Classification and distribution of Oligocene Aetiocetidae (Mammalia; Cetacea; Mysticeti) from western North America and Japan     

Lawrence G.  Barnes  Masaichi  Kimura Hitoshi  Furusawa Hiroshi  Sawamura 《Island Arc》1994,3(4):392-431

Abstract Fossil whales in the very rare, primitive, extinct cetacean family Aetiocetidae are small, relict, toothed mysticetes that persisted into Late Oligocene time after more highly derived baleen-bearing mysticetes had already evolved. No known aetiocetid could be ancestral to baleen-bearing mysticetes, but aetiocetid morphology is in many ways intermediate between archaeocetes and baleen-bearing mysticetes, demonstrating the probable transitional steps passed through in the evolution of baleen-bearing mysticetes. Their discovery indicates that mysticetes evolved from Archaeocetes, and supports theories of the monophyly of Cetacea. Late Oligocene aetiocetids have been found on both sides of the North Pacific Ocean: on Vancouver Island, British Columbia, Canada; in Oregon and Washington, USA; in Baja California Sur, México; and the islands of Kyushu and Hokkaido, Japan. The most primitive North American aetiocetid, Chonecetus sookensis Russell, 1968, is from the early Late Oligocene Hesquiat Formation on Vancouver Island, British Columbia, Canada. A more derived, Late Oligocene species, Chonecetus goedertorum Barnes and Furusawa, new species, from the Late Oligocene Pysht Formation, Olympic Peninsula, Washington, has the primitive placental mammalian tooth count of 11/11. The type genus of the family, Aetiocetus Emlong, 1966, has as its type species, A. cotylalveus Emlong, 1966, known only from the Late Oligocene Yaquina Formation on the coast of Oregon. It has 11 upper teeth on each side of the rostrum. A more derived species, Aetiocetus weltoni Barnes and Kimura, new species, from a higher stratigraphic level in the Yaquina Formation, has a more posteriorly positioned cranial vertex and a tooth count of 11/12. We describe four new species of aetiocetids in three genera from the Late Oligocene Morawan Formation near Ashoro, Hokkaido, Japan. The most primitive, Ashorocetus eguchii Barnes and Kimura, new genus and species, has a primitive stage of cranial telescoping, and is closely related to Chonecetus Russell, 1968. Another, Morawanocetus yabukii Kimura and Barnes, new genus and species, in some ways intermediate between Chonecetus and Aetiocetus, has a suite of unique derived characters, including a much foreshortened brain case. The third, Aetiocetus tomitai Kimura and Barnes, new species, is the most primitive species of Aetiocetus yet discovered. The fourth, Aetiocetus polydentatus Sawamura, new species, the most derived species of Aetiocetus known, has a highly telescoped cranium, homodonty, polydonty and a dental count of 13–14/14–15. The fossil record now indicates considerable diversity in the family, with several different contemporaneous lineages in three new subfamilies: Chonecetinae, Morawanocetinae and Aetiocetinae. Aetiocetids are not known outside the North Pacific. Many Recent mysticetes are essentially cosmopolitan, and aetiocetids might have also been relatively widely dispersed. We suspect that with time their remains will be found around other ocean basins also. If so, then they may be potentially useful in trans-oceanic geological correlations.  相似文献   

淮北煤田早二叠世化石植物古生态     

杜美利 《中国煤田地质》1994,6(4):21-25

淮北煤田早二叠世化石植物丰富，其形成于炎热多雨的热带滨海三角洲沉积体系中。下三角洲平原是该区化石植物最宜生长的地方。早二叠世该区化石植物常形成四类植物群落：森林沼泽植物群落、沿岸水生植物群落、高地植物群落、三角洲平原真蕨及种子蕨混生植物群落（早期）、树蕨－大羽羊齿类雨林植物群落（晚期）。随着时间的推移，这四类植物群落的结构及面貌发生着不断的变化；其演替显示，早二叠世晚期该区气侯更加湿热，雨林气侯更为普遍。  相似文献   

化脓性脊柱炎影像学诊断(附23例分析)     

唐桂长  郝明珠  王月训 《CT理论与应用研究》1993,(4)

笔者报告了23例化脓性脊柱炎。本文着重分析对比了X线平片和CT检查结果,通过分析对比,发现CT检查优于X线平片,并有助于对化脓性脊柱炎早期作出诊断。主要影像学表现:早期,软组织肿胀和脓肿形成,骨质呈虫蚀状破坏,随之破坏区周围出现增生硬化。CT 还能发现炎块中的气体。晚期,骨质修复占优势,即骨质增生硬化,骨桥形成,最后可产生骨性融合。  相似文献   

Variation among fossil chironomid assemblages in surficial sediments of Bodensee-Untersee (SW-Germany): implications for paleolimnological interpretation     

Alexandra Schmäh 《Journal of Paleolimnology》1993,9(2):99-108

In paleolimnology, subfossil head capsules of chironomids play an important role as ecological indicators of lake history. It is important to determine, therefore, whether fossil assemblages are representative of former biocoenoses. There is evidence that headcapsules washed in from other places can make up a significant percentage of the total. As interpretations are usually drawn from the examination of a single core, it is of special interest to know whether a fossil assemblage of a single site properly reflects limnological conditions of the whole lake. This study examined the taxonomic distribution of subfossil chironomids in the surficial sediments of the Bodensee-Untersee, with the aim of assessing the variability in chironomid assemblages. Apparently, most of the head capsules of the profundal fossil assemblages in the Untersee had been washed in from the littoral zone or from the slope. Although the Bodensee-Untersee is a rather large lake, variability is surprisingly low among all samples. Therefore a correct interpretation from a single core may be possible.  相似文献   

