page_title: Baryonyx
section_title: Postcranial skeleton
hierarchical_section_title: Baryonyx / Description / Postcranial skeleton
caption_attribution_description: Neck reconstructions of Sigilmassasaurus and Baryonyx. (A) Sigilmassasaurus; (B) Baryonyx. Scale bar equals 10 cm. Scale bar only applies to Baryonyx, for which associated material is preserved. Reconstructions are based on the holotype material for Baryonyx, and material discussed in this paper for Sigilmassasaurus. Note that the first vertebra depicted is the C2 (axis), and that reconstruction includes anterior dorsal vertebrae.
context_page_description: 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 Weald Clay Formation of Surrey, England, 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 its discovery attracted media attention. Specimens later discovered in other parts of the United Kingdom and Iberia have also been assigned to the genus.
  The holotype specimen, which may not have been fully grown, was estimated to have been between 7.5 and 10 metres long and to have weighed between 1.2 and 1.7 metric 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.
context_section_description: Initially thought to have lacked the sigmoid curve typical of theropods, the neck of Baryonyx does appear to have formed an S shape, though straighter than in other theropods. 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.
  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 deltopectoral crest and muscle attachment and the lower for articulation with the radius and ulna. The radius was short, stout and straight, and less than half the length of the humerus, while the ulna was a little longer. The ulna had a powerful olecranon and an expanded lower end. The hands had three fingers; the first finger bore a large claw measuring about 31 cm (12 in) along its curve in the holotype specimen. The claw would have been lengthened by a keratin (horny) sheath in life. Apart from its size, the claw's proportions were fairly typical of a theropod, i.e. it was bilaterally symmetric, slightly compressed, smoothly rounded, and sharply pointed. A groove for the sheath ran along the length of the claw. The other claws of the hand were much smaller. The ilium (main hip bone) of the pelvis had a prominent supracetabular crest, an anterior process that was slender and vertically expanded, and a posterior process that was long and straight. The ilium also had a prominent brevis shelf and a deep grove that faced downwards. The acetabulum (the socket for the femur) was long from front to back. The ischium (lower and rearmost hip bone) had a well developed obturator process at the upper part. The margin of the pubic blade at the lower end was turned outward, and the pubic foot was not expanded. The femur lacked a groove on the fibular condyle, and, uniquely among spinosaurids, the fibula had a very shallow fibular fossa (depression).
caption: Reconstructed necks of the spinosaurids Sigilmassasaurus (A) and Baryonyx (B), showing their curvature
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