Somasteroidea

The Somasteroidea, or Stomasteroidea, is an extinct order of asterozoan echinoderms first defined in 1951 by W. K. Spencer. Their first appearance in the fossil record was in the Early Ordovician (Tremadocian) and they had become extinct by the Late Devonian (Famennian). They are similar to the asteroids in that their bodies are flattened dorsoventrally and they have five petaloid arms with broad bases. The ambulacral plates in somasteroids are simple and unspecialized, and the arms were thought to be not flexible and were unable to assist in feeding, but the oral mouth parts were more complex.

Somasteroidea

Peter MASSICARD · CC BY 4.0 · via Wikipedia/Commons. May be a photograph of a specimen, or an artist’s reconstruction — an interpretation of a skeleton, since colour and soft tissue are almost never preserved.

On record

Recorded, not inferred
Sits inside
AsterozoaPBDB
Diet
suspension feederPBDB
Life habit
epifaunalPBDB
Motility
actively mobilePBDB
Environment
marinePBDB, for Echinodermata

Time the record covers

At least 18 million years on record.

The record covers at least 477.1 Mya to 458.2 Mya. No occurrence read is dated outside 488.9 Mya to 449.6 Mya.

Cambrian — about 0 of 13 occurrencesOrdovician — about 13 of 13 occurrencesOrdovician490–488 Mya — about 0.0 occurrences488–487 Mya — about 0.1 occurrences487–486 Mya — about 0.8 occurrences486–484 Mya — about 0.9 occurrences484–483 Mya — about 0.9 occurrences483–482 Mya — about 0.9 occurrences482–480 Mya — about 0.9 occurrences480–479 Mya — about 0.9 occurrences479–477 Mya — about 0.9 occurrences477–476 Mya — about 0.7 occurrences476–475 Mya — about 0.6 occurrences475–473 Mya — about 0.6 occurrences473–472 Mya — about 0.6 occurrences472–471 Mya — about 0.5 occurrences471–469 Mya — about 0.8 occurrences469–468 Mya — about 1.0 occurrences468–467 Mya — about 0.2 occurrences467–465 Mya — about 0.2 occurrences465–464 Mya — about 0.2 occurrences464–462 Mya — about 0.1 occurrences458–457 Mya — about 0.1 occurrences457–456 Mya — about 0.2 occurrences456–454 Mya — about 0.2 occurrences454–453 Mya — about 0.2 occurrences453–452 Mya — about 0.2 occurrences452–450 Mya — about 0.2 occurrences450–449 Mya — about 0.1 occurrences477.1 Mya458.2 Mya489.7 Mya448.8 Mya

13 occurrences of Somasteroidea on record, most of them in the Ordovician. Bar height is expected occurrences, not a count: each fossil is spread across the span it is dated to, so a tall narrow bar means tight dating and a low wide one means loose.

When

13 occurrences

These are dates about fossils, not the animal: the record can only begin after it arose and end before it died out, so either end may reach further. Shares are expected occurrences: a fossil dated to a span is counted partly in each period it straddles. More on what this infers.

Found in

8 formations

Saint-Chinian — 43.44°N, 2.89°ESaint-Chinian — 43.42°N, 2.95°ESchistes de Saint-Chinian — 43.00°N, 3.00°EFezouata — 30.49°N, 5.87°WFezouata — 30.50°N, 6.11°WSarka — 50.00°N, 14.00°ELandeyran — 43.47°N, 3.08°EFillmore — 37.90°N, 114.67°WBardahessiagh — 54.58°N, 6.92°WLower Fezouata — 30.51°N, 6.07°W

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The named rock units Somasteroidea has been recovered from, largest first. Drawn where the rock is now, not where it formed.

Somasteroidea and its relatives

Ordovician

Where Somasteroidea and its relatives were recorded in the Ordovician.

Found in the same rock

297 taxa

The Paleobiology Database records 10 sites for Somasteroidea, and this reads all of them. The number is how many of those sites it was catalogued from too. The 24 sharing the most are listed.

This is not a list of everything alive at the time. It is only what has come out of the same ground as this animal and been written down.

Entered from

10 references

Each of the 13 occurrences read was entered from one of these publications, ordered by how many each accounts for. This is not a search for papers mentioning the name. Entries link to doi.org where the Paleobiology Database holds an identifier, and to its own record where it does not. Relayed as the Paleobiology Database holds them, not checked against what they resolve to.

Media and terms

Media content2

Picture of Somasteroidea

Credit
Peter MASSICARD
Licence
CC BY 4.0
Commercial use
the licence allows it

3D model

Source
Sketchfab
Licence
CC Attribution
Commercial use
cannot be read from the licence given — check the record

Smithsonian Open Access and MorphoSource were not reached for this taxon, so this list is what the others held rather than everything there is.

The description on this site

Licence
CC BY-SA 4.0

This is what the site found, which is not the same as what exists.

Keep going

What may have been alongside itAsterozoa through timeFormations of the OrdovicianThe world it lived on

Occurrence data from the Paleobiology Database, CC BY 4.0. (Spencer 1951)