Whales , dolphins, and porpoises belong to an order of mammals known as
the Cetacea (derived from the Latin term cetos or cetus,
meaning large sea creature). Cetaceans and the Sirenians (dugongs
and manatees) are the only two orders of mammals that are adapted to a
fully aquatic existence.
Cetacean Origins
Cetaceans evolved from land mammal ancestors about 53-54 million years
ago (MYA) (Reynolds, Odell and Rommel 1999) and are represented by three
sub-orders:
the earliest to have evolved, theArcheocetes
(the ancient whales), are found in the
fossil record during the early to middle
Eocene (52-42 MYA) (Berta and Sumich 1999);
the Odontocetes (toothed whales),
an extant group that diverged from the
archaeocetes about 25-35 MYA (Berta and
Sumich 1999), that includes sperm whales,
dolphins, porpoises, beaked whales,
narwhals and belugas, and others, ;
the Mysticetes (baleen whales),
an extant group that also is believed to
have diverged from the archaeocetes during
the late Eocene, about 25-35 MYA (Berta and
Sumich 1999).
Early analysis of fossil evidence led to the belief that cetaceans had
evolved from mesonychians, an extinct group of archaic
ungulates (hoofed mammals) that had wolf-like or hyena-like proportions
and were adapted for rapid movement on land and had large heads with
powerful jaws (Berta and Sumich 1999; Reynolds, Odell and Rommel 1999,
Rice 1998). On the other hand, recent molecular studies have been
interpreted to show that the closest extant relatives of whales are
hippopotamids (Nikaido, Rooney and Okada 1999).
Recent and compelling evidence based upon analysis of several early
cetacean skeletons (Ichthyolestes pinfoldi and Pakicetus
attocki),
support the hypothesis that cetaceans share common ancestry with
Artiodactyls (even toed ungulates) such as deer, antelopes, camels,
pigs, hippopotami, and giraffes, not mesonychians (Thewissen, et al.
2001). Thewissen et al. (2001) state that cetaceans "are not the
sister group to (any) mesonychians, nor to hippopotamids." Their
analysis "stops short of identifying any particular artiodactyl family
as the cetacean sister group..." The recent work of Gingerich et
al. (2001) also indicates that "Cetacea evolved from early Artiodactyla
rather than Mesonychia ."
Cetacean Adaptations
Cetaceans are characterized by a variety of adaptations to their fully
aquatic existence. These adaptations range from obvious morphological
ones to subtler physiological ones.
The obvious morphological adaptations include:
large size to reduce the surface area to
volume ratio (SA/V) to aid in
thermoregulation;
hydrodynamically stream-lined bodies
with reduced protuberances to reduce drag;
no hind limbs;
powerful tail flukes for propulsion;
forelimbs modified as flippers use for
steering and stability;
dorsal fin (not in all species) used for
stability and thermoregulation;
nares (nostrils or blowholes) located on
the top of the head, allowing swimming and
breathing without taking on water.
The physiological adaptations are numerous including those involved in
thermoregulation, buoyancy control, diving,
water balance, sensory reception, reproduction, and
communication, to name a few.
Cetacean taxonomy
Odontocetes and Mysticetes
We recognize 11 species of mysticetes (baleen whales) and, depending
upon who you're listening to, anywhere from 67 species to 76 species of
odontocetes (toothed whales) (Klinowska 1991; Berta and Sumich 1999;
Reynolds, Odell and Rommel 1999).
Odontocetes have teeth which they use to grasp prey but not for chewing.
Typically, odontocetes swallow their prey whole. The teeth vary in size
and shape from the large conical teeth of the largest odontocete, the
sperm whale (Physeter macrocephalus), to small spade-like teeth
of the harbor porpoise (Phocoena phocoena), to the lack of
erupted teeth in the females of some beaked whale species.
Mysticetes are filter feeders and they don't have teeth as adults.
Instead, baleen whales have overlapping plates of keratinized (keratin
is a fibrous protein found in skin, hair, nails, hoofs, and feathers)
tissue called baleen hanging down from their upper jaws. Each baleen
plate is shaped somewhat like an elongated triangle, with the short end
embedded in the upper jaw at right angles to the long axis of the jaw;
one edge of the triangle is smooth and faces outward, while the inner
edge is fringed with bristle-like or hair-like keratinized tubules.
These collectively form a filtering mat of fibers. In one way or another
("gulping" or "skimming") baleen whales take in mouthfuls of food and
water, force the water out through the baleen plates and trap food
organisms. The amount of food, types of food, and volume of water varies
with species, individual, and conditions. It is interesting to note that
the size, shape, and texture of the bristles vary with species and their
typical prey. For instance, the baleen bristles of fin whales (Balaenoptera
physalus), which have a broad potential food base of relatively
larger organisms (including small schooling fish such as sand eels,
herring, tinker mackerel; squid; and crustaceans such as copepods and
euphausiids), are very coarse. However, the baleen bristles of northern
right whales (Eubalaena glacialis) which feed almost exclusively
on calanoid copepods are much finer.
Mysticetes and odontocetes differ in an array of other features as well.
