Porpoise Rib Fossils and U.S. Atlantic Coastal Plain Fossiliferous Formations

As you scroll down through the Category of Cenozoic Aquatic Fossils, you will find interesting information and identifications pertaining to six such fossil species from my collection, including:

  1. Porpoise Rib Fossil
  2. Hypural Tuna Fishtail Bone Fossil
  3. Softshell Turtle Fossil
  4. Knightia Fish Fossil
  5. Dermal Denticle Ray-Fish Fossil
  6. Billfish Bill Fossil
Cenozoic Timescale Source

U.S. Atlantic Coastal Plain Geological Formations in Brief

The Cenozoic Era aquatic fossils in my collection were unearthed along of the Atlantic Coastal Plain of the United States (with one exception). The fossiliferous Miocene Epoch aged rock layers of the Atlantic Coast crops out almost continuously from southern Florida northward to Cape Cod, Massachusetts. (Gibson, 1965). Some Miocene formations (mapped bedrock units or layers) form large overlaps over older Oligocene, Eocene, and Paleocene Epoch aged rock layers (refer to timescale) as well as Mesozoic Era of the Lower and Upper Cretaceous Period rock layers (145 to 65 mya). Some Miocene formations also underlies younger Pliocene-Holocene Epoch bedrock units. I only have information as to one specific location where some of my fossils were found; the Lee Creek-Aurora mine within the Pungo River Formation in Beaufort County, North Carolina which contain various middle Miocene aged fossiliferous sediments.

Other locations where the fossils were found, I assume, could be from the Yorktown Formation another mapped bedrock unit, Pliocene aged located in the Coastal Plain of Maryland, Virginia, North Carolina and South Carolina; the Eastover Formation, late Miocene aged located in North Carolina; the Calvert Formation located in Maryland, Virginia and Delaware, early to middle Miocene aged, one of the three formations which make up the Calvert Cliffs, all of which are part of the Chesapeake Group.

From the southern portion of the Coastal Plain, Georgia fossils date from the Late Cretaceous, 145 mya to the present, Holocene Epoch; and Florida’s surface fossil record dates back to the Eocene Epoch when the the entire state was covered by ocean.

When sea levels were high, a shallow seaway covered much or even all of the Coastal Plain. During times of lower sea levels, the area was dryland, with large rivers and broad floodplains. For this reason, Coastal Plain strata consist of alternating marine sediments (those deposited in the sea) and non-marine sediments (those formed on land).

These richly fossiliferous deposits have attracted the attention of North American paleontologists since the nineteenth century, not to mention serious fossil hobbyists today.

Porpoise Rib Fossils

Porpoise Fossils

Approximately the lower half of the Calvert Formation (described above) is dominated by porpoise fossils, including squalodonts (primitive shark-toothed porpoises). Modern-day type porpoise fossils, also, are consistently present there, indicating an environment of estuaries and rivers. Articulated (entire body) skeletons of porpoises are not uncommon throughout the Calvert Formation. The Pungo River Formation (described above), also, has unearthed many porpoise fossils, including the river porpoises. Pertaining to my porpoise rib fossils, with the lack of enough related evidence, it’s impossible to pin down an exact species.

Porpoise Evolution

Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch. Even though all modern cetaceans are fully aquatic mammals, early cetaceans were amphibious, and their ancestors were terrestrial artiodactyls (an order of mammals that comprises the even-toed ungulates (hooved mammals). Hippos are thought to be the closest living relatives of cetaceans.

Cetacean species are divided into two groups:

(1) Baleen whales – these are the “great whales” and as their name suggests, they all have baleen plates that are used to filter food consisting of plankton and small species of fish.

(2) Toothed whales – are a suborder called odontocetes and include all species of dolphin and porpoise which eat larger prey, including at times, other marine mammals.

As a general rule of thumb, baleen whales are larger and slower than toothed whales. Additionally, all baleen whales have two blowholes, whereas toothed whales have only one.

Dolphin and Porpoise Comparison Sketch

Porpoise Vs Dolphin

Porpoises and dolphins have many similarities, for example, both are highly intelligent and use echolocation, but there are several differences, as a dolphin is not a porpoise and a porpoise is not a dolphin.

  • Porpoises are quite smaller than dolphins
  • Porpoises don’t have a pronounced beak that most dolphins have
  • Porpoise teeth are spade-shaped whereas dolphin teeth are cone-shaped
  • Porpoises have a triangular dorsal fin and dolphins have a curved dorsal fin (except for those species that don’t have a dorsal fin)
  • Porpoises body form is a little more chunky than that of the leaner, more slender dolphin body form
  • Porpoises are not vocal like the talkative dolphins
  • Porpoises are more closely related to narwhals and belugas
  • Porpoises belong to the Phocoenidae family. There are only six species of porpoises in the entire world. Oceanic dolphins, however, belong to the large Delphinidae family, which consists of at least 36 species worldwide! River dolphins belong to the Iniidae family with one living genus and four extinct genera

The Six Species of Extant Porpoises

1. The Harbor porpoise, Phocoena phocoena, has a worldwide distribution including both eastern and western U.S. and Canada coasts within the temperate to arctic regions.

2. Dall’s porpoises, Phocoenoides dalliand, northwestern U.S. coast to China

3. Vaquita porpoise, Phocoena sinus, small range, Gulf of California in Mexico

4. Finless porpoise, Neophocaena phocaenoides, wide range of Indo-Pacific regions

5. Spectacled porpoise, Phocoena dioptrica, southern Atlantic to Indo-Pacific, sub-Antarctic regions

6. Burmeister’s porpoise, Phocoena spinipinnis, both coasts of South America, mid to southern regions

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