Agoniatitida

Agoniatitida, also called the Anarcestida, was an ancient group of sea creatures. They are part of a special family of cephalopods. This family includes animals like squids and octopuses, called Ammonoidea. These creatures came from a group of sea animals known as bactritoid nautiloids.

They lived in many parts of the world. These places include Africa, Asia, Australia, Europe, and North America. Their time on Earth was during a period called the Devonian. This was about 409 to 384 million years ago. They existed for around 25 million years. They disappeared during an event called the Taghanic event.

Taxonomic nomenclature

The Order Agoniatitida was named by Ruzhencev in 1957. It is another name for the Order Anarcestida, 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 think Agoniatitida is a smaller part of it. Others, like Shevyrev in 2006, follow Ruzhencev’s naming and use Agoniatitida instead.

Morphology

Agoniatitids were simple ammonoids. They had a special tube called a siphuncle that pointed backward. This showed they were related to older nautiloids. Their shells could look different, from round to roundish. They coiled in different ways, sometimes touching and sometimes not.

Fossil distribution

Fossils of these old sea animals are found in rocks from the Zlichovian (Late Pragian/Early Emsian) to the late middle Givetian times.