Fossil Friday - proboscidean ulna

Over the last few weeks we've started pulling a lot of mastodon material from the collections (more on that in a future post). Some of the bones that are turning up are pretty interesting.The large bone fragment shown above is a small part of the proximal end of the right ulna, one of the bones in the forearm. It's shown above in lateral view, and below is looking at the proximal end (part of the articular surface for the elbow):This fragment is labeled at mastodon, but comparing it to the photos in Olsen (1972) it seems to be closer to a mammoth (below). We'll have to examine it more closely and see if there's any associated material to determine for sure which taxon it belongs toWhat really caught my attention were details on the edges of the articular surface and a few other places on the bone:As we're finding with many of the large bones from Diamond Valley Lake, this bone is covered with bite marks from scavengers, in the form of notches cut into the edges of the bone. These are relatively large grooves, consistent in size with something like a coyote or dire wolf, but there are lots of possibilities.

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Reference:Olsen, S. J., 1972. Osteology for the Archaeologist No 3: The American mastodon and Wooly mammoth. Papers of the Peabody Museum of Archaeology and Ethnology, Harvard University 58:1-43.

Fossil Friday - mastodon skull

Today is World Elephant Day, recognizing the conservation difficulties faced by the surviving species of elephants. Last week, with Katy Smith's visit to WSC to examine mastodons and Bernard Means' visit to 3D-scan some of our specimens,  as well as needing more data for the Mastodons of Unusual Size Project, we had the opportunity and motivation to open a lot of mastodon jackets that have remained unexamined for years. This confluence of events make an excellent excuse for featuring another mastodon for today's Fossil Friday.It turns out that, as much as I've touted the mastodon collection at WSC, it's even better than I had realized. Shown above is one of several partial skulls we examined last week. The skull is oriented ventral up, so the palate side is visible; the lower jaw is not preserved. Anterior is to the top of the image. The two large tusks are essentially complete, as is the ventral side of the premaxillary bone that supports them. A small portion of the maxilla is preserved, which includes both upper second molars and the anterior portions of the third molars, which are more clear in the image below:The proximal end of one femur is also preserved; it's the lump of bone in the foreground.The most notable thing about this skull is the black coloring over much of the surface, including almost all of the left tusk. It appears that this specimen was burned, almost certainly after death. We see this in a fair number of bones from Diamond Valley Lake, but it's the first time we've noted it in a mastodon, leading our Marketing Specialist Brittney Stoneburg to nickname this specimen "Blaze".Blaze is missing most of his third molars, but his second molars are intact and we were able to get measurements for the Mastodons of Unusual Size Project. Katy was also able to get measurements for her studies on mastodon tusks (and, based on the size of the tusks, Blaze was almost certainly a male). Blaze's second molars were heavily worn, and the anterior portions of his third molars were in wear, suggesting that he was close to the same age as Max when he died, perhaps in his mid-30s.Today on World Elephant Day, help support elephant conservation by visiting or donating to a museum, zoo, or conservation group that furthers our knowledge and protection of these amazing animals.

