| [ PhilosophyThought ] in KIDS 글 쓴 이(By): limelite (깜찍이중독) 날 짜 (Date): 1999년 7월 30일 금요일 오전 04시 47분 48초 제 목(Title): Re: 질문: zen 질문입니다. 환상님이 중간화석을 찾으셔서 한메파스칼 백과사전과 브리테니커 사전에서 고래의 진화와 화석에 관계된 부분을 옮겨와 봅니다. 한글은 한메고, 영어는 브리테니커입니다. 저도 아직 제대로 안읽고 옮기는 것이기 때문에 내용은 묻지 마세요. ^^ ===================================================================== 〔진화와 계통〕 고래류는 크레돈타(credonta)라는 육생(陸生)의 조그만 원시 식충류(食蟲類)로부터 분화한 것으로 보인다. 지질시대인 고생대 말기부터 신생대 초기에 걸쳐 북반구의 유라시아대륙과 남반구의 곤드와나대륙 사이에 있던 테티해로 흘러드는 열대의 강어귀에서 조개류·갑각류·어류 등을 먹으며 차츰 물에 길들어서 헤엄·잠수도 할 수 있게 진화하여 고래류가 탄생했다고 추정된다. 고래류는 팔레오세의 초기에 분류되어 수생공룡류(水生恐龍類)의 절멸로 비어 있던 생태적 지위를 메우고 급속히 진화를 이루어 올리고세 중기에는 대양에서도 살 수 있게 되었다. 약 3000만 년 전에 전성기를 이루다가 마이오세 중기에 절멸한 이 옛고래는 고경아목(古鯨亞目;Archaeoceti)으로 불린다. 이 아목의 이는 일반 포유류와 같이 44개이며 이치성(異齒性)이고 콧구멍은 입술가에 위치했다. 4과로 분류되는데 그 중의 바실로사우르스과(Basilosauridae)에 속한 고래는 뱀처럼 길고 몸길이가 12∼21m였다고 한다. 이같은 고경아목과 이빨긴수염고래아목 중간의 고래는 화석으로 발견되지 않는다. 이빨고래아목 중 가장 오래된 화석은 올리고세 중기에 이미 출현했지만 이빨고래의 종류는 마이오세까지는 많지 않았다. 현재의 이빨고래는 마이오세 말기에 출현한 것이다. 긴수염고래아목 중 가장 오래된 화석은 올리고세 후기의 지층에서 발견되고 있지만, 이 종류는 플라이오세 초기에 절멸했다. 현재의 긴수염고래류는 이 세토데리움(cetotheridae)으로부터 분류되었다. 고래류의 3개 아목이 같은 조상으로부터 나왔는지의 여부는 아직 결론이 나지 못했으나, 근래에는 동일기원설이 유력해지고 있다. PALEONTOLOGY AND EVOLUTION It is generally agreed that whales originated in the early Paleocene or Upper Cretaceous (about 70,000,000 years ago) from some group of terrestrial meat-eating mammals. Some authorities believe that a likely parent group was the Mesonychidae, medium-sized, large-headed mammals of the order Creodonta, believed to be near the base stock of both the carnivores (Carnivora) and the ungulates (several orders of hoofed mammals). It has also been suggested that the whales evolved from a Paleocene member of the order Insectivora resembling the Eocene Pantolestes, a semi-aquatic carnivorous animal about the size of the modern otter (Lutra lutra). An American paleontologist, L. Van Valen, has pointed out similarities between the mesonychids (as well as the closely related arctocyonids) and the earliest archaeocete whales, the protocetids. All that can be stated with certainty is that the ancestors of the protocetids must have evolved through an amphibious stage. The earliest known whale fossil is a fragmentary shoulderblade from the lower Eocene of England (about 50,000,000 years ago). Remains of archaeocete whales of the family Protocetidae are found in middle Eocene formations. They were relatively small animals about the size of the modern porpoises (two to three metres long). The hindlimbs had already been lost, and the nostrils were midway between the terminal position found in most terrestrial vertebrates and the top of the head, where they are found in most advanced whales. The snout was elongated, but the skull bones were not telescoped as in modern forms; the teeth retained the differentiated (heterodont) condition found in terrestrial carnivores, the front teeth being tapered pegs and the cheek teeth serrated. At the time of their greatest development, in the late Eocene, some archaeocetes were large, the most striking being Basilosaurus, a slender animal that attained a length of some 20 metres (nearly 70 feet). One line of archaeocetes, the dorudontids, persisted into the early Miocene (about 20,000,000 years ago). (see also Index: fossil record) Paleontologists disagree as to whether the modern toothed whales (odontocetes) and baleen whales (mysticetes) arose from an early archaeocete relative or separately from different terrestrial ancestors. Recognizably odontocete remains are known from the upper Eocene, and even earlier odontocetes must have been contemporaries of the early archaeocetes. One early form, Agorophius, already showed some telescoping of the skull and the nostrils were above the eyes. The agorophiids appear to have had a relatively short history but were probably ancestral to the porpoise-like squalodonts, which appeared in the late Oligocene (about 28,000,000 years ago) and by the middle Miocene were the dominant toothed whales of the world's oceans. By the early Miocene most of the modern odontocete families were represented by some members. Fossils of sperm whales found in lower Miocene deposits have been assigned to the modern genus Physeter. These are among the oldest known representatives of the physeterid line, which produced a variety of other Miocene and later forms and must have existed as a well-differentiated group during the later part of the Oligocene. Two groups of fossil whales appear to be intermediate between the toothed and the baleen whales. In the Patriocetidae the nostrils were in an intermediate position between the snout and the forehead; the telescoping of the skull (in the symmetrical manner seen in later mysticetes) was only slightly evident. The other group, the Aetiocetidae, was placed in the Odontoceti on the basis of possession of teeth, but Van Valen has pointed out that Aetiocetus is mysticete in other respects and should be considered closer to the mysticete evolutionary stem. The earliest fossils definitely assignable to the Mysticeti are the middle Oligocene cetotheres, a group that became quite abundant in the subsequent Miocene. Of the three modern families of baleen whales, two (Balaenidae and Balaenopteridae) are known from scanty Miocene and abundant Pliocene fossils; the third (Eschrichtiidae) is known only from a few Pleistocene and post-Pleistocene fossils representing the sole modern genus, Eschrichtius. 어떻게 중독됐니? 몽라 우어낙 숭시가네 일이라성 @_@ |