Transitions of Reptiles to Mammals
Transitions of Reptiles to Mammals
A long long time ago, in a galaxy not too far away, was a little blue planet called Earth, and on this world not a single mammal lived. However a lot of time has past since then and we now have lots of furry creatures that are collectively called mammals. How did they get their? Where did they come from?
These are the kinds of questions that led me to my subject of choice. I will endeavor to provide examples, using specific transitional fossils, to show that mammals have evolved from a group of reptiles and were simply not placed here by unknown forces.
Before I begin, I would like to define some terms so that nobody gets left in the dust. The term transitional fossil can be used in conjunction with the term general lineage, together they help explain the how one species became another. "General lineage":
This is a sequence of similar genera or families, linking an older to a very different younger group. Each step in the sequence consists of some fossils that represent certain genus or family, and the whole sequence often covers a span of tens of millions of years. A lineage like this shows obvious intermediates for every major structural change, and the fossils occur roughly (but often not exactly) in the expected order. However, usually there are still gaps between each of the groups. Sometimes the individual specimens are not thought to be directly ancestral to the next-youngest fossils (e.g. they may be "cousins"" or
"uncles" rather than "parents"). However they are assumed to be closely related to the actual ancestor, since the have similar intermediate characteristics.
Where Does It All Begin ?
Mammals were derived during the Triassic Period ((from 245 to 208 million years ago) It began with relatively warm and wet conditions, but as it progressed conditions became increasingly hot and dry.) from members of the reptilian order Therapsida. The therapsids, members of the subclass Synapsida
(sometimes called the
A long long time ago, in a galaxy not too far away, was a little blue planet called Earth, and on this world not a single mammal lived. However a lot of time has past since then and we now have lots of furry creatures that are collectively called mammals. How did they get their? Where did they come from?
These are the kinds of questions that led me to my subject of choice. I will endeavor to provide examples, using specific transitional fossils, to show that mammals have evolved from a group of reptiles and were simply not placed here by unknown forces.
Before I begin, I would like to define some terms so that nobody gets left in the dust. The term transitional fossil can be used in conjunction with the term general lineage, together they help explain the how one species became another. "General lineage":
This is a sequence of similar genera or families, linking an older to a very different younger group. Each step in the sequence consists of some fossils that represent certain genus or family, and the whole sequence often covers a span of tens of millions of years. A lineage like this shows obvious intermediates for every major structural change, and the fossils occur roughly (but often not exactly) in the expected order. However, usually there are still gaps between each of the groups. Sometimes the individual specimens are not thought to be directly ancestral to the next-youngest fossils (e.g. they may be "cousins"" or
"uncles" rather than "parents"). However they are assumed to be closely related to the actual ancestor, since the have similar intermediate characteristics.
Where Does It All Begin ?
Mammals were derived during the Triassic Period ((from 245 to 208 million years ago) It began with relatively warm and wet conditions, but as it progressed conditions became increasingly hot and dry.) from members of the reptilian order Therapsida. The therapsids, members of the subclass Synapsida
(sometimes called the
References: Carroll, R. 1988. Vertebrate Paleontology and Evolution. W.H. Freeman and Co., New York Gingerich, P.D. 1977. Patterns of Evolution in the Mammalian Fossil Record. Elsevier Scientific Pub. Co. Gingerich, P.D. 1985. Species in the Fossil Record: Concepts, Trends, and Transitions. Paleobiology. Rowe, T. 1988. Definition, Diagnosis, and Origin of Mammalia. J. Vert. Paleontology.