Agoniatitida

Agoniatitida, also known as the Anarcestida, is an ancient group of sea creatures that lived long ago. They belong to a special family of cephalopods, which includes animals like squids and octopuses, called Ammonoidea. These creatures came from a group of sea animals called bactritoid nautiloids.

They lived in many parts of the world, including Africa, Asia, Australia, Europe, and North America. Their time on Earth was during a period called the Devonian, which was about 409 to 384 million years ago. They existed for around 25 million years before disappearing during an event known as the Taghanic event.

Taxonomic nomenclature

The Order Agoniatitida was named by Ruzhencev in 1957. It is another name for the Order Anarcestida, which was named by Miller and Furnish in 1954. The name Anarcestida comes from a group of animals called the Anarcestidae, first described by Steinmann in 1890. The name Agoniatitida comes from a different group called the Agoniatidae, described by Holzapfel in 1899.

Some scientists, like Saunders, Work, and Nikolaeva in 1999, use the name Anarcestida and consider Agoniatitida a smaller part of it. Others, like Shevyrev in 2006, follow Ruzhencev’s naming and use Agoniatitida instead.

Morphology

Agoniatitids were simple ammonoids with a special tube called a siphuncle that pointed backward, showing their link to older nautiloids. Their shells could look different, from round to roundish, and they coiled in various ways, sometimes touching and sometimes not.

Fossil distribution

Fossils of these ancient sea creatures are found in rock layers from the Zlichovian (Late Pragian/Early Emsian) to the late middle Givetian time periods.