Baryonyx

''Baryonyx'' () is a genus of theropod dinosaur which lived in the Barremian stage of the Early Cretaceous period, about 130–125 million years ago. The first skeleton was discovered in 1983 in the Smokejack Clay Pit, of Surrey, England, in sediments of the Weald Clay Formation, and became the holotype specimen of ''Baryonyx walkeri'', named by palaeontologists Alan J. Charig and Angela C. Milner in 1986. The generic name, ''Baryonyx'', means "heavy claw" and alludes to the animal's very large claw on the first finger; the specific name, ''walkeri'', refers to its discoverer, amateur fossil collector William J. Walker. The holotype specimen is one of the most complete theropod skeletons from the UK (and remains the most complete Spinosaurid), and its discovery attracted media attention. Specimens later discovered in other parts of the United Kingdom and Iberia have also been assigned to the genus, though many have since been moved to new genera.

The holotype specimen, which may not have been fully grown, was estimated to have been between long and to have weighed between . ''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 long.

Now recognised as a member of the family Spinosauridae, ''Baryonyx'' affinities were obscure when it was discovered. Some researchers have suggested that ''Suchosaurus cultridens'' is a senior synonym (being an older name), and that ''Suchomimus tenerensis'' belongs in the same genus; subsequent authors have kept them separate. ''Baryonyx'' was the first theropod dinosaur demonstrated to have been piscivorous (fish-eating), as evidenced by fish scales in the stomach region of the holotype specimen. It may also have been an active predator of larger prey and a scavenger, since it also contained bones of a juvenile iguanodontid. The creature would have caught and processed its prey primarily with its forelimbs and large claws. ''Baryonyx'' may have had semiaquatic habits, and coexisted with other theropod, ornithopod, and sauropod dinosaurs, as well as pterosaurs, crocodiles, turtles and fishes, in a fluvial environment.

History of discovery

In January 1983, the British plumber and amateur fossil collector William J. Walker explored the Smokejacks Pit, a clay pit in the Weald Clay Formation near Ockley in Surrey, England. He found a rock wherein he discovered a large claw, but after piecing it together at home, he realised the tip of the claw was missing. Walker returned to the same spot in the pit some weeks later, and found the missing part after searching for an hour. He also found a and part of a . Walker's son-in-law later brought the claw to the Natural History Museum of London, where it was examined by the British palaeontologists Alan J. Charig and Angela C. Milner, who identified it as belonging to a theropod dinosaur. The palaeontologists found more bone fragments at the site in February, but the entire skeleton could not be collected until May and June due to weather conditions at the pit. A team of eight museum staff members and several volunteers excavated of rock matrix in 54 blocks over a three-week period. Walker donated the claw to the museum, and the Ockley Brick Company (owners of the pit) donated the rest of the skeleton and provided equipment. The area had been explored for 200 years, but no similar remains had been found before.

Most of the bones collected were encased in siltstone nodules surrounded by fine sand and silt, with the rest lying in clay. The bones were and scattered over a area, but most were not far from their natural positions. The position of some bones was disturbed by a bulldozer, and some were broken by mechanical equipment before they were collected. Preparing the specimen was difficult, due to the hardness of the siltstone matrix and the presence of siderite; acid preparation was attempted, but most of the matrix was removed mechanically. It took six years of almost constant preparation to get all the bones out of the rock, and by the end, dental tools and air mallets had to be used under a microscope. The specimen represents about 65 percent of the skeleton, and consists of partial skull bones, including premaxillae (first bones of the upper jaw); the left maxillae (second bone of the upper jaw); both nasal bones; the left lacrimal; the left prefrontal; the left postorbital; the braincase including the occiput; both dentaries (the front bones of the lower jaw); various bones from the back of the lower jaw; teeth; cervical (neck), dorsal (back), and caudal (tail) ; ribs; a ; both (shoulder blades); both ; both (upper arm bones); the left and (lower arm bones); finger bones and (claw bones); hip bones; the upper end of the left (thigh bone) and lower end of the right; right (of the lower leg); and foot bones including an ungual. The original specimen number was BMNH R9951, but it was later re-catalogued as NHMUK VP R9951.

