The Pollack Farm Site, in the Cheswold sands of the lower Miocene Calvert Formation, produced a fragmentary marine mammal fauna. The Pollack location yielded at least six cetaceans (whales, porpoises), a sirenian(manatee), along with one of the earliest records of a true seal (Listed below).
Land mammal fossils were discovered in 1992 in the lower part of the Calvert formation at the Pollack Farm site. During the short time the pit was open, the collection grew to become the most diverse tertiary land mammal fauna known north of Florida on the eastern half of North America.
The lower Miocene Pollack Farm Fossil Site has yielded few avian fossils in comparison to the other classes of vertebrates and invertebrates. Only eleven fossil fragments, assignable to six taxa, were collected at the Pollack site. Of the eleven avian fossils collected, representations from three distinctive orders were recovered: Gaviiformes (divers and loons, seen below), Charadriiformes (gulls and shore birds), Pelecaniformes (cormorants and pelicans).
The Pollack Farm Site has provided the first legitimate window of Miocene reptilian life in North America east of the great plains and north of Florida. In years prior to the excavation of the Pollack site, records of particular small lizards and snakes were non-existent in locations of the mid-Atlantic and northeast, thus providing a significant value to the Miocene fossils recovered.
While sampling the lower Miocene Calvert Formation at the Pollack Farm Site, 30 fossil fish taxa were collected, consisting of 24 cartilaginous and 6 osteichthyes fishes. The fossils found in the lower Miocene bed have similar characteristics to an equally aged Formation in southern Delaware suggesting deposition occured in a subtropical, shallow-water, near shore environment.
The majority of Arthropods recovered at the lower Miocene bed are from various species of crustaceans (lobsters, shrimp, barnacles). Fossils from crustaceans often consist of small body parts such as claws. However, crustaceans such as ghost shrimp (callichirus) tend to construct burrows that resemble lumpy tubes called Ophiomorpha. These corn-stalked resembling tunnels, are created from mud and depository waste to form burrows in which the creatures reside. In comparison to claws and pincher fossils, "trace fossils", such as Ophiomorpha tubes, are often commonly found in greater number than that of various body parts.
Clams, mussels, oysters, and scallops are members to the class Bivalvia (or Pelecypodia). Bivalves have two shells, connected by a flexible ligament, which encase and shield the soft vulnerable parts of the creature. All 15,000 known species of bivalves are aquatic in nature, with close to 80% being marine (saltwater environments).
The Class Gastropoda includes the groups pertaining to snails and slugs. The majority of gastropods have a single, usually spirally, coiled shell into which the body can be withdrawn. The shell of these creatures is often what is recovered in a fossil dig. Gastropods are by far the largest class of molluscs, comprising over 80% of all molluscs.
Located in Kent County, Delaware, the Pollack Farm Site was a surprise to many to contain numerous fossils. The fossils discovered range from a simple Arthropod, small insect, to large vertebrates, such as sharks. In 1991, while Delaware Geological Survey staff collected earth minerals during a highway construction, they came across an upper shell bed full of molluscan fossils. As digging continued numerous fossils of various species and phylum were found.
The Pollack Farm Site near Cheswold, Delaware, is named for a borrow pit excavated during highway construction. The excavation exposed a portion of the Cheswold sands of the lower Miocene Calvert Formation. Two sand intervals (Cheswold C-3 and C-4) yielded a diverse assemblage of land and marine vertebrate remains and more than 100 species of mollusks. An isolated occurrence of a sandy silt (the radiolarian bed) stratigraphically between the two macrofossil-bearing units yielded only siliceous microfossilsâradiolarians, diatoms, and sponge spicules.