History:
Over time amphibian ancestors developed shorter and shorter tails, they became the first vertebrates to have tongues, their sets of ribs decreased from 8 to few or none, and they developed a hop. When you think of animals from 100s of millions of years ago which do you think of first? Dinosaurs? Can you believe that amphibian ancestors were on land even before dinosaurs, birds, or other reptiles? It’s true. Between 370-360 m.y.a. [million years ago] sarcopterygians came onto land. Maybe it was to find new habitat to replace its drying up habitat or maybe it was to avoid aquatic predators; either way these lobed-finned fishes were among the first tetrapods, (vertebrates with four limbs). They had lungs and some other features that made them somewhat similar to amphibians, but not as similar as Icthyostega and Acanthostega. These two came around 360 m.y.a. and had more well developed skeletal systems for life on land and were also able to walk.
Then around 345-245 m.y.a. the Labrynithodonts came into existence. And, going down the chain, the Labrynithodonts later evolved into Lissamphibia, which became Gymnophiona and Batrachia. From Batrachia the Caudata and Salientia were born. And from Salientia developed the order we know and love today, Anura, but from Salientia there also was Triadobatrachus massinoti, first frog-like organism which existed about 230 million years ago. By the time of the Triassic, ~230 m.y.a., frog-like creatures where around the world and the continued to developed over the last several 100 million years becoming what we know today to be an order of frogs containing about 31 families. Even within the last few 10,000 years, during the end of the last Ice Age, frogs were still evolving. That time is believed to be when some species evolved their freeze tolerance allowing them to live in cold, northern climates.
Taxonomy:
In earlier times explorers were coming across many new species in their travels and they needed a way to name them and to count and categorize them. Luckily, during the mid-1700s there was a Swedish botanist named Carl Linnaeus who came up with an idea for a system of categorizing organisms first by general characteristics that groups of organisms have in common, and getting more and more specific until an organism could be placed in its own category. Linnaeus’ system is called taxonomy and it consists of seven main parts: kingdom, phylum, class, order, family, genus, and species.
Frogs:
Kingdom: Animalia
Phylum: Chordata
Sub-phylum: Vertebrata
Class: Amphibia
Order: Anura
Family: *there are 31 known frog families
Genus: *~360 frog genera
Species: *~5100 frog species
The taxonomy of frogs during Linnaeus’ time would have been determined by physical anatomy characteristics of frog species and habitats. Species would likely even be falsely created by combining multiple frog organisms which could not even successfully reproduce with one another. But since Linnaeus’ time science has greatly improved and genetics is also a factor in placing species in taxonomic groups.
There is even an alternate form of categorizing species called phylogenetics or cladistics. Phylogenitics is greatly dependent upon genetics for determining species relationships to one another. It starts with the most common ancestor and branches out like a tree as the amount of genetic DNA species share becomes less and less.
Works Cited:
Behler, J. L., & Behler, D. A. (2005). Frogs: A chorus of colors. New York, NY: Sterling Publishing Co., Inc.
Beltz, E. (2005). Frogs: inside their remarkable world. Buffalo, NY: Firefly Books Ltd.
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Wood frog eggs (2)
Picture taken by Erin Milligan
April 12, 2009
(above)
Mongabay.com
Rhett A. Butler - San Francisco, CA.
1999-2008.
(below)
Photo taken by Caty Jones
Wood frog pict.
Spring 2008
(above)