My first visit to College of Charleston in 2012 - checking out some Oligocene toothed and toothless mysticetes for my Ph.D. research on eomysticetid whales. I had no idea that, just a few years later, I would end up working on this tremendous collection at CCNHM!
A couple of weeks ago we published a new paper in the journal Current Biology on a very large dolphin from the Oligocene of South Carolina – Ankylorhiza tiedemani. I’ve been working on this study with my coauthors Morgan Churchill, Emily Buchholtz, Brian Beatty, and Jonathan Geisler on and off (but mostly on) since summer 2017. It’s based on a fossil collected in the 1990s by CofC alum Mark Havenstein, but serious research on this taxon – affectionately known as “Genus Y” for decades – actually began in the early 1970s with the discovery of specimen ChM PV 2764, a well-preserved skeleton from the Chandler Bridge Formation of South Carolina, discovered and excavated by the late Al Sanders. Al was the Natural History curator at Charleston Museum until 2012; I first met Al a few months later in October 2012 on my very first visit to Charleston.
Al Sanders (right) and Ewan Fordyce (left) at CCNHM in 2012 discussing CCNHM 108 on the table, which five years later would become the holotype specimen of Coronodon havensteini.
Al had no advanced degrees, but was an unparalleled expert in paleontology and natural history of the southeastern USA and his knowledge, discoveries, and body of published research commanded respect in spite of that. Al was a titan in marine mammal paleontology. He was also well-situated to inherit a flood of fossils, as Charleston had significant population growth after World War II, and with the baby boom in full swing, suburbs and subdivisions were being built on the outskirts of Charleston at a rapid rate. Now, here’s the interesting bit: there were suburbs built much earlier, from 1900 to 1940 or so, that are within about five miles of downtown: West Ashley (where I used to live), North Charleston, and Mount Pleasant – but all of these are inboard of I-526, which is a ‘ring’ highway that makes a halo about 5 miles radius from downtown Charleston. As it happens, within this region the Oligocene rocks are quite buried: 5-30 meters (or more) deep, with a healthy cover of Pleistocene overburden (chiefly the Wando Formation). In the areas where phosphate mining was most extreme – West Ashley outside 526 and the area of the North Charleston airport (Charleston International/Joint Base Charleston) – the rocks are quite shallowly buried here, only 2-3 meters down – 4 meters was about the maximum depth that the strip mines during the heyday of phosphate mining would go, past that it was too much work (recall they were stripping off overburden by hand, horse, ox, and plow). By the late 1960s, subdivisions were being constructed north of the airport in North Charleston, near another zone called the Fort Bull Bulge, where the Oligocene deposits are only 2-5 meters below the surface. In one of these subdivisions in Summerville, South Carolina, Al Sanders and company found a spectacular skeleton including a nearly complete skull and vertebral column of an obscenely large dolphin.
The spectacular cast skeleton of ChM PV 2764 - "Genus Y" - on display in the old Natural History hall at Charleston Museum, which has since been revamped thanks to the efforts of our colleague Matt Gibson, NH curator at Charleston Museum. This specimen is now best identified as Ankylorhiza sp. or Ankylorhiza sp. 2.
