Sunday, August 02, 2020

Ancient sea lilies

I got side-tracked from looking at rocks by a trip to the wharf. But there was something I'd discovered among the information about pillow lavas.

This turtle has been sitting on the shelf above my desk for a while.

Carved stone turtle full of fossils

I had wondered what made those circles and stars in the rock. The pdf on the geology of Strathcona Park had a section describing their source: sea lilies.

The other side of the turtle

The circles are sections of the stems of a marine animal, crinoids, animals related to starfish and sea urchins. (The five-pointed star hints at this relationship.) They come in many forms, stalked and unstalked. The stems are made of discs of calcium carbonate. When the rest of the animal disintegrated, the mineral part of the stem remained. So what I'm seeing is cross-sections of crinoid stems.

Five-pointed star shape of the centre of a stem disc.

The crinoid column is also called a stem or stalk. The stem is made from disc-shaped pieces of endoskeleton which are stacked upon each other and are hollow in the middle. They are held together by ligaments which decomposed rapidly after death. The hollow shapes inside of the discs include: elliptical, circular, pentagonal, and star-shaped. (fossilera.com)

The turtle has two carved fishes on the top of its carapace. A reminder that the content of the stone was once underwater?

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Había estado viendo piedras (lava almohadillada) cuando lo dejé para subir fotos de alga marina y sus residentes. Pero me quedó una cosa por mencionar.

Esta tortuguita de piedra vive en el estante arriba de mi escritorio. Siempre me ha inspirado curiosidad: ¿qué criatura o proceso hizo estos círculos y estrellas?

En el documento acerca de la geología de esas lavas almohadilladas, encontré su descripción; son parte del esqueleto de unos animales marinos que vivían en este sitio cuando todo estaba al fondo del mar. Se llaman lirios marinos, o crinóideos, animales del grupo a que pertenecen las estrellas de mar y los erizos de mar.

Los animales pueden estar fijos a la roca o pueden alzarse sobre tallos. Estos tallos están hechos de discos de carbonato de calcio. Cuando el animal se muere, se desintegra, dejando solamente estos discos.

El centro del segmento puede tener el espacio en forma de círculo, pentágonos, o estrellas, con cinco puntos.

La tortuga tiene encima del carapacho, dos pescados. ¿Un aviso que lo que contiene la piedra alguna vez vivía bajo el mar?

2 comments:

  1. Fascinating! I wonder how much the old artisans really knew of fossils...

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