Temporal range: Early Cretaceous, 130–125 Ma
|Restored skeleton, Natural History Museum, London|
Charig & Milner, 1986
|Species:||† B. walkeri|
Charig & Milner, 1986
Baryonyx (//; Greek: βαρύς/barys meaning 'heavy' and ὄνυξ/onyx meaning 'claw' or 'nail') is a genus of carnivorous saurischian dinosaur first discovered in clay pits just south of Dorking, England, and later reported from fossils found in northern Spain and Portugal. It is known to contain only one species, Baryonyx walkeri. Its fossils have been recovered from formations dating from the Hauterivian to early Barremian stages of the early Cretaceous Period, around 130–125 million years ago.
Baryonyx is one of the few known piscivorous (fish-eating) dinosaurs, with specialized adaptations like a long low snout with narrow jaws filled with finely serrated teeth and gaff-hook-like claws to help it hunt its main prey.
Baryonyx was about 2.60–2.75 m (8 ft 6 in–9 ft 0 in) tall, 9.5 m (31 ft) long, and weighed in the region of 1,700–2,700 kg (3,700–6,000 lb). However, analysis of the bones suggests that the most complete specimen was not yet fully grown, so Baryonyx may have grown even larger.
Baryonyx had a large claw on the thumb of each hand, which measured about 25 cm (9.8 in) in a straight line from tip to base. Its long neck was not as strongly S-curved as in many other theropods. The skull was set at an acute angle, not the 90° angle common in similar dinosaurs. The long jaws were distinctly crocodilian and had 96 teeth, about twice as many as Tyrannosaurus. Sixty-four of the teeth were placed in the lower jaw (mandible), and 32 large ones in the upper (maxilla). The teeth had slight keels on their leading and posterior sides, with fine serrations (7 per 1 millimetre (0.039 in)). There was a knob-like protuberance on the nasal bones. The upper jaw had a sharp angle near the snout, a feature seen in crocodiles that helps to prevent prey from escaping. A similar feature is also seen in shrikes.
History of discovery
In January 1983, an amateur fossil hunter named William Walker came across an enormous claw sticking out of the side of a clay pit - Smokejacks Pit at Wallis Wood, Ockley near Dorking in Surrey (United Kingdom). He received some help in retrieving the claw and several other fossil bones from the site. Subsequently he contacted the Natural History Museum in London about his find.
The skeleton was fortunately found to be in a relatively intact state and was excavated by a team led by Alan J. Charig and Angela C. Milner of the Natural History Museum. They published their description of the type species, B. walkeri, in 1986, and named it after Walker. The skeleton can now be seen mounted at the Natural History Museum in London. About 70% of the skeleton was recovered including the skull, enabling paleontologists to make numerous deductions about Baryonyx from just this first specimen.
Some years after the initial discovery in England, a partial skull of Baryonyx was found in the Sala de los Infantes deposit of Burgos Province, Spain. Some of the famous and abundant dinosaur fossil tracks of La Rioja, near Burgos, have been identified as tracks of Baryonyx or another theropod genus very similar to it. Two more claws have been found in the Niger Republic in West Africa, and another in 1996 on the Isle of Wight. In December 1997, a store of old fossils in the Isle of Wight Museum yielded a forearm of a Baryonyx. These remains had apparently been unearthed decades earlier on the southwest coast of the island, and had sat unclassified in a box in Carisbrooke Castle since that time.
Another crocodile-like fish-eater, Suchomimus, was described in 1998, and placed together with Baryonyx in the subfamily Baryonychinae. The Baryonychinae is a subdivision of the family Spinosauridae, which contains other giant Cretaceous forms from Africa and South America, including the genera Spinosaurus and Irritator.
In 2004, paleontologists Hutt and Newbery suggested that Suchomimus tenerensis should be redefined as Baryonyx tenerensis due to new discoveries that showed the vertebrae of Baryonyx were more similar to those of Suchomimus than previously thought.
Additionally, the similarity between Baryonyx and Suchosaurus was noted by Buffetaut in 2007. Remains long attributed to Suchosaurus are now assigned to Baryonyx, and it is difficult to distinguish between remains of these two dinosaurs. Some minor differences do exist, such as ridges on the teeth of Suchosaurus. However, a similar range of variation exists among Baryonyx specimens, and even among various teeth assigned to the related Spinosaurus. Buffetaut suggested that this could mean that either various Baryonyx specimens should be broken up into separate taxa, or that Suchosaurus could be a senior synonym of Baryonyx. Buffetaut noted that if this is the case, the name Baryonyx would be replaced with Suchosaurus, which could be problematic given that the holotype specimen of Suchosaurus is only a single, worn tooth.
The crocodile-like jaws and large number of finely serrated teeth suggested that Baryonyx was a fish-eater. As confirmation, a number of scales and bones from the fish Scheenstia (species previously classified as Lepidotes) were also discovered in the body cavity of the English specimen.
It is speculated that Baryonyx would sit on a riverbank, resting on its front legs, and then sweep fish from the river with its powerful striking claw. This is similar to the modern grizzly bear.
Until the discovery of the closely related Suchomimus, Baryonyx was the only known piscivorous (fish-eating) dinosaur. On the other hand, bones of the ornithopod dinosaur Iguanodon were also found in association with the Baryonyx skeleton. A 2013 study found that the jaws of Baryonyx had stronger resistance to bending and torsion than those of Spinosaurus.
During the early Cretaceous, Wealden Lake covered the majority of what is now northern Europe. Alluvial plains and deltas spread from the uplands surrounding the area where London now stands and eventually ran into this great lake. Baryonyx was discovered in these former deltas. 
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