Tuesday, November 29, 2005

An obscure movie meme.

From Tony over at milkriverblog. Like Aydin at Snail's Tales, I have several obscure favorites. I'll just have list a few that are nowhere to be found on the IMDB top 250 (there's an extensive list of good obscure films tucked in between the obvious ones).

El Mariachi: Robert Rodriguez's debut. Filmed at a cost of about $9,000 where each scene was shot entirely with one take, this is a treat to watch. Unfettered by too much money, this is what a good action movie should be. A guitar-carrying mariachi singer tries to look for work in a small Mexican border town, while an identically dressed assassin (complete with identical guitar case) breezes into the same town. The mariachi and hit man unwittingly exchange guitar cases and hilarity ensues. Please watch this in the original spanish with english subtitles. Much better.

Rosencrantz and Guildenstern are dead: Tom Stoppard's heady, existentialist play turned into a movie. Watching the film after reading the play script, I was able to catch most of the subtle intellectual humor involved, but this movie still provides something new each viewing. Tim Roth and Gary Oldman are well paired as the two Shakespearian bit players, while Richard Dreyfus as "The Player" deftly spins the "life-as-art/art-as-life" motif.

The Snapper: Someone else already mentioned The Commitments, so I'll plug Roddy Doyle's second book/movie in the Barrytown Trilogy. It's funny, but not at the expense of the intelligence of the viewer, or dignity of the character. I haven't actually seen number three "The Van," yet, but it should probably go in with the other two as well.

Ghost Dog: The Way of the Samurai: Forest Whitaker as a mafia hit man (notice a theme in my meme?) who follows the Samurai code. The usual tale of betrayal and revenge are there, but the Haitian ice cream truck driver and the girl with whom he discusses literature make this more of a study of human nature than most action movies.

Himalaya - l'enfance d'un chef Beautiful cinematography, a classic story retold via the Tibetan salt caravan. Go read the outline on IMDB if you want. A beautiful movie - and having read the "Snow Leopard" by Peter Matthiesson gave me a better understanding of the Dolpo region.

Yin shi nan nu (Eat Drink Man Woman): Another good film. A master chef living in Taipei with his daughters, life happens and is filmed beautifully.

Well, that's a bunch more movies than I intended. I'm going to stop now before I waste all my time with this meme.

Monday, November 28, 2005

Pleistocene snails: Vallonia gracilicosta

I have tentatively identified this little charmer as Vallonia gracilicosta. A rather small snail, it is common to the Rocky Mountain regions, however, a few scattered populations exist east of the Mississippi (see map below). Scale ticks in photos are in mm.

Map of the distribution of fossil (tan) and living (blue) V. gracilicosta. The range for this species shifted from the Midwest to the Rockies after the retreat of the Laurentide Ice sheet 10,000 years ago. It is also possible that previous to the Pleistocene, V. gracilicosta inhabited the Rocky Mountain region, invading the midwest during the last glacial maximum. Map is from the US Census website, while biogeographic data comes from: Pilsbry, 1939; Nekola et al., 1999; Nekola, 2002; Frest and Dickson, 1986; Hubrict, 1985; Baker et al., 1986.

BAKER, R.G.; Rhodes, R.S., II; Schwert, D.P.; Ashworth, A.C.; Frest, T.J.; Hallberg, G.R.; Janssesns, J.A.; 1986, A full-glacial biota from southeastern Iowa, USA, Journal of Quaternary Science, Vol. 1(2), pp. 91-107.
FREST, T.J. and Dickson, J.R., 1986, Land snails (Pliestocene-Recent) of the Loess Hills: A preliminary survey, Proc. Iowa Acad. Sci. 93(3), pp. 130-157.
HUBRICHT, L. 1985, The distributions of the Native Land Mollusks of the Eastern united States. Fieldiana Zool., n.s. 24, vii+191pp.
NEKOLA, J.C., M. Barthel, P. Massart, and E. North. 1999. Terrestrial gastropod inventory of igneous outcrops in Northeastern Minnesota. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. 60 pp.
NEKOLA, J.C. 2002. Distribution and Ecology of Terrestrial Gastropods in Northwestern Minneosta. Final Report: 2001-2002 Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. 171+pp.

