32 SEA-BIRDS 



commoiij and the periods and epochs in which all our sea-bird orders, 

 and many of our sea-bird families and genera, originated are quite well 

 known. A recent paper by Hildegarde Howard (1950), of the school 

 of Wetmore, enables us to show a diagrammatic family tree of birds 

 (Fig. 3), with special reference to sea-birds, and to collate its branching 

 with the approximate time scale of the epochs, so cleverly established 

 by geomorphologists in recent years from studies of sedimentation-rate 

 and the radioactivity of rocks. It will be seen that the primary radia- 

 tion of birds and the great advances into very different habitats 

 consequent upon the first success of the new animal invention — 

 feathered flight — took place in the Cretaceous period, the first bird- 

 like feathered animals having been found as fossils in Jurassic deposits 

 of the previous period, over a hundred and twenty million years old. 

 In the Cretaceous period — the period of reptiles — ostriches were 

 already foreshadowed, as were grebes and divers, and the pelican-like 

 birds, and the ducks. 



In the Cenozoic period — the period of mammals — the radiation of 

 birds into all nature's possible niches continued rapidly, especially 

 in the first two of its epochs — Eocene and Oligocene — from sixty to 

 thirty million years ago. In these epochs grebes can be distinguished 

 from divers, and a bird of the same apparent genus {Podiceps, or, as 

 the North Americans have it, Colymbus) as modern grebes has been 

 found. Gannet-boobies of the modern genus Sula have been found in the 

 Oligocene, as have cormorants of the modern genus Phalacrocorax. 

 The only penguin fossils known are later — of Miocene age — but 

 it seems probable that they share a common stem with the tube- 

 noses, which would mean that their ancestors branched off in the 

 Eocene. The tubenoses diversified in the Oligocene — from this epoch 

 we have a shearwater of the modern genus Puffinus; and from 

 the Miocene Fulmarus and albatrosses. The ducks started their main 

 evolution in the Cretaceous, and by the Oligocene we find modern 

 genera such as Anas (mallard-like) and Aythya (pochard-like); in 

 the Pliocene we have Bucephala (Charitonetta) — one of the tribe of 

 sea-ducks. 



For the Lari-Limicolae, the order which includes waders, gulls 

 and auks, the fossil record is rather indefinite, mainly owing to the 

 difficulty of distinguishing the present families by bones alone. How- 

 ever, we know that the auk family was early — an Eocene offshoot; 

 that the waders and gulls diverged in the Oligocene; and that the gulls, 

 terns and skuas probably diverged in the Miocene — which means 



