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Incus facet morphology in carnivorous mammals from different ecosystems: Taxonomy vs. habitat
Abstract
This study is prompted by the discovery of an incus of Hyaenodon, the first known auditory ossicle of this genus and thus of any hyaenodont mammal so far. A large set of incudes of recent Carnivora, including felids, hyaenids, viverrids, herpestids, nandiniid and canids of different ecosystems, was set up for morphological comparison. This study examines especially the incudo-mallear facet. Typically, the incudo-mallear facet is composed of: (1) three articular surfaces in felids, (2) a U-shaped surface in hyaenids and (3) four surfaces in canids. Both taxonomy (on family level) and habitat (open, closed or mixed habitat preference) might have an impact on the morphology of the incus facets, the former having a major impact in our sample. The Hyaenodon incus is small, delicate and possesses an incudo-mallear facet of a general saddle-shape with two articulation facets, a large superior articulation area and a circular, inferior articulation area. Herein, its general morphology and facet shape is most similar to the felid incus morphology.
... Th ese components are divided into three adjoining compartments: external, middle, and inner ear. Th e structures found in these compartments can vary morphologically based on environmental conditions as well as phylogenetic relationships (Kardong, 2009;Ekdale, 2013Ekdale, , 2015Bastl et al., 2017). ...
... Th is head is just dorsal to the short process (fi g. 8, B). It attaches to the articulation surface on the malleus that tends to show much variation across both terrestrial and aquatic carnivores (Repenning 1972;Wyss 1987;Bastl et al., 2017;. Ossicle size aids in acuity of underwater hearing, but the enlarged head of the incus specifi cally off sets the balance of the ossicular chain, making it more easily stimulated to move or more sensitive to sound vibrations through axial rotation (Repenning, 1972). ...
... Ossicle size aids in acuity of underwater hearing, but the enlarged head of the incus specifi cally off sets the balance of the ossicular chain, making it more easily stimulated to move or more sensitive to sound vibrations through axial rotation (Repenning, 1972). In a more recent study of the incus of some felids, canids, and hyenids, it was established that the morphology of the articular facets could be used for classifi cation of carnivores at the family level (Bastl et al., 2017). Th is same study also identifi ed a stronger likelihood that the characters of the malleus help to determine ecology and the characters of the incus help to determine phylogeny. ...
Over the past century research on the morphology of the auditory apparatuses of pinnipeds, which include Phocidae (true seals), Otariidae (sea lions and fur seals), and Odobenidae (walruses) is extremely limited, in comparison to other Carnivora. Although, the auditory region and surrounding basicrania are areas that are evolutionarily conservative, most literature is unclear due to mixed terminology, inaccurate information, and indistinct, outdated illustrations. Th e lack of adequate and current studies demonstrates the need for compiling morphological information of the auditory region of modern carnivores in relation to hearing. Auditory terminology will be explored to show morphological comparisons and naming practices among the carnivoran families. By streamlining accurate terminology with straightforward illustrations, the behavioral information gleaned from auditory morphological structures will be clearer even among the diverse members of Carnivora. Th is initial assessment will detail the limited information in prior research on the hearing adaptations for transitional semiaquatic carnivores. Th is preliminary review will help to establish the adaptive patterns (from land to sea) in the basicranial morphology of early pinnipeds, especially in phocids.
... When preserved and identified, however, ossicles have greatly enhanced our understanding of both the phylogeny and auditory function of early mammals. Only a single fossil ossicle is described, namely an incus attributed to Hyaenodon (Bastl et al., 2017). It is relatively small, with a compact body slim processes, while morphological features of incudomallear facet are similar to those of felids and nandiinids and distinct from canids (Bastl et al., 2017). ...
... Only a single fossil ossicle is described, namely an incus attributed to Hyaenodon (Bastl et al., 2017). It is relatively small, with a compact body slim processes, while morphological features of incudomallear facet are similar to those of felids and nandiinids and distinct from canids (Bastl et al., 2017). Among cetaceans, the morphology of an incus attributed to Pakicetus (~50 MYA) demonstrated a close affinity to extant, terrestrial artiodactyls (Thewissen & Hussain, 1993). ...
The morphology of the mammalian middle ear – including the size, shape, and stiffness of individual ossicles – controls their vibrational response to sound and, as such, is closely related to an animal's auditory capabilities. While the relationship between middle ear morphology and hearing frequency has been explored in living carnivorans, the size and shape of ossicles in fossil carnivorans have been sparsely documented. In this study, we present the first morphological data on four iconic carnivoran taxa from the Rancho La Brea Tar Pits: Smilodon fatalis, Panthera atrox, Canis dirus, and Arctodus simus. These data are contextualized with samples of extant felids, canids, and ursids to determine the extent to which the ossicles of these iconic fossil taxa resemble their living relatives. Six, five, and seven linear measurements were taken from the malleus, incus, and stapes respectively. Comparisons of geometric means reveal that the ossicles of fossil canids and felids are similar in size to living analogs, but those of A. simus are significantly larger than those of any living ursid. Further, principal components analyses demonstrate close morphological affinities between fossil and extant taxa within canids and felids, and again, a greater disparity between fossil and extant ursids. Canids and ursids occupy distinct regions of the morphospace, yet both overlap the morphological range spanned by felids. While some elements – e.g., the stapes – require further specimens to facilitate more nuanced interpretations of variation, our findings underscore the need for concerted efforts towards identifying and preserving these bones within fossil assemblages. This article is protected by copyright. All rights reserved.
... Their morphology and size are often associated to hearing sensitivity (Fleischer, 1978;Rosowski and Graybeal, 1991;Stoessel et al., 2016a;Bernardi and Couette, 2017). However, only a few recent studies (except for Primates and aquatic mammals) focused on intraspecific variability or searched for phylogenetic characters potentially borne by this structure (e.g., Maier and Ruf, 2016b;Orliac and Billet, 2016;Bastl et al., 2017). The stapes is directly in contact with the inner ear through the stapedial fenestra or oval window. ...
