Baryonyx

***Baryonyx*** (/ˌbæriˈɒnᵻks/) is a genus of theropod dinosaur which lived in the Barremian stage of the early Cretaceous Period, about 130–125 million years ago. The holotype specimen was discovered in 1983 in Surrey, England, and the animal was named ***Baryonyx walkeri*** in 1986. The genus 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 hunter William J. Walker. Fragmentary specimens were later discovered in other parts of the United Kingdom and Iberia. The holotype specimen is one of the most complete theropod skeletons from the UK, and its discovery attracted media attention.

*Baryonyx* was about 7.5 m (25 ft) long and weighed 1.2 t (1.3 short tons), but the holotype specimen may not have been fully grown. It had a long, low snout and narrow jaws, which have been compared to those 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 many finely serrated, conical teeth, with the largest teeth in front. The neck was less curved than that of other theropods, and the neural spines of its dorsal vertebrae increased in height from front to back. It had robust forelimbs, with the eponymous first-finger claw measuring about 31 cm (12 in) long.

Now recognised as a member of the family Spinosauridae, *Baryonyx'*s affinities were obscure when it was discovered. Apart from the type species (*B. walkeri*), some researchers have suggested that *Suchomimus tenerensis* belongs in the same genus and that *Suchosaurus cultridens* is a senior synonym; 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 *Iguanodon*. The creature would have caught and processed its prey primarily with its forelimbs and large claws. *Baryonyx* lived near water bodies, in areas where other theropod, ornithopod, and sauropod dinosaurs have also been found.

## Description

In 2010, *Baryonyx* was estimated to have been 7.5 m (25 ft) long and to have weighed 1.2 t (1.3 short tons). It was estimated at 10 m (33 ft) in 1997, and 9.5 m (31 ft) long, 2.5 m (8.2 ft) in hip height, and 1.7 t (1.9 short tons) in weight in 1988. 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 attested by the size of the related *Spinosaurus*, which reached 15 m (49 ft) and 10 t (11 short tons). On the other hand, the specimen's fused sternum indicates that it may have been fairly mature. The second-best-preserved specimen (ML1190) was about the same size as the holotype skeleton.

The skull of *Baryonyx* is incompletely known, and much of the middle and hind portions are not preserved. The full length of the skull has been estimated to be 950 mm (37.4 in), based on comparison with that of the related genus *Suchomimus* (which is 20% larger). It was elongated, and the front 170 mm (6.6 in) of the premaxillae formed a long, low snout (rostrum) with a rounded upper surface. The nostrils, far back from the tip, passed horizontally from one side of the skull to the other. The front 130 mm (5.1 in) of the snout expanded into a spatulate (flared outwards to the sides), "terminal rosette" shape similar to the modern gharial, and the front 70 mm (2.7 in) of the lower margin was downturned. The snout was very narrow just behind the rosette. The creature's maxilla and premaxilla fit together in a complex articulation, resulting in a strongly curved tooth row. The gap in the row is comparable to that of *Dilophosaurus*. The front 140 mm (5.5 in) of the dentary in the mandible curved upwards towards this area, and the gap between the upper and lower jaw is known as the subrostral notch. The snout had extensive pits (which would have been exits for blood vessels and nerves), and the maxilla appears to have housed sinuses.

*Baryonyx* had a rudimentary secondary palate, 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 upper midline of the nasal bones had a triangular sagittal crest, which was narrow and sharp in front. The lacrimal bone in front of the eye appears to have formed a horn core similar to those seen, for example, on *Allosaurus*. The dentary was very long and shallow, with a prominent Meckelian groove. 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 had many foramina (openings), which were passages for nerves and blood vessels. It has been suggested that some of *Baryonyx*'s cranial bones had been misidentified (resulting in the occiput's too-deep reconstruction), and the skull was probably as low, long and narrow as that of the closely related *Suchomimus*.

Most of the teeth found with the holotype specimen were not attached to the skull; a few remained in the upper jaw, and only small replacement teeth were in the lower jaw. The teeth had the shape of recurved cones, flattened somewhat sideways. The larger teeth were less recurved than the smaller ones, but were otherwise uniform. The roots were very long, and the teeth slender. The carinae (edges) of the teeth were finely serrated with denticles on the front and back. There were seven narrow, uniform denticles per millimetre (0.039 in), more than in most theropods. Some of the teeth were fluted, with six to eight ridges along the length of their inner sides and fine-grained enamel. The inner side of each tooth row had a bony wall. The number of teeth was large, with seven teeth in the right premaxilla (other theropods have three to five) and thirty-two in the dentary, where sixteen is typical. The lower jaw would have had sixty-four teeth, and the difference between the number of teeth in the upper and lower jaws is more pronounced than in other theropods. The teeth in the dentary were more densely packed than those in the maxilla, and probably smaller. The terminal rosette in the upper jaw had thirteen dental alveoli (tooth sockets), six on the left and seven on the right side; the first four were large (with the second and third the largest), while the fourth and fifth progressively decreased in size. 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. Interdental plates were between the alveoli.

The neck formed a straighter *S* shape (a sigmoid curve typical of theropods) than that seen in other theropods; in fact, the neck was initially thought to lack the *S* curve. The shape of the cervical vertebrae indicate that they tapered towards the head and were progressively longer front to back. The neural spines of the cervical vertebrae were low, thin, and were not always sutured to the centra (the bodies of the vertebrae). The axis vertebra, small relative to the size of the skull, had a well-developed hyposphene. The centra of the dorsal vertebrae were similar in size. Like other dinosaurs, *Baryonyx* reduced its weight (skeletal pneumaticity) with fenestrae (openings) in the neural arches and with 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.

