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. A single species is known, Lomankus edgecombei, which was described by Parry et al., 2024. It is currently placed within the family Leanchoiliidae, within the larger Leanchoilida order, and represents the youngest known member of the group. Members of this family are characterized by the presence of long flagelliform structures on their frontal appendages, which were most likely used for both sensory and raptorial purposes. Lomankus is significant, as it represents the youngest known definitive megacheiran in the fossil record, as well as the only definitive member of the order from post-Cambrian strata. Although several other genera of post-Cambrian arthropods, including members of the family Enaliktidae, have been proposed as members of megacheira, their placement in the order has been contested by several papers. The discovery of definite megacheirans in Ordovician strata 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. This species is differentiated from other megacheirans due to the seeming lack of long endites on its frontal appendages, which are normally found in leanchoiliids. The endites bearing the flagella are either absent, or at least greatly reduced, so the flagella appear to attach directly to the podomeres of the appendages. This suggests that they performed a sensory role in this species, compared to the raptorial role they filled in other members of the family. Another difference is the apparent lack of eyes, which contrasts with the well developed eyes usually seen in other leanchoiliids. This species also possesses an extremely elongated flagelliform structure on its telson, the longest of any known megacheiran. Lomankus most likely lived as a deposit feeder, as the environment it inhabited is thought to have been dysaerobic (lacking in dissolved oxygen).
Background
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. Originally discovered in 1892, the site was lost when Charles Emerson Beecher, who discovered it, died in 1904. Afterwards, the majority of research conducted on the trilobite bed was done on previously excavated specimens housed within public collections. However, the trilobite bed was later rediscovered by fossil collectors Tom E. Whiteley (who also helped rediscover the Walcott–Rust quarry) and Dan Cooper in 1984, and has since been protected by the Yale Peabody Museum. 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. The rock layers that contain the fossils are around 40 mm (4 cm) thick, and were most likely deposited via strong currents due to the common alignment that the majority of the fossils from the beds show. The beds are composed of high levels of iron, as well as low concentrations of organic carbon and sulfur. 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. Another notable quality of the site are the hundreds of well preserved remains of various trilobite genera, which preserve the rare appendages (antennae, briamous limbs, etc) that are not normally preserved. However, other groups of organisms, including graptolites, brachiopods, nautiloids, ostracods and various unnamed genera are also known as well.
Discovery and etymology The fossil specimens belonging to Lomankus were discovered relatively recently from excavations in Beecher's Beds following a large scale excavation in 2004. 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. This genus was properly described by Parry et al., 2024, who analyzed five specimens from the Yale Peabody Museum. The holotype specimen of Lomankus, cataloged as YPM IP 256612, is a ventral-oriented fossil showing the underside of the megacheiran. Other specimens, including YPM IP 236743 and YPM IP 516237 preserve the arthropod in a lateral view. The arthropods genus name, Lomankus, is derived from the Greek words loma, meaning "edge", and ankos, meaning "valley"., referencing Gregory Edgecombe, who has helped greatly in the furthering the understanding of arthropod evolution. The species name, edgecombei, is also in honour of Edgecombe, making the full translation of the scientific name "Edgecombe's edgecombe".
Description
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