Hadrosaur Crests
Hadrosaurs (duck-billed donosaurs) had a variety of large, hollow,
bony structures on their heads (part of the skull). The function of the crests
is uncertain.
Construct three explanations for the crests
- one that invokes a survival strategy
- one that invokes a reproductive strategy
- one that is NOT due to natural selection
For each explanation, suggest a way to test you hypothesis.
Functions of head structures in different animals:
- Can you tell me why my cockatiel moves its crest up and down? Content birds
have their crests lowered. An alert bird raises its crest vertically. Birds
that are upset or frightened move their crests straight up. (desibird.blogspot.com)
- The Pied Heron is a small, black-and-white heron of Northern Australia.
Older birds have a distinctive black crown and crest. When breeding its crest
plumes are longer.(Herons, Egrets and Bitterns: Their Biology and Conservation
in Australia by Neil McKilligan)
- Antlers are one of the most easily recognized characteristics of the family
Cervidae. They are present only in males (with the exception of caribou) and
are capable of growing astoundingly large. Their morphology varies among species...Males
use their full-grown antlers during the breeding season in social interactions
in competition for females.(http://animaldiversity.ummz.umich.edu/site/topics/mammal_anatomy/horns_and_antlers.html)
- Rabbits' main cooling comes from their ears which act as radiators. Their
ears have the largest amount of thin fur and exposed skin on their bodies.
Pictures of Jackrabbits who live in the prairie & desert show enormous
ears.(http://www.allearssac.org/differences.html)
- The Narwhal is unlike any other cetacean. The male has a long spiralling
tusk which is not normally possessed by the female. The tusk which grows to
a length of 1.5-3m (5-10ft) is actually a modified tooth and looks like a
twisted and gnarled walking stick. During the 17th century the Narwhal tusk
was thought to have been the horn of the legendary unicorn. Studies suggest
that males engage in aggressive behavior when competing for females. Scars
attributed to tusk action have been found on the heads of adult males which
are more likely to have broken tusks.(http://www.whales.org.au/discover/narwhal/narwg.html)