Scaphites equalis

Overview

Scaphites equalis is an ammonite whose shell end departs from the spiral and then curves back. In the final section, an outline different from the circular spiral emerges. Its small shell reveals how coiling changed as it grew.^[1]

Key facts

The spiral shell does not remain round all the way to its end. In Scaphites, the shell passes through a straight section before the final body chamber curves back. Coarse, widely spaced ribs in this section are also described as a feature.^[1]

Time and place

It appears in a study of Early Cenomanian material from La Bédoule in present-day Bouches-du-Rhône, France. The Cenomanian is the first age of the Late Cretaceous. The Cretaceous as a whole spans roughly 140–66 million years ago.^[1][2]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

UJF-ID10982 was described as a complete adult shell, with a reported size of 22 mm. The straight section continuing from the spiral and the final recurved body chamber bear coarse, widely spaced primary ribs. Ribs are raised, line-like features on the shell surface.^[1]

Habitat and reproduction

Following the shell allows us to examine changes in shape left as the body grew. The final body chamber in particular shows an outline different from the earlier spiral. Together, the surface ribs and changes in coiling provide clues for recognizing the adult shell.^[1]

Fossil discovery

The ammonite study from La Bédoule described UJF-ID10982 as a complete adult. The researchers recorded the straight section at the shell end, the recurved body chamber, and the thickness and spacing of the ribs. Describing one small specimen in detail provides a basis for distinguishing similar ammonites.^[1]

References

1. Lower Cenomanian ammonites from la Bédoule, Bouches-du-Rhône, France
2. International Commission on Stratigraphy (2024) — Geological time chart
3. Gomez-Cruz et al. (2015) — Ammonite specimens from the Rosablanca Formation
4. Treatise — The names Lissonia and Hoplites riveroi

Research questions

How do the ways ammonite shell ends curve differ? The spiral portion, straight portion, and final body chamber can be compared separately. Also examining where the ribs become coarser and more widely spaced reveals differences between superficially similar shells.^[1]

Observation

Move your gaze from the small spiral along the straight section to the end that curves back. Finding where the coarse, widely spaced ribs appear also helps explain this shell's distinctive outline.^[1]