Wednesday, February 8, 2012

"New" publication - Boessenecker 2011 - a new vertebrate assemblage from California

Note: This ended up being pretty long, so enjoy. I've been meaning to write a post about this since September, but given a host of other things besides the wedding, applying to graduate school, preparing fossils, doing fieldwork, writing what is now a monograph, and all that - I've been more than a tad busy. This paper - on a new vertebrate assemblage from the Purisima Formation - was published in PalArch's Journal of Vertebrate Paleontology on September 17th, 2011, the day I got married. While I was getting dressed in my suit, and trying to cool my nerves, I happened to check my email (~two hours before the wedding) and there it was, in my inbox. Anyway, thanks to Brian Beatty and his help as editor.

During my freshmen year of college, I was interested in doing some sort of a field-based research project, and after showing my advisor - Dr. Dave Varricchio, who was in his first year of being a professor at Montana State University - a bunch of fossil shark teeth I had collected and identified from Sharktooth Hill and from the Santa Margarita Sandstone in Scotts Valley, he began to encourage me to pick an area to look at. Originally, I had two ideas: the first was Sharktooth Hill; I had been in contact with Dr. Joyce Blueford, a foram paleontologist who runs the Math Science Nucleus program in Fremont, California, and she had done fieldwork at the early Pleistocene Irvington Gravels in the 1960's and 1970's, and my second idea was to reopen field work at the Irvington gravel pits. There is still a lot of unpublished material from Irvington currently housed in UCMP collections; the last study which described a wide array of its fossils was published by Donald Savage in 1951, and Chris Bell has done some more recent work on rodent teeth from the locality.

Every summer, most of the members of my family congregate on the beach at Lake Tahoe for a week for an annual family reunion; I have quite a few cousins, and it's something we all look forward to every year. This one day in late July, 2004, I received an excited phone call from my uncle Robert, who is a blacksmith (ferrier to be exact) and surfer, and some surfer friend of his had told him about a "skeleton in the cliff near Santa Cruz". By that point in my field career, I was fairly familiar with Santa Cruz, but had not been to every locality, and was not surprised I had "missed" something. I wrote down the contact number, and patiently waited another week until we were back in the bay area so I could make it out to the coast. I got my high school buddy Tim Palladino and we drove out to the coast, after calling the surfer and getting directions; it was the surfer's son who had made the discovery, and even after explaining several times that given the location he described - it was most likely an outcrop of the Purisima Formation, and therefore marine, under 6 million years old, and probably of a whale - the poor chap asked me like seven times if it could be a dinosaur. I calmly explained that dinosaurs went extinct 65 mya, and that the fossil he found - if it were even a fossil - was at most a fraction of that, and not possibly a dinosaur. To which I heard "Uh, are you sure it's not, like, a dinosaur?" - so I just thanked him politely, and drove on.

A very large baleen whale vertebra in the rock.

Upon arriving at the locality, we found precisely where he had indicated; there was a narrow and muddy trail out to a point of rock, and then a rope dangling from a rusty piece of rebar stuck in the soil, which we were supposed to use to climb up onto a ledge, from another ledge below the promontory - which was already twenty feet above the beach - and then the fossil was about ten feet down. We thought 'to hell with that', so we continued to look around; it didn't take us more than a few minutes to start finding bone, and we found quite a lot of it, and quickly. I realized that this locality had some serious promise, and better yet - was completely unstudied and nearly completely unknown with respect to its vertebrate fossils. In fact, aside from a couple of fragmentary bones in UCMP collections that had been picked up by a private collector in the 1970's - only mollusks had been collected from the locality.

A tympanic bulla of Herpetocetus sp. in a shell bed in the Purisima Formation. Quick story about this scale bar with the scratch on it - I used it for a couple years, and then it disappeared. I requested a volume of the journal "Investigations on Cetacea" which had several articles by the through Interlibrary Loan which I had previously borrowed but not had time to scan; when I received the ILL'd book again at the library, I opened it up, and lo and behold! My missing SVP scale bar fell out, after two years.

God knows that this thing is. It's 20 feet above the beach, though, and in a location where it's impossible to get a ladder down to the beach. Unfortunately, it looks like a skull.

Another mysticete vertebra poking up out of the rock.

