Democrinus londinensis
Democrinus londinensis
View age-specific evidence and explanation
There are no currently eligible, unambiguously age-indexed published Occurrences for this Species. This does not indicate absence or rarity.
These counts describe published LBPS Occurrence records with directly assigned, unambiguous geological-unit mappings—not specimen abundance. Records at restricted Localities and ambiguous or unsupported ages are excluded. Species-level age labels are not used as proof of an age-specific Occurrence.
Specimen-based rarity requires comparable, correctly identified physical fossils, geological provenance and publication permissions. It does not estimate your chance of finding a fossil or collecting access.
Quick Identification
What to look for
- Look for an informative cup (the small plate-built structure below the feeding arms) or a connected lower stalk with evidence of root-like attachment branches.
- Where the cup is complete enough, examine its visible plate boundaries and proportions. Described cups have a height less than about 1.2 times their diameter.
- Inspect preserved stalk-joint faces: some show two rounded ligament depressions arranged around the central opening, giving a figure-of-eight appearance.
Useful check
Look for an unbroken connection between the lower stalk and its attachment structures, rather than assuming a loose branch-like fragment belongs with an isolated columnal.
Be careful
A simple circular stalk disc, an abraded joint face or a loose root-like fragment cannot securely establish Democrinus londinensis. Species-level identification needs diagnostic cup or articular characters, preferably with associated stalk or attachment evidence.
Summary
How did a delicate sea lily remain anchored in the soft mud of an Eocene seabed?
For Democrinus londinensis, the answer lay at the bottom of its long, jointed stalk. Rather than relying on the attachment structures seen in some other sea lilies, this animal developed root-like branches that could secure it in soft sediment. Above them, its body would have carried a crown of feeding arms, probably gathering suspended food particles from passing seawater as living crinoids do today.
Ordinarily, death would have scattered much of this intricate skeleton. Individual stalk pieces might survive, but their original arrangement, and especially the connection with the attachment system, would be lost.
Remarkable fossils from Gan in south-western France have revealed more. Some specimens of D. londinensis preserve sections of the lower stalk with parts of the root system still connected. Researchers interpreted these remains as evidence that the animals lived anchored in the muddy sea floor.
These fossils give us something that loose skeletal fragments rarely provide: evidence of how an ancient sea lily held its position in the world. They turn an assortment of small fossil pieces into a picture of an animal rooted in the seabed, with its feeding crown raised into the surrounding water.
Diagnostic Features
- Cup: Plate sutures are conspicuous in diagnostic material; described cup height/diameter (Hc/Dc) is below approximately 1.20. The ratio is a cup character, not an estimate of total animal size.
- Articulation: Stalk synarthries may preserve paired, figure-of-eight ligament fossae separated by a fulcral ridge around the central axial canal.
- Stalk and attachment: Distal columnals may bear attachment sockets associated with rhizoid or root-like branches. Position and preservation of these structures are critical to interpretation.
- Associated material: Connected lower-stalk and root structures documented from Gan support the interpretation of anchoring in soft sediment; the muddy-seabed setting is a palaeoecological interpretation, not a morphological diagnosis in itself.
- Identification limit: Cup construction, informative synarthries and/or demonstrably associated root-bearing stalk are required for a defensible determination. A small, worn or unpositioned isolated columnal is insufficient for species identification.
Fossil Details
Recorded Fossil Sites
No fossil-site occurrences have yet been recorded for this species.
Diagnostic Sources
- Forbes, E. (1852). Monograph of the Echinodermata of the British Tertiaries. Palaeontographical Society Monograph View reference
- Merle, D.; Roux, M. (2018). Stalked crinoids from Gan (Late Ypresian, southwestern France): exceptional stereom preservation, paleoecology and taxonomic affinities. Swiss Journal of Palaeontology, 137(2), 225–244 View reference
References
- Forbes, E. (1852). Monograph of the Echinodermata of the British Tertiaries. Palaeontographical Society Monograph View reference
- Merle, D.; Roux, M. (2018). Stalked crinoids from Gan (Late Ypresian, southwestern France): exceptional stereom preservation, paleoecology and taxonomic affinities. Swiss Journal of Palaeontology, 137(2), 225–244 View reference
- Messing, C. G.; Ausich, W. I.; Meyer, D. L. (2021). Treatise Online no. 150: Part T, Revised, Volume 1, Chapter 16: Feeding and arm postures in living and fossil crinoids. Treatise Online, 150, 1–47. University of Kansas, Paleontological Institute, Lawrence, Kansas, USA View reference
- Roux, M.; Martinez, A.; Vizcaïno, D. (2021). A diverse crinoid fauna (Echinodermata, Crinoidea) from the Lower Eocene of the Gulf of Languedoc (Corbières, Aude, southern France). Zootaxa, 4963(2), 201–242 View reference