Cyclurus is an extinct genus of amiid fishes related to the living bowfin, Amia calva. Unlike many fossil fishes known only from isolated scales or teeth, some species are represented by articulated skeletons that preserve the elongated body, fins and scales. At Messel in Germany, two fossils of C. kehreri lie with bats close to the fishes’ jaws, an unusual association that may record attempted swallowing. These fossils broaden the evidence presented across the ancient fish catalogue.
Quick facts
| Group | Amiid halecomorph ray-finned fish |
|---|---|
| Known interval | Mesozoic and Cenozoic fossil records; well-known Eocene species |
| Best-preserved species | Cyclurus kehreri from Messel, Germany |
| Key evidence | Articulated skeletons and rare fish–bat associations |
| Living relative | Bowfin, Amia calva; not a demonstrated direct ancestor |
| Feeding | Predatory or opportunistic feeding is supported, but exact routine is uncertain |
What the fossils establish
Compression alters proportions, and no fossil preserves every soft tissue.
A close relationship with living bowfins does not make Cyclurus their direct ancestor.
The association is consistent with attempted swallowing, but the exact event and cause of death are inferred.
This sample cannot describe every meal or the full diet of the species.
An amiid fish preserved as a whole animal
Cyclurus belongs to Amiidae, a lineage of halecomorph ray-finned fishes. Its closest familiar living comparison is the bowfin, Amia calva, but the fossil genus is an extinct branch rather than a proven direct ancestor of the modern species. A major phylogenetic review recognised several valid fossil species in Cyclurus, and later studies have refined individual species and their localities.
The Messel oil-shale deposit in Germany is especially known for articulated fossils of Cyclurus kehreri. Slabs can preserve the outline of the head, trunk, scales and paired and median fins. This material lets researchers discuss the body plan far more directly than they can for fish genera known only from teeth. The fossil is compressed, however, and some soft tissues and colours are absent. A reconstruction still uses comparison for details that did not fossilise.
What rare prey associations show
A 2024 study described three middle Eocene fish–bat associations from Messel: one involving a gar and two involving C. kehreri. Each bat, identified as Palaeochiropteryx tupaiodon, is preserved in close contact with the jaws of a fish. Such a configuration is direct evidence that the remains came together in an unusual way, and it makes a feeding interaction plausible.
The authors suggested that the fish may have died after a failed attempt to swallow a bat, perhaps because a wing membrane became entangled in the jaws. They also discussed opportunistic attacks on bats struggling in the water or scavenging on floating carcasses. These are interpretations of the fossil association, not observations of the event itself. The remains do not show whether a fish actively hunted a healthy bat, took a drowning animal or encountered a carcass.
A rare window into diet
Another study examined digestive contents in a sample of fifteen C. kehreri fossils and identified prey remains in one individual. That result is useful precisely because it cautions against broad claims from a small sample. Gut contents can reveal a particular meal, but their absence in other specimens may reflect digestion, decay or preservation rather than an empty stomach in life.
The bat associations demonstrate that these amiids could interact with terrestrial vertebrates at the lake surface or shoreline. They do not prove that bats formed a regular or preferred part of the diet. Comparisons with living bowfins suggest that amiids can be opportunistic predators, but a modern species is an ecological analogue, not a complete record of Eocene behaviour.
Fossil species and evolutionary relationships
The name Cyclurus dates to the nineteenth century. Fossil species occur in more than one geological interval and region, and their classification has been considered in broader studies of Amiidae. The Eocene fossils preserve one especially informative member of the genus, but they should not be used to reconstruct every older species without checking anatomical similarities.
Its relationship to the bowfin is part of a much longer history of halecomorph fishes. The living bowfin represents the surviving end of a lineage with many fossil relatives; it is not a time capsule unchanged from the Eocene. The ancient fish catalogue includes other groups where a living comparison helps explain anatomy but cannot substitute for the fossil evidence.
What an image can reconstruct
Articulated Messel fossils support an elongated fish with a broad head, scales and a continuous fin pattern. Colour, fine soft-tissue details and behaviour are not preserved. An image showing a bat at the fish’s mouth depicts one interpretation of an exceptional fossil association, not a scene directly witnessed by the rock record. Keeping that distinction clear allows the discovery to remain striking without making its uncertain details sound settled.
Explore related evidence in the ancient fish catalogue.
Frequently asked questions
Is Cyclurus the ancestor of the bowfin?
No direct ancestor–descendant relationship has been demonstrated. Cyclurus is an extinct amiid relative of the living bowfin.
What do Messel fossils preserve?
Some slabs preserve articulated skeletons with the head, trunk, scales and fins, providing a much fuller body record than isolated teeth would.
Did Cyclurus eat bats?
Two fish–bat associations from Messel are consistent with attempted swallowing or opportunistic feeding. The precise event and whether it involved hunting or scavenging remain uncertain.
Do we know its full diet?
No. A study of fifteen C. kehreri fossils found recognisable prey remains in one. Exceptional associations and small samples cannot establish the complete diet.