Baryonyx walkeri

Baryonyx walkeri ("Walker's heavy claw") is the only known species of the extinct genus Baryonyx spinosaurid theropod dinosaur, which lived in the middle of the Cretaceous period, approximately between 130 and 125 million years ago during the Aptian, in what is now Europe. The first specimen was found in England, and later reported in northern Spain and Portugal.

Description

Baryonyx was a large predator that measured about 9.75 meters in length, 2.55 meters in height at the hip and between 1.7 and 2.7 tons. The approximate dimensions have been varying for a long time with the latest technology, the previous dimensions were estimated. The fact that the skull and vertebral column elements of the holotype specimen ofB. walkeri, NHM R9951, do not appear to have been fused, suggesting that the individual was not fully grown, and the mature animal may have been larger, as in the related Spinosaurus, which reached 15 meters long and 10 tons. Furthermore, the specimen's fused sternum indicates that it may have been quite mature. The second best preserved specimen, ML 1190, was approximately the same size as the holotype skeleton.

Baryonyx is a very unusual theropod. The structure of its pelvis suggests that it was bipedal when moving from one place to another. Like dromaeosaurids, Baryonyx had a pair of large curved claws, around 35 centimeters, but unlike these, they were not located on the feet, but on the hands. The bone structure suggests the existence of powerful musculature in the forelimbs, much greater than in most theropods. The long neck was very inflexible and did not have the S shape of many other theropods. The skull was inserted at an acute angle and not a right angle, as is common in similar dinosaurs. The large jaws were uniquely crocodilian in appearance and had 96 teeth, twice as many as most of their relatives. 64 of these teeth were located in the lower jaw and 32, longer ones, in the upper jaw. It is possible that the snout had a small crest. The upper jaw had a sharp angle near the snout, a characteristic seen in crocodiles that helps prevent prey from escaping. A similar feature is also seen in shrikes.

Skull

The skull of Baryonyx is incompletely known, and much of the middle and rear portions are not preserved. The total length of the skull has been estimated at 950 millimeters, based on comparison with that of the related genus Suchomimus, which is 20% larger. It is elongated, and the front part of the 170-millimeter premaxillae formed a long, low snout with a rounded upper surface. The nostrils, away from the tip, pass horizontally from one side of the skull to the other. The front of the 130 millimeter snout was enlarged in the shape of a spatula, similar to the modern gharial's so-called "rosette snout" and the front of the 70-millimeter lower margin curved downwards. The snout was very narrow, just behind the rosette. The maxilla and premaxilla fit together in a complex joint, resulting in a strongly curved row of teeth. The gap in the row is comparable to that of Dilophosaurus. The 140-millimeter dentary in the mandible was curved upward toward this area, and the gap between the upper and lower jaw was 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 rough surface suggests the presence of a horny pad on the roof of the mouth. It had a sagittal crest above the eyes, on the upper midline of the nasal bones that was triangular, narrow and tapering in front. The lacrimal bone in front of the eye appears to have formed a horn core similar to that seen, for example, in Allosaurus. The dentary was very long and shallow, with a prominent Meckelian groove. The rest of the lower jaw was fragile. The rear third was much thinner than the front, with a leaf-like appearance. The front part of the dentary curved outward to accommodate the large front teeth, and this area formed the mandibular part of the rosette. The dentary had many holes, which were passages for nerves and blood vessels. It has been suggested that some of the cranial bones of Baryonyx have been misidentified resulting in an occipital that was too deep in the reconstruction and The skull was probably as low, long and narrow as in its close relative, 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 were in the shape of recurved cones, somewhat flattened on the side. The larger teeth were less recurved than the smaller ones, but similar. The roots were very long and the teeth were thin. The carinae of the teeth were finely toothed with denticles at the front and back. There were seven narrow, uniform denticles per millimeter, more than in most theropods. Some of the teeth were striated, with six to eight ridges along the length of their inner sides and fine-grained enamel. The inner side of each row of teeth 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 are 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 sockets, six on the left and seven on the right. 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. The interdental plates were between the alveoli.

Axial skeleton

The neck formed a straighter sigmoid shape, with a less typical S shape than that observed in other theropods. In fact, the neck was initially thought to lack the S shape. The shape of the cervical vertebrae indicates that they taper toward the head and were progressively longer from front to back. The neural spines of the cervical vertebrae were low, thin, and were not always sutured to the bodies of the vertebrae. The axis vertebra, small in relation to the size of the skull, had a well-developed hyposphene. The body of the dorsal vertebrae were similar in size. Like other dinosaurs, Baryonyx reduced its weight with fenestrae, openings in the bone, in the neural arches and with pleurocoeles, hollow depressions, in the body, mainly near the transverse processes. From front to back, the neural spines of the dorsal vertebrae changed from short and strong to tall and wide.

