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.

Road Trip!

Many people come to our Museum for a visit.  In fact, last year, we had over 2.5 million visits. But have you ever had a museum come to you for a visit?  Well, the Houston Museum of Natural Science can do that, too!  The Museum has several different outreach programs where we bring specimens to students for some hands-on learning. 

Recently the Museum brought its El Paso Corporation Wildlife on Wheels to Kipp (Knowledge is Power Program) Dream Elementary School. In this picture, you can see some of the specimens used during our Reptiles and Amphibians topic. Snake skin, tortoise shells, fossil casts (center), coprolites and even caiman skin are valuable teaching tools and definitely more portable and safer than a large, live caiman!

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In this picture below you can see some of the cutest kindergartners touching a Surinam Toad. They were very attentive and while some were nervous, most were very excited. They were also practicing safe touching technique: two finger touch, sitting “criss-cross-applesauce”, and as I learned that day, “with their spoons in their bowl” (meaning hands in their lap). The toad was pretty good too.

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Here you see a Savannah Monitor behaving himself so that the children could touch him. If you have ever worked with a monitor, that is saying something! No hesitation here, these kindergartners were ready to touch the lizard even though he was big. Behind me in the photo is a good view of the table setup for that day. All of the specimens are something the children can touch like the crocodile skull, unless of course it is fragile enough to be in a jar or behind glass like the snake skeleton in the back.

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At the end of the presentation, the children have the opportunity to come past the table and touch the specimen I had been using as part of the discussion. Here you can see the interest on their faces as they touch real crocodile teeth (without the risk of a bite!), a tortoise shell, and with only a little hesitation, fossilized dinosaur dung! This is often where I wonder what they are thinking: should I really touch poop, or would my head fit inside the croc’s mouth?

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We don’t know who had more fun during El Paso Corporation’s Wildlife on Wheels…the students or the animals!  For more information on the Museum’s Outreach Programs, visit http://www.hmns.org/education/teachers/outreach_programs.asp.

A Nature Walk through Hermann Park

Wax myrtle is a tree that is eaten by the 5 species of exotic walking sticks that we have here in the Cockrell Butterfly Center, as well as some of our grasshoppers and other herbivores. Recently, while trying to catch dragonflies (don’t ask), I stumbled upon not one, or two, but tons of these trees in Hermann Park! They were all over the place between the Japanese Gardens and the Houston Zoo. Now, every week I have a nice walk down to that part of Hermann Park to enjoy these trees, and every time I go, it’s a different adventure! 

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Creative Commons License photo credit: emills1
A handsome Wood Duck

Today I thought I would take my camera and document some of the great things I saw: vibrant wildflower plants, amazing wildlife and people enjoying a beautiful day. It’s a really nice way to get out of the office and I always look forward to what I’ll see. I love all kinds of wildlife, not just bugs of course!

Hermann Park is filled with so many different species, especially birds, many of which are ducks. The wood duck is just one of the most beautiful I’ve seen. Their colors are amazing and they have such a distinguished look. These ducks nest in trees near water sources. The ducklings jump out of the nest, falling several feet to the ground without being hurt. Many people consider them the most beautiful water bird, and I can see why. This duck was not shy with the camera!

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Creative Commons License photo credit: emills1
Great Blue Heron

Another bird that I am always happy to see is the Great Blue Heron. The first time I saw one of these take flight, I was so impressed. They are huge birds, but are so graceful and delicate. Seeing these majestic birds completely makes me forget that I’m in the middle of the 4th largest city in the United States. There were two of them today, hiding behind tall plants in the water. Luckily one came out of hiding for me! 

My visits have become even more special recently with the beginning of spring. Dragonflies and butterflies have taken to the air. Aquatic insects dart around the surface of the ponds, feeding fish, tadpoles and baby turtles. The babies are my very favorite part of spring! I’ve been lucky enough to encounter several ducklings on my last couple of visits. Their numbers have decreased, but the surviving ducklings are getting bigger and depending less on their mothers. I saw one today swimming by itself looking for food. It’s still pretty fuzzy and cute!

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Creative Commons License photo credit: emills1
A duckling – how precious!
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Creative Commons License photo credit: emills1

I was also able to photograph a dragonfly. If you’ve ever tried, you know it can be very frustrating! They scare so easily and it’s so hard to get up close. The key is definitely patience. Dragonflies are very territorial and will always come back to the same perch or one near it. If you keep at it, you will be able to catch a couple of shots of one.

Once I had gathered enough food for my insects and lollygagged around enough, I started to make my way back to work – but not without seeing the very familiar, adorable face of a squirrel. I’ve always loved squirrels for their cuteness and fun-loving personalities. They definitely have a way of helping me to forget about any stress. You can’t watch them without snickering a little bit. This squirrel seemed a little confused about what I was doing, but he gave me some really great poses.

