Fossil Sea Urchin Preserves Evidence of an Attack from a Mosasaur

Sixty-six million years ago, in a shallow sea in what is now Denmark, a sea urchin lay partially submerged on the seabed, when a keen-eyed mosasaur spotted it and went in for the kill.  The marine reptile grabbed the sea urchin and bit it, but for some reason, the attack was aborted, the invertebrate was dropped and the little sea urchin survived the encounter with the apex predator.  How do we know all this?  A remarkable fossil has been discovered by amateur geologist Peter Bennicke at Stevns Klint, a famous UNESCO World Heritage Site, one of the few places in the world where rock layers mark the Cretaceous-Palaeogene boundary providing evidence to support the extra-terrestrial impact event that contributed to the demise of the Dinosauria.

Fossil Provides Evidence of a Mosasaur Attack

Picture credit: Everything Dinosaur

Preserving Evidence of Predator/Prey Interactions

The stretch of chalk cliffs at Stevns Klint on the Danish island of Zealand (Sjaelland), was granted World Heritage Site status by UNESCO in 2014.  The chalk deposits record the K/T boundary and the cliffs provide a record of the faunal turnover from the very end of the Cretaceous (Maastrichtian faunal stage), through to the earliest stage of the Palaeogene Period (Danian faunal stage).  Sea urchin fossils are relatively common at this location, but the specimen found by Mr Bennicke is very special as it records evidence of predator/prey interaction.

The curator at the nearby Geomuseum Faxe, Jesper Milàn stated:

“It’s really an exciting find this, not only is there an exciting story to tell about it, but it also provides important information about how the animals in the Cretaceous sea lived and who ate who.  It is such a find that helps put meat and blood on the otherwise dry fossils, when you can suddenly see such a small everyday drama caught in the stone.”

The Echinocorys Specimen Showing Evidence of a Mosasaur Attack

Picture credit: Jesper Milàn

What Type of Mosasaur Attacked the Sea Urchin?

The round tooth marks are located near the top of the Echinocorys specimen, suggesting that the attack came from above and it is likely that the sea urchin was partially exposed out of the sediment on the sea floor when the attack occurred.  An examination of the morphology of the tooth marks and their spacing indicates that the attacker had slender teeth, that were circular in cross-section and that these teeth were spaced relatively far apart in the jaw.  Two types of hypercarnivorous mosasaurids are known from Denmark – Mosasaurus hoffmanni and Plioplatecarpus spp.  It could be speculated that one of these types of mosasaur was responsible for the attack.

A Mosasaurid Specimen is Used to Demonstrate the Sea Urchin Attack

Picture credit: TV OST

Lucky Escape for the Sea Urchin

Although a mosasaurid grabbed the sea urchin, it apparently abandoned the attack.  Hypercarnivores such as M. hoffmanni and Plioplatecarpus probably preyed on a variety of vertebrates and invertebrates, but their teeth are not really suited to crushing the shell of an Echinocorys.  Recently, Jesper Milàn in collaboration with other scientists, reported the discovery of a single broken tooth of a mosasaur called Carinodens minalmamar.  The tooth crown was found in the uppermost Maastrichtian chalk strata at Stevns Klint,  indicating that this mosasaur probably lived around 50,000 years before the deposition of the iridium rich K/Pg boundary material.  The shed tooth is reported to have come from the 11th or 13th position in the jaw.  The tooth represents the northernmost occurrence of the genus Carinodens found to date.  Carinodens minalmamar, was a very different type of predator compared to Mosasaurus hoffmanni and Plioplatecarpus, it was a specialist shell-eater (durophagus).  The short, thick and rounded teeth  of this type of mosasaur would have made quick work of the test of an Echinocorys.

Examples of the Teeth of Carinodens spp.

Picture credit: Holwerda and Jagt

The sea urchin may count itself fortunate to have been attacked by a mosasaur more used to catching fish, sea birds and other marine reptiles.  If a mosasaur such as Carinodens had grabbed the Echinocorys, then it is likely that the sea urchin would not have survived.

An exhibit telling the story of the sea urchin and who tried to eat it will open at the Geomuseum Faxe in February 2019.

To read an article about Stevns Klint being granted UNESCO World Heritage Site status: Famous KT Boundary gets UNESCO World Heritage Site Status.

For models and replicas of mosasaurs and other prehistoric marine reptiles: PNSO Age of Dinosaurs Figures.

Soft-tissue Evidence for Warm-blooded Ichthyosaurs

The fossilised remains of a beautifully-preserved ichthyosaur fossil from the Lower Cretaceous of Germany has revealed that “fish lizards” had blubber just like many modern, mammalian marine animals.  In addition, the fossil is so well-preserved that some of the soft-tissue associated with the specimen have retained some of their original pliability.  The fossil is an example of Stenopterygius, (MH 432; Urweltmuseum Hauff, Holzmaden, Germany) and it demonstrates aspects of convergent evolution showing how ichthyosaurs adapted to a marine environment in remarkably similar ways to what is seen in modern cetaceans.

