<P> The extinct family Sclerorhynchidae resemble sawfish, but they are only known from Cretaceous fossils, and mostly only reached lengths of approximately 1 m (3.3 ft). It has been suggested that sawfish and sclerorhynchids form a clade, the Pristiorajea, while others believe they are not particularly close, making the proposed clade polyphyletic . </P> <P> Sawfish are dull brownish, greyish, greenish or yellowish above, but the shade varies and dark individuals can be almost black . The underside is pale, and typically whitish . </P> <P> The most distinctive feature of sawfish is their saw - like rostrum with a row of whitish teeth (rostal teeth) on either side of it . The rostrum is an extension of the chondrocranium ("skull"), made of cartilage and covered in skin . The rostrum length is typically about one - quarter to one - third of the total length of the fish, but it varies depending on species, and sometimes with age and sex . The rostal teeth are not teeth in the traditional sense, but heavily modified dermal denticles . The rostal teeth grow in size throughout the life of the sawfish and a tooth is not replaced if it is lost . In Pristis sawfish the teeth are found along the entire length of the rostrum, but in adult Anoxypristis there are no teeth on the basal one - quarter of the rostrum (about one - sixth in juvenile Anoxypristis). The number of teeth varies depending on the species and can range from 14 to 37 on each side of the rostrum . It is common for a sawfish to have slightly different tooth counts on each side of its rostrum (difference typically do not surpass three). In some species, females on average have fewer teeth than males . Each tooth is peg - like in Pristis sawfish, and flattened and broadly triangular in Anoxypristis . A combination of features, including fins and rostrum, are typically used to separate the species, but it is possible to do it by the rostrum alone . </P> <P> Sawfish have a strong shark - like body, a flat underside and a flat head . Pristis sawfish have a rough sandpaper - like skin texture because of the covering of dermal denticles, but in Anoxypristis the skin is largely smooth . The mouth and nostrils are placed on the underside of the head . There are about 88--128 small, blunt - edged teeth in the upper jaw of the mouth and about 84--176 in the lower jaw (not to be confused with the teeth on the saw). These are arranged in 10--12 rows on each jaw, and somewhat resemble a cobblestone road . They have small eyes and behind each is a spiracle, which is used to draw water past the gills . The gill slits, five on each side, are placed on the underside of the body near the base of the pectoral fins . The position of the gill openings separates them from the superficially similar, but generally much smaller (up to c. 1.5 m or 5 ft long) sawsharks, where the slits are placed on the side of the neck . Unlike sawfish, sawsharks also have a pair of long barbels on the rostrum ("saw"). </P>

How does a saw fish use its saw
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