ペンギンは、今から5000万年から6000万年前に南半球で進化したと考えられています。ペンギンはアビ、ウミツバメなどの水に潜る鳥の仲間から進化したと考えられており、ペンギンの祖先は、飛ぶこともできたようです。

　

　

　ニュージーランドに生息するキンメペンギンは最もペンギンの祖先に近い、原始的な種類だと考えられています。したがってニュージーランド近海は、ペンギンが誕生した地域かもしれないと言われています。

　ペンギンは現在、世界で18種類が知られていますが、かつてはもっとたくさんのペンギンが南半球で進化したと考えられています。

　

ペンギンの起源

　世界で最初に発見された古代ペンギンの化石は1850年代にオアマル近郊の3000万年前の堆積層から発見されたものです。このペンギンは体長が1.45mもありました。

　サウスカンタベリー地方のワイタキの堆積岩からはたくさんのペンギンの化石が見つかっています。ここでは現在のブルーペンギン（1kg）のような小さいものから、体長1m、体重40kgになるコウテイペンギンよりもっと大きいものまで様々な種類が見つかっています。

　ニュージーランドで見つかったこれまでに最も古いペンギンの化石は、ノースカンタベリーから発掘された5800万年前のものです。この鳥はワイパラと呼ばれ、ニュージーランドで見られるキンメペンギンよりもわずかに大きく、長いくちばしと柔軟な肘を持ったアビに似た鳥だったと考えられています。

　

　

Penguins evolved in the Southern Hemisphere between 50 and 60 million years ago.

Their ancestors flew and probably dived. The birds most closely related to penguins are the loons (called 'divers' in Europe), petrels, albatrosses and frigate birds.

It is likely penguins originated in the Southwest Pacific, possibly in New Zealand. The living yellow-eyed penguin Megadyptes antipodes is considered to be the species 'least adapted' in terms of size, bone structure and feathering -that is, the penguin most closely resembling the first of their kind.

The 18 living penguin species are only a fraction of the number that evolved through the past 60 million years.

　

First discovery

The first penguin in the world to be described scientifically was found at Kakanui, south of Oamaru, in the 1850s. Its fossil remains were embedded in 30 million-year-old sediments. Called Palaeeudyptes antarcticus, it stood about 1.45 metres (4 ft 9 in) tall.

Many ancient penguins have been identified from fossils preserved in the sedimentary rocks of the Waitaki/South Canterbury region. They are notable for the completeness of their skeletons. These penguins ranged in size from species as small as the living blue penguin (about 1 kg) to birds much larger than the living emperor penguin, which stands about 1 metre (3ft 3 in) tall and weighs up to about 40 kg.

The ancient penguins tended to have long pointed bills. Some species were deep-chested, with large flippers and relatively short legs.

　

The original penguin

In New Zealand, the earliest evidence of the evolution of penguins is a 58 million-year-old fossil from North Canterbury, the Waipara 'proto-penguin', a loon-like wing-propelled diving bird that has been described from a fragment of leg bone. Slightly larger than today's yellow-eyed penguin, the Waipara bird is thought to have had a long delicate bill and flexible elbow.

　

　

　爬虫（はちゅう）類が大量絶滅した後、広大な海洋には、クジラ類やイルカ類といった哺乳（ほにゅう）類が進出しました。クジラ類はおよそ5000万年前に現在の有蹄（ゆうてい）類（ウシ等の仲間）から進化したと考えられています。特にオーストラリアと南極が分かれてできた南極海では、多くのクジラ類・イルカ類が進化しました。

　ワイタキ渓谷からはたくさんの原始クジラ類とイルカ類の化石が発見されています。これまでに25種類の初期のヒゲクジラ類・マイルカ類が、この場所から見つかりました。これは、この地域がかつて広い遠浅の海であったことを示しています。3500万年前の地層から発見されたイルカ類には、サメのような歯をもったものや、長いくちばしをもったものなど、絶滅してしまった珍しい種類が見られます。

　

歯からヒゲヘ

　セミクジラやシロナガスクジラといったクジラ類はヒゲクジラ類と呼ばれ、「ヒゲ」と呼ばれる歯の変化した器官を持っています。これらのクジラはヒゲを使ってオキアミや他の動物プランクトンを海中から補食します。

