North America’s most widespread turtle, fifteen million years old
Chrysemys picta ranks as the native turtle found across more of North America than any other, with an evolutionary story about fifteen million years deep. Adults span roughly thirteen to twenty-five centimetres, males smaller, shells dark and smooth with colourful limb stripes.
The genus name joins Greek words for gold and freshwater tortoise, and picta is Latin for coloured. Johann Gottlob Schneider first described the animal in 1783 as Testudo picta, and John Edward Gray moved it to Chrysemys in 1855. Chrysemys holds just two species, since the southern painted turtle is now usually treated as separate. The remaining subspecies, eastern, midland and western, are thought to have diverged when ice-age populations were cut off from one another between about 100,000 and 11,000 years ago, and they still interbreed where their ranges meet.
Each looks slightly different. The eastern form is the only North American turtle whose upper-shell plates line up in straight rows across the back, the midland carries a dark smudge in the centre of its lower shell, and the western, the largest at up to about 26.6 centimetres, has a red-tinged blotch spreading across its underside. All share a yellow-striped face with a large spot behind each eye and a notched upper jaw with a small tooth-like point on either side. Females average about 500 grams, males around 300.
The oldest fossils, dug up in Nebraska, are about 15 million years old; for the next ten million years the species appears only around Nebraska and Kansas, but remains younger than 300,000 years turn up across most of the United States and southern Canada. Its genome, with 50 chromosomes, was among the first two reptile genomes chosen for sequencing, reaching a draft assembly in 2010.
Needing outside heat, it basks for hours on logs and rocks by day and spends winter in the mud beneath the water. An antifreeze-like compound in its blood lets it endure freezing for long stretches. Eggs and hatchlings fall to rodents, snakes and wild canines, and adults to foxes, raccoons, coyotes and otters, yet a wild painted turtle can pass 55 years, and tolerance of disturbed land keeps it North America’s most abundant turtle.
Source: Painted turtle
