Stilt-legged horses roamed North America in the ice age

Researchers have discovered a previously unrecognized genus of extinct horses that roamed North America during the last ice age. 

The study on the thin-limbed, lightly built horses was based on an analysis of ancient DNA from fossils.

Before the study, the researchers thought the horse was related to the Asiatic wild ass, or another separate species belonging to the same genus as horses

However, the new results reveal that these horses were not closely related to any living population of horses. 

The study on the thin-limbed, lightly built horses was based on an analysis of ancient DNA from fossils. This illustration depicts a family of stilt-legged horses (Haringtonhippus francisci) in Yukon, Canada, during the last ice age

THE STILT-LEGGED HORSE - NOT REALLY A HORSE AFTER ALL

The extinct stilt-legged horse was first described by paleontologist Richard Harrington in the early 1970s. 

The species, recently named Haringtonhippus francisci, was thin-limbed, lightly built and had narrow hooves.

Researchers thought the horse was related to the Asiatic wild ass, or another separate species belonging to the same genus as horses.

However, a new study revealed that these horses were not closely related to any living population of horses. 

An analysis of ancient DNA from Haringtonhippus francisci fossils showed that the stilt-legged horses were much more distinct than previously thought and don't belong to the genus Equus, so a new genus was named for it - Haringtonhippus. 

The study, conducted by an international team of researchers, involved analyzing the DNA from fossils of the 'New World stilt-legged horse.'

The fossils were excavated from sites including the Natural Trap Cave in Wyoming, Gypsum Cave in Nevada, and the Klondlike goldfields of Canada's Yukon territory. 

The stilt-legged horses were though to be a species within the genus Equus, which includes living horses, asses, and zebras. 

The new study however showed that these extinct horses with narrow hooves, named Haringtonhippus francisci, are not closely related to any horses living today. 

The researchers say that the extinct North American horse seems to have diverged from the main trunk of the family tree leading to the Equus genus some 4 to 6 million years ago.

'The horse family, thanks to its rich and deep fossil record, has been a model system for understanding and teaching evolution,' said first author of the study Peter Heintzman, who led the study as a postdoctoral researcher at the University of California, Santa Cruz. 

'Now ancient DNA has rewritten the evolutionary history of this iconic group,' 

'The evolutionary distance between the extinct stilt-legged horses and all living horses took us by surprise, but it presented us with an exciting opportunity to name a new genus of horse,' said senior author Beth Shapiro, professor of ecology and evolutionary biology at UC Santa Cruz.

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Two skulls of the new genus Haringtonhippus from Nevada (upper) and Texas (lower). Coauthor Eric Scott, a paleontologist at California State University San Bernardino, said that morphologically, the fossils of Haringtonhippus are not all that different from those of Equus

Coauthor Eric Scott, a paleontologist at California State University San Bernardino, said that morphologically, the fossils of Haringtonhippus are not all that different from those of Equus. 

'But the DNA tells a fascinatingly different story altogether' he said. 

'That's what is so impressive about these findings. 

'It took getting down to the molecular level to discern this new genus.'

The findings show that the species was widespread and successful throughout much of North America, living alongside populations of Equus, but not interbreeding with them. 

In the North of Canada, Haringtonhippus survived until about 17,000 years ago - more than 19,000 years later than previously thought for this region.

The geographic distribution of Haringtonhippus francisci. Blue circles are east Beringian localities. Red circles are contiguous USA localities. Orange circles are localities with tentatively assigned Haringtonhippus specimens only. The green-star-labeled HT is the locality of the francisci holotype - a single specimen upon which the description of a species is based - in Wharton County, Texas, USA

At the end of the last ice age, both horse groups became extinct in Northern America, along with other large animals like woolly mammoths and saber-toothed cats. 

Although the Equus survived in Eurasia after the last ice age which eventually led to domestic horses, the stilt-legged Haringtonhippus was an evolutionary dead end.  

The research team named the horse after Richard Harrington, emeritus curator of Quaternary Paleontology at the Canadian Museum of Nature in Ottawa. 

Harrington, who was not involved with the study, studied the ice age fossils of Canada's North and first described the stilt-legged horses in the early 1970s. 

'I had been curious for many years concerning the identity of two horse  metatarsal bones I collected, one from Klondike, Yukon, and the other from Lock Chicken Creek, Alaska,' said Harrington. 

Before the study, the researchers thought the horse was related to the Asiatic wild ass, or another separate species belonging to the same genus as horses. However, the new results reveal that these horses were not closely related to any living population of horses

'They looked like those of modern Asiatic kiangs (wild ass), but thanks to the research of my esteemed colleagues they are now known to belong to a new genus. 

'I am delighted to have this new genus named after me.' 

'We are very pleased to name this new horse genus after our friend and colleague Dick Harington,' said coauthor Grant Zazula, a Government of Yukon paleontologist.

'There is no other scientist who has had greater impact in the field of ice age paleontology in Canada than Dick. 

'Our research on fossils such as these horses would not be possible without Dick's life-long dedication to working closely with the Klondike gold miners and local First Nations communities in Canada's North.'  

A new study revealed that the stilt-legged horses were not closely related to any living population of horses 

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