Prolecanitida
Prolecanitida is an order of extinct ammonoid cephalopods, the major Late Paleozoic group of ammonoids alongside the order Goniatitida. Prolecanitids had narrow shells, discoidal (disc-shaped) to thinly lenticular (lens-shaped). They retained a retrochoanitic siphuncle, a simple form with septal necks extending backwards. As is typical for ammonoids, the siphuncle sits along the ventral margin of the shell.
| Prolecanitida Temporal range: | |
|---|---|
| Protocanites, a Tournaisian prolecanitoid in the family Prolecanitidae | |
| Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Subclass: | †Ammonoidea |
| Order: | †Prolecanitida Miller & Furnish, 1954 |
| Superfamilies | |
Prolecanitids form a relatively small and stable order within the Ammonoidea, with 43 named genera and about 1250 species. They were a long-ranging lineage, surviving for about 108 m.y. stretching from the Devonian–Carboniferous boundary to the Early Triassic. Although not as diverse as their goniatitid contemporaries, the Prolecanatida provided the stock from which all later Mesozoic ammonoids were derived.
Most prolecanitids had goniatitic sutures. The sutures start at a narrow ventral lobe, which can range from undivided to tridentate (three-pointed). The saddles are generally rounded, with the first umbilical (or second lateral) saddle often the largest in the suture line. The lobes are usually pointed, though members of the family Daraelitidae acquire a few finely serrated lobes (as characteristic for ceratitic sutures). The first lateral saddle is proportionally small, though its corresponding lateral lobe is broad and typically bifid (two-pointed).