PALEONTOLOGY 861 



The chances of the ordinar}- mariiie animal persisting as a fossil 

 are decidedly slim but are infinitely better than those of a land 

 animal. Land animals are most likely to leave a fossil record in 

 some natural trap in which large numbers of individuals became 

 concentrated. "Well-known examples of this phenomenon are the 

 La Brea asphalt pits of California and the sandstones of the Dino- 

 saur National Monument in Utah. In one, asphalt underlay shallow 

 pools of water where Pleistocene mammals came to drink. The 

 larger herbivores often became mired and their cries would attract 

 their fellows and also the predatory carnivores. Many would be- 

 come trapped. The concentration of some kinds of skeletons in these 

 pits is astonishing. The hard Mesozoic sandstone from which so 

 many reptilian remains have been chiseled in the Dinosaur Monu- 

 ment was originally a quicksand which served as a trap. 



Since most finds of vertebrate fossils are fragmentary, the art of 

 reconstruction has been highly developed. An exaggerated idea has 

 become widespread that a paleontologist needs only a single bone 

 or tooth to reconstruct the entire animal. It is true that some fos- 

 sil species have been named, based on a single tooth or bone. In 

 some cases, more of the skeleton has been found or remains of other 

 individuals of the species have been turned up.* 



When the famous fossil Archaeopteryx was found in the litho- 

 graphic limestone of Solenhoffen, comparative anatomists and em- 

 bryologists already were agreed that the birds sprang from a branch 

 of the reptiles. The finding of this specimen, exhibiting a true half- 

 way stage and showing both reptilian and avian structures, started 

 another incorrect idea which has persisted to this day. This is the 

 notion commonly held by unscientific persons that paleontologists 

 are constantly searching for ''missing links." 



Another incorrect idea, spreading unfortunately to scientific circles, 

 concerns the gaps in the geological record. Admittedly, gaps still 

 exist, but they are far fewer and far less significant than they were 

 in the days when Darwin and Wallace commented so vigorously up- 

 on this matter. In fact, the major developments in paleontology 

 have been made since the daj's of Darwin and Wallace, and the 

 findings have been incorporated in the general disciplines of bio- 



•The methods used in reconstructinsr vertebrate fossils are describecl in Scott's 

 History of Land Mammals of the Western Hemisphere. 



