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Morphological evolution of the murine rodent Paraethomys in response to climatic variations (Mio-Pleistocene of North Africa)
Abstract
The North African murine rodent Paraethomys evolved as an anagenetic lineage from the late Miocene until its extinction in the late-middle Pleistocene. A Fourier analysis of the outlines of the first upper and lower molars of this rodent was used to quantify the evolutionary patterns of this lineage and to compare evolutionary patterns to the climatic record. Morphological evolution and long-term environmental variations are strongly correlated. A change in molar shape, which may be related to the development of a more grass-eating diet, corresponds to the global cooling beginning around 3 Ma and the subsequent increase in aridity in North Africa. Concurrently, size increased, which may be related to increased masticatory efficiency or to metabolic adaptation to the cooler environmental conditions according to Bergmann's rule. This adaptive response to changing environmental conditions corresponds to an acceleration of evolutionary rates in the lineage. The modalities of the evolutionary response in size and shape are probably controlled by intrinsic factors such as different genetic determinisms for both characters.
... Au sein de chaque lignée on note une augmentation graduelle de la taille et de la stéphanodontie, ainsi que sur la M1 une réduction du t9, une inclinaison du t6 vers l'arrière et la disparition du cingulum postérieur. Il serait trop long ici de décrire les caractéristiques dentaires de chaque espèce ; nous en référons donc aux publications précédentes (Jaeger 1975 ;Ameur 1976 ;Ameur-Chehbeur 1988 ;Coiffait & Coiffait 1981 ;Coiffait-Martin 1991 ;Geraads 1994Geraads , 1995Geraads , 1998Geraads , 2002Geraads , 2016aRenaud et al. 1999 ;Geraads et al. 2013). Tong, 1989 G. abdallahi Tong, 1989 G. campestris Loche, 1867 G. ochrae Tong, 1989 G. cingulatus Tong, 1986 G. jebileti Tong, 1989 G. grandis Tong, 1989 G. robustus Tong, 1989 moyenne Ben Kérat (Tong 1989 ;Geraads 1994Geraads , 1995Geraads , 2016aStoetzel 2009 ;Stoetzel et al. 2010 ;Geraads et al. 2013 Les Paraethomys de Ben Kérat (Fig. 5) représentent une forme dérivée proche des formes pléistocènes et distincte des formes mio-pliocènes : grande taille ; M1 et M2 avec t7 absent (ou représenté par une petite crête) et t9 absent ou réduit (sous forme de liaison élargie entre t8 et t6), t1 et t3 plus ou moins au même niveau ; sur les m1, absence de tma (ébauche sur une seule dent), cp absent ou très réduit, tF relié à tE, crête entre tF et tD, tC décalé, présence de tubercules cingulaires labiaux bien développés (c1 et c3 toujours présents, parfois petit c2) ; stéphanodontie modérée (sur les molaires supérieures, parfois petit éperon postérieur sur t3 ; sur les molaires inférieures, crête longitudinale basse peu développée), loin d'atteindre le stade ultime de Pa. ...
... Il est cependant en partie possible de contourner cette difficulté. Par exemple, pour les espèces du genre Paraethomys, l'étude de certains caractères dentaires (Petter 1968 ;Jaeger 1975 ;Jaeger et al. 1975 ;Ameur 1976 ;Coiffait & Coiffait 1981) et des analyses de morphométrie géométrique sur les molaires (Renaud et al. 1999) ont permis de poser des hypothèses sur leur régime alimentaire et leur environnement. Ainsi, les formes anciennes présentent une taille plus petite, peu ou pas de stéphanodontie et une conformation différente des formes plus évoluées, alors que ces dernières montrent au cours du temps une augmentation de la taille et de la stéphanodontie. ...
... Ainsi, les formes anciennes présentent une taille plus petite, peu ou pas de stéphanodontie et une conformation différente des formes plus évoluées, alors que ces dernières montrent au cours du temps une augmentation de la taille et de la stéphanodontie. On observe un changement marqué autour de 3 Ma, corrélé à un refroidissement et une aridification du climat (Renaud et al. 1999). L'augmentation de la taille peut ainsi être liée à une efficacité masticatoire accrue ou à une adaptation métabolique face aux conditions environnementales plus fraîches. ...