... The ear region possesses a strong phylogenetic signal (e.g., Schmelze et al., 2005;Quam et al., 2014;Mennecart and Costeur, 2016;Mennecart et al., , 2017Stoessel et al., 2016a,b;Bastl et al., 2017;Kerber and Sánchez-Villagra, 2018). Stoessel et al. (2016b) noticed that the human stapes differs from the other hominids by its height, a distinct stapedial head, and a specific kidney shape of the footplate, even if the other ossicles may be more phylogenetically informative (Stoessel et al., 2016b). ...
The stapes is the smallest bone of the mammalian skeleton. Being the innermost middle ear ossicle, it is in contact with the inner ear and is directly responsible for sound transmission into it. Today, Ruminantia are one of the most diversified groups of large mammals with more than 200 species. However, their stapes has been very little studied. Here we investigate the shape of 66 stapes from 44 species of extant and extinct Ruminantia, including intra-individual and intra-specific observations, based on 3D tomographic data. Shape differences and similarities are quantitatively discussed thanks to 3D geometric morphometrics. The overall size of the stapes scales with a negative allometry in comparison to body mass. Moreover, the overall shape of the stapes informs about phylogeny. A trend is observed from a concave posterior crus with an enlarged stapes capitulum in Antilocapridae to a relatively straight posterior crus with a little reduced stapes capitulum in Cervidae, Bovidae being intermediate. In addition, the stapes of Antilocapridae is relatively trapezoid in lateral view; that of Cervidae is more triangular in lateral view; and that of Bovidae is relatively rectangular in lateral view. The stapedial footplate shape also gives phylogenetic information. The Tragulidae stapedial footplate is antero-posteriorly asymmetrical. The stapedial footplate is ovoid in stem Pecora. It is asymmetrical in Bovidae, while it is more symmetrical in Cervidae. This is in agreement with previous studies on the ruminant bony labyrinth showing that the oval window, the counterpart of the stapedial footplate on the inner ear, bears a strong phylogenetic signal already distinguishable in early Miocene ruminants.
... The ventral trochlea of the mammaliaform incus corresponds to the malleus facet of the incus of extant mammals. While the trochlea of the incus maintained a mobile joint with the malleus in the "primary joint" of mammaliaforms (Luo and Crompton, 1994), the incus in therians has a saddle-shaped contact surface for the malleus for a synovial joint between the incus and malleus, but this joint is no longer a fully mobile hinge as in mammaliaforms (Doran, 1879;Williams et al., 1989;Bastl et al., 2017). By comparison to the cylindrical shape of the trochlea of mammaliaforms, the malleus contact of the incus is highly transformed Figure 6 Evolution of mobile suspension of incus and the incus leverage for impedance match through cynodont-mammaliaform transition. ...
Synopsis
The evolutionary origins of the modern mammalian ear structures can be traced back into their phylogenetic predecessors in the Mesozoic Era. This evolutionary history shows a step-wise acquisition of middle- and inner-ear structures along separate Mesozoic mammal lineages that led to convergence of several derived characters correlated with distinct hearing functions in extant mammals.
Species of the extinct genus Hyaenodon were among the largest carnivorous mammals from the Late Eocene through Early Miocene in North America, Europe and Asia. The origin, phylogeny and palaeobiology of Hyaenodonta are still ambiguous. Most previous studies focused on teeth and dental function in these highly adapted species, which might be influenced by convergent morphologies. The anatomy of the bony labyrinth in vertebrates is generally quite conservative and, additionally, was used in functional–morphological studies. This study provides the first anatomical description of the bony labyrinth of the extinct European species Hyaenodon exiguus in comparison to selected extant carnivoran taxa discussed from a functional–morphological perspective. Hyaenodon exiguus may have occupied a hyaena-like dietary niche with a semi-arboreal lifestyle, based on the relative height, width and length of the semicircular canals of the inner ear. However, this contradicts previous functional–morphological studies focusing on the diameter of the canals, which presumably represent the signal of locomotion mode.
Many studies have been conducted about the information contained in the anatomy of the mammalian middle ear. Most of these only use a few specimens. Thus we aim to provide a quantitative analysis of the intraspecific and interspecific variations of the middle ear, focusing on the auditory bulla. For that purpose, we focused on the mustelids, as a quite generalist taxon and, more specifically, on the European badger, Meles meles. Our study includes two types of statistical methods. We first compared the mean of a subjectively chosen measure between individuals of the same species and between individuals of different species. We then used a multidimensional scaling procedure to cluster individuals according to different measures. We conclude that the middle ear varies effectively less intraspecifically than interspecifically. However, we think that the few anatomical parameters to measure in the auditory bulla involve using more specimens or focusing on geometric morphometrics in studies focusing on middle ear.
Mammalian carnivores are rarely considered for environmental reconstructions because they are extremely adaptable and their geographic range is usually large. However, the functional morphology of carnivore long bones can be indicative of locomotor behaviour as well as adaptation to specific kind of habitats. Here, different long bone ratios belonging to a subsample of extant large carnivores are used to infer palaeoecology of a comparative sample of Plio-Pleistocene fossils belonging to Italian paleo-communities. A multivariate long bone shape space reveals similarities between extant and fossil carnivores and multiple
logistic regression models suggest that specific indices (the brachial and the Mt/F) can be applied to predict adaptations to grassland and tropical biomes. These functional indices exhibit also a phylogenetic signal to different degree. The brachial index is a significant predictor of adaptations to tropical biomes when phylogeny is taken into account, while Mt/F is not correlated anymore to habitat adaptations. However, the proportion of grassland-adapted carnivores in Italian paleo-communities exhibits a negative relationship with mean oxygen isotopic values, which are indicative of past climatic oscillations. As climate became more unstable during the Ice Ages, large carnivore guilds from the Italian peninsula were invaded by tropical/closed-adapted species. These species take advantage of the temperate forest cover that was more spread after 1.0 Ma than in the initial phase of the Quaternary (2.0 Ma) when the climate was more arid.
