The Black Mingo Fossil Site in St. Stephen, South Carolina

Construction workers always find the best fossil sites.  Over 30 years ago, some construction workers dug an 140 foot deep pit for a hydroelectric generator as part of the Santee Rediversion Canal Project.  The purpose of the project was to reduce the amount of sediment flowing into Charleston Harbor.  By happy accident, the pit cut through the Williamsburg Formation, a geological strata of Paleocene Age.  Moreover, the Williamsburg Formation is overlain by Pleistocene Strata from the Penholoway Formation, so early Pleistocene specimens of horse, tapir, and alligator mixed with the Paleocene fossils.  Collectors searched the excavated spoil piles and found all sorts of interesting fossils.  The site gets its name from nearby Black Mingo Creek and is located in St. Stephen, South Carolina.

Location of the Black Mingo Fossil Site.  The Black Mingo Formation has been renamed and is now called the Williamsburg Formation.

The Paleocene Era was an age of rebirth, following the K-T impact that wiped out the dinosaurs.  The epoch began 65 million years BP and ended 55 million years BP.  The climate in this region and in most of the world then was frost free.  This particular site was likely a river delta surrounded by tropical evergreen forest dominated by pine and palm trees, though broadleaf trees were common too.  Fossil collectors found logs, plant macrofossils, and pollen from many extinct species that belonged to well known families still extant.  They excavated 6 species of palm as well as pine, cypress, fir, tupelo, magnolia, olive, beech, walnut, alder, hickory, myrtle, ephedra, chenopods, and lillies.  However, all of the species of fossil trees found here are extinct at the genera level.  Some may be ancestral to modern genera.  Much of the fossil wood had borings made by now extinct species of insects.

Ancient fossil wood of a Podocorpoxylon found in Italy.  I couldn’t find any online photos of the fossil wood found at this fossil site in South Carolina, but one of the specimens  was related to this one.  There are some photos in the below referenced link.

Scientists found lots of Paleocene-age amber at this site.  Resins produced by conifer forests dripped into the river where it was quickly buried by sediment.  Buried resin becomes copal and after 2-10 million years copal transforms into amber.

Paleocene age amber.

Teeth from 13 species of sharks were deposited into this site.  Most of these species are also known from the Cretaceous, proving the K-T impact did not cause many extinctions of sharks.  Though the number of bony fishes surely outnumbered shark species in Paleocene oceans, only 7 species were identified here.  Shark teeth preserve better than most fish fossils.

Teeth from the extinct Paleocene shark–Cretolamna appendiculata.

Turtle shells were by far the most common vertebrate fossils excavated from the site, equaling 60% of the total.  Apparently, there was a complete turnover of turtle species from the early Paleocene to the late Paleocene, and the turtle fauna from this site included completely different genera (with 1 exception) from Paleocene fossil sites located in western North America.  All of these turtle genera have become extinct.

Three species of crocodylians that lived alongside Cretaceous-age dinosaurs continued to survive during the Paleocene.  Crocodylians survived the K-T impact by taking refuge in watery holes they dug.  Two of these species were long-snouted fish-eaters, but Bottosaurus had a broader snout and likely preyed upon a wider range of organisms.  Scientists also identified many crocodylian coprolites collected here.

Thoracosaurus skull.  It was a 14 foot long crocodylian of the Paleocene era that mostly ate fish.

This locality is the largest Paleocene mammal fossil site on the east coast of North America, though only 6 species were collected.  There were probably at least 50 species of mammals that lived in the region then and hundreds of species of birds.  Yet, few mammals and no birds were preserved via fossilization.  Bird bones are hollow and easily crushed and hence rare in alluvial fossil sites.  Most of the bird and mammal species that lived during the Paleocene became extinct without leaving a bit of fossil evidence.  Primitive mammals, some ancestral to modern mammals and some that left no modern living representatives, were among fossils found here.  A condylarth–Phenocodon grangeri–is thought to be ancestral to ungulates, though at this early date they were likely omnivorous and less specialized for eating plants.  Ectoginus gliriformes is described as a digging animal with “the body of an aardvark and the head of a pig.”  The tooth of a caniforme (an animal ancestral to dogs, bears, and weasels) reveals the presence of a mammalian predator.  Skeletel material from an animal possibly related to rabbits suggests Bugs Bunny’s ancestors lived here.  Scientists have been unable to classify a couple mammalian species excavated here and have labled them “incertae sedis.”  Without the discovery of more Paleocene fossil sites, our knowledge of this epoch will remain poor.

Charles Knight’s illustration of a Phenacodos sp., one of the condylarths that are thought to be ancestral to the ungulates.

Reference:

Sanders, Al

Paleobiology of the Williamsburg Formation

Transactions of the American Philosophical Society Volume 88 Part 4 1998

http://books.google.com/books?id=Yx4LAAAAIAAJ&pg=PA267&lpg=PA267&dq=Paleobiology+of+the+Williamsburg+formation&source=bl&ots=pzaP-By1lV&sig=OAJPzBUTqFpfL0wS-EmYPqsHldA&hl=en&sa=X&ei=JF-VUsToCYGGyAG27oCQBQ&ved=0CD8Q6AEwAg#v=onepage&q=Paleobiology%20of%20the%20Williamsburg%20formation&f=false

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