Tarsals of the extinct insectivoran family Nyctitheriidae (Mammalia): evidence for archontan relationships

Astragali and calcanea from the English late Eocene, attributed to the extinct 'insectivoran' family Nyctitheriidae, are described for the first time. They contrast with those of the strict sense insectivorans, the Lipotyphla, in which order nyctitheres have usually been placed, and compare more closely with those of Scandentia (tree shrews) and the extinct Plesiadapiformes. Functional analysis demonstrates that inversion of the foot was possible between the astragalus and calcaneum of nyctitheres, allowing them to be interpreted as having had a tree-dwelling, probably scansorial, mode of life. These tarsal bones are compared with those of other placental mammals. Cladistic analysis of tarsal characters places nyctitheres as sister group to the Plesiadapiformes within the superorder Archonta, excluding Chiroptera (bats). An independent analysis of dental characters places them as sister group to the rest of the Archonta, but still excluding bats. Combining the dental and tarsal characters places nyctitheres as sister group to Plesiadapiformes and all modern groups of archontans except bats. A new osteological synapomorphy is proposed for the Archonta, which is thus considered to comprise Chiroptera, Deccanolestes , Nyctitheriidae, Plesiadapiformes, Dermoptera (including Mixodectidae), Scandentia and Primates. Insectivorans s.l . have long been at the centre of arguments on placental origins, although lipotyphlans are usually regarded as a monophyletic group, rather than paraphyletic stem placentals. Reidentification of an extinct lipotyphlan family as having archontan relationships raises the possibility of advances in other areas of insectivoran phylogeny when more postcranial elements become known. The early Oligocene extinction of nyctitheres may be causally related to the rise of insectivorous microchiropteran bats, which, because of their flying ability, would have been able to forage more widely.     

Evolutionary and developmental dynamics of the dentition in Muroidea and Dipodoidea (Rodentia, Mammalia)

SUMMARY When it comes to mouse evo‐devo, the fourth premolar–first molar (P4–M1) dental complex becomes a source of longstanding controversies among paleontologists and biologists. Muroidea possess only molar teeth but with additional mesial cusps on their M1. Developmental studies tend to demonstrate that the formation of such mesial cusps could result from the integration of a P4 germ into M1 during odontogenesis. Conversely, most Dipodoidea conserve their fourth upper premolars and those that lost these teeth can also bear additional mesial cusps on their first upper molars. The aim of this study is to assess this developmental model in both Muroidea and Dipodoidea by documenting the morphological evolution of the P4–M1 complex across 50 Ma. Fourteen extinct and extant species, including abnormal and mutant specimens were investigated. We found that, even if their dental evolutionary pathways strongly differ, Dipodoidea and Muroidea retain common developmental characteristics because some of them can present similar dental morphological trends. It also appears that the acquisition of a mesial cusp on M1 is independent from the loss of P4 in both superfamilies. Actually, the progressive decrease of the inhibitory effect of P4, consequent to its regression, could allow the M1 to lengthen and mesial cusps to grow in Muroidea. Apart from these developmental explanations, patternings of the mesial part of first molars are also deeply constrained by morpho‐functional requirements. As there is no obvious evidence of such mechanisms in Dipodoidea given their more variable dental morphologies, further developmental investigations are needed.     

The deciduous dentition ofPercrocuta Kretzoi and the diphyletic origin of the hyaenas (Carnivora,Mammalia)

A juvenile mandible with complete deciduous dentition from the Middle Miocene locality Jianshan near Shilee (Xinan County, Honan Prov., China) belonging toPercrocuta hobeiensis Chen Guanfang & Wu Wenyu is described. The lower deciduous carnassial, which is by far the most informative element of the juvenile dentition, is distinguished from the D₄ of all other hyaenas by fundamental differences and exhibits principal similarities to that of the felids. Although these resemblances are very likely a result of parallel evolution, they can be taken as evidence of a considerable phylogentic distance betweenPercrocuta on one side and the Recent hyaenas with their forerunners on the other side. Judging from the special features of the deciduous carnassial and the high degree of hyaenid adaptation already attained in the Middle Miocene,Percrocuta probably derived from the neighbourhood of the Upper Oligocene and Lower Miocene generaStenoplesictis, Palaeoprionodon andProailurus, which in their turn take up a phylogenetically transitional position between felids and viverrids.     

