The Upper Jurassic fossil Lagerstätte of Solnhofen-Eichstätt (48° 53' 25'' N010° 58' 05'' E) of the Altmühltal Nature Park in Bavaria, Germany is the only occurrence of the Tithonian plattenkalk or platy limestone from the Altmühltal Formation worldwide. It is also where the earliest known bird was discovered called the Archaeopteryx (pronounced ark-ee-opt-er-ix) or Urvogel in German meaning “first bird”.
Both Eichstätt and Solnhofen are independent Plattenkalk Basins and our blog shall explore the area as a whole. In 2022, the Solnhofen-Eichstätt Lagerstätte was named among the “First 100 Geological Heritage Sites” designated by the International Union of Geological Sciences (IUGS).
Located in the Altmühltal Nature Park approximately 100 km north of Munich, Bavaria’s capital many of the fossils found in the quarries of the Altmühltal Nature Park are also exhibited at the museums of the region, including the Paleozoo of the Bürgermeister-Müller-Museum, the Jura Museum located in Willibaldburg castle in the town of Eichstätt, and an Archaeopteryx at the park's own "Dinosaurier Museum Altmühltal".
This area of Germany is geologically known as the Southern Franconian Alb and is bordered to the West by the Variscian massifs of the Black Forest and the Odenwald along a stretch of the 40 Km wide and 150 Km long Rhine Graben part of the European Cenozoic Rift System. The Jurassic rocks are found in the South and the Southeast.
The Solnhofen Limestone or Solnhofen Plattenkalk dates back to the Tithonian Age (152.1 - 145.0 million years ago) the last of the three ages within the Late Jurassic Epoch preceded by the Kimmeridgian Age and succeeded by the Berriasian Age of the Cretaceous Period.
The Solnhofen limestone is up to 100 meters thick and is occasionally interrupted by slump horizons known as Krumme Lagen. These are irregularly folded beds, resulting from slumped soft sediment masses that collapse downslope, possibly triggered by earthquakes. Solnhofen limestone has historically and traditionally been used for lithographic plates and in sculpture.
The Tithonian Age was named by the German stratigrapher Albert Oppel in 1865 inspired by the Greek mythological figure of Tithonus. Tithonus was the Prince of Troy who fell in love with Eos the goddess of the dawn. In this case, the Tithonian Age was romantically described as being hand in hand with the dawn of the Cretaceous Period.
The Global Boundary Stratotype Section and Point (GSSP) an internationally agreed upon reference point for the lower boundary of the Tithonian Age has yet to be officially agreed upon. Possible candidates include Mt. Crussol or Canjuers in southeast France and Fornazzo in Sicily, Southern Italy.
The lower boundary of the Tithonian Age is characterised by the ammonite biozone of Hybonoticeras hybonotum as well as the lowest occurrence of the ammonite genus Gravesia and an upper boundary marking the first appearance of the small globular calpionellid an urn-shaped planktic Protozoan species known as Calpionella alpina.
The Solnhofen limestone is described as a Konservat-Lagerstätten where the fossil remains show an extraordinary level of preservation. Such exquisite preservation requires specific environmental conditions to happen where the sediments have little or no oxygen and also inhibit any bacterial decomposition processes for enough time to allow mineral exchange, precipitation, and other chemical processes to form casts and films of delicate softer body parts.
During the Upper Jurassic epoch, the supercontinent of Pangaea broke up into the landmasses of Laurasia in the north, and Gondwana to the south. The Tethys Sea separated these two landmasses during much of the Mesozoic Era (252 - 66 million years ago) until they fragmented into the continents we now know today.
Towards the end of the Jurassic Period, a warm shallow sea with many islands and lagoons covered much of what is now Germany including the “Solnhofen Archipelago”. Sponge reefs, sponge biostroms, and corals grew along the lagoon edges. The reefs effectively isolated the lagoons and sediments were able to deposit and remain undisturbed.
Isolated from the ocean and terrestrial waters these lagoons became toxic as the salinity increased and the oxygen depleted. Only cyanobacteria and small ‘armoured’ single-celled protists known as Foraminifera were only adapted to live in these lagoons.
The lagoonal environment was optimal for both marine and terrestrial animals and plants to be preserved as either they fell into the lagoons from the land or drifted or were washed in from the ocean.
These animals were simply buried in the soft carbonate mud and not destroyed by scavengers, bioturbation, or by tidal currents.
The closest comparable geological setting to the Solnhofen Limestone is possibly the Orca Basin in the Northern Gulf of Mexico 300 Km southwest of the Mississippi River mouth on the Louisiana continental slope. Though, the Orca Basin is much deeper than the Solnhofen lagoons are thought to have been.
The Solnhofen Limestone has an astonishing diversity of organisms with over 750 species of fossils recorded.
Among the fossil record are preserved jellyfish, insects, crustaceans, squid, Actinopterygians or ray-finned fishes, pterosaurs, and possibly the most famous discovery of the Archaeopteryx lithographica and the first fossil feather or Urfeder apparently not belonging to iconic Archaeopteryx.
The Archaeopteryx was a feathered dinosaur and is considered the oldest known bird only found in the Solnhofen Limestone. Based on its wings and feathers it is believed that the Archaeopteryx likely had some flying abilities. Studies of the Archaeopteryx using 3-Dimensional digital reconstructions of the well-preserved bones suggest that the Archaeopteryx flew like a pheasant to cross barriers or escape predators but was not designed for enduring flight like a bird of prey or seabird.
The evolution of the Archaeopteryx is today a topic of much discussion as to whether it should be classed as the transitional link between the dinosaurs and the start of the bird evolutionary tree.
Though it has traits that have helped to define the taxonomy or classification of a bird including feathers, wings, wishbone, and reduced fingers. The Archaeopteryx has more in common with other theropods from the Late Jurassic and Cretaceous Periods than with modern birds.
The Archaeopteryx has more in common with Dromaeosauridae a sister group of the clade Aves which includes all birds and also potentially Troodontids of the clade Maniraptora (“Seizing Hands”). They had a full set of sharp teeth, a long bony tail, moved on two legs, and had three claws on each wing which could have still been used to grasp prey or secure themselves on trees.
It's agreed that the Archaeopteryx belongs to the dinosaur group called Deinonychosauria the evolutionary descendants or clade of paravian dinosaurs or bird-like theropods. However, new discoveries from around the world in China, Mongolia, and Argentina of numerous other small, feathery dinosaurs such as the Xiaotingia zhengi (pronounced “zhow-tin-gee-ah”) who also used its feathery hindlimbs for short-distance flights have created a conundrum for paleontologists.