CHAPTER XVII 

 FOSSILS AND PEDIGREES 



Taxonomy and the science of palaeontology. Stratified rocks. Geological 

 record. Fossil Marsipobranchs : Ostracoderms. Palaeospondylus. Placo- 

 derms: Arthrodira and Antiarcha. Fossil Selachians: Cladoselache, 

 Climatius, Pleur acanthus, etc. Origin of Bony Fishes. Palaeopterygii : 

 Palaeoniscids, Platysomids, Catopterids, Chonodrosteids, etc. Cross- 

 opterygii: Rhipidistia, Actinistia, and Dipneusti. Neopterygii: Semi- 

 onotids, Pycnodonts, Eugnathids, Pachycormids, etc. Primitive modern 

 Bony Fishes. 



An important branch of the science of fishes is that i^known as 

 taxonomy, which is concerned with the arranging or classifying 

 in natural sequence of the multitude of diverse forms of animal 

 life together constituting the three great vertebrate classes here 

 grouped together under the general name of fishes. A century 

 or so ago any scheme of classification was mainly artificial, 

 being constructed in the belief that the world had come into 

 existence quite suddenly, and that the diflferent kinds of animals 

 inhabiting it were separately created in the beginning and have 

 remained unchanged ever since. Such a view has now been 

 shown to be untenable, and slowly and steadily a mass of 

 evidence has been accumulated which shows beyond any 

 shadow of doubt that the existing species of animals have all 

 been produced from earlier and simpler types by a process of 

 racial evolution, all life having a common origin. It has been 

 demonstrated that the birds and mammals have sprung from 

 the cold-blooded reptiles, the reptiles from the amphibians, the 

 amphibians from some of the primitive fishes, while the fishes 

 themselves have arisen from some even more primitive type 

 of vertebrate, itself presumably derived from an invertebrate 

 stock. The same evidence also shows that the fishes living 

 to-day, multitudinous and diverse as they may be, represent 

 but a proportion of the total number of fishes that have flourished 

 in the seas and rivers since they were first evolved. The existing 

 forms may be compared to the topmost and finest branches and 

 twigs of the fish "family tree"; they are the successful forms 

 that have succeeded in adapting themselves to present-day 

 conditions, and have accordingly triumphed in the struggle for 



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