3/11/2023 0 Comments Baleen whale![]() ![]() Right whales appeared before about 20 Ma, and rorqual-like animals evolved perhaps by 15 Ma. Other groups of baleen whales, now extinct, indicate early "ecological experiments" which disappeared for uncertain reasons.ĭuring the Miocene (5-23 Ma), "modern" mysticetes diversified. These early baleen whales probably included the ancestors of modern rorquals (gulpers). For example, they had a blowhole nearer the skull tip than in modern whales, the ear region was less advanced, and the neck vertebrae were not particularly compressed. ![]() Like modern species, these had baleen in the thin flat upper jaw and a cylindrical toothless lower jaw, but otherwise they were quite primitive in structure. Also, by about 30 Ma, the first toothless baleen whales ("cetotheres") had evolved. Aetiocetus, North Pacific Mammaldon, Southwest Pacific). Toothed mysticetes are known from scattered localities (e.g. Mysticetes were quite diverse during Late Oligocene times (23-30 Ma). Perhaps mysticetes evolved in response to such oceanic changes. At this time, the Southern Ocean was starting to open as a result of continental drift, with changes to climate, water circulation, and oceanic ecosystems. They probably filter-fed using teeth, perhaps assisted by "proto-baleen". These animals are transitional between extinct archaic whales (archaeocetes) and modern baleen whales. The oldest southern filter-feeding whales are dated at around 34 Ma (million years old), that is, from the Eocene/ Oligocene boundary. Fossils from New Zealand and the margins of the Southern (Circum-Antarctic) Ocean, and from localities around the North Pacific, are particularly important. Recently, the fossil record has provided many insights. Many mysticetes feed in polar waters, and migrate annually to the tropics to breed.Įwan Fordyce in Japan giving a talk on mysticetesįor years, it was not clear how baleen whales evolved. Amongst living mysticetes, rorquals (Balaenopteridae) are fast-moving "gulp-feeding" predators, while right whales (Balaenidae) are slow-moving "skimmers" and gray whales (Eschrichtiidae) are "bottom-grubbing" filter-feeders. Baleen plates hang from the upper jaw in a uniquely constructed skull. Specialised feeding adaptations are particularly distinctive in mysticetes: they lack teeth, but use baleen to filter food (mainly zooplankton) from the water. These features include air-breathing, live birth, a 4-chambered heart, warm blood, and middle ear ossicles. ![]() But, they retain some typically mammalian attributes which indicate a distant origin on land. They are well adapted in terms of hydrodynamic, thermal and biological strategies to life in water. Living baleen whales (suborder Mysticeti, in the mammalian order Cetacea) include the biggest animals to have lived. ![]()
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