Sunday, January 22, 2023

Fieldwork snapshots: prospecting dredging spoils along Charleston Harbor

Amidst the panic of end-of-semester grading, exam writing and proctoring, and preparations for heading to California and Montana for the holidays, Sarah and I managed to have a day free to head out to a dredge spoil site out on Charleston harbor with our friend Ashby Gale. Ashby runs a fossil collecting tour guide business (Charleston Fossil Adventures), and has recently bought a boat that can help get out to some places a bit too far - or too rough/risky - for kayaking. Ashby and his clients have put together a pretty spectacular collection of dolphin periotics from our waterways, and these trips are a great way to add a few more - and a good opportunity to find the occasional trophy tooth. This particular day in December was one of the coldest - there was frost on our grass when I woke up and it was 43F (about 6C for our foreign readers) at the boat landing at 8am, meaning I was fairly apprehensive about getting wet or falling in the drink; the high would only be in the mid 50s (~12-13C) so drying off would be unlikely.

Captain Ashby bringing us in! This is actually Ashby's second boat, a somewhat larger Carolina skiff than the one he had before, and he had not yet installed his depth finder, so we were using the old fashioned 'stick a paddle in the water to estimate how deep it is' method. And we, as in me. Recall the frigid temperatures. Ashby was nervous about getting the propeller blades in the sand (which he had done with his first boat on the very first outing he invited me along on) or running the hull aground, as the larger, heavier boat would be more unlikely to be freed if stuck in the mud. We coasted in, and when the paddle indicated about 2' depth, Ashby told me to stop, and we coasted in for a few more seconds before he instructed me to hop off the front. I couldn't see the bottom - our water here is notoriously murky, with 18" visibility (meaning that if you see the bottom, it's shallow enough for your boots to keep you dry). Being another eagle scout I had my full faith in Ashby and jumped - into water two inches deeper than my boots! Frigid saltwater filled both up. Some choice words I won't repeat then filled the vicinity. Since I was already soaked and cold, I dropped off my bag and carried Sarah to shore so she would at least stay dry. On shore, I took off both boots and dumped out a half gallon of water each. My feet never quite went numb and my socks never quite dried out, but the fluid that was in there eventually, after about two hours, finally warmed up.

Within five minutes of getting ashore, I found this nice medium-sized tympanic bulla from a dolphin - probably an Oligocene waipatiid dolphin - with some brown siltstone matrix embedded within the tympanic cavity. If matrix inside this cavity becomes phosphatized, this is basically the only way you'll find a dolphin bulla with the outer lip attached.

Ashby quickly found this very nice dolphin periotic after paddling himself in - these periotics have a mixture of features found in eurhinodelphinid and waipatiid dolphins and are challenging to place. There's at least one soon-to-be published dolphin from the lower Miocene of Europe with similar periotics that may represent a new family. Regardless, the immediate discovery of a bulla and complete periotic helped me relax somewhat and realize that at least my freezing feet were not in vain and we would end up with at least a couple of nice earbones.

Sarah found this unusually complete and unscavenged longnose gar (Lepistoseus osseus) - who knows how it ended up here! The harbor is completely saltwater - apparently they can tolerate some salinity, but I generally don't hear about them much in the harbor; I imagine this individual died inland in a swamp or at least brackish water drainage and drifted out with the tide.

Our dredge spoils here in the lowcountry are generated from harbor excavations meant to deepen and/or maintain required depths for shipping lanes. This does two things: 1) dumps fossil-bearing sand and gravel above water onto dredge spoils and 2) occasionally incises into fossiliferous bedrock. Fossils from modern sediments were eroded out and reworked sometime, likely in the Holocene (but are all pre-Holocene). Owing to the abundant fossils in our subsurface, there's just a ton of shark teeth wherever dredging occurs. Here are a couple of sand tiger teeth (Odontaspididae).

About an hour in I found my first periotic of the day, this little beauty - which at first I thought rather looked like Papahu, a dolphin my Otago doctoral colleague Gabriel Aguirre-Fernandez described in 2014, but after brushing it off and looking it over, it rather looks like the more gracile periotic Ashby found earlier in the morning.

Here's the other side:

There really is a variety of neat stuff out there, including teeth of the considerably more rare megatoothed shark, Parotodus. Most of the teeth of Parotodus are P. benedeni, though elsewhere in Charleston an older unnamed species bearing lateral cusplets and resembling the Paleocene-Eocene species Otodus obliquus can be found. This is a small P. benedeni. Many folks go diving for meg teeth, but these ones are a bit more prized because they are considerably more rare.

