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
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
bivalves
, fish and turtles.
Discovery and naming
fossils
in white and undescribed material in red
The first
taphonomic distorsion. 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.[1]
Muséum National d'Histoire Naturelle
, Paris
After undergoing preparation in 2011, the skeleton was used as the basis, or
spinosaurid dinosaur from Asia after the Thai genus Siamosaurus in 1986 and the Chinese species "Sinopliosaurus" fusuiensis in 2009.[1][2][3] The latter may represent the same animal as Siamosaurus.[3][4] 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.[5] 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.[6]
Description
spinosaurids
(Ichthyovenator in turquoise, first from right) compared with a human
In 2016, Gregory S. Paul estimated Ichthyovenator to have been approximately 8.5 metres (28 ft) long and to have weighed 2 tonnes (2.2 short tons; 2.0 long tons).[7] The same year, Rubén Molina-Pérez and Asier Larramendi gave an estimate of 10.5 m (34 ft) in length, 2.95 m (9 ft 8 in) tall at the hips, and 2.4 t (2.6 short tons; 2.4 long tons) in weight.[8]
Ichthyovenator's teeth were conical, straight, and bore no serrations.
theropods, in which the parapophyses shifted towards the top of the vertebra during the transition from cervical to dorsal vertebrae. All of these features were also present in Sigilmassasaurus. 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] The cervical neural spines of Ichthyovenator were taller than in Sigilmassasaurus and Baryonyx but shared the blade-like shape with those two taxa at the mid-cervicals.[6] The holotype dorsal rib, which was found near the twelfth dorsal vertebra, had a head typical of the ribs of other moderate-to-large-sized theropods. The rib shaft formed a half-circle. The rib's lower end was slightly expanded both sideways and to the front and back. This condition, which differs from the tapered, pointed tips seen in the ribs of other theropods, suggests the rearmost dorsal ribs articulated with the complex of the sternum (breast bone).[1]
Like many other spinosaurids, Ichthyovenator had a
spinal column, which is over 1 m (3 ft 3 in) long, shows a very high spine on the twelfth dorsal vertebra representing a crest that rose from the back and a lower rounded sail that extended from the sacral vertebrae of the hips; the latter sail's apex was located above the third and fourth sacrals. The 54.6-centimetre (21.5 in) high spine of the twelfth dorsal vertebra widened towards the top, giving it a trapezoidal shape[1]—similar to the condition seen in a neural spine from Vallibonavenatrix[9]—whereas the spines of other known spinosaurids were roughly rectangular. It also lacked the forward or backward inclination of Spinosaurus's neural spines. Its front corner formed a 3-centimetre (1.2 in) narrow-process, pointing upwards. The spine of the thirteenth dorsal vertebra has been only partly preserved; its upper and lower ends had broken off from taphonomic causes. From its general shape, the describers inferred however, it was about as long as the preceding spine. This would imply the back edge of the front sail would form a rectangular corner, because the spine of the much lower first sacral vertebra is about 21 cm (8.3 in), creating a sudden hiatus in the sail's profile. The spine of the second sacral vertebra steeply curved upwards again, joining the 39 cm (15 in) and 48 cm (19 in) high, broad, fan-shaped spines of the third and fourth sacrals. The 40 cm (16 in) tall spine of the fifth sacral gradually descended. Unlike in the sails of most other theropods, including that of Suchomimus, the sacral spines were not fused and had no extensive contacts. The second and third sacral centra were fused; the suture connecting them was still visible. Only the rearmost two dorsal vertebrae are preserved, so to what extent the dorsal sail continued towards the front of the animal's back is unknown.[1]
Various caudal (tail) vertebrae and chevrons from the holotype
The sacral sail was continued by the spines of the first two caudal vertebrae, which were 28.4 cm (11.2 in) and 25.7 cm (10.1 in) tall respectively. They leaned backwards at 30 degrees and had smooth front and rear edges. The centra of the first two caudals were much broader than long and
restoration, with missing elements such as the head and limbs based on relatives
The 92-centimetre (36 in) long ilium of the pelvis was blade-like, and longer in proportion to the 65-centimetre (26 in) long pubic bone than that of any other known large theropod. The postacetabular ala (rear expansion) was much longer than the preacetabular ala (front expansion), which had a shelf on its central surface that formed the middle edge of the preacetabular fossa. Viewed distally (towards the centre of attachment), the lower end of the pubis had an L-shape resembling that of Baryonyx. The pubic apron—the expanded lower end of the pubis—had a large pubic foramen. On the hind rim of the pubic bone, two openings—the obturator foramen and a lower fenestra (opening)—were open and notch-like. The ischium was 49.6 cm (19.5 in) long, making it shorter in relation to the pubis than in all other known tetanuran theropods. The ischium's main body was large and extensive—atypical of the Y-shaped upper ischia of other tetanurans—and bore an oval-shaped obturator foramen in its side. The shaft of the ischium was flattened sideways, and had an unexpanded ischiadic apron, as in Monolophosaurus and Sinraptor.[1] The ischium attached to the ilium via a peg-and-socket-like articulation, unlike the flat, concave condition seen in Baryonyx. This feature was also present in 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. 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.[1]
Allain and his team considered Ichthyovenator as representing the first unequivocal spinosaurid from Asia.[1] Though prior spinosaurids had been named from the continent—including Siamosaurus from Thailand's BarremianSao Khua Formation and "Sinopliosaurus" fusuiensis from China's AptianXinlong Formation—the authors noted that palaeontologists have debated the validity of these taxa because they are only confidently known from isolated teeth.[1][10] Brazilian palaeontologists Marcos Sales and Caesar Schultz have suggested these teeth may eventually be attributed to spinosaurids similar to Ichthyovenator.[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
paraphyletic (unnatural) grouping.[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. Their cladogram can be seen below:[15]
Though no skull remains have been found for Ichthyovenator, all known spinosaurids had elongated, low, narrow snouts that allowed them to reach far for food and to quickly close their jaws in a manner similar to modern
generalist diet has also been proposed for spinosaurs, based on fossils such as the bones of a juvenile iguanodontid that was also found in the same Baryonyx specimen, an "Irritator" tooth embedded in the vertebrae of a pterosaur, and tooth crowns from Siamosaurus that were found in association with sauropod dinosaur bones. It is thus likely that spinosaurids were also scavengers or hunters of larger prey.[10][19][20][21] Though no limb bones are known from Ichthyovenator, all known spinosaurids had well-built arms with enlarged thumb claws, which they likely used to hunt and process prey.[10]
recognising members of its own species.[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. Naish also notes that it is possible similar relatives have not yet been discovered.[23]
carettochelyid and trionychid.[29] The trigoniidbivalvesTrigonioides and Plicatounio have also been recovered from the formation.[27] The Grès supérieurs Formation is the lateral equivalent of the neighbouring Khok Kruat and Phu Phan Formations in Thailand; from the Khok Kruat formation, fossils of theropods (including spinosaurids), sauropods, iguanodontians, and freshwater fish have also been recovered.[1][30]
In 2010,
biogeographical pattern for spinosaurs during the Early Cretaceous based on anatomical similarities between Ichthyovenator and the European genus Vallibonavenatrix.[9]
Media related to Ichthyovenator at Wikimedia Commons