Hoofed creatures like horses and rhinos evolved from a strange sheep-sized animal that looked like a cross between a pig and a dog, researchers claim.
Experts from Johns Hopkins University discovered the remains of the strange creature in Indian and say it dates back about 55 million years.
Named Cambaytherium, it is the direct ancestor of a specific group of hoofed mammals called perissodactyls – that included rhinoceroses and tapirs.
Also known as odd-toed ungulates, perissodactyls had five toes, weighed about four stone, and suddenly appeared 10 million years after the demise of the dinosaurs.
Lead author Professor Ken Rose said the geographic source of hoofed mammal precursor species have remained a mystery until now.
The finding is the culmination of 15 years of work by the international team of researchers and involved piecing together the complete skeletal anatomy of Cambaytherium from over 350 fossils unearthed throughout India.
Life reconstruction of Cambaytherium. Experts from Johns Hopkins University discovered the remains of the strange creature in Indian and say it dates back about 55 million years
The team searches for fossils of Cambaytherium in Tadkeshwar Mine, Gujarat, India. These new creatures then wandered onto other continents once the land connection between India – once an island – and Asia formed
Rose said the discovery of the creature in this new study provides a window into what a common ancestor of all Perissodactyla would have looked like.
It was a moderately good runner and displayed features that were a combination of perissodactyls and their more generalised mammal forerunners.
Comparing its bones with many other living and extinct mammals, showed Cambaytherium was more primitive than any known perissodactyl.
Cambaytherium, first described in 2005, is the most primitive member of an extinct group that branched off just before the evolution of perissodactyls.
The results confirm a theory first proposed 30 years ago that the origin of horses can be traced to India during its northward drift from Madagascar.
The first horses were smaller than a dog and they gradually dispersed to other continents – including Europe and the US when India slammed into Asia.
Armed with the hypothesis, Rose and colleagues obtained funding from The National Geographic Society to explore India for rare rocks of the correct age that might have fossils of perissodactyls and other groups of mammals.
The first trip to Rajasthan in 2001 had little success, providing just ‘a few fish bones’, said Rose. However, the second proved much more promising.
‘The following year our Indian colleague, Rajendra Rana, continued exploring lignite mines to the south and came upon Vastan Mine in Gujarat,’ said Rose.
‘In 2004 our team was able to return to the mine, where our Belgian collaborator Thierry Smith found the first mammal fossils, including Cambaytherium.’
It was a moderately good runner and displayed features that were a combination of perissodactyls and their more generalised mammal forerunners
Hot and dusty work in vast open-pit lignite mines in India provide evidence for origins of Perissodactyls
Comparing its bones with many other living and extinct mammals, showed Cambaytherium was more primitive than any known perissodactyl
Encouraged, the team returned to the mines and collected fossilised bones of Cambaytherium and many other vertebrates, despite challenging conditions.
Rose said: ‘The heat, the constant noise and coal dust in the lignite mines were tough – basically trying to work hundreds of feet down near the bottom of open-pit lignite mines that are being actively mined 24/7.’
Through the cumulation of many years of challenging fieldwork, the team now believe they have finally resolved the mammal mystery.
Despite the abundance of perissodactyls in the Northern Hemisphere, Cambaytherium suggests the group likely evolved in isolation – in India.
The first horses were smaller than a dog and they gradually dispersed to other continents – including Europe and the US when India slammed into Asia. Researchers gathered bones from more than 350 fossils to create a complete skeleton
Named Cambaytherium, it is the direct ancestor of a specific group of hoofed mammals called perissodactyls – that also include rhinoceroses and tapirs
Cambaytherium, first described in 2005, is the most primitive member of an extinct group that branched off just before the evolution of perissodactyls
This was during the Paleocene 66 to 56 million years ago – right after the dinosaurs were wiped out by an asteroid strike.
These new creatures then wandered onto other continents once the land connection between India – once an island – and Asia formed.
Rose added: ‘Around Cambaytherium’s time, we think India was an island, but it also had primates and a rodent similar to those living in Europe at the time.
‘One possible explanation is that India passed close by the Arabian Peninsula or the Horn of Africa, and there was a land bridge that allowed the animals to migrate.
‘But Cambaytherium thewissi is unique and suggests that India was indeed isolated for a while.’
The findings were published in the Journal of Vertebrate Paleontology.
HOW THE HORSE LOST ITS TOES
The evolution of horses has involved adapting to changing environments, predation and human domestication.
Ancestors of modern-day horses had a small body, short legs, three toes on its front feet and four toes on its back legs.
It is believed that a more exposed environment may have forced the horse to develop longer legs to run from predators and they increased in size to be harder to eat.
The loss of toes may have enabled horses to support a larger weight and move faster on their longer legs.
A single hoof better supports a horse’s weight and allows it to swing its legs more efficiently to gallop at a much greater speed.
This is one of the crucial adaptations to allow horses to move as swiftly as they do today.
Horses are the only creature in the animal kingdom to have a single toe – the hoof, which first evolved around five million years ago.
Their side toes first shrunk in size, it appears, before disappearing altogether.
Ancient horse would moved relatively slowly with a small body, short legs, three toes on its front feet and four toes on its back legs. This 1905 artist’s impression of an ancient horse was done by Charles Knight