... More recently, the molar has become a forefront model in evo-devo, with the development of an in silico model of tooth development linking variation in development with variation in morphology [31]. Within rodents, many changes have been reported, with alternating periods of stasis, gradual changes and more rapid morphological evolution [25,24]. One particularly drastic change occurred in the mouse lineage: the crown of the upper molar was drastically transformed with the acquisition of a third cusp row, making a pattern of cusp number and arrangement which is called the "murine dental plan" (Figure 1-B [18]). ...
Serial organs, such as limbs or teeth, develop with the same sets of genes and regulatory sequences. Correlated evolution is expected by default, but decoupled evolution is often achieved, as in mouse with a morphological innovation in the upper, but not the lower molar. We studied developmental evolution of hamster and mouse molars with transcriptome data. We reveal a combination of three morphogenetic changes likely causing the new morphology of the mouse upper molar. Surprisingly, most of these changes are common with the lower molar and lower molar gene expression diverged as much as, and coevolved with, the upper molar.
Hence, adaptation of the upper molar has involved changes in pleiotropic genes that also modified lower molar development but preserved its final phenotype. From the lower molar point of view, it is a case of Developmental systems drift (DSD). We think that DSD accommodates pleiotropy, explaining why in teeth and more generally in the body, the evolution of developmental gene expression is fast and correlates between organs.
HIGHLIGHTS
- The evolutionary innovation of mouse upper molar involves several morphogenetic changes
- Most of the associated gene expression changes are shared with the mouse lower molar
- Lower molar’s phenotype is conserved, thus its developmental gene expression drifted
- Adaptation with pleiotropic genes drove developmental system drift in the other tooth
African rodents of the genus Arvicanthis are presently restricted to sub-Saharan savannas and to the Nile Valley. In contrast, their distribution during the Quaternary included most of northern Africa, leading to the emergence of local fossil species. To date, there have been no comprehensive studies of Arvicanthis populations in northern Africa, neither to clarify their taxonomy nor their paleoecology. The present study aims to explore both morphology and diet of modern and fossil Arvicanthis species using geometric morphometric and dental microwear analyses on first upper molars. The geometric morphometric analysis efficiently discriminates the studied extant and fossil Arvicanthis species and allowed for the identification of probable geographical variations within the A . niloticus group. Although all extant species of the genus Arvicanthis are predominantly grass-eaters, microwear analyses also highlighted diet differences in various modern populations of A . niloticus , as well as paleodiet inferences in the A . arambourgi fossil species, but no clear link between molar size or shape and diet can be established. This work helps set the stage for a complete revision of the fossil remains of Arvicanthis from northern African Quaternary deposits, and for a better understanding of the geographical and temporal morphological variability of this genus in Africa.
Researchers have long had an interest in dental morphology as a genetic proxy to reconstruct population history. Much interest was fostered by the use of standard plaques and associated descriptions that comprise the Arizona State University Dental Anthropology System, developed by Christy G. Turner, II and students. This system has served as the foundation for hundreds of anthropological studies for over 30 years. In recognition of that success, this volume brings together some of the world's leading dental morphologists to expand upon the concepts and methods presented in the popular The Anthropology of Modern Human Teeth (Cambridge, 1997), leading the reader from method to applied research. After a preparatory section on the current knowledge of heritability and gene expression, a series of case studies demonstrate the utility of dental morphological study in both fossil and more recent populations (and individuals), from local to global scales.
Researchers have long had an interest in dental morphology as a genetic proxy to reconstruct population history. Much interest was fostered by the use of standard plaques and associated descriptions that comprise the Arizona State University Dental Anthropology System, developed by Christy G. Turner, II and students. This system has served as the foundation for hundreds of anthropological studies for over 30 years. In recognition of that success, this volume brings together some of the world's leading dental morphologists to expand upon the concepts and methods presented in the popular The Anthropology of Modern Human Teeth (Cambridge, 1997), leading the reader from method to applied research. After a preparatory section on the current knowledge of heritability and gene expression, a series of case studies demonstrate the utility of dental morphological study in both fossil and more recent populations (and individuals), from local to global scales.
Small mammal remains have been discovered in three new outcrops from the Afoud locality. This site is significant from a paleontological point of view because it has yielded fauna of European affinities (Castillomys, Occitanomys, Stephanomys, Eliomys, and Prolagus). The presence of two different species of Arvicanthis from the Afoud locality represents the oldest record in North Africa. The association of small mammals from the AF12-2 deposits provides an approximate view of the local environment and climate at the time of the formation of this locality. This faunal assemblage indicates a warm, temperate, semi-arid climate and an open vegetation cover of wooded savannah. Fossil assemblages documented in this paper expand our knowledge on the Late Miocene–Early Pliocene small mammal communities of the Aït Kandoula Basin. This study provides useful data for understanding the paleobiogeography of the Mediterranean region and faunal exchanges between North Africa and the Iberian Peninsula that took place before the Messinian Salinity Crisis.
