A very well-known limestone formation in Bavaria, the Solfhofen has been quarried since the days of the Reformation in the 15th Century. Solnhofen limestone has been used historically for lithographic plates and in sculpture.
The limestone is quite fine-grained, and it formed in stagnant, anoxic environments underwater. Being anoxic and also hypersaline meant that the salt content was incredibly high, even to a level that made the water toxic. This was the Solnhofen in a nutshell.
At this time about 150 million years ago or, the Tithonian Stage of the Late Jurassic, the Tethys Ocean flooded much of Europe and cut it into a massive archipelago.
This area in particular was made of a series of lagoons cut off from the main sea by reefs. It meant that the water in the Solnhofen lagoons was actually left there with hardly any way of flowing back out into the Tethys and so the salt in the water accumulated.
The salinity became far too extreme to support any kind of life. Not even microbial mats could survive here but the silt at the bottom of the lagoons was always fine and grainy.
This made it an excellent preservative for anything small and delicate that happened to crawl, swim or fall into the water.
Most of the vertebrates here are fish that were unfortunate enough to cross the rocky barriers lying around the lagoons. Most of the fish are actinopterygians or ray-finned fish. Also, many of these were early teleosts, which form the majority of fish alive today.
Teleosts are those fish with jaws that can protrude, and with a completely bony skeleton. These primitive genera often had armored scales, which not many have now.
However, they were still quite streamlined, sometimes looking almost like an armor-plated mackerel or barracuda.
A proper act of predation wound up in a fossil and shows us the pike-sized carnivore Aspidorhynchus getting itself into a rather complicated situation. It had attacked a pterosaur, a Rhamphorhynchus to be exact, and the pterosaur itself had a small fish called Leptolepides in its throat. The big predatory fish had then attacked the pterosaur as it passed over the water, tearing its wing membrane and dragging it down in the process. The battle probably occurred quite close to one of the lagoons, or the incredible level of preservation might not have been possible. This fossil was described properly in 2012.
Aspidorhynchus had no teeth, but an elongated upper jaw that ended in a sharp, hard spike. This made it almost like a barracuda crossed with a marlin.
One of the larger fish found here is Hypsocormus, at around a meter in length. It was a pachycormid, a very ancient type of bony fish. It was a fast predator with powerful jaws and probably swam in pelagic waters. Its relative Asthenocormus was even bigger and more streamlined. It probably resembled a large wahoo, and was more than 2 meters in length. It was actually toothless though.
Gyrodus was another rather specialized fish with a mouth used for picking out little shellfish and other debris-eating invertebrates from between rocks and marine sponges. It was thus somewhat like a large butterflyfish and many other reef fish of today. It had a rather flattened body, somewhat hexagonal in form.
Leptolepides is the small fish of the formation, somewhat like a little herring. It was a filter-feeding animal and probably formed large schools like most other small fish of today. It was also probably at the bottom of the food chain where the vertebrates were concerned.
The largest predators in these waters however, were the marine reptiles.
The only ichthyosaur known from this formation is Aegirosaurus. It was a small ichthyosaur, belonging to the family Ophthalmosauridae. Despite a great diversity in the earlier parts of the Jurassic, the ophthalmosaurs were the most robust and well adapted to pelagic life. They were also among the last of their kind, dying out midway through the Cretaceous.
Aegirosaurus is quite typical for a European ichthyosaur thanks to its convoluted taxonomy. It was about 2 meters long and was a generalist hunter that swam through the ocean in pursuit of its prey. Also, it was classified as Ichthyosaurus at times, just like most other ichthyosaurs.
There were no big plesiosaurs here unlike earlier European marine formations – Holzmaden in Germany, the formations in Svalbard and the Oxford and Kimmeridge Clay Formations in England – but instead there were carnivorous marine crocodylomorphs or stem-crocodiles.
They all belong to the large family Metriorhynchidae, composed of fully pelagic crocs with fish-like tails and flippers. None of them had any form of armor, probably lost for the sake of complete streamlining. They were probably not very capable on land either, although it is unknown if they gave birth to live young or laid eggs. The latter is more probable, for there have been no records of viviparity in any archosaurs.
They would have slithered up on dry land to lay their eggs on the beach, albeit they would have done so quite awkwardly. Unlike a turtle, the flippers of metriorhynchids are hardly tools for proper mobility. Many of the Solnhofen genera were actually discovered quite early in the history of paleontology.
One of the smallest of them was Cricosaurus, a rather delicate and inoffensive-looking animal with a long snout and small teeth. This croc would be small even by today’s standards, at just around 2 to 3 meters long. Its body was also quite long and it was probably similar in habits to most dolphins.
The genus was described by Wagner in 1852, with the type species being Cricosaurus elegans.
On the other end of the spectrum is Dakosaurus. Dakosaurus maximus belonged to a tribe of metriorhynchids known as the geosaurins. Unlike Cricosaurus and its relatives, the geosaurins were large and powerful predators with short skulls and serrated teeth for ripping flesh.
In fact, at times Dakosaurus specimens had been classified as theropod dinosaur teeth due to their unorthodox tooth and jaw shapes. The type species Dakosaurus maximus was first named Geosaurus maximus in 1846. It was redescribed 10 years later as a member of its own genus.
Dakosaurus maximus translates to \"greatest biting lizard\", an apt name for the apex predator of the Solnhofen. It was roughly twice the size of Cricosaurus and was also far more muscular and well-built. It could twist-feed thanks to the deep roots of its massive cutting teeth.
Another species from the Jurassic is the South American D. andinensis. It was found in 1987 but named in 1996. The press nicknamed the creature Godzilla after the shape of its snout, which was even shorter and stouter than that of the type species. Its closest relative Geosaurus was also part of this formation.
This was the earliest-discovered geosaurin, named as far back as 1816 as a lizard named Lacerta gigantea. Eight years later, famed naturalist and founder of comparative anatomy Baron Georges Cuvier established the name Geosaurus for the remains.
It was renamed Geosaurus giganteus, the \"gigantic lizard of the Earth.\" Despite its name it was rather small, at about 3 meters. It probably fed on smaller prey than its bigger cousin Dakosaurus, although it still had the same short skull and flesh-tearing teeth.
A far more standard-looking croc here is Steneosaurus. It is also a stem-crocodile, belonging to the Crocodylomorpha. It was a teleosaur, and was adept on both land and in the water. It still had armor plating and proper legs, thus making it indistinguishable from modern forms. It is also surprisingly speciose and has an immense stratigraphic range starting in the Early Jurassic.
Steneosaurus is also part of the Holzmaden, another German fossil bed that predates Solnhofen by over thirty million years and continues onto the Oker Formation, a few million years older than the Solnhofen. It is also known from the famous Oxford Clay in England, around 15 million years older than Solnhofen. Many species of Steneosaurus would have been similar in size and shape to a modern gharial although most were much smaller.
There were two small theropod dinosaurs from Solnhofen, both of them coelurosaurs. One was a small basal avialan called Archaeopteryx, which does not really require an introduction. It was always thought to be the first proper bird but recently its status has been questioned thanks to the older Tiaojishan fossils. Ever since its naming by Hermann von Meyer in 1861, it has been depicted as a monstrous mix of reptilian and bird parts, often in garishly colored plumage.
However, more recently it was realized that Archaeopteryx actually had black wing tips and the rest of its feathers were probably a combination of dark and light, with maybe browns and whites covering its body. Also, depictions of this animal show it clinging to trees and running around the forest floor. The islands of Solnhofen were actually somewhat desert-like and hot, being only able to sustain shrubbery. It may still have climbed the low, bushy conifers of its environment though.
We know that it was unable to flap, like most Mesozoic avialans, but probably had a downstroke-assisted glide. It was most probably an omnivore or just a generalist carnivore that fed on anything it could get its claws on. Archaeopteryx has cemented itself quite well in popular culture, with many online paleo-enthusiasts referring to it as \"Urvogel\", its German name.
Twelve specimens are known currently. The holotype is a well-preserved primary feather. As for body fossils, the Solnhofen one is the biggest while the specimen from Eichstatt is the smallest. The others are from Haarlem, Berlin, Maxberg, Thermopolis, London, Daiting, Burgermeister-Muller and Munich.
The Berlin specimen is the most complete and most iconic. The London specimen was the first discovered, and was seen by Charles Darwin himself in the Natural History Museum in London.
The top predator of the Solnhofen islands is another famous animal, Compsognathus. It is infamous for being called the \"smallest dinosaur ever\" when in reality the holotype from Germany was that of a juvenile a little less than a meter long.
A specimen from France shows us that it was as big as a turkey, while much of its length was taken up by a long tail. It was not only twice as large as we thought it was, but it was also very low-slung. Not much can be said about Compsognathus that hasn’t already been said, except that due to the completeness of the fossils, we can restore it with relative confidence.
A lizard called Bavarisaurus was actually found in the gut of the holotype. Not much can be said about the pterosaurs of the island either. They are very well preserved, so well-known in fact that they can be depicted confidently too.
There was a lot of effective niche partitioning among them. We know of the fish-eaters Pterodactylus and Rhamphorhynchus from both adult and juvenile specimens. The same is true for the filter-feeder Ctenochasma. Anurognathus hunted insects in low light conditions, while Scaphognathus was likely predaceous, preferring to hunt overland. Studies by Lars Schmitz and Ryosuke Motani in 2011 have been useful in decoding the lives of the Solnhofen pterosaurs. A few are likely to have been nocturnal, while others hunted either at dawn or dusk.
