Wednesday, March 13, 2024

Nudibranch hunting in northern California: snapshots from winter tidepooling in Half Moon Bay, CA

This post has more to do with the coastal part of the title and less to do with the paleo part - I'll be doing more of these, since I figure there's probably some interest from readers regarding live, rather than dead, marine critters.

 I found Opalescent nudibranchs like this one on my own for the first time.

I've always enjoyed tidepooling since I was a young kid - and once I left foggy northern California to go to Montana, an extremely land-locked state, I realized how lucky I was to have world-class tidepools just a half hour drive from my parent's house. I didn't have the opportunity in New Zealand (tidepools, yes, but no car) and here in South Carolina, we don't have any water clarity - and, to be honest, a pretty depauperate marine invertebrate fauna in comparison to the Pacific coast. Since our very belated honeymoon a few years ago to the Bahamas and our subsequent Caribbean Spring Break snorkeling trips, I've gotten more and more interested in it, and in 2022 Sarah and I bought Olympus TG6 cameras, recommended to me by Dr. Maureen Berg, a biologist at UC Berkeley who spends a bit of time tidepooling at some of my favorite spots - but with much higher success at finding nudibranchs. Until about three years ago, I had only ever seen one or two nudibranchs in the wild - I was thoroughly unimpressed when I was a kid, seeing a couple of yellow gelatinous blobs. While paddling a canoe in Drake's Estero with Dick Hilton in 2011 (just a month after Sarah and I got married, and a few months before we left for NZ), Dick noticed an opalescent nudibranch on a frond of giant kelp - and I was mesmerized. I had seen photographs, but never one in person - I couldn't believe how beautiful the little creature was. I really got hooked only a few years ago: on a visit to Fitzgerald Marine Preserve (Moss Beach, CA) on a good minus tide with Sarah (and about 200 of our closest friends - new years, 2022), we found about a dozen nudibranchs - all of them some of the 'boring' ones - sea lemons, Monterey dorids, an orange peel dorid, and a few San Diego dorids. That visit was the one where I decided I needed an underwater camera. In December 2022 and 2023 I visited a spot in Half Moon Bay a friend of mine recommended - I'll keep the location a secret for the time being (sorry!) since it's much less frequented. But, it's a good one: tons and tons of nudibranchs.

Winter solstice sunset in Halfmoon Bay, California.

Why nudibranchs, by the way? I've never fully understood what the obsession is among tidepoolers with finding nudibranchs. And, I say this while admitting that I've totally gotten obsessed with nudibranchs as well, without really understanding why. I have some hypotheses, however. For starters, most of them are really quite beautiful - whereas others are more modest blobs of color. Some are rather cute - some of the dorids resemble the "sea bunny" nudibranchs of the Indo-Pacific. They're highly diverse: we've got 180 species along the California coast*, so there's many to go out and find. They're also challenging to find - many folks get out and expect them to just be coming out of the woodwork, and many get bored and impatient. You need to really relax, use your eyes, and look for little tiny blobs of color (for the colorful ones anyway). When you do find one, it's a huge rush! They are, in my opinion, some of the tiniest but most satisfying critters to find. There are many more cryptically colored species that are far more common (and larger) than nudibranchs that I've never seen before in person - and honestly, I've probably passed over a bunch of live baby abalones in search of nudibranchs.

*For comparison, there are a few dozen species in the Humann et al. Reef Invertebrates guide for the Caribbean, and only about two dozen here in South Carolina. For an apples:apples comparison, has about 100 species even for Florida and the northern Caribbean and Bahamas, 17 for the Georgia Bight (northern Florida through the Outer Banks of NC), and 144 for the California coast. I've intuitively known that the California coast is exceptional in terms of nudibranch diversity - but most marine species have a diversity hotspot in the Indo-Pacific (the Caribbean, for a number of reasons, has high diversity for many groups, but is a fraction of the Indo-Pacific). In the Phillipines, there are over double the species versus the California coastline. I suspect the unusually high species diversity is driven by the highly productive kelp forest and rocky shore habitats - and there's probably a bunch of ecological and phylogenetic papers out there on the subject that I haven't read.

Giant kelp, Macrocystis pyrifera. This is not from tidepooling, but is from a rather brave attempt at snorkeling in Monterey Bay in a wetsuit that was way too thin (I made it 45 minutes before I started shivering uncontrollably) - the water was a balmy 54 degrees F, about 10 degrees colder than what I'm used to in the summer at Lake Tahoe.

One last note before we dive in: I may be labeled as a marine mammal paleontologist, and it may be the majority of what I study, but I am really a marine vertebrate paleontologist and I try to keep myself well-rounded by collecting and identifying some of the more humble fossils which can round-out the ecological context of the 'giants' that I study - from little tiny shark and ray teeth to fish bones, clams, and even shrimp claws. We have a rather unique and iconic ecosystem on the Pacific coast, beautifully showcased by exhibits at the Monterey Bay Aquarium - which captivated me as a young kid. At some point in the past ten years it clicked that I was studying organic detritus of an ancestral version of this ecosystem. During the pandemic, Sarah surprised me with an early Christmas gift, knowing I couldn't fly home to California, and bought for me a Third Edition copy of Ed "Doc" Rickett's famous book "Between Pacific Tides". So for me, tidepooling - and future snorkeling in the kelp forests of San Diego (later this year, stay tuned!) - is a way for me to connect with this same ecosystem.

