| Agoniatitida | |
|---|---|
 | |
| An image showing the siphuncle (which could be agoniatitid), the tube which connects the current living shell to the previous ones. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Subclass: | †Ammonoidea |
| Order: | †Agoniatitida Ruzhencev, 1957 |
| Suborders | |
Agoniatitida, also known as theAnarcestida, is the ancestral order within thecephalopod subclassAmmonoidea originating frombactritoidnautiloids, that lived in what would becomeAfrica,Asia,Australia,Europe, andNorth America during theDevonian from about the lower boundary of Zlichovian stage (corresponding to latePragian, after 409.1mya) intoTaghanic event during upper middleGivetian (between 385 and 384 mya), existing for approximately 25 million years.
The Order Agoniatitida, named by Ruzhencev, 1957,[1] is a subjective synonym for the Order Anarcestida, named by Miller and Furnish, 1954.[2] Accordingly, the name Anarcerstida is based on the family Anarcestidae (ex Anarcestinae) of Steinmann 1890. That of Agoniatiida is based on the family Agnoniatidae of Holzapfel, 1899.
Saunders, Work, and Nikolaeva, 1999,[3] refer to the Anarcestida, with Agoniatina a suborder, maintaining the priority as found in the Treatise. Shevyrev, 2006[4] on the other hand follows Ruzhencev, 1957 and used Agonititida.
Agoniatitids are primitiveammonoids with a ventral retrochoaniticsiphuncle (septal necks point to the rear) reflective of theirnautiloid ancestors and goniatitic sutures with a variable number of lobes. Shells vary from discoidal to globular. Coiling may be loose with whorls barely touching or tight with a dorsal impression.[2]
Fossils are restricted to strata of the Zlichovian (LatePragian/EarlyEmsian) to late middleGivetian epochs.
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