MAMMAL SPECIES DURATIONS IN THE FOSSIL RECORD: ANSWERING THE QUESTION, WHICH SPECIES HAS THE LONGEST DURATION IN THE FOSSIL RECORD?

Which species of mammal survived for the longest period of time? In order to address this question a systematic search was undertaken of mammalian species to determine which species had the longest duration in the fossil record. A species duration in the fossil record is influenced by the attributes of the species in question, in addition to the factors leading to its preservation across as much of its entire temporal range as possible. Internal factors such as specialized anatomical features, phylogenetic relationships, behavior, or ecology, may manifest itself in producing certain species that are resilient to change. While external factors may determine species durations in the fossil record because of chance, such as preservation, optimum geological periods of stability, and the lucky avoidance of extinction. Examination of genera of mammals extracted from the the Paleobiology Database and confirmed by primary literature searches indicate that 106 genera and 19 species have fossil records that extend 20 million years. These genera and species were further examined to see if they exhibited any phylogenetic, ecological, or temporal similarities. Proportions of represented long duration taxa are similar to proportions across all Mammalia, with Proboscidea being the most disproportional, with 9% of genera with 20 Ma or longer durations. Size distribution shows slight differences, with a greater skew toward larger body sizes, but with a smaller peak than modern mammal size distributions. Phylogenetic similarity of long duration taxa, show a disproportional representations of the opossum family Didelphidae. The Didelphidae family consistent of living opossums and as well as mouse-sized marsupials recognized in the fossil record based on fossilized teeth. Temporal ranges show occurrences of long lived taxa clustering between the Eocene to Miocene, with only 20.75% originating before the Eocene. The two species with the longest duration in the fossil record are the small insectivorous Lipotyphla Centetodon magnus with aduration of 25 million years, and the large proboscidean Gomphotherium angustidens with a duration of 23 million years. The great disparity between these two species highlights the element of chance in determining species longevity in the fossil record.