Finally, quiz answers

I've been a little busy recently, applying for another grant and trying to get everything together for a spring break road trip/mini expedition to the Pacific Northwest. I'll talk about that later, though.

In any event, there were only a few attempts to answer the quiz, and no one got it, so I'll give the answers and explanations here.

1). The whale vertebral column.Its difficult to see in this size, but should be more apparent when you click on the photo. One feature of this fossil indicated the anterior direction of the column - a cross section of the zygapophyses (I can't remember if these are prezygapophyses or what; perhaps I should read up on Emily Buchholtz' work). In mysticetes (and odontocetes for that matter, but they're much different in shape) these diverge anteriorly, and occur in the posterior thoracics and lumbar series. I've included a photo of a mounted Blue whale (Balaenoptera musculus) to illustrate the point. So, in the original post anterior is to the top of the photo, and here, to the left hand side. Unfortunately, this also means that if a skull is there, it is covered by about 20 feet of rock and concrete, underneath a road.

Note: The B. musculus skeleton is shown in lateral view, and the fossil is shown in dorsal view.

2). The unidentified bone. It's a mysticete scapula. The long hooklike part is the acromion process, and the wide/thick part is the glenoid fossa. So we're looking at the distal end where the humerus articulates. Here's a complete scapula for comparison: http://farm3.static.flickr.com/2398/2342861085_66b7f89293.jpg?v=0

3). Another mystery 'thing'.
The mystery thing was, another mysticete fossil (see a common theme here?). In this case, this specimen is identifiable to the genus level, even though its still in the field. A) - reconstruction of the skull of Herpetocetus bramblei; B) - Pleasure Point specimen of Herpetocetus bramblei; C) - in-situ skull of Herpetocetus sp. (late Pliocene).

Unfortunately, this skull is in one of the hardest primary sedimentary rocks I've ever seen or hammered upon, and in a block the size of a refridgerator. There's no way this thing is coming out without access to a jackhammer and a truck. There are four labeled features that help identify it as Herpetocetus. Some of these are not unique to Herpetocetus, but do not occur in any other known contemporaneous mysticetes, so can be used for purposes of identification. 1) The cranial vertex; the vertex is pyramidal in shape, bears a distinct saggital crest on the supraoccipital, which is also very acute. 2) There is a distinct deep fossa medial of the dorsal crest of the squamosal, which is an synapomorphy of the clade Herpetocetinae. 3) The zygomatic process of the squamosal is anteriorly oriented. 4) The postorbital process is elongate and finger like, which may be a reversal to the primitive condition of mysticetes.

Anyway, these are just some things you can keep an eye out for in the field to help you identify in-situ fossils. As a rule, I generally collect everything that isn't a cetacean rib or vertebra.

Bobby

Winter Break field photos, plus another quiz

View towards Seacliff State Beach and Aptos, CA.

I've finally gotten around to posting some field photographs from winter break. I didn't get out as much as I did last winter, but that didn't stop me finding a nice (and complete, mind you) odontocete skull, a partial Herpetocetus jaw, and several fur seal (Thalassoleon cf. T. macnallyae) bones, as well as a monstrous walrus astragalus.

First are some photos which constitute a quiz, selected from winter break photos.
1). Here's an articulated baleen whale vertebral column. Which way is the head? (No guessing [e.g. that means you, Sarah]. I realize its a 50/50 chance if you guess. State a reason for your answer)

2). A fossil I didn't collect (but may jacket this summer if I get really bored, and if it is still there). What is this thing?3). What the hell is this? This specimen can be identified to the genus, FYI. Morgan and Rachel can only answer this if they get the genus correct = P

OK, now for other photos. Enjoy!A small odontocete vertebra in a shellbed. This guy did not want to be collected.A huge mysticete vertebra (to right of hammer) exposed in the bottom of a shelly channel-like structure.Another small odontocete vertebra. I did collect this specimen, and after preparation, it had a bunch of clayey fecal pellets (of probable crustacean origin) adhering to it.A large mysticete cranium, most likely a balaenopterid.A sleeping california sea lion (?) pup.
Some surfer dude.Sunset at Capitola! It was hard to leave, as the tide was just going out.

Finally - answer to the quiz

Well, its been almost a month, and I apologize (I've been busy working on a manuscript).

Anyway, J. Velez-Juarbe got it right - the mystery fossil is a centrum fragment of a very large elasmobranch. In this case, it belongs to the basking shark Cetorhinus maximus, which is a fairly common member of the fish assemblage in the Purisima Formation.













A gill raker of Cetorhinus maximus from the same locality.

