''Pentacrinites'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

crinoid Crinoids are marine invertebrates that make up the class Crinoidea. Crinoids that remain attached to the sea floor by a stalk in their adult form are commonly called sea lilies, while the unstalked forms, called feather stars or comatulids, are ...

s that lived from the

Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic Period of the geologic timescale. It spans the time between 201.3 ± 0.2 Ma and 199.3 ± 0.3 Ma (million years ago). The Hettangian follows the Rhaetian (part of the Triass ...

to the

Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, and

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

. Their stems are pentagonal to star-shaped in cross-section and are the most commonly preserved parts. ''Pentacrinites'' are commonly found in the ''Pentacrinites'' Bed of the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

(Lower Lias) of

Lyme Regis Lyme Regis ( ) is a town in west Dorset, England, west of Dorchester, Dorset, Dorchester and east of Exeter. Sometimes dubbed the "Pearl of Dorset", it lies by the English Channel at the Dorset–Devon border. It has noted fossils in cliffs and ...

, Dorset, England. ''Pentacrinites'' can be recognized by the extensions (or cirri) all around the stem, which are long, unbranching, and of increasing length further down, the very small cup and 5 long freely branching arms.

Description

Like most

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

s, ''Pentacrinites'' was composed of numerous

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

plates which were arranged into different body parts. ''Pentacrinites'' had 3 kinds of body parts: arms, cup ( calyx or theca) and stem. The stem consisted of a stack of numerous 5-sided beads (or columnal plates) with a canal at their centre. The stem had flexible appendages (or cirri) that were used to attach an individual. These cirri themselves were connected to specialized columnals called nodals, leaving oval scars after breaking off. The cirri consisted of diamond-shaped plates with a central canal, less flatted further from the stem. The cup-shaped calyx was very small and consisted of two bands of five plates. These were the bases of the five arms. The top of the calyx was covered by numerous small polygonal plates and the mouth and anus were found on this surface. The arms divide frequently, like tree branches, so that at the top end there could be over 50 branches in all. The arms were formed of piles of calcite plates. The arms carried many thin feeding branches (or pinnae, like a fern frond). These pinnae had tube feet, that were covered in mucus, reached into the water and caught plankton. These arms were not very mobile. The arms plates of the arms have an insertion, that formed a grove that ran along the length of the arm and onto the calyx. This served to transport the food particles to the mouth.

Taxonomy

''Pentacrinites'' may have evolved from early, free living isocrinids, which occur today on the sea floor.

Reassigned species

* ''P. caputmedusae'' = '' Cenocrinus asterius'' * ''P. subteres'' = '' Balanocrinus subteres'' * ''P. subteroides'' = '' Balanocrinus subteroides''

Ecology

''Pentacrinites'' is a floating sea lily that was attached to driftwood during its adult life. This pseudo-

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

lifestyle Lifestyle is the interests, opinions, behaviours, and behavioural orientations of an individual, group, or culture. The term "style of life" () was introduced by Austrian psychologist Alfred Adler in his 1929 book, ''The Case of Miss R.'', w ...

enabled it to exploit food unavailable to other crinoids.

Distribution

''Pentacrinites'' became extinct and has left no direct living descendants. Its remains have been found in many different locations, suggesting it occurred throughout the world's oceans. Free living isocrinids however, still populate the seas, usually at over 150m deep. * ''P. doreckae'' is known from the Lower Jurassic (

and

Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...

). * ''P. fossilis'' occurs in the Lower Jurassic (

). * ''P. dichotomus'' has been found in the Lower Jurassic (

Toarcian The Toarcian is, in the International Commission on Stratigraphy, ICS' geologic timescale, an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic. It spans the time between 184.2 Megaannum, Ma (million ...

). * ''P. dargniesi'' was collected from the Middle Jurassic (

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.9 ±0.8 Ma to around 168.2 ±1.2 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonia ...

and

References

Sources

* ''Fossils'' (Smithsonian Handbooks) by David Ward (Page 172)

External links

''Pentacrinites''
in the

Paleobiology Database The Paleobiology Database (PBDB) is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database originated in the NCEAS-funded Phanerozoic Marine Pale ...

*http://www.fossilmuseum.net/fossils/Crinoids/Pentacrinus-fossilis/Pentacrinus.htm {{Taxonbar, from=Q3899226 Isocrinida Prehistoric crinoid genera Jurassic crinoids Prehistoric echinoderms of Asia Prehistoric echinoderms of Europe Prehistoric echinoderms of North America Sinemurian first appearances Bathonian genus extinctions