The scapulae (shoulder blades) were robust; 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 deltopectoral crest and muscle attachment and the lower for articulation with the radius and ulna. The radius was short, stout and straight, and the olecranon of the ulna apparently very powerful. The lower part of the ulna had a broad expansion. The first finger had a large claw (ungual bone) measuring about 31 cm (12 in) along its curve, which would have been lengthened by a keratin sheath in life. Apart from its size, the claw's proportions were fairly typical of a theropod; it was bilaterally symmetric, slightly compressed, smoothly rounded, and sharply pointed. A groove for the sheath ran along the length of the claw. The pubic foot of the pelvis was not expanded.

## History of discovery

On 7 January 1983 amateur fossil hunter William J. Walker discovered a large claw, a phalanx bone, and part of a rib in Smokejacks Pit, a clay pit near Ockley in Surrey, England. The tip of the claw was missing, but Walker found it a week later. British palaeontologists Alan J. Charig and Angela C. Milner examined the finds at the Natural History Museum of London and found more bones at the site on 7 February, but the entire skeleton could not be collected until May and June due to conditions at the pit. A team of eight museum staff members and several volunteers excavated two tonnes of matrix. 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 disarticulated and scattered over a 5 x 2 m (17 x 8 ft) 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. The skeleton consisted of partial skull bones; teeth; cervical, dorsal and caudal vertebrae; ribs; a sternum; coracoids; arm and hand bones; claws; hip bones, and leg bones. The original specimen number was BMNH R9951, but it was later re-catalogued as NHMUK VP R9951.

In 1986 Charig and Milner made the skeleton the holotype specimen of a new genus and species:*Baryonyx walkeri*. The genus 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). Due to ongoing work on the bones (70 percent had been prepared at the time), they called their article preliminary (a "Letter to *Nature*") 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. It was widely featured in international media, and its discovery was the subject of a 1987 BBC documentary. *Baryonyx* was nicknamed "Claws" by journalists punning on the title of the film *Jaws*. The skeleton is mounted at the Natural History Museum in London, and in 1997 Charig and Milner published a monograph describing the holotype skeleton in detail.

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 and a vertebra, have been attributed to this genus. A maxilla fragment from La Rioja, Spain, was attributed in 1995.[16] In 1999 a postorbital bone, a squamosal bone, a tooth, vertebra remains, metacarpals, and a phalanx from the Sala de los Infantes deposit in Burgos Province, Spain, were attributed to an immature *Baryonyx* (though some of these elements are unknown in the holotype), and dinosaur tracks near Burgos have been identified as those of *Baryonyx* or a similar theropod. In 2011 a specimen (ML1190) 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*, the most complete Iberian remains of the animal. The skeletal elements of this specimen are also represented in the more complete holotype NHM R9951, except for the mid-neck vertebrae.

The authors of a 2002 article about the spinosaur *Irritator* proposed that *Suchomimus tenerensis*was similar enough to *B. walkeri* to be considered a species within the same genus (*B. tenerensis*), and suggested that *Suchomimus* was identical to *Cristatusaurus*; both are from the Elrhaz Formation of Niger. In a 2004 conference abstract, palaeontologists Steve Hutt and Penny Newbery supported this view based on a large theropod vertebra from the Isle of Wight which they attributed to *Baryonyx*; this indicated that the vertebrae of the two genera were more similar than previously thought. Later studies have kept the genera separate.

In a 2003 article, Milner noted that the teeth of *Baryonyx* were very similar to those of the genus *Suchosaurus* and suggested that their remains represented the same animal. The type species of the genus, *S. cultridens*, was named in 1841 based on teeth from Tilgate Forest in Sussex; a second species, *S. girardi*, was named in 1897 based on jaw fragments and a tooth from Boca do Chapim. In 2007 Buffetaut considered the teeth of *S. girardi* very similar to those of *Baryonyx* (and *S. cultridens*) except for the stronger development of the crown ribs, 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 one worn tooth and that of *B. walkeri*is a skeleton it would be more practical to retain the newer name. In 2011 Portuguese palaeontologist Octávio 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.

## Classification

In their original description, Charig and Milner found *Baryonyx* unique enough to warrant a new family of theropod dinosaurs: Baryonychidae. They found *Baryonyx* to be unlike any other theropod group (and considered the possibility that it was a thecodont, due to apparently primitive features), but noted that the articulation of the maxilla and premaxilla was similar to that in *Dilophosaurus*. They also noted that two fragmentary snouts from Niger, assigned to the family Spinosauridae by French palaeontologist Philippe Taquet in 1984, appeared almost identical to those of *Baryonyx* and they referred them to Baryonychidae instead. In 1988, American palaeontologist Gregory S. Paul agreed with Taquet that *Spinosaurus*, described in 1915 based on fragmentary remains from Egypt which were destroyed in World War II, and *Baryonyx* were similar and (due to their kinked snouts) possibly late-surviving dilophosaurs. French palaeontologist Eric Buffetaut also supported this relationship in 1989. In 1990 Charig and Milner dismissed the spinosaurid affinities of *Baryonyx*, since they did not find their remains similar enough.

Discoveries in the 1990s shed more light on the relationships of *Baryonyx* and its relatives. A snout from Morocco was referred to*Spinosaurus* and *Irritator* from Brazil was named in 1996. Two years later the snout fragments from Niger were named *Cristatusaurus*, and *Suchomimus* was named from a partial skeleton from the country. In their description of *Suchomimus*, Sereno and colleagues placed it and *Baryonyx* in the new subfamily Baryonychinae within Spinosauridae; other members of the group were placed in the subfamily Spinosaurinae. They also united the spinosaurids and their closest relatives in the superfamily Spinosauroidea, but in 2010 Roger Benson considered this a junior synonym of Megalosauroidea (an older name).