摘要:

Septal strength index has become a prime means of establishing maximum living depths of fossil cephalopods with simple, concave septa. This method calculates palaeobathymetric limits from the septal geometry ofNautilus, based upon the premise that septa are the weakest structural .unit of the shell. We examined this proposal by evaluating data relating to ontogeny, septum formation, septal geometry, and microstructure ofNautilus. Our main results are: 1) septal strength index of embryonic and juvenile septa are not representative of the depths at which such specimens live, 2) septa become fully functional in resisting hydrostatic pressure at thicknesses significantly less than that used to compute strength index, 3) no correlation has been demonstrated between septal strength index and rupture pressure, and 4) shell microstructure does not show sufficient uniformity among cephalopods to permit an undocumented assumption of uniformity in mechanical properties of cephalopod shell material. These observations indicate that: 1)Nautilusis an improper paradigm upon which to base depth calculations for fossils, 2) strength index misidentifies septa as the weak link in cephalopod shell design, and 3) the strength index approach must be refined to accommodate the effects of sutural characteristics and other factors, before it can be regarded as providing accurate estimates for living depths of fossil cephalopods.

ISSN:0311-5518    

DOI:10.1080/03115518608619162

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0311-5518    

DOI:10.1080/03115518608619163

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A format is presented for describing the largely conservative mandible of the Triassic temnospondyls. It concentrates on those features which can be used to identify whole or sometimes partial mandibles to family level, and can be used to some extent to ascertain relationships between the families. The mandibular feature having the most diagnostic value is the postglenoid area. An example of the use of the format is given using previously undescribed material and the format is applied to some problematical examples.

ISSN:0311-5518    

DOI:10.1080/03115518608619164

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Representatives of the generaNeospiriferFrederiks andTrigonotretaKoenig are described from the Permian sequences of the Perth, Carnarvon, Canning and Bonaparte Gulf Basins of Western Australia. New or revised taxa areNeospirifer hardmani(Foord),Neospirifer foordisp. nov.,Neospirifer plicatussp. nov.,Neospirifer postplicatussp. nov.,Neospirifer amplussp. nov.,Neospirifer grandissp. nov.,Trigonotreta lyonsensissp. nov.,Trigonotreta neoaustralissp. nov.,Trigonotreta dickinsisp. nov. andTrigonotreta lightjackisp. nov. Additional material belonging toNeospiriferis briefly described and a lectotype is designated forNeospirifer timorensis(Martin) from Timor.

ISSN:0311-5518    

DOI:10.1080/03115518608619165

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor