The phosphate beds of northwestern Morocco are one of the only places in the world with extensive deposition and fossils from just before and after the Cretaceous-Paleogene extinction 66 million years ago. They are famous for their extensive fish, marine reptile and pterosaur fossils. The pterosaurs, in particular, have made an important contribution to our understanding of how the mass extinction unfolded. So far, at least seven species from three different families show that pterosaurs remained diverse and common in larger body sizes, and were not pushed to extinction by competition with birds.
The phosphate beds of the Ouled Abdoun Basin in Morocco are exposed around the town of Khouribga. They are extensively mined for their phosphate minerals today, and used to make much of the world’s fertilizer. The rocks were deposited several hundred meters under the waves of the Atlantic Ocean at a time of higher sea levels than today. Phosphate minerals are rarely found in high concentrations in the rock record and require specific conditions to be formed. Usually, winds at mid-latitudes allow nutrient rich waters to rise from the deep ocean, often leading to algal blooms and other increased biological activity. The water column must also be anoxic in its lowest depths, which allowed the phosphorus concentrated in algae and other organisms to remain on the seafloor after their death. The coast was several kilometers to the east, and was rocky and arid, resembling the mountainous coasts of modern Yemen and Oman. The phosphates in the basin were formed over a long period of time, from at least 80 million years ago in the Late Cretaceous to 55 million years ago in the Paleogene. We will be focusing on those rocks that formed at the end of the Maastrichtian Age, about 66-67 million years ago.
Although they are all known from fragmentary remains, hundreds of specimens of at least seven pterosaur species are known. They include the large pteranodontid Tethydraco regalis, probably an aerial fisher like other pteranodontids. Three nyctosaurids, which were also marine fishers, are also known from the mines: the small plunge diver Alcione elainus, medium-sized Simurghia robusta, and large Barbridactylus grandis. In addition to the marine fishers, remains were found of three azhdarchids, usually considered terrestrial carnivores. They include an unnamed species similar to, but much smaller than Quetzalcoatlus from similarly aged rocks in Texas, medium-sized Phosphatodraco mauritanicus, and a very large, but slender species, given the nickname ‘Sidi Chennane Azhdarchid.’
Dinosaur remains are very rare, known from only a few specimens washed out to sea. They include the abelisaurid Chenanisaurus barbaricus and an unnamed titanosaurian sauropod.
The seas were patrolled by a large number of predatory marine reptiles. The vast majority were mosasaurs, marine lizards closely related to monitor lizards. They include several species of the genera Mosasaurus, Platecarpus, Prognathodon, Globidens, Carinodens, and Halisaurus. Plesiosaurs were present, but less common, represented by a single unnamed elasmosaur.