Large Newfoundland Tarphys

 
The New Mexico Museum of Natural History and Science in Albuquerque NM has in its fossil collection a number of large tarphycerids, an order containing the earliest coiled nautiloid cephalopods, from Newfoundland, Canada, originally belonging to the late Dr Rousseau Flower.   Two,  Loganites and Bennettoceras, were named by him but descriptions are lacking.  Others presumed also to be from Newfoundlland are unidentified.  
                        
                                                                                
Loganites, upper left,  Bennettoceras, middle left, and a large unnamed tarphycerid, bottom right.  All are external views.  Much of the matrix was artificially stripped away using Photoshop. Loganites is on the order of 7 in in diameter ( about 18 cm),  Bennettoceras is somewhat smaller, about 5 in ( 12.5 cm).   The straight portion of the unnamed specimen is about 7 in (18cm) as well.   All are internal molds.  All are Ordovician in age

A barrandeocerid section

Shown here is a section of a barrandeocid,, housed in the collections of the New Mexico Museum of Natural History and Science,  Albuquerque, NM, http://nmnautralhistory.org.  The specimen, P-56465, is about 8 cm long (about 3 in.).

The interpretation is mine, based  on the close spaced septa and narrow tubular siphuncle.  I have yet to assign a genus name. Location is unknown, but based in the overall color and general texture I'd say it came from the Ordovician of northeastern North America, most likely Newfoundland. 

The first picture, on the left, shows the overall specimen , what's left of it, an arc segment of one of the whorls. The second , below,, shows the specimen in greater detail with the septa and narrow, tubular siphuncle, located slightly below the center, clearly shown. 

                                                                          

Ammonites vs Nautiloids

Ammonites, subclass Ammonoidea, and nautilids, subclass Nautiloidea are first of all both cephalopods with external, chambered, shells. So how are they different and how are they alike, other than for their external shells

Nautiloids came first, having first appeared in the Late Cambrian, and gave rise to the ammonoids in the Early Devonian.  Some sticklers for cladistic purity might say that ammoinoids are simply a type of nautilids.   From a purely evolutionary perspective this could be said to be so.  However ammonoids are sufficient distinct to warrant being put in a separate equal taxon to the Nautilidea.  Why?  

Nautiloides have concave septa dividing the chambers of the phragmocone, as viewed from to front, looking back toward the apex of the shell.  Sutures, marking the junction of the septa with be body of the shell are generally straight and transverse or may have shallow saddles and lobes.  A few later forms from the Late Cretaceous and early Cenozoic even have goniatitic sutures, resembling those of the Late Paleozoic ammonoid Goniatitida. None have sutures nearly as complex as those found in Mesozoic ammonoids 


The siphuncle, the tube that interconnects the chambers in cephalopod shells is varied and often complex in  nautiloids but is always a simple narrow tube in ammonoids. Ammonoid siphuncles are commonly although not exclusively found along are ventral or outer margin. Nautiloid siphuncles are commonly ventral or central or somewhere in between. In both groups there are forms with dorsal siphuncles found along the near the dorsal or inner margin


In summary, one can study ammonoids from the outside, looking at general form, ornament, and sutures.  One has to study nautiloides from the inside to get a true picture, looking at the internal details of the shell, especially those of the siphuncle.

Some early actinocerids

Here are holotypes of three actinocerids (order Actinocerida) housed at the New Mexico Museum of Natural History and Science in Albquerque, N.M. They all belong to the Wutinoceratidae, which is an early actinocerid family and all three come from the Pallisaria zone in the Antelope Valley Limestone near Beatty, Nevada. They are, with museum catalogue numbers:

Adamsoceras leonardi P-42779
Cyrtonybyoceras adamsi P-42976
Wutinoceras huygenae P- 42877




All three are from the Whiterock stage at the beginning of the Middle Ordovician. Wutinoceras is considered the ancestral form, which gave rise to the other two, as well as to the Armenoceratidae and Actinoceratidae. Adamsoceras is thought to have given rise to the Ormoceratiae. Cyrtonybyoceras apparently left no descendants.

What about Barrandeocerida

Flower, in Flower and Kummel, in A Classiification of the Nautiloidea, Journal of Paleontology Sept 1950, estalished the Barrandeocerida as a separate order, derived from the Tarphycerida. Barrandeocerids first appear in the Middle Ordovician, later than the Tarphycerida which first appear in the Lower Ordovician. Moreover Barrandeocerids have derived (evolved) characters, the principal one being thin connecting rings. So it makes, or made, sense to separate the two on an equal basis.

As recently as 1976, Flower in his paper of Ordovician Cephalopod Faunas, published by the Palaeontological Society ( Gr Br) separated the Barradeocerida from the Tarphycerida, deriving the former from the latter. This changed in 1984.

