also indicated a complex biogeographical pattern for spinosaurs during the Early Cretaceous based on anatomical similarities between Ichthyovenator and the European genus Vallibonavenatrix.