I don't always get good results shooting horizontally, but I do love trying to get "landscape" shots - or should I say, "tidepoolscape" shots. Here we see some sunburst anemones (Anthopleura sola), coralline algae, ?eelgrass, and brown tegula snails (Tegula brunnea).

 A bank of aggregating anemones (Anthopleura elegantissima) in one of my favorite individual tidepools. Each of these is about the size of a US quarter (~2.5 cm). This is actually at a completely different spot, if I'm being honest - but the same day. These anemones are smaller relatives of the famous giant green anemone (A. xanthogrammica) and also live a little higher in the intertidal zone. Because they reproduce rapidly and clonally they produce enormous colonies like this. They get up to 8 cm wide and live from 0-20 meters from Alaska to Baja California.

My only successful "over/under" shot as a photographer with my Olympus TG6 - chiefly because this camera doesn't have a big bubble lens for shooting this sort of photo. This one is taken in a tidepool that at low tide is perfectly still. More aggregating anemones, Anthopleura elegantissima.

Actually since we're on the topic of other spots, I also tried dock fouling in Princeton harbor in Half Moon Bay - I saw tons of these incredible tube worms. These are Giant Feather Duster worms, Eudistylia polymorpha. This species is a large polychaete that lives from Alaska to California from the intertidal zone down to about 400 meters. It's a large filter feeder, constructing a tube up to about 25 cm long and with a filter feeding apparatus up to about 5-6 cm wide.

 Some more giant feather dusters, Eudistylia polymporpha.

OK, now onto the photos from the tidepooling spot. Here's a six-armed sea star, Leptasterias aequalis. These sea stars only get to 5 cm in diameter (2"), and each of these were only about 2-3cm wide. This sea star lives from Washington state to southern California within the mid-intertidal zone.

First nudibranch: a pink champagne colored shag rug nudibranch, Aeolidia papillosa. These live from the low tide line down to (apparently) 900 meters; they feed on anemones, and at least in shallow water, prefer aggregating anemones (Anthopleura elegantissima), a couple of other species of Anthopleura, Metridium, and Epiactis, and Urticina. I've read that this nudibranch can take on the color of its prey - so perhaps it feeds on reddish proliferating anemones (Epiactis prolifera), which were somewhat common at this location.

A rather large (~3-4 cm) Hilton's Aeolid (
Phidiana hiltoni). These nudibranchs are less flamboyant than the opalescent nudibranchs, but are still stunning in their own right. I saw several such examples for the first time in my life on this one evening - including this individual. This is an aggressive nudibranch that has routinely been observed attacking other nudibranchs - it feeds on other nudibranchs and also hydroids. This species ranges from southern California to Marin County, which is the northernmost limit of its range, and from the intertidal zone down to about 60-70 meters.

 A tiny little baby
blue topsnail, Calliostoma ligatum! These are arguably beautiful snails as adults, but the juveniles are really quite vividly colored. These 'archaeogastropods' are in the family Trochidae and are just one of the highly diverse fauna of herbivorous gastropods on the Pacific coast (contrasting with virtually none here on the South Carolina coast). C. ligatum feeds predominantly on kelp but also opportunistically on microfauna (bryozoans, hydroids) and diatoms, inhabits rocky shores and kelp from 0-30 meters along the Pacific coast from Prince William Sound, Alaska, to San Diego.

An orange peel dorid, Acanthodoris lutea. This species feeds chiefly on one species of bryozoan! Its' bright orange coloration is a warning to predators against its toxicity from feeding on bryozoans. This species lives from Cape Arago, OR, down to northern Baja California, from the intertidal zone down to depths of 50 meters.

A tiny opalescent nudibranch, Hermissenda opalescens! These are my single favorite nudibranch species. I saw a bunch of these on my own on this tidepooling visit - and this little one was the first I ever found by myself. This individual measured about 15 mm long, but the species can get up to 50 mm (2"). This species lives from northern California to the Vizcaino Peninsula of Baja CA; at the northern part of its range it overlaps with a similar species, Hermissenda crassicornis, the range of which extends up to Alaska - they are hard to distinguish and were formerly considered one species. This species feeds predominantly on cnidarians, including hydroids and anemones, but also feeds on tunicates; it lives from the low tide line to about 30 meters.

Sea lemon butt! The gills (branchial plumes) of a noble dorid sea lemon (Peltodoris nobilis). These are some of the larger true nudibranchs from the Pacific coast, attaining incredible sizes of about 20 cm; they eat sponges, and live from Alaska to Baja California along rocky shores from 0-230 meters. Half Moon Bay, CA.