The shape of the mysticete skull is subtly asymmetrical, while that of
the odontocete is extremely asymmetrical. Odontocetes have single
blowholes, while mysticetes have double blowholes. Most odontocetes are
highly social (gregarious) animals, living in relatively stable social
groups, while mysticetes are solitary animals, found in groups only
under certain conditions (mothers and calves; courtship and mating; when
there is an abundance of food). Odontocetes and mysticetes differ in
size related sexual dimorphism (differences in size between males and
females). In mysticetes, females are larger than males of the same age.
In odontocetes, typically, males are larger than females of the same
age, although there are some taxa in which males and females are the
same size (Kogiidae), and some in which females are larger than males
(harbor porpoise, river dolphins, and beaked whales) (Reynolds, Odell
and Rommel 1999).
References cited:
Berta, A. and J. L. Summich. 1999. Marine mammals: evolutionary biology.
Academic Press, San Diego, CA.
Gingerich, Philip D., Haq, Munir ul, Zalmout, Iyad S., Khan, Intizar
Hussain, Malkani, M. Sadiq. 2001. Origin of Whales from Early
Artiodactyls: Hands and Feet of Eocene Protocetidae from Pakistan.
Science 293: 2239-2242.
Klinowska, M. 1991. Dolphins, porpoises and whales of the World. The
IUCN Red Data Book. IUCN, Gland, Switzerland and Cambridge, U.K.
Nikaido, M., A. P. Rooney and N. Okada. 1999. Phylogenetic
relationships among cetartiodactyles based on insertions of short and
long interspersed elements: Hippopotamuses are the closest extant
relatives of whales. Proceedings of the National Academy of
Sciences, USA 96: 10261-10266.
Reynolds, J. E. III, D. K. Odell, and S. A. Rommel. 1999. Marine mammals
of the world. Pages 1-14 in J. E. Reynolds III and S. A. Rommel (eds).
Biology of marine mammals. Smithsonian Institution Press, Washington,
D.C.
Rice, D. W. 1998. Marine mammals of the world: systematics and
distribution. Special Publication Number 4, The Society for Marine
Mammalogy. Lawrence, KS.
Thewissen, J. G. M., E. M. Williams, L. J. Roe and S. T. Hussain.
2001. Skeletons of terrestrial cetaceans and the relationship of
whales to artiodactyls. Nature 413: 277-281
CRESLI's Cetacean Research
Scientists from the Coastal Research and
Education Society of Long Island have been studying
cetaceans
(whales, dolphins and
porpoises) for
over two decades. Samuel Sadove and more recently Dr. Artie Kopelman,
have been investigating fin whale behavior and conducting population and
distribution surveys for all cetaceans in New York's waters. In 1996/97
these studies were extended to the Caribbean. Sadove has also worked
with baleen whales in the high Arctic. Dr. Paul Forestell has over 20
years experience working chiefly with humpback whales in the Pacific,
and spinner dolphins in the tropical Pacific. They bring their acquired
experience and knowledge to CRESLI's research and educational projects.
A number of college students and volunteers from all walks of life
assist with data collection and analysis.
CRESLI's cetacean research goals are
multifaceted, and mainly directed at photo identification (particularly
of fin whales, sperm whales and humpback whales) and collection and
analysis of basic ecological and behavioral data from all cetacean
species encountered.
Data collected by CRESLI scientists over 20
years indicate that approximately 25 species of cetaceans utilize Long
Island's waters, including
fin whales, humpback whales, minke whales, North Atlantic right whales,
sei whales,
blue whales, sperm whales, pilot whales, as well
as common dolphins, bottlenose dolphins, striped dolphins and white
sided dolphins among others (for a detailed list, please go to our
Checklist
page). Ultimately, our goal is to provide much needed information about
population sizes, genetic affinities, and the distribution and abundance
of cetacean species in our coastal waters. By monitoring populations and
understanding their biology and behavior, we can better protect these
animals and the environment we share with them.
Studying whales at sea is difficult and
expensive. Weather and sea condition are not always favorable, and
vessel and air time are extremely costly. CRESLI has developed a
diverse, innovative support network to continue these important
projects. These include CRESLI whale watch cruises which offer a
platform for research in addition to educating the public and local
fishermen and boaters who provide sighting reports and information to
researchers. These organizations and individuals make this important
work possible.
CRESLI
CETACEAN PROJECTS
CRESLI's cetacean research program includes several comprehensive
projects:
Cetacean population and distribution: Using shipboard and aerial
platforms, the species, number of individuals, and their
locations are recorded, along with meteorological and other
data. Over time this serves to give researchers a picture of
general population and distribution trends, and how
cetaceans utilize their habitat.
Sighting Network: Local commercial and recreational fishermen and
boaters are asked about sightings of cetaceans. This information supplements
data collected by CRESLI researchers.
Photo identification of individual fin whales: CRESLI researchers
developed a method of identifying individual animals by photographing each
whale's chevron pattern, dorsal fin, and any other distinguishing features.
These photographs, along with observed behavioral data, are used to study
individual animals and determine population numbers and distribution.
Fin whale biology and behavior: Intensive studies of fin whale
feeding behavior and prey species, movement patterns, and behavior.
