Bony labyrinth morphology clarifies the origin and evolution of deer

The first finding of Dictyocaulus cervi and Dictyocaulus skrjabini (Nematoda) in feral fallow deer (Dama dama) in Australia

Feral deer are widespread throughout Australia with the capacity to impact livestock production via transmission of parasites. Samples of Dama dama (fallow deer), Rusa unicolor (sambar deer), Cervus elaphus (red deer) and an unidentified deer were sourced from various locations in south-eastern Australia for examination for parasites. Adult nematodes were collected from the lungs of all deer species across four separate geographical locations. The nematodes were identified as species of Dictyocaulus through both morphological and molecular means. Species identification based on morphological features was difficult, with many measurements from described species overlapping. Molecular analyses targeting three markers, namely 18S rRNA, ITS2, and cox1 revealed the presence of two distinct species: Dictyocaulus cervi and Dictyocaulus skrjabini. These are the first genetically confirmed reports of species of Dictyocaulus in feral deer in Australia, and although cross-transmission of species of Dictyocaulus with livestock has not yet been reported, it cannot be completely discounted without further research.

The comparative anatomy of the petrosal bone and bony labyrinth of four small-sized deer

Here we provide complete 3D reconstructions of the petrosal bone and bony labyrinth of four kinds of small-sized deer (Elaphodus cephalophus, Muntiacus reevesi, Muntiacus muntjak, Hydropotes inermis) based on high-resolution CT scanning, and select one musk deer (Moschus moschiferus) as a comparative object. The petrosal bone and bony labyrinth of E. cephalophus are illustrated for the first time, as well as the petrosal bones of M. reevesi and H. inermis. Some morphological characters of petrosal bone and bony labyrinth can be used to distinguish the above-mentioned species. For example, M. moschiferus shows a prominent transpromontorial sulcus and a ventral basicapsular groove on the petrosal bone; there is a bifurcate cochlear aqueduct on the bony labyrinth of E. cephalophus; there is a distinct fusion between the lateral and posterior semicircular canals on the bony labyrinth of H. inermis. Meanwhile, there are some intraspecific variations on the subarcuate fossa, the tegmen tympani, the cochlear aqueduct, as well as the endolymphatic sac. Our results further confirm that the petrosal bone and bony labyrinth have enormous potential for taxonomy. This work will provide new anatomical data for the phylogenetic study of ruminants in the future, and it will be very practical to identify the isolated ruminants' petrosal bones that are frequently unearthed from paleontological or archeological sites.

An Eocene insect could hear conspecific ultrasounds and bat echolocation

Hearing has evolved independently many times in the animal kingdom and is prominent in various insects and vertebrates for conspecific communication and predator detection. Among insects, katydid (Orthoptera: Tettigoniidae) ears are unique, as they have evolved outer, middle, and inner ear components, analogous in their biophysical principles to the mammalian ear. The katydid ear consists of two paired tympana located in each foreleg. These tympana receive sound externally on the tympanum surface (usually via pinnae) or internally via an ear canal (EC). The EC functions to capture conspecific calls and low frequencies, while the pinnae passively amplify higher-frequency ultrasounds including bat echolocation. Together, these outer ear components provide enhanced hearing sensitivity across a dynamic range of over 100 kHz. However, despite a growing understanding of the biophysics and function of the katydid ear, its precise emergence and evolutionary history remains elusive. Here, using microcomputed tomography (μCT) scanning, we recovered geometries of the outer ear components and wings of an exceptionally well-preserved katydid fossilized in Baltic amber (∼44 million years [Ma]). Using numerical and theoretical modeling of the wings, we show that this species was communicating at a peak frequency of 31.62 (± 2.27) kHz, and we demonstrate that the ear was biophysically tuned to this signal and to providing hearing at higher-frequency ultrasounds (>80 kHz), likely for enhanced predator detection. The results indicate that the evolution of the unique ear of the katydid, with its broadband ultrasonic sensitivity and analogous biophysical properties to the ears of mammals, emerged in the Eocene.

