page_title: Ichthyovenator
section_title: Classification
hierarchical_section_title: Ichthyovenator / Classification
caption_attribution_description: English: Comparison between the pelvic region and neural spine sails of three spinosaurids. Spinosaurus is derived from: File:Spinosaurus aegyptiacus holotype skeletal.jpg Suchomimus from: File:Suchomimus tenerensis.jpg Ichthyovenator based on Allain et al. (2012)[1] and reconstructed vertebrae at the National Museum of Nature and Science in Tokyo[2].[3].
context_page_description: Ichthyovenator is a genus of spinosaurid dinosaur that lived in what is now Laos, sometime between 125 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, and comprised 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 include teeth, more vertebrae and a pubic bone from the same individual.
  The holotype specimen is estimated to have been between 8.5 to 10.5 metres long and weighed 2.4 tonnes. Ichthyovenator's teeth were straight and conical, and its neck resembled that of the closely related genus Sigilmassasaurus. Like others in its family, Ichthyovenator had tall neural spines that formed a sail on its back.
context_section_description: 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. The shrinkage of the pubis and ischium relative to the pelvis has been observed in basal coelurosaurs and allosauroids, which the describers attributed to mosaic evolution: the evolution of certain anatomical traits at different times in separate species.
  Allain and his team considered Ichthyovenator as representing the first unequivocal spinosaurid from Asia. 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. Brazilian palaeontologists Marcos Sales and Caesar Schultz have suggested these teeth may eventually be attributed to spinosaurids similar to Ichthyovenator. In addition to tooth fossils, a spinosaurid skeleton that possibly belongs to Siamosaurus was excavated from the Thai Khok Kruat Formation in 2004 and was identified as a definite spinosaur in a 2008 conference abstract by Angela Milner and colleagues, eight years prior to Ichthyovenator's description.
  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. In Allain's 2014 abstract, he found Ichthyovenator instead as belonging to the Spinosaurinae, due to the lack of serrations on its teeth and the similarities of its vertebrae to those of Sigilmassasaurus. 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. 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. Mortimer considered Ichthyovenator as incertae sedis (of uncertain taxonomic affinity) within the clade Orionides, pending description of the new material, which she states will likely confirm Ichthyovenator's spinosaurid identity. 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. The authors said with further research, Baryonychinae may be found to be a paraphyletic (unnatural) grouping. 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. Their cladogram can be seen below:
caption: Comparison of the pelvic region and neural spine sails of Suchomimus, Spinosaurus, and Ichthyovenator
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