Journal of Mammalian Evolution最新文献

Remains of megatheres have been known since the 18th -century and were among the first megafaunal vertebrates to be studied. While several examples of preserved integument show a thick coverage of fur for smaller ground sloths living in cold climates such as Mylodon and Nothrotheriops, comparatively very little is known about megathere skin. Assuming a typical placental mammal metabolism, it was previously hypothesized that megatheres would have had little-to-no fur as they achieved giant body sizes. Here the "hairless model of integument" is tested using geochemical analyses to estimate body temperature to generate novel models of ground sloth metabolism, fur coverage, and paleoclimate with Niche Mapper software. The simulations assuming metabolic activity akin to those of modern xenarthrans suggest that sparse fur coverage would have resulted in cold stress across most latitudinal ranges inhabited by extinct ground sloths. Specifically, Eremotherium predominantly required dense 10 mm fur with implications for seasonal changes of coat depth in northernmost latitudes and sparse fur in the tropics; Megatherium required dense 30 mm fur year-round in its exclusive range of cooler, drier climates; Mylodon and Nothrotheriops required dense 10-50 mm fur to avoid thermal stress, matching the integument remains of both genera, and further implying the use of behavioral thermoregulation. Moreover, clumped isotope paleothermometry data from the preserved teeth of four genera of ground sloth yielded reconstructed body temperatures lower than those previously reported for large terrestrial mammals (23 ± 5-32 ± 3° C). This combination of low metabolisms and thick fur allowed ground sloths to inhabit various environments.

Supplementary information: The online version contains supplementary material available at 10.1007/s10914-024-09743-2.

The renowned Late Miocene locality of Maragheh (northwest Iran) has yielded ample material of chalicotheres, most of which has never been described in detail. The present study concerns the taxonomic evaluation of this material and its attribution to the large schizotheriine Ancylotherium pentelicum. This allows a detailed comparison to schizotheriine material from other localities, and based on this, we provide an overview of the diagnostic features of Ancylotherium that separate it from all other chalicotheres. This improves our understanding of the type species A. pentelicum. Additionally, we discuss the palaeobiogeography of the species, which is best known from the Balkan Peninsula. Maragheh marks the easternmost occurrence of A. pentelicum, but its presence has even been suggested in Africa. Lastly, we discuss the existence of sexual size dimorphism in the species, based on the herein described material along with previously described specimens of A. pentelicum from other fossil sites, such as the famous Late Miocene localities Pikermi and Samos (Greece). Specifically, it is shown that many postcranial elements exhibit great size variability that is most probably associated with significant sexual dimorphism.

Ctenomys, the only living Ctenomyidae, is the most diverse genus of hystricomorph rodents. Here, a new extinct species from the Middle Pleistocene of central Argentina is described. It is represented by the most complete skeleton for an extinct Ctenomys species. We analyze its remains and phylogenetic position in the context of other extinct and living Ctenomys species. Additionally, we present an updated and exhaustive timetree of the genus, and include the new species into a matrix of variables with morphofunctional significance. In the parsimony phylogenetic analysis, †C. uquiensis, †C. chapalmalensis, †C. rusconii, and †C. thomasi were placed at the base of the Ctenomys total clade, while †Ctenomys sp. nov. was the sister species of the crown group. Within the crown Ctenomys, a polytomy was obtained in the basal node formed by †C. dasseni, †C. kraglievichi, the clade †C. viarapaensis-C. osvaldoreigi, the frater species group, and the major clade consisting of the remaining eight species groups. The Bayesian tipdating analysis provided divergence estimates of 4.3 and 1.8 Ma for the origin of the genus and the crown clade, respectively. In the adaptive morphospace, the new species was located in the quadrant of lower scratch- and tooth-digger specialization, close to C. pulcer, a species currently distributed in semi-fixed dunes, pointing to the requirement of similar soil conditions. Finally, the new species co-occurs with †C. kraglievichi, a crown-group member with pronounced tooth-digging specialization, suggesting that Ctenomys experienced both significant cladogenesis and substantial eco-morphological diversification during the Middle Pleistocene.

The rich micromammal fossils from Early, Middle, and Late Miocene horizons of the Damiao sequence in Nei Mongol provide an opportunity to study Miocene biostratigraphy and faunal turnover in Asia. In this study, we describe thirteen dipodid species from the Damiao sequence, including two new species, Sinozapus damiaoensis sp. nov. and Lophocricetus parvus sp. nov. Sinozapus damiaoensis sp. nov. is characterized by the metaloph connecting to the central hypocone on M1-M2, the absence of the anterior arm of the protoconid, and the posterior arm of the protoconid merging with the metaconid on m2. Lophocricetus parvus sp. nov. displays a set of transitional morphological traits between Heterosminthus and Lophocricetus. It resembles Heterosminthus in its small size, the presence of the mesocone and mesoloph on M1-M2, the vestigial pseudomesolophid, and the posterior crest of the protoconid on m1. Meanwhile, it has the characteristics of Lophocricetus, including the protostyle on M1 and the hypoconid-entoconid connection on the m1. These two new species represent the earliest records of their respective genera. The Damiao dipodid fossil records improve our understanding of Neogene dipodid diversity, and refine the biostratigraphic framework in the central Nei Mongol. The new fossil records reveal a shift from small, low-crowned, humid-adapted early taxa to ecologically diverse late Middle Miocene forms, including desert-adapted jerboas, indicating a trend towards regional aridification. Nonetheless, relict sicistines and zapodines suggest localized persistence of humid refugia within broader dry environments during the late Middle Miocene, which sheltered pliopithecids in the Mongolia Plateau.