Antler tine homologies and cervid systematics: A review of past and present controversies with special emphasis on Elaphurus davidianus

Antlers are the most conspicuous trait of cervids and have been used in the past to establish a classification of their fossil and living representatives. Since the availability of molecular data, morphological characters have generally become less important for phylogenetic reconstructions. In recent years, however, the appreciation of morphological characters has increased, and they are now more frequently used in addition to molecular data to reconstruct the evolutionary history of cervids. A persistent challenge when using antler traits in deer systematics is finding a consensus on the homology of structures. Here, we review early and recent attempts to homologize antler structures and objections to this approach, compare and evaluate recent advances on antler homologies, and critically discuss these different views in order to offer a basis for further scientific exchange on the topic. We further present some developmental aspects of antler branching patterns and discuss their potential for reconstructing cervid systematics. The use of heterogeneous data for reconstructing phylogenies has resulted in partly conflicting hypotheses on the systematic position of certain cervid species, on which we also elaborate here. We address current discussions on the use of different molecular markers in cervid systematics and the question whether antler morphology and molecular data can provide a consistent picture on the evolutionary history of cervids. In this context, special attention is given to the antler morphology and the systematic position of the enigmatic Pere David's deer (Elaphurus davidianus).

Ruminant inner ear shape records 35 million years of neutral evolution

Extrinsic and intrinsic factors impact diversity. On deep-time scales, the extrinsic impact of climate and geology are crucial, but poorly understood. Here, we use the inner ear morphology of ruminant artiodactyls to test for a deep-time correlation between a low adaptive anatomical structure and both extrinsic and intrinsic variables. We apply geometric morphometric analyses in a phylogenetic frame to X-ray computed tomographic data from 191 ruminant species. Contrasting results across ruminant clades show that neutral evolutionary processes over time may strongly influence the evolution of inner ear morphology. Extant, ecologically diversified clades increase their evolutionary rate with decreasing Cenozoic global temperatures. Evolutionary rate peaks with the colonization of new continents. Simultaneously, ecologically restricted clades show declining or unchanged rates. These results suggest that both climate and paleogeography produced heterogeneous environments, which likely facilitated Cervidae and Bovidae diversification and exemplifies the effect of extrinsic and intrinsic factors on evolution in ruminants.

Size and shape of the semicircular canal of the inner ear: A new marker of pig domestication?

Domestication has led to many changes in domestic animal biology, including their anatomy. The shape of the inner ear, part of the mammalian ear, has been found particularly relevant for discriminating domesticated species, their hybrids or differentiating the wild and domestic populations of a single species. Here we assessed the use of the size and shape of the semicircular canals (SCC) of the inner ear as a marker of pig domestication. We studied a total of 63 petrosal bones belonging to wild boar (Sus scrofa, two populations) and domestic pigs (extensively and intensively reared specimens) that were µCT-scanned and from which the size and the shape of the inner ear were quantified through geometric morphometrics, analyzing the 3D coordinates of 6 landmarks and 60 sliding semilandmarks localized on the SCC and the common crus. The domestic pigs have larger SCC than the wild boar from which they also strongly differ in shape (correct cross validation of 95.5%, confidence interval: 92.3%-98.1%). Strong shape differences were detected between the two populations of wild boar, as well as a sexual size dimorphism. All together the results highlight the taxonomic discriminant power of the SCC of the inner ear shape, and its relevance for domestication studies.