The fossil itself is from a 5.8 Ma portion of the Purisima Formation, the type locality for the cetaceans Herpetocetus bramblei and Parapontoporia wilsoni. When I collected it I noticed it was composed of fairly dense bone, so before seeing some of the more subtle features, I thought it was a large bone from a teleost such as an operculum or cleithrum.





















The specimen in question.

However, you'll notice a few distinct features: one one side are some circular concentric ridges, which are the "growth lines" on the surface of elasmobranch and teleost vertebrae. Flip it over, and there are radial ridges. And on top of that, it has a very subtle curvature to it suggestive of a partial cone. I have some similar specimens of much smaller sharks (probably Carcharodon).






















Modern specimen of a Cetorhinus maximus vertebra.

As you can see from the above photograph, the vertebrae of sharks have radially oriented laminae that buttress the two conical parts of the centrum (I'm not totally honed up on elasmobranch vertebral anatomy).

Why is it Cetorhinus, however? Certainly there are other large sharks today and the Miocene as well. Naturally a good question. Other modern sharks today that approach these sizes are Rhincodon typus (whale shark), and Megachasma pelagios (Megamouth Shark). These sharks are, however, much rarer in the fossil record. For example, Megachasma is only known from a few localities in the United States (Pyramid Hill, Early Miocene, CA; Skooner Gulch, Early Miocene, CA; Lee Creek, Early Pliocene, NC - see www.ELASMO.com-->Genera--> Neogene-->Megachasma for more information). Rhincodon is possibly even rarer. Cetorhinus, Rhincodon, and Megachasma are all gigantic filter feeding sharks, a remarkable case of convergence within elasmbobranchs. Whale sharks are obviously the largest (up to 15 m if I remember correctly), and Megamouth sharks are the freaks who weren't discovered until the late 1970's, and give idiots like Steve Alten the argument that C. megalodon might still be hiding in the depths (and thus miraculously adapted to abyssal and bathyal water depths and temperatures and was no longer adapted to feed on marine mammals). For more of this bullshit on C. megalodon still existing (and C. megalodon having its guts liquified by echolocating Brygmophyseter shigensis [its an acoustic battering ram!!]), I highly suggest consulting Jurassic Fight Club.

In addition to Rhincodon and Megachasma, there is also the baddest shark ever, Carcharocles megalodon. C. megalodon certainly had vertebrae this large, and is known from the latest Miocene and early Pliocene localities all over. However, there are no credible occurrences of Carcharocles from the Pliocene of the eastern Pacific, and the youngest occurrence of Carcharocles in the Purisima Formation is in the basal unconformity (and is likely reworked from the 7-9 Ma Santa Cruz Mudstone). There are also only two teeth of C. megalodon ever collected from the Purisima Formation; the smaller of the two resides in a private collection, and I collected the larger one the day before Christmas Eve 2007 (and is happily sitting on my desk as I type this). In any event, it appears that C. megalodon was already extinct in the eastern Pacific by the time this vertebra was deposited. This is strange, as C. megalodon occurs abundantly in the Yorktown Formation on the east coast, which is Early Pliocene in age. Carcharocles may have held out in the Atlantic longer than it did in the Pacific.

On top of this, the vertebrae of C. megalodon are much antero-posteriorly thinner than those of Cetorhinus, which has vertebrae that are nearly as long as they are wide (1:1 contrasting with an approximately 1:4 length to width ratio in Carcharocles, Carcharodon, Isurus, and other Otodontidae/Lamnidae). This is directly reflected in the 'height' or 'depth' of the cone, which in Carcharodon and Carcharocles (Gottfried et al. 1996) is rather flat, and steeper shall we say in Cetorhinus (Gottfried, 1995).

References:
Gottfried, M. D. 1995. Miocene basking sharks(Lamniformes:Cetorhinidae) from the Chesapeake Group of Maryland and Virginia. Journal of Vertebrate Paleontology, 15:443-447.

Gottfried, Michael D., Compagno, Leonard J. V., and Bowman, S. Curtis. 1996. Size and skeletal anatomy of the Giant Megatooth shark Carcharodon megalodon. pp. 55-66. IN: Klimley, A. Peter, and Ainley, David G. (editors). Great White Sharks the Biology of Carcharodon carcharias Academic Press. San Diego, CA. 517 pp.

Time for a quiz

In between grant writing fury, I thought I'd take a moment to post a picture of a very odd fossil, and see if anyone could correctly identify it.

Some hints: this is from my field area, so it is marine, from central California, and approximately 6 million years old, and it belongs to a vertebrate. Also, it is very incomplete, but there are several features that distinguish it. So - now it is your job (if you so wish) to figure out what it is. And yes, '20 questions' is okay-ish.

Only one rule: folks who have already seen this can't give it away.

Good Luck!