Cochlear Labyrinth Volume in Euarchontoglirans: Implications for the Evolution of Hearing in Primates

Armstrong, Stephanie; Bloch, Jonathan I.; Houde, Peter; Silcox, Mary

doi:10.1002/ar.21298

Cited by 13 publications

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References 16 publications

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“…A link between body mass and dimensions of the inner ear have been hypothesized for several mammal groups, particularly primates [18], and inner ear dimensions that are normalized to body mass are hypothesized to correlate with both hearing [9], [19]–[22] and agility [23]–[26]. Such assertions begin with and are necessarily dependent on the comparative morphology of the bony labyrinth among extant mammals, for which physiological capabilities can be measured directly.…”

Section: Introductionmentioning

confidence: 99%

“…The dimensions of inner ear structures are correlated to the physiological capabilities of the otic region, including both hearing and balance. Ratios between measurements and the volume of the cochlea are related to auditory frequency limits [18]–[20], [27]–[28], which correlate with vocalization and social behavior, and the dimensions of the semicircular canals relate to the sensitivity of the canals [29], which may in turn correlate to agility and locomotor behaviors [23]–[26].…”

Section: Introductionmentioning

confidence: 99%

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Comparative Anatomy of the Bony Labyrinth (Inner Ear) of Placental Mammals

2013

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BackgroundVariation is a naturally occurring phenomenon that is observable at all levels of morphology, from anatomical variations of DNA molecules to gross variations between whole organisms. The structure of the otic region is no exception. The present paper documents the broad morphological diversity exhibited by the inner ear region of placental mammals using digital endocasts constructed from high-resolution X-ray computed tomography (CT). Descriptions cover the major placental clades, and linear, angular, and volumetric dimensions are reported.Principal FindingsThe size of the labyrinth is correlated to the overall body mass of individuals, such that large bodied mammals have absolutely larger labyrinths. The ratio between the average arc radius of curvature of the three semicircular canals and body mass of aquatic species is substantially lower than the ratios of related terrestrial taxa, and the volume percentage of the vestibular apparatus of aquatic mammals tends to be less than that calculated for terrestrial species. Aspects of the bony labyrinth are phylogenetically informative, including vestibular reduction in Cetacea, a tall cochlear spiral in caviomorph rodents, a low position of the plane of the lateral semicircular canal compared to the posterior canal in Cetacea and Carnivora, and a low cochlear aspect ratio in Primatomorpha.SignificanceThe morphological descriptions that are presented add a broad baseline of anatomy of the inner ear across many placental mammal clades, for many of which the structure of the bony labyrinth is largely unknown. The data included here complement the growing body of literature on the physiological and phylogenetic significance of bony labyrinth structures in mammals, and they serve as a source of data for future studies on the evolution and function of the vertebrate ear.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Comparative Anatomy of the Bony Labyrinth (Inner Ear) of Placental Mammals

2013

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“…Encephalization Quotients (EQ) were calculated based on equations in Jerison, 1973 andEisenberg, 1981 as indicated. An estimated body mass of 74 g (based on postcranial measurements; Armstrong et al, 2011) was used for calculating EQ. olfactory bulbs in L. kayi (Fig.…”

Section: Cerebrummentioning

confidence: 99%

“…Encephalization quotient (EQ) estimates calculated from all four estimates, based on the body mass estimate for USNM 530221 (74 g; Armstrong et al, 2011), are included in Table 1 and Figure 7. These EQ estimates lie within the range calculated for plesiadapiforms, and near the top part of the range of estimates for 'archaic' non-primates from the Late Cretaceous and early Tertiary.…”

Section: Brain Size and Eqmentioning

confidence: 99%

“…One of these (USMN 530221) is part of an articulated skeleton that allows for an estimate of body mass (74 g; Armstrong et al, 2011) derived from multiple postcranial elements, an approach that may be preferable to using only dental or cranial specimens to generate an estimate (Gingerich and Gunnell, 2005). Together these specimens permit a fairly complete characterization of the endocranial morphology of L. kayi, and for the development of a set of estimates of volume for composite endocasts produced using different assumption sets.…”