Specimens that give new information on the tooth eruption sequence in European Hyaenodon are described. These specimens show a marked difference from the tooth eruption sequence established for North American Hyaenodon. The eruption of p4 after p3 and m3 and the earlier eruption of the permanent canine in European specimens versus the eruption of p4 before p3 and m3 and the eruption of the permanent canine as the last tooth in North American specimens indicate divergent evolutionary pathways for New and Old World lineages. In conjunction with other skeletal differences, described in the literature, our findings support the need for a reanalysis of the taxonomy of Hyaenodon.
Introduction and aims:
Tympanic middle ears have evolved multiple times independently among vertebrates, and share common features. We review flexibility within tympanic middle ears and consider its physiological and clinical implications.
Comparative anatomy:
The chain of conducting elements is flexible: even the 'single ossicle' ears of most non-mammalian tetrapods are functionally 'double ossicle' ears due to mobile articulations between the stapes and extrastapes; there may also be bending within individual elements.
Simple models:
Simple models suggest that flexibility will generally reduce the transmission of sound energy through the middle ear, although in certain theoretical situations flexibility within or between conducting elements might improve transmission. The most obvious role of middle-ear flexibility is to protect the inner ear from high-amplitude displacements.
Clinical implications:
Inter-ossicular joint dysfunction is associated with a number of pathologies in humans. We examine attempts to improve prosthesis design by incorporating flexible components.
Valverde's cenogram method is used to analyse mammalian communities from the late Eocene to late Oligocene ofsouthern France, mainly from the "Phosphorites du Quercy". Cenogram analysis involves plotting the size of each component species in a fauna on a semilog diagram in rank order, permitting fossil faunas to be compared with Recent ones. The conligurations of Recent communities serve as models for establishing the general environmental characteristics of fossil mammalian faunas. This method of analysis applied to faunal sequence can reveal major and sudden ecological perturbations. The paleobiogeographical event (i.e. the mammalian immigration wave) at the Eocene-Oligocene Boundary in western Europe, known as the "Grande Coupure", is here shown to represent a drastic and sudden ecological change: late Eocene tropical environments in Europe deteriorated rapidly turning to subdesert or desert environments at the beginning of the Oligocene.
Fieldwork in the 1990s produced a few records of carnivorous mammals (cre-odonts and carnivorans) in the early Oligocene through early Miocene of Lanzhou Basin, Gansu Province, China. Although only five taxa are known so far, most repre-sented by fragmentary material, the new carnivore assemblage is unique and shows little resemblance to faunas elsewhere in eastern Asia. The early Oligocene record is represented by a single premolar of a Hyaenodon, referable to H. pervagus. In the early Miocene, a new species of Hyaenodon, H. weilini sp. nov., represented by sev-eral cheek teeth, is the last record of this genus in east Asia. A horizontal ramus of an amphicyonid, here identified as Ictiocyon cf. I. socialis, is the first record of this taxon in Asia, and a very small musteloid lower carnassial, although difficult to identify to genus, is clearly a new record because nothing of this small size has been known in Asia. The overall faunal composition seems to suggest affinity with northern Eurasia rather than southern Asia.
In this article, we present FactoMineR an R package dedicated to multivariate data analysis. The main features of this package is the possibility to take into account different types of variables (quantitative or categorical), different types of structure on the data (a partition on the variables, a hierarchy on the variables, a partition on the individuals) and finally supplementary information (supplementary individuals and variables). Moreover, the dimensions issued from the different exploratory data analyses can be automatically described by quantitative and/or categorical variables. Numerous graphics are also available with various options. Finally, a graphical user interface is implemented within the Rcmdr environment in order to propose an user friendly package.
Phylogenies underpin comparative biology as high-utility tools to test evolutionary and biogeographic hypotheses, inform on conservation strategies, and reveal the age and evolutionary histories of traits and lineages. As tools, most powerful are those phylogenies that contain all, or nearly all, of the taxa of a given group. Despite their obvious utility, such phylogenies, other than summary 'supertrees', are currently lacking for most mammalian orders, including the order Carnivora. Carnivora consists of about 270 extant species including most of the world's large terrestrial predators (e.g., the big cats, wolves, bears), as well as many of man's favorite wild (panda, cheetah, tiger) and domesticated animals (dog, cat). Distributed globally, carnivores are highly diverse ecologically, having occupied all major habitat types on the planet and being diverse in traits such as sociality, communication, body/brain size, and foraging ecology. Thus, numerous studies continue to address comparative questions within the order, highlighting the need for a detailed species-level phylogeny. Here we present a phylogeny of Carnivora that increases taxon sampling density from 28% in the most detailed primary-data study to date, to 82% containing 243 taxa (222 extant species, 17 subspecies). In addition to extant species, we sampled four extinct species: American cheetah, saber-toothed cat, cave bear and the giant short-faced bear. Bayesian analysis of cytochrome b sequences data-mined from GenBank results in a phylogenetic hypothesis that is largely congruent with prior studies based on fewer taxa but more characters. We find support for the monophyly of Carnivora, its major division into Caniformia and Feliformia, and for all but one family within the order. The only exception is the placement of the kinkajou outside Procyonidae, however, prior studies have already cast doubt on its family placement. In contrast, at the subfamily and genus level, our results indicate numerous problems with current classification. Our results also propose new, controversial hypotheses, such as the possible placement of the red panda (Ailuridae) sister to canids (Canidae). Our results confirm previous findings suggesting that the dog was domesticated from the Eurasian wolf (Canis lupus lupus) and are congruent with the Near East domestication of the cat. In sum, this study presents the most detailed species-level phylogeny of Carnivora to date and a much needed tool for comparative studies of carnivoran species. To demonstrate one such use, we perform a phylogenetic analysis of evolutionary distinctiveness (EDGE), which can be used to help establish conservation priorities. According with those criteria, and under one of the many possible sets of parameters, the highest priority Carnivora species for conservation of evolutionary diversity include: monk seals, giant and red panda, giant otter, otter civet, Owston's palm civet, sea otter, Liberian mongoose, spectacled bear, walrus, binturong, and the fossa.
