Neospirifer dunbari

Overview

Neospirifer dunbari is a brachiopod with a transversely broad, wing-like shell outline. It is widest along the posterior hinge. Transverse lines and radial ridges are visible together in the small shell.^[1]

Key facts

FCMP/E1-1747 is described as an internal mould preserving the form of the shell’s interior. This differs from preservation of the organism’s hard shell itself. It encourages examination of what actually remains in a fossil.^[1]

Time and place

Material from the Ixtaltepec Formation in present-day Oaxaca, southern Mexico, was studied. Its context is the Pennsylvanian of the Late Carboniferous. The Carboniferous as a whole was roughly 360–300 million years ago.^[1][2]

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

Size, form and skeleton

Both valves are convex, and the dorsal valve is transversely broad and wing-shaped. Ridges extend forward from the umbo, and a fold and sulcus meet at the anterior margin. Structures can be read by following the direction from the posterior hinge to the front margin.^[1]

The shell of Neospirifer dunbari spreads broadly from side to side and bears strong folds. Specimens studied from New Mexico, USA, reached about 5cm in width. Follow the central groove and folds on either side to explore the three-dimensional form of this small marine animal.^[7]

Habitat and reproduction

In which direction do the two shell valves face each other? The long posterior hinge, anterior junction, and central fold and sulcus are connected structures. Dividing the hard outline into parts makes the construction enclosing the body clearer.^[1]

Fossil discovery

A 2008 study compared neospiriferids from the Ixtaltepec Formation. The species description and caption for FCMP/E1-1747 convey both the preserved region and its mode of preservation. Reading the specimen number together with the text underlies understanding of its form.^[1]

References

1. Torres-Martínez et al. (2008) — Brachiopods of the Ixtaltepec Formation, Mexico
2. International Commission on Stratigraphy (2024) — Geological time chart
3. Torres-Martínez et al. (2008) — Brachiopods of the Ixtaltepec Formation, Mexico
4. International Commission on Stratigraphy (2024) — Geological time chart
5. Pennsylvanian Invertebrate Fauna — The shell of Composita
6. International Commission on Stratigraphy (2024) — Geological time chart
7. Krainer·Lucas·Kues (2004) — Depositional environments and fossils of the Alamitos Formation, New Mexico

Research questions

What different information comes from a mould of the interior and the original shell surface? One conveys the space inside the shell, the other its external structures. Even fossils of the same organism provide different information depending on how they were preserved.^[1]

Observation

Move your gaze from the long posterior hinge past the umbo toward the anterior margin. Comparing the broad transverse outline, outward-extending ridges, and central fold in sequence reveals the shell’s orientation.^[1]