The wolverine frog (Trichobatrachus robustus) is a frog in the family Arthroleptidae endemic to Africa. Its name "wolverine frog" is due to its ability to create a claw out of its bones. The other names of this frog include the horror frog and hairy frog (due to breeding males bearing hair-like structures on the body and thighs).
It is monotypic within its genus, i.e., it is the only species within its genus, Trichobatrachus.
Physical Description & Diet
The wolverine frog has a broad head. The males measure 10-13 cm, and the females measure 8-11 cm in length from snout to vent.
The adult wolverine frog feeds on slugs, spiders, grasshoppers, beetles, and myriapods.
Habitat and Geographic Distribution
The wolverine frog is endemic to Africa and is found in Angola, Cameroon, The Democratic Republic of the Congo, Equatorial Guinea, Gabon, and Nigeria.
The natural habitat of the wolverine frog includes fast-flowing rivers, forests, and arable lands.
The Peculiar Features: "HAIRS" & CLAWS
"HAIRS"
The male wolverine frog bear "hairs" on its thighs and along the sides. It develops these "hairs" during the breeding season. These "hairs" are not true hairs. Instead, these structures are known as dermal papillae.
What is the purpose of developing these dermal papillae?
The male wolverine develops dermal papillae during the breeding season. It is believed that these hair-like dermal papillae contain arteries and increase the surface area to enhance the process of cutaneous respiration (respiration through the skin).
Why does the male wolverine frog need these dermal papillae?
It is known that frogs exhibit external fertilization. So, during the breeding season, the female lays eggs in the water. The male fertilizes it and guards it for a long period. During this time, the male wolverine frog cannot use its lungs for respiration. So, it uses cutaneous respiration (respiration through the skin) and the dermal papillae enhance the uptake of oxygen.
CLAWS
One of the notable features of the wolverine frog is its claws on the hind feet which can be exposed through the skin when needed. The claws are present on the toes II-V of the hind feet.
Even though they are called claws, they are not true claws as they are not made of keratin. These claws are actually finger bones (specifically the distal phalanges) of the frog which pierce through the skin to become a functional claw.
How does the wolverine frog break its bones to make claws?
To understand the mechanism behind the exposure and retraction of these claws, one must know the anatomy of the wolverine frog's finger bones first. Click here to see the claw anatomy.
The terminal phalanx of the wolverine frog is attached to a bony nodule with the help of collagen-rich tissue. Below this site of attachment, both structures are surrounded by dense but collagen-poor tissue.
Located at the opposite end of the point of the attachment of the terminal phalanx and the bony nodule, is present a flexor tendon. It is the activation of this flexor tendon that breaks the connection between the phalanx and the bony nodule resulting in the exposure of the claw through the skin and the formation of a claw.
The mechanism of exposure of the claws is known and the exposure is said to take place due to the action of the flexor muscles. The mechanism of retraction of the claws is still unclear. It is not known whether the retraction is active, passive, or a combination of both.
What is the purpose of these claws?
The wolverine frog's claws play a role in defense. This claim was raised by Durrell who provided the first report of handling live wolverine frogs and raised the possibility of their claws' role in defense.
Durrell's claim is verified by the local tribe of Cameroon who use long spears and machetes to kill wolverine frogs without handling them.
Prior to Durrell's claim, G. Kinsley Noble speculated that these small claws provided a better grip on a surface before leaping.
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