. Mammalian carnivores are rarely incorporated in paleoenvironmental reconstructions, largely because of their rarity within the fossil record. However, multivariate statistical modeling can be successfully used to quantify specific anatomical features as environmental predictors. Here we explore morphological variability of the humerus in a closely related group of predators (Felidae) to investigate the relationship between morphometric descriptors and habitat categories. We analyze linear measurements of the humerus in three different morphometric combinations (log-transformed, size-free, and ratio), and explore four distinct ways of categorizing habitat adaptations. Open, Mixed, and Closed categories are defined according to criteria based on traditional descriptions of species, distributions, and biome occupancy. Extensive exploratory work is presented using linear discriminant analyses and several fossils are included to provide paleoecological reconstructions. We found no significant differences in the predictive power of distinct morphometric descriptors or habitat criteria, although sample splitting into small and large cat guilds greatly improves the stability of the models. Significant insights emerge for three long-canine cats: Smilodon populator, Paramachairodus orientalis, and Dinofelis sp. from Olduvai Gorge (East Africa). S. populator and P. orientalis are both predicted to have been closed-habitat adapted taxa. The false “sabertooth” Dinofelis sp. from Olduvai Gorge is predicted to be adapted to mixed habitat. The application of felid humerus ecomorphology to the carnivoran record of Olduvai Gorge shows that the older stratigraphic levels (Bed I, 1.99-1.79 Ma) included a broader range of environments than Beds II or V. where there is an abundance of cats adapted to open environments.
Although the time of origin of viverrid and hyaenid carnivorans has not been clearly documented in the fossil record, their theater of evolution has long been established by a mid-Cenozoic fossil distribution entirely confined to the Old World. Recent examination of the basicranial morphology of important early aeluroid crania from Europe and Asia significantly alters earlier views of viverrid and hyaenid origins. The early Miocene carnivoran Herpestides antiquus, considered a potential ancestral hyaenid or herpestid in earlier studies, is identified as a true viverrid on the basis of a large sample of skulls of both juveniles and adults from Aquitanian sediments of the Allier basin, France. The basicranial morphology of Herpestides has attained the modem viverrid grade of development in the early Miocene (European Neogene mammal zone MN2a), and suggests that diversification of the Viverridae was in progress by this time. In ongoing work to be published elsewhere, the mid-Miocene Asian camivoran Tungurictis spocki, long regarded as a viverrid, is identified as an early hyaenid, following preparation and restudy ofthe auditory region of the genoholotype cranium from Tung Gur, Mongolia. These discoveries indicate that separation of the modem aeluroid families as discrete lineages had been accomplished by the beginning of the Neogene in the Old World, and that diversification within these families must have been initiated in the early to mid-Miocene.
The human ear is an evolutionary derivative of the lateral line canals of early aquatic vertebrates such as fishes. Both the organs of hearing and equilibrium are based on an “internalized” system of fluid-containing membrane-bound spaces embedded in the petrous part of the temporal bone. Movements of fluid within these ducts owing either to oscillations of atmospheric air (hearing) or to postural changes (balance, equilibrium) elicit specific sensations through the action of highly specialized receptors termed hair cells. The anatomical structures representing both sensory modalities develop from a common ectodermal primordium, the otic placode, surrounded by mesenchyme of the otic capsule. The ectodermal anlage gives rise to a vesicle (otocyst), which later is subdivided into an upper portion (labyrinth, organ of balance) and a lower portion (cochlea, organ of hearing), forming parts of the inner ear. Whereas the former is fully operational alone, the latter requires additional systems for transduction of mechanical energy (sound waves) into bioelectric signals. These systems are situated in the anatomical units called external and middle ear.
This monograph describes the directions of the structural evolution of the peripheral part of the auditory system in representatives of different ecological groups of mammals. Special attention is paid to the least studied orders of marine mammals (pinnipeds, cetaceans), being of great interest both with regards to the echolocating abilities in dolphins and the influence of the aquatic environment on the development of morphological adaptations in the structure of the outer, middle and inner ears. Undertaken for the first time, a comparative embryological study of the peripheral part of the auditory system in marine mammals allowed the author to reveal the developmental pattern of the auditory and equilibrium organs in animals with a different auditory specialization. The influence of ecological factors on the adaptive trait development in the structural organization of the outer, middle and inner ears in semi-aquatic and aquatic species is discussed. The book is illustrated with a large number of high-quality micro-photos.
The mammalian auditory periphery is a complex system, many components of which are biomechanical. This complexity increases sensitivity, dynamic range, frequency range, frequency resolution, and sound localization ability. These must be achieved within the constraints of available biomaterials, biophysics, and anatomical space in the organism. In this chapter, the focus is on the basic mechanical principles discovered for the various steps in the process of transforming the input acoustic sound pressure into the correct stimulation of mechanoreceptor cells. The interplay between theory and measurements is emphasized. In this chapter we examine the underlying biophysics of acoustical and mechanical transformations of sound by the subcomponents of the ear. The subcomponents include the pinna, ear canal, middle ear, cochlear fluid hydrodynamics, and organ of Corti. Physiological measurements and the deduced general biophysics that can be applied to the input and output transformations by the different subcomponents of the ear are presented.
