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Even-toed ungulates are a diverse order of mammals that evolved from a common ancestor resembling today’s mouse deer. They include pigs, camels, hippos, deer, giraffes, and more. They evolved in the early Eocene and became dominant herbivores due to their multi-chambered stomachs and adaptive chewing strategies. They originated in the superorder Laurasiatheria, and their evolution was influenced by the Azolla event.
Even-toed ungulates, order Artiodactyla, is a famous order of mammals with about 220 species. It includes pigs, peccaries, camels, hippos, deer, chevrotains (mouse deer), pronghorns, giraffes, antelopes, goats, sheep and cattle. The order includes many economically useful mammals, including pigs, sheep, goats, and cattle. Another unique feature of ungulates is the presence of a specially shaped bone in the ankle joints, which gives these animals greater flexibility in the legs.
The ancestry of even-toed ungulates lies in the superorder Laurasiatheria, the superorder of mammals that originate in Laurasia, a former supercontinent that consisted of North America merged together with Eurasia. Like many other mammalian orders, they evolved in the early Eocene (about 54 million years ago). The common ancestor of living ungulates probably resembled today’s mouse deer, which uncannily resembles a cross between a small deer and a rodent. These animals grew from rodent size after the extinction of the dinosaurs to fill the niches of small browsers and medium-sized herbivores. Some lineages, such as pigs and peccaries, eventually became omnivores, and some ancient relatives of modern pigs were actually effective hunters (mesonichids).
The first three branches of ungulates to evolve were the camelids (the first ruminants), the swine (pigs and relatives), and the suborder Ruminantia (deer, cattle, goats, sheep, antelopes, etc.). All of these suborders were present by the Late Eocene (46 million years ago). During most of the Eocene, hoofed animals were less numerous than ungulates (ancestors of today’s horses and rhinos). Ungulates were well adapted to digesting lush foliage, while ungulates thrived in borders, where there was more difficult-to-digest plant matter such as grass.
Around this time, the Azolla event occurred, sucking most of the carbon dioxide out of the air and leading to a drop in global temperatures. Many of the world’s great forests and rainforests have become extinct and grass has spread across the earth. This is why the Cenozoic is called the “age of herbs”. Perfectly positioned to take advantage of their multi-chambered stomachs and adaptive chewing strategies, ungulates slowly became the most dominant herbivores on the planet, as they still are today. Horses, rhinos and tapirs (odd-toed ungulates) were marginalized.
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