Specimen Number MH 432 – The Partial Skeleton of a Stenopterygius Ichthyosaur with an Accompanying Line Drawing

Picture credit: Johan Lindgren

The marine reptile lived in what is southern Germany today, during the Jurassic Period approximately 180 million years ago.  At that time, the reptile, which was probably around two to three metres in length, swam in a vast, shallow ocean that was then covering large parts of present-day Europe.

Johan Lindgren, a senior lecturer in the Department of Geology (Lund University, Sweden), led the international collaboration that resulted in the most comprehensive and in-depth examination of a soft-tissue fossil ever undertaken.  Among other things, the study revealed that the soft parts had fossilised so rapidly that both the original cells and their internal contents were preserved.

The international research team identified blubber under the smooth skin that lacked scales.  Traces of internal organs were also analysed.

Dr Lindgren observed:

“You can clearly see both the body outline and remains of internal organs.  We can even distinguish the different cellular layers within the skin.”

Finding Evidence of Blubber Under the Skin

The researchers identified blubber underneath the skin.  To date, such specialised fat-laden tissue has only been found in modern marine mammals and adult individuals of the Leatherback sea turtle (Dermochelyidae coriacea).  The discovery of blubber suggests that ichthyosaurs had metabolic rates that were higher than those of typical extant reptiles.  It suggests a degree of homeothermy in the Ichthyosauria.  In essence, these reptiles were able to sustain an internal body temperature regardless of how cold the water was they were swimming in.

The results from this study could help to explain why the Ichthyosauria had such a large geographical range during the Mesozoic.  These creatures, that first evolved in the Triassic and died out some 80 million years ago, had an almost global distribution, even in cold waters.  Their layer of blubber would have helped them to dive very deep, perhaps diving to the deepest parts of the Epipelagic zone of the ocean or even into the Mesopelagic zone (diving down more than 220 metres).

Comparing Pressure and Heat Treated Porpoise Blubber to Ichthyosaur Fossil Blubber

Picture credit: Johan Lindgren and Martin Jarenmark

The team of international scientists also examined remains of the animal’s liver, which included part of the original biochemistry (eumelanin pigment and haemoglobin residues).

Dr Lindgren stated:

“It’s truly remarkable that the biomolecules we discovered so closely match the tissues that we could identify.”

In the study, the researchers also succeeded in showing that the fossil contains tissues that still retain some of their original pliability, even though 180 million years have passed since the animal died and sank to the bottom of the sea.  The team used chemicals to remove the mineral phase of the specimen, the inorganics that once turned the animal carcass into a petrified fossil.  Subsequent tests revealed that the soft tissues still retained a degree of elasticity.

Ichthyosaurs Had Counter Shading

A study of the melanophores and their distribution across the body indicates that ichthyosaurs possessed countershading.  They were darker on top, but lighter underneath.  The upper part of the body was dark, this may have helped the animal to warm up rapidly at the surface after a deep dive.  The dark colouration would absorb more energy from the sun.  In addition, the dark upper part of the body would provide a degree of UV protection and the countershading would have provided effective camouflage.  Many, living large pelagic (actively swimming), animals exhibit countershading.

A Model of an Ichthyosaur Showing Countershading

The model (above) is from the Safari Ltd range of figures.

To view this range of models: Wild Safari Prehistoric World Models.

Identifying Pigment Cells (Melanophores) in Fossil Material

Picture credit: Mats E. Eriksson, Federica Marone and Ola Gustafsson

Improving our Knowledge of Taphonomy

The research team conclude that this fossil has provided some remarkable insights into ichthyosaur anatomy and biology.  The study also reveals how much more we have to learn about the process of fossilisation (taphonomy).  The beautifully-preserved Stenopterygius fossil demonstrates a number of adaptations that ichthyosaurs share with other, living marine creatures such as the Leatherback turtle and toothed whales such as dolphins and porpoises.  Ever since the first outlines of preserved soft tissue were recognised in ichthyosaurs, scientists have commented on their superficial resemblance to modern cetaceans.  Thanks to this new study, it seems that this resemblance goes a lot further than was previously thought.

A Close-up View of Fossilised Skin (Stenopterygius)

Picture credit: Johan Lindgren

The scientific paper: “Soft-tissue Evidence for Homeothermy and Crypsis in a Jurassic Ichthyosaur” by Johan Lindgren, Peter Sjövall, Volker Thiel, Wenxia Zheng, Shosuke Ito, Kazumasa Wakamatsu, Rolf Hauff, Benjamin P. Kear, Anders Engdahl, Carl Alwmark, Mats E. Eriksson, Martin Jarenmark, Sven Sachs, Per E. Ahlberg, Federica Marone, Takeo Kuriyama, Ola Gustafsson, Per Malmberg, Aurélien Thomen, Irene Rodríguez-Meizoso, Per Uvdal, Makoto Ojika and Mary H. Schweitzer.  The paper is published in the journal Nature.

