Loggerhead Sea Turtle

Associated Smithsonian Expert: George R. Zug, Ph.D.

Zoologist George Zug takes a break from his fieldwork studying reptiles and amphibians while in Myanmar.

Courtesy of Jeremy Jacobs

Dr. George R. Zug is an emeritus research zoologist in the Department of Vertebrate Zoology at the Smithsonian National Museum of Natural History and one of the world's foremost experts on reptiles and amphibians of the Pacific. His current research focuses on the biology and systematics of Asian and Pacific amphibians and reptiles. He first became interested in herpetology as an undergraduate when a professor asked him to join a herpetological expedition to Cuba [pre-Castro]. He majored in biology at Albright College and then went on to obtain a master's degree in zoology at the University of Florida and a doctorate degree in zoology at the University of Michigan. The thing he likes best about studying reptiles and amphibians is excitement of discovery, whether new species or aspects about a species' biology.

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This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.

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Underside of hatchling Pacific pond turtle (Actinemys marmorata)
Courtesy of Bill Stagnaro, via CalPhotos, CC-BY-SA


About Turtles (Testudines): Growth

The shell of a hatchling turtle is flexible, because it had to curl up inside the egg. The flexibility comes from bands of soft material (sutures) where the bones join. As the hatchling grows, the soft material stiffens or disappears, and the edges of the bones get jagged like interlocking teeth, making the shell rigid. The scales of material on the top of the shell (scutes), which are made of keratin like fingernails, do not grow. Instead, new scutes are formed under the old ones. Because a turtle grows faster during warm seasons than cooler ones, the scutes form growth rings like a tree that can be counted to estimate age. Depending on the species, the count is not necessarily reliable, since many turtles shed off old scutes. Regardless, turtles are famous for their long lives, with many species living more than 100 years.