A tiny brittle star! This was my first time ever seeing a brittle star on the west coast. I saw them as a little kid in Hawaii, and I've seen several in the Caribbean more recently, but not at 'home'. This one is the western spiny brittle star, Ophiothrix spiculata. This is a juvenile - the disk can get to 2cm across with arms up to 15 cm long (actually, shockingly large - ~1' diameter!). Like other brittle stars, this species is a detritivore inhabiting rocky shores and hard substrates from the low tide line to 2000 meters and ranging from Half Moon Bay to Peru - meaning that this was found at the very extreme limit of its range.

A rather fat and self-satisfied looking San Diego dorid (Diaulula sandiegensis). These large dorids can grow to 4" (~100mm) and feed on just a few species of sponges; while first described from San Diego, they range from British Columbia to Baja California. They live on rocky shores from 0-35 meters depth.

My first ever Hopkin's Rose nudibranch, Okenia rosacea! Also, the only one I've ever seen in person. It was very, very easy to spot.

Okenia rosacea are dorid nudibranchs that get to 3 cm in length. They feed predominantly on one species of bryozoan, Integripelta bilabiata - which also gives them their brilliant pink color! They're hard to miss, to be honest. This species inhabits rocky shorelines from 0-10 meters and lives along the Pacific coast from Oregon to Baja California.

And a closeup of the face of the Hopkin's Rose - now you can actually tell where the rhinophores (often mistaken as the eye stalks seen in terrestrial gastropods) are the deep dark frilly tentacles at the upper left.

My first tidepool shrimp! A broken back shrimp - Heptacarpus. Perhaps stout coastal shrimp, Heptacarpus brevirostris. This species lives from the Aleutians to Santa Cruz, CA, and lives from the low tide line to 128 m down, typically in rocky shore habitats. These guys are hard to spot because they're typically nocturnal - I came across this one at sunset and it was getting pretty dark.

A great portrait of a San Diego dorid, Diaulula sandiegensis. Even these guys can look pretty up close.

California cone snail! Californiconus californicus are the coldest water members of the highly venomous family Conidae. Most species are tropical in distribution, with the highest diversity in the Indo-Pacific. Whereas other species of conids have highly specialized diets, Californiconus is a generalist predator feeding on fish, mollusks, and worms. Since the California cone snail is the only conid on the cold California coast, a generalist habit is likely required. Californiconus lives from 0-30 meters on rocky shores and sandy flats, and ranges from Bahia Magdalena in Baja California Sur north to San Francisco - meaning that I photographed these little guys at basically the northern limit of their range.

 My first adult Opalescent nudibranch I found on my own! (Hermissenda opalescens). I personally think this is the most beautiful out of the three species in this genus. The thick-horned nudibranch, Hermissenda crassicornis, lives further north in northernmost California through Alaska.

This was by far my best Hermissenda encounter, so I took the most photos of this beautiful individual.

This, and the image above, are perhaps my two favorite shots from the entire trip.

Another California Cone snail.

A festive dorid nudibranch - Tritonia festiva. These nudibranchs feed on the polyps of soft corals and can get up to 10cm in length. They have a circum north Pacific distribution, living from California to Alaska and also in Japan and Korea. These inhabit rocky shores from 0-50 meters.

 A kelp crab (Pugettia productus) doing... something? to a red rock crab (Cancer productus) shed exoskeleton. Kelp crabs are supposed to be herbivorous, and shed exoskeletons don't exactly have much of anything nutritional on them. Honestly, no idea what the hell is happening here!

These colorful dorid nudibranchs are perhaps the most common totally flamboyant species - Clown nudibranchs, Triopha catalinae. These apparently get to 15 cm in length and live from the Aleutians to the Sea of Cortez in Mexico, from 0-35 meters along rocky shores and kelp beds. They feed only on bryozoans. Half Moon Bay, CA.

Portrait of the clown nudibranch's head.

And a closeup of the gills.

 My first ever live gumboot chiton, Cryptochiton stelleri - they really, really look like a rock (and feel like one too). Honestly, they're firm with a little give, like a car tire. Unlike most chitons, the little armor plates that make up the shell are completely covered in soft tissue. They're also difficult to spot. I assume the soft tissue covering lends them the name "Cryptochiton". I've found three or four of the armor plates (called "butterfly shells") since my early 20s, and I found a few dead individuals that had puckered up considerably - having never seen a live abalone, I thought it was the body after separating from the shell! I didn't know of the existence of this giant chiton until I was in my 30s. So, there's a third meaning for me personally for "Cryptochiton". This is the world's largest chiton, growing to 36cm/14" and a weight of nearly five pounds! They feed on algae, and are nocturnal (perhaps explaining the rarity of sightings for me). They are preyed upon rarely owing to their massive size, but lurid rocksnails (Paciocinebrina lurida) might consume parts of their mantle and they are consumed occasionally by ochre stars (Pisaster ochraceus), giant Pacific octopus (Enteroctopus dofleini), and sea otters (Enhydra lutris). They live from central California north to the Aleutians and west to Japan, and inhabit rocky shores from the low tide line to 18 meters. Ed Ricketts wondered why Native Californians did not eat the species, and wrote about experimenting with cooking some in Between Pacific Tides: "After one experiment the writers decided to reserve the animals for times of famine; one tough, paper-thin steak was all that could be obtained from a large Cryptochiton, and it radiated such a penetrating fishy odor that it was discarded before it reached the frying pan".

