INTRODUCTION TO MAMMALIAN PALEONTOLOGY 



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ProtitartotfieriuTrh emargrinaticm. 



Upper Eocene ( upper Uinta) 



Manteocems manteoceras 



Middle Eocene (upperBridger) 



Zimnohyops priscus 



M/ddle Eocene (lowerBridger) 



Eotitanops borecdzs 



Lower Eocene (Wind River) 



Figure 29. — Evolution of the skull and molar teeth in the titanotheres 



In EoUtanops the facial part of the skull is longer than the brain case (cranium). In Brontotherium the face is very short and the brain 

 ease is very long. The horn swellings (H) first appear in Manteoceras and become very prominent in the succeeding stages. The top of 

 the skull becomes deeply concave. The outer wall and the V-shaped cusps of the upper molar teeth (paracone, metacone) become 

 very deep, while the inner cusps (protocone, hypocone) retain their low, conical form. The lower molars retain the W-shaped crown 

 throughout, which increases considerably in depth. 