Phylogeny and evolution of the genus Cervus (Cervidae, Mammalia) as revealed by complete mitochondrial genomes

Mitochondrial DNA (mtDNA) lineages are recognized as important components of intra- and interspecific biodiversity, and allow to reveal colonization routes and phylogeographic structure of many taxa. Among these is the genus Cervus that is widely distributed across the Holarctic. We obtained sequences of complete mitochondrial genomes from 13 Cervus taxa and included them in global phylogenetic analyses of 71 Cervinae mitogenomes. The well-resolved phylogenetic trees confirmed Cervus to be monophyletic. Molecular dating based on several fossil calibration points revealed that ca. 2.6 Mya two main mitochondrial lineages of Cervus separated in Central Asia, the Western (including C. hanglu and C. elaphus) and the Eastern (comprising C. albirostris, C. canadensis and C. nippon). We also observed convergent changes in the composition of some mitochondrial genes in C. hanglu of the Western lineage and representatives of the Eastern lineage. Several subspecies of C. nippon and C. hanglu have accumulated a large portion of deleterious substitutions in their mitochondrial protein-coding genes, probably due to drift in the wake of decreasing population size. In contrast to previous studies, we found that the relic haplogroup B of C. elaphus was sister to all other red deer lineages and that the Middle-Eastern haplogroup E shared a common ancestor with the Balkan haplogroup C. Comparison of the mtDNA phylogenetic tree with a published nuclear genome tree may imply ancient introgressions of mtDNA between different Cervus species as well as from the common ancestor of South Asian deer, Rusa timorensis and R. unicolor, to the Cervus clade.

First Attempt to Infer Sound Hearing and Its Paleoenvironmental Implications in the Extinct Insular Canid Cynotherium sardous Studiati, 1857 (Sardinia, Italy)

Simple Summary

The microtomographic approach allows nondestructive acquisition of anatomical details of the bone labyrinth that houses the inner ear. The petrosal bone can be a gold mine of information for a variety of questions in different research fields, including taxonomic, behavioral, and genetic studies. The semicircular canals provide information on head posture and locomotor ability, whereas the cochlea provides data on hearing ability. The petrosal bone is the hardest structure in the skeleton and could be well preserved in fossil specimens. As a result, it is becoming more and more popular in current archaeological and paleontological studies. In this study, petrosal microtomographic analysis was applied for the first time to Cynotherium sardous, a highly modified endemic canid that inhabited Sardinia during the Middle to Late Pleistocene. Indications about its hearing ability may provide interesting insights to better understand the new lifestyle and behavior this canid acquired during the long evolutionary process it underwent in the peculiar insular ecosystem with a depleted fauna. The poor hearing and echolocalization capabilities of Cynotherium sardous would have been the outcome of reduced competition pressure due to the absence of predators and the abundance of prey, such as the large ochotonid Prolagus sardus, while the high-frequency hearing could be interpreted as an adaptation to detect sounds emitted by its preferred prey.

Abstract

This is the first study on the bony labyrinth of Cynotherium sardous, an intriguing extinct canid that inhabited Sardinia in the late Middle and Late Pleistocene. The morphological features of the cochlea indicate that C. sardous had a lower number of cochlear turns (2.25) than all extant canids. This feature, as well as the reduced length of the spiral canal, the cochlear curvature rate, and the narrow basal membrane, indicates that C. sardous had poor hearing abilities limited to high-frequency sounds with a low limit of 250 Hz and poor echolocalization skills. From the data available, it is not possible to infer whether C. sardous was unable to echolocalize its prey and relied on other senses (e.g., smell and sight) to locate them or whether the acoustic range of C. sardous was specialized for identifying the sounds produced by its most common prey to transmit signals for predator warnings or group communication. All things considered, the results obtained confirm the utility of cochlea morphological studies in reconstructing the hearing abilities of this species and in providing some suggestions about its ethology, but they fall short of providing any new sound evidence regarding the ecological role of C. sardous in the Late Pleistocene Sardinian ecosystem.

