MUSEUM NOTES

Southland Times, Issue 23768, 16 March 1939, Page 7

MUSEUM NOTES

FIRST BIRDS AND MAMMALS In last week’s notes we saw how the reptiles reached the height of their glory in that first great summer of life, the mesozoic period. But while the dinosaurs lorded it over the hot selvas and marshy plains and the pterodactyls filled the forests with their flutterings and possibly theii- croakings and shrieks, and pursued the humming insect life of the still flowerless shrubs and trees, some less conspicuous and less abundant forms of life were acquiring certain powers and learning certain lessons of endurance, that were to be of the utmost value to their race when at last the generosity of the sun and earth began to fade. A group of tribes and genera of hopping reptiles, small creatures of the dinosaur type, seem to have been pushed by competition and the pursuit of their enemies towards the alternatives of extinction or adaptation to colder conditions in the higher hills or by the sea. Among these distressed tribes there was a development of a new type of scale; scales that were elongated into quill-like forms and that presently branched into the crude beginnings of feathers. These quill-like scales lay over one another and formed a heatretaining covering more efficient than any reptilian covering that had hitherto existed. So they permitted an invasion of the colder regions that were otherwise uninhabited. Perhaps simultaneously with these changes there arose in these creatures a greater solicitude for their eggs. Most reptiles are apparently quite careless about their eggs, which are left for sum and season to hatch. But some of the varieties of this new branch of the tree of life were acquiring the habit of guarding their eggs and keeping them warm with the heat of their bodies. With these adaptations to cold, other internal modifications were going on that made these creatures, the primitive birds, independent of basking; they became warm-blooded. The very earliest birds seem to have been sea-birds living upon fish, and their fore-limbs were not wings but paddles rather after the penguin type. The New Zealand bird, the kiwi has feathers of a very simple sort, and neither flies nor appears to be descended from flying ancestors. In the development of the bird, feathers came before wings, and once the feather was developed, the possibility of making a light spread of feathers led inevitably to the wing. We know of the fossil remains of one bird at least which had reptilian teeth in its jaw and a long reptilian tail, but which also had a true bird’s wing and certainly flew and held its own among the pterodactyls of the mesozoic period. THE APPEARANCE OF MAMMALS The earliest mammals like the earliest birds were creatures driven by competition and pursuit into a life of hardshin and adaptation to cold. With them also the scale became quill-like and was developed into a heat-retaining covering; and they too underwent modifications, similar - in kind though different in detail, to become warm-blooded and independent of basking. Instead of feathers they developed hairs, and instead of guarding and incubating their eggs, they kept them warm and safe by retaining them inside their bodies until they were almost mature. Most of them became altogether viviparous and brought their young into the world alive. Most, but not all, mammals today have mammae and suckle their young. Two mammals still live which lay eggs and which have not proper mammae, though they nourish their young by a nutritive secretion of the under skin; these are the platypus and the echidna.

A visitor to the mesozoic world might have searched for days and weeks before finding a bird, and so, too, he might have searched in vain, unless he knew exactly where to look, for any traces of a mammal. Both birds and mammals would have seemed very secondary and eccentric and unimportant creatures in mesozoic times. Under settled conditions there is no encouragement for novelties; they do not develop and are suppressed for what is best adapted is already there. Under novel conditions it is the ordinary type that suffers and the novelty that may have a better chance to survive and establish itself.

The age of reptiles lasted, it is now estimated, about 80,000,000 years. Then there comes a break in the record of the rocks that may represent several million years. There is a veil here still, over even the outline of the history of life. When it lifts again, the age of reptiles is at an end; the dinosaurs, the plesiosaurs and ichthyosaurs, the pterodactyls, the innumerable genera and species of ammonites have gone absolutely. In all their stupendous variety they have died out and left no descendants. The cold has killed them. All their final variations were insufficient; the world had passed through a phase of extreme conditions beyond their powers of endurance. A slow and complete massacre of mesozoic life had occurred and we now find a new scene, a new and hardier flora and a new and hardier fauna in possession of the world. Trees now shed their leaves to avoid destruction by the snows of winter, and where there was formerly a profusion of reptiles, an increasing variety of birds and mammals is entering into its inheritance.