BIOLOGICAL EXTINCTION DUE TO COMPETITION. During all these changes, as the result of the struggle for existence, the competition between the outgoing aid the incoming types and floras and faunas, there resulted vast biological changes, i.e. extinctions and re-creations.
In summing up the grand results of the Ap palachian revolution and of the times immedi ately succeeding, Packard states that we should not lose sight of the fact that the changes in the earth's population were due to biological as well as geological and topographical factors. The process of extinction was favored and hastened by the incoming of more specialized forms. many of them being carnivorous and destructive. For example, nearly all fishes and reptiles live on other animals. The struggle for existence be tween those which became unadapted and useless iu the new order of things went on more actively than at present. The process of extinction of the higher, more composite amphibians (the laby rinthodonts) was largely completed by the multi tude of theromorphs and dinosaurs which over came the colossal Cheirotheriutu, Mastodonsau rus, and their allies. Woodworth also states that "the exact cause of their decline is prob ably to be sought in the development of the more powerful reptiles." The demise of the ornitho saurs or pterodactyls was assisted, says Pack ard, in two ways: Those with a feebler flight succumbed to the agile, tree-elimbing dinosaurs; while the avian type, waxing stronger in num bers and powers of flight and exceeding in intelli gence, exhausted the food-supply of volant insects, and drove their clumsier reptilian cousins to the wall, fairly starving them out; just as at the present day the birds give the bats scarcely a raison (Vitra.
At the close of the Jura-Trias period there was a widespread extinction of I he peculiar coniferous plants of the Mesozoic, and they were succeeded by forests of deciduous trees of modern types. Vast forests of deciduous trees, such as the oak. sassafras, poplar. willow, maple, elm, beeeh, chestnut, and many others, as well as of conifers and palms, clothed the uplands, while in the jungles, on the plains, and in the openings of the forests, gay flowers bloomed. The flora must
even then have been comparatively speaking, nee of long existence, because highly 1:11(•I1 composite plants, like the sunflower, occur in the Upper Cretaceous or Raritan clays of the • IP l'St'y mat.
While the changes of leuel did not a ffeel the abysses of the sea, the topography of the shah and ielast urns modified, and to this was perhaps largely due the extinction of the ammonites and their allies.
In 11062 Wood more fully discussed this mat ter, and mentioned the same cause as suggested by Packard. **This disappearance." says Wood, of the Ammonitid.e, and preservation of the autilithe, we may infer was clue to the entire change which took place in the condition of the shores at the close of the Cretaceous period this change was so complete that such of the shore-followers as were unable to adapt them selves to it succumbed, while the others that adapted themselves to the change altered their specific characters altogether. The Nautilida having come into existence long prior to the in troduction of the Ammonitidu, and having also survived the destruction of the latter family, must have possessed in a remarkable degree a power of adapting themselves to altered condi. tions." (ln the other hand, the dibranehiate cephalopods (euttles or squids), living in deeper water, being 'ocean-rangers.' were quite inde pendent of such geographical changes. Wood then goes on to say that the disappearance of the tetrabranchiate group affords a clew to that of the Mesozoic saurians, and also of cestraciont sharks, whose food probably consisted mainly of the tetrabranchiate cephalopods. "Now the dis appearance of the Tetrabranchiata, of the eestra. eionts, and of the marine saurians, was contem poraneous: and we can hardly refuse to admit that such a triple destruction must have arisen either from some common cause or from these forms being successively dependent for existence upon each other." Woodworth suggests that mammalian life in the Mesozoic age was unfavorably affected by the nature of the peneplain of the Atlantic coast and by reptilian life.