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Allometry, i.e., morphological variation correlated with size, is a major pattern in organismal evolution. Since size varies both within and among species, allometry occurs at different variational levels. However, the variability of allometric patterns across levels is poorly known since its evaluation requires extensive comparative studies. Here, we implemented a 3D geometric morphometric approach to investigate cranial allometry at three main variational levels—static, ontogenetic, and evolutionary—and two anatomical scales—entire cranium and cranial subunits—based on a dense intra- and interspecific sampling of extant armadillo diversity. While allometric trajectories differ among distantly related species, they hardly do so among sister families. This suggests that phylogenetic distance plays an important role in explaining allometric divergences. Beyond trajectories, our analyses revealed pervasive allometric shape changes shared across variational levels and anatomical scales. At the entire cranial scale, craniofacial allometry (relative snout elongation and braincase reduction) is accompanied notably by variations of nuchal crests and postorbital constriction. Among cranial subunits, the distribution of allometry was highly heterogeneous, with the frontal and petrosal bones showing the most pervasive shape changes, some of which were undetected at a more global scale. Evidence of widespread and superimposed allometric variations raises questions on their determinants and anatomical correlates and demonstrates the critical role of allometry in morphological evolution.

INTRODUCTION: The phylogeny of the Cingulata has been debated in morphological analyses for a long time (Engelmann, 1985; Gaudin &Wible, 2006; Billet et al., 2011; Delsuc et al., 2016; Mitchell et al., 2016; Herrera et al., 2017) and this incongruence was enriched by the contribution of recent molecular analyses (Delsuc et al., 2016; Mitchell et al., 2016). This is particularly the case for the emblematic group of glyptodonts whose mitochondrial genome was recently assembled (Delsuc et al., 2016; Mitchell et al., 2016). Although the cranial anatomy is relatively well known in xenarthrans, their internal cranial anatomy remains poorly studied. Yet, several studies have shown that their exploration provides systematic interest on their past and present diversity (Zurita et al., 2011; Fernicola et al., 2012; Billet et al., 2015; Tambusso & Fari˜na, 2015a; Tambusso & Fari˜na, 2015b; Billet et al., 2017; Boscaini et al., 2018; Boscaini et al., 2020; Tambusso et al., 2021). In a recent study (Le Verger et al., 2021), we describe and compare 8 cranial canals (involved in the vascularization and innervation of the cranium) and alveolar cavities (Figure 1) of 30 specimens belonging to the Cingulata. In this sampling, all extant subfamilies are represented and several large fossil groups including giant forms such as pampatheres and glyptodonts are represented. For the latter, the oldest complete crania have been studied. A sloth and an anteater were also added to the sample as outgroup. Of the total sample, 3D models of 13 specimens are made available (Table 1). The rest of the specimens are available only upon request from LGR. In this study (Le Verger et al., 2021), we present the comparativ investigation of these intracranial osseous canals and alveolar cavities using X-ray microtomography. Their 3D virtual reconstruction enabled us to compare the locations, trajectories, and shape of each homologous structure and discuss their potential interest for cingulate systematics

