Fossil Crinoid (Sea Lily)
420 Million Years Old
Scyphocrinites was a widespread crinoid with fossils discovered in Africa, the U.S., Europe, and Asia. It has a beautifully detailed and intricate calyx with many stellate plates. A floating bulbous structure called camarocrinus is often found with these crinoids, and is the reason for its widespread existence in the Upper Silurian/Lower Devonian Periods. This structure is believed to be a float, which enabled the crinoid's effortless floating on prehistoric currents.
Crinoids are also called "sea lilies" for the sessile or attached varieties and "feather stars" for the free swimming species. These marine creatures first appeared in the middle of the Cambrian period, around 525 million years -- and these creatures still survive today!
They collect food with their "arms". Each arm has a double row of tiny appendages, or "tube feet", lining a mucus tract that runs down to the mouth. Crinoids feed by extending their arms to catch particles that float past. Having caught something, they move it, with their tube feet, up their sticky food grooves and into their mouth. Their diet is limited to small organic particles and tiny organisms suspended in the warm water. Crinoids are classified as Echinoderms -- a group of organisms that also includes starfish, sand dollars and sea urchins.
Was an ancient mollusk that lived more than 400 million years ago. The name means straight horn, referring to the characteristic long, straight, conical shell. The preserved shell is all that remains of this ancestor of our modern-day squid.
The soft body lived in the last open-ended segment at the large end of the conical shell. As the body grew and the housing segment became too small, a dividing wall, called the septa, grew to separate the old home chamber from the new one. The differences in the composition of these shell parts allowed for differences in fossilization so the parts can be seen.
The siphuncle is a tube that runs the entire length of the shell, through each of the chambers. This tube had two functions. Once filled with water, the nautiloid could force the water out, propelling itself backward with a kind of jet propulsion. By releasing the water and leaving air space, the tube could serve as a bouyancy device allowing the animal to rise and lower itself to different depths.
These straight shelled nautiloids ranged in size from less than a centimeter to more than 14 feet long!
All the living relatives of these nautiloids, squid, octopus, cuttlefish, and nautilus are predators, and we can assume that orthoceras was also a hunter of the Paleozoic seas, possibly having trilobites for breakfast!
Notice the siphuncle and septa in the fossil below. The siphuncle is the line running down the center from head to tail. The septa are the short curved lines that run across or side to side.
Although relatively simple in form, ammonites are extremely rich in the information they yield to scientists. These extinct marine animals, which thrived in the Paleozoic and Mesozoic Eras, some 400 to 65 million years ago, were cephalopods, and are thus related to squid, octopus, cuttlefish, and the chambered nautilus.
Ammonites were able to swim, thanks to the unique construction of their shell, which was divided into a series of air chambers. The air in the chambers provided buoyancy for the animal to float; like modern cephalopods, they probably moved through the water using jet propulsion.
Fossils of ammonites are found all over the world. As different species of ammonites lived during different time periods, scientists can use these animals to determine the relative age of the rocks in which their fossils are found (such fossils are called "index fossils"). Because ammonites lived exclusively in marine environments, their presence also indicates the location of prehistoric seas.
Many ammonites, including this example, preserve their original shell material and are quite beautiful. Scientists at the American Museum of Natural History are currently studying the evolution and life history of these ancient creatures.