Cetaceans are thought to have evolved during the Eocene (56-34 mya), the second epoch of the present-extending Cenozoic Era. Molecular and morphological analyses suggest Cetacea share a relatively recent closest common ancestor with hippopotami and that they are sister groups. [3] .

2025年1月30日 · Cetaceans evolved from four-legged (quadruped) terrestrial animals, for which limbs played a primary role in movements, into virtually limbless aquatic creatures living in an environment where the back muscles are more important. Forelimbs are still present but are reduced to finlike flippers having shortened arm bones and no individual fingers.

2009年4月16日 · We review raoellid artiodactyls, as well as the earliest families of cetaceans: pakicetids, ambulocetids, remingtonocetids, protocetids, and basilosaurids. We focus on the evolution of cetacean organ systems, as these document the …

2024年12月21日 · The first fossil cetacean, Pakicetus, is known from the Early Eocene Epoch (55.8 million to 49 million years ago) in Pakistan. It has recently become clear that archaeocetes rapidly diversified during the Eocene, and at least five now-extinct families are recognized.

2017年6月5日 · Cetacean evolution receives wide recognition as a preeminent example of macroevolutionary change [1]. This recognition derives primarily from an excellent fossil record of their early evolution, mostly from the middle to late Eocene epoch (from ∼55–34 Ma, or …

2018年1月1日 · Cetaceans show major evolutionary patterns linked to oceanic change, supporting the idea that food resources have helped to drive cetacean history. The exact roles of physical versus biological effects, viz., bottom-up or top …

2009年1月1日 · Fossils show that cetaceans arose from terrestrial ancestors more than 50 million years ago. They have evolved to become the dominant group of marine mammals in terms of taxonomic and ecological diversity and geographic range.

A phylogeny showing the relationships among cetacean families. [1] The Cetaceans (whales, dolphins and porpoises) are mammalian marine descendants of land mammals. Their terrestrial origins are indicated by: Their need to breathe air from the surface; The bones of their fins, which resemble the limbs of land mammals