Although my grades weren't doing very well at all during my freshmen year, and my first semester of sophomore year for that matter - I was busy trying to fight the Capitola seawall proposal, which would have covered up the only Early Pliocene bearing marine vertebrate fossil locality in Northern California (and, aside from a single layer of the San Mateo Formation near Oceanside, and part of the Pismo Formation exposed on private land near San Luis Obispo, one of only three rich early Pliocene localities in Calfiornia, period) forever. I was waging this battle over the internet, writing congressmen, state legislators and assemblymen, the Sierra Club, Surfriders, drafting all manners of letters, and finally a huge petition that garnered nearly 1,000 signatures and galvanized the anti-seawall crowd (the petition was ultimately presented at the Planning Commission and City Council meetings where the proposal was rejected by the city). While attempting this, I was busy trying to get my first permit application together. In may 2004, the Planning Commision voted down the proposal based on a faulty EIR (I wrote a critique of the EIR for its shoddy treatment of paleontological resources, although reading it now makes me shudder; my writing skills have vastly improved since then), so at least I have something to show for my freshmen year of college! Jeez, that was 9 years ago now.

In June, 2005, I was up at a remote lake in the Sierras near Emigrant Gap, volunteering as an adult leader for my old boy scout troop doing their annual 'base camp' camping trip; it was a good excuse to hang out around the campfire with my brother (still in the troop) and a couple of our friends. I had not yet heard anything about the permit, so I thought I'd take a canoe and head to the dam side of the lake, and hike way up on this one hill that gets cell service, and check my voice mail (nobody else knew there was anywhere with cell service, but I had camped there in 7th grade and I remembered the spot my friend's dad found). I had one message from Dave Varricchio, in which he shared some reservations about the permit after speaking with the permitting official on the phone; I called him from the mountainside, explained a few issues, and he agreed to convince the official I was OK for the project. Looking back, I can completely understand: it's relatively unheard of for an undergraduate student to apply and receive a collecting permit, and I would have been nervous as hell if I were in Dave's shoes then. For whatever reason, I wasn't getting along with one of the fathers on the trip, and a couple days later, once again set out by canoe to the other end of the lake nearly a mile away to make some phone calls; I decided to leave the next day (three days before the end of the trip), and my friend trim and my brother paddled out again with my backpack. It wasn't on Interstate 80 before I got a call from my parents (who I would stay with during the summers), informing me that my permit had arrived in the mail - I was thrilled - my first permit had been granted! I rushed home, and within a couple days was out at the locality showing an ecologist around to the various "big" specimens that would require some site disturbance during excavation.

I spent nearly a full week out there - driving to the site each day, of course - and met Frank Perry of the Santa Cruz Museum, who acted as my technical advisor for the project; I walked Frank through the various localities, and he instructed me to pay close attention to the mollusks. One thing I have not yet mentioned is the age of the locality - previous age determinations had widely varied. Originally, based on mollusks, the locality was considered to be latest Miocene in age. However, there was a thick ash bed in the section that was chemically fingerprinted and correlated with the Ishi Tuff member of the Tuscan Formation in Northern California. Volcanic ashes, if not datable, can be chemically compared with parent volcanic rocks formed directly from cooling of lava from the same eruption of volcanic event - most times, volcanic ashes and parent volcanic rocks are chemically unique (my guess would be due to whatever crustal rocks the volcano had to "burn through" in order to erupt), hence the term "chemical fingerprinting". In this case, the Ishi Tuff is only 2.5 Ma, in start contrast to the mollusk biostratigraphic age estimate of 6-8 Ma. My study, if ample vertebrate fossils were discovered - could test these dates independently, as neither determination involved vertebrate fossils. Vertebrate fossils, although only useful in a crude sense for biostratigraphy (with the exception of some periods of time with land mammal fossils), could probably distinguish between late Miocene and late Pliocene, however.

Fossil sharks from the Purisima Formation - Squatina (5-6), Hexanchus (1-2), Pristiophorus (3-4), Carcharodon carcharias (7-18), Carcharodon sp. (19-20), and Isurus oxyrhinchus (22-26).

Within just a few days of collecting, I had already begun to find shark teeth, which are great, because they are typically identifiable to the genus or species level if complete (which they often are). Later on in the summer of 2005, I excavated a fossil balaenopterid skull (see here, here, and here) which would end up weighing around 300 lbs in its plaster jacket; while it took only four days to excavate, it ended taking five years - until 2010 - to prepare, due to an extremely tough concretion. The specimen now bears the catalog number of UCMP 219078, and it appears to be a new species of Balaenoptera which I am currently describing.

A number of fossilized palatoquadrate (3-8) and mandibular (9-14) cartilages from the Purisima Formation of a skate, Raja sp., cf. R. binoculata, with a set of modern Raja binoculata jaws for comparison.

