Some cephalopod classifications have the Order Endocerida separated from the Nautiloidea and put instead in the Subclass Endoceroidea (or Endoceratoidea), following the scheme of Curt Teichert in the Treatise on Invertebrate Paleontology. The question is, are they all that different so as to warrant their exclusion from the Nautiloidea and inclusion in another subclass. Teichert thought so, as he did for the Actinocerida, placing them in the Actinoceratoidea (or Actinoceroidea). Russeau Flower thought not, on both accounts, for which I'm in full agreement.
First of all, in brief, what are endocerids. They are cephalopods with straight or downwardly curved shells, close spaced septa, chaambers free of organic deposits, and large ventral siphuncles containing conical deposits concentrated toward the rear known as endocones. The septa are dish-shaped, concave from the front. Septal necks, protrusions of the septa that make up part of the siphuncle point to the rear. Both are characters of the Nautiloidea. These don't necessarily limit the Endocerida to the Nautiloideaas their could be other things calling for their separation. So let's take a quick look at Teichert's reasoning.
The addition of the Subclass Endoceroidea is based on the comination of the Endocerida with the Intejocerida, which turms out to be a group of unrelated cephalopods (according to Flower) whose common charater happens to be the presence of radial lamenllae in the siphuncle. In other characters such as siphuncle location they are quite different. I'll try and touch on the Intejocerida later on. Meanwhile there doesn't seem to be any reason to exclude the Endocerida from the Nautiloidea.
They aren't all that different
Monday, January 30, 2012
Saturday, January 28, 2012
What happened to the Basslerocerida.
The order Basslerocerida was established (erected in the odd parlance) by Rousseau Flower (1950) for nautiloides intermediate between straight shelled Ellesmerocerida and coiled Tarphycerida. Species included are in general, exgastrically cyrotoconic, curved like an old rocking chair rocker. Through the powers of evolution the upwardly curved shells became wound back on them selves, first as open, gyroconic spirals, then serpenticones with whorls in contact, true tarphycerids So what happened to them other than that.
Well first of all they did not disappear from the fossil record or vanish from time. The order simply stopped being used, except in historical reference. Flower (1976) simply abandoned the order and included the Bassleroceratidae in the Tarphycerida as the ancestral family, whereas William Furnish and Brian Glennister previously (1964) had included them in the Ellesmerocerida. Take your pick. Either works. As for me, I go along this time with Furnish and Glennister, for what ever it's worth which probably isn't all that much, leaving Tarphycerida for truly coiled forms.
Rousseau Flower and Bernhard Kummel, 1950. A Classification of the Nautiloidea - Journal of Paleontology
Rousseau Flower, 1976, Ordovician Cephalopod Faunas and Their Role in Correlation -Palaeontological Assoc.
William Furnish and Brian Glennister, 1964. Nautiloidea - Ellesmerocerida. --Treatise on Invertebrate Paleontology
Well first of all they did not disappear from the fossil record or vanish from time. The order simply stopped being used, except in historical reference. Flower (1976) simply abandoned the order and included the Bassleroceratidae in the Tarphycerida as the ancestral family, whereas William Furnish and Brian Glennister previously (1964) had included them in the Ellesmerocerida. Take your pick. Either works. As for me, I go along this time with Furnish and Glennister, for what ever it's worth which probably isn't all that much, leaving Tarphycerida for truly coiled forms.
Rousseau Flower and Bernhard Kummel, 1950. A Classification of the Nautiloidea - Journal of Paleontology
Rousseau Flower, 1976, Ordovician Cephalopod Faunas and Their Role in Correlation -Palaeontological Assoc.
William Furnish and Brian Glennister, 1964. Nautiloidea - Ellesmerocerida. --Treatise on Invertebrate Paleontology
Saturday, January 21, 2012
Nautiloids vs Ammonites
How to you recognise a nautiloid cephalod from an ammonoid cephalopod. It seems the distinction is not ofter readily explained.
The standard explanation, often give, is that nautiloids, represented by the living Nautilus has a central siphuncle while ammonioids (i.e. ammonites) have siphuncles that run along the outer rim of the shell. True for most ammonites by far and certainly true for Nautilus, Another explanation is that nautiloids have simple sutures whre the septa join the outer shell while ammonites have complex sutures. Certainly some ammonites have very complex, crenelated suture patterns, far more complex than any nautiloid. On the other hand no ammonite has the complexity to its siphuncle as found in some nautiloids., So what is the primary difference between the two that can be found in their shells.
