2020 was a pretty shit year for most everyone; for those who have lost nothing, at minimum it’s been pretty bleak and depressing. Many have lost far more than that. Vaccines are on their way, and the holidays, and coup attempts, have come and passed – and in the interest of sharing much-needed good news, I thought I’d write up a few posts about our own mid-pandemic whale excavation.
Skeleton of Cynthiacetus peruvianus from the late Eocene of Peru, on display at the MNHN in Paris - one of the most spectacular individual basilosaurid whale specimens ever collected. Photo credit: Shadowgate via Wikipedia Commons.
Introduction
I’ve not discussed archaeocetes on here a whole lot – until 2020, anyway. Archaeocetes are those super strange proto-whales that lost their hindlegs, began the migration of the nostrils backwards to form a blowhole, and eventually became completely marine. Basilosaurids are the archaeocetes I know best – chiefly because they are the ‘benchmark’ that paleocetologists studying baleen whales or toothed whales must make comparisons with. Basilosaurids are suspected to be the ancestral stock from which baleen whales (Mysticeti) and toothed whales/echolocating whales (Odontoceti) evolved and diverged, and chiefly known from the late middle Eocene and late Eocene, roughly 41-34 million years ago. Most basilosaurids look surprisingly similar, with very slight differences in skull shape, dental anatomy, and perhaps more profound differences in postcranial anatomy and body size. They are remarkably well-studied and their fossil record is excellent – their excellent fossil record is likely a result of high sea levels during the mid-late Eocene.
Albert Koch's monstrous chimaera Hydrarchos - actually an accumulation of basilosaurid specimens later sorted out into Basilosaurus, Pontogeneus/Cynthiacetus, and Zygorhiza - all discovered by African slaves on plantations in Alabama and Mississippi in the 1830s-1840s.
The first place in the world that archaeocetes were found was the southeastern USA – African slaves would make piles of bones they uncovered while ploughing fields in Alabama and Mississippi – and some of these piles were bought by notable ‘entertainer’ Albert Koch, and eventually formed the basis for Basilosaurus cetoides. We now know of a small fauna of three whales – the gigantic Basilosaurus cetoides, the “small” Zygorhiza kochii, and the “medium” sized Cynthiacetus maxwelli (considered by Phil Gingerich to be a junior synonym of Pontogeneus brachyspondylus, as covered earlier in the summer). Archaeocete whales were found here in South Carolina not long after – Dorudon serratus was discovered (very likely also by slaves) on the Mazyck Plantation (now flooded below Lake Moultrie) and named by Gibbes in 1845. Sadly, very little has been published on South Carolina basilosaurids – although it’s important to note that not one but two protocetids (Carolinacetus and Tupelocetus) have been described and named from late middle Eocene aged limestone in the vicinity of Jamestown, SC. It wasn’t until Al Sanders at Chareston Museum started collecting South Carolina cetaceans in the 1970s and did a few trips into the limestone quarries around Harleyville and Holly Hill, SC, that specimens with stratigraphic provenance were collected – though mostly consisting of teeth, earbones, and isolated postcranial elements. In the 1990s, the South Carolina State Museum began collecting in the mines – and one new basilosaurid, Chrysocetus healeyorum, was named by Mark Uhen and Phil Gingerich in 1998 (More on Chrysocetus later). Many additional specimens have been collected from the mines by the state museum either still reside in jackets or are unpublished (like all the Charleston Museum specimens).
What is the state of basilosaurid research? Basilosaurids of course mark the transition from a seal-like semiaquatic stage of cetacean evolution to the split between odontocetes and mysticetes. Many studies have centered on the locomotor evolution of archaeocetes – and much attention has been paid to their postcrania, though it’s critical to recall that many “well known” basilosaurids aren’t quite as well known or preserved as often thought. For example – the flipper of Zygorhiza is from a juvenile, and not as complete as depicted in Kellogg’s seminal 1936 monograph. The only published skull of Basilosaurus cetoides is only perhaps 50% complete – the most complete specimen, in the collections of the Louisiana State University Museum of Natural Science, is still unpublished. The many species contained in Dorudon osiris were all synonymized and placed in the new genus Saghacetus seemingly as an afterthought in a random table in a paper on the stratigraphy of Wadi al Hitan (Gingerich, 1992) – and no followup description, as promised in that paper, exists yet. Specimens of Platyosphys from Morocco, including the fragmentary holotype of P. aithai and a much more complete specimen reported in an SVP presentation, hint at greater diversity and anatomical disparity within the family than previously understood. So, there’s a lot of basic research left to do. We also don’t know much about their feeding ecology – at least in terms of chewing, biomechanics, and the use of a heterodont dentition – we have tooth marks of Basilosaurus on juvenile Dorudon skulls, and Basilosaurus and Dorudon specimens preserved with gut contents – so we know what they ate, but not necessarily how. We don’t know much about their hearing or why they have asymmetrical skulls. So, in addition to basic taxonomy/descriptive work, there’s more to do with their functional anatomy. What about South Carolina? There are only two described basilosaurid specimens from the entire state, collected 150 years apart. Many more exist in museum collections – my student Sam Czwalina is currently studying a specimen from Blue Circle Quarry near Harleyville that does not appear to represent Cynthiacetus, Zygorhiza, or Chrysocetus – but may represent Dorudon. Mark Uhen published a large table identifying every basilosaurid specimen in North America – including many from South Carolina – and these specimens ought to be written up so we have an idea of what the cetacean fauna here was like.