Systematics and evolution of the subfamily Gerbillinae (Mammalia, Rodentia, Muridae)

Although they represent a quarter of the mammalian species, the evolutionary relationships among as well as within, the main murid lineages are still controversial. The subfamily Gerbillinae is no exception as previous studies based on morphological, karyotypical, and allozyme characters are highly incongruent. Here, we present the first molecular phylogeny for gerbils based on cytochrome b and 12S rRNA mitochondrial genes. Results are largely congruent between the two genes as well as with the concatenated data set with most of the nodes being well-supported. Based on the topologies retrieved here, we (1) propose the identification of three main clades, (2) support the split of Tatera genus into an Asian and an African group, the latter including Gerbillurus species, and (3) provide some evidence towards the inaccuracy of subgeneric divisions within both Gerbillus and Meriones. In addition, the sharp contrast between the genetic characters and morphological data sets suggest high levels of convergence, probably as a result of strong environmental constraints imposed on these rodents adapted to arid and semi-arid regions. Finally, molecular datings for the various cladogenetic events are in good agreement with the known gerbilline fossil record and support an African origin with subsequent migrations to Asia.     

Key morphofunctional transformations in the evolution of bats (Mammalia,Chiroptera)

Study on the morphology and morphogenesis of wing membranes in bats has revealed some peculiarities in their structure and development. Understanding the embryogenesis of these animals, as well as attraction of data obtained on their molecular genetics and paleontology, allows one to single out some factors that could have initiated evolutionary modifications in development programs. A scenario of the key morpho-functional transformations in the forelimbs during the evolution of chiropterans is given.     

Post-Pleistocene evolution of Bornean shrews Crocidura foetida (Mammalia, Soricidae)

Fossil mandibles of the Bornean shrew Crocidura foetida recovered from excavations at the west mouth of Niah cave, Sarawak, Malaysia, show that the late Pleistocene population at this lowland location was comparable in size with the large subspecies Crocidura foetida doriae , presently occurring at inland, upland locations. Two Holocene specimens fall in the size range of the smaller lowland subspecies C. f. foetida . Comparable post-Pleistocene size-reduction is known among other mammals of Borneo, but this is the first instance of dated examples. The evolutionary trend conforms with Bergmann's 'rule' but, other than climate change, no selective agent is apparent.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 413–419.     

Comparative morphology and evolution of the otic region in toothed whales (Cetacea, Mammalia)

The otic region in the skull of archeocetes and odontocetes is compared and interpreted with special emphasis on the morphology and suspension of the ear bones. In archeocetes, the periotic was obviously separate from the mastoid but still integrated within the skull via a long anterior and posterior process. The rotation of the cochlear part of the periotic was already obvious. The tympanic bone was attached to a decreasing number of neighboring elements, with the periotic becoming more and more important in the later archeocetes. The accessory air sacs of the tympanic cavity had invaded some of the adjacent skeletal elements and attained a moderate-to-remarkable extension. In the evolution of the odontocetes, the periotic and tympanic were successively uncoupled from the skull and combined to a new morphological and functional unit (tympanoperiotic complex). This uncoupling was mainly achieved by shortening the periotical processes and simultaneously extending the tympanic air sacs. For functional reasons, however, the periotic (posterior process) stayed in immediate contact with the mastoid, the latter remaining in the lateral wall of skull. In advanced marine dolphins, the bony sheaths of the accessory air sacs are largely reduced, presumably because of volume fluctuations in the tympanic cavity during diving. The perfect uncoupling of the ear bones from the skull obviously was an essential prerequisite for directional hearing, for effective ultrasound orientation and communication, and finally, for the striking development of the dolphin brain.     

Skull evolution in the rhinocerotidae (Mammalia,Perissodactyla): Cartesian transformations and functional interpretations

Cartesian transformation, applied as a landmark morphometric method, is used to investigate some of the evolutionary shape changes leading to the skulls of the modern rhinoceroses. The early Oligocene genusSubhyracodon serves as the primitive shape from which the extant genera (Dicerorhinus, Rhinocerso, Diceros, andCeratotherium) have been transformed. Coordinate data for 21 landmarks, defined in lateral view, are analyzed by the computer program Thinplate Splines. Each of the four transformations are interpreted separately as shape change fromSubhyracodon. Computed results forRhinoceros are also compared with previous results obtained by visual interpretation (the classic method). Among the extant genera,Ceratotherium andRhinoceros have the most derived shapes and are opposites with respect to orientation of the occiput and relative size of the mandible angle. The significance of these foci of change is discussed in terms of the functions of the masseter and posterior temporalis muscles. In head positions associated with feeding on short vs. tall grasses, the two skull shapes are consistent with a role for these muscles in support of a large mandible against gravity. This common factor may help to explain both shapes.     

