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Saurs to reign for 155 million years. New fossils of the earliest of these sea dwellers are now making it clear just how they evolved so successfully for aquatic life, yet still no one knows why ichthyosaurs went extinct. Loss of habitat may have clinched the final demise of lizard-shaped ichthyo-saurs, whose inefficient, undulatory swimming style limited them to near-shore environments. A large-scale drop in sea level could have snuffed out these creatures, along with many others, by...

Caught In The

Thorough work on putatively ancient DNA from amber was done in 1998 at the University of Illinois and the Natural History Museum in London. Ancient DNA was not recovered from any specimens, though, suggesting that DNA in earlier reports may have been contaminated by DNA from living insects being studied simultaneously in laboratories. Nevertheless, the tissue preservation observed continues to astound. In 2001, working with Lynn Margulis and Michael Dolan of the University of Massachusetts at...

Fossil Locations

O PAKICETIDS AMBULOCETIDS PROTOCETIDS REMINGTONOCETIDS BASILOSAURIDS LLANOCETUS It might seem odd that 300 million years after vertebrates first established a toehold on land, some returned to the sea. But the setting in which early whales evolved offers hints as to what lured them back to the water. For much of the Eocene epoch (roughly between 55 million and 34 million years ago), a sea called Tethys, after a goddess of Greek mythology, stretched from Spain to Indonesia. Although the...

Powerfultoothed Giant Ratkangaroo

CARNASSIAL TEETH vertical blades for slicing through meat and hide-are the hallmark of a terrestrial mammalian killer. In highly specialized carnivores such as the marsupial lion and the African lion shown, a single tooth on each side of the upper and lower jaws has been modified for this task all the molars behind this carnassial are reduced or lost. (Only the lower jaw is drawn.) Generalized carnivores, such as the giant rat-kangaroos and foxes, which consume much vegetation, retain their...

Madagascar Then And

Early Triassic period (240 million years ago) FOSSIL-BEARING ROCKS drape western Madagascar. These rocks formed from the sand, mud and occasional remnants of dead animals that accumulated in valleys when the island began to separate from Africa. Early Triassic period (240 million years ago) FOSSIL-BEARING ROCKS drape western Madagascar. These rocks formed from the sand, mud and occasional remnants of dead animals that accumulated in valleys when the island began to separate from Africa....

Caudipteryx And Protopteryx

Chiappe Scientific American, February 1998 and a diversity of theropod dinosaur fossils with sharp integumentary details. Various dinosaur fossils clearly show fully modern feathers and a variety of primitive feather structures. The conclusions are inescapable feathers originated and evolved their essentially modern structure in a lineage of terrestrial, bipedal, carnivorous dinosaurs before the appearance of birds or flight. The first feathered dinosaur found there, in 1997, was a chicken-size...

And the African secretary bird

Saber Toothed Cat

Sil families the Bathornithidae, which appear in beds 40 million to 20 million years old in North America, and the Idiornithidae, found in certain European rock formations 40 million to 30 million years old. Some scientists believe these families are so closely related that they should all be grouped in the family Cariamidae. MOST OF THE TERROR birds were considerably larger than their living relatives. The creatures ranged in height from one to three meters just shy of 10 feet . The earliest...

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Dinosaurs ceased to walk the earth 65 million years ago, yet they still live among us. Velociraptors star in movies, and Triceratops toys clutter toddlers' bedrooms. Of these charismatic animals, however, one species has always ruled our fantasies. Children, filmmaker Steven Spielberg and professional paleontologists agree that the superstar was and is Tyrannosaurus rex. The late Harvard University paleontologist Stephen Jay Gould said that every species designation represents a theory about...

Switchbladelike claw on each semiopposable thumb

Megafauna Serrated Teeth Kangaroo

It was terrestrial, long-snouted and probably tended to take prey smaller than itself. It differed from placental wolves in being relatively poorly adapted for running and probably was not a pack hunter. Moreover, the morphology of its cheek teeth suggests that unlike most canids it was hypercarnivorous almost completely dependent on vertebrate flesh. Indeed, a tendency toward hypercarnivory is common to most large marsupial carnivores but not the majority of placental carnivores. This...

Approximate Maximum Diameter Of

ICHTHYOSAUR EYES were surprisingly large. Analyses of doughnut-shaped eye bones called sclerotic rings reveal that Ophthalmosaurus had the largest eyes relative to body size of any adult vertebrate, living or extinct, and that Temnodontosaurus had the biggest eyes, period. The beige shape in the background is the size of an Ophthalmosaurus sclerotic ring. The photograph depicts a well-preserved ring from Stenopterygius. ICHTHYOSAUR EYES were surprisingly large. Analyses of doughnut-shaped eye...

