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Hyenas have baby teeth, distant mountains are sky blue, a flea is (still) champ jumper

Q: Do other animals have separate sets of baby and adult teeth? —Yiu Wai, Brooklyn, NY

Spotted hyena teeth (adult). “Spotted hyenas are born with their baby incisor and canine teeth fully erupted (poking through),” says Kay Holekamp zoology professor, Zoology Department, Michigan State University. [Photo credit:  University of Michigan Museum of Zoology]

A: Yes, most mammals (for example, wolves, cats, hyenas, dogs, kangaroos, manatees, horses, elephants, and lamas) have two sets. Our reptile-like ancestors that lived about 250 million years ago developed the two-teeth system. Earlier vertebrates had a single set of teeth and replaced a tooth whenever it broke off or wore down. Most reptiles living now do likewise so they essentially have one set of teeth.

Most mammals are born with a set of smaller, weaker teeth called milk or baby teeth. Many species, like us, get them soon after birth. A few, like rodents, jump the gun. While they’re in the mother’s womb, their baby teeth erupt, fall out, and permanent teeth emerge before they’re born.

We humans lose our baby teeth around 5 to 9 years old. Kittens and puppies lose theirs at 3 to 6 months. Frequently they swallow them.

Elephants have baby-teeth tusks that are only two inches (5 cm) long. Throughout their life, they wear out (to the gums) six sets of foot-long (30 cm) molars, grinding abrasive leaves and vines. The final set grows in when the elephant reaches 40 and wears out by 65. They starve if they outlive their teeth.

Chinese drawings from 700 B.C. show men looking in horses’ mouths to tell their age. A horse, born toothless, starts teething at day 6. Horses get their permanent teeth by age 5 years. After this time, even experts have difficulty determining a horse’s age by looking in its mouth. The old adage survives, though. Never look a gift horse in the mouth.

Further Surfing:

Phil Myers, University of Michigan, Milk teeth and the replacement of teeth

Distant mountains are sky blue

Q: If you are standing in the foothills of a mountain, you see greens, yellows, oranges, and many other colors — but, if you are about three to seven miles away, it turns blue and all the other colors are gone. What causes this bluish mountain? Is it a blue haze or is it a scattering of light reflected from the mountain?  —Michael, Corona, California

Mountains look blue for the same reason the sky looks blue. Very distant mountains look a slightly lighter blue than medium distant ones. [NOAA]

A: We see blue low-sky light when we are far from a mountain. The farther away the mountain, the brighter blue it appears. By low-sky light, I mean the layer of air between us and the mountain.

The sky is blue because tiny air molecules of oxygen and nitrogen, water molecules, and dust motes interact with light. The small sizes of these particles means that high-frequency light (like, blue) is much more likely to interact than low-frequency light (such as red). The interaction scatters blue light in all directions. Consequently, we are more likely to see blue light than any other color. Thus, the sky looks blue.

Distant dark mountains reflect little light to our eyes. Sunlight scattered by tiny molecules between us and the mountain dominates. That’s blue low-sky light. So, the blue sky makes mountains appear blue.

Further Surfing:

WonderQuest: Why the sky is blue

Rod Nave, Georgia State University: Hyperphysics, Blue sky

A flea is (still) champ jumper

Q: I just read that a spittlebug jumps twice as high as a flea. Does that make it the highest jumper instead of the flea as you said in your column (July 15)? — Anonymous

The spittle bug gets its name from white, foamy “spittle” that nymphs produce by bubbling air out the anus. They bury in the spittle to stay moist, insulated, and hidden. [Steve Mayer, Purdue University Cooperative Extension Service]

A: Relative to body size — the flea reigns supreme — jumping 100 times its height.

The spittlebug (a small farm pest) does jump twice as high as a flea. However, the spittlebug is 6 times bigger than the flea. To out-jump the flea (relative to its size), the spittlebug must jump 6 times higher and he only jumps 2 times higher. The flea wins.

Further Surfing:

WonderQuest, Pumas jump highest:

USA Today: Study finds spittlebug can jump twice the height of a flea

Purdue University: Spittlebugs

(Answered Aug. 29, 2003)