A horseshoe crab cephalothorax plate, with a nice little erosional scour around it.

We find tons and tons of phosphatized steinkerns throughout the lowcountry, some of which are identifiable. In this case, we've got a cone snail steinkern. Cone snails, or cone shells (Conidae), are more common and diverse at tropical latitudes - and are famous for being absurdly venomous.

Here's a partial Carcharocles tooth one of us found - we've generally not had much luck with enormous teeth out here. This one's about 3 inches long (~7 cm).

A very nice little periotic I found in our third or fourth hour out there - one of about a dozen or so lowcountry specimens I believe are close to Eoplatanista italica from the lower Miocene of Italy.

A nice little Carcharocles megalodon tooth found by Sarah.

Nearly at the end of the day I found this ~3.5" (8 cm) busted up Carcharocles tooth that had escaped detection - possibly the last rain had just exposed it, though there were no shortage of bootprints in the vicinity.

I realize you've probably already seen this image a few times on other posts, but we really did have a pretty good day out there when it comes to earbones. The big partial one in the middle was found by Ashby in the last 30 minutes, and is a partial periotic of Ankylorhiza - and a great match for "Genus Y" proper, an unnamed species represented by the big skeleton over at Charleston Museum.

Sunday, January 15, 2023

Bobby's guide to whale & dolphin earbones 2: identifying toothed whale periotics

Read Part 1 here for an introduction to whale and dolphin earbones (recommended before diving right in).

This is perhaps the part that most readers are looking for – how to identify different dolphin periotic bones. For each family of cetaceans, I’ll briefly list the approximate size reported as complete periotic length (not specific measurements, this is from memory), some of the main attributes, along with any unique features of the family or higher level features within Odontoceti, similar periotic morphs they can be confused with, age, known distribution, and established localities (e.g. localities, including rock unit, where these are confirmed to have been found or are reliably known from).

This guide is not exhaustive, nor is it perfect: identifying isolated periotics has long been called a 'black art' even by seasoned whaleontologists. The attributes listed below should not be interpreted by professionals as synapomorphies - they are generalizations, which can help someone identify many isolated periotics to the family level. Some families are very obvious, but others range quite a bit in anatomy, overlapping with other families - this is particularly a problem within the Delphinoidea. Regardless, I have almost certainly glossed over some important details and missed some things - so if you want to help me improve this, let me know what I've screwed up! Also, I will likely expand this in the future. The specimens in this post are mostly in collections of the Mace Brown Museum of Natural History; genus-level identifications (upper right) for some of these should be taken with a grain of salt. All photographs are by me, unless otherwise stated.

Though many features and conditions vary considerably and have evolved and lost again and again, some major groups are united by some periotic features. Archaic dolphins generally have long anterior and posterior processes and some remnant of the suprameatal fossa, which is large and deep in basilosaurid whales. Many archaic dolphins, as well as platanistoids, have a small spur lateral to the posterior process called the articular process - in Platanista (Ganges river dolphin) it is long and hooked, and generally needs to be broken in order for the periotic to be removed from the skull. The anterior bullar facet is primitively shallow in the earliest dolphins, but deeply concave in many long-snouted early to middle Miocene dolphins (Eurhinodelphinidae, Eoplatanistidae), and the facet is lost entirely in Delphinoidea. Delphinoids also tend to have a proportionally huge pars cochlearis.

As with all other fossils, periotic bones have some degree of natural variation. Above are some photos of periotics of Parapontoporia sternbergi, reasonably interpreted by L.G. Barnes (1985) as a single species from the San Diego Formation of southern California (Pliocene). You'll notice that much of the variation is in the length and inflation of the anterior process and the particular shape of the posterior bullar facet. The cochlear morphology - especially ventrally - seems to vary the least, which according to my Ph.D. adviser Ewan Fordyce, is likely because it ossifies the earliest and is associated with the middle ear sinus. The dorsal side varies considerably as this continues to ossify during growth, so the shape and size of the body and the configuration of foramina and crests within the meatus, and the shape and size of the meatus itself, also can change during growth. What this means is that no two periotics of the same species will ever be identical, and I guarantee you will go mad picking out differences between specimens only to find out they represent different edges of the anatomical envelope of variation or juveniles v. adults. As a result, it's better to look for shared similarities and when possible, match a particular periotic morph to periotics found associated with a skull, though this is certainly more typically the realm of activities of a whaleontologist rather than an amateur collector as many such specimens needed for such comparisons are in museum collections. Image from Barnes (1985).