Mammalian Middle Ear Research Articles

Book Reviews

Book reviewed in this article: ECOLOGY AND MANAGEMENT OF EUROPEAN HARE POPULATIONS Edited by Zygmund Pielowski & Zdzislaw Pucek. Polish Hunting Association, Warsaw, 1976. THE BIOLOGY OF MARSUPIALS Edited by Bernard Stonehouse & Desmond Gilmore AFRICAN UNGULATES: a comparative review of their ethology and behavioural ecology By Walter Leuthold. ECOLOGY OF RED DEER By Brian Mitchell, Brian W. Staines & David Welch. Institute of Terrestrial Ecology THE NATURAL HISTORY OF THE WHALE by L. Harrison Matthews. THE MAMMALS OF THE PALEARCTIC REGION: a taxonomic review by G. B. Corbet. British Museum DEVELOPMENT IN MAMMALS Volume 3. Edited by Martin H. Johnson. RECENT ADVANCES IN PRIMATOLOGY edited by D. J. Chivers and others Volume 1 ‐Behaviour; edited by D. J. Chivers & J. Herbert: Pp 980, 19.20. Volume 2 ‐Conservation; edited by D. J. Chivers Volume 3 ‐ Evolution; edited by D. J. Olivers & K. A. Joysey SEX DETERMINATION AND SEXUAL DIMORPHISM IN MAMMALS by Alfred Glucksmann HANDBUCH DER SAUGETIERE EUROPAS. Band 1: Nagetiere 1. Edited by Jochen Niethammer and Franz Krapp. MAMMALS ‐ THEIR LATIN NAMES EXPLAINED by A. F. Gotch. EVOLUTIONARY PRINCIPLES OF THE MAMMALIAN MIDDLE EAR By Gerald Fleischer. Springer‐Verlag

Evolutionary Principles of the Mammalian Middle Ear.

Evolutionary Principles of the Mammalian Middle Ear.

Oldest known eutherian stapes and a marsupial petrosal bone from the Late Cretaceous of North America

Cranial remains of Late Cretaceous therian mammals are rarely found in North America and are usually limited to isolated petrosal bones. The oldest known associated stapes and petrosal bone of a Late Cretaceous eutherian are reported here. Comparison with a Late Cretaceous marsupial petrosal bone gives a further indication of the probable condition of several character states of the ancestral mammalian (or at least therian) middle ear, and also indicates the antiquity of various aspects of the middle ear of extant eutherians and marsupials.

Book Review: Evolutionary Principles of the Mammalian Middle Ear, Volume 55, Advances in Anatomy, Embryology, and Cell Biology

Book Review: Evolutionary Principles of the Mammalian Middle Ear, Volume 55, Advances in Anatomy, Embryology, and Cell Biology

Evolutionary principles of the mammalian middle ear.

Evolutionary principles of the mammalian middle ear.

A REVIEW OF SOME CURRENT CONCEPTS OF THE FUNCTIONAL EVOLUTION OF THE EAR IN TERRESTRIAL VERTEBRATES.

The evolution of the middle ear, including the origin of the mammalian ossicles, has been a major concern of palaeontologists over the last 30 years. A general consensus has been reached, which needs no elaboration here, that the malleus and incus are mostly derived from bones in the ancestral reptile made redundant by the selection of a more efficient jaw articulation system (Hopson, 1966; Hotton, 1959; Parrington, 1967, 1971; Tumarkin, 1955; Watson, 1953). As emphasized by Hopson (1966) the selective pressures which gave rise to the middle ear mechanism of mammals acted primarily on the masticatory apparatus of therapsids. Because of the nature of the fossil record however, little can be learned from it concerning the evolution of the soft parts of the middle ear and the membranous labyrinth of the inner ear. Recent comparative anatomical and physiological studies now make it possible to bring together data on the functional significance of differences in the ears of modern vertebrates. The data also give some indication why certain structural and functional arrangements were selected for in the evolution of the mammals. In this paper I will discuss the functional significance of changes in the middle ear transmission system, particularly in connection with the origin of the mammalian middle ear, the development of large inner ear potentials and dimensional changes in the inner ear.