The bony labyrinth provides a proxy for the morphology of the inner ear, a primary cognitive organ involved in hearing, body perception in space, and balance in vertebrates. Bony labyrinth shape variations often are attributed to phylogenetic and ecological factors. Here we use three-dimensional (3D) geometric morphometrics to examine the phylogenetic and ecological patterns of variation in the bony labyrinth morphology of the most species-rich and ecologically diversified traditionally recognized superfamily of Carnivora, the Musteloidea (e.g. weasels, otters, badgers, red panda, skunks, raccoons, coatis). We scanned the basicrania of specimens belonging to 31 species using high-resolution X-ray computed micro-tomography (μCT) to virtually reconstruct 3D models of the bony labyrinths. Labyrinth morphology is captured by a set of six fixed landmarks on the vestibular and cochlear systems, and 120 sliding semilandmarks, slid at the center of the semicircular canals and the cochlea. We found that the morphology of this sensory structure is not significantly influenced by bony labyrinth size, in comparisons across all musteloids or in any of the individual traditionally recognized families (Mephitidae, Procyonidae, Mustelidae). PCA (principal components analysis) of shape data revealed that bony labyrinth morphology is clearly distinguishable between musteloid families, and permutation tests of the Kmult statistic confirmed that the bony labyrinth shows a phylogenetic signal in musteloids and in most mustelids. Both the vestibular and cochlear regions display morphological differences among the musteloids sampled, associated with the size and curvature of the semicircular canals, angles between canals, presence or absence of a secondary common crus, degree of lateral compression of the vestibule, orientation of the cochlea relative to the semicircular canals, proportions of the cochlea, and degree of curvature of its turns. We detected a significant ecological signal in the bony labyrinth shape of musteloids, differentiating semi-aquatic taxa from non-aquatic ones (the taxa assigned to terrestrial, arboreal, semi-arboreal, and semi-fossorial categories), and a significant signal for mustelids, differentiating the bony labyrinths of terrestrial, semi-arboreal, arboreal, semi-fossorial and semi-aquatic species from each other. Otters and minks are distinguished from non-aquatic musteloids by an oval rather than circular anterior canal, sinuous rather than straight lateral canal, and acute rather than straight angle between the posterior and lateral semicircular canals - each of these morphological characters has been related previously to animal sensitivity for detecting head motion in space.
Here we present a brief, historical review of research into the mammalian middle ear structures. Most of their essential homologies were established by embryologists, notably including Reichert, during the 19th century. The evolutionary dimension was confirmed by finds of fossil synapsids, mainly from the Karroo of South Africa. In 1913, Ernst Gaupp was the first to present a synthesis of the available embryological and paleontological data, but a number of morphological details remained to be solved, such as the origin of the tympanic membrane. Gaupp favoured an independent origin of the eardrum in anurans, sauropsids, and mammals; we support most of his ideas. The present review emphasizes the problem of how the mammalian middle ear structures that developed at the angle of the lower jaw were transferred to the basicranium; the ontogenesis of extant marsupials provides important information on this question.
The question as to whether the incudo-malleolar joint (IMJ) is mobile or immobile at moderate sound pressure levels (SPLs) is addressed. Referring to the mechanical properties of elastic tissue, we suggest that the IMJ is mobile at any SPL. In order to test this hypothesis, we investigated the dynamics of the IMJ in nine temporal bones by means of laser scanning doppler vibrometry. The dynamic behavior of both ossicles, malleus and incus is described by three degrees of freedom, and transfer functions (TFs) are shown for each motion component [corrected]. We show that there is indeed relative motion between the malleus and the incus. This transmission loss affects the middle ear TF and results in a frequency dependent sound transmission loss. Some characteristics of our results are in agreement with middle ear TFs described in the literature. The increasing transmission loss towards higher frequencies is caused by relative motion between malleus and incus at the IMJ. The concept that the IMJ is functionally mobile is consistent with the physical properties of elastic tissues which most likely define the mechanics of this joint. Since the IMJ is indeed mobile at moderate sound intensities and audible frequencies the theory of the lever ratio being responsible for the characteristics of the middle ear TF must be reconsidered.
Anatomists and zoologists who study middle ear morphology are often interested to know what the structure of an ear can reveal about the auditory acuity and hearing range of the animal in question. This paper represents an introduction to middle ear function targetted towards biological scientists with little experience in the field of auditory acoustics. Simple models of impedance matching are first described, based on the familiar concepts of the area and lever ratios of the middle ear. However, using the Mongolian gerbil Meriones unguiculatus as a test case, it is shown that the predictions made by such 'ideal transformer' models are generally not consistent with measurements derived from recent experimental studies. Electrical analogue models represent a better way to understand some of the complex, frequency-dependent responses of the middle ear: these have been used to model the effects of middle ear subcavities, and the possible function of the auditory ossicles as a transmission line. The concepts behind such models are explained here, again aimed at those with little background knowledge. Functional inferences based on middle ear anatomy are more likely to be valid at low frequencies. Acoustic impedance at low frequencies is dominated by compliance; expanded middle ear cavities, found in small desert mammals including gerbils, jerboas and the sengi Macroscelides, are expected to improve low-frequency sound transmission, as long as the ossicular system is not too stiff.
© 2015 Anatomical Society.
Educational objectives: To conceptualize the temporal bone three dimensionally, approach temporal bone surgery rationally, and have a better appreciation of the courses and exhibits relating to the temporal bone.
