http://www.tiefes-leben.de Thu, 11 Mar 2010 02:55:28 +0000 http://wordpress.org/?v=2.7 hourly 1 http://www.tiefes-leben.de/2009/03/peer-review-in-the-russian-paleontological-journal/comment-page-1/#comment-2118 tiefes-leben » Current developments in nautiloid research - a few remarks Mon, 02 Nov 2009 00:39:20 +0000 http://www.tiefes-leben.de/?p=72#comment-2118 [...] This question is easily answered by neontologists: Nautiloidea (subclass) are the others beneath the soft bodied cephalopods, the Coleoidea (subclass). Of the several hundred known living cephalopod genera [Felley et al. 2003, 1], only two are nautiloids, Nautilus, and Allonautilus. For neontologists, nautiloids are the few cephalopods which have primarily an outer shell [Lindgren et al. 2004, 2]. More problems arise for the classification of fossil cephalopods. Because nautiloids, are simply considered as stem-group cephalopods, nautiloids in the broad, classical sense are thus all old cephalopods that are not coleoids or ammonoids (this is the practice of the Treatise). However, the evolutionary history that lies between the appearance of the first cephalopod and between the appearance of the first coleoids is long and complex, thousands of extinct genera are known. Here, the neontological bipartition of cephalopods into nautiloids, and coleoids causes a great dilemma for the classification of fossil cephalopods, because it does not allow for the erection of new total groups that would express phylogenetic hypotheses, above the subclass level fixed by the Coleoidea. There are only few exceptions. Some extinct large monophyletic offshoots (plesions) can be excluded and treated as additional subclasses (e.g. ammonoids). However, for several proposed subclasses, such as actinoceroids, and bactritoids it is not clear if they represent paraphyletic/grade groups, or even polyphyletic groups [Kröger and Mapes, 2007a, b ]. For others, such as the Orthoceratoidea it would be appropriate to include new higher taxa above the subclass and below the class level, in order to classify extinct cephalopods in total groups that are transitional between coleoids and Nautilus. One approach to do this is that of Lehmann and Hillmer (1980), which distinguish between the Palcephalopoda and Neocephalopoda. The Neocephalopoda contain the ammonoids, coleoids and the diverse cephalopods with straight and coiled shells that are classified within the “Orthoceroidea”, and “Bactritoidea”, and the Lituitida. The Palcephalopoda are the remaining stem-group cephalopods. When accepting the bipartition of cephalopods into Neocephalopods and a stem-group grade than, the Palcephalopoda would  be a subjective junior synonym of the Nautiloidea. In fact, this is the implicit usage of the term “nautiloid” that I use since a few years in my own papers and that also has been practiced by the e.g. Manda and Turek (2009): nautiloids are stem group cephalopods exclusive ammonoids, bactritoids, coleoids and orthoceroids. Here I will call them “nautiloids sensu stricto”. In contrast the classical nautiloids of the Treatise, and that of the neontologist are all non-ammonoid cephalopods with an external shell. Here I will call them “nautiloids sensu lato”. A completely different classification was suggested by Shevyrev (2005), who divided cephalopods into eight subclasses. The subclasses itself comprise very different groups (paraphyletic/grade groups, plesions, and a crown group) many of them are considered as problematic and need serious revision [see here]. [...] [...] This question is easily answered by neontologists: Nautiloidea (subclass) are the others beneath the soft bodied cephalopods, the Coleoidea (subclass). Of the several hundred known living cephalopod genera [Felley et al. 2003, 1], only two are nautiloids, Nautilus, and Allonautilus. For neontologists, nautiloids are the few cephalopods which have primarily an outer shell [Lindgren et al. 2004, 2]. More problems arise for the classification of fossil cephalopods. Because nautiloids, are simply considered as stem-group cephalopods, nautiloids in the broad, classical sense are thus all old cephalopods that are not coleoids or ammonoids (this is the practice of the Treatise). However, the evolutionary history that lies between the appearance of the first cephalopod and between the appearance of the first coleoids is long and complex, thousands of extinct genera are known. Here, the neontological bipartition of cephalopods into nautiloids, and coleoids causes a great dilemma for the classification of fossil cephalopods, because it does not allow for the erection of new total groups that would express phylogenetic hypotheses, above the subclass level fixed by the Coleoidea. There are only few exceptions. Some extinct large monophyletic offshoots (plesions) can be excluded and treated as additional subclasses (e.g. ammonoids). However, for several proposed subclasses, such as actinoceroids, and bactritoids it is not clear if they represent paraphyletic/grade groups, or even polyphyletic groups [Kröger and Mapes, 2007a, b ]. For others, such as the Orthoceratoidea it would be appropriate to include new higher taxa above the subclass and below the class level, in order to classify extinct cephalopods in total groups that are transitional between coleoids and Nautilus. One approach to do this is that of Lehmann and Hillmer (1980), which distinguish between the Palcephalopoda and Neocephalopoda. The Neocephalopoda contain the ammonoids, coleoids and the diverse cephalopods with straight and coiled shells that are classified within the “Orthoceroidea”, and “Bactritoidea”, and the Lituitida. The Palcephalopoda are the remaining stem-group cephalopods. When accepting the bipartition of cephalopods into Neocephalopods and a stem-group grade than, the Palcephalopoda would  be a subjective junior synonym of the Nautiloidea. In fact, this is the implicit usage of the term “nautiloid” that I use since a few years in my own papers and that also has been practiced by the e.g. Manda and Turek (2009): nautiloids are stem group cephalopods exclusive ammonoids, bactritoids, coleoids and orthoceroids. Here I will call them “nautiloids sensu stricto”. In contrast the classical nautiloids of the Treatise, and that of the neontologist are all non-ammonoid cephalopods with an external shell. Here I will call them “nautiloids sensu lato”. A completely different classification was suggested by Shevyrev (2005), who divided cephalopods into eight subclasses. The subclasses itself comprise very different groups (paraphyletic/grade groups, plesions, and a crown group) many of them are considered as problematic and need serious revision [see here]. [...]

]]> http://www.tiefes-leben.de/2009/05/zehn-jahre-post-doc/comment-page-1/#comment-158 daehaex Fri, 29 May 2009 14:32:10 +0000 http://www.tiefes-leben.de/?p=111#comment-158 10 Jahre PostDoc. Respekt. Etwas mehr als 1 Jahr bin ich es nun. Ich bin gespannt wie es weitergeht und was noch alles kommen wird. 10 Jahre PostDoc. Respekt.
Etwas mehr als 1 Jahr bin ich es nun.
Ich bin gespannt wie es weitergeht und was noch alles kommen wird.

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