Copyright 2005, all rights reserved

Egg-laying monotremes linger 110 million years, falling man goes fast

Q: What living mammalian species has been extant in its current form for the longest time? (Daniel, Durham, New Hampshire)

A platypus lumbers forth.  [Andrew Barthelmes © 2001, excerpted from If My Mom Were a Platypus, used with permission.  Please click here for a larger image
(with eggs!)] 

A: Perhaps the opossum or the hedgehog — but I doubt that’s what you’re really after.

The duck-billed platypus takes true honors although the species has only been around about 100,000 years. This creature’s basic design, however, has endured for about 110 million years — one of the longest-lived successful body plans, says Ondine Evans and Anne Musser of The Australian Museum. The champs with this good survival strategy are the egg-laying monotremes, a group that evolved about 110 million years ago in the mid Cretaceous period. See chart.

Chart: The first mammal evolved about 200 million years ago (mya) in the mid Cretaceous period. About 100 million years later, the monotremes evolved. That lineage leads, eventually, to the current-living species, the duck-billed platypus (which has been around as a species about 0.1 million years). The marsupial and placental mammals evolved after the monotremes. Homo sapiens is on the chart for comparison.

These primitive reptile-like creatures (few in numbers and, consequently, leaving a frightfully poor fossil record) dwelled in southern Earth when our present continents of South America, Africa, Australia, and Antarctica were one land — Gondwanaland.

Other groups formed branches on the mammalian tree before the monotremes but all these have ceased to exist. Only two other groups still survive — the marsupials (kangaroo-like creatures with pouches to carry the developing child) and the placentals (like us, with wombs and placentas). These two groups, though, probably evolved after the monotremes.

The duckbill platypus is a current member of the ancient monotreme group. Indeed she harkens back to an even earlier design — that of the mammal-like reptiles that predated the dinosaurs by 80 million years and lived in the late Carboniferous period, about 300 million years ago.

"The modern animal most like the mammal-like reptiles is the platypus," says Tom and Pat Rich of the Monash University Palaeontology Laboratory.

But, she clearly qualifies as a mammal although primitive:

By the way, reptiles don’t hear air-transmitted vibrations since they lack an eardrum and inner hearing bones that connect to nerves in the brain. Instead they "hear" with a bony rod that touches the base of the jaw and transmits only large vibrations, like foot falls or ground tremors, to the skull.

The platypus is an unusual mammal. She lays eggs. She waddles like a reptile with legs to the side rather underneath her body. She has a single orifice for all systems: urinary, excretory, and reproductive. That’s the origin of the word "monotreme": Mono – Greek for "one," trema – Greek for "hole." A simple, successful design.

Further Reading:

AustralianFauna.com: Platypus image

Australia’s Lost Kingdoms: Steropodon image

BBC: Science and Nature – prehistoric life

Monash University Palaeontology Laboratory: Dinosaur Dreaming

PlatypusMedia.com: If my mom were a platypus by Dia L. Michels

Q: What is an estimate of the time it takes for a falling person to go from 0 to 60? (Cal, Kelowna, British Columbia, Canada)

US Air Force Captain Joseph Kittinger drops from the edge of space and reaches a colossal 614 mph (990 km/hr). [US Air Force]

A: A falling man goes from 0 to 60 mph in about 3 seconds.

According to the Skydive! Archive, the average skydiver leaves the aircraft going horizontally at about 90 to 110 mph — the speed of the aircraft. Vertically, his speed is zero. He starts to fall, picks up speed, and accelerates to near his terminal velocity in the first 10 seconds. His terminal velocity is about 115 to 130 mph — an average 123 mph.

So, he approaches 123 mph in 10 seconds. ("A skydiver never actually reaches terminal velocity — it is an exponential approach," says Rod Nave,  physics professor at Georgia State University.) To complicate the picture, however, his acceleration during the 10 seconds of fall is not a constant. His net acceleration is the acceleration due to gravity (a constant) minus his air resistance (not a constant). His air resistance increases with the square of his velocity. So his net acceleration decreases as he falls faster.

The mathematics of this problem involves an inverse hyperbolic sine function and gets messy in a hurry. Fortunately, Nave has modeled the mechanics of a free-falling object. Plugging in the numbers (terminal velocity of 123 mph, acceleration due to gravity, air density, man’s mass, his drag coefficient, and area), we find that a falling man reaches 60 mph after a fall of 138 feet (42 m). It takes him 3 seconds.

Note: the 1994 Dauer 962 LeMans (race version of this car won the 1994 24 Hours of Le Mans for Porsche and is probably the fastest of the fast road cars) takes 2.6 seconds to go from 0 to 60.

Further Reading:

Skydive! Archive FAQ by Jerry Sobieski and maintained by Barry Brumitt

Hyperphysics by Rod Nave: Freefall from a specified height

Hyperphysics by Rod Nave: Terminal velocity calculations

WonderQuest: Terminal velocity of a falling man

Supercars.net: the fastest

(Answered Jan. 14, 2005)