The evolution of the terrestrial vertebrates: environmental and physiological considerations

Area of Science:

• Vertebrate Paleontology
• Evolutionary Biology
• Marine Biology

Background:

• Physiological evidence historically suggested a freshwater origin for jawed vertebrates (gnathostomes), bony fish (Osteichthyes), and tetrapods.
• This contrasts with geological evidence favoring a marine origin for vertebrates, gnathostomes, and Osteichthyes.
• Early amphibian fossils are found in tidally influenced sediments, and Devonian freshwater chemistry may have blurred marine/non-marine distinctions.

Purpose of the Study:

• To propose a new model of tetrapod evolution based on a marine ancestry.
• To re-evaluate the origins of key vertebrate adaptations in light of marine evolutionary pressures.

Main Methods:

• Review of physiological and geological evidence regarding vertebrate origins.
• Analysis of early vertebrate adaptations such as urea formation/retention and air-breathing.

Main Results:

• Geological evidence strongly supports a marine origin for vertebrates, gnathostomes, and Osteichthyes.
• Adaptations for terrestrial life, including urea retention and air-breathing sacs, may have originated in marine environments to cope with osmotic stress and gas exchange challenges.
• These adaptations were crucial for the transition to terrestrial environments.

Conclusions:

• The ancestral vertebrate lineage originated in marine environments.
• Key physiological adaptations facilitating terrestrial life evolved in response to marine environmental conditions.
• A marine origin model provides a new framework for understanding tetrapod evolution.