Traits: Cells have dna



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A2.21 Archaeopteryx lithographica (ancient wing)



Traits:

  • Cells have DNA

  • Cells have a nucleus in them

  • Cells have mitochondria

  • Multicellular

  • Cells are held together with collagen.
    Sexual reproduction

  • Early embryo forms as a hollow ball of cells called a blastula

  • This blastula opens into a tube “tail end first”

  • Has a head and is bilaterally symmetrical (you can draw one line down the middle)

  • Cells organize themselves into true tissues (muscle, nerves)

  • Cells organize themselves into true organs (heart, liver, stomach)

  • Has a hollow space between the gut and outer body wall where organs are (this space is called a coelem—pronounced “see-lome”

  • Segmented body

  • Internal bony skeleton

  • Backbone, Spinal chord and braincase

  • Had jaws
    Enamel teeth

  • Had lungs

  • Had paired appendages

  • Had four legs

  • Amniotic egg (able to lay its eggs out of water)

  • Two openings in the roof of the mouth (“palatal openings”)

  • Two openings in the side of the skull at the temple (“diapsid openings”)

  • Opening in the skull in front of eye socket (“antorbital fenestra”)

  • Has a hole in the hip socket allowing it to stand upright

  • Has grasping hands

  • Narrowing of the middle ear bone—only one middle ear bone (“slender stapes”)
    A notch in the two bone just behind the eye opening (“notch in postorbital”)
    Simple hinge-like ankle (requiring a more erect posture—no sprawling walk)
    Three toed foot

  • Three fingered hand in wing
    Pulley-shaped wrist bone

  • Backward-turned pubis bone

  • Feathers

Archaeopteryx (meaning "ancient wing") is a very early prehistoric bird, dating from about 150 million years ago during the Jurassic period, when many dinosaurs lived. It is one of the oldest-known birds.

Archaeopteryx seemed to be part bird and part dinosaur. Unlike modern-day birds, it had teeth, three claws on each wing, a flat sternum (breastbone), belly ribs (gastralia), and a long, bony tail. Like modern-day birds, it had feathers, a lightly-built body with hollow bones, a wishbone (furcula) and reduced fingers. This crow-sized animal may have been able to fly, but not very far and not very well. Although it had feathers and could fly, it had similarities to dinosaurs, including its teeth, skull, lack of a horny bill, and certain bone structures. Archaeopteryx had a wingspan of about 1.5 feet (0.5 m) and was about 1 foot ( 30 cm) long from beak to tail. It probably weighed from 11 to 18 ounces (300 to 500 grams).

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Paleontologists think that Archaeopteryx was a dead-end in evolution and that coelurosaurian theropods (a group of dinosaurs that included the Dromaeosaurs Deinonychus, Utahraptor, and Velociraptor) led to the birds.



Fossils: Amazingly detailed Archaeopteryx fossils have been found in fine-grained Jurassic limestone in southern Germany. This fine-grained limestone is used in the lithographic process, hence the species name "lithographica" given to the early Archaeopteryx specimen. The first Archaeopteryx fossil (a feather) was found in 1860 near Solnhofen, Germany, and was named by the German paleontologist Hermann von Meyer in 1861. That year he also discovered the first specimen of Archaeopteryx. A total of eight Archaeopteryx specimens have been found, plus the feather.

The Solnhofen area was a stagnant lagoon during the Jurassic period (Europe was a series of islands at this time). The lagoon's waters had little or no oxygen (anoxic) near the bottom, a situation that helped preserve many dead organisms, and boost the chances of fossil formation, since decay after death is very slow in anoxic waters.



Bird fossils are rare because bird bones are hollow and fragile, and usually deteriorate instead of fossilizing. However, a few Jurassic, mid-Cretaceous, Eocene and Miocene-Pliocene bird fossils have been found.

The Origin of Birds: In 1868, Thomas Henry Huxley interpreted the Archaeopteryx fossil to be a transitional bird having many reptilian features. Using the fossils of Archaeopteryx and Compsognathus, a bird-sized and bird-like dinosaur, Huxley argued that birds and reptiles were descended from common ancestors. Decades later, Huxley's ideas fell out of favor, only to be reconsidered over a century later (after much research and ado) in the 1970's.

In 1986, J. A. Gauthier looked at over 100 characteristics of birds and dinosaurs and showed that birds belonged to the clade of coelurosaurian dinosaurs. [Gauthier, J.A., 1986. Saurischian monophyly and the origin of birds, in: The Origin of Birds and the Evolution of Flight, California Academy of Sciences Memoir No. 8]



http://www.enchantedlearning.com/subjects/dinosaurs/dinos/Archaeopteryx.shtml 3/16/08



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