Ancient Mitogenomes Suggest Stable Mitochondrial Clades of the Siberian Roe Deer

The roe deer (Capreolus spp.) has been present in China since the early Pleistocene. Despite abundant fossils available for detailed morphological analyses, little is known about the phylogenetic relationships of the fossil individuals to contemporary roe deer. We generated near-complete mitochondrial genomes for four roe deer remains from Northeastern China to explore the genetic connection of the ancient roe deer to the extant populations and to investigate the evolutionary history and population dynamics of this species. Phylogenetic analyses indicated the four ancient samples fall into three out of four different haplogroups of the Siberian roe deer. Haplogroup C, distributed throughout Eurasia, have existed in Northeastern China since at least the Late Pleistocene, while haplogroup A and D, found in the east of Lake Baikal, emerged in Northeastern China after the Mid Holocene. The Bayesian estimation suggested that the first split within the Siberian roe deer occurred approximately 0.34 million years ago (Ma). Moreover, Bayesian skyline plot analyses suggested that the Siberian roe deer had a population increase between 325 and 225 thousand years ago (Kya) and suffered a transient decline between 50 and 18 Kya. This study provides novel insights into the evolutionary history and population dynamics of the roe deer.

The early evolution of cranial appendages in Bovoidea revealed by new species of Amphimoschus (Mammalia: Ruminantia) from China

The cranial appendage (headgear) is an iconic structure of modern ruminants, and four of the five extant pecoran families display morphological and physiological specialties. They probably share one origin from the same genetic basis, whereas the evolution of the cranial appendages is still debatable, especially in consideration of fossil taxa lacking headgear. Amphimoschus is an enigmatic pecoran that comprises no more than two species, mainly known from the late early/early middle Miocene of Western and Central Europe and considered not to possess any cranial appendages. Here, we present Amphimoschus xishuiensis sp. nov., discovered in the Tabenbuluk area, Gansu Province, China. The new species reveals the first evidence of cranial ornamentations in the genus, including a supraorbital bump, an antorbital protuberance and frontal thickening. In our phylogenetic analysis the genus was inferred as a basal member of the Bovoidea, and thus the cranial ornamentations of A. xishuiensis might provide insight into the early evolution of cranial appendages in Bovoidea. They could be interpreted as weapons to defend territories in intense intraspecific or interspecific competition during the late early Miocene.

Cochlear shape distinguishes southern African early hominin taxa with unique auditory ecologies

Insights into potential differences among the bony labyrinths of Plio-Pleistocene hominins may inform their evolutionary histories and sensory ecologies. We use four recently-discovered bony labyrinths from the site of Kromdraai to significantly expand the sample for Paranthropus robustus. Diffeomorphometry, which provides detailed information about cochlear shape, reveals size-independent differences in cochlear shape between P. robustus and Australopithecus africanus that exceed those among modern humans and the African apes. The cochlea of P. robustus is distinctive and relatively invariant, whereas cochlear shape in A. africanus is more variable, resembles that of early Homo, and shows a degree of morphological polymorphism comparable to that evinced by modern species. The curvature of the P. robustus cochlea is uniquely derived and is consistent with enhanced sensitivity to low-frequency sounds. Combined with evidence for selection, our findings suggest that sound perception shaped distinct ecological adaptations among southern African early hominins.

The petrosal and basicranial morphology of Protoceras celer

Protoceratids are an extinct family of endemic North American artiodactyls. The phylogenetic position of protoceratids in relation to camelids and ruminants has been contentious for over a century. The petrosal morphology of basal (Leptotragulus) and derived (Syndyoceras) protoceratids has suggested that protoceratids are closely related to ruminants, whereas a prior description of a disarticulated intermediate protoceratid petrosal (Protoceras celer) indicated that protoceratids were closely related to camelids. This contradictory evidence implied that there were several character reversals within the protoceratid lineage and brought into question the utility of basicranial characters in artiodactyl phylogenetics. Here, we provide descriptions of an additional P. celer petrosal. The descriptions are based on data produced by computed tomography scans, which allowed us to image the petrosal in situ in the skull. Our results indicate that the petrosal morphology of P. celer is similar to that of other protoceratids, implying that, contrary to previous evidence, petrosal morphology is conserved within the Protoceratidae.

