Miocene Fossils of Pollack Farm
Miocene Fossils of Pollack Farm johncallahanMiocene Fossils Overview
Miocene Fossils Overview johncallahanThe Pollack Farm Site, located in Kent County, Delaware, is named for a borrow pit on the former Pollack property that was excavated during 1991 and 1992 for road material used in the construction of Delaware State Route 1. While Delaware Geological Survey staff collected earth minerals during construction of State Route 1, they came across an upper shell bed full of molluscan fossils. As digging continued, numerous fossils of various species and phylum were found. The fossils discovered range from a simple Arthropod, small insect, to large vertebrates, such as sharks. By 1993, the pit was back-filled, graded, and developed into a wetlands mitigation site.
The Delaware Geological Survey has created this web page to provide a resource of facts and photos of the numerous fossils found in central Delaware. The site includes links to four main phylum, which lead to fossil photographs containing brief descriptions.
In designing this website we hope to provide you with information that will be both educational and enjoyable!
Bivalves: Phylum Mollusca, Class Bivalvia
Bivalves: Phylum Mollusca, Class Bivalvia johncallahanClams, 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).
Living at the bottom of the marine environment bivalves tend to either swim using their mantle cavity to force water movement, burrow into the sand, or attach themselves to an object with sticky strings called "byssal threads."
Below is a list of notable Bivalve species found at the Pollack Farm site.
- Dallarca sp.
- Astarte distans
- Astarte sp.
- Cyclocardia castrana
- Glossus sp.
- Iphigenia sp.
- Caryocorbula subcontracta
Click the image or the link below to view the bivalvia collection!
Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/commons.wikimedia.org/wiki/File:Cockle.jpg
Snails and Slugs: Phylum Mollusca, Class Gastropoda
Snails and Slugs: Phylum Mollusca, Class Gastropoda johncallahanThe Class Gastropoda (in Phylum Mollusca) 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.
The presence of gastropods, at the Pollack site, provides evidence to validate the researchers beliefs that, years ago, the environment was of shallow-water, near-shore locality.
Below are a few notable taxa recovered from the Pollack Farm site.
- Gastrapoda:
- Turritella cumberlandia
- Diastoma insulaemaris
- Epitonium charlestonensis
- Urosalpinx cumberlandianus
- Tritonopsis ecclesiastica
- Nassarius sopora
- Oliva simonsoni
- Inodrillia whitfieldi
Click the image or the link below to view the gastropod collection!
Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/commons.wikimedia.org/wiki/ File:Orange_slug.jpg
Birds: Phylum Chordata
Birds: Phylum Chordata johncallahanThe 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).
Fossil fragments such as the proximal end of right scapula(order Charadriiformes), Middle trochlea of left tarsometatarsus (order Pelecaniformes) are some of the few materials paleontologist were able to gather.
Other taxa represented include:
Gavia small sp. (1 specimen and possibly another) Morus cf. M. loxostylus (5 specimens)
large species of pseudodontorn (1 specimen)
Although the number of remains is relatively small to other phylum and classes collected, the groups importance can not be undermined due to the information they provide in explaining the past environment of the lower Miocene bed. Because the majority of the birds represent groups that are largely or entirely marine, it further strengthens the hypothesis that the lower Miocene formation was once a near shore area of an embayment.
Click the image or the link below to view the avian fossil collection.
Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/commons.wikimedia.org/wiki/File:TringaSemipalmata_3897.JPG
Fish: Phlyum Chordata
Fish: Phlyum Chordata johncallahanWhile 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 early Miocene Fish fossils found in Delaware are of two kinds, Chondrichthyes(consisting mainly of Sharks and rays) and Osteichthyes(commonly known as bony fish).
Paleontologists, at the Pollack Farm, were able to collect a large number of teeth and vertebrae from Chondrichthyes. However, because their bodies do not contain a true bone, full body fossils are very rare to find.
Osteichthyes, differ than Chondrichthyes, in that their skeleton is made of a stiffer bone, compared to their cartilaginous counterparts. Osteichthyes are often associated with dagger-like, isolated teeth
The stingray, dayatis americana, (shown above) is just one of the many Chondrichthyes and fish fauna found at the Pollack Farm Site, in Delaware! Click the image or the link below to view the fish collection.
Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/www.pbs.org/oceanrealm/seadwellers
Insects and Crustaceans: Phylum Arthropoda
Insects and Crustaceans: Phylum Arthropoda johncallahanThe 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.
