The Geology of Delaware

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Marine Mammals: Phylum Chordata

Marine Mammals:  Phylum Chordata<br>Source:

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).

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.


  • 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:/

Photo Gallery
L-M. Physeteridae, tooth<br>
E-F. Phocageneus venustus, posterior tooth<br>
A-B. Squalodon calvertensis, molariform tooth<br>
G. ?Phocageneus venustus, tooth<br>H. ?Phocageneus venustus, posterior tooth<br>I-J. Kentriodontidae<br>
P-Q. Physeteridae, right periotic<br>
A, C. Zarhachis flagellator, symphyseal portion of mandible<br>B. Rhabdosteus sp., symphyseal portion of mandible<br>
C. Zarhachis flagellator, symphyseal portion of mandible<br>D. Rhabdosteus sp., symphyseal portion of mandible<br>E. Zarhachis flagellator, mandible<br>
F. Leptophoca lenis, partial left calcaneum<br>G. Callophoca obscura, Pliocene North Carolina; left calcaneum<br>