September, 1928 



EVOLUTION 



Page Five 



The Animals of the Past 



By Frederick A. Lucas. Honorary Director, American Museum of Aalural History 



THE object of these articles is to tell some of the 

 interesting facts about the better known and more 

 remarkable of the extinct inhabitants of the ancient 

 world and to ease the strain on these venerable creatures 

 caused by stretching them so often beyond their due 

 proportions. 



The author expects to be taken to task for the use 

 of scientific names, but people who call for easier names 

 should reflect that such names are no harder than others, 

 simply less familiar, and when domesticated, cease to be 



hard; witness mammoth, ele- 

 phant, rhinoceros, giraffe and 

 boa constrictor. Again, one 

 just must use the scientific 

 names for the periods in 

 which these animals lived — 

 Jurassic, Eocene, Pliocene — 

 because there is no other way 

 lo do it. 



The restorations of extinct 

 inimals are according to our 

 best knowledge and may be 

 considered as accurate as it 

 is possible to make them. The 

 Dr. Frederick A. LircAs cuts are largely from the 

 Courtesy S. Ichikawa rich collection of the Ameri- 

 can Museum of Natural 

 History which contains more complete specimens of 

 fossil vertebrates than does any other. 



L How Fossils Are Formed 



Fossils are the remains or indications of animals or 

 plants that have, through natural agencies, been buried 

 in the earth and preserved for long periods of time. 

 It is not essential that the organic matter be replaced 

 by some mineral to be classed as a fossil, for the Siberian 

 Mammoths, found entombed in ice, are very properly 

 called fossils, although the flesh of one was so fresh 

 that it was eaten. Many fossils, however, merit the 

 name "petrifications" because they have changed into 

 stone by the slow removal of the organic matter and its 

 replacement by some mineral, usually silica or lime. 

 It is also necessary to include "indications of animals 

 and plants" in our definition because we sometimes learn 

 most from mere impressions, such as those of leaves, 

 made in soft mud or smooth sand which later hardened 

 into enduring stone. Such, too, are ripple marks and 

 imprints by raindrops, the trails of creeping and crawl- 

 ing things, casts of worm burrows, footprints of reptiles. 

 Fine mud, now become rock rivalling porcelain in tex- 

 ture, may bear the imprint of a bird's feathers, of a 

 reptile's skin, of each fin ray and every thread-like bone 

 of a fish, or perhaps such soft, delicate objects as jelly 

 fishes. Without some of these, we might have little 

 positive knowledge of the outward appearance of many 

 animals of the past. 



The reader may wonder why fossils are not more 



abundant; why not a trace remains of the vast majority 

 of the animals that have lived upon the earth. The an- 

 swer is that, unless conditions were such as to preserve 

 ar least the hard parts from immediate decay, there was 

 small possibility of an animal being fossilized. The 

 object must be protected from the air and practically 

 the only way this happens in nature is by being covered 

 with water or buried in wet ground. If a bone lies 

 exposed to sun and rain, frost and snow, these destruc- 

 tive agencies soon reduce it to powder. Even in a dry 

 climate, mere changes in temperature, by producing 

 expansion and contraction, soon cause a bone to crack 

 and crumble. Carnivorous animals, such as our dogs 

 or hyenas, are great bone destroyers, as are rats, mice 

 and other small rodents that attack bones for the grease 

 they contain or just to exercise their teeth. Plant root- 

 lets also enter the bone fissures, expand as they grow 

 and thus act as little wedges to force it asunder. 



If the body sinks to the muddy bottom of a lake or is 

 caught in the sandy shoals of a river, the chances are 

 good that its bones will be preserved. The chances 



Tracks of Dinosaur feet and dragging tail across ripple 

 marked sand, turned to stone. 



Courtesy Am. Museum Nat. Hist. 



are poorer in the ocean, for the waves pound them 

 to pieces witii stones or scour them away with sand, 

 v/hile marine worms and starfishes pierce and cut them. 

 There are more enemies of a bone than one would 

 imagine. But in a quiet lake, the fine mud settles gentlv 

 as dew on grass. Little by little the bones are covered 

 by a deposit that fills and preserves each groove and 

 pore, and eventually buries them as deep as you please. 

 Engulfment in quicksand is perhaps the best way of 

 all, for the body is then supported without crushing. 

 At least two examples of the dinosaur Trachodon have 

 been found with the bones all in place, the thigh bones 

 iti their sockets and the ossified tendons ruiming along 

 the backbone as they did in life. 



