GOG TOXODOXTTA. TYPOTHERIA. 



The earliest forms are from the Cretaceous of Patagonia, but the bulk 

 are from the Eocene. They extend through the Miocene into the Pliocene 

 where the first of them, Toxodon, was found by Darwin in the Pampas 

 Formation. 



The dentition though often complete and continuous is very highly 

 specialised. The grinders are peculiar and can hardly be said to be 

 ungulate -like. The skull is massive, and high behind ; the nasals project 

 freely and are sometimes short and suggest a proboscis ; the lacrymals 

 are small -and the orbits open behind. It is difficult to say what affinities 

 the skull suggests. The structure of the fore-limbs in the form of the 

 scapula, the absence of a clavicle and the tridactyle manus, recalls the 

 rhinoceros. The same may be said of the hind limb, but the third tro- 

 chanter is small or absent, and the tarsalia are successional. These points 

 militate against perissodactyl affinities, as does the presence of a centrale 

 in the carpus. On the whole it is difficult to see why these animals 

 should have been placed with the Ungulata, unless it be because they 

 cannot be related to any other group. 



Nesodon Ow., of small or moderate size, with nasal opening directed 

 forwards ; cerebrum large and much convoluted ; *c-^pmfiii 

 almost continuous series and most of the teeth rooted ; femur with small 

 third trochanter, and feet tridactyle and digitigrade ; Eocene, Santa 

 Cruz Formation. Toxodon Ow., large animals with nasal openings further 

 back, dentition reduced i f c ^ p ^ m f , all rootless, scapula without 

 acromion, radius crossing the ulna as in Proboscidea, carpalia alternating, 

 femur without third trochanter, extremities tridactyle and plantigrade, 

 Miocene, Pliocene. 



Order 11. TYPOTHERIA.* 



Extinct pentadactyle plantigrade animals, with a clavicle, 

 an entepicondylar foramen in the humerus, serial or interlocking 

 carpus, and an opposable hallux. A centrale is present in the 

 older forms, and the grinders are rodent-like. 



If it was difficult to settle the position of Hyrax in the 

 mammalian series, it must be still more difficult to settle 

 that of the present group for all its members are extinct and 

 there is no living form to assist us with its soft parts. They 

 are generally placed with the Ungulata, though it is difficult 

 to see their ungulate affinities. They show some resemblances 

 to Hyrax, and to rodents. 



Hitherto the Typotheria have only been found in South 

 America. They are first met with in the Cretaceous, but the 



* Ameghino, Contrih. al Conoc. de los Mammi/eros de la Pepubl. Argen- 

 tina, Buenos Aires, 1889, and Revista Argentina de Hist. Nat., 1, 1891. 

 Gervais, Remarques sur le Typotherium, ZooL et Paleont. generales, 1 . 

 Lydekker, A study of extinct Argentine ungulates, Ann. Mus. La Plata, 

 Palaeont. Argentina, 2, 1893, 1894. 