In 1986, Charig and Milner named a new genus and species with the skeleton as holotype specimen: ''Baryonyx walkeri''. The generic name derives from ancient Greek; βαρύς (''barys'') means "heavy" or "strong", and ὄνυξ (''onyx'') means "claw" or "talon". The specific name honours Walker, for discovering the specimen. At that time, the authors did not know if the large claw belonged to the hand or the foot (as in dromaeosaurs, which it was then assumed to be). The dinosaur had been presented earlier the same year during a lecture at a conference about dinosaur systematics in Drumheller, Canada. Due to ongoing work on the bones (70 percent had been prepared at the time), they called their article preliminary and promised a more detailed description at a later date. ''Baryonyx'' was the first large Early Cretaceous theropod found anywhere in the world by that time. Before the discovery of ''Baryonyx'' the last significant theropod find in the United Kingdom was '' Eustreptospondylus'' in 1871, and in a 1986 interview Charig called ''Baryonyx'' "the best find of the century" in Europe. ''Baryonyx'' was widely featured in international media, and was nicknamed "Claws" by journalists punning on the title of the film ''Jaws''. Its discovery was the subject of a 1987 BBC documentary, and a cast of the skeleton is mounted at the Natural History Museum in London. In 1997, Charig and Milner published a monograph describing the holotype skeleton in detail. The holotype specimen remains the most completely known spinosaurid skeleton.

Additional specimens

Fossils from other parts of the UK and Iberia, mostly isolated teeth, have subsequently been attributed to ''Baryonyx'' or similar animals. Isolated teeth and bones from the Isle of Wight, including hand bones reported in 1998 and a vertebra reported by the British palaeontologists Steve Hutt and Penny Newbery in 2004, have been attributed to this genus. A maxilla fragment from La Rioja, Spain, was attributed to ''Baryonyx'' by the Spanish palaeontologists Luis I. Viera and José Angel Torres in 1995 (although the American palaeontologist Thomas R. Holtz and colleagues raised the possibility that it could have belonged to ''Suchomimus'' in 2004). In 1999, a postorbital, , tooth, vertebral remains, (hand bones), and a phalanx from the Salas de los Infantes deposit in Burgos Province, Spain, were attributed to an immature ''Baryonyx'' (though some of these elements are unknown in the holotype) by the Spanish palaeontologist Carolina Fuentes Vidarte and colleagues. Dinosaur tracks near Burgos have also been suggested to belong to ''Baryonyx'' or a similar theropod.

In 2011, a specimen (Catalogued as ML1190 in Museu da Lourinhã) from the Papo Seco Formation in Boca do Chapim, Portugal, with a fragmentary dentary, teeth, vertebrae, ribs, hip bones, a scapula, and a phalanx bone, was attributed to ''Baryonyx'' by the Portuguese palaeontologist Octávio Mateus and colleagues, the most complete Iberian remains of the animal. The skeletal elements of this specimen are also represented in the more complete holotype (which was of similar size), except for the mid-neck vertebrae. In 2018, the British palaeontologist Thomas M. S. Arden and colleagues found that the Portuguese skeleton did not belong to ''Baryonyx'', since the front of its dentary bone was not strongly upturned. This specimen was made the basis of the new genus ''Iberospinus'' by Mateus and Darío Estraviz-López in 2022. Some additional spinosaurid remains from Iberia may belong to taxa other than ''Baryonyx'', including ''Vallibonavenatrix'' from Morella.

In 2021, the British palaeontologist Chris T. Barker and colleagues described two new spinosaurid genera from the Wessex Formation of the Isle of Wight, ''Ceratosuchops'' and ''Riparovenator'' (the latter named ''R. milnerae'' honouring Milner for her contributions to spinosaurid research), and stated that spinosaurid material from there that had previously been attributed to the contemporary ''Baryonyx'' could have belonged to other taxa instead. These specimens had previously been assigned to ''Baryonyx'' in a 2017 conference abstract. Barker and colleagues stated that the recognition of the Wessex Formation specimens as new genera renders the presence of ''Baryonyx'' there ambiguous, and most of the previously assigned isolated material from the Wealden Supergroup is therefore indeterminate. These authors also found the Portuguese specimen ML 1190 to group with ''Baryonyx'', supporting its original assignment to the genus.