Chromosomal evolution and distribution of telomeric repeats in golden moles (Chrysochloridae, Mammalia)

Golden moles (Chrysochloridae) are small, subterranean mammals endemic to sub-Saharan Africa that together with tenrecs constitute one of six orders in Afrotheria. Here we present a comprehensive karyotypic comparison among six species/subspecies of golden moles based on G-banding and chromosome painting. By expanding the species representation to include a further five species recently published in a companion paper, we were able to map the distribution of telomeric repeats in ten species/subspecies that are representative of six of the nine currently recognized genera. We conclude that: (i) the monophyly of Amblysomus is supported by the amplification of heterochromatin in several pericentric regions and one intrachromosomal rearrangement; (ii) A. hottentotus meesteri groups as sister to a clade that contains A. h. hottentotus, A. h. longiceps, A. h. pondoliae and A. robustus, an association that is underpinned by a shared intrachromosomal rearrangement and the detection of telomeric sequences in the centromeres of all chromosomes of the three A. hottentotus subspecies and A. robustus but, importantly, not in those of A. h. meesteri. These findings indicate an absence of gene flow suggesting that A. h. meesteri should be elevated to specific status. We hypothesize that the lack of gene flow may, in part, reflect hybrid dysgenesis resulting from abnormal meiotic segregation as a consequence of differences in the nature of the centromeric specific satellites; (iii) chromosomes 7 and 13 of Chrysochloris asiatica are fused in both Calcochloris obtusirostris and Eremitalpa granti, but that the position of the centromere in the fused chromosome differs in each species. This suggests that rather than being indicative of common ancestry, the fusion is more likely a convergent character which has arisen independently in each lineage. Furthermore our painting data show two centromeric shifts that are probably autapomorphic for C. obtusirostris. Finally, we conclude that (iv) golden moles are characterized by strong karyotypic conservatism but in marked contrast to the constrained rates of change exhibited by most species, A. robustus is unique in that three autapomorphic fissions define its evolutionary history, and hence the more extensive reshuffling of its genome.     

The evolution of specialized dentition in the deep-sea lanternfishes (Myctophiformes)

The evolution of heterodonty, the possession of varied tooth morphologies on the jaws of animals, has been relatively unexplored in ray-finned fishes compared to terrestrial vertebrates, and to an even lesser degree in deep-sea fish lineages. Lanternfishes (Myctophiformes) are an abundant and species-rich group endemic to deep-sea pelagic habitats. In this study, we document the presence of heterodonty on the oral jaws of lanternfishes, identifying differing anatomical and positional variations of dentition. We survey the anatomical variation in tooth morphology on the oral jaws of 114 lanternfish species across 37 genera and integrate our findings with a hypothesis of evolutionary relationships of lanternfishes to infer the number of times heterodonty evolved in this lineage. Our results indicate that heterodonty evolved at least six separate times on the oral jaws of lanternfishes, occurring as variable tooth morphologies in combination with villiform teeth. These combinations of tooth types include villiform plus hooked teeth, villiform plus hooked and recurved teeth, villiform plus spade, tricuspid, and hooked teeth, and villiform plus caniniform teeth. The reoccurring evolution of hooked teeth on the premaxilla and dentary in lanternfishes suggests heterodonty may serve an important functional role in their pelagic deep-sea environment. Hooked teeth could aid in securing and retaining prey in the oral cavity and allow for species to specialize on differing food resources, vital attributes for organisms living in open-ocean habitats.     

Australia's first fossil marsupial mole (Notoryctemorphia) resolves controversies about their evolution and palaeoenvironmental origins

Fossils of a marsupial mole (Marsupialia, Notoryctemorphia, Notoryctidae) are described from early Miocene deposits in the Riversleigh World Heritage Area, northwestern Queensland, Australia. These represent the first unequivocal fossil record of the order Notoryctemorphia, the two living species of which are among the world's most specialized and bizarre mammals, but which are also convergent on certain fossorial placental mammals (most notably chrysochlorid golden moles). The fossil remains are genuinely 'transitional', documenting an intermediate stage in the acquisition of a number of specializations and showing that one of these-the dental morphology known as zalambdodonty-was acquired via a different evolutionary pathway than in placentals. They, thus, document a clear case of evolutionary convergence (rather than parallelism) between only distantly related and geographically isolated mammalian lineages-marsupial moles on the island continent of Australia and placental moles on most other, at least intermittently connected continents. In contrast to earlier presumptions about a relationship between the highly specialized body form of the blind, earless, burrowing marsupial moles and desert habitats, it is now clear that archaic burrowing marsupial moles were adapted to and probably originated in wet forest palaeoenvironments, preadapting them to movement through drier soils in the xeric environments of Australia that developed during the Neogene.     

