Calcium Isotope Study Sheds Light on Lost World Dominated by Giant Predators

In the autumn of 2011, the BBC aired a new CGI-based dinosaur television series called “Planet Dinosaur”.  The first episode of this documentary series was entitled “Lost World” and focused on the remarkable fossil discoveries from Africa which shed light on ecosystems that seemed to be dominated by hypercarnivores (animals that have a diet that consists of more than 70 percent meat).  Viewers were introduced to giant meat-eating dinosaurs such as Carcharodontosaurus (C. saharicus) and the abelisaurid Rugops (R. primus) as well as super-sized, ancient crocodiles such as Sarcosuchus (S. imperator).  One of the questions posed in the television episode, was how could all these large predators co-exist?  Thanks to some fascinating research involving the study of vertebrate teeth from two famous African fossil deposits, scientists have been able to come with an answer.

Spinosaurus – Featured in Episode 1 “Lost World”

The documentary series highlighted the latest research on the Theropod Spinosaurus.

Picture Credit: Everything Dinosaur/BBC

A study of calcium isotopes in fossil teeth suggests that some large, carnivorous Theropods (carcharodontosaurids and abelisaurids) preferred to hunt terrestrial prey such as herbivorous dinosaurs, whilst others such as spinosaurids were mainly fish-eaters (piscivores).  The giant crocodile Sarcosuchus had a diet somewhere in between, consuming both terrestrial and aquatic prey.

Studying Fossil Remains from Niger and Morocco

Writing in the journal “The Proceedings of the Royal Society B (Biology)”, the researchers studied calcium in fossil remains from the famous Kem Kem deposits of Morocco and the Gadoufaoua deposits of Niger.  The research was conducted by the Laboratoire de géologie de Lyon : Terre, planètes et environnement (CNRS/ENS de Lyon/Claude Bernard Lyon 1 University), in partnership with the Centre for Research on Palaeobiodiversity and Palaeoenvironments (CNRS/French National Museum of Natural History/Sorbonne University).

The team set out to try and understand why there were comparatively few herbivores recorded compared to the number of large carnivores represented in the fossil material.  The French scientists examined the vertebrate fossils from the Gadoufaoua region of central Niger (part of the Elrhaz Formation, which dates from the Late Aptian to Early Albian stages of the Early Cretaceous).  These fossils represent a flood plain ecosystem that existed some 115-112 million years ago.  Vertebrate fossils from the geologically younger Kem Kem Beds of south-eastern Morocco were also studied.

The Kem Kem deposits, sometimes referred to as the Continental Red Beds, because of the abundance of red sandstone sediments, are difficult to interpret due to the amount of mixing of fossil material and re-deposition.  Dinosaur fossils from this locality are approximately 100 million years old (Cenomanian faunal stage of the Late Cretaceous).  The two sites are characterised by the overabundance of predators compared to herbivorous dinosaurs and to determine why, the researchers measured the proportions of different calcium isotopes in the fossilised remains (fish scales and tooth enamel).

Examples of Vertebrate Teeth from the Gadoufaoua Deposits (Niger)

Teeth from vertebrates represented by mid Cretaceous fossil material (Kem Kem and Gadoufaoua deposits).  Scale bar = 2 cm.

Picture Credit: Auguste Hassler / LGL-TPE / CNRS-ENS de Lyon-Université Lyon

The picture above shows examples of various vertebrate teeth associated with the Gadoufaoua deposit.  From left to right Sarcosuchus imperator (giant crocodile), a tooth from an indeterminate spinosaurid, a tooth from a non-spinosaurid Theropod (abelisaurid or carcharodontosaurid), a pterosaur tooth, a tooth from a hadrosaurid dinosaur (herbivore), the rounded and flattened tooth associated with a pycnodont (fish) and the tooth of a small crocodylomorph.

Tell-Tale Calcium

Among vertebrates, calcium is almost exclusively derived from food.  By comparing the isotopic composition of potential prey (fish and herbivores), with that of the teeth of carnivores, it is possible to map the probable diet of those meat-eaters.  The researchers found that the data from the two locations showed similar results.  Some large, meat-eating dinosaurs such as the carcharodontosaurids and the abelisaurids preferred to hunt terrestrial prey, whilst spinosaurids displayed a very distinctive isotopic signature indicating a marked preference for aquatic prey (fish).  Sarcosuchus, on the other hand, may have been more of a generalist.  Calcium isotope data showed that these large crocodiles fed on terrestrial as well as aquatic animals.

The Skull  and Jaws of Sarcosuchus

The huge skull of Sarcosuchus – a giant crocodile that preyed on terrestrial as well as aquatic prey.

Picture Credit: Patrina Malone

Resource Niche Partitioning

This study suggests that predators avoided direct competition by sharing food resources.  The distinctive taxonomic clustering in calcium isotope values recorded by the French researchers strongly supports the idea of niche partitioning, that is, different types of carnivore used the resources in the environment differently which enabled them all to co-exist.  The calcium isotope measurements allow palaeontologists to examine feeding evidence across a food chain within an ecosystem.  This research, if applied elsewhere, such as within other fossil Lagerstätte, may permit clarification of food chain roles and niche partitioning within numerous ancient palaeoenvironments.

The scientific paper: “Calcium Isotopes offer Clues on Resource Partitioning among Cretaceous Predatory Dinosaurs” by A. Hassler, J. E. Martin, R. Amiot, T. Tacail, F. Arnaud Godet, R. Allain, V. Balter published in The Proceedings of the Royal Society B.

