Exploring the mammalian sensory space: co-operations and trade-offs among senses.

The evolution of a particular sensory organ is often discussed with no consideration of the roles played by other senses. Here, we treat mammalian vision, olfaction and hearing as an interconnected whole, a three-dimensional sensory space, evolving in response to ecological challenges. Until now, there has been no quantitative method for estimating how much a particular animal invests in its different senses.

Development of the skull of the pantropical spotted dolphin (Stenella attenuata).

We describe the bony and cartilaginous structures of five fetal skulls of Stenella attenuata (pantropical spotted dolphin) specimens. The specimens represent early fetal life as suggested by the presence of rostral tactile hairs and the beginnings of skin pigmentation. These specimens exhibit the developmental order of ossification of the intramembranous and endochondral elements of the cranium as well as the functional and morphological development of specific cetacean anatomical adaptations.

Anatomy and physics of the exceptional sensitivity of dolphin hearing (Odontoceti: Cetacea).

During the past 50 years, the high acoustic sensitivity and the echolocation behavior of dolphins and other small odontocetes have been studied thoroughly. However, understanding has been scarce as to how the dolphin cochlea is stimulated by high frequency echoes, and likewise regarding the ear mechanics affecting dolphin audiograms. The characteristic impedance of mammalian soft tissues is similar to that of water, and thus no radical refractions of sound, nor reflections of sound, can be expected at the water/soft tissue interfaces.

Sound transmission in archaic and modern whales: anatomical adaptations for underwater hearing.

The whale ear, initially designed for hearing in air, became adapted for hearing underwater in less than ten million years of evolution. This study describes the evolution of underwater hearing in cetaceans, focusing on changes in sound transmission mechanisms. Measurements were made on 60 fossils of whole or partial skulls, isolated tympanics, middle ear ossicles, and mandibles from all six archaeocete families.

High-frequency hearing in phocid and otariid pinnipeds: an interpretation based on inertial and cochlear constraints (L).

Audiograms in air and underwater, determined by previous workers for four pinniped species, two eared seals (Otariidae) and two phocids (Phocidae), are supplemented here by measurements on their middle ear ossicular mass, enabling mechanistic interpretations of high-frequency hearing and audiogram differences. Otariid hearing is not largely affected by the medium (air/water). This indicates that cochlear constraints limit high-frequency hearing in otariids.

Eocene evolution of whale hearing.

The origin of whales (order Cetacea) is one of the best-documented examples of macroevolutionary change in vertebrates. As the earliest whales became obligately marine, all of their organ systems adapted to the new environment. The fossil record indicates that this evolutionary transition took less than 15 million years, and that different organ systems followed different evolutionary trajectories.

Ontogenetic and phylogenetic transformations of the ear ossicles in marsupial mammals.

This study is based on the examination of histological sections of specimens of different ages and of adult ossicles from macerated skulls representing a wide range of taxa and aims at addressing several issues concerning the evolution of the ear ossicles in marsupials. Three-dimensional reconstructions of the ear ossicles based on histological series were done for one or more stages of Monodelphis domestica, Caluromys philander, Sminthopsis virginiae, Trichosurus vulpecula, and Macropus rufogriseus. Several common trends were found.