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A group of North American Pleistocene horses was previously identified as different species. Now, mitochondrial and partial nuclear genomic studies support the idea that there is only one species, which belongs to a new genus.
Meet Haringtonhippus, a possible new genus of horse covering the extinct New World stilt-legged (NWSL) equids, which, until now, have been thought of as multiple species. Prior to this study, these thin-limbed, lightly-built horses were believed to be related to the Asiatic wild **** or onager, or simply a separate species within the genus Equus, which includes all living horses, asses, and zebras. The fossil record shows how the ancestors of these animals evolved from dog-sized, three-toed browsers to larger, one-toed grazers over a period of about 55 million years. Along the way many species became extinct.
DNA - MtDNA - Model - Morphology - New
The current mitochondrial DNA (mtDNA) -based phylogenetic model suggests that the stilt-legged morphology arose independently in the New and Old Worlds. The thought is that the two may have converged in the face of the need to adapt to arid climates and habitats. But the researchers, supported in part by the EU through the PEGASUS project, point out that this is based on two questionable sources: an unreliable data type and mitochondrial genome sequences that are incomplete or otherwise problematic.
As they explain in their recently published paper, "A new genus of horse from Pleistocene North America," they used their phylogenetic framework and comparisons between specimens identified by palaeogenomics and/or morphology, to try to determine the taxonomy of middle-late Pleistocene NWSL equids.
Fossil - Record - Horse - Family - Years
The fossil record of the horse family is robust but more recently, from around 2.5 million years ago, things get a bit confused. This is the Pleistocene and it is not clear how horses of this period relate to each other. The downside of this abundant fossil record, say the...
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