Appendicular skeleton

The scapulae were robust. The bones of the forearm were short in relation to the size of the animal, but wide and robust. The humerus was short and robust, with its wide expanded and flattened ends forming the upper part of the deltopectoral crest, the muscular anchoring area, and the lower portion for articulation with the radius and ulna. The radius was short, robust and straight, and the olecranon of the ulna apparently very powerful. The lower part of the ulna had a wide expansion. The hands had three fingers, the first finger bore a large claw formed by the nail bone that measured approximately 31 centimeters along its curve, which would have been even larger thanks to a keratin sheath in life. Aside from its size, the claw's proportions were fairly typical for a theropod. It was bilaterally symmetrical, slightly compressed, gently rounded, and pointed. A slot for the sheath ran along the length of the claw. The pubic foot of the pelvis did not expand.

Discovery and research

On January 7, 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 paleontologists Alan J. Charig and Angela C. Milner examined the finds at the Natural History Museum in London and found more bones at the site on February 7, but the entire skeleton could not be collected until May and June due to the conditions in the hole. A team of eight museum staff members and several volunteers excavated two tons of matrix. Walker donated the claw to the museum, and the Ockley Brick Company, owners of the grave, donated the rest of the skeleton and provided equipment. The area had been explored for 200 years, but nothing similar had ever been found. They published their description of the type specimen in 1986 and named the new species Baryonyx walkeri in Walker's honor. About 70% of the skeleton was recovered, including the skull. This allows paleontologists to make numerous deductions about Baryonyx from this specimen. The skeleton is on display at the Natural History Museum in London.

Most of the bones collected were encased in siltstone nodules surrounded by fine sand and silt, and the rest rested in clay. The bones were disarticulated and scattered over an area of 5 x 2 meters, 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. Preparation of 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 bones of the skull, teeth, cervical, dorsal and caudal vertebrae, ribs, sternum; coracoid, arm and hand bones, claws, hip 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 name of the genus derives from the ancient Greek, Βαρύς, barys, "heavy" or "strong" and ὄνυξ, onyx, means "claw". The specific name honors Walker for discovering the specimen. At the time, the authors did not know whether 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 that time, they called their paper preliminary and promised a more detailed description at a later date. Baryonyx was the first large early Cretaceous theropod found anywhere in the world at that time. Before the discovery of Baryonyx the last significant theropod found 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 BBC documentary in 1987. Baryonyx was nicknamed "Claws" by journalists who copied it from the title of the movie Jaws. The skeleton is mounted in the Natural History Museum, London, and in 1997 Charig and Milner published a monograph describing the holotype skeleton in detail.

Fossils from other parts of the United Kingdom and the Iberian Peninsula, mostly isolated teeth, have subsequently been attributed to Baryonyx or similar animals. Isolated teeth and bones from the Isle of Wight, including bones of the hand and a vertebra, have been attributed to this genus. In 1995, the Aranzadi Science Society announced in San Sebastián that it had identified the rest of the jaw, the left maxilla, of a theropod dinosaur, identified as that of a Baryonyx, found in Igea, La Rioja, Spain. In 1999, a postorbital and squamosal bone, a tooth, vertebral remains, metacarpals and a phalanx were recovered from the deposit of the Sala de los Infantes in the Province of Burgos, Spain, which were attributed to a Baryonyx immature, although some of these elements are unknown in the holotype, and dinosaur ichnites near Burgos have been identified as those of Baryonyx or a similar theropod. In 2011 it was attributed to Baryonyx specimen ML1190 from the Papo Seco Formation in Boca do Chapim, Portugal, with a fragmentary dentary, teeth, vertebrae, ribs, hip bones, scapula and phalanx bone, 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 middle neck vertebrae.

Later, in 2022, the remains of the Iberian Baryonyx began to be reclassified, resulting in the publication of a new spinosaurid in Portugal, the Iberospinus natarioi described by paleontologists Darío Estraviz López and Mateus. In Spain the remains of Baryonyx began to be reclassified to Baryonychinae indet the same year, however, on March 24, 2023, in a conference given by paleontologists from excavations in La Rioja (Spain), they showed an almost complete arm of a spinosaurid that according to what was declared, it would be one other than Baryonyx, in said conference it was mentioned that the leg assigned to Baryonyx in the same area would not have been from a Baryonyx walkeri either. The authors of a 2002 paper on the spinosaurid Irritator proposed that Suchomimus tenerensis is sufficiently similar to B. walkerito be considered a species within the same genus, like B. tenerensis, and suggested that Suchomimus was identical to Cristatusaurus, both from the Elrhaz Formation of Niger. Approximately 9.5 meters and 2.5 tons, Suchomimus was larger than Baryonyx. In a 2004 conference summary, paleontologists 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. However, later studies have kept the genders separate.