The answer is actually rather simple. The answer is found in their septa, the partitians that separate the chambers in that portion of the shell, known as the phragrocone, that indicates that the physiology of the two was rather distinct. As viewed from the front, looking back, all nautiloids have concave, dish-shaped septa. Ammonoids have symmetrically contoured, convex septa. Nautiloids can simply secrete a new septum from the back of the mantle after moving forward. Ammonoids have to shape their mantles before secreting new septa
The picture to the left shows the vertical cross section of a gonititid ammonite (left) and of a recent Nautilus (right). Note the difference in the profiles of the respective septa -- arched forward (convex) in the ammonite, dish-shaped (concave) in Nautilus, representing the Nautiloidea.
The standard explanation, often give, is that nautiloids, represented by the living Nautilus has a central siphuncle while ammonioids (i.e. ammonites) have siphuncles that run along the outer rim of the shell. True for most ammonites by far and certainly true for Nautilus, Another explanation is that nautiloids have simple sutures whre the septa join the outer shell while ammonites have complex sutures. Certainly some ammonites have very complex, crenelated suture patterns, far more complex than any nautiloid. On the other hand no ammonite has the complexity to its siphuncle as found in some nautiloids., So what is the primary difference between the two that can be found in their shells.
The answer is actually rather simple. The answer is found in their septa, the partitians that separate the chambers in that portion of the shell, known as the phragrocone, that indicates that the physiology of the two was rather distinct. As viewed from the front, looking back, all nautiloids have concave, dish-shaped septa. Ammonoids have symmetrically contoured, convex septa. Nautiloids can simply secrete a new septum from the back of the mantle after moving forward. Ammonoids have to shape their mantles before secreting new septa
The picture to the left shows the vertical cross section of a gonititid ammonite (left) and of a recent Nautilus (right). Note the difference in the profiles of the respective septa -- arched forward (convex) in the ammonite, dish-shaped (concave) in Nautilus, representing the Nautiloidea.
Monday, January 16, 2012
On taxonomy
Taxonomy first of all has to do with organizing things and ideas into a hierachy of logical sets. Not only should it be based on real, natural relations, i.e. have evolutionary validity, but should provide a basis for conversation. Ammonoids may have been derived from one group of nautiloids (orthocerids) but when we refer to nautiloids it should be implicit we aren't including ammonoids, nor is there any reason to do so.
I prefer the nested Linnean taxonomic approach to the less precise cladistic approach, although the latter does have application in phylogenetics. Regarding cephalopod taxonomy I generally follow the schemes of Rousseau Floower and the Treatise on Invertebrate Paleonotolgy (parts K, Nautiloidea etc, and L, Ammonoidea) with some ideas of my own.
Ammonites vs Nautiloids coming up.
I prefer the nested Linnean taxonomic approach to the less precise cladistic approach, although the latter does have application in phylogenetics. Regarding cephalopod taxonomy I generally follow the schemes of Rousseau Floower and the Treatise on Invertebrate Paleonotolgy (parts K, Nautiloidea etc, and L, Ammonoidea) with some ideas of my own.
Ammonites vs Nautiloids coming up.
Starting off
I've started this blog to share my interest and ideas on cephalopods, mainily shelled varieties, nautiloids and amminites (Ammonoidea). I'm an independent and amature (in the true sense of the word) researcher and paleontologist working part time at the New Mexico Museum of Natural History and Science with access to its large and comprehensive fossil collection. My ideas come from comprehensive review of the literature, both old and recent, and from examination of specimens, both type and general.
Most of the specimens I work with came from the late Dr Rousseau Flower who taught at New Mexico Tech in Socorro. NM, and which were transferred some years ago to the Museum after his death.
As a matter of further back ground I have a degree (BS) in geology from the University of Arizona with an emphasis on invertebrate paleontology although my professional career since took a different direction. Now retired I am able to devote time to what was to have been my passion.
Hope you enjoy
John McDonnell
Most of the specimens I work with came from the late Dr Rousseau Flower who taught at New Mexico Tech in Socorro. NM, and which were transferred some years ago to the Museum after his death.
As a matter of further back ground I have a degree (BS) in geology from the University of Arizona with an emphasis on invertebrate paleontology although my professional career since took a different direction. Now retired I am able to devote time to what was to have been my passion.
Hope you enjoy
John McDonnell
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