Arthropods include an exceedingly diverse group of taxa such as insects, crustaceans, spiders, scorpions, and centipedes. There are more species of arthropods than species in all other phyla combined. The name Arthropod means "jointed foot." All arthropods have segmented bodies and are enclosed in a jointed, protective armor called an exoskeleton. Most arthropods have a pair of compound eyes and one to several simple ("median") eyes or ocelli.
In addition to shrimp and other shellfish, barnacles are commonly found in the lower Miocene bed. Barnacles are separated into two groups sessil and stalked. Both have soft bodies that are protected by an outer wall, which resembles either an acorn (sessil) or stalk. Living in a tight grouping with other barnacles these creatures attach themselves to any suitable surface (rocks, boats, even whales and turtles!) in effort to aid in reproduction.
The trace fossils for Arhtropods found at the Pollock Site include Ophiomorpha nodosa (burrow tubes dug by shrimp) and Skolithos linearis (burrow tubes left by ground-dwelling insects).
Click the image or the link below to view the Arthropod collection.
Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/www.pbs.org/kcet/shapeoflife/animals/arthropods4.html
Land Mammals: Phylum Chordata
Land Mammals: Phylum Chordata johncallahanLand 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 gathering, collected from the lower Miocene formation, includes at least 26 species representing at least 17 families in 7 orders (listed below).
Orders:
- Soricomorpha (Shrews, moles)
- Erinaceomorpha (Hedge hogs)
- Chiroptera (Bats)
- Rodentia (Rats, mice)
- Carnivora (Bears, wolves)
- Perissodactyla (Rhinoceros, horses)
- Artiodactyla (Deer)
The Collection of Miocene land mammal fossils, especially north of Florida, is relatively minimal. Only four localities distancing between Georgia and New Jersey yielded significant Miocene fossil beds. Although single teeth and parts of postcranial elements represent the majority of land mammals of the Pollack Farm local fauna, the sites diversity of species elevates the importance of the Pollack Farms location.
Click the image or the link below to view the Land Mammal collection!
Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/www.hedweb.com/animimag/rhino.jpg
Marine Mammals: Phylum Chordata
Marine Mammals: Phylum Chordata johncallahanThe 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).
Marine mammals have the same characteristics as all other mammals, but they have adapted or adjusted to life in the ocean. For instance, many species residing in the deep oceans have a thick layer of blubber, which holds their body temperature warm. Marine mammals also have greater amounts of blood than land mammals, in proportion to their body sizes. This feature allows the blood to be sent to vital organs that in turn slows the heartbeat and minimizes the use of oxygen allowing longer dives underwater.
Species:
- Porpoises - Squalodon calvertensis, Phocageneus venustus, Zarhachis flagellator, Rhabdosteus, & kentriodontid
- Sperm Whale
- Manatee
- Seal - Leptophoca lenis
The collections of marine mammals, from the Miocene Calvert, are less diverse and more fragmentary than the other phylum. However, the Pollack site does extend the marine mammal fossil record into Delaware, which thus validates findings from other locations.
Click the image or the link below to view the Marine Mammal collection!
Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/www.seasky.org/reeflife/sea2k1.html
Reptiles: Phlyum Chordata
Reptiles: Phlyum Chordata johncallahanThe 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.
The fossils recovered from the lower Miocene bed, have provided considerable information to the regions past ecology and environment. The fossils of crocodiles and aquatic turtles gives evidence to a large shallow lake or a river oxbow setting; furthermore, the remaining reptiles probably preferred open brush or grassy environments with loose or sandy soil.
The lower Miocene dig was responsible for the findings of a number of different orders and families of reptiles. Below is a list of species with their fossils recovered from the Pollack Farm Site.
- Kinosternon sp. Mud Turtle(fragmentary costals, hyoplastra, hypoplastra)
- "Chrysemys group" turtle. Painted turtle, cooter, slider group(nuchal, costals)
- Geochelone sp. Very large land tortoise(Entoplastron, hypoplastron)
- cf. Crocodylus sp. Very large crocodile (Tooth)
- Ophisaurus sp. Legless Lizard (trunk vertebra)
- Pterygoboa delawarensis. New species of distinctive small boid genus(trunk vertebra)
- Calamagras sp. small boid (fragmentary vertebra)
- Ameiseophis robinsoni. Extinct genus and species of small colubrid snake (trunk vertebra)
- Pollackophis depressus. Distinctive new genus and species of small colubrid snake (trunk vertebra)
- cf. Crotalinae. et. sp. Viperid snake (two vertebrae)
Photographs from DGS Special Publication No. 21, 1998, R.N. Benson, ed.
Top left image: http:/www.resalliance.org/projects/images/Geochelone.jpg