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The topology of the septa, especially around the rim, results in the various suture patterns found. [5] The septal curvature in nautiloids and ammonoids also differ in that the septa curves towards the opening in nautiloids, and away from the opening in ammоnoids. [6] Regions of the suture line and variants in suture patterns Ammonite clean cut
The sutures of nautiloids are by comparison somewhat simpler, being either straight or slightly curved, whereas later ammonoids showed suture patterns of increasing complexity. One explanation for this increasing extravagancy in suture pattern is that it leads to a higher strength of the shell.
The chambers are separated by walls called septa. The line where each septum meets the outer shell is called the suture or suture line. Like other true ammonites, Baculites have intricate suture patterns on their shells that can be used to identify different species.
This ammonite has a ceratitic suture pattern on its shell (smooth lobes and frilly saddles). Evolution of the frilly saddles is thought to be due to increased pressure on the shell, at greater depth. The frilly pattern would increase the strength of the shell and allow Ceratites to dive deeper, possibly in search of food. [citation needed]
Daraelitids are probably ancestral to Ceratitida, the dominant order of Triassic ammonoids. A third proposed family, the Mississippian-age Prodromitidae, is occasionally also placed within the order Prolecanitida. [1] The affinities or monophyly of this family are uncertain due to drastic changes in their suture patterns through ontogeny.
a) juvenile; b) adult; c) sutural pattern. Mammites is a Late Cretaceous (Cenomanian to Turonian) ammonite genus included in the acanthoceratoidean family, Acanthoceratidae, and the type genus for the subfamily Mammitinae. Mammites was named by Laube and Bruder in 1887. [1] [2]
Sutures are generally ammonitic, characterized by complex saddle and lobe patterns. However, in some derived forms, the suture pattern becomes simplified, appearing ceratitic or even goniatitic. The Ammonitina are derived from the Phylloceratina, another ammonitid suborder which has its origin in the Ceratitida of the Triassic .
Early whorls have umbilical tubercles that in later whorls appear higher on the sides. Earlier whorls normally have lower and fine upper ventrolateral clavi. Ornament weakens in the adult and the last whorl may be smooth. The suture is with numerous adventitious and auxiliary elements, with saddles and lobes that are much frilled.