A number of unexpected finds were made as well. For starters, I found a ton of these weird bones I couldn't properly identify - they didn't match any marine mammal bones I had ever come across, and had these really weird articular surfaces. I took one in to Frank Perry at the SCMNH, and he said "I've seen these before, and know exactly what that is". He explained that it was a meckel's or mandibular cartilage from a skate, and that several specimens were at UCMP, and that Bruce Welton had solved that mystery in the 1970's. At my first UCMP visit in 2006, I looked at the specimens, and they were a match. After two summers of field work, I had collected over a dozen of these things (and in 2010 and 2011 when I returned with another permit to the locality, collected over a dozen more). Even better, I've now identified and collected these specimens from several other rock units in Northern California and Oregon, all of Pleistocene age (Falor Formation, Moonstone Beach Formation, and the Port Orford Formation). Eventually, I would find some of these with well preserved prismatic cartilage exposed, which confirmed the identification.

The other sharks are all represented by teeth and dermal denticles, and include great white sharks (Carcharodon carcharias), mako sharks (Isurus oxyrhinchus), basking sharks (Cetorhinus maximus), cow sharks (Hexanchus sp.), a sawshark (Pristiophorus sp.), an angel shark (Squatina sp.), a hammerhead (cf. Sphyrna), and a separate great white from the base of the section (Carcharodon sp.). The Carcharodon from the base of the section had very tiny serrations, while the Carcharodon specimens from further up in the section looked more like extant Carcharodon carcharias with coarse serrations. The modern great white evolved from the mako shark Cosmopolitodus (=Isurus) hastalis; indeed, serrationless Cosmopolitodus hastalis are known from the base of the Purisima Formation, while Carcharodon sp. teeth with minute serrations occur in the middle, and modern looking Carcharodon carcharias teeth occur near the top (late Pliocene). With the exception of serrations, the shape of Carcharodon and Cosmopolitodus hastalis teeth are identical, and this has been determined by statistical analysis of tooth shape (Nyberg et al., 2006). This is in stark contrast to the older hypothesis that modern great whites share some form of nebulous phylogenetic relationship with the "mega-toothed" sharks of the genus Carcharocles (i.e. Carcharocles megalodon, which under the older hypothesis would be regarded as Carcharodon) that has yet to really be defined properly and supported statistically or by stratigraphic studies of sequential shark tooth assemblages demonstrating gradual change from one tooth type to the modern. Instead, analysis of Carcharodon and Cosmopolitodus teeth from various well dated stratigraphic levels of sequentially younger ages from the Pisco Formation in Peru (Muizon and DeVries, 1985) first documented this gradual transition in serration development through time. This transition has now been documented in Peru, Japan, and elsewhere in California.

A few birds were also collected during the study - my first bird bone ever, a humerus of the flightless penguin-like auk Mancalla, was collected in August 2006. This turned out to be from the species Mancalla lucasi (which is sort of a replacement name for the size taxon Mancalla diegensis, which was originally named off of a femur, which is morphologically conserved in Alcidae - I'll cover Adam Smith's recent Mancalla monograph in a subsequent post). Additionally present was a previously collected humerus of a large gannet, Morus sp.; gannets do not live in the eastern North Pacific today, and there are numerous Pliocene and Pleistocene fossils of Morus, indicating a relatively recent extirpation of them locally. Also collected was a pretty dang big pedal phalanx (see 5-6, below) which I now suspect is a Pelagornis phalanx; also, that huge Pelagornis humerus (Boessenecker and Smith, 2011) was discovered at this locality as well. A couple of bony fish were present, including a tuna (Thunnus sp.) and a large flounder (Paralichthys sp.), based on vertebrae.

Fossil birds from the Purisima Formation, including Morus sp. (1-2), Mancalla lucasi (3-4), a probable pelagornithid (5-6), and an alcid tibiotarsus (7-8).

So, what did the vertebrate assemblage indicate for the age of the unit? Well, Mancalla lucasi is only known from middle and late Pliocene strata, for starters. The other bird, Morus, is known back to the middle Miocene, and of absolutely no use. Furthermore, the presence of Carcharodon with coarse serrations was also indicative of a young age. Carcharodon is restricted to the Pliocene, except in a few cases where it is from just below the Mio-Pliocene boundary or are from poorly dated rocks, or from dubious antiquated literature. This indicated that the base of the section, which already had Carcharodon that was more plesiomorphic and probably older - was already likely to be Pliocene in age. Additionally, the distinctive skate jaw cartilages have only been found in Pliocene sediments. All of this evidence pointed toward the ash date of 2.5 Ma to be correct.