Reassessment of the enigmatic ruminant Miocene genus Amphimoschus Bourgeois, 1873 (Mammalia, Artiodactyla, Pecora)

Amphimoschus is an extinct Eurasian ruminant genus, mostly recorded in Europe, without a close living relative and, hence, an unknown systematic position. This genus is known from around 50 localities from the late early to the middle Miocene. Two species were described during 180 years, but since their first description during the late 19^th century and early 20^th century, hardly any detailed taxonomic work has been done on the genus. Over the years, extensive collecting and excavating activities have enriched collections with more and more complete material of this still rare and enigmatic animal. Most interestingly, a number of skull remains have been unearthed and are promising in terms of providing phylogenetic information. In the present paper, we describe cranial material, the bony labyrinth, the dentition through 780 teeth and five skulls from different ontogenetic stages. We cannot find a clear morphometric distinction between the supposedly smaller and older species Amphimoschus artenensis and the supposedly younger and larger species A. ponteleviensis. Accordingly, we have no reason to retain the two species and propose, following the principle of priority (ICZN chapter 6 article 23), that only A. ponteleviensis Bourgeois, 1873 is valid. Our studies on the ontogenetic variation of Amphimoschus does reveal that the sagittal crest may increase in size and a supraorbital ridge may appear with age. Despite the abundant material, the family affiliation is still uncertain.

A comparative analysis of the vestibular apparatus in Epipliopithecus vindobonensis: Phylogenetic implications

Pliopithecoids are an extinct group of catarrhine primates from the Miocene of Eurasia. More than 50 years ago, they were linked to hylobatids due to some morphological similarities, but most subsequent studies have supported a stem catarrhine status, due to the retention of multiple plesiomorphic features (e.g., the ectotympanic morphology) relative to crown catarrhines. More recently, some morphological similarities to hominoids have been noted, raising the question of whether they could be stem members of this clade. To re-evaluate these competing hypotheses, we examine the morphology of the semicircular canals of the bony labyrinth of the middle Miocene pliopithecid Epipliopithecus vindobonensis. The semicircular canals are suitable to test between these hypotheses because (1) they have been shown to embed strong phylogenetic signal and reliably discriminate among major clades; (2) several potential hominoid synapomorphies have been identified previously in the semicircular canals; and (3) semicircular canal morphology has not been previously described for any pliopithecoid. We use a deformation-based (landmark-free) three-dimensional geometric morphometric approach to compare Epipliopithecus with a broad primate sample of extant and extinct anthropoids. We quantify similarities in semicircular canal morphology using multivariate analyses, reconstruct ancestral morphotypes by means of a phylomorphospace approach, and identify catarrhine and hominoid synapomorphies based on discrete characters. Epipliopithecus semicircular canal morphology most closely resembles that of platyrrhines and Aegyptopithecus due to the retention of multiple anthropoid symplesiomorphies. However, Epipliopithecus is most parsimoniously interpreted as a stem catarrhine more derived than Aegyptopithecus due to the possession of a crown catarrhine synapomorphy (i.e., the rounded anterior canal), combined with the lack of other catarrhine and any hominoid synapomorphies. Some similarities with hylobatids and atelids are interpreted as homoplasies likely related to positional behavior. The semicircular canal morphology of Epipliopithecus thus supports the common view that pliopithecoids are stem catarrhines.

