Pannoniasaurus inexpectatus – The Unexpected Mosasaur

A joint team of Hungarian and Canadian scientists have unearthed a new species of mosasaur, one that as far as the known fossil record goes, was unique amongst the Mosasauridae – it lived in freshwater.  It seems that just like some species of extant cetacean (whales and dolphins), one group of mosasaurs adapted to living in a freshwater environment.  There are river dolphins that live in the Amazon and other riverine habitats such as, until recently, the Yangtze river (Yangtze river dolphin believed to be extinct).  Now scientists have the fossilised remains of several freshwater mosasaurs to study, a number of individuals, all of which have been assigned to a new species – Pannoniasaurus inexpectatus.

Freshwater Mosasaur

Mosasaurs are members of the Order Squamata (lizards and snakes), they evolved from terrestrial reptiles but they adapted to marine environments and rapidly diversified with many different genera and something approaching eighty different species being recognised.  Mosasaurs were typically streamlined, with long, narrow jaws, four paddles and possibly a fish like tail, (new evidence suggests that some mosasaurs had tail fins like those found on extinct ichthyosaurs and extant dolphins).  As vertebrates; their backbones became specially adapted to undulate in an up and down motion to aid propulsion through water.  Some of these marine lizards evolved into giant forms such as Tylosaurus and Hainosaurus which could have been as much as fifteen metres in length.

It seems that these reptiles, whose closest living relatives today are thought to be the monitor lizards (Varanus), evolved around ninety million years ago and spread throughout the world’s oceans before dying out approximately around 25 million years later.

Pannoniasaurus inexpectatus

The holotype fossil material, plus over one hundred Pannoniasaurus fossils so far collected from the location come from alluvial (floodplain and channel) deposits which form a section of the  Csehbánya Formation of Cretaceous aged strata.  The fossils which include juveniles and bones from specimens which may have exceeded six metres in length come from various exposures at the Iharkút open-pit bauxite mine in Hungary.

An Illustration of the Skeleton of P. inexpectatus

The mosasaur that lived in freshwater.

Picture credit: PLoS One/Makádi et al

It is thought that this river mosasaur had a similar body shape to other mosasaurs as well as long, narrow, crocodile-like jaws.  Palaeontologists believe that this genus represents a basal member of the Mosasauridae, it may have retained feet with clawed toes that were capable of moving the animal about on land.  However, no lower limb bones have been found to date.  The flattened skull, may have been a useful adaptation for water-level hunting and the ambushing of terrestrial animals such as small dinosaurs that came close to water’s edge.

The research team speculate that more robust limbs with claws may have been retained by these mosasaurs as they could have used their feet and claws to clamber over the bottom of the river just as extant crocodiles do today.  At six metres in length [about the size of a modern-day Nile crocodile (Crocodylus niloticus)], these mosasaurs were the largest predators within this Late Cretaceous river environment.

Virtually all the other known mosasaur fossils have been found in strata which was laid down in marine environments.  Previously, the only exception to this was some fragmentary fossils of the marine, nektonic mosasaur known as Plioplatecarpus which was discovered in non-marine rocks in Western Canada (Alberta).  The Plioplatecarpus remains include teeth and a partial vertebra collected from the a mudstone unit in the middle of the Lethbridge Coal Zone.

These bones could have been re-deposited there after a tsunami or other flood event, or perhaps they represent individuals who went upstream from estuaries in a similar way to modern Bull sharks.

The genus name for this new mosasaur comes from the ancient Roman province of “Pannonia”, which contained this part of Hungary, the specific name “inexpectatus” means unexpected in Latin, a reference to the surprising occurrence of  mosasaur fossils in a non-marine palaeoenvironment.

A More Typical Mosasaur (Marine Reptile Museum Exhibit)

Fossil material from the freshwater mosasaur Pannoniasaurus inexpectatus.

Picture credit: PLoS One/Makádi et al

The size of the individual fossil bones collected so far indicate that these bones represent a number of differently-sized creatures.  The smallest seem to have been less than a metre in length, the average overall length would have been around three to four metres.  This suggests that many animals of various sizes and ages were present together living in these prehistoric rivers.

Everything Dinosaur supplies a wide variety of marine reptiles including replicas of mosasaurs: Papo Marine Reptiles, Dinosaurs and Prehistoric Animal Figures.