Rapid phenotypic evolution is observed in response to rapid environmental changes. These phenotypic variations can occur at different scales, from the population to the community. We intended to characterize these multiscale phenotypic responses in rodents from the archaeological site El Harhoura 2 (Rabat, Morocco), dated from the Late Pleistocene to the Holocene, and relate them to paleoenvironmental variations. Upper and lower first molars were used as proxies for phenotype. Their shape was quantified using a landmark-free method. To account for both intra- and interspecific variations, we used morpho-groups as phenotypic units. Those morpho-groups were identified using unsupervised clustering. Three shape indicators were computed: number of morpho-groups, morpho-group disparity and changes in morpho-group mean shape over time. To evaluate this little-used approach on small mammals, we compared it to three widely used biodiversity indices: number of taxa, Shannon index, and Simpson index. Phenotypic evolution between and within species was highlighted. Morpho-groups seemed to be phenotypic response units representing ecological groups that transversed species. Variations in the morpho-group mean shapes were partly related to paleoenvironmental changes; however, variations in disparity were not. Thus, environmental changes deduced from fossil microvertebrate communities did not seem to be the main determinants of the characterized phenotypic variations.
Read-only version: https://onlinelibrary.wiley.com/share/author/J39BSPUMDFDQAGW3XQPP?target=10.1002/spp2.1368 ------------ Abstract. We analyse the taxonomic status and diversity of the late Miocene Octodontoidea (Hystricognathi) Cercomys primitiva and related samples, a taxon previously known only from the holotype specimen. New findings associated with an extensive review of late Miocene and early Pliocene rodents have allowed us to recognize the occurrence of this and other related species in several localities of central and western Argentina, and in south‐central Bolivia. We discuss the invalidity of Cercomys and propose the new genus Metacaremys, which includes the type species Metacaremys primitiva comb. nov. and two new species, Metacaremys calfucalel sp. nov. and Metacaremys dimi sp. nov. Osteological, brain and dental morphology show that the new genus is not related to Brazilian Echimyidae, as previously considered, but to the southern family Octodontidae. Although the molar morphology of this genus is quite conservative, comparison of the samples shows a variation in size. We discuss the plausible evolutionary pattern explaining this variation and the implied biochronological and biostratigraphical information. It is recognized as an anagenetic lineage in which an increase in size occurs from the oldest species, M. primitiva comb. nov. (early late Miocene, c. 9.23 Ma), to the youngest species, M. dimi sp. nov. (Miocene–Pliocene boundary, c. 5.28 Ma). Metacaremys calfucalel is intermediate in size and age between these two species. The polarity of this pattern of change is consistent with that shown by other partially synchronous independent lineages of octodontoids, thus providing new evidence for the biochronological and biostratigraphic scheme of the late Miocene and early Pliocene of southern South America.
The rich small-mammal record from the Guadix-Baza Basin (Granada, southern Spain) provides a rather continuous biostratigraphic sequence from the late Miocene to the middle Pleistocene. However, the earliest Pliocene is not so well represented due to the scarcity of levels from this time. In this paper, a complete taxonomic study of the rodent fauna from Botardo-D is presented, providing a more complete information on this poorly known time interval. Representatives of the genera Stephanomys, Paraethomys, Apodemus, Castillomys, Debruijnimys and Apocricetus have been identified. The association indicates an intermediate biostratigraphic position between the levels of Negratín-1 (late Turolian, MN13) and Baza-1 (early Ruscinian, MN14), being now one of the oldest Pliocene sites in the Guadix-Baza Basin. Thereby, Botardo-D enhances our knowledge on the evolution of the rodent community recorded in this basin from the late Miocene to the early Pliocene. A qualitative palaeoecological interpretation suggests the dominance of open grasslands under relatively warm and dry climate conditions in the Guadix-Baza Basin during the deposition of Botardo-D. A tendency towards an increase in humidity from the Messinian Salinity Crisis (latest Miocene) to the Zanclean (early Pliocene) could be shown for southern Iberian Peninsula, supporting previous results.
