Journal of Mammalian Evolution最新文献

Kangaroos (Macropodoidea) display a diversity of locomotor modes, from bounding quadrupedally to hopping bipedally; but hopping has a body mass limit, which was exceeded by a number of extinct taxa. In the Pleistocene, a variety of “giant” kangaroos existed, both within the extinct subfamily Sthenurinae and the extant subfamily Macropodinae (both within the family Macropodidae). Sthenurines have been previously considered to have a type of locomotion (bipedal striding) different from extant kangaroos, but the primary locomotor mode of the large species of the extinct “giant” macropodine genus Protemnodon, closely related to extant large kangaroos, has undergone little question and has been assumed to be hopping. Here, the association between limb proportions and locomotor mode across Macropodoidea is assessed by examination of functional limb indices. We show that large (> 100 kg) Protemnodon species are unlike any other known macropodoids; their position in this functional morphospace, along with previously published evidence on humeral morphology, supports a prior hypothesis of a primarily quadrupedal mode of locomotion, likely some sort of bounding.

Analysis of largely unstudied fossil collections recovered from caves and sinkholes from western Hispaniola has resulted in the recognition of a new capromyine rodent (Zagoutomys woodsi, gen. et sp. nov.) and a new solenodontid (Solenodon ottenwalderi sp. nov.). Fossils of Z. woodsi show that it differs from other capromyine rodents in having a mandible with a relatively thin and elongated symphysis, a relatively long diastema between the lower incisor and dp4, a more procumbent incisor, and a more anteriorly positioned masseteric crest. Results from a phylogenetic analysis suggest that Z. woodsi is closely related to the Plagiodontia clade, which includes living P. aedium and two extinct species. While fossils referred to Z. woodsi are rare (n = 18) among the thousands of rodent specimens recovered from the study sites, their geographic distribution suggests it was present across western Hispaniola. In contrast, fossils of S. ottenwalderi are relatively abundant in several localities but restricted to the western portion of the Tiburon Peninsula, like other regionally endemic extinct taxa, including the platyrrhine primate Insulacebus toussaintiana and the capromyine rodent Rhizoplagiodontia lemkei. Fossils of S. ottenwalderi show that it was notably smaller than other species of Solenodontidae, reducing the body size gap between this genus and Nesophontes. A phylogenetic analysis suggests that S. ottenwalderi is sister to the extinct species S. marcanoi and both are sister to extant S. paradoxus, forming a monophyletic clade endemic to Hispaniola. Morphological and body size differences of these two new mammals with respect to their sister taxa might suggest niche differentiation with segregation of available resources in these past island ecosystems.

Raoellid mammals are small artiodactyls from the Eocene of Asia, hypothesized to be closely related to stem Cetacea. Knowledge of the cranial and dental morphology of Raoellidae comes mostly from one species, Indohyus indirae. Here we describe new material of another raoellid genus, Khirtharia, based on material retrieved from the Kalakot area, Jammu and Kashmir. This new material, comprising an almost complete, lightly deformed cranium and a partial snout with associated partial mandible, greatly adds to our knowledge of raoellid morphology. It highlights the similarity of cranial characters with Indohyus, such as a long snout with raptorial incisors, a thick and narrow supraorbital region, a strong postorbital constriction, a triangular shaped braincase, and a thickened medial wall to the auditory bulla (involucrum). The new specimen is similar to Indohyus cranially but differs dentally in being more bunodont. The presence of these traits in two different raoellid genera suggests they may be present more broadly across Raoellidae. These characters are also observed in early cetaceans, highlighting the need to investigate their phylogenetic impact. Some cranial features support aquatic habits of members of this family.

We describe new proterotheriid specimens from three Late Miocene lithostratigraphic units: the Camacho Formation of Uruguay and the Loma de Las Tapias and Cerro Azul formations of Argentina. The remains include skull and mandibular fragments as well as postcranial remains. The type of Neobrachytherium ullumense is described for the first time, and we expand its diagnosis, judging the following combination of characteristics to be diagnostic: slender and short skull; in lateral view the plane of the dorsal surface and occlusal plane of the rostrum converge on the anterior end; premaxilla anteriorly projected, not diverging from the sagittal plane; slender zygomatic arch; orbit with rostral border at the level of the posterior root of M1; occipital condyles are ventrally projected; P3-P4 with anterolingual cingulum extended are distally; M2 with a reduced metaconule of the circular base, interrupting the posterolingual groove; M3 with a well-developed hypocone separated from the protocone by a posterolingual groove and without metaconule; p4-m3 with a short trigonid and free entoconid, variably positioned relative to the hypolophulid, with paraconid oriented towards the metaconid, and cristid obliqua closing at the metaconid level. A better understanding of the diversity of the family Proterotheriidae, and especially their dental morphology, including the shape, position and development of cusps and valleys, is provided. Neobrachytherium ullumense had been previously reported for Late Miocene, in the South American Land Mammal Ages Chasicoan and Huayquerian, in levels of the San Juan (Loma de Las Tapias Formation) and Buenos Aires (Cerro Azul Formation) provinces of Argentina. This contribution expands the geographic distribution of the species 500 km East, to San José Department (Camacho Formation), Uruguay.

