Turtle Frog

AmphibianAustralia

Feb 15

Myobatrachus gouldii

The turtle frog of Western Australia uses its short but muscular front arms — rather than back legs like most frogs do — to dig more than a metre (>3.3 ft) beneath the soil. Adapted to semi-arid habitats far from water, its tadpoles develop inside their eggs and hatch as tiny frogs.

Look, there's no way around this. The turtle frog looks like a muscular scrotum with legs. The colour of its wrinkly skin covers the spectrum of our own, from pale pink to yellowish to dark brown. Its body is rotund and flattened, like a fat burger patty. Its head is a lump-like growth with beady black eyes. On the end of its flattened snout are a pair of near-invisible nostrils and, above its considerable jowls, is its thin line of a mouth. Flanking its tumorous head are the arms of a roided-up strongman, ending in thick, meaty fingers. The turtle frog is named for its superficial resemblance to a turtle sans shell, but I think that's being too harsh on naked chelonians.¹

The Exceptional Turtle Frog

The turtle frog lives around the city of Perth, between the Geraldton and the Fitzgerald Rivers, in semi-arid areas of sandy soils. The hot and dry lands of Western Australia seem a silly place for a frog to live. The blazing sun desiccates sensitive skin and bodies of water are few and far between. But where there is a niche to fill, some aberrant animal will find a way to fill it — even if it means looking like a nut sack.

Most frogs must return to the water (or remain in it) for three reasons. One is to find food, with insects often most plentiful in moist places. The turtle frog eschews aquatic dining for a more terrestrial fare in the form of termites, their colonies and great mounds serving as its waddle-in restaurants. Frogs must also maintain a strict skin moisturizing routine — another reason to be near water — since without moisture, their sensitive skin quickly dries up. For more terrestrially-adapted animals, like us, this might not be the end of the world, but for frogs, who exchange oxygen directly through their skin, it would be akin to one of our lungs drying up and ceasing to function.²

How does the turtle frog survive the searing sun and summer temperatures of up to 40°C (104°F)? It burrows beneath the ground. This in itself isn't all that exceptional. Several anuran species burrow; from the horned frogs of South America, to the spadefoot toads of North America and Europe, to the tomato frog of Madagascar, and quite a few species in Australia — from the giant burrowing toad, to the ornate, painted, and striped. What is exceptional is the turtle frog's digging technique. Most burrowing frogs scoop up dirt using their large, hind feet like shovels — or sharp "spades" of bone, in the case of spadefoots — but the turtle frog's hind limbs are relatively underdeveloped (it doesn't hop, it waddles), so instead, it uses its bulldozer arms to burrow into the ground head first.³ And it keeps digging until it reaches a depth of up to 1.2 metres (3.9 ft) below the surface, where the sun can't touch it and the sand is moist.

This deep burrow is partly how the turtle frog circumvents its last, and perhaps most inescapable, need for water. Frog eggs, even more so than frogs themselves, are prone to drying out and so must be kept in a constant state of moisture. The simple solution is to simply lay them in water, and many frogs do. But other, more terrestrial frogs have found a way around this, either by producing a frothy white mass that surrounds their eggs or, like the turtle frog, creating an incubation chamber that is cool and moist. Down in the depths of its burrow, a tiny, 5-centimetre (2 in) turtle frog mother lays as many as 50 eggs, each measuring up to 7.5 mm (0.3 in) in diameter — the largest eggs of any frog in Australia.

Following heavy summer rains, when the sand is at its wettest, male turtle frogs emerge en mass (or sometimes just poke their heads above the surface) to croak for mates. Most frogs breed either in or near bodies of water. This makes logical sense; once the deed has been done, and the female frog is fertilized, she can lay her mass of eggs directly into the water or on some vegetation just above it.⁴ Whatever body of water she's chosen — whether the edge of a vast lake or a tiny pool inside a leaf — will eventually become an aquatic nursery. The eggs hatch into tadpoles that are fully aquatic until they metamorphose into adults which, depending on the species, can take fewer than two weeks or as long as two years (on average around 3 months). All that time they're bound to, and reliant upon, the water into which they hatched.

Turtle frogs, as you may have come to expect by now, do things differently. Once a pair of turtle frogs have mated, they retire to their burrow and the female lays her eggs in moist sands where they're safe from drying out. But what next? What happens when the eggs hatch into a bunch of limbless, lungless tadpoles? The answer is, they don't. Turtle frogs go through their entire larval stage and metamorphosis — from tadpole to four-limbed, tailless, air-breathing frog — inside their eggs, and emerge as tiny, but fully formed frogs. Through this embryological trick, the turtle frog never has to search for a puddle or lake and neither its eggs nor tadpoles are exposed to the dangers — the aquatic insects, fish and other frogs — that lurk within the water. The turtle frog's entire life cycle can begin and end among the sands.

Fossorial Frogs

A southern sandhill frog (*Arenophryne xiphorhyncha*).

