SOME TRENDS OF MODERN WORK 417 



There has been for the past two decades a tendency among vertebratists 

 to keep more closely in touch with stratigraphic geology. The compara- 

 tive anatomist, especially in setting forth the evolution and specialization 

 of structures, tends to arrange his material in categories and sequences 

 that show the evolution of structures and organs, but are of course struc- 

 tural and not genetic sequences, as the animals are all contemporaneous. 

 The paleontologist, however, is dealing with true genetic sequences, exact 

 or approximate ; with the evolution of species and genera of animals, not 

 merely with illustrations of how certain structures may have evolved. 

 The time relations of his specimens must be known exactly and carefully 

 considered. This has been always to the forefront in invertebrate pale- 

 ontology. Much of the early research in vertebrate paleontology, how- 

 ever, was by men who were comparative anatomists rather than geol- 

 ogists, and the fragmentary material with which they had to deal made a 

 thorough practical acquaintance with comparative osteology the first 

 essential to its correct identification and study. It is no less important 

 today on account of the complex structure of the vertebrate skeleton ; but 

 an inevitable consequence is a certain tendency to take the anatomist's 

 viewpoint and study too much the evolution of structures and not enough 

 the actual sequence in time of the animals themselves. The corrective 

 of this tendency is a closer union with the geologists, and in the founding 

 of our Society it was hoped and expected that this would result. So far 

 as I can see, the course of American paleontology in the past two decades 

 has demonstrated the wisdom of this action. The exact records of speci- 

 mens and more careful stratigraphic studies have enabled us to define 

 horizons and diif erentiate faunas in much more precise and correct detail ; 

 and, with the far larger collections and more complete specimens, the 

 records are adequate to trace in many cases the evolution of species and 

 not merely of structures. The earlier writers on evolution did not at- 

 tempt this. Gaudiy and Hseckel, Eiitimeyer and Kowalewsky, Huxley 

 and Cope, demonstrated from the paleontologic record the evolution of 

 structure. Deperet and Schlosser, Osborn and Scott, and many others 

 have perceived and pointed out this weakness in our evidence and have 

 attempted to trace the true phyla. But it is only recently that the evi- 

 dence has been adequate to place such attempts on a really sound and 

 permanent basis, and indeed most of our work in this line is still tenta- 

 tive and provisional. Nevertheless, we may expect to see these beginnings 

 extended year by year, and the old structural phylogenies elaborated by 

 the previous generation, and scoffed at with some justice by critics as a 

 vast "schwindelbau,'^ replaced by the veritable records of the phyletic 



XXVIII — Bull. Geol. Soc. Am., Vol. 34, 1922 