The mammalian dentition is an important model for studying morphological diversity and evolutionary processes. The main characteristics contributing to this fact are its organization into interrelated modules and its self-regulated development by activating and inhibiting molecules. A previous study from our group showed that the minimum free energy of an intronic G-quadruplex (G4)-forming RNA sequence of Pax9 was correlated with the diversity of molar patterns in mammals. In this work, a similar approach was used to search for possible associations between the minimum free energy of RNA sequences in the MSX1 and the relative size of molars and premolars in eutherian mammals. A region (named hereby Int1Seq) located at the beginning of the first intron presented a significant correlation between its minimum free energies and molar and premolar relative sizes. This region presented high sequence diversity, and in many species, it had the ability to form a stable G-quadruplex (G4). Besides the correlation analyses, when Int1Seq minimum free energies were used as a proxy of the activator molecules, it also increased the correlation between molar proportions in the inhibitory molar cascade model, as well as in the molar-module-component and premolar-molar-module models. Our results indicate this region, located in the MSX1 intronic sequences, is involved in the patterning of posterior teeth and reinforces the role of G4 sequences in the diversification of mammalian dentition.

Graphic abstract

The exon-intron structure of the human MSX1 gene with emphasis on the position and relationship between the minimum free energies of the Int1Seq secondary structure and molar ratios for Saimiri sciureus, Mus musculus, Homo sapiens, and Bos taurus*.

*The images of the dental arches are for illustrative purposes only and do not represent the skulls of the specimens used for measurements in this study.

The Late Miocene natural traps of Cerro de los Batallones (Madrid, Spain) have yielded thousands of fossils of vertebrates, mostly carnivoran mammals such as hyaenids, amphicyonids, ailurids, mustelids, ursids, and felids, especially Batallones-1 and Batallones-3. Among these carnivorans, the tiger-sized saber-toothed felid Machairodus aphanistus was the top predator of the association, and one of the most abundant taxa, represented by thousands of fossils, including several examples of bone pathologies that have never been studied. In this work, we carry out a paleopathological analysis of some of these pathologies from the Batallones sample of this large early machairodontine, with a description of the pathological changes that occurred in the affected bones, a possible diagnosis, and the ethological and ecological consequences of the presence of these diseases in the living animal. The pathological sample of M. aphanistus studied here included a calcaneus and a Mc III from Batallones-1, and a mandible from Batallones-3. The fossils were X-rayed, and their pathologies were described and compared to non-pathological bones. The calcaneus showed a bone callus indicative of osteitis/osteomyelitis or a tumor; the mandible had evidence of the development of an abscess located in the left mandibular body; and the Mc III shows a marked osteosclerosis. These injuries affected the hunting ability of these individuals and gradually weakened them, very likely contributing to their final entrapment in the Batallones cavities, where they were attracted by the presence of previously trapped animals.

No suid remains have been reported from the Miocene site of Can Missert (Terrassa; Vallès-Penedès Basin, NE Iberian Peninsula), variously correlated to MN7+8 (late Aragonian) or MN9 (early Vallesian) due to the uncertain presence of hipparionin equids. The recent donation of fossils collected decades ago by amateur naturalists has confirmed the presence of Hippotherium and enabled the description of a sample of 27 suid teeth from Can Missert 2. They are here attributed to the suine Propotamochoerus palaeochoerus and the tetraconodontine Parachleuastochoerus valentini, while Listriodon splendens is also recorded from Can Missert based on a previously unpublished male upper canine. The co-occurrence of Pr. palaeochoerus and hipparionins at Can Missert strengthens the view that the former is a biochronological marker of the Vallesian. In turn, the described tetraconodontine remains support the distinction of Pa. valentini from Conohyus simorrensis—considered its senior subjective synonym by some authors—but do not contribute to the ongoing debate about their potential congeneric status. The co-occurrence of Pr. palaeochoerus and Pa. valentini has also been recorded from the earliest Vallesian sites of Creu de Conill 20 and Castell de Barberà within the same basin. However, the composition of the Can Missert 2 suid assemblage more clearly differs from that of Castell de Barberà, where both Listriodon splendens and Albanohyus castellensis are also abundant. Given the restricted size of Can Missert sample, it is uncertain whether such differences are indicative of more open and/or seasonal paleoenvironmental conditions at Can Missert or just the result of sampling biases.

