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The upper jaw, or maxilla [12] [13] is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible (lower jaw), which is also a fusion of two halves at the mandibular symphysis. In bony fish, the maxilla is called the "upper maxilla," with the mandible being the "lower maxilla".
The body is kite-shaped with a long, thorny tail. The back is covered in numerous thorny spines, as is the underside in older females. [2] [4] Adult fish can grow to 1 metre (3.3 ft) in length, although most are less than 85 centimetres (33 in). This ray can weigh from 4.5 to 8.75 lb (2 to 4 kg). [5]
In all jawed fish (gnathostomes), the first arch pair (mandibular arches) develops into the jaw, the second gill arches (the hyoid arches) develop into the hyomandibular complex (which supports the back of the jaw and the front of the gill series), and the remaining posterior arches (simply called branchial arches) support the gills.
Oplegnathus punctatus, commonly known as the spotted knifejaw, is one of seven species in the Oplegnathidae family of knifejaws. These perciform fish, an order of ray-finned fish that are "perch-like", characteristically have teeth fused into a parrot-like beak during adulthood.
The Osteostraci (bony armored jawless fish) are generally considered the sister taxon of Gnathostomata. [3] [9] [10] Jaw development in vertebrates is likely a product of the supporting gill arches. This development would help push water into the mouth by the movement of the jaw, so that it would pass over the gills for gas exchange.
The lower jaw and maxilla are then pulled back to close the mouth, and the fish is able to grasp the prey. By contrast, mere closure of the jaws would risk pushing food out of the mouth. By contrast, mere closure of the jaws would risk pushing food out of the mouth.
Extant fish with crushing teeth, such as wolf eels and horn sharks, generally have such teeth at the front of the jaw, separate from the coronoids. Although Megamastax differs from these fish by having its teeth and coronoids run the entire length of the jaw, this could simply be a result of having a different method of prey capture. [ 1 ]
Jawless fish and sharks only possess a cartilaginous endocranium, with the upper and lower jaws of cartilaginous fish being separate elements not attached to the skull. Bony fishes have additional dermal bone, forming a more or less coherent skull roof in lungfish and holost fish. The lower jaw defines a chin.