The turtle frog belongs to a family called the Myobatrachidae, alternatively known as Australian water frogs — since many do live in or around water, such as the stream-dwelling torrent frogs — as well as Australian ground frogs — because a few, like the turtle frog, lead fossorial lives. The sandhill frogs (2 species) burrow beneath the ground, doing so head first, their front limbs shovelling — the only frogs, along with the turtle frog, that do so. And like the turtle frog, their eggs hatch not as tadpoles, but as miniature versions of adult frogs. Apart from burrowing and hatching fully formed, these frogs have another thing in common; they're all exceptionally rotund, belying the common sense assumption that a sleek body is the best body for burrowing. The sandhill frogs are even alternatively known as Australian dumpy frogs, which is a bit uncalled for, but not inaccurate. The turtle frog may be a little weird, but at least it's not weird alone.

¹ There isn't really such a thing as a naked turtle — not "naked" in the sense of being shell-less at least. A turtle's shell isn't an outfit it can slip in and out as seen in cartoons, or a portable shelter like those of hermit crabs (who exchange their shell-homes as they grow larger), but a permanent part of the turtle's body that grows along with it. The shell has two parts which sandwich all the turtle's organs between them; there is the flat plastron at the bottom and the domed carapace at the top, joined together by a structure called the bridge where they meet. Both the plastron and carapace are made of an underlying structure of bone and covered by a layer of interlocking scutes (those geometric plates) made of keratin — the same protein that forms our nails, hair, and outer skin. The bony under-layer of the carapace is primarily formed from the turtle’s vertebrae and ribs, which have expanded, flattened, and fused with dermal bone to create the iconic dome shape. So removing a turtle's shell is less analogous to someone undressing and more like them ripping out much of their internal skeleton.

There are, however, a few aberrant turtles with unusual shells. Take the leatherback sea turtle — the largest of all living turtles — which lacks a bony shell and instead has a carapace of flexible, leathery skin, strengthened by thousands of tiny bone plates underneath known as osteoderms. Softshell turtles (a family of freshwater turtles) have a visible layer of solid bone at the centre of their carapace, but the outer edges are leather-like and pliable. Needless to say, for these turtles, "undressing" isn't an option either.

You can learn more about flexible turtle shells from the Chinese softshell turtle!

² They may not be born with them, but frogs still have lungs which they use to breathe. And although a large portion of a frog's respiration happens through its permeable skin (known as cutaneous respiration), if a frog's lungs fill with water, it can still drown — it can also drown if the water it's immersed in lacks sufficient oxygen for "skin breathing".

³ Somewhat ironically, the turtle frog doesn't dig like most turtles. When it comes time to lay their eggs, turtles (such as sea turtles and snapping turtles) use their hind flippers to dig nests and, once they lay their eggs, to refill and flatten them. Burrowing tortoises, on the other hand (like the gopher tortoise), do use their forefeet to dig, so perhaps it would be more accurate to call it a tortoise frog.

⁴ A Western Australian neighbour to the turtle frog, the moaning frog is likewise a dweller of semi-arid lands and it too lays its eggs at the bottom of a moist burrow, but unlike the turtle frog, its eggs hatch as fully aquatic tadpoles. You can learn more about it here!

**Where Does It Live?**

⛰️ Semi-arid and sandy areas, often far from any bodies of water.
📍 Western Australia; between the Geraldton and the Fitzgerald Rivers.

‘Least Concern’ as of 18 May, 2021.

IUCN

Size // Tiny
Length // Up to 5 cm (2 in)
Weight // N/A
Activity: Nocturnal 🌙
Lifestyle: Solitary 👤
Lifespan: N/A
Diet: Carnivore (Insectivore)
Favorite Food: Ants and termites 🐜
Class: Amphibia
Order: Anura
Family: Myobatrachidae
Genus: Myobatrachus
Species: M. gouldii

The turtle frog looks big and buff in close-up shots — in reality, it only grows to be 5 centimetres (2 in) long.
This species is named for its resemblance to a shell-less turtle (or at least what a turtle would perhaps look like if it could be separated from its shell).
This frog is from Western Australia, where it lives in semi-arid and sandy habitats, often far from any bodies of water.
It survives by digging beneath the ground, but unlike most frogs (and turtles) — who use their hind limbs to scoop up soil — the turtle frog uses its roided-up front arms to reach a depth of up to 1.2 metres (3.9 ft), where the sun can't touch it and the sand is moist.
Down in its burrow, this tiny frog lays as many as 50 eggs, each measuring up to 7.5 mm (0.3 in) in diameter — the largest eggs of any frog in Australia.
The turtle frog goes through its entire larval stage and metamorphosis — from tadpole to four-limbed, tailless, air-breathing frog — inside its egg, and emerges as a tiny, but fully formed frog. As a result, and unlike the vast majority of anurans, the turtle frog never has to enter water.
Close relatives of the turtle frog include the sandhill frogs; two species that also burrow with their front limbs, undergo their tadpole stage within the egg, and are equally rotund.