In the grand scheme of planetary history, 180 million years doesn’t seem that long. The “big bang” happened sometime between 12 and 14 billion years ago. Between 4 and 500 million years, fungus and plants appeared. Amphibians and reptiles emerged , leading up to the age of dinosaurs at roughly 200 million years ago.
Now ponder this snippet – it wasn’t until 180 million years that species sex was determined by an X or Y chromosome. Not possible you say? How could all those species manage without sexual determination at conception?
Even today many reptiles become male or female based on the temperature of incubation. Alligators whose eggs incubate at 30 degrees Celsius become female, incubation at 33 degrees produce males and temperatures falling in between produce some of each.
Henrik Kaessmann of the Swiss Institute of Bioinformatics published his findings in the journal Nature – tissue samples from mammals, marsupials, and egg laying mammals were studied. They compared genetic sequences of male and females, working backwards as they eliminated similarities. Keeping only sequences corresponding to the Y chromosome. I won’t even pretend truly understanding the science, but will say it’s mind boggling to ponder all those early creatures dependent on temperature for gender.