Lack of Females May Have Done in Dinosaurs

WASHINGTON (Reuters) - An asteroid may have wiped out the dinosaurs 65 million years ago not simply by changing the world's climate and causing years of dark skies, but also by causing too many of them to be born male, U.S. and British researchers say.

If dinosaurs were like modern-day reptiles such as crocodiles, they change sex based on temperature, David Miller of the University of Leeds in Britain and colleagues noted Tuesday. And even a small skewing of populations toward males would have led to eventual extinction.

Most experts agree that one or more asteroid impacts probably triggered a series of global changes that killed off the dinosaurs and many other species of life on Earth. The impacts would have kicked up dust that cooled the air and also triggered volcanic activity that would have created even more dust and ash.

No one really knows if dinosaurs were more like reptiles, or something closer to mammals. Reptiles have very different metabolisms than mammals and also have various ways of determining the sex of offspring.

In mammals, if a baby gets an X and a Y chromosome, it will be male and if it gets two X chromosomes it will be female, with a few very rare exceptions. Similar mechanisms work for birds, snakes and some reptiles such as lizards.

But in crocodilians, turtles and some fish, the temperature at which eggs are incubated can affect the sex of the developing babies.

Miller's team ran an analysis that showed a temperature shift could theoretically have led to a preponderance of males. Other studies have shown that when there are too few females, eventually the population dies out.

"The earth did not become so toxic that life died out 65 million years ago; the temperature just changed, and these great beasts had not evolved a genetic mechanism (like our Y chromosome) to cope with that," said Dr. Sherman Silber, an infertility expert in St. Louis who worked on the study.

But crocodiles and turtles had already evolved at the time of the great extinction 65 million years ago. How did they survive?

"These animals live at the intersection of aquatic and terrestrial environments, in estuarine waters and river beds, which might have afforded some protection against the more extreme effects of environmental change, hence giving them more time to adapt," the researchers wrote.

Wow, I didn't know that! It might be a useful saying when I go to certain parts of Seattle.

This theory might be as half-baked as dinosaur eggs, but it did remind me of something I've advocated for modern times. If we could come up with a simple pill to make the conception of males very much more likely, and get it out into the Muslim world, our problems of the last thousand years might be over with in a generation or two. Making sure the pill was illegal would make it nearly guaranteed that it would be used.

Seems like a good plan for Africa, and any other society that makes women into property.

But crocodiles and turtles had already evolved at the time of the great extinction 65 million years ago. How did they survive?

"These animals live at the intersection of aquatic and terrestrial environments, in estuarine waters and river beds, which might have afforded some protection against the more extreme effects of environmental change, hence giving them more time to adapt," the researchers wrote.

Paleocene hadrosaurs?

Fassett, J, R.A. Zielinski, & J.R. Budahn, 2002. Dinosaurs that did not die; evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico. In: Catastrophic events and mass extinctions; impacts and beyond. (Eds. Koeberl, C. & K. MacLeod): Special Paper - Geological Society of America 356: 307-336. (2002).

AB: Palynologic and paleomagnetic data confirm a Paleocene age for the Ojo Alamo Sandstone (and its contained dinosaurs) throughout the San Juan Basin of New Mexico. The recently reported discovery of 34 skeletal elements from a single hadrosaur in the Ojo Alamo provides unequivocal evidence that these bones were not reworked from underlying Cretaceous strata. Geochemical studies of samples from several single-dinosaur-bone specimens from the Paleocene Ojo Alamo Sandstone and the underlying Late Cretaceous (Campanian) Kirtland Formation show that mineralized bones from these two rock units contain distinctly different abundances of uranium and rare-earth elements and demonstrate that Cretaceous and Paleocene bones were mineralized at different times when mineralizing fluids had distinctly different chemical compositions. These findings indicate that the dinosaur bone from the Paleocene Ojo Alamo is indigenous and not reworked. These data show that a relatively diverse assemblage of dinosaurs survived the end-Cretaceous asteroid-impact extinction event of 65.5 Ma. The San Juan Basin's Paleocene dinosaur fauna is herein named the Alamoan fauna. Magnetic-polarity chronology shows that these survivors lived for about one million years into the Paleocene and then became extinct around 64.5 Ma. We suggest that a plausible survival mechanism for this Lazarus fauna may have been the large numbers of buried dinosaur eggs, laid just before the asteroid impact occurred. These buried eggs would have provided a safe haven for developing dinosaur embryos for the first one to two years after the impact, thereby making it possible for them to survive the worst of the impact's early devastation.

COMPELLING NEW EVIDENCE FOR PALEOCENE DINOSAURS IN THE OJO ALAMO SANDSTONE, SAN JUAN BASIN, NEW MEXICO AND COLORADO, USA.

The fully documented Paleocene dinosaur bone from the Ojo Alamo Sandstone at the San Juan River site, bolsters conclusions [5, 1] that the dinosaur-bone assemblage from the Ojo Alamo Sandstone in the vicinity of Alamo Wash is also of Paleocene age, even though vertebrate paleontologists have assigned a Lancian age to that assemblage.

"My take on the extinction of the dinosaurs? It wasn't an extinction. Megafauna dinosaur forms died out, but birds, the small fauna form of dinosaurs, survived and thrived, and mammals took over the megafauna niches."

You have a point. I, too, consider birds to be the dino legacy. However, the Cretaceous extinction did happen, and the paleontological evidence is indisputable. Many, many genera disappeared at, or near, the end of the Cretaceous. Vertebrate paleontologists, such as Robert Bakker, point out that the large dinosuars were in decline for some time prior to the Cretaceous/Tertiary (K/T) boundary. In fact, early large dino forms died out at the Jurassic/Cretaceous boundary!

I have a book on the K/T boundary that I purchased at a geological convention a few years ago. I am convinced that there is evidence for dinosaurs geologically above (younger than) the so-called asteroid impact iridium layer of Alvarez, et al., 1980. The asteroid impact may very well have happened, and may have had significant climatological effects, but it doesn't explain everything about the K/T extinction. Though the dinosaurs were greatly impacted, lizards, snakes, turtles, and crocs survived.

For instance, why did the ammonoids completely die out and yet, their close cousins, the nautiloids, survive? Why did many species of plants die out, and yet others that occupied similar niches survive? Why did the rudist bivavles go extinct as compared to the other bivalve genera?

I am very familiar (professionally) with the micropaleontology of the K/T boundary. Many diatoms, nannoplankton, and forams suddenly disappear, while others remain abundant. It can not all be accounted for by ecological niche or geographical distribution.

I suspect that with the terrestrial lifeforms, climate change, loss of habitat, and disease contributed greatly. I can easliy imagine a species or genus becoming so enfeebled that it cannot continue on. With the aquatic forms you can add change in ocean chemistry as a causitive factor. This is especially true with the micro-assemblages. Maybe what is most remarkable is that mammals and amphibians sailed right through. Why so? How were they better able to adapt?

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