Variations in the middle ear of the Mammalia

The comparative morphology of mammalian middle ear structures has been studied by examining the histological sections of the ears of 144 specimens of mammals which had been collected, with a few exceptions, in two expeditions to the Caribbean area. Fifty‐four species of six orders of mammals were represented. Sixteen structural features or relationships were specifically studied and the bearing of taxonomic groupings on the variability was analysed.A taxonometric analysis using these middle ear features indicated that Microdipodops may lie nearer to Dipodomys than to Perognathus.A table presenting the detailed results has been deposited with the British Museum (Natural History).

The origin of the mammalian middle ear.

A functional explanation is presented for the shift of the reptilian articular and quadrate into the mammalian middle ear to become the malleus and incus. Modification of the masticatory apparatus of therapsids results in reduction of stresses on the jaw joint and consequently in reduction of posterior elements of the jaw. In the late therapsid, Bienotherium , the quadrate and post-dentary jaw bones resemble the mammalian malleus and incus which together form a lever. The therapsid articular possesses a downturned retroarticular process (for insertion of M. depressor mandibulae) homologous with the manubrium (force lever arm) of the malleus. About the time of origin of the mammalian (dentarysquamosal) jaw joint and following the origin of the mammalian depressor, the reptilian depressor is lost. This allows the enlarging reptilian tympanum to become attached to the retroarticular process. The new lever system thus formed by articular and quadrate increases the sensitivity of the ear and the reptilian one-bone system is replaced. In early mammals the reflected lamina of the angular migrates posteriorly with the angle of the dentary so that it contacts and assumes support of the tympanum. Non-homology of the monotreme and therian depressors indicates a multiple origin of the mammalian middle ear.

The Weberian Apparatus of Hybognathus placitus and H. nuchalis (Cyprinidae)

The Weberian apparatus of Hybognathus placitus is described and compared with that of H. nuchalis. Although considerable variation in the Weberian components was observed, the many differences indicate that full specific rank should be retained for both Hybognathus placitus and H. nuchalis. The lateral proc- esses of the first and second vertebrae are regarded as modified ventral ribs. The ascending processes of the scaphium and intercalarium are believed to be homologous to postzygapophyses. The pit into which the articulating process of the scaphium fits is regarded as homologous to those accommodating the third neural pedicle and fourth neural arch. The neural complex is probably composed of the third neural spine plus interspinous bones. The os suspensorium is part of the fourth pleural rib. The most conspicuous difference between these species involves the shape of the pharyngeal process of the basioccipital and the muscles inserted on it. Hybognathus placitus Girard and Hybognathus nuchalis Agassiz present some taxonomic difficulty, but have long been regarded as dis- tinct species. Bailey (1956) concluded that environmental variations, at the time of early development, are translated into structural dif- ferences that can be perceived throughout the life of the fish. He con- sidered both H. Nuchalis and H. placitus as phenotypes of H. nuchalis. The purpose of this study was to test this hypothesis, using the mor- phology of the Weberian apparatus. The Weberian apparatus was named in honor of the discoverer, E. J. Weber, by Bridge and Haddon (1889). Since Weber used nomencla- ture as applied to the ossicles of the mammalian middle ear, not homol- ogous with those of fishes, Bridge and Haddon proposed the nomen- clature currently used. Readers interested in the literature pertinent to the morphology and embryonic development of the Weberian ap- paratus should consult the works of Evans (1924-1925), Watson, (1939), Krumholz (1943), Nelson (1948), 1949, 1955), and Butler (1960). Materials for this study were from a large part of the ranges of the two species, from the Rio Grande to the Missouri River Basin in South Dakota and Montana. We are indebted to Dr. R. M. Bailey, of the 1 Contribution from the Research Foundation and No. 344 from the Zoology De- partment, Oklahoma State University, with partial support from the National Science Foundation.

