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Forasiepi A.M.,CONICET | Forasiepi A.M.,Palaontologisches Institute und Museum | Sanchez-Villagra M.R.,Palaontologisches Institute und Museum
Paleobiology | Year: 2014

In marsupial mammals and their extinct relatives-collectively, metatherians-only the last premolar is replaced, but the timing of dental eruption is variable within the group. Our knowledge of fossils metatherians is limited, but is critical to understanding several aspects of the evolution and morphological diversification of this clade. We analyzed the sequence of eruption of 76 specimens of metatherians, including Sparassodonta, an extinct clade of specialized carnivores from South America. In Sparassodonta (1) the P3/p3 erupt simultaneously, in common with some didelphids (in other didelphids, p3 erupts before P3, whereas in the remaining didelphids, some peramelids, one caenolestid, and Pucadelphys this order is reversed); (2) the upper and lower molars at the same locus erupt more in synchrony than in other carnivorous metatherians in which the lower molars clearly precede the upper equivalents; (3) the upper canine in thylacosmilids and proborhyaenids is hypselodont; (4) species with similar molar morphologies have different morphologies of the deciduous premolars, suggesting diverse diets among the juveniles of different taxa; (5) deciduous teeth are functional for a long period of time, with thylacosmilids even retaining a functional DP3 in the permanent dentition. The retention of the DP3 and the hypertrophied and hypselodont upper canine of thylacosmilids represent clear heterochronic shifts. Specializations in the timing of dental eruption and in the deciduous tooth shape of sparassodonts are evolutionary mechanisms that circumvent constraints imposed by the metatherian replacement pattern and increase morphological disparity during ontogeny. © 2014 The Paleontological Society.

Korn D.,Leibniz Institute For Evolutions Und Biodiversitatsforschung | Klug C.,Palaontologisches Institute und Museum | Mapes R.H.,Ohio University
Palaeontology | Year: 2014

The wrinkle layer is a dorsal shell structure occurring in a number of ammonoids, but its function is still debated. Here, we describe, from Moroccan material of the Early Carboniferous species Maxigoniatites saourensis (Pareyn), the most conspicuous wrinkle layer known within the Ammonoidea. This additional shell layer occurs in the ventrolateral portion of the adult body chamber and forms continuous lamellae, which range about two millimetres into the lumen of the body chamber. Possible functions are discussed and the most likely interpretation for the structure is 'fabricational noise', which is related to the coarsening of the shell ornament of the terminal body chamber. © The Palaeontological Association.

Hautmann M.,Palaontologisches Institute und Museum | Hagdorn H.,Muschelkalkmuseum Ingelfingen
Palaontologische Zeitschrift | Year: 2013

Middle Triassic marine deposits of the Germanic Basin (Muschelkalk) record a significant proliferation of cementing bivalves from different families. Based on previously undescribed, excellently preserved material from the Willebadessen Member (late Anisian, Illyrian) of the Upper Muschelkalk Trochitenkalk Formation of Willebadessen (Germany), we propose the new genus Noetlingiconcha, type species N. speculostreum sp. nov., for strongly plicate prospondylids lacking auricles. The new genus differs from Terquemia and Enantiostreon in being plicate rather than costate, and from Newaagia in the absence of auricles. We demonstrate that N. speculostreum was invariably attached by its right valve, in contrast to an externally similar species from the Lower Muschelkalk Freudenstadt Formation (lower Anisian, Bithynian) that was exclusively cemented by its left valve and thus represents the geologically oldest known oyster species. Previous reports of amphi-pleurothetic cemented bivalve species from the Muschelkalk probably result from lumping together these two externally similar species. The constancy of sinistral attachment in the geologically oldest Ostreidae suggests that left-pleurothetic valve orientation was already established in the ancestry of this family. Palaeontological data are therefore in accordance with genetic and larval shell morphology analyses that identified Pterioidea as the sister taxon of Ostreoidea, because Pterioidea contains several Permian-Triassic genera with an anatomically lower left valve. © 2012 Springer-Verlag.

