Wednesday, September 27, 2023

Bucket-o-earbones from a lowcountry river site: preliminary findings and analysis

Last weekend I had a river tour for Charleston Fossil Adventures get cancelled owing to some pretty nasty thunderstorms, and so Ashby Gale and I instead went and worked a table at the first annual fall Artifact and Fossil show at Cypress Gardens*. I saw a number of familiar faces, including Cade Kaufmann, a tour guide for Charleston Outdoor Adventures - Cade takes folks kayaking around the lowcountry, and makes many visits to some fossil sites that are difficult for just about anyone else to get to. I know exactly where they are, but 1) of course won't share publicly and 2) wouldn't go there without asking Cade to show me. Back in 2016, Cade donated a few pieces to CCNHM collections (Mace Brown Museum of Natural History) including a nice partial tooth of Coronodon, which we published in our ginormous PeerJ monograph earlier this year. He also donated a tympanic bulla of a waipatiid dolphin at the time. For a while he's been telling me he had saved up quite a few earbones from his sites. When I first saw him at the show last weekend, it had been a couple years, but he nonchalantly reminded me that he "had a few earbones" for me. Now, I'm happy to find one periotic bone a week out on the river - so I was not expecting much, a couple of specimens, at most. I expressed some gratitude, and quickly forgot about it as I began setting up our table.

*Cypress Gardens is where they filmed many scenes from The Patriot, including all of the cypress swamp scenes and the small Spanish mission where Mel Gibson's militia was hiding out. Most of the movie was filmed in and around Charleston!

 Cade Kaufmann and his bucket of earbones! Cade is a guide for Charleston Outdoor Adventures.

About an hour later Cade comes by and hands me a small 14 oz container like what a small to-go salad might be kept in - and it was overflowing with dolphin periotics! The number of periotics was so absurd my reaction was just maniacal laughter - followed by a quick reversal to polite, but effusive thanks to Cade. I asked him whether he had locality data for all these - and he indicated that they were all from ONE small location! I was floored. These specimens were from one dredge site, most are nearly complete, and most are well-preserved enough to be of publication quality. Now, Ashby Gale has found many periotics (and bullae) over the past 6-7 years or so doing his fossil tours, and he was just as floored as I was. 

 The bucket-o-earbones.

I've already started work on a sample of about 200-300 periotics collected by Ashby, his clients, and Sarah and I from various Lowcountry waterways - some locations a bit secret, and from other well-known fossil sites like Folly Beach, Northbridge Park, and Drum Island - and this single bucket-o-periotics increased the sample by ~25-20% or so! This increases the sample size, and also the amount of work considerably - almost ensuring that this study will end up being a short monograph in length (that's a LOT of periotics to figure!).

All of the earbones laid out in approximate taxonomic groupings.

 So, I thought it might be fun to do a blog post about what we can learn from this collection. First off, sample size: there are 48 periotics and 24 tympanic bullae in here. That's a damned good sample! For example, the periotic sample from the entire Purisima Formation in California where I started my whaleontological studies, with the exception of one private collection, is less than that. 

 Xenorophid periotics - Xenorophus above, Albertocetus below.

1) Xenorophidae

Two periotics are identifiable as xenorophids. One is larger than the other, and is a good match for Xenorophus sloanii; the other is likely Albertocetus meffordorum.

 Periotics of "spear-toothed" waipatiid dolphins, including those similar to skulls I've preliminarily identified as aff. Waipatia.

 A beautiful periotic closely resembling Ediscetus osbornei.

2) 'Waipatiidae'

Ten periotics and eight bullae are identifiable as waipatiids - noting of course that waipatiids may be an evolutionary 'grade' rather than a clade. Several periotics closely resemble one morphotype from the Chandler Bridge Formation with a skull that closely resembles Waipatia maerewhenua from New Zealand, although the periotics are not quite so close a match; they are distinctive in having a bit of a wedge-shaped pars cochlearis. This taxon I have preliminarily identified as aff. Waipatia. One periotic with a more spherical pars cochlearis has a pronounced articular process, making it a rather good, albeit imperfect, match for Ediscetus osbornei and is perhaps best identified as Ediscetus sp. for the time being.

