The Wall of Birds by Jane Kim

Author:Jane Kim
Language: eng
Format: epub
Publisher: HarperCollins
Published: 2018-08-20T16:00:00+00:00

Our story of evolution begins on a small corner wall at the east end of the first floor, with a nine-foot Tiktaalik roseae swimming toward its descendants. The ancient fish represents an early tetrapod, the group of four-limbed animals to which both humans and birds belong. As a transitional form, it had the gills and scales of fish in addition to anatomical structures similar to modern terrestrial animals. Spiracles on the top of its head suggest it had primitive lungs in addition to gills, and a lack of bony plates near the gills make it the earliest known fish with a neck. Perhaps of greatest significance are its fins—bony, weight-bearing protolimbs that eventually allowed for a transition to life on land. Fins evolved into legs and arms; arms became wings.

On the wall, just below Tiktaalik, swims a 365-million-year-old tetrapod called Acanthostega gunnari. While the limbs of this primitive air-breathing tetrapod were probably not weight bearing, its pelvis, attached to its vertebral column, represents a major anatomical step toward ambulation. Eight digits on each limb foreshadowed the development of hands and feet. I don’t know if each digit would have been visible on a living Acanthostega, but these characteristics were significant enough from an evolutionary perspective that I wanted to highlight them conspicuously. The Acanthostega’s neck allowed it to turn its head independently of its body—a crucial trait on the path to flight.

A few feet and about 125 million years removed from Acanthostega crawls Euparkeria capensis, a reptilian ancestor of archosaurs, a group that includes modern birds and crocodiles. Euparkeria demonstrates an early example of quadrupedal locomotion and hints at the eventuality of a bipedal gait. Its hind legs have migrated underneath its body, and with its shorter forelimbs, it may have been able to stand clumsily upright. Given its anatomical similarities to modern crocodiles, I positioned it in a crocodilian high walk, with its belly and most of its tail off the ground. Like birds, Euparkeria almost certainly laid hard-shelled eggs, allowing it to reproduce freely on dry ground.

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Tiktaalik roseae

Acanthostega gunnari

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