As it turned out, while I was writing this, my colleague Chuck Powell at the Menlo Park USGS published a huge paper on Purisima Formation stratigraphy (Powell et al., 2007), and they recovered a diatom flora from the base of the section indicative of a latest Miocene to earliest Pliocene age (6.4-5.6 Ma), and another date from an ash below the aforementioned deposit which correlated with a 3.35 Ma volcanic unit. Altogether, the new data meshed well; in the end, the mollusk age determination turned out to be sort of right, although many of the mollusks were misidentified or too poorly preserved to be identified properly, and there aren't any mollusks actually preserved in the section that is that old (Powell, 1998). Additionally, I found the large scallop Patinopecten healyi at the locality (which had also been collected previously), which is a Pliocene index fossil.

The paper eventually took the long winded title "A new marine vertebrate assemblage from the Purisima Formation in Central California, Part 1: fossil sharks, bony fish, birds, and implications for the age of the Neogene Purisima Formation west of the San Gregorio fault." This paper took me about five years to write, and was my first manuscript I started; Chuck Powell went through I think four drafts before I decided it was good enough. I spent a bit of time during my second year of grad school revamping an older, piece of crap draft - a week of late nights in the graduate student office at MSU, literally cutting a printed copy into pieces and rearranging the better "chunks" into coherent sequences of more meaningful words, and scribbling out terrible sections with a red pen. In summer of 2010, I finally got the courage up to finish it, setting a deadline of one week - and miraculously, I finished it in 5 days. Getting rid of this manuscript and seeing its publication has been one of the more meaningful and satisfying endeavors of the past few years.

Since June, I have been furiously working on "A new marine vertebrate assemblage from the Purisima Formation in Central California, Part 2", and I am pleased to report that it is nearing completion. I have one skull left to finish preparing and to describe, about ten figures left, and some reviewing, a couple gaps to fill in, and finish peppering the manuscript with citations (and add them into endnote). As of late last night, the manuscript is now 139 double spaced pages, nearly twice the length of Part 1, and it will likely grow another 10-20 pages. There are now 30 marine vertebrate taxa from the assemblage. Publication of Part 2 will be the first time a marine vertebrate fossil assemblage from the western United States has been described and published in its entirety (with the possible exception of Sharktooth Hill, which by the time Remington Kellogg described the marine mammals, nearly the entire known assemblage had been published upon, although now only a fraction of the marine mammals are published due to a backlog of unstudied material at LACM and UCMP).

Boessenecker, R.W. 2011. A new marine vertebrate assemblage from the Purisima Formation in Central California, Part 1: fossil sharks, bony fish, birds, and implications for the age of the Neogene Purisima Formation west of the San Gregorio fault. PalArch's Journal of Vertebrate Paleontology 8(4):1-30.

Boessenecker, R.W.
and N.A. Smith. 2011. Latest Pacific basin record of a bony-toothed bird (Aves, Pelagornithidae) from the Pliocene Purisima Formation of California, U.S.A. Journal of Vertebrate Paleontology 31(3):652-657

Muizon, de, C. & T.J. DeVries. 1985. Geology and paleontology of late Cenozoic marine deposits
in the South Pacific (Sacaco area, Peru). – Geologische Rundschau 74: 547-563.

Nyberg, K.G., C.N. Ciampaglio & G.A. Wray. 2006. Tracing the ancestry of the great white shark, Carcharodon carcharias, using morphometric analyses of fossil teeth. – Journal of Vertebrate Paleontology 26: 806-814.

Powell, II, C.L. 1998. The Purisima Formation and related rocks (Upper Miocene- Pliocene), greater San Francisco Bay Area, Central California. Review of literature and USGS collection
(now housed at the Museum of Paleontology, University of California, Berkeley). – US Geological Survey Open File Report 98-594.

Powell, II, C.L., J.A. Barron, A.M. Sarna-Wojcicki, J.C. Clark, F.A. Perry, E.E. Brabb & R.J. Fleck. 2007. Age, stratigraphy, and correlation of the late Neogene Purisima Formation, central
California coast ranges. – U.S. Geological Survey Professional Paper 1740.

Smith, N.A. 2011. Taxonomic revision and phylogenetic analysis of the flightless Mancallinae
(Aves, Pan-Alcidae). – ZooKeys 91: 1-116.

1 comment:

Brian Lee Beatty said...

Nice work Bobby, it's especially nice to hear more of the backstory.