Cycleryon propinquus

Overview

Cycleryon propinquus is a crustacean of Jurassic seas. Spines along the carapace’s lateral margins and dorsal ridges catch the eye. Small differences on the carapace provide clues for distinguishing similar fossils.^[1][4]

Key facts

Which side of a fossil is exposed also matters. Specimen B13436 at the Paris natural history museum is recorded as a compressed fossil with its ventral side visible. Even the same organism appears different depending on whether the back or underside is exposed.^[2]

Time and place

The record of specimen A33518 leads to Eichstätt in present-day Bavaria, Germany. The museum introduces its age as Tithonian. Imagine the marine landscape near the end of the Late Jurassic, different from the land there today.^[4][5]

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

Size, form and skeleton

Researchers examined spiny lateral carapace margins and dorsal ridges in specimens assigned to this species. Each side has a weak ridge bearing small tubercles, while the central ridge has more prominent tubercles. The margins and dorsal ornament are considered together.^[1]

A Cycleryon propinquus fossil introduced by the Bavarian State Collection of Palaeontology and Geology is about 15cm long. Preserved in thin limestone from the Mörnsheim area of present-day Germany, it reveals the size of a crustacean that lived in the sea about 150 million years ago.^[8]

Habitat and reproduction

Warm, shallow seas covered southern Germany in the Late Jurassic when the Solnhofen lithographic limestones formed. Fine calcareous sediment accumulated in thin layers in lagoons between reefs and preserved traces of organisms. Fossils from this region offer views of both ancient seas and the places of preservation.^[5]

Fossil discovery

A 2012 study examined five specimens of this species held at the Paris natural history museum. Material from Solnhofen and Eichstätt was joined by specimens of unknown locality. B13436 retains a record of the Milne-Edwards collection, linking fossil provenance with museum collecting history.^[1][2]

References

1. Charbonnier·Garassino (2012) — Solnhofen arthropods in the Paris Natural History Museum
2. National Museum of Natural History, Paris — Cycleryon specimen B13436
3. National Museum of Natural History, Paris — Cycleryon specimen A42006
4. National Museum of Natural History, Paris — Age and locality of specimen A33518 from Eichstätt
5. Bavarian Environment Agency — Solnhofen lithographic limestone and the Jurassic sea
6. Treatise Online 174 — Diagnosis of the genus Dusa and specimens of Dusa monocera
7. National Museum of Natural History, Paris — Age and locality of specimen A33518 from Eichstätt
8. Nose·Pyrzynska (2023) — Fossil of the month: Cycleryon

Research questions

Could fossils given different names be males and females of one species? While introducing the first thoracic leg of specimen A42006, the 2012 study relays Schweigert’s interpretation of C. spinimanus as the female of this species. This research compares whether differences among similar crustaceans represent species or sexes.^[1][3]

Observation

First follow the carapace outline to find spines along the lateral margins. Then move your gaze to the ridges along the center and sides of the back. Alternating between the outline and dorsal ornament makes clues for distinguishing fossils clearer.^[1]