Nautiloid
Live reconstruction of extinct nautiloid
- Worldwide
The nautiloids ( Nautiloidea ) are a subset of the cephalopods ( Cephalopoda, Mollusca ), up to an enduring family today, the nautilus ( Nautilidae ), is extinct. This taxon was very rich in form with about 800 known species. 90% of them lived in the era of the Paleozoic, the Triassic about 26 in Jungmesozoikum ( Jurassic and Cretaceous ), 9 in the Paleogene and 3 were still about 30 genera ago, in Neogene. Today two genera, Nautilus live with four species and Allonautilus with a kind Both come in the central Indo-Pacific from the Philippines to Samoa before.
In the classical rank-based classification, the Nautiloidea have the status of a subclass within the cephalopods ( Cephalopoda ).
- 6.1 Literature
- 6.2 Notes and references
Features
Housing
All nautiloids have an outer casing, which can be of very different shape, often a highly specialized Sipho and concave, unfolded in most cases septa. The smallest housing are just over an inch long, the largest reaching lengths of nearly ten meters, with a maximum diameter of about 30 cm. The case was elongated and straight ( ORTHOCON ) or curved ( cyrtokon ), Barrel ( brevikon ) or rolled ( gyrokon ). The latter can be rolled in a plane (flat spiral ) and different like a snail shell in the room rolled ( torticon ). In some genera the housing forms changed in the course of their ontogeny. The cross sections of the housing are roundish or oval, with tightly coiled shells mostly high - in rarer cases, transverse oval. The mouth of the case is usually not entire. Often a sinusoidal recess for the hopper available ( hopper bay ). Inwardly bent housing projections may constrict the mouth, but it can also extend like a trumpet. When stretched housings, the extension of the living chamber is variable; it can take the largest part of the housing, or only a small portion. In tightly coiled shells they usually comprises a half dealing, sometimes a little less. For very tight enclosures it can take a whole turn. The cuttlebone, which by septa ( septa ) Adjoining the living chamber to chambered rear lifting body. The septa divide the interior of the housing transversely or obliquely. You can narrow are what has small chamber lumen result, or far with large chamber lumen. Towards the mouth they are concave curved and follow the inner wall of a piece. The free part of the septum has a pearly surface tier. The line will be at the meet the septa inside the casing and fused him called suture. The support ring with which the sutures are fused with the housing interior is called Muralleiste. The Muralleiste that separates the living room from the cuttlebone, also serves as the attachment point for the adhesion and the visceral sac Retraktormuskulatur the nautiloids.
The chambers of the cuttlebone are connected to each other through the siphon. This can pull through the chambers ( through the center of the septa ) or have a dorsal upper ventral margin more or less central location. At the points of passage through the septa these are tube-like, extended by pointing away from the living chamber Siphonalduten whose morphology is very versatile. The siphon can reach a thickness of nearly half the housing bore diameter or, as in Nautilus, be very thin. In genera with thick Sipho is believed that he also absorbed a portion of the intestines
In addition to the enclosures, which consist of calcite jaws of nautiloids are in the fossil record, especially from the Triassic, more rarely from the Paleozoic. Most of them are so-called Rhychotheuten, upper jaw, which are divided by ridges into three or four sections. Less common are calcified maxillary tips ( Rhychocholiten ) similar to those of today's Nautilus. Even rarer are the mandible ( Conchorhynchen ). From the Carboniferous there is a single find of a nautiloid - radula, which is quite similar to the recent Nautilus.
Of the Ammonites ( Ammonoidea ), the nautiloids can be distinguished primarily on the basis of externally smoother housing, the simple sutures and the complex built Sipho. When the Ammonites, the outer housing surface is often more or less ripped strong, the sutures are complex and Sipho easy.
Soft parts
Soft tissues are not fossil preserved. It is generally assumed that similar to were the body of extinct nautiloid Nautilus. Early forms that had barrel-shaped, vertically oriented housing, could have owned a worm -like crawling foot.
Evolution
Apart from Nectocaris from the Middle Cambrian nautiloids which are the oldest cephalopods. The earliest date back to the upper Cambrian. They were tapered, relatively wide and short casing in which the housing chamber or the largest part of the overall housing occupied, and which was oriented perpendicularly in the living animal. Cephalopods probably evolved from Contracts Manager - like organisms and the first forms possessed probably still a screw-like crawling foot. The main trend in the early evolution of nautiloids is the acquisition of buoyancy through the development of cuttlebone to a float.
In the diversity of Ordovician nautiloids increased sharply and with forms like Cameroceras which had a nearly ten meters long housing, provided the nautiloid the largest occurring at that time living beings. In Devon the Nautilida, the Group is one of the Nautilus and has survived as the only published today. All Nautiloideengruppen to the Nautilida and Orthocerida who survived until the Triassic, became extinct at the end of the Devonian or during the Carboniferous. From the Orthocerida probably developed the Bactritida, which in turn were the ancestors of the Ammonites and the squid ( Coleoidea ).
At the end of the Triassic and the Nautilida died out except for a single genus, which then became the origin of a new nautiloid - radiation during the Mesozoic.
System
The following cladogram shows the position of the nautiloids as a basal group within the cephalopods ( Cephalopoda ):
Nautiloidea
Orthocerida [ An 1 ]
Ammonites ( Ammonoidea )
Bactritida
Belemnites ( Belemnoidea )
Squid ( Coleoidea )
Untertaxa
The sub-groups of nautiloids, in the classical rank-based system with the rank of orders or sub-orders are listed here in order of occurrence in time:
- † Plectronocerida
- † Ellesmerocerida
- † Endocerida
- † Orthocerida [ An 1 ]
- † Actinocerida
- † Tarphycerida
- † Barrandeocerida
- † Discosorida
- † Oncocerida
- † Ascocerida
- Nautilida