''Yorkicystis'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

edrioasteroid Edrioasteroidea is an extinct class (biology), class of echinoderms. The living animal would have resembled a pentamerously symmetrical disc or cushion. They were obligate encrusters and attached themselves to inorganic or biologic hard substrate ...

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea ...

that lived 510 million years ago in the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

aged

Kinzers Formation The Kinzers Formation is a geologic formation in Pennsylvania. It preserves fossils dating back to the Cambrian Period. The base of the Kinzers Formation is primarily a dark-brown shale. The middle is a gray and white spotted limestone and, lo ...

in what is now

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

. This genus is important as it provides some of the oldest evidence of echinoderms losing their hard mineralized outer

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

s. ''Yorkicystis'' also shows that some echinoderms lost their skeletons during the Cambrian, which is a greatly different time as to when most other species lost theirs.

Discovery

Fossils of this genus were first discovered in May 2017 by Christopher Haefner in a churchyard in

York, Pennsylvania York ( Pennsylvania Dutch: ''Yarrick''), known as the White Rose City (after the symbol of the House of York), is the county seat of York County, Pennsylvania, United States. It is located in the south-central region of the state. The populati ...

in shale deposits in the Emigsville Member of the

. Two specimens were found, and numbered NHMUK EE 1659-1660. Aside from ''Yorkicystis'' other echinoderms like ''Lepidocystis'' and ''

Camptostroma ''Camptostroma roddyi'' is an extinct echinoderm from the ''Bonnia''-''Olenellus'' Zone the Early Cambrian Kinzers Formation near York and Lancaster, Southeastern Pennsylvania. In life, it would have resembled a cupcake, with the axial skeleton ...

'' have been found in the formation. The species name is in honor of Haefner, who discovered the fossils, and the genus name is derived from the town of York.

Description

''Yorkicystis'' is unique because it has a non-mineralized skeleton. Most echinoderm groups around today like

starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...

and

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...

s have a mineralized skeleton, and others like derived crinoids and

holothurians Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothurian ...

(sea cucumbers) have one, but it is greatly reduced.

Classification

''Yorkicystis'' is a member of the

edrioasteroidea Edrioasteroidea is an extinct class of echinoderms. The living animal would have resembled a pentamerously symmetrical disc or cushion. They were obligate encrusters and attached themselves to inorganic or biologic hard substrates (frequently har ...

, a class of echinoderms that lived by cementing themselves to hard surfaces like

hardgrounds Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer, 1992). A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limestone ...

, and sometimes to living creatures like brachiopods. These are some of the oldest echinoderms in the fossil record with some species having been found in Cambrian aged

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

s, and possibly

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

sediments in the form of ''

Arkarua ''Arkarua adami'' is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of five small dots from the middle of the disk center. Fossils ...

'' (but the taxonomy of those specimens has been quite controversial). In the 2022 paper, researchers found ''Yorkicystis'' to form a larger clade with edrioasteroids

Isorophus ''Isorophus'' is an extinct genus of Echinoderm belonging to the class Edrioasteroidea. It is commonly found in deposits dating to the Ordovician period. There are several species, with one (''Isorophus cincinnatiensis'') being the official fos ...

, Argodiscus, and

Kailidiscus ''Kailidiscus'' is an extinct genus of echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchi ...

. Due to its unique appearance and age, ''Yorkicystis'' was placed in the new family Yorkicystitidae.

Paleoecology

The Kinzers Formation dates from the middle Dyeran to the Delamaran stage of the

middle Cambrian Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (di ...

. The formation was identified by the presence of ''Wanneria walcottana'' and ''Olenellus roddyi'' found in the same deposits. High quality fossil specimens were obtained from the Noah Getz Quarry, one mile north of

Rohrerstown, Pennsylvania East Hempfield Township is a township (Pennsylvania), township in west-central Lancaster County, Pennsylvania, Lancaster County, Pennsylvania, United States. At the 2020 census the population was 26,350. East Hempfield is one of the six immediate ...

, but the quarry location is overgrown and disturbed by development. The fossils are from the Emigsville Member and include the trilobites '' Olenellus thompson'', ''Olenellus roddyi'', and ''Wanneria walcottana.'' The radiodont '' Lenisicaris pennsylvanica,'' and the bivalved arthropod '' Tuzoia getzi.'' Also found is the bizarre

frondose Frondosity (from Latin ''frondōsus'' meaning 'leafy') is the property of an organism that normally flourishes with fronds or leaf-like structures. Many frondose organisms are thalloid and lack the organization of tissues into organs, with the ...

organism ''

Margaretia dorus ''Margaretia'' is a frondose organism known from the middle Cambrian Burgess shale and the Kinzers Formation of Pennsylvania. Its fronds reached about 10 cm in length and are peppered with a range of length-parallel oval holes. It was ori ...

''.

References

{{Improve categories, date=July 2022 Fossil taxa described in 2022 Edrioasteroidea