Plesiosaur fossils found in strata associated with a 100-million-year-old river system prove that some plesiosaurs, traditionally thought to be marine animals, may have lived in freshwater. These long-necked, piscivores co-existed with the giant dinosaur Spinosaurus (S. aegyptiacus).

Freshwater Plesiosaurs

Scientists from the University of Bath and University of Portsmouth in the UK, and Université Hassan II (Morocco), have reported evidence small plesiosaurs from Kem Kem Group deposits in Morocco.

The fossils include bones and teeth from three-metre-long adults and an arm bone (humerus) from a 1.5- metre-long juvenile. They hint that these creatures routinely lived and fed in freshwater, alongside frogs, crocodiles, turtles, fish, and the huge aquatic dinosaur Spinosaurus.

When is a “Marine Reptile” a Marine Reptile?

The Plesiosauria clade was a long-lived and widely distributed group of marine reptiles. Most fossils, which date from the Upper Triassic to the end of the Cretaceous (Maastrichtian faunal stage), are associated with marine deposits, but a few specimens have been found in strata associated with brackish and freshwater environments. The researchers report plesiosaurs from river deposits of the Kem Kem Group. The numerous shed teeth show heavy wear similar to that observed in in the teeth of coeval spinosaurids. Contemporary plesiosaur fossils from the Bahariya Formation of Egypt have been identified as examples of the Polycotylidae plesiosaur family.

Kem Kem Fossils

The Kem Kem fossils probably represent leptocleidid plesiosaurs. Most Leptocleididae fossils come from shallow nearshore, brackish or freshwater palaeoenvironments suggesting that these small-bodied plesiosaurs were adapted to shallow, low-salinity environments.

As the fossil plesiosaur teeth show the same signs of wear as the teeth of Spinosaurus, the researchers imply that the plesiosaurs were eating the same food – chipping their teeth on the armoured fish that lived in the river. This indicates that they spent a lot of time in the river, rather than being occasional visitors.

As other types of Mesozoic marine reptile (mosasaurids and the crocodile-like teleosaurids), are thought to have inhabited (at least some of the time), freshwater environments, this suggests that so-called “marine reptiles” may have thrived in non-marine habitats.

Co-author of the scientific paper, Dr Nick Longrich (University of Bath Milner Centre for Evolution), commented:

“It’s scrappy stuff, but isolated bones actually tell us a lot about ancient ecosystems and animals in them. They’re so much more common than skeletons, they give you more information to work with. The bones and teeth were found scattered and in different localities, not as a skeleton. So, each bone and each tooth is a different animal. We have over a dozen animals in this collection.”

Diverse and Varied Kem Kem Group Freshwater Fauna

While extant marine mammals like whales and dolphins wander up rivers, either to feed or because they are lost, the number of plesiosaur fossils in the river deposits suggest that is unlikely. The team identified cervical, dorsal and caudal vertebrae, lots of teeth and the humerus from a juvenile. The researchers postulate that the plesiosaurs were able to tolerate fresh and salt water, like some whales, such as the beluga whale (Delphinapterus leucas).

Co-author Dr Samir Zouhri said:

“This is another sensational discovery that adds to the many discoveries we have made in the Kem Kem over the past fifteen years of work in this region of Morocco. Kem Kem was truly an incredible biodiversity hotspot in the Cretaceous.”

Plesiosaurs – Freshwater Incursions

The researchers compiled a list of all the geological formations that have shown evidence for the presence of members of the Plesiosauria clade in brackish or freshwater. Having collated this information, they re-examined the data identifying the different types of plesiosaur associated with the deposit.

As a result, a map documenting the incidences of freshwater incursions by different plesiosaur types was produced.

For the key to the geological formations see the end of this article.

Co-author David Martill (University of Portsmouth) exclaimed:

“What amazes me is that the ancient Moroccan river contained so many carnivores all living alongside each other. This was no place to go for a swim.”

Plesiosaurus Swam Alongside Spinosaurus

Key to the Geological Formations Featured in the Plesiosaur Map

Geographic distribution of non-marine Plesiosauria Formations: 1, Dinosaur Park Formation (Campanian); (2), Horseshoe Canyon Formation (Campanian – Maastrichtian); 3, Isachsen Fm. (Late Aptian); 4, Strand Fiord Formation (Turonian – Coniacian); 5, Great Estuarine Group (Bathonian); 6, La Colonia Formation (Upper Campanian – Lower Maastrichtian); 7, Wadhurst Clay Formation (Valanginian); 8, Tunbridge Wells Sands Formation (Upper Valanginian); 9, Wessex Formation (Barremian); 10, Upper Weald Clay Formation (Barremian); 11, Vectis Formation (Barremian – Aptian); 12, Obernkirchen Sandstone (Late Berriasian);
13, Bükerberg Formation (Berriasian); 14, Kem Kem beds (Cenomanian – Albian?); 15, Chenini Formation (Albian); 16, Bahariya Formation (Cenomanian), 17, Sunday River Formation (Valanginian); 18, Lianmugin Formation (Upper Aptian); 19, Xinhe Formation (Middle Jurassic); 20, Ziliujing Formation (Toarcian); 21, Xintiangou Formation (Middle Jurassic), 22, Xiashaximiao Formation (Middle Jurassic); 23, Shezi Formation (Upper Triassic); 24, Razorback Beds (Sinemurian); 25, Evergreen Formation (Pliensbachian – Toarcian); 26, Griman Creek Formation (Albian); 27, Eumeralla Formation (Aptian) 28; Wonthaggi Formation (Valanginian – Aptian), 29 Eumeralla Formation (Upper Aptian – Lower Albian). Note that some formations contain more than one occurrence.

