''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 A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

discovered in the late Carboniferous ( Pennsylvanian) Francis Creek Shale (

Mazon Creek fossil beds The Mazon Creek fossil beds are a conservation ' found near Morris, in Grundy County, Illinois. The fossils are preserved in ironstone concretions, formed approximately in the mid- Pennsylvanian epoch of the Carboniferous period. These concret ...

) of the Carbondale Formation, north-east

Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rockf ...

, United States. ''Pohlsepia mazonensis'' is named after its discoverer, James Pohl, and the type locality, Mazon Creek. Its

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

was the shallows seawards of a major

river delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ra ...

in what at that time was an inland ocean between the Midwest and the

Appalachians The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

. 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 shown that it may not be a mollusk. The

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

is reposited at the Field Museum of Natural History in

Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

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 An ink sac is an anatomical feature that is found in many cephalopod mollusks used to produce the defensive cephalopod ink. With the exception of nocturnal and very deep water cephalopods, all Coleoidea (squid, octopus and cuttlefish) which dwell ...

. 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 having ten arms, 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 ''Pohlsepia mazonensis'' would be most 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 octopi to have first arose in the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

. 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 Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrell ...

and

sea anemones Sea anemones are a group of predatory marine invertebrates of the order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria, ...

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 Francis Creek Shale Member and like most fossils found in Mazon Creek, is preserved as carbon film. 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. These organisms were immediately buried due to bursts of water and their remains were protected before most decomposition could start. In storm surges organisms would be submerged in sediments, creating an environment where their fossils were extremely well protected.

Field Museum of Natural History

The ''Pohlsepia mazonensis'' fossil is currently located at the Field Museum of Natural History in Chicago, Illinois. Located eighty miles from the fossil's discovery, the museum is one of the largest natural history museums in the world. It also houses similar fossils in the Mazon Creek Fossil Invertebrates Exhibit. These fossils include spoon worms, ribbon worms, bristle worms, millipedes, and cockroaches.“Mazon Creek Fossil Invertebrates.” The Field Museum, 2 Oct. 2014, www.fieldmuseum.org/science/blog/mazon-creek-fossil-invertebrates.

References

External links

The Octopus News Magazine Online: Fossil Octopuses
{{Taxonbar, from=Q7207783 Fossil taxa described in 2000 Controversial taxa Species known from a single specimen