Northwestern Africa is today characterized by high geographical, climatic and ecological diversity; it is recognized as a hotspot of biodiversity and a major area for both human and faunal evolution. Studies of North African fossil microvertebrates have increased considerably in recent years, but they no longer just provide palaeontological descriptions of the species found in the assemblages. They also aim at better understanding the evolution of faunal communities in relation to Quaternary climate changes and at reconstructing the palaeoenvironmental background of prehistoric human occupations, in well-established taphonomic and chronological contexts. These studies are also increasingly adopting an integrative approach by combining archaeology, palaeontology, (palaeo)genetics, taphonomy, palae-oecology and systematics, and using new methods such as geometric morphometrics and isotopic analyses on both fossil and modern specimens. This paper aims to present a history of the studies on Quaternary terrestrial microvertebrates from northwestern Africa, and show how recent multidisciplinary studies have provided new perspectives and evidence on the respective influences of climate change and increasing human pressure on their evolution.
The exceedingly rich middle Pleistocene mammalian fauna from the classic Ensenadan Tarija basin in southern Bolivia contains a diversity of medium to large-bodied herbivores consisting of both endemic (†Toxodontia, †Litopterna, Xenarthra) and immigrant (Rodentia, Proboscidea, Perissodactyla, and Artiodactyla) taxa. In order to characterize feeding ecology and niche differences, a suite of morphological characters was measured for each of 13 species of herbivorous mammals from the Pleistocene of Tarija; these were combined with carbon isotopic results from tooth enamel. (The Xenarthra were excluded from this study because they lack tooth enamel.)
Several different bivariate and multivariate combinations of characters can be used to characterize the feeding adaptations, niches, and guild composition of the Tarija mammalian herbivores. During the Pleistocene the browsing guild in the Tarija basin is interpreted to include the tapir ( Tapirus tarijensis ), extinct llama ( Palaeolama weddelli ), peccary ( Tayassu sp.), and deer ( Hippocamelus sp.). The mixed-feeding guild included two horse species ( Hippidion principale and Onohippidium devillei ), litoptern ( Macrauchenia patachonica ), and capybara ( Neochoerus tarijensis ). The grazing guild included the numerically dominant horse ( Equus insulatus ), two lamine species ( Lama angustimaxilla and cf. Vicugna, provicugna ), notoungulate ( Toxodon platensis ), and gomphothere proboscidean ( Cuvieronius hyodon ). The grazing guild has the widest range of body sizes relative to the two other guilds. Closely related sympatric species within the Equidae and Camelidae differentiate their niches from one another using a combination of body size, feeding ecology, and probably local habitat. Most of the paleoecological reconstructions resulting from this combined morphological and isotopic analysis corroborate previous studies based primarily on morphology; there are, however, some notable surprises.
Gastropod evolution during the early Paleozoic featured active trends (i.e., differential replacement of morphologies) for at least three shell characters. Selective sorting, either of individual organisms or of whole species, is an obvious mechanism for such active trends. Sorting of individuals should result in a disproportionate number of ancestor to descendant transitions being in the same direction as the trend, whereas sorting of species should result in species with particular morphologies producing more daughter species. Sorting of species can occur over long periods of time or it can be concentrated over a particular interval, such as an extinction event. Constraints on morphologic evolution also can drive trends, especially in cases where it is easier to produce a particular morphology than it is to change it. Finally, active trends can be artifacts of unrelated differential diversification within a clade (i.e., species hitchhiking), which might result from sorting of species based on phylogenetically associated characters or simply by chance. Unlike other active trends, trends attributable to species hitchhiking do not support hypotheses about selection or evolutionary constraints.
