Wednesday, June 17, 2009

Holzmaden: Marine Reptiles and lots of squids

When I was in first and second grade, my favorite video series from the library was called “Dinosaurs!” The series was narrated by Walter Cronkite and took you through the history of paleontology from the naming of the “terrible lizards” through the 20th century where I was introduced to many of my paleontological heroes. The historic sections used Ken Burns-style pans over old paintings and photographs spliced with historical reenactments.
A display in the Holzmaden Museum that showed the fossils found at each successive layer. They forgot to include a mannequin of a shocked German miner.

Once scene showed a German miner diligently chipping away at a slab of slate. His lantern light catches a strangely colored rock embedded in the slate. He takes his chisel to the rock and reveals the body of a dolphin-like reptile. It caused a sensation. This was an antediluvian sea-monster! I remembered that excavation and fossil, but didn’t remember where exactly that scene took place. I walked into the Holzmaden Museum, and there it was: The dolphin-lizard. I had a weird feeling of déjà vu.
A massive Ichthyosaurus trying his derndest to be a whale.

160 million years ago, South-western Germany was part of a huge inland sea, something like the seas of the Caribbean or Southeast Asia. The tranquil water was filled with squid, both the modern fleshy kind that get turned into calamari and shelled squids called ammonites that formed the base of the Mesozoic Marine ecosystem. All this tentacled protein brought in the sea monsters. Ichthyosaurs were fully committed marine reptiles. That look almost exactly like modern dolphins and are a classic example of convergent evolution. They mastered the art of live-birth (as revealed by fossils that preserve juveniles stuck in the birth cannal!) and were able to transform their limbs into fins and tails into flukes. Their enormous eyes indicate animals that relied on keen eyesight to track down their prey.
The glare is terrible, but if it wasn't you would be able to see a neophyte marine reptile a little south of her stomach.

Also splashing around Germany were the plesiosaurs, long-necked, four-flippered animals that are usually brought into discussions of the Loch Ness Monster. Presumably these ungainly animals had to haul themselves onto the beach to lay their eggs, making it impossible for them to become as perfectly adapted to the marine environment as the Ichthyosaurs. No one is really knows how they used that long neck to snap up food, but it must have worked out for them since they thrived throughout the Mesozoic.
A plesiosaurs missing his squishy parts. There's no scale, but this guy is about the size of a dolphin.
A plesiosaurs put back together going after a small squid. No one is quite sure how lashing your neck around like that affects your hydrodynamic abilities.

He smiled for the camera.

The seas also supported marine crocodiles with diminutive forelimbs and powerful, finned hind limbs. Sharks were on the scene, but they didn’t achieve their mega-carnivore status until the reptiles left some open niches 65 million years ago. In the Jurassic they looked more fish-like with stubby noses and wide, multi-finned bodies. One of the fossils in the museum’s collection shows a primitive shark with dozens of squid shells piled up in his stomach. Modern squids their shells inside their bodies. This is a dense piece of calcite that resembles a 22-caliber bullet. The shells that killed the shark are piled up in his gut, a fossil telling the story of some pretty awful indigestion.
Sharks have carilage skeletons, so they usually don't fossilize very well. You're looking at it's stomach (ventral view). The mouth of this guy is to the right, the gill slits V towards the top and bottom and the shells that killed him are piled up in his stomach to the left.

The most spectacular fossil in the museum is a log roughly 30 yards long. Anchored to the Jurassic driftwood are over one hundred crinoids (Sea lilies). Crinoids are like starfish on sticks. They anchor themselves to the substrate and collect food as it passes through their fans. These crinoids decided to go for a ride, latching onto every available spot on the log that eventually ran aground burying everyone on board (It’s unclear if the captain went down with the ship). The fossil takes up an entire wall and took 15 years to prepare (always remember every pretty fossil you see took hours of delicate work from a preparation specialist who carefully removed the obfuscating rock).
A mess of crinoids. A crinoid salad if you will. All log of boyant freedom run aground.

When we went to the shale quarry we were once again set loose on an uninspiring landscape where spoil piles of chipped shale were heaped on the edge of the industrial pit. As I walked towards the chipping group I saw the yellow gleam of a shell. I had found an ammonite squid and I hadn’t even swung my hammer! After an hour of chipping I discovered the shells were ubiquitous and you would need good luck not to find one. I also found bullet like squid shells, but no vertebrate pieces. The shells sit in my room, waiting to be added to the collection in my parent’s garage.

We had taken this excursion during a school holiday and the pit was filled with children and their parents smacking away at the rocks. The sight of four year olds wielding hammers might have been cute if I didn’t fear for my digits every time they drifted near my small excavation area.
A six-year old doing some serious fossil hunting. My money says he finds a squid.

With new insight into the Jurassic high seas where sea monsters apparently risked constant headaches thanks to millions of drifting, shelled mollusks, it was back to the road. Soon we would be examining a very different Jurassic ecosystem…

The business end of a Mesozoic squid roughly the size of a semi-truck tire.

1 comment:

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