Based on the multi-wavelength laser-based photoacoustic tomography,
non-invasive in vivo imaging of functional parameters, including the
hemoglobin oxygen saturation and the total concentration of hemoglobin,
in small-animal brains was realized. The high sensitivity of this
technique is based on the spectroscopic differences between oxy- and
deoxy-hemoglobin while its spatial resolution is bandwidth-limited by
the photoacoustic signals rather than by the optical diffusion as in
optical imaging. The point-by-point distributions of blood oxygenation
and blood volume in the cerebral cortical venous vessels, altered by
systemic physiological modulations including hyperoxia, normoxia and
hypoxia, were visualized successfully through the intact skin and skull.
This technique, with its prominent intrinsic advantages, can potentially
accelerate the progress in neuroscience and provide important new
insights into cerebrovascular physiology and brain function that are of
great significance to the neuroscience community.
Cheek teeth of extant Carnivora were examined, and different microwear patterns were found for taxa with different dietary habits. A broad taxonomic sample including Hyaenidae, Felidae, Canidae, Viverridae and Nandiniidae was chosen in order to elucidate the microwear pattern for a bone/meat, meat/bone, meat, mixed carnivorous (meat/plant matter) and fruit based diet. Enamel microwear for the hyaenodont Hyaenodon was compared to this extant sample. Heavy gouging and extensive pitting and scratching of enamel surfaces, as well as the occurrence of zigzag Hunter–Schreger bands in the enamel microstructure analyses, indicate the inclusion of tough foods like bone in the Hyaenodon diet. Species from different continents (North America and European taxa) occupied slightly different dietary niches.
A new genus and new species of Proviverrinae from the Early Eocene of Europe, Morlodon vellerei, is described. This new taxon is morphologically close to the Middle Eocene genus Matthodon, with which it shares tendencies towards a robust dentition; the two genera also share the reduction of P1. In order to examine the phylogenetic relationships of the new genus Morlodon with Early and Middle Eocene European Proviverrinae, a phylogenetic analysis of the earliest hyaenodontidans was conducted. The taxa analysed range from Late Palaeocene to Middle Eocene and are from Africa, Asia, Europe and North America. The new phylogeny of earliest hyaenodontans clarifies the systematics of the paraphyletic assemblage ‘Proviverrinae’ and results in the recognition of five major clades. The monophyly of the Limnocyoninae and Koholiinae is supported, and two new subfamilies are erected from the ‘Proviverrinae’: Sinopaninae and Arfianinae. A new definition of the Proviverrinae is proposed: only European hyaenodontidans from Early and Middle Eocene are included in this subfamily. However, the phylogenetic relationships between the five subfamilies remain to be established. An ancestral morphotype for the Hyaenodontida is proposed in order to identify the different subfamilies. On the basis of the analysis and of data presently available, an African origin for Hyaenodontida is proposed. Hyaenodontidans are involved in the faunal dispersals that occurred around the Palaeocene–Eocene (P/E) boundary. They dispersed from Africa to Asia during the Late Palaeocene (Limnocyoninae), and at the P/E boundary from Africa to Europe (Proviverrinae) and to North America through Europe (Sinopaninae and Arfianinae). Proviverrinae remain an endemic European group, whereas Sinopaninae, Limnocyoninae and Arfianinae mainly evolved in North America. Koholiinae represents the sole endemic African group. The probable African origin of the Hyaenodontida supports the diphyletism of ‘Creodonta’ and abandonment of this taxon.
By comparison with murine rodents such as rats, the middle ear structures of many subterranean mammals appear to be enlarged and thus adapted toward low-frequency sound transmission. However, comparison with closely related terrestrial outgroups has not always been undertaken, and apparent specializations in some cases might reflect phylogeny rather than habitat. Examination of the middle ear of the nonsubterranean degu (Octodon degus) under light microscopy revealed a septated middle ear cavity, a circular tympanic membrane lacking a pars flaccida, a malleus with elongated head, synostosed with the incus, a typically bicrurate stapes, and no stapedius muscle. Many of these features are shared with closely related, subterranean octodontoids in the genera Ctenomys (tuco-tucos) and Spalacopus (coruro). Caviomorph rodents in general share a very similar middle ear morphology, regardless of habitat, which suggests that sensitive low-frequency hearing is plesiomorphic for this group, rather than being specifically associated with a subterranean lifestyle.
A large data set, comprising certain measurements of middle ear structures in mammals, was compiled both from measurements made by the author and from the literature. Parameters of the middle ear apparatus believed to be important to audition were compared between fossorial and non-fossorial species, in an attempt to identify general trends among fossorial groups. Although their tympanic membranes are not of unusual size, many fossorial mammals possess enlarged stapes footplate areas, resulting in low anatomical area ratios. Low anatomical lever ratios are also common, and the reduction or loss of middle ear muscles seems to be a consistent trend. These characteristics might be associated with poor sensitivity to airborne sound. Other features of the middle ear apparatus are more variable both between and within fossorial families. The middle ear ossicles of fossorial rodents, talpid moles and some golden moles were not found to differ in mass from those of non-fossorial mammals of similar body size. The similar ossicular morphologies of these animals suggest convergent adaptation towards a subterranean environment, but the middle ear structure alone does not seem to explain the restricted hearing range observed in certain of these species. Some genera of golden moles possess extraordinarily hypertrophied auditory ossicles, which, relative to body mass, are the largest of all mammals for which data are available. These ossicles seem to be adaptations towards a form of inertial bone conduction, used for the detection of substrate vibrations. In stark contrast, the marsupial mole Notoryctes has particularly small ossicles. The unusual middle ear structures of this animal may well be degenerate.
Cover title. Title on spine: Créodontes européens. Thesis (doctoral?)--Université Pierre et Marie Curie, Paris, 1979?. Bibliography: p. 192-201.
