Changes: Vertebrate paleontology

Revision as of 23:09, 31 December 2006

Vertebrate paleontology seeks to discover the behavior, reproduction and appearance of extinct spined animals, through the study of their fossilized remains. It also tries to connect, on the evolutionary timeline, the animals of the past and their modern day relatives.

The fossil record clearly shows the evolutionary progression from early aquatic vertebrates to mammals. The earliest known fossil vertebrates were heavily armored fish discovered in rocks from the Ordovician Period about 500 to 430 million years ago. (The phrase 'million years ago' is shortened to 'mya' in most paleontological references). The Devonian Period (395 to 345 mya) brought in the changes that allowed primitive air-breathing fish to remain on land as long as they wished, thus becoming the first terrestrial vertebrates, the amphibians.

Amphibians developed forms of reproduction and locomotion and a metabolism better suited for life exclusively on land, becoming more reptilian. Full fledged reptiles appeared in the Carboniferous Period (345 to 280 mya).

The reptilian changes and adaptations to diet and geography are chronicled in the fossil record of the varying forms of therapsids. True mammals showed up in the Triassic Period (225 to 190 mya) around the same time as the dinosaurs, which also sprouted from the reptilian line.

Birds appeared in the Jurassic Period (190 to 136 mya) as dinosaurs were trying to find ways to adapt to their ever-changing world.

One of the people who helped figure out this progression was French zoologist Georges Cuvier (1769-1832) who realized that fossils found in older rock stratas differed greatly from more recent fossils or modern animals. He published his findings in 1812 and although he steadfastly refuted evolution, his work proved the (at the time) heretical theory of extinction of species.

Paleontology really got started though, with the publication of Recherches sur les poissons fossils (1833-1843) by Swiss naturalist Louis Agassiz (1807-1873). He studied, described and listed hundreds of species of fossil fish, beginning the serious study into the lives of extinct animals.

In modern times, some have said that Alfred Romer (1894-1973) wrote the definitive textbook on the subject, called Vertebrate Paleontology, which shows the progression of evolution in fossil fish, and amphibians and reptiles through comparative anatomy. Romer became the first president of the Society of Vertebrate Paleontology in 1940. Others would claim that the current definitive book on the subject was written by Robert L Carroll of McGill University in his 1988 text Vertebrate Paleontology and Evolution. Carroll was president of the Society of Vertebrate Paleontology in 1983. The Society keeps its members informed on the latest discoveries through newsletters and the Journal of Vertebrate Paleontology.

Even though some of the most brilliant, creative people who have ever lived have spent their careers advancing the field of vertebrate paleontology, the fact remains that new and previously unknown species are found every week. It becomes increasingly clear that we haven't even scratched the surface of all that we could know about the animals that lived on Earth before us.

Paleontological Vertebrate Classification

This is a 'traditional' classification scheme, which can technically be described as paraphyletic. This means that the classification scheme does not necessarily represent the evolutionary history of the classes. For instance, birds are generally considered to be the descentandts of Saurischian dinosaurs; but in this system both are listed as separate classes.

(For an alternative system see List of dinosaur classifications )

Kingdom Animalia

Phylum Chordata (vertebrates)
- Class Agnatha (jawless fish)
- Class Placodermii (armoured fish)
- Class Chondrichthys (sharks)
- Class Osteichthys (bony fish)
- Class Amphibia
- Class Reptilia
  - Subclass Anapsida
    - Order Cotylosauria
    - Order Chelonia
  - Subclass Synapsida
    - Order Pelycosauria
    - Order Therapsida
  - Subclass Euryapsida
    - Order Sauropterygia
    - Order Ichthyosauria
  - Subclass Diapsida (lizards & snakes too)
    - Order Thecodonta
    - Order Crocodilia
    - Order Saurischia (dinosaurs)
    - Order Ornithischiaa (dinosaurs)
- Class Aves
- Class Mammalia
  - Subclass Prototheria
    - Order Monotremata (duckbill platypus)
  - Subclass Theria
    - Infraclass Metatheria
      - Order Marsupialia (kangaroos)
    - Infraclass Eutheria (placentals)
      - Order Insectivora
      - Order Chiroptera (bats)
      - Order Creodonta
      - Order Carnivora (dogs/cats)
      - Order Perissodactyla (horses)
      - Order Artiodactyla (cattle)
      - Order Proboscidea (elephants)
      - Order Edentata
      - Order Cetacea (whales)
      - Order Rodentia (mice/rats)
      - Order Lagomorpha (rabbits)
      - Order Primates (apes/humans)

@@ Line 5: / Line 5: @@
 [[Amphibia|Amphibians]] developed forms of reproduction and locomotion and a [[metabolism]] better suited for life exclusively on land, becoming more reptilian. Full fledged [[reptile]]s appeared in the [[Carboniferous]] Period (345 to 280 mya).
-The [[Reptile|reptilian]] changes and adaptations to diet and geography are chronicled in the fossil record of the varying forms of [[therapsid]]s. True mammals showed up in the [[Triassic]] Period (225 to 190 mya) around the same time as the [[dinosaur]]s, which also sprouted from the reptilian line.
+The [[Reptilia|reptilian]] changes and adaptations to diet and geography are chronicled in the fossil record of the varying forms of [[therapsid]]s. True mammals showed up in the [[Triassic]] Period (225 to 190 mya) around the same time as the [[dinosaur]]s, which also sprouted from the reptilian line.
 [[aves|Bird]]s appeared in the [[Jurassic]] Period (190 to 136 mya) as [[dinosaur]]s were trying to find ways to adapt to their ever-changing world.