Field guide

Learn about tortoises

Everything we keep coming back to while raising Shelldon — sex differences, the world's species, what a tortoise looks like underneath, and how to read what a shell is telling you.

Male vs female: how to tell

Tortoise sex is read from the back end of the animal, not the head. None of these signs are reliable in hatchlings — you usually need a juvenile that's been growing steadily for a few years before the differences are obvious.

TraitMaleFemale
Plastron (underside)Concave — scooped inward so he can sit on top of the female during mating.Flat or slightly convex — gives more room for carrying eggs.
TailLong, thick, often tucked sideways under the shell. Vent (cloaca) sits past the edge of the carapace.Short and stubby. Vent sits at or inside the edge of the carapace.
Anal scutesWider V-shaped notch at the back of the plastron to let the tail swing.Narrower, more closed notch.
SizeSmaller in most species (yellow-foot, red-foot, Russian, Greek).Larger overall in those same species — opposite of Sulcatas and leopards, where males are bigger.
BehaviorMore territorial. Head-bobs, ramming, mounting attempts once mature.Generally calmer; digs nesting pits when gravid.
Reliable age to sexUsually 4–6 years / palm-sized; earlier in fast growers.Same window — hatchlings cannot be reliably sexed by eye.

Note on temperature-dependent sex: in most tortoises, incubation temperature decides the hatchling's sex. Warmer eggs (~31–32 °C) usually produce females; cooler eggs (~27–28 °C) usually produce males.

Tortoises of the world

There are roughly 50 recognized tortoise species spread across every continent except Australia and Antarctica. These are the ones you're most likely to read about — wild, in captivity, or in conservation news.

The underside (plastron)

A tortoise's underside is called the plastron. It's the second half of the shell — fused to the upper dome (the carapace) by a bony bridge on each side. The plastron is made of paired scutes, and once you can name them, sexing and health checks get a lot easier. Tap a region to inspect it.

gularhumeralpectoralabdominalfemoralanalGularHumeralPectoralAbdominalFemoralAnalBridge
Plastron viewed from below. Each named region is a pair of scutes, left and right.

Abdominal

The largest pair — middle of the belly. Where you'll see the male's concave dish most clearly.

Reading the shell

A tortoise's shell is a living record of how it's been kept. Growth rate, humidity, diet, lighting, and injury all leave marks. Tap a concept to see it on the shell.

HEADTAIL
Top-down view of a tortoise carapace. Vertebral scutes down the center, costal scutes flanking them, marginal scutes around the rim.

Growth rings

The concentric ridges inside each scute are growth bands — new keratin laid down as the tortoise grows. They're not annual like tree rings: a fast-growing hatchling can lay down several in a year, an adult might add almost none. Wide, evenly spaced rings = steady growth. Cramped, irregular rings = stop-start growth (often diet or temperature swings).

None of this replaces a reptile vet. Use it to know when something looks off, then get a professional opinion — especially for shell rot, MBD, or any crack.