This dolphin was dubbed the informal name “Genus Y” in a landmark paper by Frank Whitmore and Al Sanders in 1977 – which was able to review all published Oligocene cetaceans (worldwide) in about 16 pages. They also made reference to a “Genus X” and in notes and labels spread throughout Charleston Museum collections, there is also a Genus Z, Genus A, B, C, and so on. This was necessary as there was so little published at the time on these sorts of cetaceans, Al’s early research was truly groundbreaking. At the same time, Al faced an “embarrassment of riches” issue: there was almost too much to study. In about 15 years, Al and others collected about 10-20 lane cabinets worth of fossils, and many unopened jackets and unprepared fossils await attention or are currently being worked on by our good friend Matt Gibson, the current Natural History curator of Charleston Museum. Sadly, Al only published a few of his cetacean discoveries – these did, however, crucially included the publication of Eomysticetus whitmorei, which was the cornerstone paper that made my own Ph.D. research possible. Others included the naming of the ur-dolphin Ashleycetus planicapitis (one of the most plesiomorphic dolphins ever discovered), a redescription of Xenorophus sloanii (in the same paper, no doubt a lifelong goal of Al's that would unlock the taxonomy of the more diverse collection of South Carolina xenorophids), and the naming of Micromysticetus rothauseni (proposed to be a "cetotheriopsid", later strongly recovered within Eomysticetidae by my Ph.D. research). When visiting Charleston Museum in 2012, I got to see specimens of the “Charleston toothed mysticetes”, which Al and Larry Barnes were supposed to have published. An independently discovered skull was later published as Coronodon havensteini in 2017 by Jonathan Geisler, Brian Beatty, Mace Brown, and myself, and Al was fortunately alive to see a name applied to one of these toothed mysticetes – though Ankylorhiza is the “one that got away”, so to speak. On the other hand, it’s critical to remember that Al published on a wide variety of fossils and geology and had a long, remarkable, and successful career – this included naming the Chandler Bridge Formation, revising the entire record of Plio-Pleistocene mammals from the state, and the entire record of dinosaurs and other Mesozoic reptiles from South Carolina. While this study did not describe Al’s Genus Y skeleton (ChM PV 2764), it would not have been possible were it not for that discovery, so thanks to Al.
The presumed holotype tooth of Saurocetus gibbesi, from Allen (1924), along with a lower postcanine of CCNHM 103, Ankylorhiza tiedemani.
The story *really* begins in 1848 with the discovery of an isolated tooth from the Ashley Phosphate Beds, which THE Louis Agassiz named Saurocetus gibbesii – a big triangular molar with some serrations, longitudinally fluted enamel, and possibly double-roots. The specimen was never figured, and the specimen number was not cited by Agassiz, and then lost for about 50 years (because of course that happened to an unfigured specimen of unknown catalog number…). Some three decades later, a partial rostrum (snout) of a skull of a very large dolphin – though not containing any teeth resembling Saurocetus – or, any well-preserved teeth for that matter – was dredged from the Wando River on a phosphate barge, and presented to the American Museum of Natural History by a Mr. I.B. Tiedeman, and published in 1887 by J.A. Allen as Squalodon tiedemani. Of course it was placed in Squalodon; it had a similar rostrum with some European specimens of Squalodon. Generally, any large odontocetes with heterodont teeth were placed into Squalodon, and Remington Kellogg attempted to sort through this quagmire in 1924 when he named Squalodon calvertensis – an actual species of Squalodon. On Squalodon tiedemani, Kellogg wrote that it was much larger than any known “squalodont”, and was perhaps the first to cast doubt on squalodontid affinities, noting “A careful comparison of the types of Squalodon atlanticus and Squalodon tiedemani has failed to convince the writer that these two cetaceans are closely related to one another.” Kellogg did mention that the incompleteness of the specimen meant that “considerable uncertainty exists as to whether or not Squalodon tiedemani should be placed nearest the squalodonts or the zeuglodonts [=basilosaurids]”.
The holotype rostrum of "Squalodon"(now Ankylorhiza) tiedemani - from Allen (1887).
Sadly, the age of the “S.” tiedemani holotype was completely
unknown, and for a long time, widely assumed to be Miocene. By the 1970s,
fossils of superbly large squalodontids from the Chesapeake Group (Pungo River
Formation and Calvert Formation) were being identified at the Smithsonian as S.
tiedemani, first and foremost a phosphatized skull with clam borings from the
mid Miocene Pungo at the Lee Creek Mine (Boreske et al., 1972), identified by
Frank Whitmore. Sometime later, a giant Squalodon skeleton from the mid
Miocene Calvert Formation of Virginia was identified in Alton Dooley’s Ph.D.
thesis as S. tiedemani – but he later changed his mind, concluding later that
“S.” tiedemani has something to do with the “Genus Y” skeleton of Al Sanders.
