Goniatitida - Ancestor to Later Ammonites

Middle Devonian through Late Permian
392 to 251 million years ago

The Goniatida were the most important order of the Paleoammonoids serving as the ancestors to all subsequent ammonite species. 

Diversity, Geographic Range and Habitat

• The Goniatitida demonstrate a wide range of body types and therefore many different orders, genera and species
  • Click here to see graph data
• Some species were distributed widely throughout a given region and the species themselves experienced short turnover rates which means that a species died out quickly (after only a few million years) and were replaced by another short-lived group.
  • This rapid turnover rate enables them to serve as Index Fossils - fossils used by scientists to identify and date geologic strata. 
• Their fossils are found in plentiful supply in both anoxic and aerobic environments
  • The fact that their fossils are found in many types of rocks indicates that they lived in a variety of habitats ranging from shallow to deep waters and preferring tropical to sub-tropical environments

Characteristics

Shell Structure

• Most Goniatites were on the small side - usually less than 6 inches in diameter
• Involute shells
• Some were globular in shape while others were discoidal (disc-shaped)

Siphuncle

• Ventral position although the siphuncle would begin in a central position before moving towards the ventral position as the animal grew.

Septal Neck

• Prochoanitic (points forward, toward the body chamber)

Suture Lines

• They had simple suture lines which formed the famous goniatitic suture pattern with strongly-pointed lobes and rounded saddles
  • It's important to note that not all Goniatitic ammonites bore the classic suture patterns; indeed, some had displayed the Ceratitic pattern while others tended towards a more ornate pattern resembling the Mesoammonoids.
• Other Ammonite groups also share the Goniatitic suture patterns
  • Many Anarcestida
  • Clymeniida
  • Prolecanitida
  • Actually, typical of many, if not most, paleoammonoids
• Nevertheless there are a considerable number of Goniatitida that had Ceratitic sutures

Ornamentation

• Some were smooth while others had lightly ribbed ornamentation
• Some species had ribs that spiraled around the shell while others had ribs that ran the length of the coiled shell

Ancestry and Descendants

• Ancestor:  It is thought that the Goniatitida derived from the Anarcestida
• Descendants: All other Jurassic and Cretaceous Orders orders: Phylloceratida, Ammonitida, Lytoceratida and Ancyloceratida

Other

• Goniatites may have had a small hyponomic sinus

Ammonitella

• Small - initial chamber around 07 mm in diameter
• The ammonitella had a short, curved prosiphon which was the beginning of the siphuncle
• Longitudinal ribs ran along the lenght of the shell similar to many of the adults.