Antiquity of the vertebrate pattern of activity metabolism and its possible relation to vertebrate origins.

Vertebrates generally possess well developed capacities for anaerobic metabolism, resulting in formation of lactic acid. Those capacities have traditionally been interpreted in terms of adaptation to hypoxic environments or to special situations such as diving. However, anaerobic metabolsim in striated muscle tissue is frequently a major source of ATP utilized during periods of intense activity. The evolutionary significance of anaerobically supported activity has not been discussed, although the interrelationships of capacities for aerobiosis and activity have received considerable attention. We present here evidence that the pattern of activity metabolism utilized by extant species probably dates back to the earliest vertebrates. It is also postulated that the evolution of extensive capacity for anaerobically supported burst activity may have been closely related to the evolution of vertebrates from invertebrate chordates.