What are birds?

Birds are members of the animal kingdom; they have their own class, known as Aves. (A possible origin of the word bird is thought to be the Old English brid, which originally referred to the young of animals.) Birds are vertebrate animals, warm-blooded, reproduce by laying eggs, and have feathers and beaks. They have four limbs, with the front two limbs modified into wings.

While you definitely wouldnt have heard Polly want a cracker! during the Cretaceous period, evidence has been found suggesting an ancient ancestor of the parrot may have existed during that time (iStock).

How are birds classified?

Birds have a class all their own called Aves. Within this broad class is a subclass called the Neornithes. This grouping includes the approximately 10,000 species of living birds. Another classification term for these birds is Neoaves, a basal division of birds that includes 95 percent of all living birds. In turn, this grouping is further divided into four suborders based on the palate anatomy of the birds. (There also are some different classification systems for birds, including one that divides the Neornithes only into the Palaeognathae and the Neognathae; for purposes of this discussion, we will use the four suborder classifications.) The four suborders are the Palaeognathae, which are divided into two subgroups, the ratites (such as ostriches, rheas, emus, and other large, flightless birds) and tinamous (such as the South American tinamous); Impennes (penguins); the Odontognathae (fossil birds); and Neognathae (all other living birds, from hummingbirds to plovers).

Were any birds around when dinosaurs roamed Earth?

Yes. Scientists believe that the ancient ancestors of several modern birds were around during the latter part of the Cretaceous period. Originally, scientists thought that only aquatic birds, such as ancestors of the loons, seabirds, and albatrosses populated Earth during prehistoric times. More recently, ancient bones resembling a modern parrot have been discovered. As more bones have been found and confirmed, scientists have concluded that certain birds also flew when the dinosaurs roamed Earth about 65 to 70 million years ago.

Did some early scientists believe birds were related to dinosaurs?

Yes, some early scientists believed there was a similarity between birds and reptiles, an idea that was noted as far back as 400 years ago. But the relationship connection did not come to the forefront of science until the mid-nineteenth century, especially after the discovery of bird-like bones from a German rock quarry.

Who first published papers noting the resemblance of birds to dinosaurs?

In 1867, paleontologists Edward Drinker Cope (1840-1897) and Othniel Charles Marsh (1831-1899) were the first to publish papers noting the resemblance of birds to dinosaurs.

What is Archaeopteryx lithographica?

Archaeopteryx lithographica (literally ancient wing from lithographic limestone) fossils are dated at around 150 million years old and are some of the worlds most famous fossils. Thought by many modern paleontologists to represent the oldest bird yet discovered, it was a small bird about the size of a crow. The first fossil of an Archaeopteryx lithographica was found in 1855. The fossil remains were found in sedimentary rock from the Late Jurassic period in the Solnhofen quarries in southern Germany. Interestingly enough, the fossil would not be recognized as a bird until 1970.

Who first proposed the idea that birds were descendants of dinosaurs?

English naturalist Thomas Henry Huxley (1825-1895), an authority on bird evolution and a champion of Charles Darwins theory of evolution, first noted characteristics shared by dinosaurs and birds. Huxley observed that a particular species of chicken raised in his area (called a Dorking fowl) had leg bones similar to those of theropod dinosaurs. He also cited as evidence the fossil of a bird-like dinosaur, Archaeopteryx lithographica, discovered in 1855 in Germany. Between 1868 and 1869, using a method of anatomical comparison resembling modern cladistic analysis, Huxley decided birds had descended from dinosaurs. Years later, the Archaeopteryx lithographica represented the transition between dinosaurs and birds, and it was thought of as proof that birds descended from dinosaurs.

English naturalist Thomas Henry Huxley was the first to theorize that birds may have descended from dinosaurs (iStock).

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