Extinct early whales listened like their relatives on land, fossil evidence shows

June 8, 2017

Whales rely on a keen sense of hearing for their underwater existence. But whales show surprisingly vast differences in hearing ability. Baleen whales tune into infrasonic sounds—at frequencies too low for humans to hear—to communicate over long distances. Toothed whales do just the opposite, relying on ultrasonic frequencies too high for humans to hear.

Now researchers reporting in Current Biology on June 8 have fossil evidence from extinct early whale species to suggest that those differences in hearing arose only after whales evolved into the fully aquatic animals we know today. That's based on their findings that whales known as protocetes, which spent time both in water and on land, appear to have hearing more like their terrestrial, even-toed ungulate relatives, including pigs, hippos, and camels.

"We found that the cochlea of protocetes was distinct from that of extant whales and dolphins and that they had hearing capacities close to those of their terrestrial relatives," says Maeva Orliac of CNRS and Université de Montpellier in France.

Protocetes' lack of hearing specialization suggests that the early whales were unable to echolocate and communicate through long-distance calls in the way that modern-day cetaceans, the group including whales and dolphins, do.

The researchers came to those conclusions based on studies of 45-million-year-old protocetid whale remains found in marine deposits from Togo in West Africa. The researchers studied the bony labyrinth, a hollow cavity that would have housed the hearing organ, in two species of early whales.

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Pandas hear more than we do

Sensitivity beyond human range may have conservation implications

Date: March 22, 2016

Source: Zoological Society of San Diego

A study published in the journal Global Ecology and Conservation may help field conservationists better understand the potential for human activities to disturb endangered giant pandas in native habitats. Using pandas located at the San Diego Zoo, conservation scientists worked with animal care specialists to determine pandas' range of hearing sensitivity, discovering that they can detect sound into the ultrasonic range. Because giant pandas depend in large part on information transmitted through vocalizations for reproductive success, noise from human activities in or near forest areas could be disruptive.

"An understanding of a species' hearing provides a foundation for developing estimates of noise disturbance," said Megan Owen, associate director of giant panda conservation, San Diego Zoo Global. "For the giant panda, vocalizations are typically emitted in proximity to conspecifics (members of the same species), however the ability to discriminate between fine-scale differences in vocalizations is important for successful reproduction; and so, a thorough understanding of acoustic ecology is merited in order to estimate the potential for disturbance.

"In order to learn about panda hearing, researchers at the San Diego Zoo worked with giant pandas to teach them to respond, if they could hear sounds at a particular pitch and loudness, thus communicating their ability to hear across the acoustic spectrum," Owen said.

"Through this study, the pandas at the San Diego Zoo have made a significant contribution to our understanding of what may be affecting panda reproduction in habitats in China," said Ron Swaisgood, director of applied animal ecology, San Diego Zoo Global. "It is only because of the strong relationship that animal care staff have with the bears at the Zoo that we have been able to gather this information."

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Offshore wind turbine construction could be putting seals' hearing at risk

Date: May 19, 2015

Source: British Ecological Society (BES)

Summary: Noise from pile driving during offshore wind turbine construction could be damaging the hearing of harbour seals around the UK, researchers have found. They say more research is needed on how noise affects marine mammals' hearing and into engineering solutions to reduce noise levels.

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Bats use both sides of brain to listen -- just like humans

Date:April 27, 2015

Source:Georgetown University Medical Center

Summary:Researchers have shown that, like humans, mustached bats use the left and right sides of their brains to process different aspects of sounds. Aside from humans, no other animal that has been studied, not even monkeys or apes, has proved to use such hemispheric specialization for sound processing -- meaning that the left brain is better at processing fast sounds, and the right processing slow ones.

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Lungfish, salamanders reveal how hearing evolved

Provided by Christian Bech Christensen, Aarhus University

Lungfish and salamanders can hear, despite not having an outer ear or tympanic middle ear. These early terrestrial vertebrates were probably also able to hear 300 million years ago, as shown in a new study by Danish researchers.

Lungfish and salamander ears are good models for different stages of ear development in these early terrestrial vertebrates. Two new studies published in the renowned journals Proceedings of the Royal Society B and The Journal of Experimental Biology show that lungfish and salamanders can hear, despite not having an outer ear or tympanic middle ear. The study therefore indicates that the early terrestrial vertebrates were also able to hear prior to developing the tympanic middle ear. The research findings thus provide more knowledge about the development of hearing 250-350 million years ago.

The physical properties of air and tissue are very different, which means in theory that up to 99.9% of sound energy is reflected when sound waves reach animals through the air. In humans and many other terrestrial vertebrates, the ear can be divided into three sections: the outer ear, the middle ear and the inner ear. The outer ear catches sound waves and directs them into the auditory canal. In the middle ear, pressure oscillations in the air are transferred via the tympanic membrane (eardrum) and one or three small bones (ossicles) to fluid movements in the inner ear, where the conversion of sound waves to nerve signals takes place. The tympanic middle ear improves the transfer of sound energy from the surroundings to the sensory cells in the inner ear by up to 1,000 times, and is therefore very important for hearing in terrestrial vertebrates. This is reflected in the fact that different configurations are found in the vast majority of present-day terrestrial mammals, birds, reptiles and amphibians. However, available palaeontological data indicate that the tympanic middle ear most likely evolved in the Triassic period, approximately 100 million years after the transition of the vertebrates from an aquatic to a terrestrial habitat during the Early Carboniferous. The vertebrates could therefore have been deaf for the first 100 million years on land.

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Baleen whales hear through their bones

Date:

January 29, 2015

Source:

San Diego State University

Summary:

Understanding how baleen whales hear has posed a great mystery to marine mammal researchers. Biologists reveal that the skulls of at least some baleen whales, specifically fin whales in their study, have acoustic properties that capture the energy of low frequencies and direct it to their ear bones.

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Study pumps up the volume on understanding of marine invertebrate hearing

Date:

December 22, 2014

Source:

Woods Hole Oceanographic Institution

Summary:

Noise pollution in the ocean is increasingly recognized as harmful to marine mammals, affecting their ability to communicate, find mates, and hunt for food. But what impact does noise have on invertebrates -- a critical segment of the food web?

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Whales hear us more than we realize: Sonar signal 'leaks' likely audible to some marine mammals

Date:

May 1, 2014

Source:

Pacific Northwest National Laboratory

Summary:

Killer whales and other marine mammals likely hear sonar signals more than we’ve known. That’s because commercially available sonar systems, which are designed to create signals beyond the range of hearing of such animals, also emit signals known to be within their hearing range, scientists have discovered.

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Desert Tortoises Can Hear Better Underwater

Desert tortoises, as their name suggests, don't encounter many large bodies of water. But surprisingly, all turtles, even desert tortoises, can hear better underwater, recent research finds.

"If a desert tortoise decided to stick its head underwater, it could hear better," said Katie Willis, a University of Maryland doctoral student and co-author of a study published online this week in the journal PLoS ONE.

The findings shed light on the evolution of turtles, suggesting they all share an aquatic ancestor, the researchers said.

Read more:  http://www.livescience.com/26361-turtles-hear-better-underwater.html