西藏申扎永珠乡晚石炭世和早二叠世的腕足动物化石     

刘发 《吉林大学学报(地球科学版)》1991,(3)

申扎地区石炭二叠系发育良好,化石丰富。本文描述的化石采自上下两个层位,下部化石少,以石燕贝类为主, 其组合特征反映了石炭纪腕足类的特点与改则县玛米雪山地区上石炭统所产相似;上部化石丰富,以石燕贝类的Spiriferella和Syrin-gothyris的出现为特征,共生还有长身贝类的Chonetinella,Echinauris,Tylo-pecta等。这个化石组合与西藏其他地区相同时代的化石组合不同。特别是Syringothy-ris在下二叠统的发现具有重要意义。  相似文献   

Definition of subfossil meandering palaeochannels     

Karol Rotnicki  Ryszard K. Borwka 《地球表面变化过程与地形》1985,10(3):215-225

The determination of the bottom of a subfossil meandering palaeochannel is important for investigations of the palaeohydrology of valley bottoms, and crucial for the quantitative estimation of past river discharges. The authors present a procedure on the basis of which the bottom of a palaeochannel can be precisely determined. It is based on an analysis of the stratigraphic variability of such features of deposits as: mean diameter, standard deviation of the grain-size composition, the percentage of sand, and ignition loss.  相似文献   

Structures caused by repeated freezing and thawing in various loamy sediments: A comparison of active,fossil and experimental data     

Brigitte Van Vliet-Lanoë  Jean-Pierre Coutard  Albert Pissart 《地球表面变化过程与地形》1984,9(6):553-565

In this paper, the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments. Experimental data are compared with observations performed on active forms in High Arctic and Alpine Mountain environments. Those observations are also compared with phenomena observed in fossil periglacial formations of Western Europe. Platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation. When a long series of alternating freezing and thawing affects platy structures, the fabric evolves, also being influenced by slope and drainage conditions: cryoturbations, frostcreep, and gelifluction can appear. They are characterized by specific microfabrics which are better developed with an increasing number of cycles: this is clear in experiments where hydraulic and thermal parameters are better controlled. Vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils. The genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost-created aggregates under the mechanical work of soil air escape during soil saturation by water at thaw.  相似文献   

豫西前寒武纪汝阳群遗迹化石   总被引：18，自引：3，他引：18  

杨式溥  周洪瑞 《地质论评》1995,41(3):205-210

本文研究的遗迹化石：Ｒｕｙａｎｇｉｃｈｎｕｓ ｌｏｙｕｅｎｓｉｓ ｉｃｈｎｏｇｅｎ，ｅｔ ｉｃｈｎｏｓｐ．ｎｏｖ．，Ｔｏｒｒｏｗａｎｇｅａ ｒｏｓｅｉ ｗｅｂｂｙ，Ｃｈａｎｇｃｈｅｎｇｉａ ｉｃｈｎｏｓｐ．，Ｓｑｕａｍｏｄｉｃｔ ｙｏｎ（？）ｉｃｈｎｏｓｐ．等发现于河南西部鲁山县和汝阳县的汝阳群云梦山组和北大尖组。根据同位素年龄值，微古植物和叠层石资料，产遗迹化石的汝阳群应相当于中元古代，可以和蓟  相似文献   

化脓性脊柱炎影像学诊断（附23例分析）     

房桂云  郝明珠 《CT理论与应用研究》1995,4(1):46-50

笔者报告了２３例化脓性脊柱炎。本文着重分析对比了Ｘ线平片和ＣＴ检查结果，通过分析对比，发现ＣＴ检查优于Ｘ线平片，并有助于对化脓性脊柱炎早期作出诊断。主要影像学表现：早期，软组织肿胀和脓肿形成，骨质呈虫蚀状破坏，随之破坏区周围出现增生硬化。ＣＴ还能发现炎块中的气块，晚期骨修复占优势，即骨质增生硬化，骨桥形成，最后可产生骨性融合。  相似文献   

南山坪古油藏的形成及其破坏因素分析   总被引：1，自引：0，他引：1  

凡元芳  丰勇 《矿产与地质》2005,19(3):296-298

南山坪古油藏以南山坪背斜(圈闭)为依托，油藏的形成、破坏与背斜(圈闭)的形成及演化息息相关。加里东晚期-海西早期的构造运动形成了南山坪背斜的雏形，与之对应的是最初的油藏形成；南山坪背斜在印支运动得到加强，形成构造圈闭，与之对应的是原油藏裂解生气及烃源岩进入生气阶段，形成气藏及部分沥青。之后的燕山运动Ⅱ幕使得南山坪背斜(圈闭)被褶皱和断层复杂化，形成由东南向北西的逆冲断裂，其上覆盖层抬升、剥蚀，原油藏彻底破坏，成为古油藏。分析认为，南山坪古油藏的破坏因素主要是印支期的热裂解和燕山运动Ⅱ幕的构造抬升、剥蚀，且后者更为主导因素。比较南山坪古油藏、余杭泰山古油藏及威远气藏，力图寻找其共性及差异性，从而为中国南方的油气勘探提供借鉴意义。  相似文献