August 6, 1909] 



SCIENCE 



181 



the dentition of the extinct Patagonian " un- 

 gulates " and edentates, and showed in how 

 many instances they exhibit strong but en- 

 tirely homoplastic resemblances in the denti- 

 tion to mammals of the northern hemisphere. 

 The second memoir' made similar comparisons 

 with respect to the limbs and endeavored to 

 determine the pose of some of these anomalous 

 creatures. The third' showed that all the fos- 

 sil mammals of Patagonia (at least those from 

 the older formations) belonged to peculiar 

 southern groups which had followed their own 

 lines of evolution independently of the mam- 

 mals of the rest of the world. The fourth" 

 memoir developed the idea of economy in na- 

 ture. It showed that although the Patagonian 

 groups had, as stated, followed their own lines 

 of evolution, yet in many cases they had made 

 the same structural responses to changing 

 habits and conditions as had the northern 

 forms, the principal difference being that the 

 characters were never associated in exactly the 

 same combinations in northern and southern 

 groups. M. Gaudry concludes from this that 

 it is unnecessary " to admit two centers of 

 creation," i. e., that more probably both north- 

 ern and southern groups originally had a 

 common center of distribution. The same 

 memoir contained a discussion of the sequence 

 and probable time equivalents of the principal 

 mammal-bearing horizons of South America. 



The memoir on Pyrotherium, which has 

 recently appeared as a posthumous publica- 

 tion, was intended to be the first of a series on 

 Asirapotherium, Colpodon and other impor- 

 tant genera which the aged but no less pro- 

 ductive author had hoped to describe before 

 his death. 



Pyrotherium is not the least puzzling of 

 these curious forms. Its upper and lower 

 cheek teeth are of the bilophodont tjTse, that 

 is, with two straight cross crests, and they are 



'Idem, " Les Attitudes de quelques animaiix," 

 Ann. de Palinntologie, t. I., 1906 (53 text figures). 



'Idem, "Etude sur une portion du Monde ant- 

 arctique," ibid., t. I., 190G (27 text figures). 



' Idem, " De rEeonomie dans la nature," ibid., 

 t. III., 1908 (71 text figures). 



at first sight so much like those of the Miocene 

 proboscidean Dinotherium of Europe that Dr. 

 Fl. Ameghino, the original describer of Pyro- 

 therium, has regarded it as an ancestral pro- 

 boscidean. It has also a single pair of pro- 

 cumbent lower incisor tusks which grew con- 

 tinuously and had the enamel band confined 

 to the anterior surface, as in rodents and 

 early proboscideans, while the manus ascribed 

 to it by Ameghino, but later declared by M. 

 Tournouer to belong to Asirapotherium, cer- 

 tainly resembles in most characters the pro- 

 boscidean type. 



Fragmentary remains of the genus under 

 consideration are characteristic of the so- 

 called " Pyrotherium beds " of Chubut and 

 Deseado. The age of these beds is very dif- 

 ferently estimated by the leading authorities. 

 Ameghino places them in the uppermost Cre- 

 taceous, but the majority of northern paleon- 

 tologists, including M. Gaudry, are unwilling 

 to concede that the Pyrotherium beds are older 

 than the Middle or Upper Eocene. 



M. Gaudry's material, although by far the 

 most complete so far collected, still leaves us 

 with a very imperfect knowledge of the skull 

 and feet; but it includes specimens in an ex- 

 cellent state of preservation of the following 

 parts: the upper and lower jaws, with the milk 

 and permanent dentitions, the atlas, axis, a 

 cervical vertebra, a lumbar, a caudal, the lower 

 part of the scapula, and a part of the ilium, a 

 sternal bone, and fore and hind limbs com- 

 plete except for the manus and pes, which are 

 represented only by a lunar, cuneiform carpi, 

 astragalus and cuboid. 



M. Gaudry's observations upon the special 

 characters of Pyrotherium may be summar- 

 ized briefly as follows : The dentition differs' 

 in important details from the proboscidean 

 types (including Mceritheriurn) : for instance, 

 the mode of wear of the cheek teeth is entirely 

 different, the premolars are different, the milk 

 teeth are different, the section of the procum- 

 bent lower tusks shows no suggestion of the 

 peculiar proboscidean " engine turning." The 

 palate is very narrow, the orbit is placed above 

 the fourth premolar. The atlas and axis dif- 

 fered widely from the proboscidean type, the 



