Killer Walrus From Sth Not So Fierce After All

[RichW9090]

One of our esteemed members has just had an article published on Wednesday:

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A "killer walrus" thought to have terrorized the North Pacific 15 million years ago may not have been such a savvy slayer after all, researchers say.

A new analysis of fossil evidence of the prehistoric beast shows it was more of a fish-eater than an apex predator with a bone-crushing bite.

Traces of the middle Miocene walrus, named Pelagiarctos thomasi, were first found in the 1980s in the Sharktooth Hill bone bed of California. A chunk of a robust jawbone and sharp pointed teeth, which resembled those of the bone-cracking hyena, led researchers to believe the walrus ripped apart birds and other marine mammals in addition to the fish that modern walruses eat today.

But a more complete lower jaw and teeth from the long-gone species were recently discovered in the Topanga Canyon Formation near Los Angeles. Researchers say the shape of the teeth from this new specimen suggest the walrus was unlikely adapted to regularly feed on large prey. Instead, they think it was a generalist predator, feasting on fish, invertebrates and the occasional warm-blooded snack.

"When we examined the new specimen and the original fossils, we found that the teeth really weren't that sharp at all — in fact, the teeth looked like scaled-up versions of the teeth of a much smaller sea lion," researcher Robert Boessenecker, a geology doctoral student at the University of Otago in New Zealand, told the PLOS ONE Community Blog.

Using a model to estimate body size based on the size of the jaw, Boessenecker and Morgan Churchill of the University of Wyoming found that Pelagiarctos was quite large — about 770 pounds (350 kilograms), or similar in size to some modern male sea lions. But they noted that a big body alone likely wouldn't indicate that the species was a dominant predator. That's because both large and small modern species in the pinniped family — which includes seals, sea lions and walruses — are dietary generalists that tend to eat mostly fish.

Boessenecker added that the new findings give a clearer picture of the modern walrus' evolutionary past.

"Right now, there is only one modern walrus species but back then, walruses were a very diverse group," the researcher told the PLOS blog. "Many of these other extinct walruses had strange adaptations — such as the development of upper and lower tusks, gigantic body size, ultradense bones, unusually short forelimbs, and even the loss of all teeth aside from tusks. The myriad types of extinct walruses — Pelagiarctos included — beautifully demonstrate the often convoluted path that evolution can take."

The study was published online Wednesday (Jan. 16) in the journal PLOS ONE. Funding came from the University of Otago, the Geological Society of America, The Palaeontological Society, and the National Science Foundation.

*********************************** http://www.livescien...rus-fossil.html

Congratulations!

Edited January 18, 2013 by RichW9090

[Auspex]

This does deserve a broad celebration on the boards!

The article was posted in the Fossil News forum: LINK , but a mention here in General Discussion will get more air play

EDIT: Here's the correct link: BOBBY'S PAPER

I am terribly sorry to have caused this confusion!

[FossilDAWG]

I don't think that link refers to the same fossil. The paper is here, and the discussion here.

And here is a link to Bobby's CV at the University of Otago, for those who want to know a bit more about his work. I must say that he is a most amazingly productive researcher. Anyone who complains about paleontologists who sit on finds for decades before publishing (if they ever do) will find an excellent antidote in Bobby, who has already published 9 peer-reviewed papers and has just recently started his PhD. I need to catch some of whatever he's got!

Don

[jpc]

They are the same fossil. Bobby was focusing on fossil whales while he was still an undergrad.... cool. The interesting question, though, is why of all the paleo papers that are published, did this one get picked up by so many press outlets? Not complaining, mind you, but just curious. On the other hand it is nice to see the press get excited by something that is non-dinosaur. Go walruses.

Edit... I used the links FossilDAWG's post to find the same fossil.

Edited January 18, 2013 by jpc

[FossilDAWG]

I'm confused. I believe Bobby's paper is this one:

Boessenecker RW, Churchill M (2013) A Reevaluation of the Morphology, Paleoecology, and Phylogenetic Relationships of the Enigmatic Walrus Pelagiarctos. PLoS ONE 8(1): e54311. doi:10.1371/journal.pone.0054311

The link in Auspex's post brings me to a post by Paul (Oxytropidoceas) with links to news articles concerning this paper:

Benoit J, Adnet S, El Mabrouk E, Khayati H, Ben Haj Ali M, et al. (2013) Cranial Remain from Tunisia Provides New Clues for the Origin and Evolution of Sirenia (Mammalia, Afrotheria) in Africa. PLoS ONE 8(1): e54307. doi:10.1371/journal.pone.0054307

How can a fossil walrus jaw from Orange County be the same fossil as a cranial element from Tunisia?

Or does Auspex's link take you to a different post than the one it takes me to?

Don

[AgrilusHunter]

Hi Don,

I had the same result. Bobby's article was recently posted on elsewhere in the Forum ... somewhere. I'm guessing the link above just points to the wrong article.

Bobby,

The more I read your work the more impressed I am. Keep up the great research!

Edited January 18, 2013 by AgrilusHunter

[Auspex]

...I'm guessing the link above just points to the wrong article...

Oops...I'll have to rectify this

Here's the correct link: LINK

[Boesse]

Hey guys, thanks a bunch for the compliments (whether deserved or not)! I'm pretty surprised by how much press attention it's gotten. When I started this project I thought it would be one of my better chances at it - but I'm still pretty surprised by it. And fairly pleased, as well. I totally agree with JP - it is refreshing that the press is interested in something non-dinosaur for once. Although to be honest, maybe it's just that mammalian paleontologists don't bother trying to popularize our research as much as dinosaur paleontologists. With some of the attention that fossil whales, dolphins, sea cows, and pinnipeds can get, it's something myself and other marine mammal paleontologists should try to change.

