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McLean, D. M., 1979, Abstracts with Programs, Geological Society of America, Southeastern Section meeting, April 26-27, 1979, p. 205.


Dewey M. McLean

The late Pleistocene mammalian extinctions of about 15,000 to 9,000 years ago coincided with global warming following intensely cold late-Middle Weichselian conditions 20,000 to 17,000 years ago. Application of modern mammalian thermoregulation and reproduction concepts to the late Pleistocene mammals suggests adaptive difficulties of large, heavily insulated mammals to rapid warming following cold conditions. Extinctions in northern Europe 13,000 to 11,000 years ago coincided with the Late-glacial Interstadial (Coupe, 1975) which warmed in the early stages (indicated by Coleoptera) at perhaps lC per decade. Extinctions in North America peaked about 11,000 years ago during the time of steepest gradient of climatic change (Wright, 1976). Primarily large, terrestrial mammals were eliminated.

Body size and insulation geared to heat retention would have caused retention of excessive body heat during rapid environmental warming to above adaptive levels, causing widespread thermoregulatory disruption and hyperthermia. Among modern mammalian females, even normally hot summer temperatures cause hyperthermia which disrupts uterine blond flow, an embryo's nutrient, oxygen, and water source, generating widespread reproductive disruption. Late Pleistocene temperature elevation to above adaptive levels could only have generated widespread reproductive disruption among female mammals.

Among late Pleistocene male mammals, temperature elevation to above adaptive levels by suppressing the thyroid gland which regulates metabolic activity, and thus the quality of male sperm, would have reduced reproductive capability by depressing spermatogenesis.