Exploring the ontogenetic development of the inner ear in Aardvarks

The aardvark is the last living Tubulidentata, an order of afrotherian mammals. Afrotheria is supported strongly by molecular analyses, yet sparingly by morphological characters. Moreover, the biology of the aardvark remains incompletely known. The inner ear, and its ontogeny in particular, has not been studied in details yet, though it bears key ecomorphological characters and phylogenetical signal. The aim of this study is to decipher and discuss the ontogenetic development of the different areas of the inner ear of Orycteropus afer. We focused in particular on their relative size and morphological rates of development. Specimens were scanned with 3D imaging techniques. 3D and 2D geometric morphometrics coupled with qualitative descriptions of the petrosal ossification allowed us to evidence several stages through development. Based on our sample, the cochlea is the first structure of the inner ear to reach adult size, but it is the last one to acquire its adult morphology close to parturition. In contrast, after a delayed growth spurt, the semicircular canals reach their mature morphology before the cochlea, concomitantly with the increase of petrosal ossification. The ontogeny of the aardvark inner ear shows similarities with that of other species, but the apex of the cochlea presents some autapomorphies. This work constitutes a first step in the study of the ontogeny of this sensorial organ in Afrotheria.

A test of the lateral semicircular canal correlation to head posture, diet and other biological traits in "ungulate" mammals

For over a century, researchers have assumed that the plane of the lateral semicircular canal of the inner ear lies parallel to the horizon when the head is at rest, and used this assumption to reconstruct head posture in extinct species. Although this hypothesis has been repeatedly questioned, it has never been tested on a large sample size and at a broad taxonomic scale in mammals. This study presents a comprehensive test of this hypothesis in over one hundred "ungulate" species. Using CT scanning and manual segmentation, the orientation of the skull was reconstructed as if the lateral semicircular canal of the bony labyrinth was aligned horizontally. This reconstructed cranial orientation was statistically compared to the actual head posture of the corresponding species using a dataset of 10,000 photographs and phylogenetic regression analysis. A statistically significant correlation between the reconstructed cranial orientation and head posture is found, although the plane of the lateral semicircular canal departs significantly from horizontal. We thus caution against the use of the lateral semicircular canal as a proxy to infer precisely the horizontal plane on dry skulls and in extinct species. Diet (browsing or grazing) and head-butting behaviour are significantly correlated to the orientation of the lateral semicircular canal, but not to the actual head posture. Head posture and the orientation of the lateral semicircular canal are both strongly correlated with phylogenetic history.

Demography and adaptation promoting evolutionary transitions in a mammalian genus that diversified during the Pleistocene

Species that evolved in temperate regions during the Pleistocene experienced periods of extreme climatic transitions. Consequent population fragmentation and dynamics had the potential to generate small, isolated populations where the influence of genetic drift would be expected to be strong. We use comparative genomics to assess the evolutionary influence of historical demographics and natural selection through a series of transitions associated with the formation of the genus Capreolus, speciation within this genus during the Quaternary and during divergence among European roe deer (C. capreolus) populations. Our analyses were facilitated by the generation of a new high-coverage reference genome for the Siberian roe deer (C. pygargus). We find progressive reductions in effective population size (N_e ), despite very large census sizes in modern C. capreolus populations and show that low N_e has impacted the C. capreolus genome, reducing diversity and increasing linkage disequilibrium. Even so, we find evidence for natural selection shared among C. capreolus populations, including a historically documented founder population that has been through a severe bottleneck. During each phylogenetic transition there is evidence for selection (from dN/dS and nucleotide diversity tests), including at loci associated with diapause (delayed embryonic development), a phenotype restricted to this genus among the even-toed ungulates. Together these data allow us to assess expectations for the origin and diversification of a mammalian genus during a period of extreme environmental change.

