Chromosomal and Serological Studies of the Caenolestidae and their Implications for Marsupial Evolution

Abstract

SIMPSON¹ recognizes five superfamilies of living marsupials, three of them Australasian (Dasyuroidea, Perameloidea, Phalangeroidea) and two American (Didelphoidea, Caenolestoidea), and regards none of these as specially related at a higher categorical level. Since Thomas's² description of Caenolestes obscurus, however, the affinities of the American marsupial superfamily Caenolestoidea have been in doubt largely because of the diprotodont incisors, a feature of their dentition that caenolestoids share with the Australasian phalangeroids. Thus, some authors^2–4 have proposed a special relationship between these groups, while others^5,6 have rejected the dental similarities as convergent and grouped caenolestoids with the polyprotodont marsupials which include both American and Australasian forms; still others^7,8 treat Caenolestoidea as representative of another principal group of marsupials. The question of caenolestoid affinities is thus a problematical one, to which morphological study has contributed little since Osgood's study³. Chromosomal and serological analyses might be expected to be relevant as there have been extensive studies of the chromosomes^9–12 and serum proteins¹³ of four of the marsupial superfamilies. We present here, for the first time, data on the karyotypes and comparative serology of the Caenolestoidea, encompassing three of the seven extant species representing two of the three genera. Details of the localities, ecology and behaviour of these species will be published elsewhere.