Everything Dinosaur acknowledges the assistance of a media release from the University of Bath in the compilation of this article.

The scientific paper: “Plesiosaurs from the fluvial Kem Kem Group (mid-Cretaceous) of eastern Morocco and a review of non-marine plesiosaurs” by Georgina Bunker, David M. Martill, Roy Smith, Samir Zouhri and Nick Longrich.

For models and replicas of plesiosaurs and Spinosaurus figures: CollectA Deluxe Prehistoric Life Scale Replicas.

A new scientific paper on the Early Cretaceous tyrannosauroid Eotyrannus lengi has been published. It is confirmed as a valid genus and the phylogenetic assessment places the enigmatic Megaraptora clade within the Tyrannosauroidea superfamily.

First named and scientifically described back in 2001 (Hutt et al), Eotyrannus is helping to provide significant insights into the early evolution of tyrannosauroids as well as potentially redefining how enigmatic “megaraptors” such as Australovenator, Megaraptor and the recently described Maip macrothorax fit within the Theropoda.

The Carnivorous Dinosaurs of the Wessex Formation

Since the first fossils of Eotyrannus were found (1997), this theropod has attracted a lot of scientific interest. It is one of numerous carnivorous dinosaurs associated with the Wessex Formation (part of the Wealden Supergroup), indeed, back in 2021 we blogged about two new members of the Baryonychinae named and described from fossil remains found on the Isle of Wight (Wessex Formation). Last month, we wrote about an even bigger predator, an as yet, unnamed spinosaurid known as the “White Rock spinosaurid”.

For the article on the recently described baryonychids Ceratosuchops inferodios and Riparovenator milnerae: Two New Spinosaurids from the Isle of Wight.

To read about the Isle of Wight “White Rock spinosaurid”: Super-sized Isle of Wight Carnivorous Dinosaur.

The newly published paper provides further information on Eotyrannus autapomorphies (characteristic traits) that help to distinguish it from the often, fragmentary remains of other theropods associated with the Wessex Formation.

Deciphering the Fossil Evidence

Many of the fossil bones associated with the Eotyrannus genus remain entombed in their concrete-like matrix. Anatomical traits helping to define and classify this dinosaur are only beginning to emerge and there is a substantial amount of further preparation work required to permit a comprehensive analysis.

However, by combining all the new data since the formal description, the authors (Darren Naish and Andrea Cau) were able to produce a new skeletal reconstruction. The maxilla is confirmed as being quite rectangular in shape. Eotyrannus did not have the long, narrow snout (longirostrine) as seen in other early tyrannosauroids such as Dilong and Xiongguanlong from the Early Cretaceous of China. This suggests that longirostry evolved several times within the Tyrannosauroidea, perhaps in response to adaptations to permit these theropods to exploit a particular predatory niche.

Where do the Megaraptora Fit?

The scientific paper also incorporated a revised phylogenetic analysis of Eotyrannus. No significant support was found for Eotyrannus having a close evolutionary relationship to Juratyrant (J. langhami), known from the Late Jurassic of Dorset or indeed to the Late Jurassic early tyrannosauroid Stokesosaurus (S. clevelandi) from the western United States.

Instead, it is grouped with gracile, mid-sized tyrannosauroids that represent a more derived state than proceratosaurids, stokesosaurs and Juratyrant.

If megaraptoran dinosaurs are tyrannosauroids and therefore coelurosaurs, then this challenges long-held views on Theropoda classification and suggests that after the Early Cretaceous most of the hypercarnivore niches within dinosaur dominated ecosystems were increasingly occupied by coelurosaurs. It also suggests that tyrannosauroids were much more diverse and widespread during the Cretaceous than previously thought.

Eotyrannus remains a fascinating dinosaur, a genus that has led to new insights into the evolution and radiation of the Theropoda. It offers a tantalising glimpse into the ecology represented by the Wessex Formation deposits and how a mid-sized theropod co-existed with other, larger members of the ever-widening collection of Wessex Formation meat-eating dinosaurs.

Everything Dinosaur Helping to Fund Research

The authors wanted to make their paper available to everyone. To do this they set up a GoFundMe campaign to cover publishing costs. Everything Dinosaur assisted with the funding.

A spokesperson from Everything Dinosaur stated:

“We were happy to support this excellent paper and we helped to make such studies possible. Your purchases from Everything Dinosaur genuinely help science”.

The scientific paper: “The osteology and affinities of Eotyrannus lengi, a tyrannosauroid theropod from the Wealden Supergroup of southern England” by Darren Naish and Andrea Cau published in PeerJ.