Baryonyx
Baryonyx | |
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Reconstructed skeletal mount at the National Museum of Nature and Science, Tokyo | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Family: | †Spinosauridae |
Subfamily: | †Baryonychinae |
Genus: | †Baryonyx Milner, 1986
|
Species: | †B. walkeri
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Binomial name | |
†Baryonyx walkeri Charig & Milner, 1986
|
Baryonyx (
The holotype specimen, which may not have been fully grown, was estimated to have been between 7.5 and 10 metres (25 and 33 feet) long and to have weighed between 1.2 and 2 metric tons (1.3 and 2.2 short tons; 1.2 and 2.0 long tons). Baryonyx had a long, low, and narrow snout, which has been compared to that of a gharial. The tip of the snout expanded to the sides in the shape of a rosette. Behind this, the upper jaw had a notch which fitted into the lower jaw (which curved upwards in the same area). It had a triangular crest on the top of its nasal bones. Baryonyx had a large number of finely serrated, conical teeth, with the largest teeth in front. The neck formed an S-shape, and the neural spines of its dorsal vertebrae increased in height from front to back. One elongated neural spine indicates it may have had a hump or ridge along the centre of its back. It had robust forelimbs, with the eponymous first-finger claw measuring about 31 centimetres (12 inches) long.
Now recognised as a member of the
History of discovery
In January 1983, the plumber and amateur
Most of the bones collected were encased in
In
Assigned specimens
Fossils from other parts of the UK and
In 2011, a specimen (Catalogued as ML1190 in
In 2021, the palaeontologist Chris T. Barker and colleagues described two new spinosaurid genera from the
Possible synonyms
In 2003, Milner noted that some teeth at the Natural History Museum previously identified as belonging to the genera
In 1997, Charig and Milner noted that two fragmentary spinosaurid snouts from the
Description
Baryonyx is estimated to have been between 7.5 and 10 m (25 and 33 ft) long, 2.5 m (8.2 ft) in hip height, and to have weighed between 1.2 and 2 t (1.3 and 2.2 short tons; 1.2 and 2.0 long tons). The fact that elements of the skull and
Skull
The skull of Baryonyx is incompletely known, and much of the middle and hind portions are not preserved. The full length of the skull is estimated to have been 91–95 centimetres (36–37 inches) long, based on comparison with that of the related genus Suchomimus (which was 20% larger).
Baryonyx had a rudimentary secondary palate, similar to crocodiles but unlike most theropod dinosaurs.[44] A rugose (roughly wrinkled) surface suggests the presence of a horny pad in the roof of the mouth. The nasal bones were fused, which distinguished Baryonyx from other spinosaurids, and a sagittal crest was present above the eyes, on the upper mid-line of the nasals. This crest was triangular, narrow, and sharp in its front part, and was distinct from those of other spinosaurids in ending hind wards in a cross-shaped process. The lacrimal bone in front of the eye appears to have formed a horn core similar to those seen, for example, in Allosaurus, and was distinct from other spinosaurids in being solid and almost triangular. The occiput was narrow, with the paroccipital processes pointing outwards horizontally, and the basipterygoid processes were lengthened, descending far below the basioccipital (the lowermost bone of the occiput).[3][42][45] Sereno and colleagues suggested that some of Baryonyx's cranial bones had been misidentified by Charig and Milner, resulting in the occiput being reconstructed as too deep, and that the skull was instead probably as low, long and narrow as that of Suchomimus.[45] The front 14 cm (5.5 in) of the dentary in the mandible sloped upwards towards the curve of the snout. The dentary was very long and shallow, with a prominent Meckelian groove on the inner side. The mandibular symphysis, where the two halves of the lower jaw connected at the front, was particularly short. The rest of the lower jaw was fragile; the hind third was much thinner than the front, with a blade-like appearance. The front part of the dentary curved outwards to accommodate the large front teeth, and this area formed the mandibular part of the rosette. The dentary–like the snout—had many foramina.[3][38]
