Uintacrinus socialis (fossil crinoids in chalk) (Niobrara Formation, Upper Cretaceous; western Kansas, USA) 3

Uintacrinus socialis Grinnell, 1876 - fossil crinoids in chalk from the Cretaceous of Kansas, USA. (public display, Nebraska State Museum of Natural History, Lincoln, Nebraska, USA)

Crinoids (sea lilies) are sessile, benthic, filter-feeding, stalked echinoderms that are relatively common in the marine fossil record. Crinoids are also a living group, but are relatively uncommon in modern oceans. A crinoid is essentially a starfish-on-a-stick. The stick, or stem, is composed of numerous stacked columnals, like small poker chips. Stems and individual columnals are the most commonly encountered crinoid fossils in the field. Intact, fossilized crinoid heads (crowns, calices, cups) are unusual. Why? Upon death, the crinoid body starts disintegrating very rapidly. The soft tissues holding the skeletal pieces together decay and the skeleton falls apart.

Shown here is a relatively thin plate of chalk with multiple, intertwined, complete specimens of Uintacrinus socialis stemless crinoids. The chalk is from the Upper Cretaceous Niobrara Formation of western America. Many plates have nothing but Uintacrinus on them. Most Uintacrinus slabs come from western Kansas, but the genus was near-cosmopolitan in its distribution.

The subspherical calices (heads) of Uintacrinus crinoids were covered with thin calcite plates. Extremely long arms extended from the calyx; the arms are often seen tangled together. The largest slabs consistently show the arms of all specimens pointing toward the center of the plate. Preservation of crinoid soft parts (e.g., tegmen, anal tube, ambulacra; see Meyer & Milsom, 2001) has been identified in some Uintacrinus slabs, which permits use of the term "lagerstätte" for this occurrence. Black, organic-rich laminations are present and have been suggested to represent degraded microbial mats, which may have promoted preservation of the crinoid tangles.

Stemless, float-like calices of Uintacrinus suggest that these crinoids lived at the sea surface, unlike Paleozoic or modern crinoids, which are mostly sessile benthic. The Niobrara seafloor was not suitable for crinoids having encrusting holdfasts or root-like anchors. Inoceramid bivalves are also found in Niobrara Formation chalks - they had large, spread-out shells to prevent sinking in the originally-soupy, calcareous ooze sediments.

Classification: Animalia, Echinodermata, Crinoidea, Articulata, Uintacrinida, Uintacrinidae

Stratigraphy: Smoky Hill Member (a.k.a. Smoky Hill Chalk Member; Smoky Hills Member), Niobrara Formation, upper Santonian Stage, mid-Upper Cretaceous

Locality: western Kansas, USA
---------------
Reference cited:

Meyer & Milsom (2001) - Microbial sealing in the biostratinomy of Uintacrinus lagerstätten in the Upper Cretaceous of Kansas and Colorado, USA. Palaios 16: 535-546.
---------------
See info. at:
en.wikipedia.org/wiki/Crinoid

Some rights reserved

Taken on: July 18, 2011

Tags:

Uintacrinus

crinoids

fossil

fossils

chalk

Niobrara

Formation

Cretaceous

Kansas « less

Sets appears in: • Chalk • Niobrara Formation (Upper Cretaceous; western USA) more » • Kansas Rocks & Fossils • Cretaceous Rocks, Minerals, Fossils • Crinoid & Eocrinoid Fossils « less

Stats: 2,924 views

close tools panel

Badge creator

Use Flickriver Badge Creator to create a badge linking to your photos, your group or any other Flickriver view.

You can place your badge on your Flickr profile, Blog or Website.

Add to your iGoogle or Netvibes page

Flickriver widget for iGoogle or Netvibes can display almost any Flickriver view - most interesting today, by user, by group, by tag etc. Once added to your personalized homepage, just edit widget settings to select your desired view.

Clickr on one of the buttons below to install:

Embed on your Web site

To embed this view, Copy and Paste the following HTML code:

Black background (preview):

White background (preview):

Firefox and Chrome addons

Adds a 'Flickriver' button to your browser. While viewing any Flickr photos page, click on this button to open the same view on Flickriver.

Install in Firefox
Install in Chrome

Search plugin

Add 'Search on Flickriver' to your browser's search box. Works with Firefox and Internet Explorer. Install search plugin

"View on Flickriver" Greasemonkey script

A Greasemonkey script that adds Flickriver links to various Flickr photo pages - user photos, favorites, pools etc, allowing to quickly open the corresponding Flickriver view.

Also, allows quickly viewing any Flickr photo on black background in large size.

Install "View on Flickriver" script

Bookmarklet

While viewing any Flickr photos page, click on the bookmarklet to open the same view on Flickriver.

To install: drag and drop the following link to your Bookmarks toolbar.
IE users - add the link to your Favorites under the Links folder