Cetaceans Evolution
Until recently, the evolutionary origin of cetaceans has been a mystery. Cetaceans are aquatically specialized mammals that exhibit body streamlining, have no hair or hind limbs, but adapted flippers and flukes for underwater movement. This group includes porpoises, dolphins, and whales (Thewissen et al., 2001). Despite having features so specifically adapted for aquatic life, cetaceans, according to scientists, have actually evolved from land animals. Some scientists even argue that cetaceans evolved from artiodactyls, which are land-dwelling ungulates (Rose., 2001). Artiodactyls include mammals such as cattle, deer, hippopotami, and pigs (Spaulding et al., 2009). In fact, some scientists go as far as to claim the hippopotamids are a sister group to cetaceans (Rose, 2001). Other scientists claim cetaceans actually evolved from mesonychians, which are an extinct group of carnivorous ungulates. To make their claims, scientists use morphological data from recent cetacean fossil discoveries, such as pakicetids, as well as genetic and molecular studies. Morphological evidence tends to support mesonychian origin, while molecular studies indicate cetaceans have evolved from artiodactyls
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In addition, study of the pakicetid ankle indicate a morphology that was specifically seen in artiodactyls (Thewissen et al., 2001). According to Rose (2001), it is highly unlikely that such an adaptation is a result of convergent evolution because cetaceans have evolved to be more equipped for an aquatic lifestyle. Rather, it is a remnant feature of life on land (Rose, 2001). Despite this evidence, other scientists argue that tooth morphology of ancient cetaceans is not consistent with artiodactyls. Instead, tooth and some skull features are more similar to the carnivorous mesonychians. However, this morphology is argued by opponents to be most likely a result of convergent evolution (Rose,
In addition, study of the pakicetid ankle indicate a morphology that was specifically seen in artiodactyls (Thewissen et al., 2001). According to Rose (2001), it is highly unlikely that such an adaptation is a result of convergent evolution because cetaceans have evolved to be more equipped for an aquatic lifestyle. Rather, it is a remnant feature of life on land (Rose, 2001). Despite this evidence, other scientists argue that tooth morphology of ancient cetaceans is not consistent with artiodactyls. Instead, tooth and some skull features are more similar to the carnivorous mesonychians. However, this morphology is argued by opponents to be most likely a result of convergent evolution (Rose,