NATURE NOTES.

New Zealand Herald, Volume LXVII, Issue 20650, 23 August 1930, Page 1 (Supplement)

NATURE NOTES.

EARLY FOSSILS.

BY J. DRUMMOND, F.L.S., F.Z.S.

Fossil remains found in Now Zealand and in many other parts of the world testify to the dominance once held by strange little creatures whoso bodies aro formed of three lobes, a character that has earned them the title of trilobites. No general text-book on fossil creatures can afford to ignore the trilobites. They have attracted more attention than any other very early fossils. They are found in the oldest fossil-bearing rocks. They have not been found in rocks later than those of the dim, distant and mysterious Palaeozoic era. So many widely differing estimates havo been offered of time measurement according to the geological clock that even the latest may be accepted with hesitancy. These estimates are difficult and perplexing. Necessarily, they must be very rough. The latest and, admittedly, the most reliable are based on charts in radio-active substances. Uranium, a radio-active element thut occurs in different minerals, changes very slowly into other elements. finally, it becomes a kind of lead, inseparable from ordinary lead if mixed with it. The rate at which the changes take place, although almost indescribably slow, is known fairly accurately. The percentage of lead in a mineral that contains uranium makes it possible to estimate the time since the mineral was first deposited in rock. The changes from uranium to lead would require that time. On this basis the Palaeozoic era began about 550,000,000 years ago, and continued for some 350,000,000 years, when it drifted into the Mesozoic era, the era of Middle .Life. Trilobites are extinct. Later than the Palaeozoic era they are unknown. They reached their highest developmnt early in the Palaeozoic era, about 480,000.000 years ago with the estimate on the radioactive basis. They then became less plentiful. In the Devonian period, 350,000,000 years ago, their decline was marked. In the Carboniferous period, which followed the Devonian, they were face to face with extinction. They do not seem to have survived the Carboniferous period in Europe, but in America one form has been found in rock of the Permian period, which brought the great Palaeozoic era to a close. Even at the beginning of the Palaeozoic era trilobites were highly organised creatures. If the theory of evolution is sound, the history of the trilobites shows that evolution had been in force for a long time before Palaeozoic times. Evolutionists do not regard the highly organised condition of the first trilobites known as a blow to their theory. They say that in rocks earlier than the Palaeozoic the remains of animals have been destroyed or made unrecognisable. Fossil remains, since the beginning of.the Palaeozoic convince them that life on the earth since that time has been continuous without a break to this day, and that great groups of plants and creatures have appeared in the order expected by the theory that each has arisen from a more lowly group.

The trilobites represent the earliest crustaceans known. They are the only known order of crustaceans that lias no living representatives. Their remains are found in almost every country that has Palaeozoic rocks. They seem to have lived exclusively in the sea. They crawled oil the bottom "or swam slightly above it at all depths. 'Muddy, sandy or rocky bottom, it was all one to them. r ihey resembled somewhat the modern sowbug or wood-lice. Most species were two or three inches long. Some were only a quarter of an inch. Giants which lived in New Zealand seas and in other parts were from ten to twenty inches long. Trilobites were carnivorous. • Their amazing plentifulness is evidenced by the remains that crowd some of the ocean floors. Their limbs are seldom found. As these usually are important means of classifying the group to which they belonged, difficulty has been experienced by systematists in dealir% with the trilobites. Some of them died while lying flat. Others, when overtaken by death, had rolled themselves up in exactly the same way as a wood-louse rolls itself up when alarmed. At least one species had the end of its body drawn out to a long spine. By analogy with living allies, it is concluded that this species obtained food by thrusting its head forward into the mud, and using its spiny tail as a support. Its eyes, highly developed, show that it did not live buried in the mud. Its eyes were useless in searching for food. Their purpose, apparently, was to warn their owner of the approach of an enemy. All the appendages of some trilobites were used for crawling, swimming and seizing food. More highly developed and specialised trilobites had a greater division of labour in their appendages. Some of these were used as jaws only, others for crawling only, _ others for swimming only. Ordinary trilobites seem to have lived on the bottom of (he ocean, with power to crawl and swim. Members of some divisions were mud-grabbers all their lives. These had heads like shovels, thrust into the mud easily, and eves in positions where they would not be in the mud. in some cases raised on long stalks. Some had no eyes whatever.

There is a great deal of interesting, useful and valuable information in a set of " Discovery Reports" sent by the discovery committee, the Colonial Office, London, on behalf of the Government of the Dependencies of the Falkland Islands. The 'reports are based on a scientific expedition to Antarctic waters in the Discovery, Captain Scott's vessel, which in Captain Scott's day was associated with New Zealand's history. The development of tlio whaling industry in the Dependencies is the main reason for the expedition, which is still in band, and the investigations bear largely on the lives and habits of whales, but admirable work has been done, and is being clone, bv able members of the staff in other directions. The investigation has a very wide scope. This gives many opportunities for supplying knowledge of purely scientific interest, Work of this class often has yielded results of high economic importance, giving it a collateral interest. Thero is evidence of thia in a study of the physical and chemical constituents of the water. Dependent on theso are the microscopical plants called diatoms and other tiny plants that float near the surface. A period of great reproductive activity among diatoms is followed by unusual abundance of crustaceans called Euphausia, which fc®d on those plants. Some species of whales feed exclusively, or almost exclusively, on Euphausia. Whaling fluctuates gieatl} from season to season, and the causes of the fluctuations can be traced finally to the physical and chemical constituents 01 the water. In this case, pure science has an indirect, but important, application to a big industry. The whale bulks largely in its _ big volume of the reports, but thero is a volume on the elephant-seal and another on the birds of South Georgia, including the same species of large seagull as is seen on every New Zealand coast, and the same species of albatrosses as nest on New Zealand's islands. Fresh light is thrown on the courting and nesting habits of these birds and others. The reports are issued from the time-honoured Cambridg -University Press, whose work needs no praise.