WE report here the discovery of the first ear ossicle, an incus, of a Plio-Pleistocene hominid. It is substantially different from that of modern man, and the dissimilarity exceeds that between the ear bones of Homo sapiens and of the African apes. The new incus is of interest particularly in view of the unique advantages that ear ossicles have for taxonomic and phylogenetic studies. (The only other fossil hominid ear ossicles are from Qafzeh1 and are indistinguishable from those of modern man.)
Mammals are a highly successful group of animals in that they have conquered even the most hostile environments and developed impressive specializations in the process. Some, like the shrews Suncus or Crocidura, weigh only a few grams and are thus smaller than the largest insects. The whales, on the other hand, are millions of times more massive, the blue whale, Balaenoptera musculus, reaching a weight of 100 metric tons and more. Some species, like the Bathyergidae, stay below the ground throughout their life, while others live in the desert, or climb in the mountains, wade through swamps, or even venture out into the open sea without ever returning to the shore. Petaurus, Cynocephalus, as well as a variety of others are gliders and the Chiroptera are all highly skilled flyers, while others, like the antarctic Weddell seal, Leptonychotes, spend most of their time near or under the ice, diving for food. The bats use a sophisticated echo-location system, based on the emission an reception of ultrasonic sounds, as do the dolphins. Mysticetes are capable of communicating over large distances using very low frequences. Last but not least, man owes much of his superiority to the development of language.
Compared to acoustically unspecialized mammals (soricids and murids), the middle ear of subterranean insectivores and rodents (twelve species of six families examined) was clearly distinguished and characterized by many common features: rather round and relatively larger eardrum without a pars flaccida; reduced gonial; loose or no connection between the malleus and the tympanic bone; reduced and straightened transversal part of the malleus; enlarged incus; increased and rather flat incudo-mallear joint; rather parallel position of the mallear manubrium and incudal crus longum in some species (and their fusion in bathyergids); reduced or even missing middle ear muscles. Convergent occurrence of these structural features in taxa of different origin and their generally derived character suggest that they cannot be categorized as degenerative. The form of the stapes can be considered as a non-adaptive trait; it was taxon specific yet remarkably polymorphous in some species and exhibited no convergent features among subterranean mammals. Structural retrogression resulting in a columella-like stapes was observed in some species lacking the stapedial artery. The stapedial base was relatively larger than in unspecialized mammals. The subterranean mammals did not exhibit conspicuously enlarged eardrums as would be required for sensitive tuning to low frequencies. It is, however, argued that while selective pressures in the subterranean ecotope promoted hearing of low frequencies, hearing sensitivity did not have to be enhanced.
The amplitude and phase of the tympanic membrane and malleus vibrations were measured over a wide frequency range with a homodyne interferometer. When sound pressure was maintained constant near the tympanic membrane, the malleus frequency response followed the typical pattern up to 10 kHz as measured by previous investigators. At higher frequencies the response changes dramatically. Instead of decreasing with frequency, between 10 and 20 kHz the vibration amplitude oscillates around a value which is only about 20 dB lower than the low frequency plateau level. Measurements of malleus vibration at several points along its length indicate that its mode of vibration changes at high frequencies, and no longer consists of a simple rotational component. All points on the tympanic membrane vibrate in phase with the malleus up to a frequency of 1 kHz. Above 5 kHz discrete resonances are observed, and the response varies strongly with position on the tympanic membrane.
In a series of 100 cases, morphological variations of human ossicula tympani were studied. These have seldom been considered either in classic or recent descriptions. Among them, the malleus and stapes are the most variable ones. A geometric model is proposed to systematically study any variation from the typical ossicles. These morphological variations of ossicles could be related to age, sex, race, and could bring out peculiarities in acoustic transmission.
In the cortex of barbiturate-anesthetized cats, area AI was identified by its tonotopic organization, and single neurons in that field were examined with regard to the shapes of their spike count-versus-intensity functions, the organization of their frequency-intensity response areas, and their responses to wide-spectrum noise, using calibrated sealed stimulating systems. Neurons whose pure tone rate intensity functions were monotonic in shape displayed V-shaped response areas that were open-ended at high tone intensities. In contrast, cells displaying nonmonotonic tone intensity functions tended to have circumscribed response areas; these cells were responsive to tones over limited ranges of both frequency and intensity. Monotonic neurons almost always responded to wide-spectrum noise stimuli, while nonmonotonic neurons often did not. The mean minimum latent period of monotonic cells (14.0 ms) was significantly shorter than that for nonmonotonic neurons (19.1 ms). For those cells that responded to both tones and noise, minimum latent periods for the two stimuli were similar or identical. Monotonic neurons tended to be horizontally segregated from nonmonotonic neurons across AI's middle cortical layers. The implications of these data for the nature of some neural mechanisms underlying the stimulus selectivity of cortical cells are discussed.
This study considers the general question how animal size limits the size and information receiving capacity of sense organs. To clarify this in the case of the mammalian middle ear, I studied 63 mammalian species, ranging from a small bat to the Indian elephant. I determined the skull mass and the masses of the ossicles malleus, incus and stapes (M, I and S), and measured the tympanic membrane area, A1. The ossicular mass (in mg) is generally negatively allometric to skull mass (in g), the regression equation for the whole material (excluding true seals) being y = 1.373 x(0.513). However, for very small mammals the allometry approaches isometry. Within a group of large mammals no distinct allometry can be discerned. The true seals (Phocidae) are exceptional by having massive ossicles. The size relations within the middle ear are generally rather constant. However, the I/M relation is slightly positively allometric, y = 0.554 x(1.162). Two particularly isometric relations were found; the S/(M + I) relation for the ossicles characterized by the regression equation y = 0.054 x(0.993), and the relation between a two-dimensional measure of the ossicles and the tympanic membrane ares, (M + I)2/3 /A1. As in isometric ears the sound energy collected by the tympanic membrane is linearly related to its area, the latter isometry suggests that, regardless of animal size, a given ossicular cross-sectional area is exposed to a similar sound-induced stress. Possible morphological middle ear adaptations to particular acoustic environments are discussed.
