Mala-whaaa? Discover the incredible world of mollusks in the Strake Hall of Malacology

One of the most awesome parts of working for a Museum (especially one as large as ours) is how many people you get to meet and work with – all with something different that gets them excited about science! It’s easy to celebrate your inner geek when you can find fellow geeks who you can geek out with in a geeky fashion while geekily reveling in unique parts of the Museum.

You could ask anyone here and they’d be able to tell you which part of the Museum brings this out in me: the Strake Hall of Malacology.

“Mala-whaaaa?” you may ask.

Malacology is the study of mollusks, an incredible group of creatures that includes octopi, scallops, and my favorite, snails (but more on them later). They’re invertebrates belonging to the phylum Mollusca, and there are over 85,000 species of them in the world!

These invertebrates all have three features in common but are otherwise extremely diverse. They have a mantle containing a cavity used for breathing and excretion; a radula, which is used for feeding; and the same structure to their nervous systems, with two pairs of nerve chords: one serving the internal organs and another for locomotion.

Mollusks are also able to use their internal organs for multiple purposes. For example, their heart and kidneys are used in their reproductive, circulatory, and excretion systems.

Mollusks are more varied than any other phylum. Think about it: squids, octopi, cuttlefish, nautili, clams, mussels, oysters, conch, slugs, snails — they all have many diverse species and yet they’re all still mollusks! And this is due, in part at least, to how long they’ve been around. While there’s still significant scientific debate about their precise lineages, we know that they’ve been around since the Cambrian period (541 to 485 million years ago). This has allowed them to diversify to fit in many, many niches all around the world — from the depths of the ocean to mountain tops.

Now for my favorite: SNAILS! Perhaps it’s because of my name (Gary, like Spongebob’s pet snail) but I think snails are really cool. They account for 80% of mollusks, and are perhaps the most diverse of them all. They’re found everywhere, in part because some have evolved to have gills while others have lungs.

But that’s not all! Some species with gills can be found on land, others with lungs are found in freshwater — with a select few even found in marine environments! They’re in ditches, deserts, large bodies of water and everywhere in between. Most are herbivores, but there are also omnivores and predatory snails. They’re also found in many sizes, from giant African land snails 35 cm in length to some just 1.5 mm long.

So come to HMNS to the Strake Hall of Malacology to learn everything there is about these marvelous mollusks!

The Formation and Preservation of the Solnhofen Fossils

Our new Archaeopteryx exhibition has stunning complete fossils of fish, turtles, crocodiles, shrimp, sharks and much more, all from Solnhofen, Germany. In this blog, Dr. Bakker explains why Solnhofen produced and preserved so many spectacular, intact specimens.

The Mystery of Tropical Germany

From the first diggings in the late 1700’s,  Solnhofen presented a profound puzzle: Why was  Germany tropical in the Jurassic?

The fossil evidence was perplexing:

Fish
Amiopsis Lepidota

Big, long-lived reefs grow only in the tropics – how could northern Europe have supported the Solnhofen reef?

Large crocodiles thrive only in the warmest climate – how could giant sea-crocodiles flourish at Solnhofen?

Huge tree ferns today are emphatically warmth-loving plants – how could tropical ferns grow luxuriously at Solnhofen?

The mystery was world-wide. In the Jurassic, big crocodilians, tree ferns and reefs had spread all over Europe, Asia and North America. The tropical belt must have extended into Alaska and far south into Argentina.

Solnhofen was part of the proof that the Jurassic was one of the warmest periods in the history of life. Since the end of the Jurassic, on average Europe and North America suffered a gradual decrease in winter warmth.

Solnhofen – A Real Jurassic Park

Big-Budget movies have made the Jurassic Period  the most famous sector of geological time in our modern world. But in fact, the Jurassic was already world-renowned by the 1830’s. The first carnivorous dinosaurs known from good skeletons came from the Jurassic of Oxford. The first dinosaur tracks discovered in abundance were from the Jurassic of Massachusetts. The first complete skeletons of giant sea-reptiles were excavated from the Jurassic of southern England.

But no locale has gave finer fossils from the Jurassic than Solnhofen, Germany. Beginning in the mid 1700’s, Solnhofen has provided a never-ending stream of petrified animals and plants.

Fish
Liodesmus Sprattiformis

The exquisite skeletons lie in lithographic limestone, a rock that records not only bones but  impressions of skin and other soft tissue. Vertebrate bodies are preserved in exceptional detail. The pterodactyls at Solnhofen often have fossilized wing membranes. Crustaceans and mollusks are often fossilized as complete bodies. Even the most delicate  parts of squid – tentacles, eyes, and ink sacs – are recorded as high-resolution impressions.