Another Orange Peel dorid.

A lovely, somewhat larger opalescent nudibranch (Hermissenda opalescens).

 Just before it got dark I saw this large yellow blog, mistaking it at first for a sea lemon - when I approached, I realized it was actually a scallop! A rare first sighting for me: a juvenile (2-3cm wide) giant rock scallop (
Crassodoma gigantea) - a rather unique species of scallop that is mobile only as a juvenile and cement themselves to rocks like an oyster. Rock scallops are thick-shelled sessile scallops (Pectinidae) that end up living much more like oysters than the typically highly mobile scallops (which can swim) - they pick a spot and settle at about 4 cm diameter (~40 days old). They can grow to 15 cm width in the intertidal zone and up to 25 cm below the low tide line; they live down to 80 meters depth. This species lives on rocky coasts from British Columbia to Baja and the subtropical west coast of Mexico. Isolated thick scallop shells found on California beaches are immediately identifiable based on a deep purple patch near the hinge joint of the shell - giving this species another nickname - the purple hinge rock scallop. In the second picture you can see the dozens of jewel-like baby blue eyes that line the edge of each shell.

A similar color scheme to the clown nudibranchs but far more extravagant - Cockerell's dorid, Limacia cockerelli. This very showy sea slug is modestly sized at 25 mm maximum length, and lives from Vancouver to San Diego. This species lives from 0-35 meters, and in the southern part of its range is seen less frequently as it is typically subtidal. It preys exclusively on a single species of bryozoan.

Another, somewhat larger clown nudibranch (Triopha catalinae).

And a headshot of the clown nudibranch.

Three-colored topsnail, Calliostoma tricolor. This species presumably feeds on diatoms, hydroids, and other microinvertebrates like other Calliostoma topsnails; this individual is at the northernmost limit of its range, as it inhabits the coast from San Francisco to northern Baja California. These are supposedly entirely subtidal (5-20 meters deep) - so a rare find near the low tide line - and there are only a handful of records of this species in tidepools in the area - making this pretty little snail one of the more unusual sightings for me. There are only 356 observations for the entire species on iNaturalist.

Another shag rug nudibranch, Aeolidia papillosa - but less fun coloration than the pink one.

Black and white dorid (Acanthodoris rhodoceras). These little dorid nudibranchs are the closest nudibranchs we have to the Indo-Pacific "sea bunnies" that pop up on social media all the time. This species lives from Cape Arago, Oregon, to the Sea of Cortez in Mexico. They are thought to feed predominantly on bryozoans and attain a maximum length of 30 mm. Little data is published on their depth, but at least 0-15 meters from what I've read online. 

 An ominous looking kelp crab, Pugettia productus. These are emblematic of tidepools and kelp forests on the Pacific coast; the carapace can get up to about 8 cm across. Despite their prickly occurrence and temperament, these are mostly herbivorous crustaceans that feed on algae, and kelp in particular! They live from Alaska to northern Mexico at depths of 0-75 meters.

A brave Hermissenda opalescens heading off into the red algae.

That's all for now! No more tidepooling until May when we drive back to the Pacific coast. Many family and friends - land lubbers, extinct, and little colorful subtidal ones - are waiting for us.

Thursday, March 7, 2024

The Oligocene dolphin Xenorophus, part 2: new specimens of Xenorophus

Welcome to Part 2 of my series on Xenorophus. To read Part 1, click here. Part 3 is on its way!

We've been in the middle of buying a new house - which is very exciting! And, also, exhausting. We're preparing for our move in 2.5 months to sunny San Diego - so things are a bit hectic, and I haven't had as much time to devote to blogging. I had intended to write this post over a month ago, but the Valenictus paper dropped - early - and I had to write that one instead!

 ChM PV 4823, what is now the Xenorophus simplicidens paratype specimen - on display at Charleston Museum.

A quick note: type specimens for beginners

You're going to see 'holotype', 'paratype', and 'referred specimen' thrown about a lot in this post. This blog is directed towards an informed audience comfortable with at least semi-technical language. In some cases, precise wording exists because it would take too damn long to describe the concept in layman's terms. I also firmly believe that most people are smart enough to not need their hand held. So, to define these terms:

Holotype: the single best specimen known at the time when a new species is named. All future identifications need to based on comparisons and observations of the holotype specimen. You can only designate type specimens once - when the species is being named.

Paratype: often the second best specimen of a new species. In many cases the paratype will be designated as it preserves some bit of anatomy better than the holotype, even though it might be a bit worse for wear.

Referred specimen: all other specimens identified as (or 'referred' to) a particular species, either in the initial study, or in all followup studies. Remember a type specimen can only be named once - if you find a much more complete skull later on, it cannot be designated a holotype since one already exists. You've got yourself a referred specimen.

