Friday, December 30, 2005

Snail biogeography

I drew the above distribution map for Columella columella alticola based on several sources (see graphic), including my own research. The open circles are Pleistocene fossils and the dark dots are modern sites where they are found. The species name indicates it's simlilarity to the European species C. alticola. So how does a snail so similar to its European cousin get across North America? Aydin at Snail's Tales discussed the distribution of another holarctic land snail. One of his suggestions for distribution on two continents was via plate tectonics. Personally, I think genetic drift would have resulted in greater phenotypic difference over the 200 million years since Europe and North America were last next door neighbors.

Columella columella alticola and snail eggs as Pleistocene fossils from the midwest.

If not tectonics, then what? Looking at the distribution, I wonder if many species of snail took advantage (if I may anthropomorphize a little) of the Bering land bridge. Given that there are several species that share this holarctic distribution (eg: Z. harpa, C. columella, P. muscorum). So, how do they do it? Birds, wind, large mammals? And how might one differentiate between distrubution via tectonics versus land bridges? DNA studies for one, but the other would be better time control on fossil distribution. A project too grand in scope for my own dissertation, but perhaps there are some paleontologists who have already started on this project?

Food for thought on the penultimate day of 2005...

Friday, December 09, 2005

Snail dispersal idea.

I have been wondering about snail dispersal - do they really get caught up with large mammals and birds? I'd be interested in doing a country-wide study next hunting season: taking a flea comb and looking for snails caught in the fur of deer taken during hunting season. Anyone else interested in looking for snails caught up in megafauna?

Sunday, December 04, 2005

A bird in the hand...

Last year my wife and I took a trip to Rocky Mountain National Park. Normally, one might go to a beautiful spot like RMNP and not take their camera out until they get within the park. But, this little campground just south of Estes Park provided me with the signature image of that trip. It's a Broad Winged Hummingbird female, waiting to get a shot at the nectar feeders set up near the camp check-in. Keep your camera handy - you never know when an image will come.

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.

Sunday, October 30, 2005

Sharp-Shinned Hawk Age Coloration

I posted this on one of the larger nature photography critique sites, I'm posting it here partially to fill up some space, but also to fill in some of the natural history information available on this blog. Anyway, here it is, republished here.

Spent some time at Hawk Ridge this morning, and they had banded a nice succession of female sharpies, from 1st year to 3rd. Sharp-Shinned hawks are accipiters, woodland hawks that are very agile and feed on songbirds (although they've been reported to attack jays and robins - birds comparable in size to the sharpie). Males are about a 3rd smaller than the females, but coloring is pretty much the same.

First Year

First year plumage is readily apparent by the feathers on the breast with a more vertical pattern of color blotches that are more of a rusty-brown color. Feathers on the crown are mostly brown with some streaks of white. The shoulders are brown, with some gray, eyes and nares are yellow. Nearly 80% of Sharpies don't make it past the first year (starvation, predation, disease, window strikes, etc take a big toll).

Second Year

Second year birds show more of the classic accipiter color patterns like the breast coloration is more horizontally oriented and more of a ruddy brown, while the crown is slate gray with a little brown. Shoulders are a slate grey, with some hints of brown still visible. Note the iris is an orange color, while the nares are still yellow. Sharpies become sexually mature after 2 years, so this female may have hatched a brood this year.

Third+ Year

In the third year, the feather pattern takes the final coloration, and it's near impossible to specify the age after year 3. Note that the shoulders are gray and the crown a darker gray, the banding on the breast is a little more red and distinct. The eye, however, is what should grab you. The red color is well-developed now. Most Sharp-shinned Hawks live for about 10 years in the wild.

Hawk Ridge offers a nice little interpretive program to visitors during the fall migration, and for a donation, one can 'adopt' the bird: they get to release the banded bird and receive updates if that bird is ever spotted at other stations. Fall raptor migration is in full swing now, and for more information plus daily species counts, go to:

There it is, unedited as such, but the photos and info are the same. Sharpies are pretty much gone from my area, but I'm already looking forward to seeing them again.

Saturday, October 29, 2005

Tales From the Crypt: It's not just dirt, part I

Some of you may drive past something like this every day. To you, it might just seem like so much dirt near the side of the road, but to me it is a great deal more. The tan material shown in the photo is part of a Pleistocene (Ice Age) river terrace. How do I know it's Pleistocene? Well, perhaps that's a subject for another post. But suffice to say that in the Driftless Area (the area of Wisconsin, Minnesota, Iowa and Illinois that were not covered by the last glacial advance) contains buried treasure.

