Parallel patterns and trends in functional structures in extinct island mammals

Abstract

Endemic mammalian species on islands are generally known to have followed a different evolutionary pathway than their mainland relatives. General patterns, such as body size trends, have been described regularly. However, most island mammal species are unique and each of them is adapted to a specific local niche as part of an equally specific ecological assemblage. Therefore, comparing island species across taxa, islands and time is inherently dangerous without understanding the adaptational value of the studied feature in the compared taxa and without taking the ecological setting of the taxa into account. In this contribution, general and recurring patterns are described per taxon. Some features, like body mass change and sturdy limbs, are relatively general, whereas most features, like bone fusions and change of orbital axis, occur only in a very few taxa. Some features are even contradictory, such as brain size and degree of hypsodonty, with each taxon having its own particular design. In conclusion, general patterns are more often than not just trends and need to be applied with caution.

Paleoecological reconstruction of Late Pleistocene deer from the Ryukyu Islands, Japan: Combined evidence of mesowear and stable isotope analyses

“…It is not inferred from the browsing diet of C. astylodon that the hypsodont molars may be the adaptive response to wear-induced diets. Rather, the hypsodont molar may have evolved in combination with the elongated longevity of C. astylodon, similar to the case of M. balearicus (Jordana et al, 2012;van der Geer, 2014). For M. balearicus, not only the longevity but also other life history traits (time of weaning and sexual maturity) were modified to represent a slow life history or K-selection strategy (Marin-Moratalla et al, 2011;Jordana et al, 2013).…”

Bone lesions in a Late Pleistocene assemblage of the insular deer Candiacervus sp.II from Liko cave (Crete, Greece)

“…In this contribution, the taxonomy of De Vos (1996) is followed because 95.3% of the material from Liko cave belongs to size II. This size is commonly referred to as Candiacervus sp.II (De Vos, 1996;Van der Geer et al, 2006Van der Geer, 2014;Kolb et al, 2015).…”

A dwarf elephant and a rock mouse on Naxos (Cyclades, Greece) with a revision of the palaeozoogeography of the Cycladic Islands (Greece) during the Pleistocene

“…Until further analysis, Palaeoloxodon antiquus is considered ancestral to all Mediterranean dwarf elephants, with the exception of Mammuthus creticus (=Elephas creticus in Bate, 1905) and Mammuthus lamarmorai (= Elephas lamarmorae in Major, 1883), based on morphological grounds (for discussion and characters, see supporting information to Herridge and Lister, 2012). This new analysis should take secondarily derived characters and changes due to allometry into consideration (see for a discussion on convergent morphologies in unrelated insular taxa Van der Geer, 2014); in fact, this applies to the type species Palaeoloxodon naumanni as well, which is an insular species of Japan.…”

“…Due to reduced endurance as a result of their size reduction, it is likely to assume that they could cover a fraction of the distance their full-grown ancestors could cover. In addition, the loss of a strong pneumatisation of the dwarf elephant skull Van der Geer, 2014) and absolutely shorter trunk may have reduced their swimming capacities even further. In all likelihood, the various Southern Aegean dwarf species of Palaeoloxodon are the result of independent colonisation events from the mainland.…”