Possible synonyms

In 2003, Milner noted that some teeth at the Natural History Museum previously identified as belonging to the genera ''Suchosaurus'' and '' Megalosaurus'' probably belonged to ''Baryonyx''. The type species of ''Suchosaurus'', ''S. cultridens'', was named by the British biologist Richard Owen in 1841, based on teeth discovered by the British geologist Gideon A. Mantell in Tilgate Forest, Sussex. Owen originally thought the teeth to have belonged to a crocodile; he was yet to name the group Dinosauria, which happened the following year. A second species, ''S. girardi'', was named by the French palaeontologist Henri Émile Sauvage considered the teeth of ''S. girardi'' very similar to those of ''Baryonyx'' (and ''S. cultridens'') except for the stronger development of the flutes (or "ribs"; lengthwise ridges), suggesting that the remains belonged to the same genus. Buffetaut agreed with Milner that the teeth of ''S. cultridens'' were almost identical to those of ''B. walkeri'', but with a ribbier surface. The former taxon might be a senior synonym of the latter (since it was published first), depending on whether the differences were within a taxon or between different ones. According to Buffetaut, since the holotype specimen of ''S. cultridens'' is a single tooth and that of ''B. walkeri'' is a skeleton, it would be more practical to retain the newer name. In 2011, Mateus and colleagues agreed that ''Suchosaurus'' was closely related to ''Baryonyx'', but considered both species in the former genus ''nomina dubia'' (dubious names) since their holotype specimens were not considered diagnostic (lacking distinguishing features) and could not be definitely equated with other taxa. In any case, the identification of ''Suchosaurus'' as a spinosaurid makes it the first named member of the family.

In 1997, Charig and Milner noted that two fragmentary spinosaurid snouts from the Elrhaz Formation of Niger (reported by the French palaeontologist Philippe Taquet in 1984) were similar enough to ''Baryonyx'' that they considered them to belong to an indeterminate species of the genus (despite their much younger Aptian geological age). In 1998, these fossils became the basis of the genus and species '' Cristatusaurus lapparenti'', named by Taquet and the American palaeontologist Dale Russell. The American palaeontologist Paul Sereno and colleagues named the new genus and species ''Suchomimus tenerensis'' later in 1998, based on more complete fossils from the Elrhaz Formation. In 2002, the German palaeontologist Hans-Dieter Sues and colleagues proposed that ''Suchomimus tenerensis'' was similar enough to ''Baryonyx walkeri'' to be considered a species within the same genus (as ''B. tenerensis''), and that ''Suchomimus'' was identical to ''Cristatusaurus''. Milner concurred that the material from Niger was indistinguishable from ''Baryonyx'' in 2003. In a 2004 conference abstract, Hutt and Newberry supported the synonymy based on a large theropod vertebra from the Isle of Wight which they attributed to an animal closely related to ''Baryonyx'' and ''Suchomimus''. Later studies have kept ''Baryonyx'' and ''Suchomimus'' separate, whereas ''Cristatusaurus'' has been proposed to be either a ''nomen dubium'' or possibly distinct from both. A 2017 review paper by the Brazilian palaeontologist Carlos Roberto A. Candeiro and colleagues stated that this debate was more in the realm of semantics than science, as it is generally agreed that ''B. walkeri'' and ''S. tenerensis'' are distinct, related species. Barker and colleagues found ''Suchomimus'' to be closer related to the British genera ''Riparovenator'' and ''Ceratosuchops'' than to ''Baryonyx'' in 2021.

Description

''Baryonyx'' is estimated to have been between long, in hip height, and to have weighed between . The fact that elements of the skull and vertebral column of the ''B. walkeri'' holotype specimen (NHM R9951) do not appear to have co-ossified (fused) suggests that the individual was not fully grown, and the mature animal may have been much larger (as is the case for some other spinosaurids). On the other hand, the specimen's fused sternum indicates that it may have been mature.

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 long, based on comparison with that of the related genus ''Suchomimus'' (which was 20% larger). It was elongated, and the front of the premaxillae formed a long, narrow, and low snout ( rostrum) with a smoothly rounded upper surface. The (bony nostrils) were long, low, and placed far back from the snout tip. The front of the snout expanded into a spatulate (spoon-like), "terminal rosette", a shape similar to the rostrum of the modern gharial. The front of the lower margin of the premaxillae was downturned (or hooked), whereas that of the front portion of the maxillae was upturned. This morphology resulted in a sigmoid or S shaped margin of the lower upper tooth row, in which the teeth from the front of the maxilla were projecting forward. The snout was particularly narrow directly behind the rosette; this area received the large teeth of the mandible. The maxilla and premaxilla of ''Baryonyx'' fit together in a complex articulation, and the resulting gap between the upper and lower jaw is known as the . A downturned premaxilla and a sigmoid lower margin of the upper tooth row was also present in distantly related theropods such as '' Dilophosaurus''. The snout had extensive (openings), which would have been exits for blood vessels and nerves, and the maxilla appears to have housed sinuses.

''Baryonyx'' had a rudimentary , similar to crocodiles but unlike most theropod dinosaurs. 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 were lengthened, descending far below the (the lowermost bone of the occiput). Sereno and colleagues suggested that some of ''Baryonyx'' 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''. The front 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

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