Tuesday, November 22, 2005

I and the Goose #1

The Canada Goose - what an interesting bird. Seen as a pest by many golf course groundskeepers, we have learned much about bird migration from these large fowl. I have also found them to be striking photographic subjects. Many an early fall or winter morning I would crawl a dozen meters or so through goose poop to catch them looking interesting in decent light. Two of my favorites:

Goose in flight.

A very cold (-13°F) January morning and they still would prefer to paddle around on what open water there was.

From the flight photo it should be obvious that geese are powerful fliers. They aren't the fastest, or the most efficient - on their own, anyway. When they flock together in large "V's," they reduce overall drag and expend less energy as a group. But if you've ever been close to a group of them taking off, the sound is amazing. The wings beat so forcefully that the buzz of air past the primary feathers sounds just like a jet engine. Not the highly maneuverable aerobatic stunt plane (anyone who's seen a flock of geese try to land together on a small pond can tell you that), or the high altitude sailplane, but the long-range cargo transport of the avian world.

Wednesday, November 09, 2005

I and the Bird #10

While I tend to focus on items of the molluscan kind, I do fancy myself as a general naturalist and have a particular vertebrate fancy for birds (and all dinosaurs).

I've got an entry for I and the Bird #10 about Sharpie coloration over at Thomasburg Walks. I'll probably have to put something together for #11.

In other news, I've got more samples, including several specimens of Strobilops that I have to identify yet. I'm down at my school of learning to meet with my advisor and some other folks to try and set up another hoop in the process of my PhD (well perhaps "planning the way in which I will get through said hoop" is a better way to put it.

Andy Knoll is giving a talk tomorrow at UW Madison. I'm going to see it. Had I been planning ahead, I would have gotten in town earlier. But that's just the way things are, I guess.

Monday, November 07, 2005

The identification of a snail

Here is a snail whos ID I have been working hard at confirming. The two likliest candidates are Discus shimeki, or Discus whitneyi. I am leaning towards D. shimeki, but there are just enough characters that aren't conclusive to keep things interesting. First, here are some photos (The top photo is a different individual, but from the same geographic location and deposit).

Here is a list of the characters listed for D. whitneyi, taken from the BC Museum's "Living Landscapes" website.

Shell small (width, 6.7 mm), depressed-heliciform; subtranslucent brown or occasionally pale coloured; spire low; whorls 4.5, convex or a little angular (especially in juveniles); suture deep; protoconch without riblets; teleoconch with nearly equally spaced axial riblets, extending onto the base, and fine axial striae; aperture rounded and without denticles; outer lip unthickened; umbilicus rather large, about 33-40% of the width of the shell.

And here is the same for D. shimeki:

Shell small (width to 6.5 mm), more or less depressed-heliciform, subtranslucent, yellowish brown; spire moderately elevated or flattened; whorls 4.5, convex; periphery rounded; protoconch smooth; teleoconch with regular, strong axial riblets with fine axial striae between; riblets rarely extending onto the base and becoming lower and irregular on the last whorl; aperture typically rounded, or more ovate in the flattened form of the species; aperture without denticles; outer lip unthickened; umbilicus rather large, about 30% of the width of the shell.

So what do I have? My snails are about the right size for either, although some of them are a wee-bit larger. Most of them are mostly rounded, some do have a sub-angular periphery. I haven't seen any axial striae between the riblets, but the riblets generally are indistinct along the base - especially on the largest specimens. The biggest reason I'm calling it D. shimeki is because of the umbilicus. The umbilicus is about 33% or less of the total diameter on all specimens. I will have to get my measuring ocular out and confirm this statistically, I bet. Lucky for me I'll be heading back to Madison and the library this week.

