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How was the sex of dinosaurs determined?
In the book, "The Red Queen", Matt Ridley mentioned several ways that the
sex of animals is determined.
In mammals, 2 X chromosomes make a female. In birds, 2 X chromosomes are
required to develop a male. In both, the Y chromosome have greatly diminished
(Is the X only called the X because it is longer?).
In alligators, warm eggs hatch into males. In Crocodiles, intermediate
temperature hatches into males. In iguanas, XY is Male. In snakes, XY is
female. Some fish change from female to male if they are large and no males
are present. In some life forms, unfertilized eggs are male. In others, there
are male and female parts (hermaphrodites).
How was the sex of the dinosaur determined? Were vast nesting grounds
around river elevations and the use of plant material to generate heat
suggestions that temperature might possibly have been used to determine the sex
in some species, as presumably was the ancestral condition like that was found
in crocodilians. Different sizes of the sexes might suggest the larger sex was
from the warmer egg.
Or, were they more like birds? This would seem to make sense as it
presumably would have allowed dinosaurs to get away from heat determination and
allow them to raise young of both sexes at many more locations and climates,
especially away from rivers and streams where warm water adapted predators
In fact, might this not be one reason that a replaceable toothed predator
could have occupied new niches at the climatic boundaries at the expense of its
heat determined cousins. Might it have allowed early dinosaur ancestors to
occupy the same ecological niches as early mammals (who may have also initially
expanded their range and domination for the same reason), putting them in
competition where their replaceable teeth would be an advantage? Did this sex
determination allow the ancestors of birds (or later generations of birds) to
build nests and hatch eggs in trees? For that matter, did sex chromosomes aid
in the sucess of lizards and snakes (compared to similar animals)?
How could a cladistic analysis show the importance of such an evolved
ability (if there is one)? This appears to be cladistics problem with enhanced
metabolism, flow through lungs, 4 chamber hearts, live birth, food digestion
help with the use of gastroliths, immune system improvements, and other
boneless modifications in extinct animals.
Has anyone looked into the determination of sex in regards to dinosaurs?
Does anyone have any opinions on how the sex was determined? Do any sexual
dimorphisms shed any light?