Flower, in Bodeiceras; a New Mohawkina Oxycone; ... Journal of Paleontology Nov. 1984, showed that the first two families of the Barrandeocerida, the Barradeoceratidae and Plectoceratidae are derived from different genera in the Tarphyceratidae, making the Barrandeocerida polyphyletic and therefore invalid, which according to Flower, should be abolished. Families that were included in the Barrandeocerida now belong in the Tarphycerida, which as a result has become greatly expanded. However Teichert, 1988, in has review paper on Main Features of Cephalopod Evolution in The Mollusca Vol 12, Academic Press, retained the Barrandeocerida as a distiinct group, but as a suborder of the Tarphycerida, the Barrandeocerina. The other suborder of course being the Tarphycerina.

Flower's claim that the Barrandeoceratidae are derived from Centrotarphyceras and that the Plectoceratidae are derived from Campbelloceras is not stated with clear evidence, but is left for the reader to simply accept, or reject. For this reason the claim that the Barrandeocerida (sensu Flower 1950) is polyphyletic can not be taken as an absolute. It is obvious however that barrandeocerids form a group that evolved from earlier tarphycerids and might just as well be included as a suborder pending further evidence of separate origins for the Barradeoceratidae and Plectoceratidae.

No more Basslerocerida

The late Rousseau Flower in Flower and Kummel, 1950, in the Journal of Paleontology, Sept 1950 set up the Bassleroceratida as an order of nautiloid cephalopods intermediary between the more primitive, generally straight shelled Ellesmerocerida and the more evolved, coiled Tarphycerida and later Barrandeocerida. Basslerocerids are exemplified by the upwardly curved genus Bassleroceras in which the lower or ventral side is longitudinally convex and the upper or dosal side is curved in the opposite sense. The order at that time included two families, the Bassleroceratidae and Graciloceratidae.

Seven years later, Flower 1957 in Flower and Teichert, in a University of Kansas publication on the Discosorida, abandoned the Bassleroceratida and instead included the Bassleroceratidae, with thick connecting rings in the Tarphycerida and the Graciloceratidae with thin connecting rings in the Oncocerida.

Taking a somewhat difference approach, W.M, Furnish and Brian Glenister in the original, 1964 edition of Part K of the Treatise on Invertebrate Paleontology, included the Bassleroceratidae in the ancestral Ellesmerocerida . Walter Sweet on the otherhand followed Flower's perspective and retained the Graciloceratidae in the Oncocerida. Later, Flower, 1976, in a publication of the Palaeontological Society ( Gr Br) on Ordovician Cephalopod Faunas, shows the Bassleroceratidae in the Tarphyceratida (same as Tarphycerida), with the earlier more primitive forms giving rise to the Tarphyceratidae and the more derived forms later giving rise to the Oncocerida following his original (1957) idea.

So, to conclude, no more Basslerocerida. The order should be regarded as unnecessary, more so than "invalid". Never-the-less Shevyrev, 2006, according to the Paleobiology Database website, retained the Basslerocerida as a distinct nautiloid order, with the Barrandeocerina its sole suborder. This follows neither the sense of Flower (1950, 1957, and 1976), of the Treatise Part K, 1964, Teichert et al, or of Teichert 1988. For one thing the Barrandeocerina ( ex Barrandeocerida) are clearly derived from the Tarphyceratidae and therefore cannot be part of the Basslerocerida, regardless. Since what is presented on line is not necessarily what is in the original, perhaps Basslerocerida should really be Barandeoceida, which makes more sense.

Heteromorphs

Heteromorphic ammonites, or simply heteromorphs, hold a great fascination for some. It's easy to see why, what with their sometimes odd shapes that look as though the animal wasn't quite sure what it was doing. Shapes vary from simple coils that straighten out, some ending in hooks, to helically wound coils that then become planar, to straight shells that shift to the opposite direction connected by U-turns; and more and in between.

The term, heteromorph, or heteromorphic, means having more than one form or shape. While many heteromortph ammonites are heteromorphic, not all truly are. Some like the Crioceratidae have what are really openly coiled monomorphic (single form) shells, and others like the Turrilitidae have tall spired helically wound shells that are also monomorphic. Because these are related to truly heteromorphic forms, they are generally included in the heteromorphs. Truly hetermorphic forms include the Ancyloceratidae, Macroscaphitidae, Heteroceratidae, Ptychoceratidae, and even the Baculitidae.

A better. and more scientific approach is to refer to these taxonomically, to the Ancyloceratina for Cretaceous forms, or to the Ancyhloceratina and Turrilitina if the distinction is correst, and to the Choristcerataceae (Choristoceratoidea if you want to go along with the rank ambiguous requirement of the ICZN) for Upper Triassic forms.