Evolution of Life

Chapter 19

The Paleozoic Era (570 to 240 million years ago) Global conditions were seasonal with

changes in winds, ocean currents, and nutrient deposits.

The nutrient supply was stable, but limited. Many of the animals had flattened bodies

that allowed for nutrients to be easily taken up.

Animals ranged from sponges to some vertebrates and were very diverse.

Fossils from this area have many nicks, punctures, and other evidence of healed wounds.

This suggests that there were definite predator-prey interactions.

Trilobites were very common in the early part of the era, but seemed to die out in later years.

Towards the middle of the era, the sea levels changed drastically for reasons scientists have yet to understand.

This abrupt change led to mass extinction.

As organic matter (resulting from the mass extinction) built up and decayed, it formed into the coal deposits we have now.

Ancestral seed bearing plants were abundant – cycads, gingkos, and other conifers dominated the forests.

Some small dinosaurs existed at this time.

Animals of the Paleozoic

During this era many new life plants and animals formed.

This is also the first time there are many fossils for scientists to study.

The Paleozoic Era ended when many kinds of animals and plants became extinct, probably because of climatic changes.

Plants were the first life forms to go on land, and they did so in this era.

Major swamp-forests, causing the coal of today, were around during the middle of this era.

At the end of the era, the greatest of all known mass extinctions occurred.

It wiped out all but about 5% of the species that existed at that time.

The Mesozoic Era (251 to 65.5 million years ago) Divided into the Triassic, Jurassic, and

Cretaceous periods. This is known as the Age of the Reptiles

and saw the existence of the great dinosaurs – velociraptor, triceratops, tyrannosaurus, and others.

The supercontinent Pangea divides into Laurasia in the north and Gondwana in the south.

The climate is hot and tropical worldwide. On land, the dinosaurs reign supreme. In the oceans are various kinds of marine

reptiles, as well as molluscs and many other invertebrate groups.

Plants include ferns and gymnosperms. Mammals are small and insignificant, but

probably numerically common.

Age of Reptiles

During the Paleozoic, several mass extinctions occurred.

In each case, one or two of the big groups was completely eliminated, the rest were changed, and the old ecological balances of the Paleozoic were very thoroughly unbalanced. 

The entire Triassic, and most of the Jurassic, was spent getting all that sorted out. 

At the end of this period -- about the Late Jurassic and earliest Cretaceous -- there was another burst of evolutionary creativity associated with rising seas and relatively warm, equable climate throughout the world. 

Familiar examples include birds, placental mammals and angiosperm (flowering) plants.

The Mesozoic Era lasted more than 180 million years. 

During this time, many modern forms of plants, invertebrates, and fishes evolved. 

On land, dinosaurs were the dominant animals, while the oceans were populated by large marine reptiles, and Pterosaurs ruled the air. 

For most of this period, the climate worldwide was warm and tropical, and shallow seas covered low-lying landmasses.

At the beginning of the Mesozoic, all of the world's continents were joined into the supercontinent of Pangea, which rifted into Laurasia in the north and Gondwana in the south. 

By the end of the era most of continents had separated into their present form.

The Mesozoic Era is divided into three periods, each lasting many millions of years: the Triassic, Jurassic, and Cretaceous. 

The Triassic saw the emergence of many modern invertebrate groups, and on land the archosaur reptiles replaced the therapsids. 

In the oceans Ichthyosaurs such as Shonisaurus became as large as whales.

The Jurassic was the height of the dinosaur era, with giants such as Brachiosaurus, Stegosaurus, etc, and mammals tiny and shrew-like. 

Distinctive plants like ferns, Cycads, Bennettitales, and Cheirolepidiaceae conifers characterized the landscape.

During the Cretaceous period, the first flowering plants appeared, birds and fish diversified, and new types of dinosaurs appeared. 

The climate cooled and unique dinosaurs evolved on different continents.

The Mesozoic came after the Paleozoic.  The Paleozoic Era ended with the Permian

Period, which ended with a sort of general meltdown, sometimes called the "PT" or "End-Permian" extinction. 

 The Mesozoic era came to an end with the great terminal extinction event known as the K-T (Cretaceous-Tertiary) event.  

It is generally believed that an asteroid strike led to this extinction event.

The Cenozoic Era (the last 65.5 million years) The Age of Mammals. During the 65 million years of the Cenozoic

Era (also spelled "Cainozoic"), or Age of Mammals, the world took on its modern form. 

Invertebrates, fish, reptiles etc were essentially of modern types, but mammals, birds, protozoa and flowering plants still evolved and developed during this period.

Animal Life of the Cenozoic

During the Paleogene the climate worldwide was warm and tropical, much as it had been for most of the preceding Mesozoic. 

The Neogene saw a drastic cooling in the world's climate.

During the Pleistocene, the continuing cooling climate resulted in an ice age, or rather a series of ice ages with interspersed warm periods.

The Paleogene saw the diversification of many mammalian and bird groups, flourishing in the tropical conditions. 

During the early Paleogene the continents were isolated by shallow seas, and different lineages of Mammals evolved on each one. 

Mammals included many giant yet small-brained rhinoceros-like types - the Asiamerican uintatheres, and brontotheres and the African arsinoitheres.

There were huge flightless carnivorous birds - the Laurasian diatrymids and the South American phorusrhacids - 2 meters tall with cruel curved beaks, that mimicked the great theropod dinosaurs of the Mesozoic. 

All these animals lived in tropical forests.  The champsosaurs, crocodile-like "eosuchian" reptiles - living fossils of their time - survived the dinosaurs and the K-T extinction but died out later in the Paleogene. 

In the seas the first archaic toothed whales appeared. 

Bivalve and Gastropod molluscs were basically the same type as today. 

Echinoderms, corals, bryozoa and sponges were basically of modern type. 

On land insects were generally of modern type.  

Ants were even more numerous then they are today.

During the Neogene modern mammals and flowering plants evolve, as well as many strange mammals that are no longer around. 

The most astonishing thing to happen during the early Neogene was the evolution of grass. 

This led to the evolution of long-legged running animals adapted to life on the savanna and prairie.

The horse family - Equiidae - was a special success story during the Neogene. 

Horses and other grazing mammals evolved high-crowned teeth to cope with a diet of abrasive grass. 

There were still many forest animals however.  The Mastodons lived on every continent

except Australia.  Many strange mammals - litopterns,

notoungulates, ground sloths, borhyeanas, etc - continued to evolve in isolation in South America before a land bridge formed and allowed a devastating invasion of forms from the north. 

The oceans were inhabited by whales basically like modern forms, which had replaced the archaic toothed whales. 

In the north Pacific were the Desmostylids - a sort of cross between an elephant and a seal. 

Also in the seas were the largest carnivorous sharks ever to live - the Carcharodon megalodon, a predecessor of the modern White Pointer but much larger and heavier.

The Pleistocene period saw essentially modern flora and invertebrate species. 

However many mammalian types were of species and genera now extinct, and generally of large size - the various species of mammoth, the Irish "elk" (left), a large diversity of rhinos, the giant ground sloths, the diprotodonts of Australia, and many more.  

A combination of human hunting ("stone age overkill") and climatic change served to kill off most worlds megafauna.

Works Citedhttp://www.infoplease.com/ce6/sci/

A0837345.htmlhttp://library.thinkquest.org/20886/

paleozoic.htm http://www.palaeos.com/Mesozoic/

Mesozoic.htm#biotahttp://www.palaeos.com/Cenozoic/

Cenozoic.htmhttp://www.ucmp.berkeley.edu/

education/events/cowen1b.html