December 18, 2008

Bird polygamy linked with dinosaurs

U.S. scientists say polygamous, but devoted, paternal care exhibited by male emus and other ground-dwelling birds can be traced to their dinosaur ancestors.

Researchers said they have long wondered about the origins of polygamy and paternal care patterns among modern-day Paleognathes -- an ancient avian lineage that branched off after birds evolved from dinosaurs and includes ostriches, emus and tinamous.

No such reproductive behavior exists among the majority of other vertebrates, with males contributing to parental care in less than 5 percent of mammal and non-avian reptile species, scientists said.

In the new study, paleobiologist Gregory Erickson of Florida State University and colleagues from Montana State University, the American Museum of Natural History and Texas A&M University said they connected the evolutionary dots linking the polygamous, paternal reproductive patterns of extant (living) birds to the behavior of their extinct dinosaur kin.

In those cases where adult dinosaurs have been found on top of nests, we found the volume or mass of the egg clutch is very large relative to the size of the nesting animals, Erickson said. This suggests multiple females contributed the eggs and the male guarded them. Notably, the ratio of egg volumes to the nesting animal's size is consistent with those in living birds where the male is the sole or primary nest attendant.

The research is reported in the journal Science.