What are the Characteristic Fossil Groups? 



Porifera 



The sponges or Porifera comprise the simplest group of multiceliea 

 animals. They typically are attached forms of marine environment. Sponges 

 are of greatly varied shape, being globular, cylindrical, conical, or irregular. 



The soft body of a sponge is generally supported by an internal skeleton 

 composed of organic fibers or spicules. The most commonly found fossil 

 representatives of sponges in Western New York are spicules. Sprcuies 

 show considerable range in shape, size, composition, and structure. They 

 consist fundamentally of simple spines or of spines radiating from a point. 

 Size of these spicules is small, averaging less than one-fourth of an irwrh 

 in length. 



In many extinct sponges the spicules were the most prominent hard 

 parts. They frequently became thickened and united to form a solid trellis 

 or framework which retained the form of the sponge during fossilization. 

 Fossil sponges include isolated spicules of calcium carbonate or silica, frag- 

 mentary or whole skeletons, and, rarely, the distorted outlines of complete 

 bodies. Sponge fossils are usually poorly preserved and difficult to recognize. 



Coelenterates 



Corals are bottom-dwelling marine coelenterates which have an exten- 

 sive fossil record and are still abundant in warm shallow seas. These 

 animals secrete calcium carbonate skeletons about the sides and base of 

 their barrel-shaped bodies. This encases the lower part of the coral in a 

 conical or cylindrical tube or forms a flattish basal expansion. Radiating 

 calcareous vertical partitions called septa are built by infolded parts of the 

 body covering. These partitions help to strengthen the animal. The animal 

 lives in the depression at the top of the coral. As it grows, the skeleton 

 is built upward; earlier parts are abandoned, and new supporting structures 

 are built beneath itself. These horizontal plates are termed tabulae and 

 together with septa are often significant features of fossil corals. 



Corals may live singly but many kinds are of a colonial nature, hundreds 

 of individuals being attached to each other by their outer skeletal walls. 

 The corals that form isolated fossils are called cup corals or horn corals. 

 They range from almost microscopic in size to two feet or more in length 

 and over twenty inches in width. These conical-shaped fossils often display 

 the radiating septa at the top. The outer surface of the walls varies. It 

 may be wrinkled and irregular with encircling growth lines, or may show 

 vertical septa when the outer wall is worn away. 



A cup coral common in Western New York is Heliophyllum halli. It 

 averages three to four inches in length. The major radiating septa extend 



CUP CORAL Heliophyllum halli 



CoLdxiAL CORALS Favosites 



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