What do today’s body-building studs and 125-million-year-old birds have in common? They are both playing into sexual dimorphism in order to find a hot date. Sexual dimorphism is the difference in morphological appearance between males and females of the same species. Think Lion King: Simba’s father sported a big bushy orange mane, whereas his mother had no showy neck fur to speak of. Many species today adhere to this rule: male elks grow antlers, their female counterparts do not; male mallard ducks have shiny green heads, their girly pals, however, are a simple gray/brown shade. In most cases, the male exhibits a more extravagant appearance in order to better attract a female mate. It’s an evolutionary advantage—whoever can better find a mate can better reproduce and therefore that organism’s genes are passed along. According to a recent study in the journal Nature Communications, an ancient bird species exhibited sexual dimorphism too.

Anusuya Chinsamy-Turan, from the University of Cape Town in South Africa, and Luis Chiappe of the Natural History Museum of Los Angeles County’s Dinosaur Institute, authored the research that analyzed the bones of a 125-million-year old bird species called Confuciusornis sanctus. The fossils were discovered in northeastern China, in what was once a forest studded with lakes. In lake deposits, scientists found hundreds of specimens that were clearly segregated into two groups: one group of fossils had long, elaborate tail feathers; the other group did not. Scientists surmised this could be due to sexual dimorphism—but there was no way of knowing for sure until Chinsamy-Turan and Chiappe’s study found something very interesting. In the fossils that lacked the showy feathers, the researchers discovered medullary bone—a type of bone only female birds have that helps in the production of eggshells, thereby providing undeniable evidence that males had the ostentatious plumage to attract mates, while females did not.

The researchers’ excitement didn’t stop at discovering evidence of sexual dimorphism. They also found that medullary bone existed in specimens whose skeletons were not yet fully mature. Birds today mature sexually at a similar pace to their bone maturity, meaning they can’t reproduce until their skeletons are fully-grown. It seems that this ancient bird could reproduce before the skeleton was fully mature, similar to large dinosaurs. Not only does this study give scientists insight into mating patterns from long ago, but it gives credence to the widely-accepted theory that birds evolved from dinosaurs.

Discover more about this ancient bird at www.livescience.com.

Find the scientific study in the journal Nature Communications.

The Paleontological Research Institution, Ithaca, New York, is pleased to sponsor Paleontology content for This View of Life. Founded in 1932, PRI has outstanding programs in research, collections, and publications, and is a national leader in development of informal Earth science education resources for educators and the general public.

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Published On: January 28, 2013

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