Helical Growth

As growth proceeds, the feather emerges from its superficial sheath. The feather then unfurls to obtain its planar shape. When the feather reaches its final size, the follicle collar forms the calamus, a simple tube at the base of the feather. As growth proceeds, the feather emerges from its superficial sheath. The feather then unfurls to obtain its planar shape. When the feather reaches its final size, the follicle collar forms the calamus, a simple tube at the base of the feather. In a...

Flaming Cliffs

Novacek, Mark Norell, Malcolm C. McKenna and James Clark The Gobi Desert of Central Asia is one of the earth's desolate places. Its million square kilometers of sand dunes, sculpted badlands and saw-toothed mountains are alternately scorched by summer's high-latitude sun and frozen by winter's Siberian winds. It is not a place to explore unprepared crossing vast, uninhabited areas between a sprinkling of oases requires careful planning akin to the siege tactics for scaling a...

Pennaceous Feather

Paired barbs fused to the central rachis create the defining vane of a pennaceous feather. In the closed pennaceous portion of the vane, tiny hooklets on one barbule interlock with grooves in the neighboring barbule detail and middle micrograph to form a tight, coherent surface. In the open pennaceous portion, the barbules do not hook together. Closed pennaceous feathers are essential for avian flight. PLUMULACEOUS DOWNY FEATHER A plumulaceous feather has no vane. It is characterized by a...

Modern Mysticete

Mesonychid Astragali

Physiological changes that allowed cetaceans to establish permanent residency in the ocean realm. Some of the earliest of these adaptations to emerge, as Pakicetus shows, are those related to hearing. Sound travels differently in water than it does in air. Whereas the ears of humans and other land-dwelling animals have delicate, flat eardrums, or tympanic membranes, for receiving airborne sound, modern whales have thick, elongate tympanic ligaments that cannot receive sound. Instead a bone...

Dawn Mist Blankets The Rain Forest

Thylacoleo Carnifex Pictures

In northeastern Australia, 15 million years ago. A bandicoot family emerges to dip snouts warily into a shallow freshwater pool. Their ears swivel, ever alert to a sudden crack or rustle in the undergrowth drinking is always a dangerous activity. Suddenly, a dark, muscular form explodes from behind a bush, colliding with a young bandicoot in one bound. The shaggy phantom impales its victim on long, daggerlike teeth, carrying the carcass to a quiet nook to be dismembered and eaten at leisure. In...

The Antarctic

Antarctic Birds

IN THE EARLY CRETACEOUS PERIOD, about 100 million years ago, Australia lay alongside Antarctica, which straddled the South Pole as it does today. Australia's southeastern corner, now the state of Victoria, lay well inside the Antarctic Circle. At that time, the region hosted an assemblage of animals and plants that lived under climate conditions having no modern analogue. The average temperature appears to have ranged from frigid to low temperate. Through the long winter, the sun did not shine...

Evodevo And The Feather

Form critical tasks as the feather unfolds to its final form. These molecular data confirm that feather development is composed of a series of hierarchical stages in which subsequent events are mechanistically dependent on earlier stages. For example, the evolution of longitudinal stripes in Shh-Bmp2 expression is contingent on the prior development of an elongate tubular feather germ. Likewise, the variations in Shh-Bmp2 patterning during pennaceous feather growth are contingent on the prior...

By Stephen Jay Gould

Ophthalmosaurus

The history of life is not necessarily progressive it is certainly not predictable. The earth's creatures have evolved through a series of contingent and fortuitous events. Cover illustration by Alfred T. Kamajian. Scientific American Special ISSN 1048-0943 , Volume 14, Number 2, 2004, published by Scientific American, Inc., 415 Madison Avenue, New York, NY 1001 -1111. Copyright 2004 by Scientific American, Inc. All rights reserved. No part of this Issue may be reproduced by any mechanical,...

How Feathers Grow

Photos Feather Cells

AS IN HAIR, NAILS AND SCALES, feathers grow by proliferation and differentiation of keratinocytes. These keratin-producing cells in the epidermis, or outer skin layer, achieve their purpose in life when they die, leaving behind a mass of deposited keratin. Keratins are filaments of proteins that polymerize to form solid structures. Feathers are made of beta-keratins, which are unique to reptiles and birds. The outer covering of the growing feather, called the sheath, is made of the softer...