Day One: Invitation and an initial foray
Given the potential for discovery and the unanswered questions regarding basilosaurid evolution – and the possibility of finding other Eocene marine vertebrates just on the other side of the Eocene-Oligocene boundary – I was pleased to get an invitation from our buddy Rich Familia, a local collector and environmental scientist who has collected extensively from the Eocene mines around Harleyville and donated some Eocene and Oligocene specimens to the Mace Brown Museum of Natural History (CCNHM). Back in September when it was still relatively hellish I suggested waiting until it cooled down some – in white limestone mines here in the south, you cannot safely work in 90+ degree weather for more than about two or three hours before heat exhaustion begins to take it’s toll. One day I worked at an Oligocene locality about three miles from our house for about three hours in 105 degree weather and 80% humidity - and lugged about 80 lbs of bonebed matrix in grocery bags – hung from each end of my jacob’s staff (geologist’s measuring stick) – in about three or four trips. After three hours I had drank two gallons of water and still felt dehydrated thanks to all the sweat – and limped into a convenience store and enjoyed the AC for several minutes before gulping down a gatorade. If I had more than a hundred yard walk back through deep mud I would’ve been in trouble.
The Wednesday before Thanksgiving a group of us including Rich, CCNHM collections manager Sarah, CCNHM curator Scott Persons, myself, and several private collectors who are friends of the museum – Jordy Taylor and Mark Bunce – met at Giant Cement Quarry near Harleyville, South Carolina, at around 3pm. Rich got us signed in and through the checkpoint at the mine entrance, and once parked, we headed through the mud up to the mine slope: an excavated ramp exposure of the early late Eocene Pregnall Member of the Tupelo Bay Formation – a gray, sandy, massively bedded and sparsely fossiliferous limestone. Two other Eocene units are deposited on top – the Parkers Ferry Formation, a shell-rich, softer, yellow limestone, and the poorly exposed but richly fossiliferous Harleyville Formation – an olive greensand unit locally called “the green cap”.
Some of the miscellaneous specimens found on our first trip out there, clockwise from upper left: a tooth of the early mako Isurus/Macrorhizodus praecursor; an osteoderm of an ostraciid boxfish [and the latest known specimen before the Eocene-Oligocene climate crash); a scallop (Pectinidae); an early tiger shark (Galeocerdo ?latidens); tooth of a dwarf cow shark (Hexanchus agassizi); and cutlassfish teeth (Trichiurus sp.).
We collected a number of shark teeth shortly after arriving – though the light gray color of the limestone makes spotting fossils difficult in direct sunlight; finding fossils here is much, much easier when overcast. We found typical shark teeth including the dwarf cow shark Hexanchus agassizi, the requiem shark Abdounia, sand tigers (Odontaspidae), early makos (Isurus/Macrorhizodus praecursor), the early megatoothed shark Carcharocles auriculatus, and bat/cownose rays (Myliobatidae). A few fish vertebrae were found – and I found one of the more exciting non-mammal specimens: a ridge osteoderm from the ‘corner’ of a boxfish (Ostraciidae) – notably rare fossil fish in the rock record, and on the Atlantic coast, restricted to the Paleocene (until now) – they are tropical, and the Eocene represents the last suitable climate for them at temperate latitudes.
Sarah Boessenecker (right) and Rich Familia (left) examining some of the exposed bone fragments of Mark Bunce's whale.
After only about 40 minutes of prospecting, Mark Bunce called me down the hill and pointed out fragments of a tympanic bulla of a basilosaurid whale. One of the bone fragments I looked at looked a lot like a sea turtle shell fragment – and I was nearly convinced that the cluster was a sea turtle rather than a whale. In fact, a cylindrical bone was so porous I thought it was another sea turtle element – perhaps a scapula fragment. Sea turtle bones are notoriously porous with very thin cortical bone – and when it is present, it is often somewhat fibrous in a manner that somewhat resembles fish bone. Basilosaurid bones are not generally very porous – and some basilosaurids are decidedly quite dense – but this unusually porous texture would be clarified the next morning. After about twenty more minutes or so we found regular bone fragments, and fragments of the other bulla – left and right, as well as rib fragments, and a partial vertebra indicating we had found associated skull bones. We started clearing off mud and found what I thought was part of a mandible, back near the jaw joint. Rich Familia started clearing off what I suspected was a vertebra. We found a scatter of bones perhaps 1.5 x 1 meter – not terrible, and part of me thought we could get the specimen excavated and jacketed the next day.