The evolution of the vestibular apparatus in apes and humans

Phylogenetic relationships among extinct hominoids (apes and humans) are controversial due to pervasive homoplasy and the incompleteness of the fossil record. The bony labyrinth might contribute to this debate, as it displays strong phylogenetic signal among other mammals. However, the potential of the vestibular apparatus for phylogenetic reconstruction among fossil apes remains understudied. Here we test and quantify the phylogenetic signal embedded in the vestibular morphology of extant anthropoids (monkeys, apes and humans) and two extinct apes (Oreopithecus and Australopithecus) as captured by a deformation-based 3D geometric morphometric analysis. We also reconstruct the ancestral morphology of various hominoid clades based on phylogenetically-informed maximum likelihood methods. Besides revealing strong phylogenetic signal in the vestibule and enabling the proposal of potential synapomorphies for various hominoid clades, our results confirm the relevance of vestibular morphology for addressing the controversial phylogenetic relationships of fossil apes.

The systematics of the Cervidae: a total evidence approach

Systematic relationships of cervids have been controversial for decades. Despite new input from molecular systematics, consensus could only be partially reached. The initial, gross (sub) classification based on morphology and comparative anatomy was mostly supported by molecular data. The rich fossil record of cervids has never been extensively tested in phylogenetic frameworks concerning potential systematic relationships of fossil cervids to extant cervids. The aim of this work was to investigate the systematic relationships of extant and fossil cervids using molecular and morphological characters and make implications about their evolutionary history based on the phylogenetic reconstructions. To achieve these objectives, molecular data were compiled consisting of five nuclear markers and the complete mitochondrial genome of 50 extant and one fossil cervids. Several analyses using different data partitions, taxon sampling, partitioning schemes, and optimality criteria were undertaken. In addition, the most extensive morphological character matrix for such a broad cervid taxon sampling was compiled including 168 cranial and dental characters of 41 extant and 29 fossil cervids. The morphological and molecular data were analysed in a combined approach and other comprehensive phylogenetic reconstructions. The results showed that most Miocene cervids were more closely related to each other than to any other cervids. They were often positioned between the outgroup and all other cervids or as the sister taxon to Muntiacini. Two Miocene cervids were frequently placed within Muntiacini. Plio- and Pleistocene cervids could often be affiliated to Cervini, Odocoileini or Capreolini. The phylogenetic analyses provide new insights into the evolutionary history of cervids. Several fossil cervids could be successfully related to living representatives, confirming previously assumed affiliations based on comparative morphology and introducing new hypotheses. New systematic relationships were observed, some uncertainties persisted and resolving systematics within certain taxa remained challenging.

Convergent evolution in toothed whale cochleae

Background

Odontocetes (toothed whales) are the most species-rich marine mammal lineage. The catalyst for their evolutionary success is echolocation - a form of biological sonar that uses high-frequency sound, produced in the forehead and ultimately detected by the cochlea. The ubiquity of echolocation in odontocetes across a wide range of physical and acoustic environments suggests that convergent evolution of cochlear shape is likely to have occurred. To test this, we used SURFACE; a method that fits Ornstein-Uhlenbeck (OU) models with stepwise AIC (Akaike Information Criterion) to identify convergent regimes on the odontocete phylogeny, and then tested whether convergence in these regimes was significantly greater than expected by chance.

Results

We identified three convergent regimes: (1) True’s (Mesoplodon mirus) and Cuvier’s (Ziphius cavirostris) beaked whales; (2) sperm whales (Physeter macrocephalus) and all other beaked whales sampled; and (3) pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales and Dall’s porpoise (Phocoenoides dalli). Interestingly the ‘river dolphins’, a group notorious for their convergent morphologies and riverine ecologies, do not have convergent cochlear shapes. The first two regimes were significantly convergent, with habitat type and dive type significantly correlated with membership of the sperm whale + beaked whale regime.

Conclusions

The extreme acoustic environment of the deep ocean likely constrains cochlear shape, causing the cochlear morphology of sperm and beaked whales to converge. This study adds support for cochlear morphology being used to predict the ecology of extinct cetaceans.