In the paper, published in the on line scientific journal PLoS One (Public Library of Science), the research team state that their studies suggest no fossilisation bias and that the Pannoniasaurus fossils probably represent the population quite accurately.  This suggests that a population of these reptiles was living in the river system, it is unlikely that the fossils ended up in non-marine strata as mosasaurs migrated upstream to take advantage of seasonal food opportunities or in order to give birth in freshwater rather than in the open sea.

This part of Europe during the Late Cretaceous consisted of a series of tropical islands, other fossils found in the Csehbánya Formation include fish, amphibians, crocodiles, turtles, several dinosaur genera, pterosaurs and birds.

The scientific paper: “The First Freshwater Mosasauroid (Upper Cretaceous, Hungary) and a New Clade of Basal Mosasauroids” by László Makádi, Michael W. Caldwell and Attila Ősi published in PLoS One.

Pauline avibella – A new Species of Silurian Ostracod named after Professor’s Wife

It may be difficult to believe, especially after the sub-zero temperatures endured by many people in the United Kingdom over recent days, but once the landmass that was to form England sat much closer to the equator than it does today.  Back in the Silurian, much of the land that we now know as the UK was underwater, part of an extensive, shallow sub-tropical sea that marked the boundary between two landmasses, Laurentia in the west and Baltica in the north.  Scientists from the University of Leicester (East Midlands), have identified a new species of crustacean, an animal that lived in this warm, shallow sea something like 425 million years ago.

Silurian Ostracod

The one centimetre long shelled creature had been found in rocks in Herefordshire, from a site that University of Leicester researchers describe as a “treasure trove” of fossil material.  It seems that part of the sea bed had been covered by a fine layer of volcanic ash as a volcano to the west erupted.  This ash layer buried much of the lifeforms that existed in the area at the time, preserving their bodies and hard shells in exquisite detail.  The fossils have soft tissue and even components such as eyes and mouth parts have been preserved.

Pauline avibella

Professor David Siveter, who led the research, has named the new species Pauline avilbella in honour of his late wife who supported him throughout his career.  Ostracods are relatively abundant in the fossil record.  These primitive shelled arthropods of the Order Crustacea are related to crabs, lobsters, barnacles and shrimps.  The fossils of these tiny creatures first appear in Cambrian rocks and although these creatures first evolved in a marine environment, many modern species can be found in freshwater.  Like all Arthropoda, these animals have bilateral symmetry and their paired body parts are usually enclosed in a hinged, bivalve-like shell made of magnesium calcite.  One piece of the shell structure is normally bigger than the second part of the shell and these shells are commonly preserved in the fossil record, however, being able to identify soft tissue parts in Silurian aged fossils is extremely rare.

A Computer Generated Image of the New Ostracod Species

425 million year old Ostracod with a shell shaped like a “bird’s wing”.

Picture credit: Press Association/University of Leicester

An Important Discovery

Commenting on the new species, Professor Siveter, the lead author of the scientific paper, stated that this was a very important discovery as it represented one of only a handful of fossil Ostracods with the soft-tissues preserved.  The species name “avibella” was chosen as the two piece shell resembles the shape of a bird’s wing.  Most Ostracod shells are kidney or bean shaped, but this particular shallow water species had a shell that was swept back, similar to the shape of the wing of a bird.  The name “avibella” means “beautiful bird”.

The process of extracting the tiny microfossils from the surrounding limestone matrix involves slowly grinding the specimen down, micron by micron with scanning photographs taken at each stage.  When the mechanical process is completed the data is fed into a powerful computer which can produce a detailed three-dimensional image of the organism, including its delicate soft body parts.  With each specimen more than five hundred images were produced, resulting in an extremely detailed picture of the organism – a sort of “virtual fossil”.

Diversity of Marine Fauna During the Silurian

The work of the Leicester University based team is helping scientists to understand the diversity of benthic (animals and plants that live on the sea floor), marine fauna during the Silurian period, an important period in the evolution and diversity of marine organisms as rising sea levels created a number of warm, shallow sea environments and fauna was almost entirely restricted to marine habitats.

For figures and replicas of iconic animals from the fossil record such as famous invertebrates like ammonites and trilobites: Ammonites, Belemnites, Trilobites and Other Prehistoric Animal Models (CollectA).