Pachycormus macropterus

Overview

Pachycormus macropterus is a Jurassic fish characterized by a spindle-shaped body and long pectoral fins. The front-to-back positions of several fins also provide clues to its construction. Examine the elongated side profile together with the arrangement of fins.^[1]

Key facts

A large ammonite was found inside the belly of one exceptional specimen. Researchers proposed that the fish may have swallowed it accidentally. Unexpected contents preserved in one fossil raise questions about the relationship between fish and cephalopods.^[2]

Time and place

SMNS 52472, from a quarry at Zell unter Aichelberg in Germany, was studied. It is material from the Posidonia Shale of the Toarcian Age of the Early Jurassic. Broadly, this places it in the earlier part of the Jurassic, roughly 200–140 million years ago.^[2]

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

Size, form and skeleton

Genus and species descriptions include a spindle-shaped body, long pectoral fins, and the positions of dorsal and anal fins. The genus diagnosis also addresses the absence of pelvic fins. The broad outline and fins in individual regions can be compared separately.^[1]

Body length is introduced as about 1m. A 2024 comparative study of marine organisms regarded a nearly complete specimen of about 95cm as having been slightly longer in life and summarized it at about 1m.^[9]

Habitat and reproduction

Fossils preserving internal contents provide special clues to food. The ammonite in SMNS 52472 was interpreted as hard material actually swallowed by the fish. This one case became a new question for exploring connections among marine organisms.^[2]

Fossil discovery

SMNS 52472 was collected in 1977. Later research examined the articulated skeleton, preservation, and ammonite in its belly together. Even a fossil kept for a long time can yield an unexpected story.^[2]

References

1. Cawley et al. (2019) — Morphology of Pachycormus
2. Study — Pachycormus specimen containing an ammonite
3. Study — Pachycormus specimen containing an ammonite
4. Padian (2008), Dorygnathus banthensis — Author’s abstract
5. Tübingen Museum — Microcleidus specimen
6. Study — Plesiosaurs of the Posidonia Shale
7. Study — Pachycormus specimen containing an ammonite
8. Cawley et al. (2019) — Morphology of Pachycormus
9. Pimiento et al. (2024) — Extinct large marine organisms of the Phanerozoic

Research questions

What might be missed by looking only at a fossil fish’s outline? Another organism’s shell preserved inside provides a different kind of information from external shape. Examining one specimen closely can offer a clue to relationships among marine organisms.^[2]

Observation

Move your gaze from the long pectoral fins to the positions of the dorsal fin and the anal fin at the rear of the belly. Considering the spindle-shaped outline together with the front-to-back relationships of each fin makes the body’s construction clearer.^[1]