Strontium Isotopes Support Small Home Ranges for Extinct Lemurs

Abstract

Among mammals, including anthropoid primates, the primary factors that affect mobility are body size (larger-bodied species move more than smaller ones), diet (frugivores and trophic omnivores are more mobile than folivores), and habit (terrestrial taxa have larger home ranges than arboreal ones). If similar factors hold for Lemuriformes, we would expect large-bodied (particularly frugivorous) extinct lemurs to have been more mobile than smaller-bodied (particularly folivorous) extant species. Yet multiple lines of evidence (e.g., low Retzius Periodicities, small semicircular canal size, small relative brain size) suggest that extinct lemurs were relatively inactive. If so, they may have had relatively small home ranges, perhaps on par with smaller-bodied extant lemurs. We used strontium isotopes (87 Sr/ 86 Sr), which vary spatially primarily as a function of geology, to compare mobility for eight lemur genera: Eulemur, Lemur, Lepilemur, and Propithecus (extant), and Archaeolemur, Megaladapis, Pachylemur, and Palaeopropithecus (extinct). Subfossils came from two sites: Ankilitelo/Mikoboka, a series of sinkholes in a limestone plateau, and Ampasambazimba, a wetland underlain by a variety of igneous and metamorphic rocks. Within either site, we expected more mobile taxa to exhibit more variable 87 Sr/ 86 Sr, reflecting larger movement across a diversity of geologies. We found no differences in median 87 Sr/ 86 Sr or variance between extinct and extant lemurs at either site (Wilcoxon and Bartlett p > 0.05 for all comparisons). There were apparent but insignificant differences among genera (Kruskal-Wallis and Bartlett p > 0.05). Isotopic variability was greater at Ampasambazimba than at Ankilitelo/Mikoboka, reflecting differences in the underlying geology. One Palaeopropithecus from Ankilitelo/Mikoboka and one Eulemur from Ampasambazimba had unusually elevated 87 Sr/ 86 Sr. Both of these individuals could have been deposited at their respective sites by a predatory bird. These results demonstrate the value of 87 Sr/ 86 Sr for testing hypotheses related to the behavior of now-extinct species. Strontium isotopes support low mobility for extinct lemurs, and suggest that Lemuriformes as a whole differ from anthropoids in having relatively depressed basal metabolic rates and reduced activity levels. These traits reduce energetic expenditure, and likely developed in response to Madagascar's harsh environments. However, small home ranges also make lemurs more vulnerable to extinction.

Mid-Cenozoic climate change, extinction, and faunal turnover in Madagascar, and their bearing on the evolution of lemurs

“…These include adaptations to minimize energy expenditure, maximize energy intake from foods of varying quality, and survive episodes of food scarcity whether seasonal or due to environmental resource unpredictability. Some are preserved in the morphology or chemistry of bones of extinct animals – for example, in strontium isotopes which suggest that the extinct lemurs had small home ranges [ 53 ], in skeletal adaptations for slow locomotion [ 54 – 56 ], or in the relative size of the semicircular canals which offer independent confirmation of reduced activity levels [ 57 , 58 ]. The ancestral lemuriform exhibited high folivory [ 59 ], “lemur syndrome” adaptations such as reduced sexual dimorphism and dominance of adult females over males [ 60 ], and depressed Retzius periodicity [ 5 ] (the latter perhaps associated with risk-averse life histories).…”

Bioavailable Strontium, Human Paleogeography, and Migrations in the Southern Andes: A Machine Learning and GIS Approach

“…Building on these finds, the authors suggest that the deposition and reworking of unradiogenic volcanic sediments by aeolian, fluvial, and glacial erosion homogenized the isotopic landscape, decoupling to some extent bioavailable variation from underlying bedrock geology. This study indicates that recent geomorphic processes have an impact in the spatial resolution in terms of that can be achieved by means of bioavailable 87 Sr/ 86 Sr data to assess past landscape use (Crowley and Godfrey, 2019;Scaffidi and Knudson, 2020;Serna et al, 2020;Snoeck et al, 2020;Miller et al, 2021).…”

Tooth chipping patterns in Archaeolemur provide insight into diet and behavior

“…The available evidence suggests Archaeolemur had an omnivorous diet consisting of fruits, plants, vertebrates and potentially crustaceans (e.g., Burney et al, 1997;Crowley & Godfrey, 2019;Dumont et al, 2011;King et al, 2001;Schwartz et al, 2002;Vasey et al, 2012). This diet required substantial processing using the ante- (Hogg & Walker, 2011;Maas & Dumont, 1999;Towle et al, 2020).…”