ISOCRINIDA

ISOCRINIDA

Origins: 231 million years ago (late Triassic period, Carnian stage)

Extinction: Still extant

Isocrinidans are an order of crinoids, also colloquially known as sea lilies, that originated in the Triassic period and lasted until today, where four living families are known, with extinct forms also being known, such as the pentacrinitids. These crinoids have a "heteromorphic" stalk that consists of a series of nodes with cirri, with the addition of a whorl of cirri at the base of the stalk to perch into other surfaces, as well as a calyx (the name given to the base of the crown of the crinoid) that consists of five basals and five radials.

main source: Wikipedia

Phylogeny

Echinodermata

- Praetetracrinus kutscheri

- Isocrinida

- Pentacrinites dichotomus

- Seirocrinus subangularis

NAME: Pentacrinites dichotomus

SIZE: 40-100 centimeters

DESCRIBED BY: McCoy, 1848

CLOSEST LIVING RELATIVES: Isocrininan sea lilies

DEPICTED IN: The Life of a Temnodontosaurus episodes 8 and 15

Pentacrinites dichotomus was a species from the genus Pentacrinites that lived from the early Jurassic Hettangian stage to the middle Jurassic Bathonian stage (201 - 165 million years ago), being found all across the world, in Asia, Europe, North America, and New Zealand.

Its stem is characterized for being consisted of a stack of five sided columnal plates with a canal passing at their center. It had a very small cup-shaped calyx consisted of two bands of five plates. Its arms were branched and had pinnae, which then harboured series of tube feet, covered in mucus, to catch plankton that is floating in the water column. Its arms were not very motile, mostly bending around as a response to the water currents.

It evolved from early, bottom-dwelling isocrinidan crinoids that lived in the sea floor, only later evolving a lifestyle that involved their growth around floating tree trunks.

Establishing in floating driftwood proved a major success for the genus, allowing them to exploit a planktonic lifestyle that few other crinoids were exploiting, granting its ubiquitousness.

It is one out of other four known species of Pentacrinites, being specific to the early Jurassic Toarcian stage, with the other species ensuring a wider temporal range for the genus, until its eventual demise.

NAME: Seirocrinus subangularis

SIZE: Up to 26 meters

DESCRIBED BY: Miller, 1821

CLOSEST LIVING RELATIVES: Isocrininan sea lilies

DEPICTED IN: The Life of a Temnodontosaurus episodes 8 and 15

Seirocrinus subangularis is one of the largest species of crinoids to have ever lived. Belonging to the genus Seirocrinus, it is consisted of driftwood dwelling crinoids that would have adopted lengths way beyond that of any animal that has ever existed until the evolution of larger sauropods in the middle and late Jurassic. It grew in massive colonies that gathered around floating wood, filtering food in the water column and creating an authentic ecosystem for smaller animals to refuge in the pelagic environment. Large Seirocrinus typically grew in large tree trunks, where a foundation of smaller organisms thrived around their stems. These wooden rafts could last up to 5 years, an immense amount of time for these echinoderms to grow to massive sizes. These would have proved essential ecosystem engineers, permitting the spread of several organisms across the early Jurassic seas, but all of that changed in the middle Jurassic, when raft wood predators started arriving, destroying this unique oceanic feature, and leading Seirocrinus and other driftwood dependant species to their extinction.