Section: Introductionmentioning

confidence: 99%

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Endocranial morphology ofLabidolemur kayi(Apatemyidae, Apatotheria) and its relevance to the study of brain evolution in Euarchontoglires

Silcox

Dalmyn

Hrenchuk

et al. 2011

Journal of Vertebrate Paleontology

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Apatemyids are known from the Paleocene and Eocene of Europe, and the Paleocene to Oligocene of North America, and may share a special relationship with Euarchontoglires. The only endocast previously described for an apatemyid pertains to Carcinella sigei from the late Eocene of France. Here we present a composite virtual endocast of Labidolemur kayi derived from high-resolution X-ray computed tomography data, based on partial crania from the late Paleocene (Clarkforkian) and early Eocene (Wasatchian) of the Clarks Fork Basin, Wyoming. Like C. sigei, L. kayi had voluminous, transversely expansive olfactory bulbs, accounting for approximately 12-15% of the endocranial volume. This is similar to Cretaceous eutherians, but contrasts with the relatively smaller olfactory bulbs in both the basal gliran Rhombomylus turpanensis and in primitive primates (Ignacius graybullianus, Microsyops annectens). Similar to R. turpanensis, I. graybullianus, and the inferred ancestral condition for Microsyops, but unlike C. sigei, L. kayi exhibited exposed caudal colliculi, supporting the inference that this condition was primitive for Euarchontoglires and Euarchonta. The cranial capacity of L. kayi is estimated at 0.5-0.6 cc, yielding encephalization quotient (EQ) estimates of 0.23-0.28 or 0.42-0.50 depending on the equation used. These values are much lower than estimates for C. sigei, suggesting significant increase occurred in brain size in Apatemyidae, perhaps related to elaborations in the family's specialized manual extractive feeding regime. Similarities with primitive primates in EQ and the inferred position of the rhinal sulcus may allow for inferences about encephalization and neocorticalization in the common ancestor of Euarchontoglires.

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Inner Ear Evolution in Primates Through the Cenozoic: Implications for the Evolution of Hearing

Coleman

Boyer

2012

The Anatomical Record

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Mammals are unique in being the only group of amniotes that can hear sounds in the upper frequency range (>12 kHz), yet details about the evolutionary development of hearing patterns remain poorly understood. In this study, we used high resolution X-ray computed tomography to investigate several functionally relevant auditory structures of the inner ear in a sample of 21 fossil primate species (60 Ma to recent times) and 25 species of living euarchontans (primates, tree shrews, and flying lemurs). The structures examined include the length of the cochlea, development of bony spiral lamina and area of the oval window (or stapedial footplate when present). Using these measurements we predicted aspects of low-frequency and high-frequency sensitivity and show that hearing patterns in primates likely evolved in several stages through the first half of the Cenozoic. These results provide temporal boundaries for the development of hearing patterns in extant lineages and strongly suggest that the ancestral euarchontan hearing pattern was characterized by good high-frequency hearing but relatively poor low-frequency sensitivity. They also show that haplorhines are unique among primates (extant or extinct) in having relatively longer cochleae and increased low-frequency sensitivity. We combined these results with additional, older paleontological evidence to put these findings in a broader evolutionary context. Anat Rec,

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Cochlear Labyrinth Volume in Euarchontoglirans: Implications for the Evolution of Hearing in Primates

Cited by 13 publications

References 16 publications

Comparative Anatomy of the Bony Labyrinth (Inner Ear) of Placental Mammals

Comparative Anatomy of the Bony Labyrinth (Inner Ear) of Placental Mammals

Endocranial morphology ofLabidolemur kayi(Apatemyidae, Apatotheria) and its relevance to the study of brain evolution in Euarchontoglires

Inner Ear Evolution in Primates Through the Cenozoic: Implications for the Evolution of Hearing

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