EXOTIC DEATH ASSEMBLAGE OF U-SHAPED HETEROMORPH CRETACEOUS AMMONITES

Duck Creek Formation - Tarrant County, Texas, U.S.A.

CRETACEOUS PERIOD (EARLY UPPER ALBIAN STAGE) :  101 million years ago

For the advanced invertebrate fossil collection, this is an exotic and highly uncommon specimen of a U-shaped heteromorph ammonite of the species Anisoceras armatum.  It was collected from the Cretaceous Duck Creek Formation in Texas, U.S.A..  Heteromorph ammonites differ from the more common coiled homomorph varieties in that the heteromorphs have an open, partially uncoiled shell more delicate in nature.  Little is understood about heteromorphs but scientists believe that these were planktonic creatures that floated in the open ocean allowing themselves to be carried by currents rather than relying on their own propulsion and needing a hydrodynamic design to their shell.  Heteromorph ammonites most likely drifted in the mid or upper waters of the prehistoric sea feeding on small animals that happened to get too close to their roving tentacles.  

The rock matrix is original and whole.  Several specimens were buried in a mass mortality bed and can be seen in their natural host rock.  NO REPAIR AND NO RESTORATION.

We highly recommend this rare specimen.  Most ammonite fossil collections lack ANY genuine HETEROMORPH AMMONITE FOSSILS.  This is not only a unique example but will likely be the most affordable specimen you will find for sale.  Absolutely a MUST for the connoisseur of ammonites and invertebrate life-forms from prehistory.  Ammonite specimens from the U.S.A. are NOT common and not mined commercially compared to the much more prevalent Moroccan and Madagascar types always seen for sale.  This strange extinct creature hails from the same time period as many of North America's famous dinosaurs and is a well preserved as well as a wonderfully aesthetic display fossil. 

Ammonites are extinct members of the Cephalopod class.  Modern members include nautilus, squid and octopus.  They first appeared during the Silurian Period (435 million to 410 million years ago) and were abundant and widespread in the seas of the Jurassic and Cretaceous periods (175 million to 65 million years ago).  Ammonites are important index fossils—that is, they often link the rock layer in which they are found to specific geological time periods.

Ammonites varied greatly in size.  The largest known as small as 2 cm (0.75 in) in diameter.  During the Jurassic and Cretaceous periods, ammonites evolved more streamlined shells for swimming and the structure of the shell became stronger.  Different shell shapes emerged as well, such as snail-like or uncoiled.   

The shells of ammonites had hollow chambers separated by walls called septa.  A tube called the siphuncle, connected the body with the chambers allowing the animal to fill them with water or air, changing its buoyancy in order to rise or drop in the ocean.  Only the last and largest chamber was occupied by the living animal.  

Ammonites probably lived for one to six years, with the majority living two to four years.  They fed on plankton (tiny free-floating organisms), sea lilies, and smaller orthoceras.  Although many fed off the ocean floor, others may have caught plankton while floating or swimming via jet propulsion, expelling water through a funnel-like opening to propel themselves in the opposite direction.

Because ammonites lived exclusively in marine environments, their presence also indicates the location of prehistoric seas.

RARE HETEROMORPH AMMONITE MASS MORTALITY FOSSIL SPECIMEN FROM THE U.S.A.!

FAR NICER IN PERSON THAN APPEARS IN PHOTOS!

7.75" wide x 5.4" high

$195     AM-035    INCLUDES STAND     Actual Item - One Only

195