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The traditional hypothesis of cetacean evolution, first proposed by Van Valen in 1966, [9] was that whales were related to the mesonychians, an extinct order of carnivorous ungulates (hoofed animals) that resembled wolves with hooves and were a sister group of the artiodactyls (even-toed ungulates). This hypothesis was proposed due to ...
Basilosaurus, one of the first of the giant whales, appeared in the fossil record. 38 Ma Earliest bears. 37 Ma First nimravid ("false saber-toothed cats") carnivores — these species are unrelated to modern-type felines. First alligators and ruminants. 35 Ma Grasses diversify from among the monocot angiosperms; grasslands begin to expand.
The whale was first mentioned in ancient Greece by Homer. There, it is called Ketos, a term that initially included all large marine animals. From this was derived the Roman word for whale, Cetus. Other names were phálaina (Aristotle, Latin form of ballaena) for the female and, with an ironic characteristic style, musculus (Mouse) for the male.
Whales evolved from land-living mammals, and must regularly surface to breathe air, although they can remain underwater for long periods of time. Some species, such as the sperm whale, can stay underwater for up to 90 minutes. [2] They have blowholes (modified nostrils) located on top of their heads, through which air is taken in and expelled.
The first fully terrestrial vertebrates were reptilian amniotes — their eggs had internal membranes that allowed the developing embryo to breathe but kept water in. This allowed amniotes to lay eggs on dry land, while amphibians generally need to lay their eggs in water (a few amphibians, such as the common Suriname toad, have evolved other ways of getting around this limitation).
The larynx evolved when the first land vertebrates started breathing air and needed to separate food from air to prevent choking. Whales evolved from land mammals roughly 50 million years ago.
The pygmy right whale shares several characteristics with the right whales, with the exception of having a dorsal fin. Also, pygmy right whales' heads are no more than one quarter the size of their bodies, whereas the right whales' heads are about one-third the size of their bodies. [11] The pygmy right whale is the only extant member of its ...
An unusual journey. In her 26 years working with right whale sighting networks, Albert has seen right whales travel into the Gulf fewer than a half-dozen times.