Many genera of arvicolid rodents (voles) contain species that spend a considerable amount of time underground. Incisors provide a considerable effort in the digging process and a difference in the ...enamel microstructure of incisors is expected between species that spend most of their life above ground and those who have greater specializations for a subterranean habitat. The ratio between the thicknesses of the two layers composing the enamel of the incisors has proved to be an effective proxy to infer fossorial activity of extinct forms of
Arvicola but this ratio exhibited no phylogenetic signal (although lifestyle was in a greater extent related to phylogeny). We were able to infer ancestral lifestyles (of extinct populations and of nodes of the phylogeny) from enamel morphologies. Inclusion of fossils did not solve the uncertainties associated with the lifestyle for the last common ancestor of extant
Arvicola species and it did not change the inferred lifestyle of several other, less inclusive, clades.
De nombreux genres de campagnols (Rodentia, Arvicolinae) incluent des espèces au mode de vie clairement fouisseur et chez lesquelles les incisives jouent un rôle actif lors du fouissement. Cette situation permet d’envisager que la microstructure de l’émail des incisives pourrait révéler des différences entre espèces qui vivent surtout en surface et celles qui ont un mode de vie souterrain marqué. Ce travail montre que le rapport des épaisseurs des deux couches de l’émail des incisives est un bon d’indicateur du caractère fouisseur des formes actuelles et qu’il pourrait s’appliquer aux formes éteintes d’
Arvicola. Ce rapport n’est pas corrélé à la phylogénie (bien que le mode de vie soit dans une grande mesure relié à la phylogénie). L’inclusion des populations éteintes n’améliore pas les incertitudes sur les inférences des modes de vie ancestraux pour le dernier ancêtre commun des espèces actuelles d’
Arvicola et elle ne change pas les états ancestraux des clades moins inclusifs.
Abstract We report a specimen of an insular black rat ( Rattus rattus ) from Illa den Colom (Menorca, Western Mediterranean) displaying a singular dental characteristic. It has no molar teeth but ...displays regular incisors. Its mere occurrence as a regular adult rat is puzzling and we attempted to evaluate what diet and morphological changes in jaw shape were promoted by the total lack of molars, and allowed the successful survival of this specimen. Two approaches were performed: first, bone tissue was analysed to obtain δ15 N and δ13 C values in order to estimate dietary preferences of the rat. Second, the shape of the jaw was analysed through elliptic Fourier analysis, using outlines as markers of diet. The values for C and N fractionation (−19.89‰ and 10.06‰, respectively) suggest that the molarless rat included animal food in the diet and not exclusively plant material as observed in other mainland rat populations. The morphometric analysis in which the shape of the molarless mandible falls into the range of omnivorous groups leads to a similar conclusion. The adult age of the specimen suggests that it fed efficiently enough with its incisors to allow a normal growth. Although displaying a lack of molar teeth, no deep changes in remodelling jaw morphology can be observed and its shape falls into the variation of regular murines. The molarless rat exemplifies that special ecological features on small islands allow the survival of aberrant morphotypes.
Within a group of organisms, some morphologies are more readily generated than others due to internal developmental constraints. Such constraints can channel evolutionary changes into directions ...corresponding to the greatest intraspecific variation. Long term evolutionary outputs, however, depend on the stability of these intraspecific patterns of variation over time and from the interplay between internal constraints and selective regimes. To address these questions, the relationship between the structure of phenotypic variance covariance matrices and direction of morphological evolution was investigated using teeth of fossil rodents. One lineage considered here leads to Stephanomys, a highly specialized genus characterized by a dental pattern supposedly favoring grass eating. Stephanomys evolved in the context of directional selection related to the climatic trend of global cooling causing an increasing proportion of grasslands in southwestern Europe. The initial divergence (up to 6.5 mya) was channeled along the direction of greatest intraspecific variation, whereas after 6.5 mya, morphological evolution departed from the direction favored by internal constraints. This departure from the “lines of least resistance” was likely the consequence of an environmental degradation causing a selective gradient strong enough to overwhelm the constraints to phenotypic evolution. However, in a context of stabilizing selection, these constraints actually channel evolution, as exemplified by the lineage of Apodemus. This lineage retained a primitive diet and dental pattern over the last 10 myr. Limited morphological changes occurred nevertheless in accordance with the main patterns of intraspecific variation. The importance of these lines of least resistance directing long‐term morphological evolution may explain parallel evolution of some dental patterns in murine evolution.
Hypnomys morpheus is a giant endemic dormouse from the Pleistocene deposits of Mallorca and Menorca (Balearic Islands, Spain). The present paper aims to interpret the morphological divergence between ...the mandibles of Hypnomys and of its extant relative Eliomys, the outline of the mandible being used as a marker of the morphological divergence. By comparison with the mandible of Eliomys, the more massive mandible of Hypnomys has recorded an ecological shift of the insular lineage towards a more abrasive diet, including hard vegetable matter, and a different niche. A microwear analysis of the teeth of Hypnomys was simultaneously performed as it can shed light on the diet, and is independent from the comparison of the mandibles. Hypnomys possibly ate harder food items than Eliomys, and likely occupied most of the island environments. Hypnomys appears to have differentiated from its ancestral type toward a more generalized morphology because of the lack of competitors.
A Pleistocene new material of dormice (Genus Glis) is described. Three morphological species are recognized on the basis of size and morphology of the teeth: Glis sackdillingensis Heller, 1930, Glis ...mihevci nov. sp., and Glis perkoi nov. sp. The two new species, larger than G. sackdillingensis, are morphologically less evolved than the present day Glis glis of Slovenia, which has larger teeth.
Fossil bone collagen
14C dating and
δ
13C and
δ
15N isotopic measurements of the rodent
Canariomys bravoi from Tenerife (Canary Islands, Spain) were used to test two different hypotheses about the ...causes of extinctions of endemic vertebrates on islands, climate versus humans. For the Tenerife giant rat, we show that it survived the climatic change that occurred between the Middle and Late Holocene, but not the settlement of humans on the island.
To cite this article: H. Bocherens et al., C. R. Palevol 5 (2006)
.
L'extinction des vertébrés endémiques insulaires : le cas du
Canariomys bravoi (Mammalia, Rodentia) de l'île de Tenerife (archipel des Canaries, Espagne).
Datations
14C et mesures des abondances isotopiques
δ
13C et
δ
15N à partir du collagène d'ossements du
Canariomys bravoi de Tenerife (îles Canaries, Espagne) démontrent que ce rongeur insulaire, aujourd'hui éteint, a survécu aux variations climatiques du passage Holocène moyen–Holocène supérieur, avant de s'éteindre à l'arrivée des premiers humains sur l'île. Comme un âge
14C établit que le rongeur et l'Homme ont été contemporains, il souligne la responsabilité probable de ce dernier dans l'extinction de
Canariomys bravoi.
Pour citer cet article : H. Bocherens et al., C. R. Palevol 5 (2006)
.
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