Friday, November 04, 2005

Some more ice age land snails

I was looking at this photo and I noticed I have what seem to be two succineids in this sample. Compare the one on the upper right to the one in the lower middle. There is a distinct difference here that I hope isn't just ontogenetic.

From top to bottom: an egg, Columella alticola, Pupilla muscorum, Vetigo cf. modesta, a succineid (Catinella sp.?), and Discus cf. shimeki

Discus cf. shimeki and one round snail egg.

Thursday, November 03, 2005

Some Ice Age Land Snails

Okay, if anyone is looking at this blog, it's likely they've glazed over once they saw my long qualifier answers. That's to be expected, so to make up here's a post with few words and lots of images. Below each is my tentative ID. If anyone has corrections, please let me know.

Glyphalinia indentata?

Heliodiscus parallelus?

Succinea sp.?

Discus shimeki?

Wednesday, November 02, 2005

Quals, vol. 2

Another lengthy post from my qualifiers. In hopes of getting this stuff up for feedback is part of it (but first I need visitors I guess). After answering this question, my committee member (Richard Slaughter at the UW Geology Museum) mentioned something that I had overlooked. The most important information fossil snails provides is information about snails, and that I should not be ashamed of looking at snails for snail's sake. That's true, just try getting grant money to do that. It seems that to do "research," one has to be looking at something grand, and big picture. And too often I think they enter into a project with that mindset - whereas most of my interesting "big picture" revelations have come after first just learning about a thing for the sake of knowing.

I apologize for errors in grammar, spelling and such - this was essentially an extemporaneous writing exercise.

Question 6:
What are the major problems and limitations involved with using late Quaternary terrestrial gastropods as environmental proxies? Conversely, how are terrestrial gastropods assemblages superior to vertebrate and pollen records with respect to reconstructing late Quaternary environments?

Gastropods can make excellent paleoenvironmental indicators, but there are several overlying problems that need to be either addressed, or at least acknowledged in order to accurately interpret any environmental signal contained in gastropod deposits.

Taphonomy is a very real problem. It affects nearly every other aspect of terrestrial gastropod paleontology as well. The processes that occur to a shell deposit can erase any real effect of environment and introduce false ones. Preferential preservation can remove the trace of some species of gastropods, leaving others behind. One could misinterpret the abundance of the surviving shells as the ones that were most abundant, but in actuality, another species with a shell more susceptible to destruction may have been more abundant. This is a problem with some terrestrial gastropods as their shells are usually thinner than their lacustrine or marine relatives and some species of terrestrial gastropod produce shells that contain almost no calcium carbonate. In some cases, this may be a problem that we never know about – since it is often impossible to ‘know’ for sure that all the species living in a particular environment are present in a fossil assemblage. In fact a safe assumption is that there will always be species not represented in the fossil record. However, it is probably safe to assume that the fossil assemblage bears more than just a superficial similarity to the actual diversity.

A concentrated deposit of gastropod shells may reflect an actual abundance at one particular time, or they may be winnowed from more dilute deposits, producing a time-averaged concentration of shells. This would have the effect of making a particular species appear more abundant that it might have been, and an overall assemblage seem more diverse than it was. A common problem with reconstructing past environments is to depict a little bit of everything from a site living contemporaneously with each other. African mammals are often depicted as roaming the landscape in densely populated, diverse herds. However, any trip to the African savannah shows that the actual density is far less – one can travel for miles without seeing much of wildlife, a far cry from the wildebeast and rhino behind every corner that is often conjured up by descriptions of the region.

Alluvial terraces often contain terrestrial gastropod fossils, not necessarily because the gastropods were living near the stream, but they were washed down off of the high valley ridges and into a more mixed deposit. A high rate of deposition could make what is a diverse assembage of gastropods look sparse because there will be a greater volume of sediment included with the sample.