Northwestern Argentina (NWA), together with the Pampean region (PR), has produced one of the most complete late Neogene continental sequences in Argentina. A diversity of palaeofauna has been recognized from NWA, among which glyptodonts stand out due to the high abundance of their remains. Recent evidences suggests that the Late Miocene was a period of extra-Patagonian diversification in southern South America for glyptodonts, perhaps stimulated by the expansion of C4 grasses and open environments; this has been called the as “Edad de las Planicies Australes”. Here, we focus on one of NWA's most poorly known clades of glyptodonts, the Plohophorini, from the Villavil-Quillay Basin (Catamarca Province). Our results show that, like other clades (e.g., Doedicurini), a single species can be recognized, Stromaphorus ameghini (Ameghino, 1889; ex Moreno, 1882), whose stratigraphic record spans the latest Miocene to the Pliocene (ca. 7.14–3.3 Ma; Messinian-Zanclean). Cladistic analysis confirms the status of the tribe Plohophorini as a natural group within Hoplophorinae (“austral clade”), in which S. ameghini appears as the sister species of the Pampean species S. trouessarti (Moreno, 1888) comb. nov. The oldest precise records of S. ameghini (ca. 7.14 Ma) provide a minimum age for the Plohophorini lineage. The evidence suggests that the diversity of glyptodonts from the late Neogene of NWA is composed of endemic species that are different from those of the PR; however, both areas share the same genera, as observed in other mammalian clades such as Hegetotheriidae (Notoungulata) and Dasypodidae. The cladistic analysis reveals, in a broader context, that the spine-like structure observed in the caudal tube of some genera (i.e., Nopachtus, Propanochthus, and Panochthus) is a homologous structure rather than a convergence as usually interpreted. By contrast, the similar ornamentation pattern represented by the multiplication of peripheral figures in the carapaces of the genera Stromaphorus and Nopachtus is, in fact, a convergence.

Peradectidae are Paleogene ‘opossum-like’ stem-metatherians, largely Laurasian, whose evolutionary history remains unclear. Based on new remains (mainly dental) discovered in several French localities, we carry out a comprehensive systematic revision of all early Eocene peradectids from Europe (~MP7 reference level to MP10-11 interval). We describe well-preserved specimens from Palette (Southern France, MP7-MP8 + 9 interval) documenting the earliest European peradectid, Peradectes crocheti sp. nov. This new species exhibits an interesting mosaic of characters, including plesiomorphic traits found in the North American type species, Peradectes elegans Matthew and Granger, 1921. Molars allocated to the strikingly ubiquitous Peradectes crocheti sp. nov. are found in eight additional localities from northwestern and southwestern Europe, all limited to the time interval MP7-MP8 + 9. Moreover, the study of unpublished material of the MP8 + 9 and ~MP8 + 9 peradectids allows us to recognize two younger coeval species (Peradectes louisi Crochet, 1979, and Peradectes russelli Crochet, 1979). Our taxonomic conclusions are supported a posteriori by the first quantitative assessment of the variation in height of metatherian stylar cusps. The holotype of Peradectes louisi is reinterpreted, and Peradectes ‘mutigniensis’ Crochet, 1979 appears to be a junior synonym of Peradectes russelli. In addition to size, the otherwise similar Peradectes louisi and Peradectes russelli can be distinguished based on subtle yet consistent differences, such as lower molar proportions. Phylogenetic analyses using a novel matrix of dental characters shed new light on the relationships among Eocene peradectids, confirming the paraphyly of Peradectes with respect to Armintodelphys and Mimoperadectes. Our results suggest a single dispersal from North America to Europe in the evolutionary history of peradectids, which likely occurred immediately after the Paleocene-Eocene Thermal Maximum, Peradectes crocheti sp. nov. being recovered as the earliest offshoot of the European clade. Scarce lower molars from the MP10 reference locality and ~MP10 localities analyzed within this constrained phylogenetic framework reveal a trend towards shrinking of the entoconid in the European lineage throughout the early Eocene.

