Pohlsepia

''Pohlsepia mazonensis'' is a species of fossil organism with unknown affinity. Although it was originally identified as an extinct cephalopod, later studies denied that interpretation. The species is known from a single exceptionally preserved fossil discovered in the late Carboniferous ( Pennsylvanian) Francis Creek Shale (Mazon Creek fossil beds) of the Carbondale Formation, north-east Illinois, United States.

''Pohlsepia mazonensis'' is named after its discoverer, James Pohl, and the type locality, Mazon Creek. Its habitat was the shallows seawards of a major river delta in what at that time was an inland ocean between the Midwest and the Appalachians. In its initial description, it was considered to be the oldest known octopus, but later studies have considered this classification dubious. In 2022, it was even suggested that it may not be a mollusk.

The type specimen is reposited at the Field Museum of Natural History in Chicago, Illinois.

Fossil

The ''Pohlsepia mazonensis'' fossil found by James Pohl is the only known example of the species. Most notably, the fossil has ten arms. The extra two arms are shorter, while the other eight are similar in length.Kluessendorf J, Doyle P. 2000 Pohlsepia mazonensis, an early "Octopus" from the Carboniferous of Illinois, USA. Palaeontology 43(5): 919-926

The wide fossil is “sack-shaped” with indistinct features including a poorly defined head. While it is unclear, one of these features could be an ink sac. The fossil lacks arm hooks and suckers and all of these factors combine to make the assigning of the order Cirroctopoda controversial.Eyden, Phil. “Fossil Octopuses.” The Octopus News Magazine Online, Nov. 2004, www.tonmo.com/pages/fossil-octopuses/.

Etymology

Genus name ''Pohlsepia'' is came from its discoverer James Pohl. He is the son of Joe Pohl and together they have collected fossils in the Mazon Creek area. Originally from Wisconsin and Minnesota, Pohl is a native Midwesterner. He and his father have donated their fossils to museums in the area, including ''Pohlsepia mazonensis'' to the Field Museum.

Classification

In 2000, Joanne Kluessendorf assigned ''Pohlsepia mazonensis'' to the order Cirroctopoda. Many other researchers disagreed, citing the lack of internal structure. The possible evidence of fins and the huge time difference between the ''Pohlsepia mazonensis'' fossil and first confirmed cirrate octopus fossils is problematic. However, the species can be classified as an octopod. Despite the number of arms being unclear, the fact that the fossil has an indistinct head, sac like body and similar fins to cirrate octopods gives enough evidence to classify ''Pohlsepia mazonensis'' in the order Cirroctopoda.

When looking at the groups Teudopsidae, Trachyteuthididae, the Vampyromorpha, cirrate octopods, incirrate octopods and the fossil Loligosepiina, the describing authors proposed that ''Pohlsepia mazonensis'' would be most closely related to the octopods based on its lack of a shell.

However, later studies found the placement within Octopoda to be dubious, due to the fossils poor preservation, and the fact that other fossils have now shown true octopuses to have first arisen in the Jurassic. In 2021, it is considered that is even unlikely to be cephalopod or mollusk. Lack of a shell is a highly unlikely combination in a Carboniferous cephalopod. In addition, its appendages lack hooks, suckers, cirri, an arm web, and the characteristic 8/10 arm count. There is neither a beak, unambiguous ink sac, nor radula. The bulbous body outline and presence of appendages more likely to show the affinity as a cnidarian, a phylum of invertebrate animals including jellyfish and sea anemones. In 2019, fossils included some fossils including ones from Mazon Creek like vertebrates, '' Tullimonstrum'', and ''Pohlsepia'' are examined, to consider affinity of ''Tullimonstrum''. Although this study treated ''Pohlsepia'' as cephalopod, melanosomes cannot be identified from its eyespot.

Mazon Creek

Located in what is currently northern Illinois, the Mazon Creek preserved the ''Pohlsepia mazonensis'' fossil extraordinarily. The ''Pohlsepia mazonensis'' fossil was found specifically in the Pit 11 region, within the Francis Creek Shale Member.Kluessendorf, J. and Doyle, P., 2000. Pohlsepia mazonensis, an early ‘octopus’ from the Carboniferous of Illinois, USA. Palaeontology, 43(5), pp.919-926. Like most soft tissue fossils found in Mazon Creek, it is preserved as a 2D light-on-dark discolouration of the matrix.Clements, T., Purnell, M. and Gabbott, S., 2019. The Mazon Creek Lagerstätte: a diverse late Paleozoic ecosystem entombed within siderite concretions. Journal of the Geological Society, 176(1), pp.1-11. The Francis Creek Shale Member of the Carbon Formation has a diverse array of preserved plants and animals.Baird, G. C., et al. “Taphonomy of Middle Pennsylvanian Mazon Creek Area Fossil Localities, Northeast Illinois: Significance of Exceptional Fossil Preservation in Syngenetic Concretions.” PALAIOS, vol. 1, no. 3, 1986, pp. 271–285. JSTOR, JSTOR, www.jstor.org/stable/3514690.

Previously, it was thought that these organisms were immediately killed and buried in storm surges, where bursts of water would submerge the organisms in sediments, creating an environment where their remains were protected from scavengers before most decomposition could start. However, there is limited geological evidence for the hypothesis of storm surges, and the kill mechanism in the Mazon Creek is not fully understood but high sedimentation could have choked, killed, and buried organisms rapidly

References

External links

The Octopus News Magazine Online: Fossil Octopuses
{{Taxonbar, from=Q7207783
Fossil taxa described in 2000
Controversial taxa