Amphibians
Pumpkin Toadlet
Brachycephalus ephippium · also called pumpkin toadlet, saddleback toad
The pumpkin toadlet is barely the size of a thumbnail, blazing orange, poisonous, and so small that its inner-ear balance organs have stopped working — it physically cannot land a jump, tumbling through the air and crash-landing every time. Its bones glow blue-green under ultraviolet light.
Overview
Pumpkin toadlets live in the leaf litter of Brazil’s Atlantic Forest, in the mountains of the southeast. Just 1–2 cm long, among the smallest vertebrates on Earth, they are bright pumpkin-orange and hunt springtails, mites, and tiny insects.
Too small to land
Its inner-ear balance canals are the smallest of any adult vertebrate, too small to sense the spin of a jump, so it tumbles through the air and crash-lands every time.
Glowing bones, toxic skin
Patches of bone fluoresce blue-green under UV light through its thin skin, and its skin carries tetrodotoxin, the pufferfish poison, advertised by its bright orange warning colour.
Status
The pumpkin toadlet is Least Concern, locally common but confined to the highly fragmented Atlantic Forest.
Pumpkin Toadlet: common questions
Why can't the pumpkin toadlet land properly when it jumps?
Research using high-speed video has shown that when a pumpkin toadlet leaps, it launches reasonably well but then loses all control in the air, spinning and tumbling before crash-landing on its back, side, or head rather than touching down on its feet as most frogs do. The cause is its extreme small size, because the semicircular canals of its inner ear, the fluid-filled loops that detect rotation and allow an animal to sense and correct its orientation, are the smallest known of any adult vertebrate and are simply too small to register the rapid spinning of a jump accurately. Since the toadlet is tiny and light, these hard landings do not injure it, and it relies more on walking and its toxic defences than on jumping to escape.
Why do the pumpkin toadlet's bones glow?
Certain bones in the toadlet's skull and back contain compounds that fluoresce, absorbing ultraviolet light and re-emitting it as a bright blue-green glow, and because the toadlet's skin over these areas is unusually thin and somewhat translucent, the glowing bone pattern shows through to the outside. Scientists are still investigating the exact function, but leading ideas are that the fluorescent pattern may be visible to potential mates or rivals, possibly supplementing the toadlet's poor hearing as a communication signal, or that it may play a role alongside the bright orange colour in signalling to predators.
Is the pumpkin toadlet poisonous?
Yes. Its skin and internal organs contain tetrodotoxin, the same extremely potent neurotoxin found in pufferfish and blue-ringed octopuses, which blocks nerve signalling and can be dangerous or lethal to an animal that eats enough of it. The toadlet does not deliver this toxin through a bite or sting, it is purely a defence against being eaten, and its brilliant, highly visible pumpkin-orange colouring functions as aposematism, a warning signal that advertises its toxicity so that predators learn to leave it alone rather than testing it.
How does the pumpkin toadlet reproduce without a tadpole stage?
Rather than laying eggs in water that hatch into swimming tadpoles, the pumpkin toadlet lays a very small clutch of relatively large eggs directly onto the damp leaf litter or moss of the rainforest floor, where the entire larval development takes place inside the egg. What eventually hatches is a fully formed, miniature version of the adult toadlet, ready to walk and hunt immediately, a reproductive strategy called direct development that frees the species from any dependence on standing water and is common among small frogs living in consistently moist forest environments.