In a 2003 paper, Milner noted that the teeth of Baryonyx were very similar to those of the genus Suchosaurus and suggested that its remains represented the same animal. type species of the genus,S. cultridens, was named in 1841 based on teeth from Tilgate Forest in Sussex. A second species,S. giradi, was named in 1897 based on jaw fragments and a tooth from Boca do Chapim.

In 2007 Buffetaut considered the teeth of S. giradi very similar to those of Baryonyx and S. cultridensexcept for the stronger development of the crown ribs, suggesting that the remains belonged to the same genus. Buffetaut agreed with Milner that the teeth ofS. cultridenswere almost identical to those of B. walkeribut with a bordered surface. The former taxon could be an older synonym of the latter since it was published first, depending on whether the differences were within a taxon or between different taxa. According to Buffetaut, since the holotype specimen ofS. cultridens is a worn tooth and that of B. walkeri is a skeleton it would be more practical to retain the newer name. In 2011, Portuguese paleontologist Octávio Mateus and his colleagues agreed that holotypic specimens of Suchosaurus were closely related to Baryonyx, but considered both species in the former genus doubtful since their are not considered diagnostic, lacking distinctive features and cannot be definitively equated with other taxa.

Classification

In their original description, Charig and Milner found Baryonyx unique enough to justify a new family of theropod dinosaurs, Baryonychidae. They found that Baryonyx was different from any other group of theropods 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 of Dilophosaurus. They also noted that two fragmentary snouts from Niger, assigned to the family Spinosauridae by French paleontologist Philippe Taquet in 1984, appeared almost identical to those of Baryonyx and referred them to Baryonychidae instead. In 1988 The American paleontologist Gregory S. Paul agreed with Taquet that Spinosaurus, described in 1915 from fragmentary remains from Egypt that were destroyed in World War II, and Baryonyx were similar and due to their possibly late surviving dilophosaurid snouts. French paleontologist Eric Buffetaut also supported this relationship in 1989. In 1990 Charig and Milner rejected the affinities of Spinosaurus and Baryonyx, since they do not They found 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 after a partial skeleton from that same country. In describing Suchomimus, Sereno and his colleagues placed it alongside Baryonyx in the new subfamily Baryonychinae within Spinosauridae. Other members of the group were placed in the subfamily Spinosaurinae. Spinosaurids and their closest relatives were also joined in the superfamily Spinosauroidea, but in 2010 Roger Benson considered this a more modern synonym of Megalosauroidea, an older name. The specimen of the holotype ofB. walkeriremains the most completely known spinosaurid skeleton.

Phylogeny

The following cladogram shows the position of Baryonyx within Spinosauridae, according to Barker and colleagues, 2021. In this new arrangement the status of Irritator is not specified, but It is considered a derived member of Spinosaurinae.

The following cladogram shows a 2010 analysis showing the position of Baryonyx within the superfamily Megalosauroidea.

Paleobiology

Diet and feeding

In 1986 Charig and Milner were the first to suggest that Baryonyx's elongated snout with many finely serrated teeth indicated that its diet was piscivorous, speculating that it crouched on a river bank and used its claw. grappling hook pulled fish out of the water, similar to the modern grizzly bear. In 1984, Taquet noted that the snouts of Niger spinosaurids were similar to those of the modern gharial and suggested behavior similar to herons or storks. In 1997 Charig and Milner rejected his initial proposal that the joint between the premaxilla and maxilla was mobile. In 1987 Andrew Kitchener disputed the piscivorous behavior of Baryonyx and suggested that it would have been a scavenger, using its long neck for feeding on the ground, its claws for snapping into a corpse, and its long snout, with far-flung nostrils for breathing, for investigating the body cavity. Kitchener argued that Baryonyx's jaws and teeth were too weak to kill other dinosaurs and too heavy to catch fish, with too many adaptations for fishing. According to R.E.H. Reid, a scavenger would have fed that had been destroyed by its predator and that large animals, such as grizzly bears, are capable of fishing at least in shallow waters.

