304 RECENTLY DISCOVERED TERTIARY VERTEBRATA OF EGYPT. 



lives of the two groups also agree in a number of points. Thus in 

 both there are (1) pectoral mammae, (2) abdominal testes, (3) bilo- 

 phodont molars, with a tendency to the formation of additional lobes 

 behind, (4) the same arrangement of the intestines, and (5) to some 

 extent the same character in the placenta. Altogether there seems to 

 be very good reasons for regarding the Proboscidea and the Sirenia 

 as offshoots of a common stock, the one being adapted for a terrestrial 

 the other for an aquatic mode of life. 



All the carnivora collected belong to the primitive group, the Cre- 

 odonta, and all the species can be referred to genera already known 

 from Europe or North America. A few of the limb bones found seem 

 to indicate that some of these animals had adopted a semiaquatic 

 mode of life, and it is possible that the seals originated from some 

 such type. 



Far more interesting than the Creodonts themselves is a group 

 that is now definitely knoAvn to have originated from them, namely, 

 the Zeuglodonts, usually — and probably rightly — regarded as primi- 

 tive toothed-whales. Remains of the later members of this group 

 are found Avidely spread over the world in the Eocene beds, occur- 

 ring in North America, New Zealand, and Europe. It is only quite 

 lately that any light has been thrown on the origin of these animals. 

 Prof. E. Fraas described, from the lower Middle Eocene limestones 

 of the Mokattam Hills, a skull wdiicli in all essential respects is that 

 of a Zeuglodon, but at the same time the dentition is that of a Creo- 

 dont carnivore, none of the peculiar characters of the Zeuglodont 

 teeth being present. This specimen, to which the name Protocetus 

 was given, proves fairly conclusively that the Zeuglodonts originated 

 from some Creodont ancestor Avhich acquired aquatic habits, and 

 probably this happened on the northern coasts of the Ethiopian con- 

 tinent. From beds of a little later age in the Fayum an animal 

 almost precisely intermediate between Protocetus and Zeuglodon^ 

 has been described under the name Prozeuglodon. In this creature 

 the skull approximates still more closely to that of the true Zeuglo- 

 donts, and the teeth have also acquired the serration characteristic 

 of the group, though at the same time some of the premolars and 

 molars have a third inner root, which is lost in the later forms. In 

 the upper beds of the Middle Eocene of the Fayum typical Zeuglo- 

 donts, e. g., Zeuglodont osiris, occur; so that in this region we have 

 a complete passage from Protocetus^ in which the teeth are those of 

 a Creodont, to Zeuglodon osiris, in which they are typically Zeuglo- 

 dont — that is, the molars are two-rooted and have serrated cutting 

 edges. At the same time the narial opening shifts back, and although 

 it is still well in front of the orbits and the nasal bones are long, 

 the change is in the direction of the type of skull found in the early 

 Odontoceti; and, although the relationship of these animals to the 



