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In effect, "tetrapod" is a name reserved solely for animals which lie among living tetrapods, so-called crown tetrapods. This is a node-based clade , a group with a common ancestry descended from a single "node" (the node being the nearest common ancestor of living species).
During the Paleocene Epoch (about 66 - 55 million years ago), the ancient whale Pakicetus began pursuing an amphibious lifestyle in rivers or shallow seas. It was the ancestor of modern whales, dolphins, and porpoises. The cetacea are extensively adapted to marine life and cannot survive on land at all.
Whale skulls have small eye orbits, long snouts (with the exception of monodontids and ziphiids) and eyes placed on the sides of its head. Whales range in size from the 2.6-metre (8.5 ft) and 135-kilogram (298 lb) dwarf sperm whale to the 34-metre (112 ft) and 190-metric-ton (210-short-ton) blue whale.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.
This Decade-Old Whale Carcass Still Supports Life by wildestanimal - Getty Images When a large marine mammal like a whale dies, its body drifts to the ocean floor in a process known as whale fall.
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 ...
"The Good Whale" covers the challenges animal experts faced in the years they spent trying to prepare Keiko — a whale who entered captivity as a calf and was raised by humans — for life as a ...
A humpback whale has stunned scientists with a journey that spanned three oceans and more than 8,000 miles, setting the record for the longest known migration between breeding grounds.