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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 
lived. 
   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?