While most gastropods die from dehydration or starvation, predation can affect the relative diversity of a gastropod deposit. Is the deposit a shell midden, where the shrew, or bird deposited its preferred prey species? Or, is this deposit missing an important species of gastropod because they were more likely to be preyed upon? Larger gastropods especially seem to bear the signs of predation, but at the same time their shells are more likely to survive after the soft organism itself is eaten. It is easier to just eat the entire snail, shell and all for small gastropods, while larger snails can be fished out of their shell without destroying the whole shell.

Often, gastropods are used as environmental proxies because of the foods they eat. However, it is more likely gastropods are temperature and precipitation dependent, and will find foodstuffs in that preferred climatic range, rather than foodstuffs in a different climatic setting.

A demonstrated problem for aquatic gastropods is ecophenotypy. Some species of gastropods exhibit different shell structure dependent upon the substrate or water energy present. There is some evidence to indicate that some species of terrestrial gastropod are also ecophenotypic – if demonstrated, ecophenotypy can be extremely useful for interpreting a snail fossil’s environment. However, it can also lead to false interpretations such as overestimated diversity.

Stable isotopes are often used as climate proxies. Variations in the ∂13C values of carbonates in shells has been used to determine shifts in C3 versus C4 grasses and therefore shifts in precipitation. However, there are kinetic fractionation effects from the shell material and any environmental stable isotope signal can be overwritten by the physiology of the snail.

So, with all the problems associated with gastropod fossils, why study them at all? One of the strengths of gastropods is they are very sensitive to changes in their environment. Unlike a tree, which will remain in an area and produce pollen long after the conditions are no longer ideal for it, snails have a very limited residence time. And, unlike vertebrates, which migrate easily, snails can’t run away from unfavorable environmental conditions. Gastropods do have the ability to survive short-term fluctuations in the environment – some species can remain dormant for several years, thus outlasting long droughts. Large-scale changes in regional climate, however, will affect the distribution and makeup of gastropod assemblages.

Gastropods can be found in tremendous numbers. While the total number of mammoth skeletons in North America is quite small, a single liter of sediment can contain hundreds of thousands of gastropod shells. The sheer volume provides a more statistically significant population size from which to base environmental interpretations.

Processing material for quaternary fossils requires a varying degree of field effort and lab work. Charismatic megafauna take considerable time and effort to excavate. Microvertebrate skeletons, while easier to collect, disassociate into a tedious piles of skeletal elements that must be sorted and identified in order to measure abundance. Pollen work involves long lab preparation with hazardous chemicals and many hours under high-powered microscopes. Pollen can rarely be identified beyond genus, and some can’t be identified beyond the family level.

Gastropod deposits are often easily collected in bags or buckets of unlithified sediment that is easily dried and washed through a series of screens. A simple, low-powered binocular microscope and a sable brush are all that is really needed for identification and sorting. Most gastropods are identifiable to species-level based solely on the shell.
Most Pleistocene gastropod species are extant today, and it is reasonable to assume that the modern climatic preferences of gastropods were similar to those of their Pleistocene relatives. Mapping the biogeography of terrestiral gastropods has the potential to produce a higher-resolution climatic interpretation of the environment.

Terrestrial gastropod biogeography can also show paths of recolonization – directions from which populations expanded their range. This has important implications for population and conservation genetics especially as it relates to extremely rare species, such as Discus macclintocki. They also provide an interesting study in evolutionary biology, as D. macclintocki is an extremely isolated species while a close relative, D. chronkheitei is widely distributed, even occurring west of the Rocky Mountains. Steven J. Gould used the tropical genus Partula to study the mechanisms of speciation. It is not inconceivable that the changes in distribution among species of Discus can provide information on the diversity of North American gastropods.

Finally, terrestrial gastropods are the single most threatened group of land animals. Understanding how changes in ancient climate affected gastropods, can help us anticipate future their future changes. They also have the potential to quantify the extent to which the present day climate is changing by providing a comparison to the variability of the early and mid-holocene.

Tuesday, November 01, 2005

It's a circus alright

Ayden over at Snail's Tales has put together a little smorgasboard of invertebrate writing (writing about, not by), at the The Circus of the Spineless, 2nd ed.