Endangered Species Handbook

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It's Too Late

Introduction

      Skeptics ask why it should matter whether the tiger (Panthera tigris) or other endangered species become extinct.  Aren't all extinctions natural events?  Yet enormous differences exist between the extinctions of the dinosaurs and other animals that faded out eons ago and those of recently disappeared species.  Dinosaurs proliferated into a great diversity of species and dominated other life over a period of many years.  Some dinosaur families endured tens of millions of years on Earth ‒ others far less ‒ before fading into extinction.  It is difficult to grasp the reality of their immense sojourn, as some species existed for only a hundred thousand years.  The Ornithischia, one major group of dinosaurs, had an enormous number of living species 135 million years ago at the dawn of the Cretaceous Period, but slowly died out over the next 60 million years.  The last of the line became extinct some 65 million years ago as the last of the dinosaurs expired. 
 
     Extinctions of dinosaurs and millions of other species that disappeared from Earth at that time were natural in origin.  These extinctions had many causes; changes in climate resulting from meteors colliding with Earth may have killed off the last dinosaurs.  Many scientists believe the impact raised a dust cloud that blocked sunlight and reduced the enormous amounts of vegetation needed by the dinosaurs, and it may have cooled the climate as well.  Another major cause of ancient extinctions was the movement of the Earth's tectonic plates, which broke up huge land masses into smaller ones.  Some species became isolated on islands too small for their habitat requirements, and stronger species caused the extinctions of weaker or less adaptable species when continents were joined.  Continents and islands moved into different climate zones as well.  The Earth's climate and atmosphere have undergone major changes over the ages and species that could not adapt have fallen into extinction.  Volcanic eruptions have spurred extinctions by inundating land with lava and cooling the climate with dust.  Islands produced by volcanic eruptions have risen from ocean bottoms, become covered with vegetation and home to unique wildlife, only to sink into the sea some time later.
 
     In the past, ecological roles left empty by extinctions were soon filled by the evolution of new species.  After the last of the dinosaurs died out some 65 million years ago, mammals and other animals proliferated on Earth.  The overall diversity of species remained stable or increased.  At present, however, diversity of life on Earth is in steep decline as species are dying out without being replaced. 


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    ©1983 Animal Welfare Institute