The Earth Story

geology.life

Arthroacantha Crinoid Fossil Calyx.

Pentagon This critter, now on display at Wittenberg University on Ohio, is a spectacular example of a Mississippian aged crinoid. Crinoids are filter-feeding animals related to starfish and other echinoderms, with 5-fold symmetry patterns in them. Originally this critter was attached to the ocean floor by a stalk and extended its limbs up into the water to catch food that floated by. The full animal formed plates out of calcium carbonate and attached those plates together using soft tissues. Most of the time, these soft tissues decay and the pieces fall apart, but here the animal is mostly still in tact. The stalk that held it to the ground has since detached, but the calyx, the pentagon-shaped center of the animal that held the mouth and the anus, is still in tact and attached to the arms. Make sure you spot the pentagon pattern in the fossil. -JBB Image credit: James St. John. https://flic.kr/p/22UofMh Read more: http://www.kgs.ku.edu/Extension/fossils/crinoid.html

Pretty as a flower

Crinoids, or sea lilies, resemble flowers, however, they are not plants. Crinoids are marine animals that are related to starfish, brittle stars and other echinoderms. These critters can be found both in shallow waters and at great depths of around 9,000 meters.

These critters are plankton eaters and they have muscles, a gut, a nervous and reproductive systems and some other features of advanced animals that you would not expect to see in an animal that looks more like a plant.

Crinoids have pentaradial symmetry, which is typical from echinoderms. These animals present three main sections: stem (or column), calyx (where the body cavity and digestion takes place) and the arms (which are responsible to filter food). Most of the species live attached to the seabed, but there are some free-swimming species. Early crinoids from the Paleozoic were completely immobile. Mobility is a feature that only appeared later, since crinoids were vulnerable to predators and they had to adapt.

These creatures have been present on Earth since the Ordovician period (roughly 490 million years ago) and they still exist to this day, which shows how successful they are. Crinoids not only survived the Permian and the Cretaceous-Tertiary mass extinction events, but they also were able to diversify and proliferate into hundreds of species, many of them still alive today (around 625 species).

Due to its beauty, crinoid fossils are quite desired by collectors. A good thing is that these animals are common fossils, however, notice that wholly preserved crinoids (with stem, calyx and arms) are a rare finding. This happens because the plates of the animal’s skeleton fall apart when ligaments and muscles decompose after death. Crinoids that underwent a quick burial are the ones with the best chances of producing a complete fossil and they are quite esteemed by paleontologists for the scientific value and by collectors due to its aesthetic.

The calyces of crinoids are a common find if you look for them in Paleozoic sedimentary rocks that present noticeable crinoid columnals, however, if you do not see these, then it is not likely for you to find any calyces. In my case, I would definitely need the help of a professional, and if that is your situation as well, you should reach a paleontologist from a university or from a natural history museum. At the end of the day, that would surely be a great field trip.

Sources: http://bit.ly/2w0BiY0 http://bit.ly/2vZl7ek

Photo credits: http://bit.ly/2wEbqiq - photo by Vassil http://bit.ly/2vPgzXf - photo by Alexander Vasenin http://bit.ly/2uAto4d - photo by Kevinzim/Kevin Walsh http://bit.ly/1Zh8SyM - photo by Berengi

Rugose coral

Commonly referred to as ‘horned coral’, due to the unique shape of the solitary species of coral the extinct order Rugosa emerged during the Middle Ordovician, and became extinct in the Late Permian, approximately 250 million years ago. Like their contemporaries the rugose corals were benthic and lived on the seafloor, with some species able to form large colonies. Some species of coral also formed symbiotic relationships with Stromatoporoidea, and were especially common in the Silurian.

A common feature of rugose coral is the ‘wrinkled’ outer surface from which their name was derived (Rugose being the Latin word for wrinkled). Each individual horn coral resided within the cup-like structure, called a calyx. The calyx often displayed a series of ridges or grooves, called septa. Each septa acted as the skeletal support for individual polyp. The horn faced outwards, anchored to the sea bed by a single stem, with the living coral polyp on top using its tentacle to trap small organisms. Although there is no direct fossil evidence, it is suggested that like modern coral, they possessed tentacles armed with stinging cells used to catch prey.

AHP

Sources http://bit.ly/1Osh5wI http://bit.ly/1P9jUim http://bit.ly/1ms8OPd http://bit.ly/1R8yKfm http://bit.ly/1R8yKfm Image http://bit.ly/1ms8OPd