Ancyloceratida - the Heteromorphs

Early Jurassic thru Late Cretaceous

199 to 65.5 million years ago

This heteromorph order consisted of ammonites of unusual shell configurations. Their longevity as an order and their wide distribution speaks to their successful adaptation to a wide range of environments.  Some of the most widespread and most common ammonites are in this order.

There were Five Main Groups of Ancyloceratida

• Ancylocerataceae
• Deshyesitaceae
• Douvilleicerataceae
• Turrilitaceae
• Scaphitaceae

Diversity, Geographic Range and Habitat

• Remained widespread through the Late Cretaceous in contrast to the Ammonitida which were in decline by the Late Cretaceous
• Their diversity, geographic range and rapic turnover make them perfect tools for biostratigraphical studies

Characteristics of the Five Main Groups

Ancyloceataceae

• They appeared during the late Jurassic
• This group is the most primitive of the five groups
• Went Extinct in the Late Cretaceous
• Their shells were spiraled except for the body-chamber which hung beneath the spiral in a hook-shape

Deshayesitaceae

• Most common and widespread during the Cretaceous although by the Late Cretaceous they were gone
• They are an important biostratigraphy species for the Late Cretaceous
• Their shell is a regular coiling spiral
• Generall have an evolute shell with strong ribbing and are often display many spines

Douvilleicerataceae

• Common and widespread during the Cretaceous
• Extinct by the Late Cretaceous
• This group is also an important biostratigraphy marker
• Their shells are regularly coiled and usually evolute
• Their ornamation consists of pronounced ribbing and numerous spines

Turrilitaceae

• Appeared in the Cretaceous and rapidly radiated into a wide array of shapes
• They are the ancestors to the Scaphitaceae, although their relationship to the Ancylocerataceae is less clear

Scaphitaceae

• Cretaceous
• Involute, spiral shells
• The body chamber was slightly uncoiled forming a characteristic shallow living chamber
• Derived from the Turrilitaceae

Characteristics

Suture Lines

• All have a 4-lobed suture pattern despite their differing styles of coiling.  The 4-lobe pattern is somewhat similar to the Lytoceratidea. 
• In some groups, the adult specimens display further subdivision of the 4 lobes, increasing the complication of the pattern