Lomankus is an extinct genus of megacheiran (great appendage) arthropod known from the upper Ordovician aged Beecher's Trilobite Bed, within the larger Frankfort shale in the state of New York.

Located within Oneida County, New York, and the larger Frankfort Shale, Beecher's Trilobite Bed is a Konservat-Lagerstätten fossil site that dates to the Katian stage of the upper Ordovician.

[4][5] The site itself exists within a small quarry located in Cleveland's Glen, and is found in between fine grained turbidite beds, and on top of mudstone layers containing fossilized burrows.

[6] Beecher's Beds are most well known for its exceptional mode of preservation, where soft body parts are replaced by pyrite, giving the fossils a shiny, gold-like appearance.

[8] This discovery shows that Beecher's Beds still hold a number of undiscovered remains, even after the various expeditions that took place after the site was rediscovered.

[8] The frontal appendages of this group show a great deal of morphologcial diversity, with claw-like endites, and whip-like flagella being found in various genera.

[8] The discovery of Lomankus not only extends the temporal range of the Megacheira into the upper Ordovician, but also adds more evidence to the theory that the Cambrian–Ordovician extinction event was not as severe as once suggested, and the lack of "Cambrian type organisms" in later Paleozoic strata is instead a result of taphonomic bias.

[8][16] Although several other post-Cambrian arthropods, including Enalikter aphson and Bundenbachiellus giganteus, have been suggested to represent late surviving megacheirans, this placement has been contested by other studies.

[17][14][10] Because of this Lomankus represents the youngest definitive megacheiran so far described, and its unique anatomy helps show how the group evolved into the Ordovician.

[8] Lomankus posseses several unique traits compared to other megacheirans, including a terminal flagella, lack of eyes, and more greatly reduced endites and frontal appendages.

[20] The depth of the area is indicated by the presence of other blind animals, including the trilobite Cryptolithus, and the majority of the other taxa known occupying deposit and suspension feeding niches.

[20][8] The contemporary fauna included various trilobites, graptolites, brachiopods, nautiloids, ostracods, poriferans, bryozoans, annelids, phyllocarids, bivalves, and echinoderms.