Taphonomy everywhere

A big part of understanding paleontology is to understand the way things work today. In interpreting fossils, paleontologists first look to the modern world for analogs, whether it's identifying a species, interpreting behavior and ecological relationships, or even understanding how a fossil came to be preserved at all – the subbranch of paleontology known as taphonomy.A few weeks ago Brett and I were visiting the San Diego Zoo's Safari Park, located in Escondido about 45 minutes from the museum. While photographing Przewalski's horses and Bactrian camels (above, both of which have Pleistocene relatives preserved at Diamond Valley Lake), Brett noticed an odd shape located on a hillside in the exhibit (inside the red circle below):Fortunately I have a camera with a pretty powerful zoom lens, so I was able to get a closeup look at the area:A skeleton! There's enough here to make an attempt at some identifications:Quite a lot of this skeleton is present, and we can say a fair amount about it. First, the presence of an antler is significant. We can tell it's an antler and not a horn from the multiple tines (at least three), and because it has a growth pedicle. That puts this in the Cervidae, the deer family. Unless it's an exotic animal from the zoo collection or some other source (unlikely) that means a mule deer, Odocoileus hemionus.The skeleton is mostly intact and articulated, and there are still a few bits and pieces of skin and fur attached in places. The neck has bent backwards, a common occurrence after death. As the carcass dries out, the nuchal ligament that runs along the back of the neck tends to shorten, pulling the head backwards over the back.There has been some disturbance to the skeleton. The head has been pulled off the body. With the attached atlas vertebra, it has been flipped upside down (relative to the body) and rotated 180 degrees so that the snout is facing the back. The lower jaw is missing entirely. The lower parts of the hind limbs are probably obscured by vegetation, but the front limbs including the shoulder blades are missing. With the skeleton sitting on a steep hillside, we wondered if some the bones had ended up downhill, and we spent a half hour or so with the camera examining the hillside, with some success. About 10-20 m down the hill we located an ulna:... a partial scapula:...and a humerus:We never did find the lower jaw.So, what's the story of this skeleton? I'm not sure why the deer was in the enclosure in the first place, but there are steep cliffs in the area; I suppose it's possible the deer could have fallen in, and maybe even been killed in the fall. There was some disturbance of the carcass after death, but probably not by really large scavengers. I assume zoo staff would have removed the carcass or left it alone entirely, so they probably aren't responsible for the disturbance. I also think it's unlikely that large carnivorans such as coyotes, black bears, and mountain lions are allowed to roam freely with the zoo's herbivores, and they likely would have torn up the skeleton more than what we see. Small carnivores are a different matter. On the same trip we saw squirrels passing back and forth through small openings in some of the fences; a feral cat could have passed through the same openings. For that matter, squirrels and other rodents will also scavenge carcasses, mostly looking for calcium in the bones. But the most likely culprits are scavenging birds such as ravens, crows, and turkey vultures. These birds are large enough to strip a carcass and even remove some pieces (like the skull and the front legs), but often leave large parts of the skeleton intact, and, of course, they have no difficulty in gaining access to the enclosure.Since this skeleton is in a zoo, it's somewhat protected from the full range of taphonomic processes it would be exposed to in the wild, such as large mammalian scavengers, but that alone isn't enough to save it. Over time, the skeleton will break down in the sun. The outer cortical bone will deteriorate and flake away, and once the interior bone is exposed the breakdown will occur even faster. Occasional rainstorms will speed this process, as will insects and rodents feeding on the bone itself. More robust fragments, such as the ends of limb bones and flakes of tooth enamel may survive a bit longer and wash down the hill. There is a small stream at the bottom of the hill, so it's conceivable (if unlikely) that a few of these more robust fragments could be buried in stream sediments. Within a few years, if anything of this deer survives, that will probably be all there is.

Fossil Friday - Stories from Bones exhibit

For Fossil Friday this week, I want to highlight Western Science Center's new exhibit "Stories from Bones", which opens tomorrow.While WSC has excellent paleontology exhibits, as with any museum with a large collection many of the specimens are not on public display. There are a variety of reasons for this. Of course, the biggest obstacle is money; cases, information panels, interactive, floor space, and other requirements for an effective display are all expensive, and even the healthiest museums operate on a shoestring budget. Besides money issues, many specimens are just not suitable for display. Perhaps they're too fragile to risk moving around too much, or too fragmentary to interpret for the public (a specimen that visually looks like a piece of junk can still produce valuable scientific data). Even with all these limitations, we strive to make as much of our collections accessible to the public as possible. "Stories from Bones" is a result of that effort.

Mammoth jaw display in "Stories from Bones".

