xx. 3 CLASSIFICATION 563 



The fact is that marsupials, having radiated perhaps over 60 million 

 years ago, present us today with a number of distinct types of 

 organization. Simpson groups them into six superfamilies and it is 

 perhaps better not to attempt any higher grouping of these. The 

 absence of Australian Tertiary deposits before the Pleistocene in- 

 creases the difficulties of study of marsupial phylogenesis. 



Infraclass 2. Metatheria 

 Order Marsupiala 

 Superfamily 1. Didelphoidea. Upper Cretaceous-Recent. Europe 

 and America 

 *Eodelphis. Upper Cretaceous, N. America; Didelphis, opos- 

 sum, Pliocene-Recent, N. and S. America; Chironectes, water 

 opossum, Central and S. America 

 *Superfamily 2. Borhyaenoidea. Palaeocene-Pliocene. S. America 



*Thylacosmihis, Miocene; *Borhyaena, Oligocene-Miocene 

 Superfamily 3. Dasyuroidea. Pleistocene-Recent. Australasia 

 Dasyurus, native cat; Sarcophilus, Tasmanian devil; Thylacinus, 

 Tasmanian wolf; Myrmecobius, banded ant-eater; Notoryctes, 

 marsupial mole; Sminthopsis, pouched mouse 

 Superfamily 4. Perameloidea. Pleistocene-Recent. Australasia 



Perameles, Bandicoot 

 Superfamily 5. Caenolestoidea. Eocene-Recent. S. America 

 *Palaeothentes (= *Epanorthiis), Oligocene-Miocene; Caeno- 

 lestes, opossum-rat, Ecuador, Colombia, Peru 

 Superfamily 6. Phalangeroidea. Pliocene-Recent. Australasia 

 Trichosurns, Australian opossum; Petaiirns, flying opossum; 

 Phascolarctos, koala bear; Vombatus, wombat; Macropus, 

 kangaroo; Bettongia, rat kangaroo; *Diprotodon, Pleistocene; 

 *ThyIacoleo, Pleistocene. 



3. Opossums 



The opossums (Didelphoidea) were the earliest group to appear 

 and the other families have probably evolved from them, with syn- 

 dactyly appearing twice. They are arboreal, mainly nocturnal and 

 omnivorous or insectivorous animals, with a prehensile tail, occurring 

 over the southern United States and Central and South America (Fig. 

 339). The pouch is generally absent. Similar forms are found back to 

 the Upper Cretaceous (*Eodelphis) and the American opossums are 

 certainly the closest of living marsupials to the ancestors of the group, 