Periotics most closely resembling Ankylorhiza (and Squalodon).

3) 'Agorophiidae' - Ankylorhiza spp.

Four periotics and two bullae represent 'giant' dolphins in the genus Ankylorhiza, which in a couple of phylogenies form a clade with Agorophius and may represent a redefined Agorophiidae*. There are at least a couple of periotic morphotypes present, and none of these are massive enough to represent "Genus Y", the still-unnamed larger species of Ankylorhiza from the Chandler Bridge Formation; Ankylorhiza tiedemani is still not yet known from specimens with periotics.

Though the skull is quite different, the periotics of Ankylorhiza - and these - do share many features in common with true Squalodon, and detailed comparisons with Squalodon, Agorophius, and Eosqualodon are clearly warranted.

*Agorophiidae used to include virtually all stem odontocetes more primitive than Squalodon, including the xenorophids, and has been considered a wastebasket taxon. A redefined Agorophiidae would include Agorophius, Patriocetus, and Ankylorhiza, which form a reasonably supported clade in some analyses - for example, in our 2020 paper introducing Ankylorhiza.

 The best example periotic of a squalodelphinid from the sample; the remainder are partials.

4) Squalodelphinidae

Four periotics and five bullae represent the squalodelphinids, the sister taxon of the Platanistidae. These are somewhat longirostrine dolphins with thickened bone over the orbit, and typically possessing somewhat large single-rooted teeth with rugose, conical tooth crowns. Several species formerly assigned to the Platanistidae such as Dilophodelphis and Araeodelphis now appear to represent squalodelphinids along with Squalodelphis, Notocetus, Huaridelphis, and Phocageneus. The best-preserved periotics here most closely resemble periotics formerly assigned to Phocageneus from the Pungo River Formation/Limestone at the Lee Creek Mine, but are somewhat smaller; I described a similarly small periotic from the Oligo-Miocene Belgrade Formation at Belgrade Quarry, North Carolina, last year.

Two periotics of eurhinodelphinids, the top one representing Xiphiacetus, perhaps X. bossi. The bottom one is not clearly any described eurhinodelphinid taxon, differing somewhat from Xiphiacetus, Schizodelphis, and Eurhinodelphis.

5) Eurhinodelphinidae

Nine periotics and nine bullae represent the Eurhinodelphinidae, with one complete periotic closely resembling Xiphiacetus bossi from the Calvert Formation of Maryland and Pungo River Formation of North Carolina (Lee Creek Mine). Eurhinodelphinids are common Miocene longirostrine dolphins with a distinctive toothless extension of the rostrum beyond the mandible, much like a swordfish (hence why I call these "swordfish dolphins" when talking to the public). There is certainly more than one morphotype represented here.

 Four of the periotics assignable to Eoplatanista or Eoplatanistidae.

For comparison, here is the figure showing three periotics of Eoplatanista spp. from Muizon's 1988 paper on the "Acrodelphidae".

6) Eoplatanistidae

Six adorable periotics represent Eoplatanista or something similar within the Eoplatanistidae. These periotics were a bit of a mystery to me until I re-read Christian de Muizon's 1988 paper on the "Acrodelphidae" in which he included some great figures of periotics of Eoplatanista from Europe: they closely resemble eurhinodelphinid periotics but are tiny and have very short anterior and posterior processes. The tympanic bullae of Eoplatanista have a convex ventral side and are otherwise very similar to eurhinodelphinids - no such bullae are present in this sample. I reported cf. Eoplatanista from the Belgrade Formation of NC last year, based on such a bulla. Eoplatanista is otherwise unknown outside Europe; there are a shocking number of these periotics found in the South Carolina lowcountry, always close to the coast. Surprisingly, no such specimens have ever been reported from Calvert Cliffs and no skulls of Eoplatanista were reported in the Lambert et al. 2023 chapter on odontocetes from the Calvert Formation, aside from the newly described Caolodelphis milleri which has some similarities with Eoplatanista, and was reported from low in the Calvert Formation (early Burdigalian Pope's Creek Sand member, ~19 Ma). Similarly, no such periotics are known from the spoils of the Lee Creek Mine.