Bone pathologies have great potential to provide information on the palaeobiology of fossil organisms. Some were likely related to inter/intraspecific fighting behaviors. Among the iconic and conspicuous Late Pleistocene armored mammals, Panochthus Burmeister, 1866 is notable for being one of the largest, most abundant, and diversified genera. A particular feature of Panochthus species is the presence of a caudal armor including a solid bony structure known as a caudal tube that would have played an important role in intra/interspecific contests. In this contribution, we report and describe a caudal vertebra of Panochthus that shows strong evidence of pathologies that may be related to the performance of strong tail movements that could correspond to offensive/defensive behaviors. The specimen (MFA-G-PV 1740) was recovered from Late Pleistocene deposits (MIS 5–3 cycles) cropping out in the cliffs of Northern Salado River, Santa Fe Province, Argentina. Based on morphological and radiological features, the lesions observed are related to a traumatic lesion that would have affected the ligamentum flavum and probably the articular capsule of the postzygapophysis, generating a severe enthesopathy and related septic arthritis. The involvement of this ligament in particular is crucial because it connects adjacent vertebral laminae and restricts mobility, offering resistance to extreme vertebral flexion and protecting the remaining vertebral structures when confronted with large forces. Although it is challenging to determine the exact way in which this species performed fighting tail movements, the joints with the greatest range of movement correspond to the most anterior caudal vertebrae. This also implies that any strong impact would have directly affected these vertebrae and associated soft tissues, including ligaments. Based on this evidence, we consider that the pathology described here represents strong evidence to support the idea of an active use of the caudal tube in Panochthus.

Nothrotherium maquinense, an extinct sloth species that existed alongside other megafauna during the Pleistocene, has been a subject of intense debate regarding various aspects of its life. This study integrates an examination of specific forearm bone fracture (paleopathology) with forelimb functional indices (paleoecology) in N. maquinense in order to infer its likely mode of locomotion and substrate preferences. Our findings provide compelling evidence suggesting that N. maquinense possessed climbing abilities and likely had a semi-arboreal lifestyle. Additionally, we report the first occurrence of calcium pyrophosphate deposition disease (CPPD) in this species, indicating that this type of arthritic condition was present in this sloth.

Multistate morphological characters are routinely used in phylogenetic analyses. Individual multistate characters may be treated as linearly ordered, partially ordered, or unordered. Each option implies a hypothesis of character evolution, and significant debate surrounds the appropriateness of ordering multistate characters. Several previous analyses support ordering multistate morphological characters when the character states form a morphocline. Here, we explore the effects of ordering a subset of characters in the largest morphological character matrix that is available for placental mammals. All multistate characters were assessed and were ordered only if the character states were meristic or hypothesized to form a morphocline. We then performed parsimony analyses, with and without molecular scaffolds, to examine the effects of ordering on placental mammal phylogeny. We also performed pseudoextinction analyses, which treated designated extant taxa as extinct by eliminating them from the molecular scaffold and scoring soft-tissue characters as missing, to determine if ordered or unordered characters would more accurately reconstruct the relationships of pseudoextinct placental orders. Character ordering affected the placement of a variety of taxa in non-scaffolded analyses, but the effects were less evident in scaffolded analyses. Nevertheless, one of the islands of most parsimonious trees with the ordered data set and a scaffold for extant taxa supported the inclusion of Leptictida, including the Late Cretaceous Gypsonictops, inside of crown Placentalia. Our analyses rarely supported the monophyly of Tamirtheria, the Late Cretaceous-Paleogene stem-based clade that is hypothesized to be the sister to Placentalia. Pseudoextinction analyses using ordered and unordered characters both reconstructed 12 of 19 pseudoextinct orders in positions that are incongruent with a well-supported molecular scaffold. These results suggest that the use of ordered multistate characters does not increase the proportion of well-supported molecular clades that are reconstructed with the largest available phenomic data set for placental mammals.

The “Diahot Tooth” is an isolated postcanine tooth of a large herbivorous mammal, discovered in the Diahot region of northern New Caledonia in 1875. Most authors have identified it as an upper premolar of a rhinocerotid, but an alternative proposal is that it belongs to a diprotodontoid marsupial that has been named Zygomaturus diahotensis. Either possibility raises biogeographical difficulties, because New Caledonia has been isolated from other major landmasses for 80 million years, and neither rhinocerotids nor diprodotontoids appear to be good candidates for such a long-distance overwater dispersal event. Here, we present a novel interpretation of the affinities and origin of the Diahot Tooth, based on qualitative study of its preserved morphology and quantitative phylogenetic analyses that include both rhinocerotids and diprotodontoids. We show that the Diahot Tooth most closely resembles the first deciduous premolar of Western Eurasian Miocene teleoceratine rhinocerotid Brachypotherium brachypus, with the few discrepancies relating to traits that are known to be variable in B. brachypus. Our phylogenetic analyses also support this relationship. The preservation of the Diahot Tooth closely resembles that of B. brachypus teeth from the “Faluns Sea” of the Loire basin, and we propose that the New Caledonian specimen originated there and was taken to New Caledonia by a European colonist during the mid-19th century, where it was lost, rediscovered, and incorrectly assumed to be autochthonous.