50 



SCIENCE. 



[Vol. XXII. No. 547 



As a word of introduction I would remark that most of the re- 

 mains from the Puerco are in a poor state of preservation, and 

 this applies particularly to the skeleton. The teeth are often 

 well preserved, so that in working out the affinities of these 

 mammals we are generally dependant upon the character of the 

 teeth to discover their relationship to other forms. A very strik- 

 ing peculiarity in the dentition of the Puerco mammals, as 

 pointed out by Professor Cope, is the fact that their superior mo- 

 lars are generally of the tritubercular pattern, and these upper 

 teeth are associated with inferior molars, which are tubercular- 

 sectorial, or a modification of the latter. In the tubercular-sec- 

 torlal tooth the anterior portion is raised above the posterior or 

 talon, and consists of three elevated cusps. By the modification 

 of the latter pattern of molar, both the highly speciahzed secto- 

 rial tteth of the Carnivora and the quadritubercular teeth of the 

 Ungulates have been derived. 



In general we may say that, besides the characters of the teeth, 

 the mammals of the Puerco epoch, in their skeletal structures, as 

 far as known, are of a decidedly primitive type. The skull is 

 short and heavy, vpith the orbit well forward over the teeth; the 

 various processes of the skull for muscular attachment are 

 prominent. Correlated with their low structure in general was 

 the exceedingly small brain, as illustrated by the genus Perip- 

 tychus. As the structure of the skeleton in the latter genus is 

 the best known, I will enumerate some of its characters. The 

 feet of Periptychus were plantigrade. The hind foot had five 

 toes, the external one being not much shortened. The struct- 

 ure of the astragalus is well known in Periptychus and im- 

 portant, as teaching us one of the characters of the structure of 

 the primitive foot in general. This bone is short and strongly 

 depressed ; the neck of the same is short and heavy. In all mod- 

 ern mammals which ;are digitigrade the trochlear surface of the 

 astragalus, articulating with the tibia, is deeply grooved, whereas 

 in Periptychus this surface is plane and flat. Another very im- 

 portant and primitive character of the astragalus in Periptychus 

 is that it is perforated by a well-marked foramen. I am not 

 aware that this perforation of the astragalus occurs in any recent 

 Ungulate. The astragular foramen is of constant occurrence in 

 Puerco mammals and also is present in some of their descendants 

 in the Wasatch (Coryphodon) . ~ 



In one respect the foot of Periptychus is more advanced than 

 that of the genus Phenacodus, which is from a later formation 

 (Wasatch) ; I refer to the articulation of the cuboid bone with 

 the astragalus, but in general the foot structure of Phenacodus is 

 far advanced in its evolution over that of Periptychus. Phena- 

 codus was a digitigrade mammal, with the outer toes much 

 shorter than the median. The long bones of the skeleton in 

 Periptychus are short and heavy ; this applies particularly to the 

 humerus, which is an exceedingly heavy bone; its distal extrem- 

 ity is perforated by an entepicondylar foramen, another primitive 

 character of this genus. The character of the humeral condyles 

 in Periptychus is peculiar and different from all modern Ungu- 

 lates. In the latter group the trochlear surface of the humerus is 

 interrupted by a strong ridge separating the external from the 

 internal articular surface. Now in Periptychus, as well as in 

 Phenacodus, there is no such interruption of the condylar sur- 

 face of the humerus, and it has the same character as in the mod- 

 ern Carnivora, thus showing how these two widely separated 

 orders at the present time approach each other in their osteolog- 

 ical characters in the Eocene. The ulna and fibula are large in 

 Periptychus and more nearly approach the size of the bones of 

 the preaxial side of the limbs than in modern forms. 



Now the question arises, what great groups of mammals of 

 later epochs than the Puerco are represented in this formation. I 

 think that we may safely say that there were only a few main 

 stems of Puerco mammals which persisted until later periods, 

 and I shall endeavor to show that these stem forms were the di- 

 rect ancestors of later types. As in so many cases, in seeking to 

 determine phylogenetic relationships, we must turn to the inves- 

 tigations of Professfir Cope to decide this question in part at 

 least. He has described mammals from the Puerco which be 

 considers to be Ungulates in their affinity, others to be related to 

 the Carnivora, and still other types which resemble the Lerau- 



roidea in the structure of their teeth. As I am only dealing with 

 the Ungulates in this paper I shall speak of certain genera which 

 Professor Cope and other paleontologists have determined to be 

 closely related to this group. 



