Lyric discussion by PandaPounce 

Cover art for Mammal lyrics by They Might Be Giants

I haven't been able to find any information on the reproduction method of Allotheria, except that "their narrow pelvis suggests they bore tiny live young that required extended lactation, as is the case in marsupials." (http://ijolite.geology.uiuc.edu/02sprgclass/geo143/lectures/lect21.html) But are the Johns implying that Uncle Allotheria has a more eccentric system of reproduction than Brother Marsupial, seeing as how he's a little removed from the sibling unit?