Article VIII.— THE FOUR PHYLA OF OLIGOCENE 

 TITANOTHERES.' 



TITANOTHERE CONTRIBUTIONS, No. 4.'^ 



By Henry Fairfield Osborn. 



My first review of this group, entitled 'Cranial Evolution 

 of Titanotherium ' (Titanotherium Contributions No. 3), was 

 based upon examination of only part of the original material; 

 it included a preliminary revision of the species by the dis- 

 tinction of growth, sexual and variable characters, and by 

 the method of sections of different parts of the skull. 



Two errors invalidated this review. First, the stratigraph- 

 ical or geological sequence of the types examined was not fully 

 known, and, second, as a consequence, the group was treated 

 as more or less monophyletic with certain side branches. 



This second review is an abstract of a portion of the results 

 obtained for the U. S. Geological Survey monograph, ' The 

 Titanotheres,' now in preparation. It covers practically 

 all the type material in the Yale, National, American, and 

 Harvard Museums, and advantage has been taken of the 

 invaluable field observations by Hatcher of the levels on 

 which the different skulls in the National Museum collection 

 were discovered. The section method also has been very 

 greatly extended and, taken in connection with the teeth and 

 the detailed structure of the skull, has proved to be a sure 

 criterion of specific and phyletic character. 



Beginning in January, 1901, the work for the monograph 

 advanced uninfluenced by any theory as to the evolution of 

 these mammals until finally, in July, all the data were put 

 together with most interesting results, which may be briefly 

 summarized as follows: 



' The late Professor O. C Marsh of Yale University devoted many years to the 

 collection of materials and preparation of plates and figures for a monograph on the 

 group treated in this paper. He also completed several valuable papers, but left no 

 manuscript. Full acknowledgment of this important service to palaeontology will be 

 made by the writer in the final treatise. 



° See contributions 1-3 in Bibliography. 



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