Wilson L.A.B.,Kyoto University | Madden R.H.,Duke University | Kay R.F.,Duke University | Sanchez-Villagra M.R.,Palaontologisches Institute und Museum
Paleobiology | Year: 2012

A developmental model, based upon murine rodents, has been proposed by Kavanagh et al. (2007) to explain lower molar proportions in mammals. We produce a clade-wide macroevolutionary test of the model using the dental evolutionary trends in a unique radiation of extinct mammals endemic to South America ("Meridiungulata") that comprise a diverse array of molar morphologies. All of the South American ungulate groups examined follow the inhibitory cascade model with the exception of two groups: Interatheriidae (Notoungulata) and Astrapotheria. For most taxa studied, ratios between lower molar areas are greater than 1.0, indicating a weak inhibition by m1 on the subsequent molars in the tooth row, and a trend to greater absolute size of the posterior molars. Comparisons of mean ratios between clades indicate that a significant phylogenetic signal can be detected, particularly between the two groups within Notoungulata Typotheria and Toxodontia. Body mass estimates were found to be significantly correlated with both m3/m1 and m2/m1 ratios, suggesting that the larger body size achieved the weaker inhibition between the lower molars. Molar ratio patterns are examined and discussed in relation to the independent and numerous acquisitions of hypsodonty that are characteristic of dental evolution in "Meridiungulata. © 2012 The Paleontological Society. All rights reserved.

Carter J.G.,University of North Carolina at Chapel Hill | Hautmann M.,Palaontologisches Institute und Museum
Journal of Paleontology | Year: 2011

New shell microstructure data for the Triassic pectinid Pleuronectites reinforce shell morphological data suggesting that its family Pectinidae was derived from the superfamily Aviculopectinoidea and not from the Pernopectinidae-Entolioidesidae-Entoliidae clade. This would make the superfamily Pectinoidea, as defined by recent authors, polyphyletic. This would also imply that alivincular-alate ligaments evolved independently in the Pernopectinidae-Entolioidesidae-Entolidae and Pectinidae clades. © 2011 The Paleontological Society.

Hautmann M.,Palaontologisches Institute und Museum
Paleobiology | Year: 2014

Model calculations predict that pathways of alpha- and beta-diversity in diversifying ecosystems notably differ depending on the relative role of competition, predation, positive effects of species' interactions, and environmental parameters. Four scenarios are discussed, in which alpha- and beta-diversity are modeled as a function of increasing gamma-diversity. The graphic illustration of this approach is herein called α-β-γ plot, in which the x-axis indicates increasing diversification rather than absolute time. In purely environmentally controlled systems, beta-diversity maintains near-maximum values throughout the diversification interval, whereas mean alpha-diversity increases linearly, with a slope being reciprocal to beta-diversity. A second scenario is based on the assumption that increasing richness will have predominantly positive effects on the addition of further species; here, alpha- and beta-diversity increase simultaneously (though not necessarily at the same rates) and without reaching a predictable upper limit. In ecosystems that are characterized by low competition between species, mean alpha-diversity asymptotically approaches a saturation level, whereas the increase in beta-diversity accelerates until alpha-diversity stagnates, and then continues to rise linearly. If competition is high, addition of species first increases beta-diversity until no further habitat contraction is possible, followed by a period in which alpha-diversity increase through adaptive divergence becomes the principal drive of diversification. Because there is a continuous transition between the late stage of the low-competition model and the early stage of the high-competition scenario, both can be combined in a single model of diversity partitioning under the premise of a diversity-dependent increase of competition. This summary model predicts three phases of diversity accumulation: (1) a niche overlap phase, (2) a habitat contraction phase, and (3) a niche differentiation phase. The models herein discussed provide a potential tool to assess the question which factors primary controlled the diversification of life over geological times. © 2014 The Paleontological Society.

Wilson L.A.B.,Palaontologisches Institute und Museum | Sanchez-Villagra M.R.,Palaontologisches Institute und Museum
Proceedings of the Royal Society B: Biological Sciences | Year: 2010

It has been hypothesized that most morphological evolution occurs by allometric differentiation. Because rodents encapsulate a phenomenal amount of taxonomic diversity and, among several clades, contrasting levels of morphological diversity, they represent an excellent subject to address the question: how variable are allometric patterns during evolution? We investigated the influence of phylogenetic relations and ecological factors on the results of the first quantification of allometric disparity among rodents by exploring allometric space, a multivariate morphospace here derived from, and encapsulating all, the ontogenetic trajectories of 34 rodent species from two parallel phylogenetic radiations. Disparity was quantified using angles between ontogenetic trajectories for different species and clades. We found an overlapping occupation of allometric space by muroid and hystricognath species, revealing both clades possess similar abilities to evolve in different directions of phenotypic space, and anatomical diversity does not act to constrain the labile nature of allometric patterning. Morphological features to enable efficient processing of food serve to group rodents in allometric space, reflecting the importance of convergent morphology, rather than shared evolutionary history, in the generation of allometric patterns. Our results indicate that the conserved level of morphological integration found among primates cannot simply be extended to all mammals. © 2009 The Royal Society.