The evolution of hyoid apparatus in Xenarthra (Mammalia: Eutheria)

The hyoid apparatus reflects aspects of the form and function of feeding in living and extinct organisms and, despite the availability of information about this structure for Xenarthra, it remains little explored from an evolutionary perspective. Here we compare the morphology of the hyoid apparatus in xenarthrans, describing its general morphology and variation in each major clade and score these variations as phylogenetic characters, which were submitted to ancestral states reconstructions. The general hyoid morphology of Xenarthra consists of a v-bone (basihyal fused with the thyrohyals) and three paired bones (stylohyal, epihyal and ceratohyal), which are unfused in the majority of taxa. The clade-specific morphology observed here, allowed us to obtain additional synapomorphies for all major clades of Xenarthra (Cingulata, Pilosa, Folivora and Vermilingua), for Glyptodontididae, and for Nothrotheriidae. The fusion of hyoid elements are convergentelly achieved among the diphyletic extant tree sloths, some extinct ground sloths and glyptodontids. Despite the heavy influence of adaptive evolution related to feeding habits, the morphology of the hyoid apparatus proved to be a valuable source of phylogenetic information.     

Cope's rule and the evolution of body size in Pinnipedimorpha (Mammalia: Carnivora)

Cope's rule describes the evolutionary trend for animal lineages to increase in body size over time. In this study, we tested the validity of Cope's rule for a marine mammal clade, the Pinnipedimorpha, which includes the extinct Desmatophocidae, and extant Phocidae (earless seals), Otariidae (fur seals and sea lions), and Odobenidae (walruses). We tested for the presence of Cope's rule by compiling a large dataset of body size data for extant and fossil pinnipeds and then examined how body size evolved through time. We found that there was a positive relationship between geologic age and body size. However, this trend is the result of differences between early assemblages of small-bodied pinnipeds (Oligocene to early Miocene) and later assemblages (middle Miocene to Pliocene) for which species exhibited greater size diversity. No significant differences were found between the number of increases or decreases in body size within Pinnipedimorpha or within specific pinniped clades. This suggests that the pinniped body size increase was driven by passive diversification into vacant niche space, with the common ancestor of Pinnipedimorpha occurring near the minimum adult body size possible for a marine mammal. Based upon the above results, the evolutionary history of pinnipeds does not follow Cope's rule.     

Enamel microstructure evolution in anthracotheres (Mammalia,Cetartiodactyla) and new insights on hippopotamoid phylogeny

Investigations on enamel microstructure provided new data for the debate on hippopotamid origin. Observations indicated a diversity of patterns relevant to phylogenetic inferences. Within Hippopotamoidea, the distribution of these patterns seems to be in favour of a hippopotamid origin within the Palaeogene African anthracotheres. Enamel microcharacters therefore prove to be particularly relevant for future phylogenetic analysis of the superfamily, and have implications for our understanding of ecological transitions within hippopotamoids at the end of the Miocene. Indeed, unlike equids or bovids, which developed grass feeding thanks to their hypsodont molars, hippopotamoids may have had another way to exploit this resource. The combination of inter‐row sheets, which appeared early in the evolutionary history of the group, and the increased thickness of radial enamel could have eased the consumption of highly abrasive graminoids. © 2014 The Linnean Society of London     

Origin and evolution of the endemic Canary Island shrews (Mammalia: Soricidae)

Until recently the North Atlantic Islands were believed to house only mammals introduced by humans. Recent work has demonstrated that at least the Canary Islands house(d) a native mammal fauna. New data including chromosome numbers, genetic distances and analysis of vocalizations are given for the two extant shrew species, Crocidura canariensis and C. osorio , and their possible sister taxa are evaluated. Evidence is presented for the hypothesis that the two island species originated from two different lineages of the Palaearctic branch of the genus Crocidura. The data support the present status of the Canary Island shrews as local endemics of high conservation priority.     

The mole's thumb -- evolution of the hand skeleton in talpids (Mammalia)

Osteological specimens representing 15 out of the 16 currently recognized talpid genera were examined and scored for seven discrete morphological characters of the hand. The phylogenetic distribution of these characters was studied in the context of alternative hypotheses of talpid relationships, using three species of shrews and a hedgehog as outgroups. All talpids show a similar number and arrangement of carpal bones. The most obvious differences concern the presence of additional sesamoid bones, the relative size of the os falciforme when present, and the degree of fusion of the scaphoid and lunate in the proximal carpal row. Marked differences in the relative length and proportions of the metacarpals also exist. The development of the carpals in Talpa europaea was studied through examination of histological sections of the hand of an embryo and a neonate. Whereas carpal anatomy in the neonate mirrors the arrangement and proportions of the adult, in the embryo the scaphoid and lunate are still separate, there are no signs of the os falciforme, and the size proportions of metacarpals to carpals are obviously different to those of the adult. A prehallux or tibial sesamoid, serial homologue to the os falciforme or prepollex (a radial sesamoid), does not have an obvious functional role, and its presence might be the result of a common epigenetic control in the hand and the foot resulting in a non-adaptive structure in the latter.