Animals Before 2Ian 



perfect jaws, and these are all we find until 

 much later on. These specimens indicate small 

 animals, ranging from the size of a mouse to 

 that of a rat, and without exception flesh-eaters 

 or insect-eaters. Some were related to the mar- 

 supials, while others were relatives of those 

 egg-laying mammals, the echidna and platy- 

 pus,"^ in spite of the fact that these have no 

 teeth. But study of the very young stages of 

 platypus has shown that teeth are then present, 

 and while these fail to develop, their presence 

 indicates that teeth existed and w ere used by 

 the far-distant ancestors of these animals. 



Owing to the numerous small points or tu- 

 bercles on the grinding teeth of these Jurassic 

 monotremes, the order in w hich they have been 

 placed has been named Multituberculata. 



The jaws of some of these little multituber- 

 culates show a very curious set of teeth ; two 

 in front, something like the lower teeth of a 

 rat and back of these three that seem made for 



* Recently some doubts have been cast on the egg-laying habits 

 of the platypus, and although eggs are found in these animals, it 

 is thought that they may be retained until hatching. 



188 