Ökomorphologische Konvergenz tritt auf, wenn Arten mit demselben Lebensstil unabhängig voneinander ähnliche morphologische Merkmale evolvieren. Neue Fallstudien können dabei helfen, die diesem Prozess zugrunde liegenden Mechanismen aufzuklären. Diese Arbeit befasst sich mit einigen konvergent evolvierten, langsamen, baumbewohnenden Säugetieren, d. h. zwei Linien baumlebender Faultieren, dem Zwergameisenbär, den Lorisiden, zwei Kladen ausgestorbener Lemuren, d. h. Paläopropithekiden und Megaladapis, und dem Koala. Es werden funktionsmorphologische Konvergenzen in diesen Taxa erforscht, indem ihr Humerus und ihr Femur sowie jene ihrer nah verwandten, aber ökologisch unterschiedlichen Taxa untersucht werden. Erstmals werden Knochen mittels phylogenetisch vergleichender Methoden auf vier anatomischen Ebenen, d.h. äußere Form, diaphysäre Mikrostruktur und Anatomie sowie epiphysäre Trabekelarchitektur, analysiert. Viele langsame, baumbewohnende Säugetiere teilen eine geringe kortikale Kompaktheit, was wahrscheinlich mit ihrer extrem niedrigen Stoffwechselrate und ihren biomechanischen Anforderungen zusammenhängt. Langsame, arboreale Xenarthra, d. h. baumbewohnende Faultiere und der Zwergameisenbär, weisen ein Muster unvollständiger Konvergenz für eine Reihe äußerer und innerer anatomischer Merkmale auf, was möglicherweise durch die relativ unterschiedliche Ökologie des Zwergameisenbären erklärt wird. Auf einer breiteren Säugetierskala konvergieren andere Merkmale, die möglicherweise mit der Ökologie der langsamen baumbewohnenden Lebensweise in einigen der untersuchten Taxa zusammenhängen, obwohl komplexe Muster auch durch andere evolutionäre Prozesse erklärt werden können. Nur suspensorisch lebende Taxa tragen signifikant zur Konvergenz bei. Diese Arbeit hebt die stärkere Konvergenz hervor, die sich in der inneren Struktur des Knochens widerspiegelt., Ecomorphological convergence occurs when similar morphological traits are independently evolved by species with the same lifestyle. Novel case studies can help to elucidate the underlying mechanisms of this process. This work addresses some convergent slow arboreal mammals, i.e. two lineages of ‘tree sloths’, the silky anteater, ‘Lorisidae’, two clades of extinct lemurs, i.e. palaeopropithecids and Megaladapis, and the koala. Functional morphological convergences are searched in these taxa, studying their humerus and femur as well as those of their closely related ecologically distinct taxa. For the first time, bones are analyzed at four anatomical levels, i.e. external shape, diaphyseal microstructure and anatomy and epiphyseal trabecular architecture, through phylogenetic comparative methods. Many slow arboreal mammals share a low cortical compactness, probably related to their extremely low metabolic rate and biomechanical demands. Slow arboreal xenarthrans, i.e. ‘tree sloths’ and the silky anteater, exhibit a pattern of incomplete convergence for a set of external and internal anatomical features, possibly explained by the relatively distinct ecology of the silky anteater. On a wider mammalian scale, other traits possibly related to slow arboreal ecology converge in some of the studied taxa, although with complex patterns also explained by other evolutionary processes. Only suspensory taxa significantly contribute to convergence. This thesis highlights the stronger convergence reflected by bone internal structure. By providing potential explanations for convergence in slow arboreal mammals, the inherent complexity of this process is here emphasized.

Miocene deposits of South America have yielded several species-rich assemblages of caviomorph rodents. They are mostly situated at high and mid- latitudes of the continent, except for the exceptional Honda Group of La Venta, Colombia, the faunal composition of which allowed to describe the late middle Miocene Laventan South American Land Mammal Age (SALMA). In this paper, we describe a new caviomorph assemblage from TAR-31 locality, recently discovered near Tarapoto in Peruvian Amazonia (San Martín Department). Based on mammalian biostratigraphy, this single-phased locality is unambiguously considered to fall within the Laventan SALMA. TAR-31 yielded rodent species found in La Venta, such as the octodontoid Ricardomys longidens Walton, 1990 (nom. nud.), the chinchilloids Microscleromys paradoxalis Walton, 1990 (nom. nud.) and M. cribriphilus Walton, 1990 (nom. nud.), or closely-related taxa. Given these strong taxonomic affinities, we further seize the opportunity to review the rodent dental material from La Venta described in the Ph.D. volume of Walton in 1990 but referred to as nomina nuda. Here we validate the recognition of these former taxa and provide their formal description. TAR-31 documents nine distinct rodent species documenting the four extant superfamilies of Caviomorpha, including a new erethizontoid: Nuyuyomys chinqaska gen. et sp. nov. These fossils document the most diverse caviomorph fauna for the middle Miocene interval of Peruvian Amazonia to date. This rodent discovery from Peru extends the geographical ranges of Ricardomys longidens, Microscleromys paradoxalis, and M. cribriphilus, 1,100 km to the south. Only one postcranial element of rodent was unearthed in TAR-31 (astragalus). This tiny tarsal bone most likely documents one of the two species of Microscleromys and its morphology indicates terrestrial generalist adaptations for this minute chinchilloid.