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COMPARATIVE PLACENTATION
Author(s) -
Edwards M. J.
Publication year - 1979
Publication title -
australian veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.382
H-Index - 59
eISSN - 1751-0813
pISSN - 0005-0423
DOI - 10.1111/j.1751-0813.1979.tb07062.x
Subject(s) - placentation , citation , library science , information retrieval , computer science , world wide web , biology , pregnancy , fetus , genetics , placenta
The ancestry of horses from five-toed species via the small Eohippus of the American continent has been a prime topic of study for evolutionary biologists. It is best traced in two contributions: by Simpson (1951), and by Thenius & Hofer (1960). Coming from the American continent, the equid ancestors distributed to Eurasia while speciating into the extant members during their expansion to the West and into Africa. In the process, chromosomal fusions occurred in the equidae, causing karyotypes to evolve that range from 66 to 32 chromosomes, whilst preserving the same amount of DNA. The current domestic horse is thought to have derived from the Mongolian wild horse, Equus przewalskii. Other authors, however, have considered the extinct Tarpan to be the ancestral species of the domestic horses. A very large number of different horse breeds have been produced during their domestication, ranging from large tract animals to very small ponies.