Acoustic and anatomical measurements were made on the middle ear of a deceased lion and compared with measurements from the domestic cat. The acoustic input impedance and sound-transmission ratios measured in the two species have similar features but differ quantitatively. Three-dimensional anatomical reconstructions show that the middle-ear structures of the lion and cat are similarly arranged but have large differences in absolute and relative size. In all fields, a bony septum divides the middle-ear air space into two cavities that are coupled through a small opening. A six-element analog-circuit model based on this distinctive structure captures the main features of both sets of middle-ear frequency responses, except at high frequencies. The element values are consistent with the structural dimensions of the cavities. The results suggest that quantitative measures of middle-ear cavity structure could allow prediction of frequency-dependent features of acoustic sensitivity for the entire cat family.
The question as to whether the incudo-malleolar joint (IMJ) is mobile or immobile at moderate sound pressure levels (SPLs) is addressed. Referring to the mechanical properties of elastic tissue, we suggest that the IMJ is mobile at any SPL. In order to test this hypothesis, we investigated the dynamics of the IMJ in nine temporal bones by means of laser scanning doppler vibrometry. The dynamic behavior of both ossicles, malleus and incus is described by three degrees of freedom, and transfer functions (TFs) are shown for each motion component [corrected]. We show that there is indeed relative motion between the malleus and the incus. This transmission loss affects the middle ear TF and results in a frequency dependent sound transmission loss. Some characteristics of our results are in agreement with middle ear TFs described in the literature. The increasing transmission loss towards higher frequencies is caused by relative motion between malleus and incus at the IMJ. The concept that the IMJ is functionally mobile is consistent with the physical properties of elastic tissues which most likely define the mechanics of this joint. Since the IMJ is indeed mobile at moderate sound intensities and audible frequencies the theory of the lever ratio being responsible for the characteristics of the middle ear TF must be reconsidered.
Our current understanding of the evolution of the mammalian middle ear was first suggested by embryological studies from the 19th century. Here, site-specific recombinase-mediated lineage tracing was used to define the second branchial arch contribution to the middle ear of wild-type and Hoxa-2 mutant embryos. The processus brevis of the malleus was found to arise from second arch tissues, making it the likely homologue of the retroarticular process of nonmammalian tetrapods. The second arch also formed a portion of the otic capsule. In light of avian lineage studies, second arch cells were probably incorporated into the otic capsule before avian and mammalian lineages diverged. In Hoxa2 mutant embryos, middle ear skeletal duplications occurred at sites where first and second arch elements are normally apposed. The dorsoventral positions at which second arch skeletal elements formed and the early migration of second arch neural crest cells were not altered by the absence of Hoxa2 function.
We have reconstructed the phylogenetic relationships of 23 species in the dog family, Canidae, using DNA sequence data from six nuclear loci. Individual gene trees were generated with maximum parsimony (MP) and maximum likelihood (ML) analysis. In general, these individual gene trees were not well resolved, but several identical groupings were supported by more than one locus. Phylogenetic analysis with a data set combining the six nuclear loci using MP, ML, and Bayesian approaches produced a more resolved tree that agreed with previously published mitochondrial trees in finding three well-defined clades, including the red fox-like canids, the South American foxes, and the wolf-like canids. In addition, the nuclear data set provides novel indel support for several previously inferred clades. Differences between trees derived from the nuclear data and those from the mitochondrial data include the grouping of the bush dog and maned wolf into a clade with the South American foxes, the grouping of the side-striped jackal (Canis adustus) and black-backed jackal (Canis mesomelas) and the grouping of the bat-eared fox (Otocyon megalotis) with the raccoon dog (Nycteruetes procyonoides). We also analyzed the combined nuclear+mitochondrial tree. Many nodes that were strongly supported in the nuclear tree or the mitochondrial tree remained strongly supported in the nuclear+mitochondrial tree. Relationships within the clades containing the red fox-like canids and South American canids are well resolved, whereas the relationships among the wolf-like canids remain largely undetermined. The lack of resolution within the wolf-like canids may be due to their recent divergence and insufficient time for the accumulation of phylogenetically informative signal.
The present study describes and analyzes new Neandertal and early modern human auditory ossicles from the sites of Qafzeh and Amud in southwest Asia. Some methodological issues in the measurement of these bones are considered, and a set of standardized measurement protocols is proposed. Evidence of erosive pathological processes, most likely attributed to otitis media, is present on the ossicles of Qafzeh 12 and Amud 7 but none can be detected in the other Qafzeh specimens. Qafzeh 12 and 15 extend the known range of variation in the fossil H. sapiens sample in some metric variables, but morphologically, the new specimens do not differ in any meaningful way from living humans. In most metric dimensions, the Amud 7 incus falls within our modern human range of variation, but the more closed angle between the short and long processes stands out. Morphologically, all the Neandertal incudi described to date show a very straight long process. Several tentative hypotheses can be suggested regarding the evolution of the ear ossicles in the genus Homo. First, the degree of metric and morphological variation seems greater among the fossil H. sapiens sample than in Neandertals. Second, there is a real difference in the size of the malleus between Neandertals and fossil H. sapiens, with Neandertals showing larger values in most dimensions. Third, the wider malleus head implies a larger articular facet in the Neandertals, and this also appears to be reflected in the larger (taller) incus articular facet. Fourth, there is limited evidence for a potential temporal trend toward reduction of the long process within the Neandertal lineage. Fifth, a combination of features in the malleus, incus, and stapes may indicate a slightly different relative positioning of either the tip of the incus long process or stapes footplate within the tympanic cavity in the Neandertal lineage.