Prolecanitida
Encyclopedia
The Prolecanitida are extinct ammonoid cephalopods with discoidal to thinly lenticular shells with goniatitic or ceratitic sutures and which retained the simple retrochoanitic siphuncle
with backward extending septal necks. As typical for ammonoids the siphuncle is along the ventral margin. Prolecanitids form a relatively small and stable order within the Ammonoidea with 43 named genera and about 1250 species, but with a long-ranging lineage of about 108 m.y. stretching from the Lower Carboniferous
to the Triassic
. Although not as diverse as their goniatitid contemporaries, the Prolecanatida provided the stock from which all later Mesozoic ammonoids were derived.
which was originally included in the Anarcestida but recently removed ot the Goniatitida. Following their inception, the Prolecanitida divided into two lineages, idenfied by superfamilies; the earlier U Dev – M Perm Prolecanitaceae
in which the shells are fairly smooth and characteristiclly have a large umbilicus and the later U Miss-Trias Medlicottiaceae
in which the umbilicus is small and there is moderate sculpture along the flanks. The Prolecanitaceae, through the derived family Daraelitidae
is the source for the Ceratitida
, beginning with the Xenodiscidae
Prolecanitids showed long-term, gradual changes in shell geometry and the most limited use of available forms (euphamistcally morphospace) as compared to the dominant goniatitds. Prolecanitid genera averaged 14.7 m.y. in duration as compared to 5.7 m.y. for Upper Carboniferous goniatitids.
Suture morphology in the Prolecanitida changed dramatically over time, from very simple sutures in the earliest (Devonian) genera to extremely complex-sutured genera in the late Paleozoic. The increase in suture complexity over the 108 m.y. duration resulted from the iterative of addition of umbilical lobes, serration of lobes, and the subdivision of lateral and ventral lobes As many as 12–15 replicate, U-shaped umbilical lobes, originating at the umbilicus and migrating across the flanks were added to the sutures during both ontogeny and phylogeny
Not only did the Prolecanitida evolve their sutures differently than in the Goniatitda, by increasing the number of umbilical lobes rather than by subdivision of the lateral saddle, their body chambers were short by comparison. This brings up the question of, just how closely related were the Prolecanitida and their Mesozoic descendants to the goniatitids.
Siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...
with backward extending septal necks. As typical for ammonoids the siphuncle is along the ventral margin. Prolecanitids form a relatively small and stable order within the Ammonoidea with 43 named genera and about 1250 species, but with a long-ranging lineage of about 108 m.y. stretching from the Lower Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
to the Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
. Although not as diverse as their goniatitid contemporaries, the Prolecanatida provided the stock from which all later Mesozoic ammonoids were derived.
Evolution and Phylogeny
The Origin of the Prolecanitida may be found in the ProlobitidaeProlobitidae
Prolobitidae is a family of middle and upper Devonian ammonoid cephalopods currently included in the goniatitid suborder Tornoceratina and superfamily Dimeroceratoidea, but previously included in the ancestral Anarcestida....
which was originally included in the Anarcestida but recently removed ot the Goniatitida. Following their inception, the Prolecanitida divided into two lineages, idenfied by superfamilies; the earlier U Dev – M Perm Prolecanitaceae
Prolecanitaceae
Prolecanitaceae is a taxonomic superfamily of ammonites, fossil cephalopods. This is one of two superfamilies in the Prolecanitida. The other is the Medlicottiaceae....
in which the shells are fairly smooth and characteristiclly have a large umbilicus and the later U Miss-Trias Medlicottiaceae
Medlicottiaceae
The Medlicottiaceae is the second of the two superfamilies that make up the Prolecanitida, the first being the Prolecanitaceae.The Medlicottiaceae are recognized by their discoidal to thinly lenticular, and involute shells with small umbilici; flat, often grooved venters, and variably complex sutures...
in which the umbilicus is small and there is moderate sculpture along the flanks. The Prolecanitaceae, through the derived family Daraelitidae
Daraelitidae
The Daraelitidae form a family in the ammonoid order Prolecanitida from the Upper Mississippian - Middle Permian characterized by discoidal shells with no prominent sculpture, moderately large umbilicus, and goniatitic or ceratitic sutures with a trifid ventral lobe and few auxiliary lobes.The...
is the source for the Ceratitida
Ceratitida
The Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian, the exception being the phylloceratids which gave rise to the great diversity of post Triassic ammonites....
, beginning with the Xenodiscidae
Prolecanitids showed long-term, gradual changes in shell geometry and the most limited use of available forms (euphamistcally morphospace) as compared to the dominant goniatitds. Prolecanitid genera averaged 14.7 m.y. in duration as compared to 5.7 m.y. for Upper Carboniferous goniatitids.
Suture morphology in the Prolecanitida changed dramatically over time, from very simple sutures in the earliest (Devonian) genera to extremely complex-sutured genera in the late Paleozoic. The increase in suture complexity over the 108 m.y. duration resulted from the iterative of addition of umbilical lobes, serration of lobes, and the subdivision of lateral and ventral lobes As many as 12–15 replicate, U-shaped umbilical lobes, originating at the umbilicus and migrating across the flanks were added to the sutures during both ontogeny and phylogeny
Not only did the Prolecanitida evolve their sutures differently than in the Goniatitda, by increasing the number of umbilical lobes rather than by subdivision of the lateral saddle, their body chambers were short by comparison. This brings up the question of, just how closely related were the Prolecanitida and their Mesozoic descendants to the goniatitids.