Everything Dinosaur acknowledges the assistance of a press release from Lund University in the compilation of this article.

Visit the Everything Dinosaur website: Everything Dinosaur.

Weewarrasaurus pobeni – Hints at Different Kinds of Dinosaur Communities

The fortuitous discovery of pieces from the lower jaw of a small, plant-eating dinosaur is helping scientists to discover more about the Cretaceous dinosaurs that once roamed Australia.  Writing in the academic journal “PeerJ”, the researchers provide evidence to support the idea that there were numerous small-bodied ornithopods at high latitudes in south-eastern Australia, whilst further north, in what would have been slightly warmer environments, these types of dinosaurs co-existed with much bigger ornithopods and titanosaurs.

The dinosaur has been named Weewarrasaurus pobeni (pronounced wee-whah-rar-sore-us poe-ben-eye) and it is the first new dinosaur to be described from New South Wales for nearly 100 years.

A Life Reconstruction of the Newly Described Gondwanan Ornithopod Weewarrasaurus pobeni

Picture credit: James Kuether

A Lucky Fossil Find

Adelaide-based opal buyer Mike Poben spotted the fossil pieces in a bucket of opal rubble from the Wee Warra opal field at Lightning Ridge (New South Wales, Australia).  The dinosaur was named in honour of the location and the trivial name recognises the contribution of Mr Poben who donated the specimens for research.

Numerous opalised dinosaur fossils are known from the Lightning Ridge area.  The material, including fragments of bones and isolated teeth come from the Griman Creek Formation.  Recent radiometric dating indicates that these deposits are around 100 to 96 million years old (Cenomanian stage of the Late Cretaceous), making these rocks some 10 million years younger than equivalent exposures containing dinosaur fossils found in northern Queensland.

The Fossil Jaw Fragments (Right Dentary) of Weewarrasaurus pobeni

Picture credit: PeerJ

Unfortunately, the underground mining process involves breaking up the rocks, so any specimens found tend to consist of isolated broken pieces, however the presence of a scalloped-shaped tooth in the object immediately caught the attention of Mr Poben, so he was able to quickly appreciate that this was part of a jawbone.  Lightning Ridge is the only place in the world where dinosaur bones and teeth routinely turn to opal.  Corresponding author of the scientific paper, Dr Philip Bell (University of New England), explained that researchers were now looking into acquiring more fossil material from opal mines.

Dr Bell stated:

“Unfortunately, the fossil remnants we see are almost always part of mining spoil… but on another hand, we would never get to see even those fragments if it wasn’t for mining.”

Opal Helps to Identify a Dinosaur

One of the benefits of the presence of opal in the fossil is that the distinctive banding pattern formed helped the scientists to identify that the two fossil pieces belonged to the same jawbone.

Views of the Jawbone Fossil (Weewarrasaurus pobeni)

Picture credit: PeerJ/Dr Bell (University of New England)

The picture above shows three views of the fossils, (A), medial; (B), dorsal; and (C) lateral views.   The dashed black line shows the outline of the missing pieces that would have comprised a more substantial part of the dentary.  The dashed red lines indicate the distinctive banding pattern in the opal used to estimate the extent of the missing area.  Another jawbone fragment (LRF 766), representing a right dentary with teeth in situ from the nearby Three Mile opal field has also been assigned to this new dinosaur species.

Faunal Differences in Different Regions of Prehistoric Australia

The Griman Creek Formation fossils from Lightning Ridge indicate that there were numerous small Ornithopods living in this environment during the Cenomanian stage of the Late Cretaceous.  This research provides further evidence to support previous studies that favour a general abundance of small-bodied basal Ornithopods in high-latitude localities of south-eastern Australia.  These little dinosaurs, most of which were under two metres in length, inhabited a verdant flood plain, but this part of the Gondwana was at approximately 60 degrees south.  Today, Australia is much further north, the city of Sydney (New South Wales), is located at approximately 33.86 degrees south.  During the Cretaceous, the dinosaurs that inhabited the part of Australia we now call New South Wales, would have had to endure periods of darkness in the year when the sun dipped below the horizon, although the presence of ectothermic reptiles such as crocodyliforms and turtles indicate that average minimum temperatures may not have fallen below 5 degrees Celsius.

Even so, the climate may have been too extreme for sauropods.  Cretaceous deposits in Queensland (Winton Formation), have revealed several titanosaurs, but the colder temperatures experienced further south may have limited sauropod distribution.

The researchers conclude that although future dinosaur fossil discoveries have the potential to alter these interpretations, it is suggested that the Griman Creek Formation at Lightning Ridge occupied a “meeting point” between more northern sauropod-dominated faunas and the ornithopod-dominated faunas that existed further south.

Computer Generated Images from Fossil Scans Helped to Identify Ornithopod Characteristics

Picture credit: PeerJ

To read a recent article about an opalised dinosaur toe bone found in South Australia: Lost Dinosaur Toe Bone Turns Up on the Internet.

Visit the award-winning Everything Dinosaur website: Everything Dinosaur.