In 1997, Charig and Milner demonstrated direct dietary evidence in the stomach region of the holotype ofB. walkeri. The first evidence of a piscivorous diet in a theropod dinosaur are scales damaged by stomach acid and teeth of the common fish Scheenstia mantelli, then classified in the genus Lepidotes, and remains of bones from an Iguanodon young. An apparent gastrolith, gizzard stone, was also found. They also presented circumstantial evidence of piscivorous feeding, such as crocodile-like adaptations for catching and swallowing prey, long, narrow jaws with their 'terminal rosette', similar to those of a gharial, and the tip and notch of the snout. down. In his opinion, these adaptations suggest that Baryonyx would have captured small to medium-sized fish in the manner of a crocodile, grasping them with the notch of the snout, giving the teeth a "stab function" #34;, tilting the head back and swallowing them from the head. The larger fish would be torn apart with their claws. The teeth of the lower jaw were smaller, more crowded and numerous than those of the upper jaw, which may have helped the animal grasp food. Charig and Milner argued that Baryonyx would have primarily eaten fish, although it would also have been an active predator and an opportunistic scavenger, but was not equipped to be a top predator like Allosaurus. They suggested that Baryonyx primarily used its forearms and large claws to catch, kill, and tear apart larger prey.

In 2004, a pterosaur neck vertebra from Brazil with a spinosaurid tooth embedded in it confirmed that the latter were not exclusively piscivores. A 2007 finite element analysis of a CT scanner scanning the snouts indicated that The biomechanics of Baryonyx were more similar to those of the gharial and unlike those of the American crocodile and more conventional theropods, supporting a piscivorous diet for spinosaurids. Their secondary palate helped them resist bending and twisting their tubular snouts. A 2013 beam theory study compared the biomechanics of CT-scanned spinosaurid snouts to those of extant crocodiles and found the snouts of Baryonyx and Spinosaurus are similar in their resistance to bending and torsion. Baryonyx was found to have relatively high resistance in the snout to dorsoventral bending compared to Spinosaurus and the gharial. The authors concluded, in contrast to the 2007 study, that Baryonyx functioned differently than the gharial. Spinosaurids were not exclusively piscivores, and their diet was determined by their individual size.

A 2016 study found that adult spinosaurids could laterally move their mandibular rami, halves of the lower jaw, when the jaw was depressed, allowing the pharynx, the opening that leads from the throat to the stomach, to expand. This jaw joint is similar to that seen in living pterosaurs and pelicans, and would also have allowed spinosaurids to swallow large prey such as fish and other animals. Another 2016 study found that spinosaurid jaws were convergent with those of spinosaurids. pike. These fish also have laterally compressed jaws, while crocodile jaws are compressed from top to bottom, an elongated snout with a "terminal rosette" bearing dilated teeth, and a notch behind the rosette with smaller teeth. This type of jaw probably evolved to catch prey in low-light aquatic environments and may have aided in prey detection.

Movement and 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, away from the tip, and the shape of the posterior skeleton. -cranial, but he thought it was capable of swimming, like most terrestrial vertebrates. It was speculated that the elongated skull, long neck, and strong humerus of Baryonyx indicated that the animal was a facultative quadruped, unique among theropods. In their 1997 paper they found no skeletal support for This, but they maintained that the forelimbs would have been strong enough for a quadrupedal stance and would probably have caught aquatic prey while crouching on all fours near or in water. A 2014 redescription of Spinosaurus based in new remains suggests that it was a quadruped, based on its previous center of body mass. The authors found that quadrupedality was unlikely for Baryonyx, since the better-known legs of the closely related Suchomimus did not support this posture.

In 2017, David E. Hone and Thomas R. Holtz noted that, like other theropods, there was no reason to believe that the forelimbs of Baryonyx were capable of pronation, and therefore both being able to rest or walk on your palms. Resting or using the forelimbs for locomotion may have been possible, as indicated by the tracks of a resting theropod, but if this was the norm, the forelimbs would probably have shown adaptations for this. Hone and Holtz further suggested that the forelimbs of spinosaurids do not appear optimal for catching prey, but rather appear similar to the forelimbs of burrowing animals. They suggested that the ability to dig would have been useful when excavating nests, digging for water, or to reach some type of prey. Hone and Holtz also believed that spinosaurids would have waded and dipped in water rather than submerged, due to the widespread nature of aquatic adaptations.

