Happy Fossil Friday!
Two weeks ago, fossil collector Lee Cone (President of the Special Friends of the Aurora Fossil Museum) donated a spectacular skeleton of a large baleen whale (Mysticeti) from the Lee Creek Mine (read about it here). A skeleton of a mysticete like this is unprecedented as it includes a partial skull, earbones, mandibles, vertebrae, and ribs. However, it also includes a number of other fossils that decidedly do not belong to the whale – including non-cetaceans, parts of at least one or two additional mysticete whales, and at least two pygmy sperm whales (Kogiidae).
Associated fish, sea turtle, and bird remains
Several bones mixed in with the whale record the presence of sea turtles, a sea bird, a sturgeon, and a billfish. Several bones from the edge of a turtle shell – called marginals – record the presence of sea turtles, likely Syllomus aegyptiacus or Caretta, possibly Caretta patriciae, the two most common species from the Lee Creek Mine according to Zug (2001). Another fragmentary bone is identifiable as a parasphenoid bone – a bone located deep in the skull – of a billfish (swordfish and marlins). Sturgeons are represented by a fragment of dermal or skull bone with distinctive pitting – sturgeon are among the more common fish from the mine. The fourth non-cetacean is a proximal humerus fragment from some kind of large alcid bird – possibly Pinguinus alfrednewtoni, an extinct flightless penguin-like auk, and the fossil ‘ancestor’ of the recently extinct (ca. 1840s) Great Auk. More detailed comparisons with razorbills (genus Alca) are necessary.
Pygmy sperm whales
Shortly after Lee brought in the remaining parts of the skeleton, I made a surprising discovery – three additional squamosal bones of a much smaller cetacean. The squamosal is a paired skull bone, so there should only be two – not only does the skull of Lee’s whale have a squamosal, it’s also gigantic. So, there is a minimum of three cetaceans present (based on squamosals) – one large mysticete, and two smaller cetaceans. The smaller squamosals are identifiable as pygmy sperm whales (Kogiidae) based upon their size and shape. Shortly after I began noticing fragments of bone mixed in that were composed of a much finer porosity – individual pores in the bone were tiny and under half a millimeter rather than the much coarser pores in the mysticete. The bones are also much, much lighter, and a distinct difference in density was apparent. After an hour or so I had pulled out dozens and dozens of fragments – indicating that much of the skulls would come together. After about 5 or 6 hours of piecing, it is apparent that not only are there two individual pygmy sperm whales, but at least two genera present.
One of these is similar to Aprixokogia kelloggi already reported from the Yorktown Formation (Whitmore and Kaltenbach, 2008), but also a second smaller taxon that appears closer to Scaphokogia cochlearis from the upper Miocene of Peru – though incomplete, the second skull has a more elongate rostrum than other kogiids. Sperm whales in general are freaky – they have highly asymmetrical skulls, and pygmy sperm whales are even weirder, completely lacking nasal bones. Scaphokogia has a bizarre elongate rostrum that makes other kogiids look well-adjusted and normal odontocetes.
More baleen whales
The first part of the skull I saw was the well-preserved earbones – and I saw this gorgeous little petrosal with attached posterior process and an associated bulla, and remarked “ooh it’s a minke whale!” The earbones are the same taxon which was identified earlier by Whitmore and Kaltenbach (2008) as Balaenoptera sp., cf. B. acutorostrata – something close to the modern minke whale. He then showed me a second petrosal, which I thought was a gray whale and not associated with the skeleton. Later on, I flipped the braincase over and the posterior process was in place still – and much, much larger than the minke whale petrosal. Instead, the gray whale petrosal fit in right in place. This meant that based on earbones, at least two baleen whales were present in Lee’s assemblage!
The plot thickened yet again when I started looking at vertebrae, because various smaller vertebrae are mixed in to the assemblage. A second atlas and axis are present – and are much smaller, possibly representing the same Balaenoptera individual. Unfortunately, the atlas is much larger than the axis, and they do not fit together – meaning that there is a minimum of three baleen whales based on vertebrae!
Why so many species?
In sum, at least one sea turtle, one bird, two types of fish, two pygmy sperm whales, and three baleen whales are preserved in Lee’s assemblage. How could all this get deposited in the same spot? The Yorktown Formation is characterized by slow sedimentation rates, and is punctuated by several internal bonebeds formed during periods of slow or non-deposition. Slow deposition need not rearrange skeletal assemblages to the point of completely mixing them, but hundreds or thousands or hundreds of thousands of years may have passed with the deposition of only a single meter of sediment – enough to keep the main skeleton’s bones together, but providing ample time to preserve additional specimens vertically near the horizon of the skeleton. This is called a “condensed section” in stratigraphy.
Secondly, all of this went through a dragline and was dumped – so the skeleton shifted somewhat, requiring much piecing together, but the skull and jaws and vertebrae were sort of close to anatomical position. It’s therefore possible that mining operations may have mixed in material as well. Regardless of the process by which these remains were concentrated – geological or anthropogenic – we truly received a gift that has kept on giving. Once again, Thanks Lee!
S. L. Olson and P. C. Rasmussen. 2001. Miocene and Pliocene birds from the Lee Creek Mine, North Carolina. Smithsonian Contributions to Paleobiology 90:233-365
N. A. Smith and J. A. Clarke. 2011. An alphataxonomic revision of extinct and extant razorbills (Aves, Alcidae): A combined morphometric and phylogenetic approach. Ornithological Monographs 72(1):1-61
J. Velez-Juarbe, A. R. Wood, and C. Pimiento. 2016. Pygmy sperm whales (Odontoceti, Kogiidae) from the Pliocene of Florida and North Carolina. Journal of Vertebrate Paleontology e1135806
F. C. Whitmore and J. A. Kaltenbach. 2008. Neogene Cetacea of the Lee Creek Phosphate Mine, North Carolina. Virginia Museum of Natural History Special Publication 14:181-269
G. R. Zug. 2001. Turtles of the Lee Creek Mine (Pliocene: North Carolina). Smithsonian Contributions to Paleobiology 90:203-218