THE EVOLUTION OF THE MAMMALIAN EAR

Recent discussions of the mechanisms which have brought evolution 'about have led to a wide spread concurrence of opinion about the factors involved in the production of geographical races and the isolation of species, but they have not achieved the same general acceptance in their consideration of major evolutionary events, the coming into being of the various phyla or of such a class as the Mammalia, or of such great steps as the evolution of the craniate eye. Here a different process, with a different mechanism macro-evolution has been invoked by some workers. It is evident that we shall never know the steps which led up to the craniate eye, but we can expect to see and to understand much of the evolutionary history of the sound transmitting mechanism of the mammalian middle ear, one of the great steps for which an independent macroevolution is invoked. The problems presented by the evolution of the mammalian middle ear may be stated historically as follows: In 1601 A.D., J. Casserius showed that mammals possessed three bones in their middle ear, and birds, as represented by a goose, only one. By 1800, names had been given to these elements, and it had been recognized that in mammals the lower jaw was a single bone on each side which articulated with the squamosal bone of the skull, whilst in reptiles the lower jaw was made of several bones one of which, the articular, moved on a quadrate bone which was part of the skull. By 1820, Meckel showed that the mamnalian malleus first appeared as the hinder part of cartilage and corresponded with the reptilian articular, and lby 1818, C. G. Carus had suggested that the incus is the quadrate. In 1837, Reichert gave a connected account of the development of the visceral arches in mammals and birds, adopting Cartis' and Meckel's suggestions, and the whole story is now commonly known by his name. The great difficulty in envisaging interm-iediates between the modern reptile and the mammalian condition led to many alternative suggestions, so that the publication by E. Gaupp (1913) of an exhaustive treatise on the problem which established, by a consideration of all then available 'lines of evidence, the fact that the old reptilian jaw articulation was represented in mammals by that between the incus and malleus, was important. An admirable account of the whole matter will be found in E. S. Goodrich, Studies on the Structure and Development of Vertebrates, London 1930, chapter VIII.

The Mammalian Middle Ear

IN a recent communication in Nature1, certain implications of new work on the anatomy of the middle ear region of mammal-like reptiles were discussed. Some further aspects of the evolution of the mammalian middle ear are here briefly noticed. A new synthesis, based on palaeontological evidence, was recently offered2 to 'explain' the nature of the mammalian tympanic cavity. It was suggested that the primitive reptilian tympanic cavity was, in at least some therapsids, supplemented by a recessus mandibularis related to the region of the notched angular bone; and that the mammalian tympanic membrane was formed from the thin external wall of this recess by extension of the old tympanic membrane.

New Light on the Mammalian Ear Ossicles

In spite of many criticisms, the Reichert-Gaupp theory of the mammalian ear ossicles1, 2, 3, 4 has, in its main points, been confirmed by a considerable body of work on the developmental anatomy of recent mammals and reptiles, and on the structure of therapsid reptiles. There can be little question that the stapes, incus and malleus (except for its dermal component, the goniale of Gaupp) are essentially homologous respectively with the reptilian columella auris (proximal part or otostapes), quadrate and articular. The existence of vestiges of other elements of the reptilian lower jaw and extrastapes in the mammalian middle ear has been suggested by numerous investigators. Thus the goniale is usually equated with the pre-articular1, 2, 3, 4, etc., and the elements of Paauw and Spence have been regarded as parts of the extrastapes5. But in general there has been little agreement on the detailed homology of the parts of the stapes, of the crura of the incus, and of the various processes of the malleus; this is largely because most of our information on these points is based on the anatomy of adult and embryonic stages of living mammals and reptiles, while mammals originated from the extinct therapsid reptiles, which differ from Lacertilia and Sphenodon in important respects. Until recently, too little was known in detail about the middle ear and lower jaw of therapsids, though Broom6 showed the position of the tympanic membrane and the presence of an ossified portion of the extrastapes in some Therocephalia (see also ref. 7). E. C. Olson8 has now provided, among other interesting things, an account of the structure of the otic region of several therapsids (Anomodontia, Therocephalia, Gorgonopsia, Cynodontia) based on serial sections. The structure of the middle ear region is greatly illuminated by this work; but some of his conclusions seem to be open to question, while others can be further supported.