 An important aspect of planning an effective exhibit is developing a theme. An exhibit is telling a story, and you need to be aware of what that story is as the exhibit is being designed. The theme might be "We have a bunch of stuff!", but while that was a common theme in museums a century ago (and one I personally appreciate), it does not generally make for the most informative exhibit experience for the majority of visitors.Once the theme is established, it's important to stick to it, so that the exhibit story remains coherent. Imagine reading a mystery novel in which three chapters are devoted to a history of the development of the gunpowder used in the crime, and an additional chapter describes the etymology of the last name of the victim, when neither is important to the outcome of the story. Each of these things might be individually interesting, but if you try to talk about all of them then you risk obscuring everything. There is a real risk of this "mission creep" in an exhibit based on a data-rich field such as paleontology. We might talk about evolutionary relationships, paleoenvironmental indicators, biogeographic information, site-specific descriptions, or an array of other things. Talking about any of these might be a good idea; talking about all of them is a bad idea.The permanent paleontology exhibit at WSC does this very well. The exhibit is basically a review of the Diamond Valley Lake Local Fauna; what was here, how does it compare to the rest of Southern California, and (as a secondary point) what does it tell us about the local Pleistocene paleoenvironment. In contrast, "Stories from Bones" asks "What do these fossils tell us about the lives and deaths of these individual animals?".To that end, "Stories" has a series of displays that talk about how paleontologists determine how old an animal was when it died. We have several cases that look at tooth replacement in proboscideans, horses, and bison, such as the two mammoth jaws above (they're close to the same size, but one animal was about 30 years older than the other), or the three bison dentaries shown below that represent young, middle-aged, and elderly animals.

Bison jaw display in "Stories from Bones".

 We have several examples of bones that were broken and healed, evidence of events that took place during an animal's life:

Broken and healed bones in "Stories from Bones".

 We also have several cases that describe taphonomic features, looking at what happened to an animal at or immediately after death.We designed and built a number of interactive displays for this exhibit. The most prominent is a cast and video of the CT scans of Max the Mastodon's lower jaw, taken back in August.

Max's CT-scan station in "Stories from Bones" during installation, under the watchful eye of  @MaxMastodon.

 We're proud of the fact that several of our interactive displays ask visitors to map or measure specimens and reach conclusions based on their data:A more extensive version of the bison tooth display shown here is also available as a guided activity for school groups visiting the museum, and as a kit available for purchase.If you're a regular reader of this blog, you'll find that "Stories from Bones" draws heavily from my past "Fossil Friday" posts. For most of those specimens, this is the first time they've ever been on public display, so if you're near Southern California make sure to stop by the museum. "Stories from Bones" opens on October 31, and will remain open into May 2016.

Fossil Friday - wildfires

A large wildfire, called the "Lake Fire", is currently burning in the San Bernardino National Forest. Even though the fire is about 50 km north of Hemet, smoke from the fire is clearly visible from the Western Science Center.Wildfires such as this are widespread in Southern California during the summer, driven by dry vegetation and frequent afternoon and evening winds. The regularity of these fires is evident in the fleet of Cal Fire aerial tankers based at the Hemet Airport, which are currently making regular flights to combat the Lake Fire:Anthropogenic climate change and the ongoing drought have resulted in ideal conditions for wildfires in this area, but wildfires are not a new occurrence in California. In fact, a quick records search of the Diamond Valley Lake fossil collection housed at the museum turned up at least 80 Pleistocene specimens that show evidence of burning. The DVL fossils all predate the arrival of humans in California, so these aren't animals that were cooked for food. They represent animals that were exposed to wildfire at or fairly close to the time of death.In some cases the evidence for burning is subtle, but in others there is no room for doubt:   Above are two views of the left tibia (shin bone) of the camel Camelops. Most of the bone is missing, with only the distal end preserved (there is also a box full of associated fragments). The bone is completely burned, inside and out, and has almost a charcoal-like texture on the surface. The burning extends to the broken surface, so presumably the bone was broken when it burned. It's possible that the bone had been exposed on the ground for awhile and had already started cracking up when the fire came through, but it's also possible that a relatively fresh bone cracked and broke due to the heat from the fire. Regardless, specimens like this show that, much like today, wildfires were a regular occurrence in Southern California during the Pleistocene.