Vertebrate paleontology

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (July 2007)

Vertebrate paleontology seeks to discover the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord, through the study of their fossilized remains. It also tries to connect, by using the evolutionary timeline, the animals of the past and their modern-day relatives.

The fossil record does not clearly show the evolutionary progression from early aquatic vertebrates to mammals, but there is some evidence. The earliest known fossil vertebrates were heavily armored fish discovered in rocks from the Ordovician Period about 500 to 430 Ma (megaannum, million years ago). The Devonian Period (395 to 345 Ma) 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 Ma).

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

Birds first diverged from dinosaurs between 100 Ma and 60 Ma ^[1].

History

One of the people who helped figure out the vertebrate progression was French zoologist Georges Cuvier (1769-1832), who realized that fossils found in older rock strata 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.

Thomas Jefferson is credited with initiating the science of vertebrate paleontology in the United States with the reading of a paper to the American Philosophical Society in Philadelphia in 1797. Jefferson presented fossil bones of a ground sloth found in a cave in western Virginia and named the genus (Megalonyx). The species was ultimately named Megalonyx jeffersonii in his honor.^[2][3][4]

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, alongside co-founder Howard Chiu. 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.

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 descendants 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 Placodermi (armored 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 (crocodiles, alligators etc)
      • Order Saurischia (dinosaurs)
      • Order Ornithischiaa (dinosaurs)
  • Class Aves
  • Class Mammalia
    • Subclass Prototheria
      • Order Monotremata (platypus and the echidnas)
    • Subclass Theria
      • Infraclass Metatheria
        • Order Marsupialia (kangaroos, dunnarts, opposums, wombats etc)
      • Infraclass Eutheria (placentals)
        • Order Insectivora
        • Order Chiroptera (bats)
        • Order Creodonta
        • Order Carnivora (dogs/cats)
        • Order Perissodactyla (horses)
        • Order Artiodactyla (cattle and other ungulates)
        • Order Proboscidea (elephants)
        • Order Edentata
        • Order Cetacea (whales and dolphins)
        • Order Rodentia (mice, rats etc)
        • Order Lagomorpha (rabbits)
        • Order Primates (monkeys, apes and primates)

References

1. ^ Hackett, S.J., Kimball, R.T., Reddy, S., Bowie, R.C.K., Braun, E.L., Braun, M.J., Chojnowski, J.L., Cox, W.A., Han, K-L., Harshman, J., Huddleston, C.J., Marks, B.D., Miglia, K.J., Moore, W.S., Sheldon, F.H., Steadman, D.W., Witt, C.C. and Yuri T. (2008) A phylogenomic study of birds reveals their evolutionary history. Science. 320: 1763-1768.
2. ^ Jefferson, Thomas, "A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia", Read before the American Philosophical Society, March 10, 1797. The "certain bones" consisted of three large claws and associated smaller bones. He theorized that they were the remains of an extinct lion which he named Megalonyx ("giant claw"). In 1799, Dr. Caspar Wistar correctly identified the remains as belonging to a giant ground sloth. In 1822 Wistar officially named it Megalonyx jeffersonii.
3. ^ Jefferson, Thomas (1799), “A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia”, Transactions of the American Philosophical Society, Vol. 4 pp. 246-260.
4. ^ Wistar, Caspar (1799), “A Description of the Bones Deposited, by the President, in the Museum of the Society, and Represented in the Annexed Plates", Transactions, pp. 526-531, plates.