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Endangered Species - The Hawksbill Turtle

The hawksbill turtle's status has not changed since it was listed as endangered in 1970. It is a solitary nester, and thus, population trends or estimates are difficult to determine. The hawksbill is a small to medium-sized sea turtle. The following characteristics distinguish the hawksbill from other sea turtles: two pairs of prefrontal scales; ...

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EndangeredSpeciesHawksbillTurtle
Geology

Is The Sea Really On The Level?

When we measure the height of mountains, we measure from a constant number called sea level. For instance Mount Whitney in California is 14,494 feet (4,418 m) above sea level. We start at 0 feet and ... Continue reading

SeaLevel
Astronomy

Mercury

The small and rocky planet Mercury is the closest planet to the Sun; it speeds around the Sun in a wildly elliptical (non-circular) orbit that takes it as close as 47 million km and as far as 70 ... Continue reading

Mercury
Astronomy

Ancient Planet

Long before our Sun and Earth ever existed, a Jupiter-sized planet formed around a sun-like star. Now, almost 13 billion years later, NASA's Hubble Space Telescope has precisely measured the mass of ... Continue reading

AncientPlanet
Astronomy

Exercising In Space

What did astronaut Shannon Lucid like least about her six months on Space Station Mir? The daily exercise. 'It was just downright hard,' she wrote in Scientific American (May 1998). 'I had to put on a ... Continue reading

ExercisingInSpace

How Does The Turtle Get Its Shell?

HowDoesTheTurtleGetItsShellMany invertebrates, such as beetles and lobsters, have shells, but the turtle is the only living vertebrate with a shell (except for the armadillo or course). A turtle's top shell is called the 'carapace', and the matching bottom shell is called the 'plastron.' How does a turtle get his pair of protective shells? Why he grows them of course!

While still inside the egg, a turtle embryo begins to look different from other vertebrates. Instead of curving around to form the familiar rib cage, the turtle embryo's ribs grow straight out from its backbone to form the oval framework of the carapace. The rest of the carapace is formed from calcified tissue deep in the skin of the back. This hardened layer is called dermal bone, and it grows around and fuses to the framework of ribs.

The lower shell, or plastron, is also made of calcified dermal tissue. The front part of the plastron, under the neck, is formed from the shoulder bones, called clavicles (these are dermal too). The rest of the plastron is made of dermal bone. The picture shows that even before it hatches, a baby turtle has begun to form its shell. When it hatches it will look just like an adult turtle, shell and all, only smaller.