Limnomis delaneyi (early ray-fin fish)

Individual specimen of Limnomis delaneyi. The head is at the right while the tail is at the lower left. (Photo courtesy of Ted Daeschler, ANS.)

Limnomis delaneyi is one of several new species recovered from Red Hill. It is also one of the site's most abundant fossils. Most of the several hundred specimens were collected from a lens of the floodplain pond facies. Dense concentrations of fossilized individuals in these reduced sediments suggest some kind of mass mortality, but the paucity of curled specimens indicate that such a die-off was not caused by dessication. Additional specimens were collected from red sandy siltstone deposits that were probably part of the shallow stream channel margin.

Limnomis was a small fish measuring a maximum of 6 cm. Its streamline body, large eyes and numerous small but sharp teeth suggest that it was an active sight-feeder that fed on small invertebrates in slow-moving and shallow water. It may have been an important prey item for several of Red Hill's larger predators, including Hynerpeton.

Limnomis is a primitive ray-fin (actinopterygian) belonging to a group commonly referred to as the Palaeoniscoids. (Many scientists question the systematic validity of this group and prefer the term "stem actinopterans" or "stem ray-fins".) Unfortunately, the relationship of Limnomis to other stem ray-fins is uncertain because its remains are limited to dermal bones whereas the remains of the better known species include well-preserved endochondral (internal) bones. The comparison of dermal elements suggest that Limnomis is most similar to two well-known Late Devonian species, Mimia and Howqualepis. However it's considerably smaller than these marine fishes and had either lost or greatly reduced its pelvic fins.

You can also learn more about other ray-fin fishes.

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Scientific Papers:: Daeschler, E.B., 2000. "An early actinopterygian fish from the Catskill Formation (Late Devonian, Famennian) in Pennsylvania, U.S.A." Proc. Acad. Nat. Sci. Phila. 150: 181-192.
Image Credits:: The reconstruction of Limnomis is copyrighted © 2002, Dennis C. Murphy. (See Terms of Use.) It's based on Daeschler (2000).

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