Rio Grande cooter
Adults reach 23.5 cm in carapace length. The elongated, oval carapace is dorsally flattened with a slight medial keel and serrate posterior marginals. The pleural scutes are etched by shallow longitudinal grooves. The vertebrals are broader than long, although the 1st may be slightly elongated. Carapace color is olive to greenish brown with a pattern of blotches of alternating yellow and black rings on each scute. The 2nd pleural has a pattern of four distinct blotches of concentric black and yellow rings. A similar blotch of alternating yellow and black lies across each ventral intermarginal seam. Two dark transverse bars mark the bridge of juveniles, but in adults may be confined to the axillary and inguinal areas. The narrow, hingeless plastron has an anal notch. It is yellow with black seam borders in juveniles, but the dark borders fade with maturity, leaving only black gular-humeral and humero-pectoral seam borders in adults. The upper jaw is smooth, lacking a medial notch or flanking tooth-like cusps. The triturating surfaces of both jaws bear a cluster of well-developed denticulations. The skin is green with yellow stripes on the head, neck, limbs and tail. The oval postorbital blotch is a dark-bordered, yellow centered ocellus. The temporal stripe curves dorsally over the postorbital blotch, broadens anteriorly, and ends at the level of the posterior corner of the mouth. A wide sagittal stripe runs from the nape to the tip of the snout, but no prefrontal arrow occurs because supraorbital stripes are absent. A broad Y-shaped stripe is present on the chin.
Males have elongated, thin foreclaws and thicker tails with the vent situated posterior to the carapacial rim. Females are larger, have more vaulted carapaces, and have the anal vent positioned beneath the posterior marginals.
This cooter occurs in the Rio Grande watershed of Texas and northeastern Mexico from Brownsville to the Big Bend north of Del Rio, and in the Pecos River drainage of northwestern Texas and southeastern New Mexico.
No subspecies are recognized, but Ward (1984) discussed clinal variation in head and shell patterns in populations from New Mexico, Texas and Mexico.
In New Mexico, it is principally riverine (Degenhardt et al., 1996); it also lives in turbid pools with soft, muddy bottoms (Degenhardt and Christiansen, 1974).
A 24 cm female collected on 23 May in Eddy County, New Mexico contained nine oviductal eggs, which averaged 42 x 31 mm and hatched after artificial incubation for 70 days (Degenhardt et al., 1996). Four of the hatchlings averaged 33.9 mm in carapace length. On 17 August four naturally incubated muddy hatchlings with caruncles were found in Eddy County that had average carapaces of 37.8 mm. Another recently emerged young was found on 27 October, but some hatchlings overwinter in the nest in New Mexico (Degenhardt et al., 1996).
Pseudemys gorzugi is drawn to traps baited with fresh fish, canned sardines, lettuce, or watermelon (Degenhardt et al., 1996). Faecal masses of New Mexico individuals contained green algae and other plant materials, and fragments of crawfish (Degenhardt et al., 1996). Captive hatchlings will eat dead fish, crawfish, lettuce, spinach, and parts of various wild aquatic plants.
Pseudemys gorzugi is a confirmed basker, and is often observed sitting in the sun on drift wood or rocks.
IUCN Red List Status (1996)
Lower risk: near threatened.