Yorkshire and Pregnant Ichthyosaurs

Yorkshire might be famous for its beautiful countryside, its puddings and of course, its cricket team, but this part of England also has some remarkable geology.  Through the Vale of Pickering to the North Sea, there are magnificent exposures of Mesozoic-age rocks.  Parts of the Yorkshire coast are a haven for fossil hunters and much of the coastal area of “God’s own country”, as many Yorkshire residents call their county, provides the geological standard for comparing less well exposed areas inland and also for the geology of the North Sea basin.  Yorkshire Museum has recently opened permanent galleries that tell the amazing story of Yorkshire’s prehistoric past and a star exhibit is a fossil block that contains the remains of several Ichthyosaur embryos.

An Illustration of the Pregnant Ichthyosaur

A pregnant pause in deep time. Fossilised Ichthyosaur embryos have been found in Yorkshire.

Picture Credit: Nobumichi Tamura (Manchester University)

Ichthyosaurs – Superbly Adapted Marine Reptiles

Ichthyosaurs were marine reptiles that superficially resembled dolphins.  They evolved during the Triassic and numerous different genera have been named.  Fossils of Ichthyosaurs have been found in many parts of the world, the first marine reptile to be scientifically described was an Ichthyosaur.  The fossilised remains were discovered at Lyme Regis on the Dorset coast and this animal was later identified as a specimen of a giant “fish lizard” known as Temnodontosaurus platyodon.  Superbly adapted to a marine existence, Ichthyosaurs had streamlined bodies, steered with their front flippers and propelled themselves through the water with their powerful tails.  These reptiles gave birth to live young (viviparous), rather than returning to land to lay eggs.

A Trio of Ichthyosaurs

Dolphin-like prehistoric animals, the Ichthyosaurs were a highly successful group of marine reptiles.

An Important Ichthyosaur Specimen

The Yorkshire Museum Ichthyosaur specimen, complete with the remains of between six and eight tiny embryos between its ribs, was collected from the Whitby area of North Yorkshire back in 2010.  We at Everything Dinosaur, suspect that the fossil was found in sediments that make up the Whitby Mudstone Formation.  The fossil was in the possession of a local collector, Martin Rigby, he thought the block could contain the remains of unborn Ichthyosaurs and this was confirmed when the specimen was examined by palaeontologists from the University of Manchester.   The specimen consists of a polished block which exposes several large ribs of the mother and numerous strings of tiny vertebrae and small bones that constitute the remains of the unborn “fish lizards”.  The fossil has been acquired by the Yorkshire Museum and forms an integral part of the Museum’s new permanent exhibition “Yorkshire’s Jurassic World”.

Rare British Fossil Revealing Embryos

Only five Ichthyosaur specimens from the British Isles have ever been discovered with embryos preserved and never before has a British Ichthyosaur fossil been found with so many.  All five known specimens were collected from Jurassic-aged rocks in the south-west of England, they are aged between 200 to 190 million years old.  However, the Yorkshire specimen, heralds from younger Jurassic sediments dating from the Toarcian faunal stage of the Early Jurassic.   It is around 180 million years old.

Commenting on the significance of the discovery Manchester University palaeontologist Mike Boyd, who along with colleague Dean Lomax, studied the specimen, stated:

“We also considered the possibility that the tiny remains could be stomach contents, although it seemed highly unlikely that an Ichthyosaur would swallow six to eight aborted embryos or new-born Ichthyosaurs at one time.  This does not seem to have been the case, because the embryos display no erosion from stomach acids.  Moreover, the embryos are not associated with any stomach contents commonly seem in Early Jurassic Ichthyosaurs, such as the remains of squid-like Belemnites”.

Eight different species of Ichthyosaur have been documented with embryos.  By far, the most commonly found Ichthyosaur genus with embryos is Stenopterygius.  Over a hundred specimens of Stenopterygius from the Holzmaden area of southern Germany have been found with embryos, ranging from one to eleven in number.

Co-author of the scientific paper and visiting scientist at the University of Manchester, Dean Lomax added:

“The German sites are approximately the same age as the new specimen from Whitby and it is possible that the new specimen is also Stenopterygius, but no identifiable features are preserved in the adult or embryos.  Nonetheless, this is an important find.”

A Cast of a Stenopterygius Specimen with an Embryo Expelled (Possibly Post Mortem)

Stenopterygius Ichthyosaur fossil originally from Germany.  Expelled embryo is indicated by the white arrow.

Picture Credit: Everything Dinosaur

Everything Dinosaur has been selected by the Yorkshire Museum to help supply prehistoric animal themed craft materials in support of the Museum’s outreach activities.  In addition, the UK-based company has supplied dinosaur and marine reptile themed merchandise to the Yorkshire Museum’s retail outlet.

Commenting on the permanent exhibition and the significance of the Manchester University research, a spokesperson from Everything Dinosaur stated:

“It is fantastic to see a museum celebrating the fossil heritage of Yorkshire and the research undertaken by the dedicated scientists at Manchester University has helped to give the opening of the permanent galleries even greater significance.”

The scientific paper: “The Youngest Occurrence of Ichthyosaur Embryos in the UK: A New Specimen from the Early Jurassic (Toarcian) of Yorkshire” by Boyd, M. J. and Lomax, D. R. (2018) published in the Proceedings of the Yorkshire Geological Society.