Evolution of Cetaceans - Earliest Ancestors

Earliest Ancestors

The traditional theory of cetacean evolution was that whales were related to the mesonychids, an extinct order of carnivorous ungulates (hoofed animals), which resembled wolves with hooves and were a sister group of artiodactyls (even-toed ungulates). These animals had unusual triangular teeth similar to those of whales. This is why scientists long believed that whales evolved from a form of mesonychid. But more recent molecular phylogeny data suggest that whales are more closely related to the artiodactyls, specifically the hippopotamus. The strong evidence for a clade combining cetaceans and artiodactyls is further discussed in the article Cetartiodactyla. However, the anthracothere ancestors of hippos do not appear in the fossil record until millions of years after Pakicetus, the first known whale ancestor.

The molecular data is supported by the recent discovery of Pakicetus, the earliest proto-whale (see below). The skeletons of Pakicetus show that whales did not derive directly from mesonychids. Instead, they are artiodactyls that began to take to the water soon after artiodactyls split from mesonychids. Proto-whales retained aspects of their mesonychid ancestry (such as the triangular teeth) which modern artiodactyls have lost. An interesting implication is that the earliest ancestors of all hoofed mammals were probably at least partly carnivorous or scavengers, and today's artiodactyls and perissodactyls became herbivores later in their evolution. By contrast, whales retained their carnivorous diet, because prey was more available and they needed higher caloric content in order to live as marine endotherms. Mesonychids also became specialized carnivores, but this was likely a disadvantage because large prey was not yet common. This is why they were out-competed by better-adapted animals like the creodonts and later Carnivora which filled the gaps left by the dinosaurs.

Read more about this topic:  Evolution Of Cetaceans

Famous quotes containing the words earliest and/or ancestors:

    Oh! snatch’d away in beauty’s bloom,
    On thee shall press no ponderous tomb;
    But on thy turf shall roses rear
    Their leaves, the earliest of the year;
    George Gordon Noel Byron (1788–1824)

    In different hours, a man represents each of several of his ancestors, as if there were seven or eight of us rolled up in each man’s skin,—seven or eight ancestors at least, and they constitute the variety of notes for that new piece of music which his life is.
    Ralph Waldo Emerson (1803–1882)