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Creative Commons License photo credit: emills1

I really should bring my camera every time, as today was actually kind of a slow day for wildlife. I’ve also seen nutria, red-eared sliders, box turtles, whistling ducks, sea gulls, bull frogs, and tons of insects! Hermann Park really is a gem. It is such a historically significant part of our city and it is filled with so many simple, wonderful things to do. I encourage everyone to get out every once in a while to enjoy nature wherever it may be. You never know what you will see and how it can brighten your day!

Happy nature watching! 

Ike-ster…what a mess of things you made!

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Creative Commons License photo credit: tiny white lights

Thus far, my previous blogs have been exploiting some of my old camp journals that are just collecting dust at home.  I’m going to be a bit radical this week and write about a recent topic rather than an event that occurred a decade or two ago.  Today’s blog involves some brief anecdotes I jotted down regarding the recent Hurricane that struck our beloved Houston early in the morning (dark) on 13 September 2008. 

When friends and relatives asked me how it went post-hurricane, without power and many of the creature comforts our society has grown so used to, I replied, “it feels balmy and tranquil, much like my old study site in Amazonia” (which, incidentally, will be the focus of next month’s entry).  A long-time friend of mine named John described the events at his house as ‘Hurrication,’ where the teens were forced to interact with the rest of the family through playing board games, consuming massive quantities of perishable food during marathon cookouts, and everyone generally having a great time despite circumstances.  With no power, roads blocked by downed trees and electrical lines, and lines to purchase gasoline not worth the struggle, it was a great time to deflate and smell what remained of the flowers.  My family and I went on many walks to cool off since the outside was overall cooler than the inside the house.  During this time we made various observations of how the storm affected the local urban wildlife, which I will attempt to recount below.

- Vegetation was mangled, or completely removed in many cases.  Huge pine trees with a diameter exceeding a yard were snapped clean off at the base like a toothpick.  The animals which depended on such plant communities to thrive had their lives thrown into complete chaos, through their habitat being mangled, or completely removed. 

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Creative Commons License photo credit:
BobMacInnes

- It had been a couple of years since we had seen any Blue Jays (Cyanocitta cristata) in our yard, yet several individuals passed through after the storm, trying to stake out a new territory.  One pair even chased a large Buteo hawk into a tree in our front yard, where it rested briefly before being found and further harassed by the jays.

- We figured mosquitoes would be abundant from the rain that followed the storm, but not a one.  Most wildlife was noticeably lacking.  I was extremely disturbed at absolutely no sign of any of the four species of doves commonly found in the neighborhood, and you can guess my relief when they began to return six days after the storm.  It is very likely that many of the birds left the region well in advance of the storm.  Wildlife seems to have an internal barometric gauge.  For example, prior to the massive typhoon in south-east Asia, much of the wildlife left the coastal forest for the higher interior forest.

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Creative Commons License photo credit: mandj98

- Whereas some wildlife left prior to the storm, other species stayed and were noticeably more active.  An unusually high number of Carpenter Bees (Xylocopa sp.) were all over our house gardens, perhaps trying to find new resources since their former founts were now gone.  Similarly, displaced Fox Squirrels (Sciurus niger) were actively scurrying about in search of a new dwelling in light of the huge piles of fallen trees and limbs.

- A Red-eared Slider (Trachemys scripta) was found dead on the road on the corner of Haddon and Morse.  These aquatic turtles are not native to this region, but introduced through the pet trade.  The fact that it was at least a mile or two from Buffalo Bayou was amazing.  All the rain and mild flooding that followed the tail end of the storm may have transported this turtle from the bayou to the suburbs, where it sadly met its death.  We knew it was a young turtle, as the carapace (upper shell) was only 12.5 cm (5 inches) in diameter.

- Another casualty from the storm involved a flock of approximately 20 House Sparrows (Passer domesticus).  These were all over the sidewalk of a small alley by a Marble Slab ice cream shop in a strip shopping center near our house.  Perhaps they had taken cover in the only thing they were able to find once the storm got really rough, where they sadly met their death.  Like the turtle mentioned above, these non-migratory (i.e., annual resident) birds were also introduced to the U.S.

Without a doubt, for me personally, the most unfortunate aspect of Ike’s wrath was the devastation it did to various reserves that are crucial to migrating Neotropical songbirds.  High Island, Bolivar Peninsula, Sabine Woods and Anahuac National Wildlife Refuge are only a few of these sites that were hit really hard.  However, with time and effort by loyal volunteers, these refuges will again be hotspots for Neotropical avian migrants passing through our beloved state of Texas.

-D.B., 13 October 2008
(1 month after Ike hit)