Did dinosaurs lack daughters?
See-sawing climate may have fatally unbalanced sex ratio.
23 April 2004
HELEN PEARSON

Dinosaurs may have been forced into extinction partly because there were too
few females, say researchers in the UK. The claim revives a venerable
debate.

The creatures died out roughly 65 million years ago, around the time that a
huge meteor slammed into earth. Some scientists believe that the immense
dust cloud thrown up caused swings in the climate that the dinosaurs were
unable to survive.

However, it is not clear exactly how the temperature change killed them off.
Now David Miller of the University of Leeds and his colleagues are proposing
in Fertility and Sterility that if dinosaurs used temperature to determine
the sex of their offspring, climate changes could have messed up the ratio
of males to females.

This idea is based on the reproduction of modern day reptiles such as
crocodiles, to which dinosaurs are related. Crocodiles' sex depends on the
temperature at which their eggs are incubated. Male crocs hatch in moderate
temperatures, while females emerge if the heat rises or falls by a few
degrees.

In the case of dinosaurs, Miller suggests that changes in temperature after
the meteor impact favoured the birth of males. Over time females would
become rare, causing fewer young dinosaurs to be born and species to dwindle
to extinction. "They'd probably have had it," he says.

Read the rest at Nature
http://www.nature.com/nsu/040419/040419-11.html

Comment:
Reptiles do not have sex chromosomes, hence the heat determination of
offspring.  But birds are thought to be strongly related to dinosaurs, and
birds DO have sex chromosomes (though not the same as other animals.  Male
birds have two W chromosomes and females have a W and a Z chromosome.)

Posted by
Robert Karl Stonjek.
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