The group of primitive Ungulates which Professor Cope has 

 designated the Condylarthra is not a very homogeneous one, it ap- 

 pears to me, and perhaps with Schlosser we had better speak of a 

 condylarthrous stage, through which all Ungulates are supposed 

 to have passed rather than to attempt to confine these early 

 forms all in the suborder Condylarthra. At least as shown by 

 Professor Osborn, the characters laid down by Professor Cope as 

 limiting the Condylarthra, would not include some of the forms 

 (Periptychus) which Professor Cope has embraced in this sub- 

 order. 



When we attempt to separate the Ungulates from the Ungui- 

 culates of the Puerco we are met with the obstacle that in most 

 cases the distal phalanges of the feet have not been preserved. 

 Accordingly we are dependant upon the character of the denti- 

 tion to diagnose and separate these two groups. However, so 

 low down geologically speaking as the Puerco, the different 

 groups of Ungulates are not supposed to be distinctly differenti- 

 ated, and then again in most cases the structure of the skeleton, 

 and especially of the carpus and tarsus of these forms, is totally 

 unknown. I believe, however, that the stems leading to the 

 main types of the Ungulates which we meet with in the Wa- 

 satch, are fairly well separated in the Puerco, and more so than 

 has been generally accepted. For example, when we consider 

 another group other than the Ungulata, the Creodonta, we find a 

 number of well-marked families of this order in the Puerco, 

 which are distinct and lead up in some cases to types of later 

 epochs. The Creodonta, with low-crowned, purely bunodont 

 teeth, such as are included in the Triisodontidte, the more spe- 

 cialized and trenchant dentition of the Provivirridss (Deltathe- 

 riiiin), and again the low-crowned and nearly quadritubercular 

 lower molars of the Arctocyonidee (Claenodon, Scott). The last- 

 named genus is very likely the ancestor of the Wasatch {Anaco- 

 don). 



Turning again to the Ungulates, what are the types of this 

 order which we can distinguish in the Puerco? To attempt to 

 decide this question we must rely on the characters of the teeth 

 in nearly all cases. To ascend to the mammals of the Wasatch 

 period for a moment we observe in that formation the Perisso- 

 dactyles are distinct from the Artiodactyles. The former group 

 has superior molars with six cusps, which may be either distinct 

 or fused; the lower molars are quadritubercular. In the Artio- 

 dactyles of the Wasatch the superior molars are of the trituber- 

 cular pattern and the lower teeth are sexitubercular, or more 

 nearly of the primitive tubercular-sectorial type already men- 

 tioned. Again, the premolars of the Perissodactyles are more 

 complex than these of the Artiodactyles. Returning to the 

 Puerco we find the same state of things well foreshadowed, al- 

 though these two stems may have not passed the condylarthrous 

 stage. In the genus Euprotogonia {= Protogonid), we have the 

 supposed condylarthrous representative of the Perissodactyles, 

 and in the genus Protogonodon of the Puerco I believe we are 

 dealing with an ancestral Artiodactyle. I am aware of the fact 

 that the skeletons of these two genera are totally unknown, so 

 until they are discovered we will be unable to say whether these 

 two forms were true Condylarthra or if they had assumed more 

 of the characters which are typical of the two great divisions of 

 the Diplarthra. I think that from a study of the teeth of the 

 above genera that the two lines of the Diplarthra were fairly 

 well separated even in the Puerco. 



The upper true molars of Euprotogonia in the typical form, E. 

 puercensis, consist of six tubercles. The superior premolars are 

 simpler than in Phenacodus. A character of the upper molars of 

 Euprotogonia, and separating it well from Phenacodus, is the ab- 

 sence of the parastyle and mesostyle. When we study the struct- 

 ure of the lower teeth in Euprotogonia, we are surprised to find 

 them so highly developed for a Puerco form. The last lower 

 premolar is nearly as complex as it is in the Wasatch Phenaco- 

 dus, and in the typical species the crescents of the inferior true 

 molars are as plainly marked as in the last-named gpnus. In 