Large-scale evolutionary trends may result from driving forces or from passive diffusion in bounded spaces. Such trends are persistent directional changes in higher taxa spanning significant periods of geological time; examples include the frequently cited long-term trends in size, complexity, and fitness in life as a whole, as well as trends in lesser supraspecific taxa and trends in space. In a driven trend, the distribution mean increases on account of a force (which may manifest itself as a bias in the direction of change) that acts on lineages throughout the space in which diversification occurs. In a passive system, no pervasive force or bias exists, but the mean increases because change in one direction is blocked by a boundary, or other inhomogeneity, in some limited region of the space. Two tests have been used to distinguish these trend mechanisms: (1) the test based on the behavior of the minimum; and (2) the ancestor-descendant test, based on comparisons in a random sample of ancestor-descendant pairs that lie far from any possible lower bound. For skewed distributions, a third test is introduced here: (3) the subclade test, based on the mean skewness of a sample of subclades drawn from the tail of a terminal distribution. With certain restrictions, a system is driven if the minimum increases, if increases significantly outnumber decreases among ancestor-descendant pairs, and if the mean skew of subclades is significantly positive. A passive mechanism is more difficult to demonstrate but is the more likely mechanism if decreases outnumber increases and if the mean skew of subclades is negative. Unlike the other tests, the subclade test requires no detailed phylogeny or paleontological time series, but only terminal (e.g., modern) distributions. Monte Carlo simulations of the diversification of a clade are used to show how the subclade test works. In the empirical cases examined, the three tests gave concordant results, suggesting first, that they work, and second, that the passive and driven mechanisms may correspond to natural categories of causes of large-scale trends.
The Middle East region incorporates all known types of major plate boundaries in its territory as well as significant active intraplate deformation. Until recently, understanding the tectonics in this complex region has been hindered by a relative lack of data and the complexity of the geologic and tectonic problems. Even with the increase in the amount of data in the past decade or so, the complexities of the region require a multidisciplinary approach to understand the geology and tectonics. In order to handle large, multidisciplinary data sets with varying quality and resolution, we have adopted a Geographic Information System (GIS) approach for construction of a multipurpose database to look at these problems in a comprehensive and unconventional way. Here, we present new compilation maps of surficial tectonic features and depth to the Moho for the Middle East, and describe a cross-section tool to work with data in a GIS format. These maps are available at our web site at http://atlas.geo.cornell.edu.
A new Fourier method is presented to quantify shapes too complex to be described by conventional polar Fourier analysis. The length along a closed curve serves as the independent variable. The centroid of the curve is determined and for each point on the curve two different dependent variables are defined, based on: 1) the angle defined by the starting point, the centroid, and the point on the curve; and 2) the radial distance from the centroid to the point on the curve. The method is used to describe the trilobite cranidium, and 12 harmonic coefficients are found to summarize 99 percent of the shape information contained in the cranidial outline. In an application to trilobite evolution during the Cambrian and Ordovician, it is found that higher taxa of trilobites become progressively more distinct morphologically. -from Author
We believe that punctuational change dominates the history of life: evolution is concentrated in very rapid events of speciation (geologically instantaneous, even if tolerably continuous in ecological time). Most species, during their geological history, either do not change in any appreciable way, or else they fluctuate mildly in morphology, with no apparent direction. Phyletic gradualism is very rare and too slow, in any case, to produce the major events of evolution. Evolutionary trends are not the product of slow, directional transformation within lineages; they represent the differential success of certain species within a clade—speciation may be random with respect to the direction of a trend (Wright's rule).
As an a priori bias, phyletic gradualism has precluded any fair assessment of evolutionary tempos and modes. It could not be refuted by empirical catalogues constructed in its light because it excluded contrary information as the artificial result of an imperfect fossil record. With the model of punctuated equilibria, an unbiased distribution of evolutionary tempos can be established by treating stasis as data and by recording the pattern of change for all species in an assemblage. This distribution of tempos can lead to strong inferences about modes. If, as we predict, the punctuational tempo is prevalent, then speciation—not phyletic evolution—must be the dominant mode of evolution.
We argue that virtually none of the examples brought forward to refute our model can stand as support for phyletic gradualism; many are so weak and ambiguous that they only reflect the persistent bias for gradualism still deeply embedded in paleontological thought. Of the few stronger cases, we concentrate on Gingerich's data for
Hyopsodus
and argue that it provides an excellent example of species selection under our model. We then review the data of several studies that have supported our model since we published it five years ago. The record of human evolution seems to provide a particularly good example: no gradualism has been detected within any hominid taxon, and many are long-ranging; the trend to larger brains arises from differential success of essentially static taxa. The data of molecular genetics support our assumption that large genetic changes often accompany the process of speciation.
Phyletic gradualism was an a priori assertion from the start—it was never “seen” in the rocks; it expressed the cultural and political biases of 19th century liberalism. Huxley advised Darwin to eschew it as an “unnecessary difficulty.” We think that it has now become an empirical fallacy. A punctuational view of change may have wide validity at all levels of evolutionary processes. At the very least, it deserves consideration as an alternate way of interpreting the history of life.