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...work out which of these two groups has, on average, more species per family. Answer Figure 14 shows approximately 40 families of living reptiles. So the average number of species per family is 12 000 divided by 40 ≈300. There are about 150 families of living mammals and 6000 species, giving an average of 6000 divided by 150 ≈40. Thus living reptiles have far more...

...work of pumping. As well as being large (up to 1m long), icefish are active predators that swim in the surface waters and use oxygen at about the same rate as red-blooded antarctic fish such as Pleuragramma or Notothenia (see Figures 23a and b). Icefish blood contains solutes and a few white blood cells, so it is a yellowish, watery fluid similar to mammalian lymph. Large...