And I've only gotten 6 papers published (but I have four more in review at the moment). Anyway, let me know if you guys have any questions about the research. Bobby

[jpc]

Hey Bobby-

We are doing a members Only Peep Show at the Tate next week. One of the draws I am using is "Come see the Tate's very own specimen of the killer (or not) walrus".

[siteseer]

Hey Bobby,

Great article. I've been interested in this animal since I first heard about it sometime in the early 90's. I had heard someone found a skull in the Topanga but it appears the jaw sections are the facts behind the rumor.

The Barnes description stressed the reason for its extreme rarity is that it was an apex predator and your paper points out that some modern pinnipeds do not hang around in any particular area and Pelagiarctos might have been one of those or perhaps it was an animal preferring a climate not prevailing where it has been found. I think it is also possible that Pelagiarctos may not have frequented bays/inland seas and lived primarily off the coast perhaps basing from offshore islands like the Steller's sea lion does today (I read that in an old copy of "Marine Mammals of California").

I have noticed that a couple of shark genera, Alopias and Parotodus, are also extremely rare in the STH Bonebed. Today, Alopias is represented off the California coast by two species that range from coastal to open water, but one species is rarely seen near shore. Parotodus, an extinct lamniform, has been considered a pelagic shark due to its extreme rarity in nearly all of its known localities.

In the STH bonebed a megalodon tooth is considered rare. If you collected 5-6 days out of a week, you might find one meg tooth specimen per calendar month, a specimen defined as at least 51% of a crown and tooth. If you collected the same 5-6 days per week for a year, you might find 1-2 Parotodus in that year. I don't have a number for one Pelagiarctos tooth collected per unit of time, my numbers being shark-focused and unscientific anyway - just scattered notes on what I saw or heard about being found in Bob Ernst's quarries during the last fourteen years of his life). However, I would say that a Pelagiarctos tooth is at least 3 times rarer than a Parotodus and maybe as much as 6 times rarer.

Jess

Hey guys, thanks a bunch for the compliments (whether deserved or not)! I'm pretty surprised by how much press attention it's gotten. When I started this project I thought it would be one of my better chances at it - but I'm still pretty surprised by it. And fairly pleased, as well. I totally agree with JP - it is refreshing that the press is interested in something non-dinosaur for once. Although to be honest, maybe it's just that mammalian paleontologists don't bother trying to popularize our research as much as dinosaur paleontologists. With some of the attention that fossil whales, dolphins, sea cows, and pinnipeds can get, it's something myself and other marine mammal paleontologists should try to change.

And I've only gotten 6 papers published (but I have four more in review at the moment). Anyway, let me know if you guys have any questions about the research. Bobby

[Boesse]

Yes, I've heard rumors of a skull as well, but I don't think there's any substance to them; rumors including that the new specimen was from the Topanga means that it's probably based on our specimen. Then again, I don't know what's in the belly of LACM collections.

In the paper we intentionally didn't say geographically where Pelagiarctos could have lived - just that it probably lived someplace else with occasional vagrants coming in to southern California waters. Meaning, it could have lived further north, further south, or further west (pelagic). There's no way to tell unless someone does some oxygen isotope sampling (which we didn't do, so it wasn't worth speculating). Regarding offshore rookeries of Steller's sea lion, this is probably a post-sealing "artifact" as there used to be many continental rookeries, and now the only one left is Sea Lion Caves. I can't remember what the zooarchaeological record tells us about Eumetopias, but a better example of an offshore pinniped would be Callorhinus ursinus or Arctocephalus townsendi.

The first Pelagiarctos tooth was collected in 1973, with 5 teeth and the "chin" published in 1988, and post 1988, three more have been collected and put within museum collections; I've seen photos of maybe a dozen more teeth in private collections (BVMNH included). So, that's roughly twenty teeth over a forty year period (1 specimen every two years).

[jpc]

one specimen every two years... dang I was lucky.

[siteseer]

Bobby,

With the teeth so rare would a researcher damage one of them to get an oxygen isotope sample or is there some unwritten rule about waiting for some minimum number of specimens before choosing one less useful (damaged) for other studies but still referrable to the genus? I saw a documentary in which a researcher chipped a piece off of a perhaps equally-rare, essentially complete C. megalodon vertebra for some study. I thought he should have done that to a more beat-up one.

With the history of Pelagiarctos specimen collecting starting in 1973 but with STH collecting going back another 100 years, it makes me wonder how many teeth were collected in that time and considered just another weird "seal" or dolphin tooth.

Jess

There's no way to tell unless someone does some oxygen isotope sampling (which we didn't do, so it wasn't worth speculating). Regarding offshore rookeries of Steller's sea lion, this is probably a post-sealing "artifact" as there used to be many continental rookeries, and now the only one left is Sea Lion Caves. I can't remember what the zooarchaeological record tells us about Eumetopias, but a better example of an offshore pinniped would be Callorhinus ursinus or Arctocephalus townsendi.

The first Pelagiarctos tooth was collected in 1973, with 5 teeth and the "chin" published in 1988, and post 1988, three more have been collected and put within museum collections; I've seen photos of maybe a dozen more teeth in private collections (BVMNH included). So, that's roughly twenty teeth over a forty year period (1 specimen every two years).

[Boesse]

It's certainly possible that more specimens were collected prior to 1973 - but if they were, they weren't in LACM or UCMP collections, as Larry Barnes scoured those pretty thoroughly.

I'm sure that one of the specimens could be easily sampled for oxygen isotopes - fortunately with Pelagiarctos, we have multiple teeth. Some species known only from the holotype have been sampled for isotopes. I wouldn't have any qualms about somebody sampling our specimen, or even the holotype.