New discoveries

Over the past 30 years, a number of new specimens of Xenorophus had turned up - many of these ended up in Charleston Museum collections (ChM), and several collected since the late 1990s ended up at the Mace Brown Museum of Natural History (CCNHM). All told, when I started this project, there were over ten specimens including skulls - a phenomenal sample! Jonathan Geisler made it clear from an early stage that there was likely to be more than one species. Al Sanders had considered most of the new specimens to represent a new species - which he wanted to call Xenorophus simplicidens (an unpublished manuscript name which we ultimately used in recognition and honor of his work - keep reading). The most complete specimen that Al and Jonathan examined back in the early 2000s when Jonathan was working on his dissertation research (eventually published as Geisler and Sanders, 2003) was ChM PV 4823, a nearly complete skull collected from an unusual bed of the Chandler Bridge Formation near the Edisto River. Two additional braincases from the same stratigraphic unit were also present in ChM collections - ChM PV 4266 and 4822. Two additional specimens including a mostly complete juvenile skull, ChM PV 7677, and a somewhat deformed skull with much of the vertebral column, ChM PV 5022, had been collected from the Ashley Formation. A few partial mandibles with teeth, also from the Ashley Formation, were curated at ChM.

All of the skulls of Xenorophus from the Ashley Formation in lateral view. At the beginning of this project I was unsure if any were conspecific with the Xenorophus sloanii holotype specimen (USNM 11049, upper right). We ended up concluding that these are all one species (see below). From Boessenecker and Geisler (2023).

All of the skulls of Xenorophus from the Ashley Formation in dorsal and ventral view. From Boessenecker and Geisler (2023).
The "Jaap" specimen of Xenorophus, CCNHM 168. From Boessenecker and Geisler (2023).
Three skulls of Xenorophus from the Chandler Bridge Formation - eventually considered referable to Xenorophus simplicidens, the top skull being designated as the paratype specimen. From Boessenecker and Geisler (2023).
Same three skulls of Xenorophus from the Chandler Bridge Formation, in dorsal view. From Boessenecker and Geisler (2023).

Same three skulls of Xenorophus from the Chandler Bridge Formation - ventral view. From Boessenecker and Geisler (2023).

The upper dentition of CCNHM 168, Xenorophus sloanii. From Boessenecker and Geisler (2023).

The well-preserved basicranium of CCNHM 168, Xenorophus sloanii. From Boessenecker and Geisler (2023).

The basicranium and in situ periotic bone (inner ear bone) of CCNHM 1077, Xenorophus sloanii. From Boessenecker and Geisler (2023).

Periotics (inner ear bones) of Xenorophus sloanii in dorsal (top) and ventral (bottom) views.From Boessenecker and Geisler (2023).

 Mandibles of
Xenorophus sloanii that are associated with the key skulls reported in the paper. From Boessenecker and Geisler (2023).
Some of the isolated mandibles of Xenorophus sloanii we reported.From Boessenecker and Geisler (2023).

Meanwhile, a bunch of specimens were collected in the late 1990s and 2000s that ended up in CCNHM collections. These included two nearly complete skulls: CCNHM 104, the "Bailey" specimen, and CCNHM 168, the "Jaap" specimen - the latter is a virtually complete skull, missing only the right orbit, and also preserves left and right mandibles and some postcrania. Both of these specimens were from the Ashley Formation as well. A juvenile skull, CCNHM 5995, also from the Ashley Formation, was collected just before I got to Charleston. A few months after I arrived, Mace and I went to visit Mark Havenstein - a College of Charleston alumnus - and he agreed to donate a bunch of fossil cetaceans from his collection which he had earmarked for museums. Among these was a series of blocks including a massive block of limestone with a very large posterior skull and articulated mandibles; the rostrum had been taken off by a bulldozer. We had a nearly complete postcranial skeleton for this specimen - unfortunately, missing the flippers, of course.* Preparation of this specimen took about two years in fits and starts, and unfortunately an undergraduate taking a preparation class for credit destroyed much of the postcrania by waiting until finals week to get back to working on it, and pulled out many fragments from the blocks, did not write down where they went, and then just left all of the separated fragments in a pile and left for summer vacation. Moral of the story - never assign fossil preparation projects to undergraduate students for credit. I spent a lot of time searching desperately through the postcranial fragments for potential bits of vestigial pelvic elements - never found any.

*Flipper/forelimb elements are, frustratingly, not known for a single specimen of any xenorophid.

The Aylor specimen of Xenorophus, CCNHM 8720, after we pried off all of the globbed on plaster. This rather ugly looking lump of bone ended up becoming the Xenorophus simplicidens holotype.

 Preparator Shelley Copeland removing some of the chewing gum from a tooth of the Aylor

 Teeth emerging from the siltstone.

The palate of the Aylor Xenorophus starting to take shape.

A selfie Shelley took from her apartment during lockdown! This is about the first week of April, 2020. I'm glad we managed to get it to work - fossil prep is not the easiest 'work from home' opportunity for a student.