Periotics belonging to unidentified family/genera of early odontocetes: the top two resemble an unnamed dolphin from Europe, and the bottom one resembles Papahu taitapu and cf. Papahu from the early Miocene of New Zealand.

7) Family Uncertain

A number of strange periotics with a mix of waipatiid-like and eurhinodelphinid-like features have also turned up in the South Carolina lowcountry, also close to the coastline, and within Cade's sample there are twelve of these. Some of these approach Papahu taitapu (early Miocene, New Zealand) in some features and there are also some similarities with Yaquinacetus meadi. There is an unpublished odontocete from Europe that these periotics may be referable to, but I won't spoil it for now and will update this post after the beast is published. These periotics are similarly not known from the spoils from the Lee Creek Mine or from Calvert Cliffs.

Geology, Age, and Interpretations

I obviously won't "spoil" the location at all since it's Cade's secret - but I can share that these are dredge spoils along a local riverbank. The fossils are a bit different from what Ashby and I collect from our tours through Charleston Fossil Adventures; our specimens are virtually all black, dark grey, and occasionally have a bit of brown. At Cade's locality, these periotics are a variety of earth tones including quite a bit of red - the earbones from Cade's collections are just *pretty*.

Now, what formation are they from? It's a simple question with a complex answer, I'm afraid. There are loads of dredge islands all over the South Carolina lowcountry. River channels have been deepened and canals have been dug all over the lowcountry in order to permit maritime shipping: the Ashley, Cooper, and Wando rivers during the 19th century, the Intracoastal Waterway in the late 19th and early 20th century, and Charleston harbor pretty continuously since the age of steam. What candidate rock units could our fossils come from? 

Ashley Formation: the major bedrock unit here in the lowcountry and typically the unit that all manmade holes bottom-out within. This is a light tan to khaki and occasionally olive green sandy limestone with sparse invertebrates, phosphate pebbles, and well-preserved vertebrate remains; the unit is quite thick, 10-30+ meters, and the bottom is only ever exposed locally in deep core samples. The Ashley Formation is late Rupelian in age (early Oligocene), dating to 28-30 Ma. Fossil cetaceans include the toothed baleen whale Coronodon, eomysticetids like Micromysticetus, xenorophid dolphins (Xenorophus, Albertocetus), waipatiid dolphins (Ediscetus), and giant dolphins (Ankylorhiza).

Chandler Bridge Formation: the major fossil-producing unit in West Ashley, North Charleston, and Summerville: a thin (10-100 cm) unit consisting of sand and silt with abundant phosphate pebbles, shark teeth, and other marine vertebrates that is completely leached of all calcareous material - however, this unit is generally not exposed, even in the subsurface, south of highway 17 or within the I-526 corridor - in other words, generally not present near the coast or near downtown. It's been eroded away - but may produce fossils that were reworked into the basal Pleistocene unconformity, which is mantled with a mix of Oligocene-Pleistocene fossils wherever it is present in Charleston. This unit is late Oligocene in age, approximately 24-23.5 Ma. The Chandler Bridge Formation preserves cetaceans including: Coronodon; Eomysticetus; xenorophids like Xenorophus, Albertocetus, Echovenator, and Cotylocara; waipatiid dolphins (all unnamed taxa, but NOT Ediscetus); and the giant dolphin Ankylorhiza.