Solnhofen lithographic stone has captured a more complete picture of Jurassic life than any other kind of sediment. Fossils are not common – hundreds of rocks slabs must be split to expose a single animal. Fortunately, the discovery of fossils is encouraged by commercial interests. Beginning in 1798, the lithographic stone has been quarried to make stone plates used to print high-resolution images of paintings, etchings and, later, photographs.

Many scientific publications about Solnhofen fossils have been illustrated by drawings of specimens reproduced via lithographic limestone plates.

Why are Solnhofen fossils so magnificent? The environment  around a tropical reef  was perfect for preservation. Reef-building organisms – sponges, microbes, corals – built up an arc of hard calcium carbonate that shielded a quiet lagoon. All manner of salt-water fish and invertebrates hunted for food in the upper warm waters. Land-living animals came to the beach to search for washed-up carcasses. In the air flew ‘dactyls and, on occasion, a  bird.

When an animal died and sank to the bottom of the lagoon, the water chemistry offered protection from  the forces of decay and dismemberment. The hot tropical climate concentrated the salts in the quietest part of the lagoon, so that most decomposers – organisms that would destroy the carcass – were kept away. Salt-loving microbes spread a thin film over the bottom, and this film functioned like a death-shroud, further protecting the body of dead animals. Perfect fossils were formed when the microbial mat excluded every crab, snail and  bottom-living shark that would otherwise destroy the body.

Extinct Sea Turtle
Eurysternum Wagleri

Solnhofen brings to us a picture of half-way evolution. The rich fish fauna was being modernized by natural selection. Old-fashioned armored fish were going extinct. New styles of jaws and fins were being developed among what would become the dominant fish families in the modern world. Many Solnhofen fish were living-fossils in their own day, representing evolutionary designs that had first appeared two hundred million years earlier. Other Solnhofen fish were the first successful members of clans that dominate today.

Pterodactyls and sea-reptiles too were about half-way in their Darwinian trajectory. Sea-turtles had not yet evolved their specialized flipper. Sea-crocodiles were about to suffer extinction and replacement by the new ocean-going species of the Cretaceous Period. Crustaceans were starting the wave of evolution that would continue as modern crabs and shrimp and lobsters.

There collection displayed here in our exhibit is one of the finest samplings of the entire Solnhofen biota. The Archaeopteryx at the center of the exhibit is the only Archaeopteryx in the New World.

The Eyes Have It: Evolutionary Development and DNA

Today’s guest blogger is Neal Immega. He has a Ph.D. in Paleontology and is a Master Docent here at HMNS. In his post below – originally printed in the Museum’s volunteer newsletter – Neal discusses Evolution Development and DNA.

Popular media crime shows, like CSI: Crime Scene Investigation, show amazing applications of DNA technology. For example, a person can be traced to a specific location by means of cells he left on a door knob.

A new science called “Evo-Devo,” shorthand for Evolutionary Development, can tell us even more amazing information. Evo-Devo techniques probe deeply into the structures of DNA to look at how DNA actually codes for the growth of body parts, telling us more about the animal kingdom than we ever dreamed possible. It shows genetic similarities between very different organisms and lets us understand how two organisms, like mice and men, can have DNA that is 85% similar and, yet, code for very different organisms.

We all know the basics of DNA molecules, where the genetic code is stored by a very long sequence of four proteins strung together in various arrangements. That is the easy part! What we need to
worry about is how these genes blueprint a living being. Geneticists, like Sean Carroll (whose popular books are listed in the references box), have discovered that the DNA code is made up of some large master programs that control things, such as eyes, and lots of very small programs (they call them switches) that control what kind of eye will be displayed.

Normal Fruit Fly
Image courtesy of The Exploratorium

Let’s confine ourselves to understanding and experimenting on simple life forms, such as fruit flies. To figure out which specific piece of DNA causes some feature to appear in a developing embryo, geneticists experimentally inactivate a segment of DNA, transplant the complete strand (including the inactivated segment) back into the egg, fertilize that egg, and then see what turns up missing. If that missing part is not vital for survival, the egg might even grow into an adult fly. Compare the drawings of a normal fly with the one below it where the master program for eyes has been deleted.

Eyeless Fruit Fly 
Image courtesy of The Exploratorium

Such experiments have found that the master program for making eyes can cause an eye to grow on a fly’s leg, body, antenna, or inside the body, depending on where it is placed on the DNA strand. Check out the drawing showing the results of moving the master program for legs to the site of the antenna. Note that the extra legs are fully formed but lack the neuron connections to the brain and so are not functional. (In the references box is a link to an electron microscope image of a real fruit fly that shows a mutation in which eyes replace antennae.)