Sanchez-Villagra M.R.,Palaontologisches Institute und Museum
Proceedings of the Royal Society B: Biological Sciences | Year: 2010

The study of fossilized ontogenies in mammals is mostly restricted to postnatal and late stages of growth, but nevertheless can deliver great insights into life history and evolutionary mechanisms affecting all aspects of development. Fossils provide evidence of developmental plasticity determined by ecological factors, as when allometric relations are modified in species which invaded a new space with a very differ-ent selection regime. This is the case of dwarfing and gigantism evolution in islands. Skeletochronological studies are restricted to the examination of growth marks mostly in the cement and dentine of teeth and can provide absolute age estimates. These, together with dental replacement data considered in a phylo-genetic context, provide life-history information such as maturation time and longevity. Paleohistology and dental replacement data document the more or less gradual but also convergent evolution of mam-malian growth features during early synapsid evolution. Adult phenotypes of extinct mammals can inform developmental processes by showing a combination of features or levels of integration unrecorded in living species. Some adult features such as vertebral number, easily recorded in fossils, provide indirect information about somitogenesis and hox-gene expression boundaries. Developmental palaeontology is relevant for the discourse of ecological developmental biology, an area of research where features of growth and variation are fundamental and accessible among fossil mammals. © 2010 The Royal Society.

Wilson L.A.B.,Palaontologisches Institute und Museum
Journal of Mammalogy | Year: 2011

The relationship between prenatal and postnatal ontogenetic allometry is poorly known, and empirical studies documenting prenatal allometry are few, precluding an understanding of changes in growth patterns during life history and their relation to proximal, physiological, and ultimate evolutionary variables. In this study I compare prenatal and postnatal ontogenetic allometry of the cranium in a cleared and stained developmental series of the African striped mouse (Rhabdomys pumilio). Eighteen cranial measurements, reflecting the dimensions of individual elements, were analyzed using bivariate and multivariate estimates of allometry and methods of matrix comparison. Prenatal allometry is characterized in R. pumilio by a relative rapid lengthening of cranial elements, particularly the frontal, parietal, basisphenoid, premaxilla, and palatine, as evidenced by larger bivariate allometric coefficients (>30% increase) and, across all variables measured, a greater proportion of cranial elements growing with a positive allometry than in the postnatal period. Growth dynamics are found to shift for measurements of several elements including the parietal, frontal, and palatine, indicating a nonlinearity of ontogenetic allometry with respect to birth; similar shifts have been found between prenatal and postnatal growth for some regions of the human cranium. Application of common principal component analyses, a generalized extension of principal component analysis, revealed that the prenatal and postnatal matrices shared a highly similar structure, further quantified by high correlations (>0.78) using the random skewers method of matrix comparison. These results indicate a close correspondence between morphology-based variance structures over the course of ontogeny in R. pumilio. © 2011 American Society of Mammalogists.

Klug C.,Palaontologisches Institute und Museum | Schweigert G.,Staatliches Museum fur Naturkunde | Fuchs D.,Free University of Berlin | Dietl G.,Free University of Berlin
Lethaia | Year: 2010

A recent discovery of an unusually preserved belemnite from Nusplingen comprises the extraordinarily rare remains of beaks and nearly in situ arm hooks, as well as the ink sac and an incomplete phragmocone. So far, Hibolithes semisulcatus (Münster, 1830) is the only belemnite known from the Nusplingen Lithographic Limestone (Upper Jurassic, Late Kimmeridgian, Beckeri Zone, Ulmense Subzone; SW Germany) that has the same phragmocone shape and size, and thus we assign the new specimen to this taxon. The rostrum was probably lost due to a lethal predation attempt in which the prey was killed but not entirely eaten. For the first time a specimen reveals details of the belemnite beak morphology, which we compare with the beaks of other Jurassic coleoids. This specimen presently represents the only known rostrum-bearing belemnite of post-Toarcian age with preserved non-mineralized body parts. With the new discovery, Nusplingen now represents the only locality which has yielded complete beak apparatuses from all major Jurassic cephalopod groups. Beaks, Belemnitida, Coleoidea, Germany, Late Jurassic, morphology, taphonomy. © 2009 The Authors, Journal compilation © 2009 The Lethaia Foundation.

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