A year or two later (fall 2018), I was alerted to the existence of an unprepared skeleton in a couple of blocks that some local amateur collectors had found and were trying to sell for an exorbitant amount of money. They even brought it by the museum, and were confused when I explained that I was a college professor and didn't have any money, and that the museum didn't have an operating budget (not a dime; "you're lucky the school doesn't charge the museum rent" was the prevailing quote from superiors at the time). I told them, honestly - local blue collar workers like them probably made more money than I did, and that I couldn't help them. We would gladly take a donation though, and set them up with an appraiser for the purposes of getting a tax writeoff. They declined. It was a shame, because it was a real beautiful specimen - they had even gotten it CT scanned at a local hospital; nearly complete skull, with at least one earbone, partial postcranial skeleton, and much of one mandible. Eventually I forgot about this interaction or at least mentally suppressed it until Sarah got a phone call about a year later - early December, 2019 - and a local attorney (David Aylor*) was wanting to donate a specimen. A brief verbal description of the fossil on speakerphone, with the two of us listening in eagerly - suggested that it was the same specimen. We politely asked for some photos of the specimen to be emailed to the museum - and a few hours later, these photos confirmed that the specimen was the very same. We set up an appointment to visit David's house on the Ashley River - a gorgeous view! David signed the deed of gift, and we loaded as much of the specimen as we could into the trunk of our Honda accord and carefully drove it back to the museum, just a couple miles away - but there are speed bumps, and of course, lots of potholes (a South Carolina staple!). When we returned to get the skull block, we were horrified to learn that David was gone, and the two young gentlemen who told us they'd be back in one hour when we returned - had also vanished. We tried calling David's phone - no response, car gone, doors locked. The specimen was in his garage space, with an open door - but it weight like 200 lbs, way too much for Sarah and I to get by ourselves. We waited for about a half hour. Fortunately, his neighbor was walking by with his golden retriever and I politely explained the pickle we were in (it was also approaching 5pm, and I had to be back in the classroom for a 6pm lab). I gave him my business card to explain I wasn't a crazy person and offered to show the deed of gift, but he said it wasn't necessary - and agreed to help lift the fossil into the car, meanwhile muttering something about those two gardeners working for him as well and not being terribly reliable, which connected some dots (sounded like it was beer-thirty). We lifted the fossil, sitting on a plywood sheet, onto an old ass radio flyer toy wagon with all flat tires, and pulled the pathetic contraption to the back of the car, taking care not to let the fossil get jostled - and managed to make the last lift into the car. Once back at the college, we drafted some students into lifting it onto a cart and placed it safe and sound in the museum - and I hurried off to teach, just in time!

*Sadly, David Aylor passed away in January 2023.

The palate and dentition of the Aylor Xenorophus, almost at completion!

In September 2020 student employees were allowed back on campus and so Shelley spent a lot of time catching up on preparation of the skull.

 We cracked open the jacket a few days later - it was a mess. No burlap, three inches of plaster just globbed on over a layer of muddy sand that had been applied like play-dough over the bone, but separated from the bone by a single layer of tin foil. The silty sand had since dried, and hardened to nearly like rock; it was Chandler Bridge Formation matrix, which is soft as hell when wet, but hardens again when dry. So the plane of weakness was at the foil layer - the silty sand rock and plaster tended to come off in big chunks. Fortunately - and I don't say this lightly - either the plaster was so damn hot, or the muddy layer that had been applied contracted significantly when it dried out - there were some large cracks in the plaster. We couldn't saw through it because the plaster was too thick, so we had to actually chisel off the plaster in places where there were no contraction cracks. When we finally got through to the fossil, about a half dozen teeth had been coated with wads of chewing gum (trident cinnamon gum by my reckoning), which had since bonded to the teeth completely. My first fossil preparator, hired through funds I raised on my own, spent several days just carefully rehydrating the disgusting chewing gum and scraping it from the tooth enamel. Shelley continued on the skull block in January when classes resumed, and had the palate and upper dentition in pretty good shape by March 2020 - and you know what happens next - the Covid-19 pandemic. Shelley was in desparate need of work, so after I returned from our poorly timed spring break vacation to Turks and Caicos* I got permission to enter the museum and assemble a 'fossil preparation from home' kit and dropped off the detached rostrum block from the same specimen along with vinac, brushes, toothbrushes, dental picks, and even plaster and burlap if she needed to make a support cradle for it.

*We went snorkeling every day, but it was kind of hard to enjoy the trip while watching the world fall apart - two days in my parents texted me photos of downtown San Francisco without a single car or person on the street in front of my dad's office).

After Shelley graduated, Sam started out as our next preparator - and we flipped the jacket in summer 2021, and got most of the dorsal side prepped out - even if a few pieces were broken when a bunch of high school students were admitted to the laboratory by someone else.

 After Sam graduated, Megan Dia volunteered a couple days a week during spring 2022 - here we are trimming off excess plaster from our temporary jacket.

And lastly, Ana Sillsbury finished preparation of the specimen before SHE graduated! Sarah and I put the specimen out on exhibit in summer 2022.