Most of the teeth found with the holotype specimen were not in articulation with the skull; a few remained in the upper jaw, and only small replacement teeth were still borne by the lower jaw. The teeth had the shape of recurved cones, where slightly flattened from sideways, and their curvature was almost uniform. The roots were very long, and tapered towards their extremity.[3] The carinae (sharp front and back edges) of the teeth were finely serrated with denticles on the front and back, and extended all along the crown. There were around six to eight denticles per mm (0.039 in), a much larger number than in large-bodied theropods like Torvosaurus and Tyrannosaurus. Some of the teeth were fluted, with six to eight ridges along the length of their inner sides and fine-grained enamel (outermost layer of teeth), while others bore no flutes; their presence is probably related to position or ontogeny (development during growth).[3][38] The inner side of each tooth row had a bony wall. The number of teeth was large compared to most other theropods, with six to seven teeth in each premaxilla and thirty-two in each dentary. Based on the closer packing and smaller size of the dentary teeth compared to those in the corresponding length of the premaxilla, the difference between the number of teeth in the upper and lower jaws appears to have been more pronounced than in other theropods.[3] The terminal rosette in the upper jaw of the holotype had thirteen dental alveoli (tooth sockets), six on the left and seven on the right side, showing tooth count asymmetry. The first four upper teeth were large (with the second and third the largest), while the fourth and fifth progressively decreased in size.[3] The diameter of the largest was twice that of the smallest. The first four alveoli of the dentary (corresponding to the tip of the upper jaw) were the largest, with the rest more regular in size. Small subtriangular interdental plates were present between the alveoli.[3][38]
Postcranial skeleton
Initially thought to have lacked the sigmoid curve typical of theropods,[3] the neck of Baryonyx does appear to have formed an S shape, though straighter than in other theropods.[46] The cervical vertebrae of the neck tapered towards the head and became progressively longer front to back. Their zygapophyses (the processes that connected the vertebrae) were flat, and their epipophyses (processes to which neck muscles attached) were well developed. The axis (the second neck vertebra) was small relative to the size of the skull and had a well-developed hyposphene. The neural arches of the cervical vertebrae were not always sutured to the centra (the bodies of the vertebrae), and the neural spines there were low and thin. The cervical ribs were short, similar to those of crocodiles, and possibly overlapped each other somewhat. The centra of the dorsal vertebrae of the back were similar in size. Like in other theropods, the skeleton of Baryonyx showed skeletal pneumaticity, reducing its weight through fenestrae (openings) in the neural arches and pleurocoels (hollow depressions) in the centra (primarily near the transverse processes). From front to back, the neural spines of the dorsal vertebrae changed from short and stout to tall and broad. One isolated dorsal neural spine was moderately elongated and slender, indicating that Baryonyx may have had a hump or ridge along the centre of its back (though incipiently developed compared to those of other spinosaurids). Baryonyx was unique among spinosaurids in having a marked constriction from side to side in a vertebra that either belonged to the sacrum or front of the tail.[3][6][45]
The coracoid tapered hind-wards when viewed in profile, and, uniquely among spinosaurids, connected with the scapula in a peg-and-notch articulation. The scapulae were robust and the bones of the forelimb were short in relation to the animal's size, but broad and sturdy. The humerus was short and stout, with its ends broadly expanded and flattened—the upper side for the
Classification
In their original description, Charig and Milner
Discoveries in the 1990s shed more light on the relationships of Baryonyx and its relatives. In 1996, a snout from Morocco was referred to Spinosaurus, and
Barker and colleagues found support for a Baryonychinae-Spinosaurinae split in 2021, and the following cladogram shows the position of Baryonyx within Spinosauridae according to their study:[26]
Spinosauridae |
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Evolution
Spinosaurids appear to have been widespread from the
Several theories have been proposed about the
Candeiro and colleagues suggested in 2017 that spinosaurids of northern Gondwana were replaced by other predators, such as
Palaeobiology
Diet and feeding
In 1986, Charig and Milner suggested that its elongated snout with many finely serrated teeth indicated that Baryonyx was
