Difference between revisions of "Arctic Life/Arctic Animals/Birds/Fossils"

Revision as of 17:06, 31 August 2019

Archaeopteryx

The first specimen of Archaeopteryx lithographica was discovered in a limestone quarry in Bavaria in 1861. It was the first fossil that clearly showed the reptilian ancestry of birds. Although Archaeopteryx clearly had well-developed feathers, most ornithologists doubt that it could fly, but agree that it may have been able to glide. The name Archaeopteryx means "ancient wing". Archaeopteryx gained its species name, lithographica, from its discovery in fine limestone that was used to produce the printed illustrations in books; this type of printing is called lithography.

Hesperomis

Hesperornis was a large, flightless, diving bird from the Cretaceous Period. It had vestigial wings, a stubby tail, and legs placed far back on the body. Superficially, Hesperornis resembled modern loons.

Confuciusornis

Confuciusornis sanctus is a recently discovered Jurassic species from China. It is the earliest known fossil of a toothless, beaked bird. Several partial fossils of this species also provided the first indisputable evidence for a body covered with contour feathers. It appears that Confuciusornis was adapted for climbing tree trunks.

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 ==Archaeopteryx==
-[[File:Archaeopteryx_fossils.jpg|frameless|right]]
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 The first specimen of Archaeopteryx lithographica was discovered in a limestone quarry in Bavaria in 1861. It was the first fossil that clearly showed the reptilian ancestry of birds. Although Archaeopteryx clearly had well-developed feathers, most ornithologists doubt that it could fly, but agree that it may have been able to glide.
 The name Archaeopteryx means "ancient wing". Archaeopteryx gained its species name, lithographica, from its discovery in fine limestone that was used to produce the printed illustrations in books; this type of printing is called lithography.
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 ==Confuciusornis==
 Confuciusornis sanctus is a recently discovered Jurassic species from China. It is the earliest known fossil of a toothless, beaked bird. Several partial fossils of this species also provided the first indisputable evidence for a body covered with contour feathers. It appears that Confuciusornis was adapted for climbing tree trunks.
-==Cretaceous Ancestry==
-Most early bird groups disappeared during the mass extinction at the end of the Cretaceous, but a few survived, and along with a hypothesized second major bird radiation near the Cretaceous/Tertiary boundary, are the ancestors of modern birds. Some hypothesized survivors of the Cretaceous/Tertiary extinction, present in the Arctic region today include:
-Order Gaviformes – Loons
-Order Gruiformes – Cranes, Rails, Coots, and Gallinules
-Order Charadriiformes, Family Scolopacidae – Sandpipers
-==Tertiary Ancestry==
-Most of the Orders of birds that we see today first appeared in the Tertiary period, 65 to 2 million years ago. Many of these are represented in the Arctic today, including:
-Order Anseriformes – Ducks, Geese, and Swans
-Order Charadriiformes – Family Laridae (Gulls and Terns)
-Order Falconiformes – Falcons, Hawks, Eagles, and Osprey
-Order Passeriformes – Perching Songbirds
-==Quaternary Events==
-The Quaternary Period, the one in which we now live, has thus far been a period of great climatic change and intense glaciation. Early in this period, over half of the approximately 21,000 bird species then present died out, leaving us with the 9,500 or so alive today.
-In the Pleistocene, repeated glaciation, sometimes covering half of the North American continent, caused rapid changes in weather patterns and sea levels. Great dispersals of many bird species occurred, as did widespread extinction.
-==Controversies==
-Many ornithologists today disagree on exactly how the Class Aves evolved, and even when the first bird appeared. Fossil evidence from Texas may have pushed back the origin of the first birds by 50 million years, but the jury is still out. Also, new fossils from Mongolia are being uncovered at a rapid pace, so in ten years our understanding of avian evolution may be completely different from that which exists now!
-The ability to sequence DNA has enabled us to look more closely at the relationships between organisms, but it has also created problems. For example, how much of a genetic difference is required for two organisms to be considered separate species? Or separate families? Estimates have been proposed, but agreement is rare. In 1988, Charles Sibley and Jon Ahlquist, two U.S. scientists, proposed a new classification of Class Aves based on DNA-DNA hybridization. Nearly a decade later, their classification is still turning ornithology on its ear!