A 2010 study proposed that spinosaurids were semi-aquatic, based on the oxygen isotopic composition of spinosaurid teeth from around the world compared to that of other theropods and extant animals. Spinosaurids probably spent much of the day in the water, like crocodiles and hippos, and had a similar diet to the former. Both were opportunistic predators. Since most spinosaurids do not appear to have anatomical adaptations for an aquatic lifestyle, the authors proposed that water immersion was a means of thermoregulation similar to that of crocodiles and hippos. Spinosaurids may also have converted to aquatic and piscivorous habitats to avoid competition with more terrestrial theropods.

A histological study of growth lines conducted in 2017 found that the Portuguese Baryonyx specimen had died between the ages of 23 and 25 years and was near its maximum size and skeletal maturity. This contradicts a younger age indicated by non-fused neurocentral sutures, and the presence of both mature and sub-adult features may be due to paedomorphosis, where juvenile traits are maintained into adulthood. Paedomorphic traits may be related to swimming locomotion, as has been suggested in other extinct animals thought to have been aquatic, such as plesiosaurs and temnospondyls. The study also found that the animal had reached sexual maturity at the age of 13 to 15 years, due to a decrease in growth rate at this point.

Paleoecology

During the Early Cretaceous, the primitive Lake Wealden covered most of what is now northern Europe. The floodplains and river deltas that ran through the higher lands of what is now London flowed here. Baryonyx was discovered in these ancient deltas.

The formation of the Weald clay consists of sediments ranging from the Hauterivian, lower Weald clay to the Barremian, upper Weald clay, approximately 130-125 million years old. The holotype ofB. walkeriwas found in the latter, a clay representing non-marine still water, which has been interpreted as a riverine or mud environment with shallow waters, lagoons and swamps. During the early Cretaceous, the Weald area in Surrey, Sussex, Kent was partly covered by the large freshwater to brackish Lake Wealden. Two large rivers drained the northern area, where London is now located, Flowing into the lake through a river delta. The Anglo-Paris basin was in the south. Its climate was subtropical, similar to the current Mediterranean region. Since the Smokejacks pit consists of different stratigraphic levels, the fossil taxa found are not necessarily contemporaneous. Dinosaurs from the locality include the ornithopods Mantellisaurus, Iguanodon, and small sauropods. Other vertebrates include sharks, such as Hybodus, bony fishes, including Scheenstia, crocodiles, and pterosaurs. Members of ten insect orders have been identified, including Valditermes, Archisphex and Pterinoblattina. Other invertebrates include ostracods, isopods, concrustaceans, and bivalves. Plants such as Weichselia and the aquatic herbaceous Bevhalstia were common. Other plants found include ferns, horsetails, lycopodia and conifers.

Charig and Milner presented a possible scenario explaining the taphonomy, changes during fossilization, of the holotype specimen of B. walkeri. The fine-grained sediments around the skeleton, and the fact that the bones were found close and together, elements of the skull and forearm at one end of the excavation area and the pelvis and hindlimb members at the other, indicate that the environment was little disturbed at the time of fossilization and the water currents did not carry the carcass far, possibly because the water was shallow. The area where the specimen died appears to have been suitable for a piscivorous animal. It may have caught fish and swept across the mud flat, getting stuck before dying and ending up buried. Since the bones are well preserved and had no scavenger marks, the carcass appears to have been left intact, suggesting that it was quickly covered by sediment. The disarticulation of the bones may have been the result of the decomposition of the soft tissues. Parts of the skeleton appear to have weathered to different degrees, perhaps because water levels changed or sediments shifted, exposing parts of the skeleton. The shoulder girdle and bones of the forelimbs, the dentary and a rib were broken before fossilization, perhaps by trampling by large animals while they were buried. The orientation of the bones indicates that the corpse was lying on its back, which may explain why all the lower teeth had fallen out of their sockets and some upper teeth were still in place.

Other dinosaurs from the Wessex Formation of the Isle of Wight include the theropods Neovenator, Aristosuchus, Thecocoelurus, Calamospondylus i> and Ornithodesmus, in addition to the spinosaurs Riparovenator and Ceratosuchops. The ornithopods Iguanodon, Hypsilophodon and Valdosaurus; The sauropods Pelorosaurus and Chondrosteosaurus and the ankylosaurian Polacanthus. The Papo Seco Formation of Portugal, where Baryonyx has been identified >, is composed of marl, which represents a lagoon environment. Other dinosaur remains from the area include fragments provisionally assigned to Mantellisaurus, a macronarian sauropod, and a megalosaurid. Most of the bones of the Portuguese specimen ML1190 were damaged, and some scratches may be marks of small scavengers. The disarticulation of the specimen indicates that it was transported from a more terrestrial environment since many bones are missing, but those found were very close together.