(Troost, in Harlan, 1835)
Alligator snapping turtle
The large, rough, dark-brown or dark-gray carapace is strongly serrated posteriorly, and has three rather high, persistent keels. Knobs on the keels are elevated and somewhat curved posteriorly. Vertebrals are broader than long, and there is a short, broad cervical. Beneath the vertebrals is a series of 6-9, usually hexagonal neurals and a suprapygal. The pygal bone may be medially divided. Costals 1-8 are reduced laterally, leaving small fontanelles between them in juveniles (absent in adults) and the 11 peripherals on that side. A row of three to eight supramarginal scutes (usually three) occurs between the marginals and the first three pleurals on each side. There are 23 marginals. The bridge is small, and the hingeless, gray to mottled plastron is reduced, giving a cross-shaped appearance. It has a T-shaped entoplastron and a median fontanelle. Abdominals are reduced, do not usually meet at the midline, and are separated from the marginal scutes by a series of inframarginal scutes. The plastral formula is: fem >< pect > an > hum > gul > abd. The head is large with a pointed snout, a strongly hooked upper jaw, and large, lateral orbits. There is little emargination of the temporal region; the squamosal bone contacts the long postorbital but not the parietal. The maxilla does not touch the quadratojugal; the quadrate bone completely surrounds the stapes. The prootic bone forms little of the roof of the internal carotid canal, which continues within the pterygoid bone. No secondary palate is present, and there is only a weak medial ridge on the ventral surface of the vomer. There are numerous dermal projections on the side of the head and on the chin and neck. The jaws are powerful, but lack medial ridges on the premaxilla or maxilla. There is a wormlike process on the tongue, attached approximately at its center to a rounded muscular base, leaving both ends freely movable. In the young, each end of this elongate process may bear a small branch, but in larger specimens the ends are entire. Skin is dark brown to gray above and lighter below; there may be darker blotches on the head. The tail is about as long as the carapace and has three rows of low tubercles above and numerous small scales below.
The diploid chromosome number is 52: 24 macrochromosomes (14 metacentric or submetacentric and 10 telocentric or subtelocentric; the third pair lacks the conspicuous short arm, secondary constriction and telocentric condition found in Chelydra), 26 microchromosomes, and a large metacentric chromosome pair unique to Macroclemys (Killebrew, 1977b, Haiduk and Bickham, 1982).
Males have longer preanal tail lengths than females, and have the vent posterior to the carapacial rim.
Macroclemys ranges south in the Mississippi Valley from Kansas, Iowa, and southern Illinois to the Gulf and on the coastal plain from southeastern Georgia and northern Florida to east Texas.
The alligator snapper occurs most frequently in the deep water of rivers, canals, lakes, and oxbows. It has also been found in swamp bayous and ponds that are situated near deeper running water, and it sometimes enters brackish coastal waters. Mud bottoms and abundant aquatic vegetation usually are present.
The smallest mature male found by Dobie (1971) had a 39 cm carapace. Testes of males collected in Louisiana from March to July and in December contained viable sperm (Dobie, 1971). Ovaries of Louisiana females collected from mid-April to late July by Dobie (1971) showed that follicles reach ovulation diameter (20-31 mm) in December and are present in postovulated females in May. Dobie could find no evidence of more than on clutch being laid per year.
Mating in the wild occurs in February, March, and April in Florida but probably occurs later in the Mississippi Valley (April to mid-June in Missouri; Nickerson, in Pritchard, 1989; October in Oklahoma, Grimpe, 1987). The most complete description of the courtship and mating behavior of M. temminckii was made from captives in northeastern Louisiana by Harrel et al. (1996). Adult males and females were kept separated for six months before being placed together in the same tank on 10 March. The first mating was observed that same day. Matings occurred underwater near or on the bottom of the tank. The male first pursued the female and sniffed her nose, bridge and base of tail, in that order. When satisfied the other turtle was a female, he positioning himself on top of the female with his plastron resting on her carapace. His forefeet were positioned at the level of her bridge, while his hindfeet grasped the rear marginals of her carapace. In this way he could control the movements of the female. He wrapped his tail beneath that of the female, which was horizontal and positioned slightly to her right. The male bent his head downward and frequently pushed his nose into the back of the female's neck and positioned his head so that his chin rested on top of her head. Both turtles rocked side to side while the male bit the back of the female's neck. The male's tail was thrust upward until intromission was accomplished. The female bit aggressively at him at this point. When the female moved slightly, the male released his forefeet and floated vertically in a rigid position, held in place by his hindfeet. Coitus lasted six minutes (Allen and Neill, 1950, reported copulations of 5-25 minutes). A dominance system was set up among the males, and females occasionally behaved as if possibly courting of a male by approaching him from the rear and smelling about his cloacal vent. Mating activity decreased approximately 72 hours after the two sexes were brought together, but such behavior was noted as late as 16 March. Other behaviors by males included bubble explosion from the nose and combat.
The nesting season in Florida and Georgia extends from April to June (Allen and Neill, 1950; Ewert, 1976; Powders, 1978), and Louisiana females contain shelled eggs as early as April (Dobie, 1971). Nesting is diurnal, and the nest cavity may be either flask or funnel shaped, and over 70 m from the nearest water. The female constructs a body pit before actually digging the nest proper. Nest chambers measured by Ewert (1976) were 28.0-39.0 cm deep and 15.0-25.5 cm wide.
Eggs are nearly spherical (diameter 30-51 mm) and have a hard, unglazed shell. Clutches vary from 8 to 52 eggs. Natural incubation may last from 100 to 140 days, and most young emerge in September or October.
The hatchling (35.5-45.0 mm) is brown, with a roughened carapace and a long, slender tail. Its head is covered with elaborate papillae, and the eye is ringed with conical tubercles. The dark skin may show some lighter mottling. The jaws are long, relatively narrow, and pointed at the tip. The inside of the mouth is light gray brown with black mottling.
The diet of Macroclemys is quite varied, it probably feeds on any animal it can capture and subdue: leeches, snails, freshwater mussels, crayfish, crabs, salamanders, fish, turtles, snakes, small alligators, water fowl, and small mammals (Pritchard, 1989; Ernst et al., 1994; Sloan et al., 1996). Harrel and Stringer (1997) identified the otoliths of six genera of teleost fish (Dorosoma, Lapillus, Centrarchus, Lepomis, Micropterus, Pomoxis), plus unidentified otoliths from several others, in the scats of Louisiana Macroclemys. Sloan et al. (1996) found fish remains in over 72% of the stomachs they examined, and 36% of their males had eaten turtles. Plant material has also been found in its stomach: wood, acorns, pecan nuts, hickory nuts, plant tubers, briar roots, wild grapes, tupelo fruit, palmetto fruits, persimmons (Ernst et al., 1994; Sloan et al, 1996). Sloan et al. (1996) found wood in 54% of male stomachs and 65% of female stomachs; 52% of the females had eaten acorns. Carr (1952) suggested that Macroclemys forages actively by night and reserves the use of the "worm" to provide an occasional fish during the more passive daytime period. The "worm"—gray at rest but suffused with blood when active—is the double-ended movable process on the tongue. Captives have been seen to open the jaws, wriggle the process, and lure fish into the mouth.
IUCN Red List Status (1996)
Vulnerable (A1cd). Pritchard (1989) has prepared a book on the species that covers its status, general biology and conservation recommendations. A major decline in numbers occurred as a result of a collection by trappers paid by one of the major soup manufacturing companies in the United States (Pritchard, 1989), but still is taking place at an alarming rate (Sloan and Lovich, 1995).