Bats appear in the fossil record on multiple continents during the early Eocene. More than seventy Eocene bat species have been named to date, including stem bats, probable members of crown families, and others of uncertain affinity. Most phylogenetic analyses of Eocene bat relationships have focused on the handful of taxa known from nearly complete skeletal material, whereas the taxonomic relationships of more incomplete fossils have been based largely on phenetic similarities. Here we evaluate the evolutionary relationships of over 60 species of Eocene bats—including many taxa known only from fragmentary craniodental remains—in an explicitly phylogenetic context. Our analysis is based on nearly 700 morphological characters scored in 82 taxa, including 20 extant species representing all living bat families other than Pteropodidae. We found that phylogenetic relationships of Eocene bats are more complex than previously thought. Numerous families (e.g., †Archaeonycteridae, †Mixopterygidae, †Palaeochiropterygidae) and genera (e.g., †Archaeonycteris, †Icaronycteris, †Carcinipteryx) were found to be non-monophyletic as previously recognized, requiring adjustments to chiropteran taxonomy. Four major clades of stem bats were recovered in our analyses. †Microchiropteryx folieae (~ 54 Ma, India) was recovered as the earliest crown bat, occurring as the most basal lineage of Vespertilionoidea, whereas many putative crown bats were recovered among stem Chiroptera. †Tachypteron franzeni was found to be a crown bat in our analyses, as in previous studies, but it was recovered unexpectedly as a stem miniopterid. The phylogenetic relationships presented here represent the most comprehensive analysis of Eocene bat relationships completed to date, substantially improving our understanding of the position of many fossil taxa within Chiroptera and providing a foundation for future analyses of bat evolution.

The Periptychidae, an extinct group of archaic ungulates (‘condylarths’), were the most speciose eutherian mammals in the earliest Paleocene of North America, epitomizing mammalian ascendency after the Cretaceous–Paleogene (K–Pg) mass extinction. Although periptychids are mostly known from fragmentary gnathic remains, the Corral Bluffs area within the Denver Basin, Colorado, has yielded numerous exceptionally well-preserved mammalian fossils, including periptychids, from the earliest Paleocene. Here we describe a partial cranium and articulated dentaries plus an additional unassociated dentary fragment of a small-bodied (~273–455 g) periptychid from ca. 610 thousand years after the K–Pg mass extinction (Puercan 2 North American Land Mammal ‘age’) at Corral Bluffs. Based on these new fossils we erect Militocodon lydae gen. et sp. nov. The dentition of M. lydae exhibits synapomorphies that diagnose the Conacodontinae, but it is plesiomorphic relative to Oxyacodon, resembling putatively basal periptychids like Mimatuta and Maiorana in several dental traits. As such, we interpret M. lydae as a basal conacodontine. Its skull anatomy does not reveal clear periptychid synapomorphies and instead resembles that of arctocyonids and other primitive eutherians. M. lydae falls along a dental morphocline from basal periptychids to derived conacodontines, which we hypothesize reflects a progressive, novel modification of the hypocone to enhance orthal shearing and crushing rather than grinding mastication. The discovery and thorough descriptions and comparisons of the partial M. lydae skull represent an important step toward unraveling the complex evolutionary history of periptychid mammals.

Immune response is known to be under constant evolutionary pressure from different factors including pathogens. Although different selection regimes are expected to act on the magnitude of immune response, there are limited studies that have investigated the different patterns of selection pressures on the immune response quantitatively. I employed evolutionary models (Ornstein-Uhlenbeck models) to identify different patterns of selection on the antiviral immune response of fibroblasts derived from 18 mammalian species and one vertebrate stimulated by viral ligand, poly I: C, or Interferon alpha cytokine. I found stabilizing selection to be the dominant form of selection on the immune response. Out of 59 genes that were found to be responding in at least 15 species, 50 genes were found to be under stabilizing selection. Moreover, the evolutionary variance was found to differ among these conservatively responding genes implicated in fighting viruses. For instance, ADAR was found to have low evolutionary variance while TRIM14 response showed the opposite trend suggesting different evolutionary pressures acting on the magnitude of response. Directional selection was also detected in specific infra-orders of primates such as apes and old-world monkeys in response of innate immune effectors.