Dooley named this new skeleton from Virginia as Squalodon whitmorei in
2003. A following study by Frank Whitmore accordingly reversed course (Whitmore
and Kaltenbach, 2008) and assigned the reworked Boreske et al. skull to S.
whitmorei. However, they also referred a couple of large odontocete specimens
including a titanic dentary from the rivers of Charleston to S. whitmorei.
Not to skip ahead, but in our supplementary info, we concluded it was probably
actually Ankylorhiza, reidentifying the Charleston mandible as Ankylorhiza
sp.
The absolutely monstrous holotype skull of Squalodon whitmorei, which is a bit more derived and a bit larger (S. whitmorei likely had a skull at least 15-20 cm longer than CCNHM 103, and is roughly the same size as the larger, undescribed species of Ankylorhiza represented by ChM PV 2764).
My first look at CCNHM 103, in October 2012 after the Society of Vertebrate Paleontology meeting in Raleigh, NC.
In the late 1990s Mark Havenstein and colleagues discovered an enormous dolphin skeleton during construction of the Crowfield Plantation subdivision, sandwiched between Summerville, Ladson, and Goose Creek in South Carolina – about a 15 minute drive from my house. The skeleton needed to be removed quickly, so as not to interfere with construction activities; considerable piecing was needed in order to put it back together. The benefactor of our Mace Brown, acquired the specimen sometime later and spent years piecing the skull and skeleton back together – and in 2010, the skeleton was donated and became one of the first specimens to be catalogued into our collection as CCNHM 103* (our catalog begins at CCNHM 100). When I first visited CCNHM in October 2012, I met Mace and saw this specimen on display – on the same hanging platform it occupies right now. I thought “sweet jesus that’s a big dolphin” but was too preoccupied with examining eomysticetid remains and the fossil I would eventually help publish as Coronodon havensteini five years later (unbeknownst to me at the time!) to consider that specimen any further. That same week, I didn’t even examine Genus Y at Charleston Museum; I wouldn’t see it in person until 2015. Nor would I examine CCNHM 103 in detail until 2016.
*CCNHM is the original acronym, after “College of Charleston Natural History Museum”, and appears in the Geisler et al. (2014) publication on Cotylocara (CCNHM 101). Shortly thereafter, the museum was renamed (in early 2015 I believe) the Mace Brown Museum of Natural History, after Mace’s voluminous contributions to the collection and well-being of the museum.
Coauthor Jonathan Geisler examining the teeth of CCNHM 103 back in 2017. The braincase and rostrum of the larger, undescribed species, CCNHM 1075, sits off to the right hand side. The orange specimen is our referred skull from the Ashley Formation, CCNHM 220.
We went back and forth on the naming for a while, we were uncertain if there was one or two species of “Genus Y”, and CCNHM 103 had been nicknamed “Genus Y not” or Genus Y°” by Brian. I tend to be a lumper rather than a splitter (I did most of my paleontological education at Montana State University after all), so it took a bit of convincing and lots and lots hand wringing between the initial members of the team. Alternative hypotheses were: 1) Genus Y and Genus Y not were different species; 2) different sexes of the same species; and 3) different growth stages. Some specimens do have a significantly wider vertex than others – it’s quite narrow in CCNHM 103, somewhat narrow in ChM PV 2764, and surprisingly wide in the largest specimen, CCNHM 1075. Since the occipital shield on the back of the skull anchors in the neck muscles that stabilize the head, it’s perhaps not surprising that this might scale with body size (bigger head, after all). However, we finally settled on a few consistent differences: in CCNHM 103 and the holotype of “S.” tiedemani, the rostrum is turned up a bit and dorsoventrally thickened, with the first incisor positioned dorsal to the second; secondly, the cheek teeth of CCNHM 103 differ from Genus Y proper (ChM PV 2764 and CCNHM 1075) in lacking large accessory cusps – they are there, but instead take the form of tiny, 1-2 millimeter wide “beads” of enamel on the cutting edges. So we settled eventually on the two species idea, and sure enough, our phylogenetic analysis grouped the specimens precisely how we hypothesized – which was a satisfying vindication. At this stage, however, we were full steam ahead on naming a new genus and species.