Treasure for someone looking for fossil land snails, at least. The material, complete with the remains of critters like land snails (even beetles) fills the river valleys as it washes in from the ridges and slopes above. These older river sediments are sometimes preserved in terraces like that pictured above. If one were to take a sample of that material and wash it through a series of sieves (down to .425mm) the remaining fraction might include fossils like those shown below:

What you see are the remains of land snails picked out of that very sediment shown in the top photo. Ostensibly, these critters washed into the valley from the ridges and hills above, but to what degree and how much downstream transport played a role is part of my Ph.D. dissertation.

Specimens in the above sample include: Discus shimeki (the larger helicoid shells). D. shimeki is known only as a pleistocene fossil in this area - modern populations are found at high elevations to the west. Columella alticola, another pleistocene fossil sometimes referred to as C. columella alticola, is one of the pupillid forms along with Vertigo modesta (yet another pleistocene fossil). Columella can be told apart from Vertigo quickly by looking at the body whorl as compared to the pentultimate whorl. The pentultimate whorl on Vertigo appears wider than the body whorl. There's one more pupillid hiding in that photo that I haven't keyed out yet. There is also some type of succineid, but without soft tissue, there's no hope of getting it down to species. The little round ball at the lower right is probably a snail egg.

Given how pristine these shells are (and the large number of intact eggs) it's not likely they were transported very far. I have other samples that do seem to have traveled. Perhaps I'll show some pictures of a well-traveled shell at some point. Just remember - to a Pleistocene paleontologist, it's always more than just dirt.

Friday, October 28, 2005

How not to do science, case in point.

MIT prof fired for 'faking' research.

Reminds me of a story floating around in some grad school circles about a mineralogist who 'found' a new mineral - by completely faking data.

Thursday, October 27, 2005

It's exactly like the Mel Brooks movie except it isn't...

Another image from today:

Vertigo sp. I am pretty sure I have specimens of V. modesta modesta in my samples, but here I'm not sure. I can make out two lamellae, but the others are either covered by sand, or indistict. Anyway, I think this is my second favorite snail from my collection (after Discus). By the by, that's Abe Lincoln's nose on the left.

I suppose I could talk about where V. modesta lives now and what that says about the climate in the Pleistocene, but I'll just say that it was colder. I think that's a fair bet. Once I get my assemblage data, perhaps I can talk about things in more detail.

it's like the festiva: a big smallness...

Just a test to see if what blogger does to one of my pics. The above pictured is Discus shimeki, wich has not [yet] been described in Wisconsin. I think I have good evidence to extend its range beyone Iowa - where the nearest pleistocene records exist. I hope I'm right on the species, as this would make my project more interesting. It does have the characters of shimeki where the ribs are indistinct on the lower surfaces, about 4 whorls, and the umbilicus seems right (pic to follow later).

I do invite any malacologist who sees this entry to correct me on the ID. For your info, the hash marks on the right are mm, and the umbilicus is 1/3 or less the total diamter (of about 6mm). I would have a pic, but the camera/computer setup I was using failed me and wrote a crapped-out CD where I could only use 2 images. Oh well.

Quals, vol. 1

This semester, I passed my qualifying exam. More of a formality than any real test, but it was still a lot of work. The format in the sed/paleo department at Madison consists of eight essay questions with an hour (sans notes) to answer the question. I'm going to try and put some of those questions and my answers up here in vain hopes of getting some comments from other paleontologists.

Anyway, here's the first in what may or may not be a series:

Why do some ancient lake deposits have diverse fauna that evolved through time, whereas in other deposits of similar duration the fauna appear less diverse and relatively static?

To fully answer this question would be a complete Ph.D. in itself. However, there are many factors that could play a role in the disparity between different lacustrine faunas. In a broad sense, there is a large body of evolutionary thought that holds the more stable an environment is, the more diverse the corresponding flora and fauna will be. And conversely, the less stable the environment, the less diverse the corresponding flora and fauna.

As an example, Lake Tanganyika contains more than 300 species of Cichlid fish, while nearby lake Malawi does not support nearly that many. So why are there so many cichlid species within Lake Tanganyika? The answer lies partially within its stability. It is a large, hydrologically open lake. Tectonic processes have kept it more or less open for the past several million years. Lake Malawi appears to have been more varied in its hydrology – and perhaps water chemistry.

