344 PRINCIPLES OF ANPMAL BIOLOGY 



became bent in various Avays, at least at their edges, so that the sutures 

 were curved or anguhir (see Fig. 293). Forms whose sutures were of 

 this curved and angular form are called goniatites, and they were al)un- 

 dant in the Carboniferous period. These were to a large extent super- 

 seded in Triassic time by other genera, still tightly coiled but with sutures 

 thrown into a number of regular curves and sawteeth, which may be 

 described as "crooked." These forms with crooked sutures are known 

 as ceratites, from a very common genus keratites. And finally, in the 

 forms known as ammonites, the sutures became finely crimped in a com- 

 pound fashion, often producing exquisite foliaceous patterns. Fossil 

 ammonites are most abundant in the Jurassic to Cretaceous strata. 



Though there were many irregidarities and overlappings in the series 

 of tetrabranchiate cephalopods, the fossils show on the whole clear evi- 

 dence of progress from a straight shell to one tightly coiled, and from 

 nearly straight sutures to sutures that were bent, angular, crooked, and 

 finely lobed. 



Prehistoric Man. — The human line of evolution is not comi)lete 

 enough to offer as an example of such lines, but it has an extraordinar^y 

 appeal to the modern representatives of it. Man is one of the ortler 

 of primates, other members of which are the lemurs, monkeys, and 

 manlike apes. There is some reason to believe that the primates evolved 

 from the insectivores, the group to which moles and shrews belong. 

 If a series of fossils were available to show human evolution, it should, 

 assuming our surmises to be correct, lead from the insectivore t,ype, 

 through forms resembling lemurs, monkeys, and apes. The later stages 

 of this series would be especially useful as connecting the apes with man. 

 Unfortunately, not man.y primate fossils have been foimd. The probable 

 reason for the lack of fossils is that the primates have been tree-dwellers. 

 Dead individuals would have dropped to the groiuid, and forested areas 

 offer little chance for burial under either wind- or water-borne material. 

 Fossils of man himself were not preserved in numbers until burial customs 

 arose. As a result of these customs, more fossil men are known than 

 fossil apes. Kinship of man and the apes must therefore be judged 

 largely from homologies. Paleontology can begin to h(>lp only after 

 considerable divergence has occiu-red. Nevertheless, the earliest man- 

 like fossils show unmistakable leanings toward the ape structure in 

 certain respects. 



One of the most primitive of the fossils appearing to connect man 

 with the apes, a form usuall}^ regarded as belonging to middle Pleistocene 

 tim(;, is Pilhccanthropus crectus, uncovered in some excavations in 1891 

 hi Java by a Dutch army surgeon. A femur, parts of the skull, and 

 several teeth were in the original find, and parts of several skulls and 

 jaws and additional teeth have been added from near-by locations since. 



