• Blog Post Origin and Evolution of Birds
  • Origin and Evolution of Birds

    Consider for a minute the diversity of birds. There are nearly 10,000 species! Is it possible to trace these birds back to one common ancestor? If so, who is it?

    One of the major criticisms of Darwin’s Origin of Species was
    the apparent lack of any evidence showing the evolution of birds. Then,
    as luck might have it, only two years after he first published his book,
    Archaeopteryx appeared in a site in Germany.

    Today there are 8 preserved fossils of Archaeopteryx in various
    museums of the world. What an amazing find for science because it stirred
    scientists to try to figure out how birds were related to other creatures.

    caudipt

    Archaeopteryx
    was amazing for a few reasons. First it superficially resembled both a
    bird and a reptile. In fact, except for the feathers, the
    bird-like feet
    , and the fact that it had a wishbone
    (furcula) it didn’t really look like a bird. The jaws
    had teeth
    in them, of which no bird today has teeth. It also
    had the ankle bone fused to the shinbone. Clearly this
    bird had features of dinosaurs AND birds. So where did birds evolve?

    Three hypothesis on origin of birds finally arose:

    1. Therapod dinosaur hypothesis: The first was a hypothesis
      that they came from the therapod dinosaurs. Therapods are meat eating
      dinosaurs such as Allosaurus.
    2. Crocodiles – the second hypothesis was that they
      came from crocodiles because they had an endolymphatic duct. Yet, as
      more research was conducted, they discovered that there was a tremendous
      amount of variation in this duct even among the lizards and other reptiles.
      Not many people today give much attention to this hypothesis
    3. Neither crocodiles or dinosaurs:Neither on the dinosaur
      line or the crocodile line. Reasoning because several dinosaurs were
      very specialized already.

    Today we can show that birds are related in many ways to Dinosaurs. By
    using key characters we can use cladistics to understand better the relationships.
    For instance we can look at features they share in common with animals
    such as reptiles, and ancient dinosaurs in order to figure out where they
    may have evolved. They can thus, be linked generally to Ornithodira
    and more specifically to Manirapterans.

    If you look at a cladogram
    of Diapsids
    which includes snakes, lizards, crocodiles (archosaurs),
    and dinosaurs and birds, you can get a better picture as to where birds
    fit in.

    Dinosaur cladogram:

    Looking in particular at the Ornithodira, Dinosaurs, Saurischian
    dinosaurs, Therapods, Tetanurae, Coelesaurs, Manirapterans
    . (list
    heirchial)

    Ornithodira Advanced metatarsal ankle
    Dinosauria 3+ sacral vertebrae; reduced fibula
    Ornithischia 5+ sacral vertebrae, opptisthopubic pelvis, predentary
    bone in lower jaw
    Sauropodomorpha 10+ sacral vertebrae, ankles have an ascending process
    Theropoda Elongate, narrow metatarsus; hollow bones, metatarsal 5 reduced
    Tetanurae (Allosaurus etc.), has a tooth row on the upper row that
    does not extend back past the orbital (eyes). Also has a antorbital
    fanestra
    .
    Maniraptora because has a semi-opisthopedic pelvis. Means that
    the pubis bone of the pelvis is rotating backwards and has a foot.
    Aviale Presence of feathers

    Summarization of the set of derived characters that link them
    to the dinosaurs:

    • Pelvis

    • Clavicles

    • Wrist

    Once the idea that birds came from dinosaurs began, there was a scurry
    to find fossil evidence that could link birds back to their dino-roots.
    Several different dino-birds arose in the last century. One was Caudipteryx

    Caudipteryx:

    In China a fossil
    was found that was dinosaur-like but had feathers. It seems that the wings
    would have been too small to allow it to fly, but, the fact that it had
    wings made it big news! Thus, the idea was that the initial evolution
    of feathers may not have been for powered flight. In fact, if you look
    at the tail feathers, it looks as though they are symmetrical around the
    shaft. This finding forced a reconfiguration of the systematics of the
    group.

    Microraptor

    Another fossil was found that, although it was not a fossil with wings,
    it was a closely related dinosaur to birds that was very small and appeared
    to be arboreal. This tiny fossil is only about 10 cm long and if it lived
    in the trees could have glided from tree to tree.

    ORIGIN OF FLIGHT.

    How did it evolve?

    For almost a century scientists have been debating this issue. The common
    belief was that flight must have evolved from the trees down. This is
    because every known modern semi-airborn animal (glider), seems to be arboreal.
    Yet, another competing theory is that the wings are used to catch insects
    and thus evolved from the ground up.

    Leaping

    One set of reasoning for the ‘ground-up‘ hypothesis is that dinosaurs
    could have been leaping to catch insects and wings allowed them to come
    down in one piece. Part of the evidence is that the capturing of prey
    was the same movement for flight.

    Wing-Assisted Incline running. (copy
    of the study
    ).

    In a 2003 article in science, Kenneth Dial proposed his theory of ‘wing-assisted
    incline running’ as a way for wings to evolve. In the study he used chucker
    partridges and had them run up grades from 0 to 90 degrees. From 0 to
    45 degrees, they just used their legs, but greater than 45 they used their
    wings too. When they flap their wings, they put traction on the surface
    and thus, increase their ability to run up the incline

    Links about Bird Evolution and the Evolution of flight:

    By Rob Nelson

    Written by Rob Nelson

    Rob is an ecologist from the University of Hawaii. He is also an award winning filmmaker. As principle director of the Untamed Science productions his goal is to create videos and content that are both entertaining and educational. When he's not making science content, he races slalom kayaks and skydives.

    You can follow Rob Nelson
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