Various mollusks (like clams, snails, and octopuses) grow eyes that vary in complexity from very simple sensitive pits to complex eyes that would compete well with human eyes. The EXACT SAME eye master program from a fruit fly can replace the eye master program for a squid, and it will grow a perfectly functional squid eye. You might be tempted to say that fruit flies and squids are cousins.

Fruit fly with extra legs
replacing the antennae 
Image courtesy of The Exploratorium

That is an amazing statement, but to take it even further, the same experiment with a mouse eye master program will grow fly eyes on flies and squid eyes on squids. They only differ by the small switch segments. These experiments establish a link between vertebrates and invertebrates that paleontologists are unlikely to find in the rock record. This also helps explain the amazing degree of structural similarity between mice and men—although many of the master programs are similar, the really critical parts of the DNA are the small switches that control the details.

Mollusks have just one master program that is controlled by different switches. Pectens, for example, have the most complex vision arrangement of any animal with three different types of eyes on its body. The DNA can be experimentally adjusted to grow any of these eyes anywhere on the body. Random mutations could thus cause novel arrangements, and survival would judge their fitness—evolution in action.

The switch concept explains how mice, chimps, and humans can have a similar number of genes. The switches control the result of the master programs. You can pick up any modern textbook and read that men and chimps have nearly identical genes. It is the switches that make us different and that provide the evolutionary means for dramatic changes, good and bad.

The fossil record is full of cases where a dramatic new species just appears. Paleontologists have often wondered if this was caused by a missing rock interval, by migration, or by rapid evolution. The concept of rapid evolution has often been discounted because it seemed to violate the incremental nature of evolution. We now can see how rapid evolution may just be a single point mutation in a switch. There are numerous biological examples where altering one protein is lethal, as in Tay-Sachs disease, or altering another might bear strongly on survival, as in changing
the color of hair from white to black.

Geneticists can now explain things in a way that profoundly affects how we think about evolution. Biologists and paleontologists have always wondered if evolution had to generate complex structures like eyes from scratch for each phylum. The reuse of master programs from very simple life forms through complex ones means that evolution can build on what went on
before. Critics of evolution often claim that eyes are too complex to have evolved. (The “half-an-eye-is-nogood” argument is derived from the first sentence of the Darwin quote in the box below.) Now, with Evo-Devo tools, we can see commonalities between the genetics of simple life forms and complex life forms– between clams and people.

The possibilities just became more complex.

REFERENCES:
Wyoming Dinosaur Center: http://www.wyodino.org/

Sean B. Carroll:
Endless Forms Most Beautiful: The New Science of Evo-Devo, (paperback) 2006
The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution,
(paperback) 2007
Remarkable Creatures: Epic Adventures in the Search for the Origins of Species, 2009

Lynn Helena Caporale:
Darwin in the Genome: Molecular Strategies in Biological Evolution, 2002

SEM (scanning electron microscope) photograph of eyes replacing antenna in a fruit fly by Naoum
Salame. http://1tv4.sl.pt

Fly Eye Genetics:
http://www.pbs.org/wgbh/evolution/library/04/4/text_pop/l_044_01.html
Renowned scientist Dr. Walter Gehring discusses master control genes and the evolution 
of the eye.

Darwin, 1859, The Origin of Species, http://darwin-online.org.uk/contents.html. In most editions, the quote appears on pp143-4.

Get your hands on science!

Seeing our dinosaurs up close is exciting – but getting your hands on science is an even more amazing experience. Which is why we try to bring you hands-on, educational activities that make you the scientist.

Visitors search for shark’s teeth in our Paleo Hall

Several mornings a week we have a volunteer on-hand in our Hall of Paleontology to help you experience the work of a paleontologist and malacologist.

Come by soon – you can help us sift through the shells and gravel collected by our teams in Bryan, Texas for fossils that are from the Eocene era, from species that lived over 35 million years ago. Help us separate the fossils – old snail shells, clams, mollusks, otoliths, coral and gastropods – and view them in tiny detail under the magnifying glass. Hold barracuda, manta ray and shark teeth in your hands, and help us to categorize them while you learn about ocean life both past and present.

Sift through shells, gastropods, and teeth
that are over 35 million years old

If sorting through our shell collection isn’t hands on enough for you, sign up to go on our family or adult day excursions with one of our curators. Go bird watching with Dan Brooks or collect your own shells on a malacology trip with David Temple. Sign up at hmns.org, and keep your eye open for future science trips.