FOSSIL FISH

Gisborne Times, Volume LXXX, Issue 12263, 26 May 1934, Page 7

FOSSIL FISH

FOUND IN TERTIARY BEDS . NEAR DUNK.DIN. ANCESTORS OF RATH! A COOT A. A few months ago professor W . N. Henson, of Otago 'University, iflok over to Melbourne the fossil remains of a fish that lmd been found in the older Tertiary beds at Burnside, Green Island, Dunedin. New Zealand. A close examination of this fossil fish showed that it had a, relationship to living fishes of the family wh<ch (includes ihe wellknown food-fish, the barracoota. When a search was made for other 'related fishes that have been recorded a.s fossils in rocks of similar age to the New Zealand specimen, evijdon.ee wots mb turned which considerable light on the ancestral types ol our living bariaeootn. • 'Phis fish is known scientifically as Thyrsitcs at mi. and lor accuracy of reference the Latin name is preferable to the vernacular, lor the similar name “barraeouda” is given by il,e West Indians to the sea-pike, a predatory fish only distantly related. Tim barracoota, is very widely distributed owing to its high specialisation and efficiency in procuring Its food. Its distribution embraces all the southern polar seas, through Australian waters to- New Zealand, Booth Africa, and on to the coast of Chile. It is found'in great shoals in the surface waters, hut-is not confined to that- habitat, for it often ranges down to the son-bod.

The attenuated form of the body, with, ’is worm-like mobility, along with iis cruql ja.w armed with trenchant- teeth. show i; to be one ci the most -specialised fish cannibals m the waters -of the- southern hemisphere. Mackerel, mullet, garfish, and many other kinds of fish fall aTI oasv prov io the barracoota, which also attacks even much larger fish than itself, tearing off great pieces of flesh in irs furious onslaughts.

ANCESTRAL SMOOTH AND SCALY KINDS. In the Swiss'Alps, at a place earned the Glams, the rocks that one* wore horizontal have eeen so worrolded that the older Triassic is now found lying on the younger J ertiary 'beds. These Tertiary beds are here composed or a black silty mud, once a sea-becl over which swarmed shoals of fishes, mainly of the robber m predacious kinds. Owing to ihe enormous pressure, exerted on the mud? of this o’d fish-bearing net*. the sediment has been altered into a glossy black slate, a condition unknown elsewhere among the Tertiary rocks. It i= strange to sec such a slate, resembling our own Victorian gold-bearing slates of Palaeozoic age, of so modern an origin. Jlut there is no question of the age of the (Hams plate, since it contains several kinds of Tertiary fishes. These are all of the specialised “robber-fish" typo, showing the lithe body. and. in seme cases, enormously developed .'lender teeth. Among these is the fish called Lopidopus (“seaiy-eye''.-, and also Thyrsirocephnlns (“barra-coota-head’'). Tlie naturalist Yon Rath, who .described 1 -this fish in 1850. does not ‘mention anything about the scales of the fish, and figures only the skeleton, so that we have no direct- evidence, beyond the bon v structure, of a close relationship with the New Zealand fossil.

HOW THE NEW ZEALAND FOSSIL ANCESTOR DIFFERS

Th© name chosen for Hie Dunedin fossil is Eothyrsites (“dawn barracoota'’), for it agrees in many characteristics with the familiar 1 ‘coots'' (Thyrsit-os), excepting that it was a shorter and proportionally deeperbodied fish, closely covered with scales. If we look at the skin of the herring, mackerel, pike, or carp we shall see that the -scales are round, with closely sot rings of growth, the exposed part of the scale being -toughened by radiating wrinkles. These scales aro of the kind called cycloid, and suck aro found covering the body oi' the ancestor of the barracoota. When one comes to look at on© Jiving barracoota one may at first see no scales, but on the general surface the skin is marked out in rounded areas suggesting vestiges of former scales. Descriptions of the living barracoota are strangely silent- upon this general absence of scales, and even Professor Al'eCoy in his lucid description of tiiyisites m the “Prodromes of Zoology' ’ does not- mention scales on the body ot the barracoota. .But a most interesting discovery -was mads by closely examining the skin of a fresh barracoota, for along the slime canat of the lateral lines of the fish there was found a delicate protective covering of tiny cycloid scales, such as w© saw ail over the body in th© fossil fish of Dunedin. Here, then was the secret of its lineage. Millions’or years ago our barracoota was a,respectable, stout-bodied kind of fish, hut of smaller size and more delicately structured, clothed in. protective covering of rounded scales, like the well-known tunny. It was, however, left far behind by robbor-fislies like lepidopus of the sea-beets of the Swiss Alps, beautiful specimens ot which, by the way,® 1 may ho seen in the fossil gallery of tho National Museum in Melbourne. But thrysites soon mndoHoeway, and far ouJStripl pod the olliers; probably during Alio-

{•one limes to the present, by logins tiioLs.* scales, excepting on the lateral ones. They iiec.uiie almost ecl-like, and developed a most ferocious system ol teeth—making one think of the hungry packs of wolves that raid snowbound villages in 'Northern Europe.

EVOLUTION AND SPECIALISATION. Huxley once remarked that- the host support of the theory of evolution must be looked for in-the study of fossils. The evidence of palaeonogy, as wo are aware, points not only to tho progression from lower to higher types, but. also to regression or degeneration. This degeneration, or catagenesis, as tho learned call'it, Is often accompanied by specialisation, such .as we find in the barracoota. Tho unravelling of the story of even a common fish "may reqmro a great deal of observation, the digging up of evidence from among the fossils, and the patient sorting out of the relevant from the non-relovanti data. " . • ■

The specialisation of the»/'barracoota has conquered the tendency to degenerate, for, although it. has lost nearly all of its--early armour, it is sufficiently protected by its habit of hunting in massed formation, and is undoubtedly a terror to the world of fishes to-day in the southern seas.