Over the next two years, I had three additional preparators work on the specimen - Sam Czwalina, Megan Dia, and Ana Sillsbury - with the finishing touches done to the delicate mandible in Fall 2022. At this stage, I had already written about half of the eventual Xenorophus monograph, and at this stage I had planned on focusing on specimens from the Ashley Formation, and a separate paper later on Chandler Bridge specimens (more on that reasoning later). The prolonged preparation time of this specimen stretched my credulity, but at some stage I realized a few things that made me comfortable with including the specimen - chief among these was my inability to get the manuscript finalized well ahead of preparation. Once I realized the specimen would be completed in another couple of months, I got to work - starting with description of the skull, and then mandible, as soon as it was prepared and curated. With the cradle made for the mandible, all of the Xenorophus material was finally ready for study - after eight years of observations and waiting.

What defines Xenorophus?

In the prior post I surveyed xenorophid diversity - it's pretty clear what defines some of the oddballs like Inermorostrum (small size, short rostrum, toothlessness) and Cotylocara (deep postnarial fossa with median ridge, loss of the intertemporal constriction) but what about Xenorophus? At the outset, the taxon was basically restricted to the holotype - which admittedly is a bit of a weird specimen. I'll talk about the weirdness of the holotype skull below and what it means for species in Xenorophus, but for now, just focus on what features these specimens share with it and what makes the genus Xenorophus.

First and foremost, while the new specimens are large - indeed, the largest known xenorophids - the X. sloanii holotype is also large in comparison to other xenorophids, though not quite as big as some of the large specimens like CCNHM 1077, 168, and ChM PV 5022. This readily distinguishes these specimens from Inermorostrum, Albertocetus, and Echovenator. These specimens have a well-developed intertemporal region with a sagittal crest, have a flat plateau of the frontal bone between the eye sockets (lacking a postnarial fossa), and large teeth set into a wide rostrum - clearly differentiating these specimens from Cotylocara and an unnamed species represented by ChM PV 2758*. One thing that sets Xenorophus apart from all other xenorophids, aside from Albertocetus - are its small, rectangular nasals. They're somewhat more elongated in others, and rather than possessing a median ridge as in Cotylocara, they frequently have a median groove or furrow. The wide rostrum is very distinctive, being proportionally wider than in all other xenos. It's also got the absolutely and proportionally largest teeth of any xenorophid. Most critically, however, it has some unusual patterns of asymmetry - I'll cover these more in the third post, but for the purpose of defining Xenorophus - it has asymmetrical palatines with the right palatine being wider than the left and extending further forward by nearly a centimeter in most specimens.

*Somewhat ironically, this specimen was initially interpreted as a referred specimen of Xenorophus by Whitmore and Sanders (1977) as it was the first xenorophid discovered in over 50 years - but later realized by Sanders that there were in fact many xenorophids, and that specimen ended up being somewhat more distantly related to Xenorophus sloanii than others (such as those discussed in this post).

How many species of Xenorophus?

Regardless of what these specimens share with the type specimen of Xenorophus, they all look a bit different from it. Recall above - I mentioned that Al Sanders initially didn't think any of these specimens represented Xenorophus sloanii. I thought that the X. sloanii holotype was pretty weird looking - what exactly made it weird? A few things. First, it's got big teeth: the teeth are absolutely (and especially proportionally) large, fairly cuspate, and rugose - perhaps more rugose than other specimens, and larger and more ornate/cuspate than many others including the Jaap specimen (CCNHM 168), Havenstein specimen (CCNHM 1077), and the Crowfield ditch specimen (ChM PV 5022). However, CCNHM 168 and ChM PV 5022 didn't have the posteriormost 'molars' preserved, perhaps tainting our observations. Next up, the X. sloanii holotype has some pretty dinky nasal bones - they're very short and nearly rectangular. Lastly, and this is the one that started to make things click for me: it's small. Still bigger than Albertocetus and Echovenator, but quite a bit smaller than any other specimen. I did not appreciate this until I saw the specimen in person in May 2016 right after my colleague Dr. Rachel Racicot's wedding (like true scientists, Morgan Churchill, Sarah, and I bundled a wedding with a research visit to the Smithsonian).

The small size of the X. sloanii holotype finally clicked when I thought about the spacing between the teeth. Are the teeth absolutely large, or just proportionally large? Why are the teeth so crowded? An then it struck me one afternoon at home during Covid: it's weird and small with proportionally large teeth because it's a baby! Well, not a baby, but a juvenile. You see, xenorophids probably only had one set of teeth - like modern odontocetes. When mammalian permanent teeth erupt, they're usually in half-grown individuals, and so look comically big. My background in fossil pinnipeds gave me additional important background: in juvenile pinnipeds, the teeth erupt and are overlapping and crowded, eventually being pulled apart in a much larger adult mandible as it grew larger and larger - and because the teeth do not change size, the gaps between them grow during growth! The same was true for Xenorophus. After I connected these dots, I decided to measure tooth size and count the cusps on them:

The teeth of the X. sloanii holotype are certainly the largest out of the sample, at least on this chart (tooth length X number of distal accessory cusps) - but not by much, only by a millimeter or so. They also overlap in terms of cusp counts with specimens like CCNHM 168. Further, the teeth of CCNHM 104 are probably actually larger: the measure nearly the same length, despite being highly worn down. So, the holotype's teeth are on the periphery of variation in Xenorophus - but fall within the range of variation. What about the nasal bones? Nasals are short in most odontocetes, but long in the largest Xenorophus specimens. I had a hunch that the nasal bones might lengthen during growth - I demonstrated a lengthening of all rostral bones including the nasals during my PhD research on eomysticetid whales, and in particular, in the species Waharoa ruwhenua. Juvenile mammals typically have shorter, stubbier, 'cuter' rostra than the adults. Sure enough, the smallest specimens like the holotype have the shortest nasal bones. The largest specimens - like CCNHM 1077, ChM PV 5022, and CCNHM 168 - have the longest nasals. Other specimens that are somewhat larger - referred to conveniently as subadults - have intermediate length nasals (CCNHM 104, ChM PV 7677). One of these in particular, ChM PV 7677, has nasals that are only slightly longer - and critically, are starting to grow this posterolateral splint that really gets long and accounts for most of the length in the old, large specimens.

Nasal growth in Xenorophus. From Boessenecker and Geisler (2023).

Xenorophid biochronology in the South Carolina. From Boessenecker and Geisler (2023).

The holotype skull block of Xenorophus simplicidens with the skull in dorsal view. CCNHM 8720. From Boessenecker and Geisler (2023).

The holotype skull block of Xenorophus simplicidens with the skull in ventral view. CCNHM 8720. From Boessenecker and Geisler (2023).

 And another view with just the skull highlighted.
From Boessenecker and Geisler (2023).

The postcanine dentition and palate of the Xenorophus simplicidens holotype, CCNHM 8720. From Boessenecker and Geisler (2023).

 The exceptionally nice mandible of
Xenorophus simplicidens, CCNHM 8720, and a view of the postcanine teeth. From Boessenecker and Geisler (2023).

The Ashley and Chandler Bridge formations are about five million years apart: the Ashley dates to 28-30 myo and the Chandler Bridge to 24.5 or so. In this context, I typically think that it's unlikely to find the same species in each unit, and that stratigraphically separated species are likely. In two cases, I've found good evidence for species longevity: Ankylorhiza tiedemani, and Albertocetus meffordorum - at least based on published material; there are more specimens out there that may, of course, lead me or others to reinterpret these hypotheses. In this context, I started looking for any evidence of 1) difference between the Ashley and Chandler Bridge samples of Xenorophus and 2) any evidence of two, rather than one, species in either rock unit. I failed to find any evidence of multiple species, and noticed a number of differences between the Chandler Bridge and Ashley Formation specimens. Specimens from the Ashley Formation tended to be larger, with longer nasals, and somewhat more complex teeth - CCNHM 8720 and ChM PV 4823 in particular have fewer accessory cusps and one less double rooted tooth position than the Ashley Formation sample, as well as less rugose enamel throughout the dentition. Al Sanders chose the name Xenorophus simplicidens largely based on ChM PV 4823 - the Edisto river specimen - though the teeth are perhaps less extremely simplified than he let on privately. Nonetheless, we duplicated most of Al's observations in CCNHM 8720 (the Aylor Xenorophus). While CCNHM 8720 had a bit of a squashed and incompletely exposed skull, it does have two things the admittedly nicer skull of ChM PV 4823 lacked: a virtually complete upper dentition, a mandible, and a nearly complete lower dentition. So, we honored Al Sanders with using the species Xenorophus simplicidens for the species from the Chandler Bridge Formation with somewhat simpler teeth. We also found that the Chandler Bridge Formation skulls are somewhat smaller and less robust than Xenorophus sloanii. We chose ChM PV 4823 as a paratype specimen, since it is a very nice virtually complete skull though it critically lacks many of the teeth preserved in CCNHM 8720, which we chose as the holotype.

All told, this sample demonstrated that 1) there are two, stratigraphically separated species of Xenorophus and that all specimens from the Ashley Formation belong to Xenorophus sloanii; 2) all specimens from the Chandler Bridge Formation belong to the new species Xenorophus simplicidens; 3) there are some interesting ontogenetic trends including the lengthening of the rostrum and nasal bones, and other changes I'll talk about in part 3!


Boessenecker, R.W., and Geisler, J.H. 2023. New skeletons of the ancient dolphin Xenorophus sloanii and Xenorophus simplicidens sp. nov. (Mammalia, Cetacea) from the Oligocene of South Carolina and the ontogeny, functional anatomy, asymmetry, pathology, and evolution of the earliest Odontoceti. Diversity 15:1154.

Geisler, J.H., and Sanders, A.E. 2003. Morphological evidence for the phylogeny of Cetacea. Journal of Mammalian Evolution 10:23–129.