Whales, dolphins and
porpoises, collectively known as cetaceans (for their classification
in the mammalian order Cetacea) have long captured the attention of
humans. From early drawings etched on the walls of Paleolithic caves,
to 21st century satellite tags tracking the underwater movements of
these denizens of the deep, the lives of humans and whales have been
inexorably entangled. This connection has been a compelling story of
the discovery and scientific study of large, charismatic sea animals
tempered by darker times of intense human hunting and whaling that
left many species hovering on the brink of extinction.
The approximately 90
living species of cetaceans inhabit nearly every ocean basin in
addition to a few river systems, occupying diverse habitats that
include polar, temperate and tropical waters. Whales evolved more
than 50 million years ago in present-day India and Pakistan. Evidence
from anatomy as well as genetics supports a close relationship
between whales and even-toed ungulates (e.g. deer, giraffes, hippos,
pigs, cows) with hippos positioned as their closest kin. The land to
sea transition made by whales involved anatomical and physiological
adaptations (e.g. feeding, locomotion and respiration) that are well
represented in the fossil record. For example, recent discoveries
indicate that the earliest whales like their terrestrial ancestors
had well developed fore and hind legs and lived on land as well as
the water.
One of the
best-documented examples of evolutionary change in the fossil record
is the loss of hind limbs in whales and recent study of whale embryos
has revealed its genetic basis.
Whales are divided into
two major groups: odontocetes (toothed whales) and mysticetes (baleen
whales). Odontocetes are more diverse with 76 living species compared
to 14 species of mysticetes. As the name suggests odontocetes possess
teeth and most eat fish although some have very reduced dentitions
and are specialized for suction feeding squid.
A key adaptation that
enables odontocetes to pursue prey involves using high frequency
sounds produced in the nasal region.
Mysticetes do not
echolocate and recent research suggests that they may find prey using
sensitive vibrissae (whiskers) on the rostrum. Although mysticetes
possess teeth at birth (also present in early fossil mysticetes) they
are resorbed and adults feed using baleen, keratin based structures.
Plates of baleen are suspended in racks from their enormous
mouths that act as a comb to bulk filter feed large aggregations of
fish and zooplankton.
The biology of whales
has been enriched by remarkable recent advances in integrated
research in paleontology, ecology, behavior, and genetics. Modern
techniques such as attaching digital acoustic tags (DTAG) to whales
have elucidated extraordinary feeding behaviors and foraging
strategies. Not only do these tags provide information on body
orientation (i.e. acceleration, pitch, roll and heading) they also
record sounds made by and heard by the tagged whale as well as
recording environmental parameters such as water temperature and
depth. Isotope studies reveal ocean temperature changes through time
providing evidence that the diversification of modern whales was
associated with increased food production.
Exciting breakthroughs
in understanding the anatomical structures and pathways involved in
sound production and reception in whales have been facilitated by CT
scans and 3D imagery. Genetic and genome studies have explored
evolutionary relationships among cetaceans as well as providing
valuable life history and population data critical to the development
of thorough management and conservation plans.
Knowledge
of the biology of whales provides a framework that is essential for
helping us understand how best to protect and conserve them. Further,
as top predators, whales are indicator species of the health of the
ecosystem and serve a vital role as sentinels of climate change.
Beautifully
illustrated throughout, “Whales Dolphins and Porpoises” edited by
Annalisa Berta, combines highlights from the latest scholarly studies
of the nature and behaviour of the world’s whales, dolphins and
porpoises, with a fully comprehensive species directory, that offers
detailed profiles of each species alongside all the information needed to identify
them in the wild.
Annalisa Berta has
been Professor of Biology at San Diego State University, California,
for more than 30 years, specialising in the anatomy and evolutionary
biology of marine mammals. Past President of the Society of
Vertebrate Palaeontology and co-Senior Editor of the Journal of
Vertebrate Palaeontology, Berta has authored and co-authored numerous
scientific articles and several books for the specialist and
non-scientist.
Edited by Annalisa
Berta
Available 21
September 2015
ISBN:
978-1-78240-152-0
£29.99