Edisto Formation: a bit of a mystery unit that dates to about the Oligocene-Miocene boundary (~23-23.5 Ma). This unit is quite thin and mostly exposed in the subsurface, but is a light yellow-brown sandy limestone, somewhat similar in lithology to the Ashley Formation. Much of the commercially mined phosphate from the "Ashley Phosphate Beds" is hypothesized to have been derived from this unit - the type locality of which does not exist, since it was named based on a block of white phosphate. Supplementary sections have since been defined along the Edisto River, and it's been identified in the subsurface from auger holes and core samples. However, it looks quite similar to the Ashley Formation from what I can tell and is never separated from it by the Chandler Bridge, so the capacity for misidentification of this unit is high - the Ashley Formation, after all, does vary quite a bit in lithology. Some land mammals (Daeodon mento, Anchippus texanus) from the "Ashley Phosphate Beds" have been reported that indicate earliest Miocene age (e.g. late Arikareean/Hemingfordian NALMA correlative) but have adhering calcareous matrix, clearly post-dating the Ashley and must derive from the Edisto Formation.* Barry Albright suggested in his 2019 monograph that the matrix adhering to the holotype rostrum of Ankylorhiza tiedemani may better represent the Edisto rather than Ashley Formation; we suggested the latter in our 2020 paper, but Barry may be correct as we reported an S. tiedemani skeleton from the Chandler Bridge Formation (but, also, from the Ashley Formation). No other fossil cetaceans are certainly known from the Edisto Formation.

*This suggests I may have been too cavalier in referring isolated specimens from our rivers to the Ashley Fm., and some specimens might actually be derived from the Edisto Formation.

Mark's Head Formation: another unit that's locally a bit enigmatic as it is only exposed in the subsurface. However, it is thick and well-exposed along river bluffs in Georgia where it was named, and is contemporaneous with zones 7-8 of the Calvert Formation further north in Maryland, and Burdigalian in age (early Miocene, ~18 Ma). When exposed or penetrated by auger holes, this unit is an olive brown calcareous sandstone/sandy limestone.

So, what are the likely stratigraphic origins of these dolphin specimens? The xenorophid periotics could originate from either of the two well-known Oligocene units, the Ashley or Chandler Bridge formations - and in theory, the Edisto Formation as well. The waipatiid Ediscetus is so far known only from the Ashley, suggesting that at least some of these Oligocene specimens originate from the basalmost unit out here. The other waipatiids more closely resemble Chandler Bridge formation morphotypes, which doesn't necessarily preclude Ashley or Edisto formation origin. Eurhinodelphinid specimens, on the other hand, are strictly Miocene, and the occurrence of one so similar to Xiphiacetus bossi strongly suggests origin from the Mark's Head Formation.

More puzzling are the specimens that belong to taxa not recorded anywhere else in the North Atlantic: Eoplatanista, and the unusual unidentified periotics. We have plenty of early middle Miocene and late early Miocene dolphins from places like the Calvert Cliffs, Lee Creek Mine, and the copious assemblages from Belgium, but very, very few earliest Miocene (Aquitanian) dolphin assemblages along the western Atlantic margin. Given how intensely sampled Calvert Cliffs and Lee Creek are, it's tempting to suggest that these periotics belong to dolphins and/or originate from some unit that is younger than the Chandler Bridge and older than the fossil assemblages further north from the Calvert and Pungo River formations. The Edisto Formation would be such a prime candidate - however, there is also the Parachucla, another 'ghost' unit present in a few auger holes west of Charleston that are correlated with thicker deposits further south in Georgia and Florida. There's also a mystery bed of the Chandler Bridge that continually produces unusually derived-looking fossil cetaceans - we encountered it and documented it in 2018 at a nearby construction site, where it consisted of two meters of clean, quartzose sandstone with eurhinodelphinid-and squalodelphinid-like odontocetes (in addition to Ankylorhiza and xenorophids).

Ultimately, it's anyone's guess - informed or no - where some of these specimens are derived from. However, there is adhering matrix on most of these specimens, and perhaps something can be gleaned from it. Regardless, it does indicate that Cade's locality represents spoils either produced by dredging that cut through multiple rock units, or that these rock units were all eroded into and a composite lag was then dredged and dumped into a spoil pile. In reality, both are likely. Further study and expansion of the collection will help - along with publication of more specimens of Oligocene and early Miocene dolphins with associated earbones, from all corners of the globe.


Bruce C. Lampright said...

Wow, Wow, WOW! I'm wondering if some of the Miocene whale material I've collected from Port Royal Sound in Beaufort County is from the Marks Head Formation...or is it the Hawthorne Formation?

Robert Boessenecker said...

Great question! If memory serves, the late middle Miocene to early late Miocene Ebenezer Formation is also present in that area.