　ニュージーランド南島から発見されるクジラ類の化石には、原始的なヒゲを持つものや、歯とひげが組合わさっているものなど、歯がひげに進化していった過程を示すものがたくさん見られます。最も古い歯のないヒゲクジラの化石はおよそ3000万年前に発見されたもので、おそらく退化した後ろ脚を持っていただろうと考えられています。

　

　

オサガメ

　現在、熱帯地方に生息するウミガメの一種で、サウスカンタベリーのワイハオ渓谷などで化石が発見されています。当時（3800万年〜4000万年前）の北オタゴの海岸は現在よりずっと暖かだったようです。

　

アカマンボウ

　北オタゴの2500万年前の石灰岩から発見された巨大な魚です。現在ではとれほど大きくはなく、外洋にしか見られません。

　

巨大なサメ

　ワイタキ渓谷の2600万年前の地層からは体長8m、重さ8tと推定されるサメの化石が見つかっています。この化石は完全に揃った150本の歯と30本の椎骨を残しており、世界でも稀な、貴重な標本です。現在のホオジロザメに近縁な種類と考えられています。

　

　

The extinction of the marine reptiles left a yawning niche. Enter the cetaceans - the whales and dolphins, an extraordinarily successful order.

Worldwide, whales evolved from four-legged land mammals called Mesonychids about 50 million years ago. Now extinct, the Mesonychids were distantly related to modern hoofed mammals such as cattle.

As the Southern Ocean opened up after the parting of Australia and Antarctica, whales and dolphins evolved rapidly. More than 25 species of early baleen whales and toothed dolphins, all extinct, have been identified from fossil remains in the Waitaki Valley.

Was the Waitaki area, covered by the sea for eons, once a breeding ground for these early whales? Limestone and greensand was deposited here in an extensive but sheltered, shallow sea, allowing the bones of many deceased animals to be preserved intact. Islands or bars may have given protection from the open ocean.

Early dolphins are also well represented in the Waitaki Valley fossil record. Originating about 35 million years ago, they include shark-toothed species and small long-beaked forms, all of which are extinct.

　

　

TEETH TO BALEEN

The fossil evidence from Southern New Zealand demonstrates an evolutionary path for whales from teeth to filter-feeding baleen. In some transitional species teeth may have been used as proto-baleen to filter food. Others combined teeth and baleen.

About 30 million years ago the first toothless baleen whales evolved. They had a blowhole near the front of the skull (modern whales have the blowhole seated further back) and perhaps vestigial hind legs. In baleen species, plates of an elastic horny substance known as whalebone hang down from the upper jaw, enabling the whale to capture krill and other zooplankton by trawling or gulp-feeding.

Living baleen whales include the southern right whale, which is making a recovery in Southern New Zealand, and the blue whale, the world's largest animal.

　

LEATHERBACK TURTLE

Extinct leatherback turtles as large as the existing tropical species inhabited the North Otago-South Canterbury coast 38-40 million years ago, when sea temperatures around New Zealand were warmer. The main specimen was found in the Waihao Valley, South Canterbury, in the early 1990s. Dermal (skin) armour and a few bones - ribs and vertebrae - have survived. It was named Psephophorus terrypratchetti. Judging by its location in Waihao greensand, it appears to have died in quiet sea conditions on the continental shelf in depths of up to 100 m.

Closely related species have been found in other parts of the world, sometimes associated with archaeocete whales. A few early paleontologists wrongly assumed the bony plates came from the whales.

　

LAMPRIS MOONFISH

From 25-million-year-old North Otago limestone comes a remarkable find - an enormous fish, related to the living Lampris moonfish. Today such fish occur in open oceans around the world and they are brightly coloured and deep-bodied, although not as large as the Oligocene specimen. The fossil Lampris was carefully dug out of a cliff at Tokarahi and brought to Dunedin in three large blocks.

The tail is in the smaller block to the left and fragments of skull are in the large block to the right.

　

A FORMIDABLE SHARK

Sharks, which evolved about 350 million years ago, were among the marine groups that survived the mass extinction at the end of the Cretaceous Period. Their long successful history is well portrayed by the discovery of a 26-million-year-old species, Carcharodon angustidens, in the Duntroon area of the Waitaki Valley. Its length is estimated at eight metres and it weighed about 8 tonnes. It is closely related to the smaller living white shark Carcharodon carcharias. Its fossil remains include some 150 teeth, a complete set, and 30 vertebrae - a rare find of world significance.