Physiological and life history strategies of a fossil large mammal in a resource-limited environment

Abstract

Because of their physiological and life history characteristics, mammals exploit adaptive zones unavailable to ectothermic reptiles. Yet, they perform best in energy-rich environments because their high and constant growth rates and their sustained levels of resting metabolism require continuous resource supply. In resourcelimited ecosystems such as islands, therefore, reptiles frequently displace mammals because their slow and flexible growth rates and low metabolic rates permit them to operate effectively with low energy flow. An apparent contradiction of this general principle is the long-term persistence of certain fossil large mammals on energy-poor Mediterranean islands. The purpose of the present study is to uncover the developmental and physiological strategies that allowed fossil large mammals to cope with the low levels of resource supply that characterize insular ecosystems. Long-bone histology of Myotragus, a Plio-Pleistocene bovid from the Balearic Islands, reveals lamellar-zonal tissue throughout the cortex, a trait exclusive to ectothermic reptiles. The bone microstructure indicates that Myotragus grew unlike any other mammal but similar to crocodiles at slow and flexible rates, ceased growth periodically, and attained somatic maturity extremely late by Ϸ12 years. This developmental pattern denotes that Myotragus, much like extant reptiles, synchronized its metabolic requirements with fluctuating resource levels. Our results suggest that developmental and physiological plasticity was crucial to the survival of this and, perhaps, other large mammals on resource-limited Mediterranean Islands, yet it eventually led to their extinction through a major predator, Homo sapiens.islands ͉ artiodactyl ͉ paleohistology ͉ growth rate ͉ metabolism

Evidence of correlated evolution of hypsodonty and exceptional longevity in endemic insular mammals

“…In this work, we provided evidence of a relationship between the extreme molar crown height and the delay in timing and rates in crown formation and tooth eruption, which doubles that of extant bovids of similar body size. This slow pace of dental development in M. balearicus was coupled to a general delay in the growth period and, hence, in maturity [33]. This evolution towards a slow life history [57] has been suggested to result from changes in energy allocation from reproduction to growth and maintenance that facilitated survival in a resource-limited environment without predators [36].…”

“…We used the endemic goat-like bovid M. balearicus, a fossil species that survived for a long geological time span under the characteristic ecological conditions of islands [12,13]. The pristine laboratorylike environmental conditions unaltered by anthropogenic interventions make the genus Myotragus an ideal model to study evolutionary trends in life-history traits on islands [33,34,54].…”

“…The fossil genus Myotragus [32] (Bovidae, Caprinae) is an ideal model to study evolutionary trends on islands [14,33,34]. Myotragus balearicus is the terminal species of this endemic genus that survived under complete geographical isolation for over 5 million years, from the Pliocene to the Holocene, until its extinction more than 3000 years ago [14].…”

The Cova des Pas de Vallgornera (Llucmajor, Mallorca): a singular deposit bearing an exceptional well preserved Early Pleistocene vertebrate fauna

“…Changes in the longevity have been reported in the most recent species, M. balearicus (Köhler & Moyà-Solà, 2009;Jordana & Köhler, 2011).…”

Reptilian all the way?

“…In endotherms LAGs are known from giant insular moas, and the mainland parrot Amazona (2), but are unknown in insular or mainland mammals (1). The authors interpret this as evidence for a late onset of reproduction, an adaptation to lower energetic needs in islands where they claim resource levels are chronically low.…”