An analogy would be the fauna found on tidal flats versus the fauna in carbonate reefs. Organisms that are tolerant of environmental extremes often dominate the tidal flats. The dramatic fluctuations in water level on a daily basis and the seasonal fluctuations of temperature and tide strength favor organisms that are generalists. These generalists can occupy several niches, and the intense competition for scarce resources keeps overall diversity low. The highly productive carbonate reefs, however, do not experience the seasonal extremes, nor the heavy tides associated with the flats. Instead, these environments are relatively stable, allowing organisms to exploit very specific niches. This specialization can reduce competition for varying niches, allowing a greater diversity of specialists within the same ecospace as compared to the tidal flats.

Another part of the explanation lies in the organisms themselves. Some organisms appear more prone to speciation than others. For instance, there have been relatively few species of lake sturgeon, despite it being a very long-lived group. Cichlids, by comparison, haven’t been around as long, but are an extremely diverse group. There is a group of cichlid fish that do nothing but feed on the scales of other cichlids. Within this scale-eating group of cichlids, there is one species with jaws that curve off to the side so that it can better grab scales off the body of a nearby fish. There is a separate species whose jaws curve the opposite direction, which allows them to more easily grab scales off the other side.

However, this “diversity” can be misleading. What the above example describes is phenotypic diversity – different physical forms, exploiting specific resources. There is another kind of diversity that can remain hidden from the observer: genetic diversity. Another cichlid example involves a group where the male grows very large and protects a harem of smaller females. The females hide in the empty shells of gastropods. Males will try to steal females from other males by taking the snail shells (complete with female resident). Larger males will have larger harems and produce more offspring. However, there is an alternate breeding strategy employed by some males of this species. Instead of being very large, they instead are rather small, and resemble the females. These males sneak into the harems of the larger males and mate with the females, right under the proverbial nose of the bigger males – thus making more of the small males. These are the same species of fish, with presumably low genetic diversity within the group but a high phenotypic (physical) diversity within the group.

Another example comes from the Green River Formation. Goniobasis tenera exhibits a great deal of variation in the decoration on its shells. Some are very subtle, with relatively flat whorls, and little sculpture. Others have very rounded whorls and prominent bumps and ridges on its shell. These are, however, the same species – and it is very likely they are the same species because nearly all pleurocerid gastropods (the family that includes Goniobasis) show this type of phenotypic plasticity. Goniobasis dominates the gastropod fauna within the Luman Tongue (or member, if you prefer) and several beds of the Laney Member. Viviparous sp. fossils are common in the Tipton Member, and one might be tempted to interpret the Luman and Laney units as being a longer-lived and more stable lake environment. However, the actual genetic diversity may very well be higher in Viviparous sp. from the Tipton than in Goniobasis tenera from the Luman or Laney.

Another reason might have to do with taphonomy. A lake with a relatively low sedimentation rate might have a high diversity of fossils within a lithologic unit, yet the fossils within that unit might not represent the actual diversity at any given time in the history of the lake. While a lake with a high sedimentation rate might only appear to have a low diversity: the abundant organisms separated by the relatively high volume of sediment dumped into the lake. These time-averaged deposits can make a low-diversity deposit seem abundant, and an abundant environment seem almost empty.

There are also biases in preservation – some organisms might be quite abundant, but contain relatively few hard parts to be fossilized. Shelled organisms dominate the described faunal character of the Cambrian, but how much of that is a bias in preservation. There is also a bias in perception (which partly plays into the genotypic versus phenotypic argument): much of paleontology seems vertebro-centric. Vertebrate fauna can appear at first glance to be more diverse than invertebrate ones, but most often the reverse is the case.

While it is likely that stable environments do often contain a more diverse fauna than unstable ones (even though the environments may account for a similar length of time), the actual diversity needs to be carefully considered. How much of the diversity is a bias, whether in preservation or the observer, and how much of that diversity is actual? For long-lived lakes, we can study modern diversity both on the phenotypic and genetic levels. For fossil lakes, such as Lake Gosiute, we are often left with searching for modern analogs and cannot separate the sedimentology from the paleontology. Only the combination of the two may provide a complete answer.

Wednesday, October 26, 2005

Once more into the breach dear friends.

This is my PhD. There are many like it, but this one is mine. My PhD is my best friend. It is my life. I must master it as I must master my life. Without me, my PhD is useless. With out my PhD, I am useless.

And so it goes...