Head to head: the case for fighting behaviour in Megaloceros giganteus using finite-element analysis

The largest antlers of any known deer species belonged to the extinct giant deer Megaloceros giganteus. It has been argued that their antlers were too large for use in fighting, instead being used only in ritualized displays to attract mates. Here, we used finite-element analysis to test whether the antlers of M. giganteus could have withstood forces generated during fighting. We compared the mechanical performance of antlers in M. giganteus with three extant deer species: red deer (Cervus elaphus), fallow deer (Dama dama) and elk (Alces alces). Von Mises stress results suggest that M. giganteus was capable of withstanding some fighting loads, provided that their antlers interlocked proximally, and that their antlers were best adapted for withstanding loads from twisting rather than pushing actions, as are other deer with palmate antlers. We conclude that fighting in M. giganteus was probably more constrained and predictable than in extant deer.

Carnivoran hunting style and phylogeny reflected in bony labyrinth morphometry

Carnivorans are a highly diverse and successful group of mammals, found on the top of the food chain. They originated in the Palaeocene (ca. 60 Ma) and have developed numerous lifestyles, locomotion modes and hunting strategies during their evolutionary history. Mechanosensory organs, such as the inner ear (which houses senses of equilibrium and hearing), represent informative anatomical systems to obtain insights into function, ecology and phylogeny of extant and extinct vertebrates. Using µCT scans, we examined bony labyrinths of a broad sample of various carnivoran species, to obtain new information about hunting behaviours of ancient carnivorans. Bony labyrinths were digitally reconstructed and measurements were taken directly from these 3D models. Principal component analyses generally separated various hunting strategies (pursuit, pounce, ambush and occasional), but also support their phylogenetic relationships (Canoidea vs. Feloidea). The height, width and length of all three semicircular canals show functional morphological adaptations, whereas the diameter of the canals, the height of the cochlea and particularly the angle between the lateral semicircular canal and the cochlea indicate a phylogenetic signal. The results demonstrate that the bony labyrinth provides a powerful ecological proxy reflecting both predatory habits as well as phylogenetic relationships in extinct and extant carnivorans.

The bony labyrinth of toothed whales reflects both phylogeny and habitat preferences

The inner ear of toothed whales (odontocetes) is known to have evolved particular shapes related to their abilities to echolocate and move under water. While the origin of these capacities is now more and more examined, thanks to new imaging techniques, little is still known about how informative inner ear shape could be to tackle phylogenetic issues or questions pertaining to the habitat preferences of extinct species. Here we show that the shape of the bony labyrinth of toothed whales provides key information both about phylogeny and habitat preferences (freshwater versus coastal and fully marine habitats). Our investigation of more than 20 species of extinct and modern odontocetes shows that the semi-circular canals are not very informative, in contrast to baleen whales, while the cochlea alone bears a strong signal. Inner ear shape thus provides a novel source of information to distinguish between morphologically convergent lineages (e.g. river dolphins).

Recent inner ear specialization for high-speed hunting in cheetahs

The cheetah, Acinonyx jubatus, is the fastest living land mammal. Because of its specialized hunting strategy, this species evolved a series of specialized morphological and functional body features to increase its exceptional predatory performance during high-speed hunting. Using high-resolution X-ray computed micro-tomography (μCT), we provide the first analyses of the size and shape of the vestibular system of the inner ear in cats, an organ essential for maintaining body balance and adapting head posture and gaze direction during movement in most vertebrates. We demonstrate that the vestibular system of modern cheetahs is extremely different in shape and proportions relative to other cats analysed (12 modern and two fossil felid species), including a closely-related fossil cheetah species. These distinctive attributes (i.e., one of the greatest volumes of the vestibular system, dorsal extension of the anterior and posterior semicircular canals) correlate with a greater afferent sensitivity of the inner ear to head motions, facilitating postural and visual stability during high-speed prey pursuit and capture. These features are not present in the fossil cheetah A. pardinensis, that went extinct about 126,000 years ago, demonstrating that the unique and highly specialized inner ear of the sole living species of cheetah likely evolved extremely recently, possibly later than the middle Pleistocene.