Day two: the case of the incredible expanding whale
Mark, Rich, Sarah, and I agreed to come back the day after at 10am. Because so few bones were exposed by our initial poking around, I fully expected to have a small jacket we could completely trench, undercut, plaster, and flip. We spent about an hour carefully uncovering bones, and found that the upper 3-4 inches of the rock had been fairly weathered – with many loose bits of bone, and firm limestone below. Sarah started working on the large flat element – and I took a walk to go use the facilities. I heard from down the quarry some animated talking – and when I returned to the spot, Sarah announced out loud that she had found teeth! My pace quickened – and Sarah clarified that the teeth were in that suspected jaw. When I got there, I saw the second and third lower molars in place – indicating that it was a right mandible, and an unusually small one. The teeth had unusually smooth enamel, and in concert with their tiny, tiny size – perhaps only half the size of the generally smallish whale Dorudon atrox – allowed me to quickly identify this whale as none other than Chrysocetus healeyorum. After a few more minutes of brushing, Sarah had uncovered the first molar – and at that point, I estimated where the tip of the mandible was, and suggested that she quit exposing it – keep a bit of matrix in place to pad it – and focus on trying to find the tip of the mandible, and probe around to see if we could make a jacket just around the mandible. We started excavating a shallow trench, but kept on finding more and more bone.
Sarah shown here deepening the runoff trench, which was about two meters from the main bone scatter and ran in a large arc to collect most groundwater running along the top of the bedrock exposures and divert it around the pit. It mostly worked, reducing perhaps 60% of the water from reaching the pit.
Sarah began digging a trench towards the back of the mandible, and uncovered a cluster of vertebrae and ribs – which would expand the size of the jacket to a 7’ x 3’ wide oval – a bit gigantic. Meanwhile, Rich had been working on trenching around a vertebra about 2’ away from the mandible, and finding more and more bone between it and the mandible – and more bone opposite, with just enough room for a narrow trench between them. It would mean we would need some smaller jackets on that side. By about 2pm, I was starting to get quite nervous: the bone scatter was growing, and no trenches were being dug: our attempted trenches kept on stepping outward away from the middle of the bone scatter, and my hopes for a quick and simple excavation were dashed. With each new bone I was becoming increasingly more panicked – realizing that I had bitten off way more than I could chew. Rich also had to leave around 1pm to go hunting, so we were down to three. Mark had to leave around 3 – and fortunately, CCNHM ally Ashby Gale – who was doing an educational program in Columbia – had gotten off early and would meet us at the quarry around 3pm. Calling in that lifeline was very much needed, as we were starting to get tired and sloppy – and making mistakes. Late in the day, especially with tired muscles, it’s harder to swing a pick or hit a chisel with a hammer. As your accuracy with a pick decreases, it becomes ever easier to hit something unintended – most often the fossil itself (rather than, say, somebody’s foot) – or accidentally smash your non-dominant hand holding the chisel instead of the chisel itself. That’s precisely what I did that afternoon – well, I actually hit the chisel quite well, but that one in particular has a hemispherical striking surface and the hammer glanced off and pounded me pretty hard on the left index finger – and I had a moderately blueish finger for a week.
We still needed to find the edges and define a trench, so I started swinging our Estwing paleo pick – the modern equivalent of the famous Marsh pick, and a bit smaller and more versatile than a railroad or garden pick – and was picking off large blocks, up to the size of a football or so. This activity was on the “left” side of the skeleton, where we thought we had the cluster of vertebrae. It was going well, until I pried loose a 15 lb block – that had broken right through several articulated vertebrae. I was partially pissed and partially relieved: there were still some bits in the ground, but it was a clean break; articulation generally means you can follow a skeleton’s anatomy and accurately predict where elements will be – up until now, most of the bones had been in a confusing jumble, clearly disarticulated after death. Unfortunately, this also meant that, at minimum, the bone scatter grew outwards by at least a foot. One good development was Sarah’s discovery of the periotic of our whale – I had her leave it alone after exposing just a little bit of it.
It's hard to see but that funky little thing on the right is part of the periotic (inner earbone) - very few basilosaurid specimens have a periotic that is both freed from the skull and figured and described properly, and this is also the first periotic known for this genus. Later I had nightmares that it was actually just a weird fish bone, prompting me to open up the foil jacket over the weekend and confirm its identification. It is in fact a beautiful earbone!
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