Cenozoic Life
Cenozoic Life: Learning Objectives
Mammals are the dominant group during the Cenozoic. Continental fragmentation encourages biological diversity and radiation of species.
Plants:
Angiosperms dominate and spread across the globe.
In the Miocene grasses will appear. See lecture notes for the impact that grasses had on vertebrate evolution.
Fish:
Fish diversify to the numerous species seen today. Sharks become abundant and go through a giant phase. (a cool read is "Meg")
Amphibians: Amphibians have remained essentially unchanged since the Paleozoic.
Reptiles: Poisonous snakes appear in the Miocene. Snake poison evolved as mammals evolved and specifically acts as a neuro- and hemo- toxin to mammal physiology.
Birds:
There was a great diversification among birds in the Cenozoic. Large flightless birds evolved and some lived until recent times.
Mammals:
Characteristics common to all mammals:
hair
mammary glands
warm blooded
single lower jaw bone
differentiated dentition
7 neck vertebrae
expanded brain case
3 bones in the ear
secondary hard palate
Paleontologists assume that the change in climate at the end of the Mesozoic favored warm bloodedness which allowed mammals to become the dominant form. The first mammal appeared in the Triassic and was a small shrew like organism. It is believed that during the Mesozoic mammals evolved and improved nervous, circulatory and reproductive systems. Developed more efficient temperature regulation and developed greater speed and agility.
Three types of mammals exist today:
1) Monotremes: the most primitive, monotremes lay eggs but do suckle their young. Only three species exist today: the platypus and 2 species of spiny anteaters.
2) Marsupials: "pouch animals", young are born at a very early stage and are not viable-they must finish development within a pouch structure on the mother. Succeeded in South America and Australia. When North and South America became joined at the end of the Cenozoic marsupial mammals declined as placental mammals migrated into South America.
3) Placental: young nurtured within the mother's body and is fully viable when born.
There is a wide variety of mammals. They are divided into classes as follows:
A) Edentates: includes armadillo, sloth and anteater. During the Cenozoic there were VERY large armadillo and
giant ground sloth. Both of these have gone extinct.
B) Rodents: very successful group, includes rats, mice squirrels and beavers. In the Cenozoic beavers the size of bears existed.
C) Bats: the only flying mammal, modern forms have existed since the Eocene.
D) Carnivores: includes dogs, felines and other carnivore species. The evolution of the carnivore and herbivore are linked, as one improved and evolved the other responded. Cenozoic carnivores include wild dogs and the sabre tooth tiger.
E) Pinnepeds: carnivores that spend time in the ocean. Including seals, sea lions and walruses, pinnepeds spend a majority of their life on land but are adapted to feeding in the oceans.
F) Cetaceans: complete marine adaptation. Whales spend all of their time in the ocean and none of its land. Cetaceans evolved from a carnivore similar to a wolf.
G) Ungulates: herbivores with hooves. Classified by the number of toes on the foot.
Perissodactyl: odd number of toes on the foot. Center of evolution is North America and includes horses, tapirs and rhinos.
Artiodactyl: even number of toes on the foot. Center of evolution was Asia and Africa, more abundance and diversity than the perissodactyl. Three major modern groups:
Swine: pigs, hippos; 4 toes but weight on middle two (cloven hoof)
Camel: also include llama
Ruminant: cud chewers, include deer, sheep, cattle, goat, giraffe
H) Proboscidians: animals with trunks, first appear as trunkless. In the Cenozoic
Mastodon and
mammoths were abundant. These animals were very large and some species had elaborately curving tusks. Extinct 8000 years ago. Two theories for this
extinction:
