Cambridge Greensand Formation




This Early Cretaceous fossil bed contains some of England's highest concentrations of big marine pterosaurs. The majority of them are ornithocheirids with a long and confusing taxonomic history, and some of their findings date back to the earliest days of paleontology. The Cambridge Greensand is a marine chalk formation and is mostly situated in Cambridgeshire and the surrounding areas.

It also stretches out towards East Anglia, and contains a rich variety of oceanic animals. Some of the invertebrates here include ammonite species, echinoderms like sea urchins and fossil foraminiferans, most of which make up the chalk with their shells.

The formation preserves a large, shallow marine environment marked by the prolific diversity of large and medium-sized fish. Many of these fish are sharks like Hybodus, Coelodus and Acrodus, common and long-lived genera from now-extinct families.

Some of the other predatory fish include Saurocephalus, a swift-moving meter and a half-long hunter with an elongate body. It bore powerful teeth and jaws for sawing off big chunks of flesh. They were clearly the barracuda analogues of their day, despite being unrelated. Lepidotes is a very common, bottom-feeding fish, a semionotid that is very well-known from this and other marine formations of the time.

Of course the best-known big animals from the formation are the ornithocheirids, all of which were expert fishermen.

Among these is the famous Ornithocheirus simus itself, which rose to new heights of fame after the documentary miniseries Walking With Dinosaurs aired in 1999. Despite this fame, the animal was still a taxonomic muddle at the time and its size had been greatly exaggerated. These massive specimens were reclassified in the genus Tropeognathus.

Many of the other pterosaur genera here were created when Ornithocheirus was split over the years. One of these related pterosaurs was the small Lonchodectes, a creature with a 2-meter wingspan. While most other ornithocheirids were fish-hunters, this one was doing something very different.

Recent studies of its limb proportions by David Unwin in 2008 have shown that it was probably more like an azhdarchid than a regular ornithocheirid. So it may have hunted by walking on land and picking up small animals in its beak. The genus Lonchodectes was once put in Pterodactylus in 1851, but Harry Seeley reassigned it to Ornithocheirus in 1870.

It was only reclassified yet again, in 1914 by Walter Reginald Hooley. The trouble with these pterosaurs is that they are known from the most fragmentary of remains. Lonchodectes for example is known from parts of the jaw, the same with its relatives. These include Lonchodraco and Amblydectes, both included as part of Pterodactylus in the 19th Century.

The dinosaurs from this formation are just as confusing as the pterosaurs. One of the "best-known" dinosaurs found here is the possibly armored Anoplosaurus. The animal was named and described by Harry Seeley himself in 1879. Yet the animal is not at all well-known, certainly not from complete fossils. It has been bouncing back and forth between being an armored anklyosaur and an ornithopod like Iguanodon or Camptosaurus.