In 1997, Charig and Milner demonstrated direct dietary evidence in the stomach region of the B. walkeri holotype. It contained the first evidence of piscivory in a theropod dinosaur, acid-etched scales and teeth of the common fish
A 2005
In a 2014 conference abstract, the palaeontologist Danny Anduza and Fowler pointed out that grizzly bears do not gaff fish out of the water as was suggested for Baryonyx, and also ruled out that the dinosaur would not have darted its head like herons, since the necks of spinosaurids were not strongly S-curved, and their eyes were not well-positioned for
A 2016 study by the palaeontologist Christophe Hendrickx and colleagues found that adult spinosaurs could displace their mandibular rami (halves of the lower jaw) sideways when the jaw was depressed, which allowed the
A 2023 study by Barker and colleagues based on CT scans of the braincases of Baryonyx and Ceratosuchops found that the brain anatomy of these baryonychines was similar to that of other non-
Motion and semi-aquatic habits
In their original description, Charig and Milner did not consider Baryonyx to be aquatic (due to its nostrils being on the sides of its snout—far from the tip—and the form of the post-cranial skeleton), but thought it was capable of swimming, like most land vertebrates.
In 2017, the palaeontologists David E. Hone and Holtz hypothesized that the head crests of spinosaurids were probably used for sexual or threat display. The authors also pointed out that (like other theropods) there was no reason to believe that the forelimbs of Baryonyx were able to
A 2010 study by the palaeontologist Romain Amiot and colleagues proposed that spinosaurids were semi-aquatic, based on the
Sales and Schultz agreed in 2017 that spinosaurids were semi-aquatic and partially piscivorous, based on skull features such as conical teeth, snouts that were compressed from side to side, and retracted nostrils. They interpreted the fact that
Palaeoenvironment
The Weald Clay Formation consists of sediments of
Other dinosaurs from the Wessex Formation of the Isle of Wight where Baryonyx may have occurred include the theropods Riparovenator, Ceratosuchops,
It is generally thought that large predators occur with small taxonomic diversity in any area due to ecological demands, yet many Mesozoic assemblages include two or more
Taphonomy
Charig and Milner presented a possible scenario explaining the taphonomy (changes during decay and fossilisation) of the B. walkeri holotype specimen.[3] The fine-grained sediments around the skeleton, and the fact that the bones were found close together (skull and forelimb elements at one end of the excavation area and the pelvis and hind-limb elements at the other), indicates that the environment was quiet at the time of deposition, and water currents did not carry the carcass far—possibly because the water was shallow. The area where the specimen died seems to have been suitable for a piscivorous animal. It may have caught fish and scavenged on the mud plain, becoming mired before it died and was buried. Since the bones are well-preserved and had no gnaw marks, the carcass appears to have been undisturbed by scavengers (suggesting that it was quickly covered by sediment).[3]
The disarticulation of the bones may have been the result of soft-tissue decomposition. Parts of the skeleton seem to have weathered to different degrees, perhaps because water levels changed or the sediments shifted (exposing parts of the skeleton). The girdle and limb bones, the dentary, and a rib were broken before fossilisation, perhaps from trampling by large animals while buried. Most of the tail appears to have been lost before fossilisation, perhaps due to scavenging, or having rotted and floated off. The orientation of the bones indicates that the carcass lay on its back (perhaps tilted slightly to the left, with the right side upwards), which may explain why all the lower teeth had fallen out of their sockets and some upper teeth were still in place.[3][2]
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External links
- Natural History Museum – "Baryonyx: the discovery of an amazing fish-eating dinosaur" – four minute video presented by Angela C. Milner
This article was submitted to WikiJournal of Science for external academic peer review in 2018 (reviewer reports). The updated content was reintegrated into the Wikipedia page under a CC-BY-SA-3.0 license (2018). The version of record as reviewed is:
Michael Bech; et al. (2019). "Baryonyx" (PDF). WikiJournal of Science. 2 (1): 3. {{cite journal}}
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