CCNHM 220, our less spectacular specimen of Ankylorhiza tiedemani from the Ashley Formation - still a very important specimen as it documents this same species as being present in the early Oligocene.
At some point I couldn’t shake the idea that we very likely were not dealing with a completely new species, even though Al Sanders had concluded otherwise. I had extensive discussions on lumping v. sinking with my Ph.D. adviser Ewan Fordyce – and Ewan is very much in favor of stabilizing old names with newer, better preserved and more anatomically informative fossils that improve the diagnosis. After all, he had done this for many taxa, and declaring others nomina dubia or cetaceans of uncertain affinities (incertae sedis). This was necessary given his arrival on scene in the late 1970s, where the New Zealand cetacean fossil record had been almost criminally abused by various workers, and much of his dissertation through U. Canterbury consisted of mopping up this enormous mess. Ewan on occasion cited the extreme example of Zarhachis flagellator – originally based on a caudal vertebra (doubtfully diagnostic), later stabilized with the referral of a skeleton by Remington Kellogg. The name is now indelibly associated with the nicely preserved skeleton that Kellogg published, and so if someone really wanted to declare it a nomen dubium and commit some opportunistic taxonomic piracy and name a new genus and species off the skeleton (as is frequently done in the frankly overcrowded realm of archosaur paleontology) – there’s actually enough of a case to ‘preserve’ Zarhachis under ICZN rules. After all, this sort of thing played out recently with Zygorhiza kochii – the holotype of which is a piece of junk braincase without any redeeming diagnostic features other than size, and meanwhile everyone mentally pictures Kellogg’s beautiful skeleton (USNM 11962) when they think of Zygorhiza. The taxonomic viewpoints of Gingerich v. Uhen on Eocene basilosaurids would make for a great post… later. While I would not go so far as to did what Kellogg did with Zarhachis (and I imagine even the most conservative paleocetologists today would not either), I was determined to find if we truly had something new or something old. In the end, it was a bit of both.
A slide from an updated SVP presentation showing the features linking CCNHM 103 with the holotype of Ankylorhiza tiedemani, AMNH FM475. Also, these are both shown to scale: CCNHM 103 is a bit smaller and slightly less robust - this is a BIG dolphin!
After trawling through all the papers on early large odontocetes I could, I re-read Allen (1887) and remarked upon the similarity between CCNHM 103 and the “S.” tiedemani holotype: the “double decker” incisors, the expanded premaxillae, the upturned rostrum, and very large size. Jonathan Geisler visited the AMNH and identified another similarity: clusters of foramina within the embrasure pits that the lower teeth fit into when the mouth was closed. He also determined that there is some adhering matrix – indicating that the holotype of “S.” tiedemani originated from the Ashley Formation, which is early Oligocene – 28-30 myo, a little older than our skeleton CCNHM 103 from the 23-24 myo Chandler Bridge Formation. So, that settled it for me: we agreed that CCNHM 103 was referable to “S.” tiedemani, necessitating a new genus name, because there’s no way this thing was related to Squalodon – tacitly acknowledged 96 years ago by Kellogg. So we assigned it to the new genus Ankylorhiza, and referred CCNHM 103 to that species. The other species of Ankylorhiza, represented by Al Sanders’ Genus Y skeleton ChM PV 2764 and our specimen CCNHM 1075, is not yet named.
Further Reading
Allen, 1887. http://digitallibrary.amnh.org/handle/2246/1611
Allen, 1924. https://academic.oup.com/jmammal/article-abstract/5/2/120/837661?redirectedFrom=fulltext
Boessenecker et al., 2020. https://www.cell.com/current-biology/fulltext/S0960-9822(20)30828-9?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982220308289%3Fshowall%3Dtrue
Boreske et al., 1972. https://www.jstor.org/stable/1302923
Dooley, A. C. 2004. A new species of Squalodon (Mammalia, Cetacea) from the middle Miocene of Virginia. Virginia Museum of Natural History Special Publication 8:1-43.Whitmore, F.C., 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.
Whitmore and Sanders, 1977. https://academic.oup.com/sysbio/article-abstract/25/4/304/1653287?redirectedFrom=fulltext
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