Revisiting the vertebrate invasion of the land

Seven papers that expand upon recent research into the origin of tetrapods and their invasion of the land during the Devonian period appear in the September/October 2004 issue of Physiological and Biochemical Zoology.

Although the fossil record of this transition remains far from complete, new discoveries have increased the resolution of the morphological sequence, documented the relative rapidity and geographic distribution of the tetrapod appearance, and fueled new controversy over the environmental and biological factors involved. Topics in this state-of-the-art issue range from the fish-tetrapod fossil record to diverse aspects of the behavior, physiology, biochemistry, and ecology of the extant fish species that use either or both terrestriality and air breathing.

Research findings include:

• The first demonstration of the presence of SP-D in the air-breathing organs of nonmammalian species and SP-B in actinopterygian fishes.
• Selection pressures imposed by life in the intertidal zone are insufficient to have resulted in the requisite aerial respiratory capacity or the degree of separation from water required for the vertebrate land transition.
• An examination of the effects of hypoxia and exercise on the partitioning of aquatic and aerial oxygen uptake in the Pacific tarpon.
• Beach spawning provides habitat segregation at different points in the life history, with air emergence early in the life cycle and a return to water at hatching.
• With regard to excretory nitrogen metabolism, modern tropical air-breathing fishes exhibit a variety of strategies to survive on land, and they represent a spectrum of specimens through which we may examine various biochemical adaptations that would have facilitated the invasion of the terrestrial habitat by fishes during evolution.

These articles are from two merged symposia (“How to Live Successfully on Land If One Is a Fish: The Functional Morphology and Physiology of the Vertebrate Invasion of the Land” and “Evolution of Air Breathing”) presented at the Sixth International Congress of Comparative Physiology and Biochemistry, Mount Buller, Victoria, Australia, 2003.