On first look, the blue whale and the chevrotain (with the common name mouse-deer) couldn't be more different.
As well as obvious distinctions in appearance and size, one is found within the icy depths of the oceans, whereas the other is found in the forests of southeast Asia and India, and in parts of Africa.
But both creatures are ungulates. Stuart Blackman explains what ungulates are, and why it makes these two creatures more closely linked than previously thought.
What is an ungulate?
In common parlance, an ungulate is a hoofed mammal. Cattle, deer, antelopes, sheep, pigs, horses and tapirs have all transformed their toenails into hooves. In zoological terms, though, the group also includes hippos, camels and rhinos, which lack hooves, and others that don’t even have legs.
What are the characteristics of an ungulate?
The vast majority of ungulates are vegetarian. Many possess complex digestive systems, including multiple stomachs that contain symbiotic microbes that help them break down tough plant material, and are adorned with defensive horns or antlers.
What is the common ancestor of the ungulate?
Ungulates share a common ancestor that was pottering around 50-odd million years ago on conventional five-toed feet: the Condylarthra group. Its descendants, though, have lost some of those toes. Cattle, deer, antelope, hippos, camels, giraffes, sheep and pigs, known as even-toed ungulates, or artiodacts, have two or four toes on each foot. Horses, rhinos and tapirs are odd-toed ungulates, or perissodacts, with one or three toes per foot.
What is the biggest ungulate?
The biggest animal ever to have existed – the blue whale – is an ungulate. Whales and dolphins might have replaced their legs with flippers and become strictly carnivorous, but their closest living relative is the hippopotamus, which means they sit squarely on the ungulate branch of the evolutionary tree.
What is the smallest ungulate?
The smallest ungulate is the chevrotain – or the mouse-deer. There are 10 species of chevrotain, with the Malay mouse-deer measuring around 75cm (29 inches) long; their tail adds another 9cm (3.5 inches).
Despite their common name, mouse-deer aren't related to deer or rodents, but instead part of its own unique family. Chevrotain are ruminants, like cows, which means they have four stomachs. It also has tiny tusk-like incisors, or 'fangs', which are thought to be used in place of horns or antlers.
In 2007, researchers identified a small deer-like animal as the oldest ancestor of modern whales. Indohyus was a wading creature that spent much of its time in water, and its later ancestors evolved into whales after taking to the water to avoid predators: the mouse-deer employs a similar technique today.
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