Dinosaurs also are compared to those of formations whose ages are known

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Srauorrnus: Many dinosaur niunes later prove to belong to genera or species that have already been named. (Realistic dinosaur costume)In such cases the rules of zoological nomenclature demand that the first valid name nearly always be used, because this helps cut down on the confusion. Often the secondary narnes are well known, so the major qmonyrns are listed in order that the reader will not think that they have been forgotten or ignored. For example, the current title of the big tyrannosaur Alberfosoums was hardly used until recently; it used to be known by the more widely recognized Gorgosaurus.(Walking dinosaur costume)In other cases, a generic name that is appropriate for some species has been incorrectly used for others-Megoloscurus, for instance. No attempt is made to list all the minor synonyrns.

 

The type is the specimen that the species is based upon.More properly called the holotype, it can vary widely in quality. Paratypes are secondary specimens that are used to bolster the identity of the species, especially when the holotype specimen is not very good. Paratypes are not specifically indicated. The best specimen or specimens aside from the types are also listed, as are institutions in which skeletons are displayed for public view.

 

The age of a species depends on the age of the formation it is found in. This, more often than not, is not as certain as we would like. (Dinosaur costume)There are two complementary ways of aging a for mation. Briefly, if the formation has the proper material in it, usually one or more layers of volcanic ash, then it can be directly aged. This is done by measuring the relative proportions of certain radioactive isotopes in the ash. Radioactive materials “decay” at very precise rates, but sampling problems and the like still leave us with a plus or minus error of up to 5 percent, and as we go back in time a 5 percent eruor means an increasing error in absolute time.(Animatronic dinosaur) Other problems may bias the sample even more. Also-and contrary to conunon images-the age of dinosaurs was not especially volcanic compared to today, so many formations cannot be aged directly. When that is the case, then a second method is used: the fauna and flora of the formationespecially microfossils, but dinosaurs also-are compared to those of formations whose ages are known. This is best done with marine organisms, so terrestrial dinosaur formations that merge with marine formations are the most readily dateable by this method. Of course, not all dinosaur formations do this, and those that do not pose particular problems. Recently, the reversals of the magnetic poles as recorded in certain rocks have become important in aging. It is all very complicated, with many methods used on a given formation.