Sunday, 9 February 2014

#503 In the studio: Birds . . . evolution and anatomy


Birds appeared more than 150 million years ago, during the Jurassic or possibly the Triassic period.
The recent discovery of vast beds of fossil birds and "feathered dinosaurs"  in deposits in northeast China
and central Asia has opened argument about whether birds descended from dinosaurs or earlier
 archosaurs but also clarified an ongoing question:  Birds and two-legged creatures such as
the carnivore, Tyannosaurus rex, are on the same branch of the evolutionary tree.

The earliest known bird was the Archaeopteryz - pronounced arky-OP-tuh-ricks - the word means "ancient wing" in Greek.  A fossil discovered in Bavaria in 1861 shows that the creature who grew to the size of a crow, had feathers, claws, and other features that scientists think is the link to modern birds.   Six specimens of "arky" have been found . . .
all in limestones in southern Germany and all dated between 200 and 140 million years ago.

Below, is a photo of Archaeopteryz . . . "arky" for short.

Although "arky" had many unmistakable bird features, much of its skeleton is akin to those of reptiles.
Scientists think a bird's scaly legs are the last reminders of a reptilian ancestor and that feathers originated as
reptilian scales . . . feathers are made from the same horny substance of which fingernails are made.   

Feathers - not flight - set birds apart from other animals. . . many species, such as ostrich, have evolved with an inability to fly.  The evolution of powered flight required major skeletal modifications to change its early gliding wing movement to flapping flight.  The small,  two-legged, carnivorous dinosaur designed for a life of gliding from tree to tree in a gloomy Jurassic jungle evolved into today's modern bird and Archaeopteryz is the missing link.

Most, but not all birds fly.  The bones are light but remarkably strong, and some contain air sacs connected to the lungs.  Below, is a drawing of a bird skeleton and illustrates a number of modifications that make flight possible.
(1): Heavy teeth have been replaced by a light bill

(2): The bones of the skull are thin.

(3) and (4): The bones of the wings and legs are composed of thin-walled, honey-combed  tubes.
Nature has sluffed off weight to enable flight.

Although the information presented in this post is current . . .  as new discoveries are made,
both in the field and with DNA, scientists will continue to fine-tune,
fill in the details, provide a more complete picture, and debate the evolution of birds.

The fact remains that "arky" was unique for it possessed feathers.
The development of feathers was one of the crucial steps in the evolution of birds.

Blog, text, photos, drawings, and sculpture . . . © Sandy Scott and Trish Smith


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