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May 21, 2007 · Marine Mammal Diversity. Living groups of marine mammals vary greatly in their diversity. Rice (1998; Table 1 therein) reports that living Cetacea include 83 species in 39 genera; living Pinnipedia include 36 species in 21 genera; and Recent Sirenia include 5 species in 3 genera. Since then, several new species of cetaceans have been described ...
- Mark D. Uhen
- 144
- 2007
- 21 May 2007
- Before The Canids: Creodonts, Mesonychids, and Friends
- The First Canids: Hesperocyon and The "Bone-Crushing Dogs"
- The First True Dogs: Leptocyon, Eucyon, and The Dire Wolf
Modern dogs evolved from a line of carnivorous mammals called "canids," after the characteristic shape of their teeth. Before (and alongside) the canids, though, there were such diverse families of predators as amphicyonids (the "bear dogs," typified by Amphicyon, which seem to have been more closely related to bears than dogs), prehistoric hyenas ...
Paleontologists agree that the late Eocene(about 40 to 35 million years ago) Hesperocyon was directly ancestral to all later canids — and thus to the genus Canis, which branched off from a subfamily of canids about six million years ago. This "western dog" was only about the size of a small fox, but its inner-ear structure was characteristic of lat...
Here's where things get a bit confusing. Shortly after the appearance of Hesperocyon 40 million years ago, Leptocyon arrived on the scene — not a brother, but more like a second cousin once removed. Leptocyon was the first true canine (that is, it belonged to the caninae subfamily of the Canidae family), but a small and unobtrusive one, not much bi...
- Bob Strauss
- Bob Strauss
- Fish and Sharks. Between 500 and 400 million years ago, vertebrate life on earth was dominated by prehistoric fish. With their bilaterally symmetric body plans, V-shaped muscles, and notochords (protected nerve chords) running down the lengths of their bodies, ocean dwellers like Pikaia and Myllokunmingia established the template for later vertebrate evolution It also didn't hurt that the heads of these fish were distinct from their tails, another surprisingly basic innovation that arose during the Cambrian period.
- Tetrapods. The proverbial "fish out of water," tetrapods were the first vertebrate animals to climb out of the sea and colonize dry (or at least swampy) land, a key evolutionary transition that occurred somewhere between 400 and 350 million years ago, during the Devonian period.
- Amphibians. During the Carboniferous period, dating from about 360 to 300 million years ago, terrestrial vertebrate life on earth was dominated by prehistoric amphibians.
- Terrestrial Reptiles. About 320 million years ago, give or take a few million years, the first true reptiles evolved from amphibians. With their scaly skin and semi-permeable eggs, these ancestral reptiles were free to leave rivers, lakes, and oceans behind and venture deep into dry land.
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When did mammals evolve?
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By Katie Pavid. 680. Early ancestors of the ocean's biggest animals once walked on land. Follow their extraordinary journey from shore to sea. Although whales are expert swimmers and perfectly adapted to life underwater, these marine mammals once walked on four legs. Their land-dwelling ancestors lived about 50 million years ago.
Oct 30, 2012 · The first marine mammals, including the first whales, appear in the seas, and the first primates appear on land. Large mammals make their first appearance on land, then die off by the end of the epoch. Carnivores include the first members of the dog, weasel, bear and cat families. Most modern orders of bird had appeared by the Eocene.
Oct 16, 2021 · In fact, the first mammals evolved from a population of vertebrates called therapsids (mammal-like reptiles) at the end of the Triassic period and coexisted with dinosaurs throughout the Mesozoic Era. But part of this folktale has a grain of truth. It was only after the dinosaurs went kaput that mammals were able to evolve beyond their tiny ...
The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid- Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this ...
