The earliest ichthyosaur fossil specimen discovered to date has been found on the Arctic island of Spitsbergen. The fossil represents a marine reptile that lived around 252 million years ago. The bones indicate that this animal was not a transitional form, but a fully adapted marine reptile.

Picture credit: Esther van Hulsen

Ichthyosaur Evolution

The evolutionary history of the ichthyosaurs remains contentious. No transitional forms representing land-dwelling tetrapods adapting to a marine habit have been found. However, small, basal ichthyosauriforms are known from the Lower Triassic of China, and the fossils of at least one, primitive Early Triassic, dolphin-shaped member of the Ichthyopterygia has already been described from Spitsbergen (Grippia longirostris).

Thanks to the work of a joint team of Swedish and Norwegian palaeontologists a fresh perspective on the origins of the “fish lizards” is provided by these newly described fossil bones.

Picture credit: Everything Dinosaur

For models and replicas of typical ichthyosaurs and other marine reptiles: Wild Safari Prehistoric World Models.

The Ichthyopterygia (Ichthyosauria)

Ichthyosaurs were a highly successful, globally distributed group of marine reptiles. The evolved, a “dolphin-like” streamlined body and were active, nektonic predators surviving into the Late Cretaceous.

The first marine reptiles, such as the mesosaurs evolved during the Early Permian. The end-Permian mass extinction event devasted both terrestrial and marine faunas. The cataclysmic event was thought to have led to an evolutionary reset which permitted animals such as the Ichthyosauria to evolve, exploiting niches vacated after the extinction event.

Tetrapods (land-based vertebrates), invaded shallow coastal environments to take advantage of marine predator niches that were left vacant after the mass extinction event. Over millions of years, these early amphibious reptiles became more efficient at swimming and eventually modified their limbs into flippers, developed a ” dolphin-like” body plan, and started giving birth to live young (viviparity). With the evolution of viviparity, there was no need to come ashore in order to lay eggs, so the last ties these creatures had with a terrestrial existence was lost.

The newly described fossil material from Spitsbergen is helping to revise and re-write this previous hypothesis.

Picture credit: Benjamin Kear

Flower’s Valley Fossils

On western Spitsbergen a valley (Flower’s Valley), cuts deep into the surrounding mountains and provides access to Lower Triassic marine sediments, approximately 250 million years old. The rocks represent mud deposited at the bottom of an ancient sea and snow melt has gradually eroded the mudstone exposing rounded limestone boulders known as concretions. These objects are formed from limey sediments that coalesced around decomposing animal remains, subsequently preserving them in amazing, three-dimensional detail.

In 2014, the field team removed a number of concretions from the Flower’s Valley site. The rocks were taken back to the Natural History Museum at the University of Oslo for further study.

Scientists from The Museum of Evolution at Uppsala University have identified bony fish remains and bizarre “crocodile-like” amphibian bones, together with 11 articulated caudal vertebrae from an ichthyosaur.

Found in Rocks Thought to be Too Old for Ichthyosaur Fossils

Surprisingly, these tail bones occurred within rocks that were supposedly too old for ichthyosaurs. Also, the fossil bones do not represent a transitional form, but they show characteristics associated with geologically younger ichthyosaurs.

The vertebrae are identical to those of geologically much younger, larger-bodied ichthyosaurs, and even preserve internal bone microstructure showing adaptive hallmarks of fast growth, elevated metabolism and a fully oceanic lifestyle.

Picture credit: Øyvind Hammer and Jørn Hurum

Dating the Surrounding Rock (Geochemical Testing)

Geochemical testing of the surrounding matrix dated the age of the fossils at approximately two million years after the end-Permian mass extinction. When the estimated timescale of marine reptile evolution is considered, this suggests the origins and early diversification of the Ichthyosauria took place during the Permian and prior to the Mesozoic Era.

These fossils suggest that the popular hypothesis of ichthyosaurs evolving to exploit niches vacated as a result of the end-Permian mass extinction is incorrect. Ichthyosaurs were present prior to the end of the Permian.

The discovery of the oldest ichthyosaur rewrites the popular vision of Age of Dinosaurs (Mesozoic Era), as the emergence timeframe of major reptile lineages. It now seems that at least some groups predated this landmark interval, with fossils of their most ancient ancestors still awaiting discovery in even older rocks on Spitsbergen and elsewhere in the world.

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

The scientific paper: “Earliest Triassic ichthyosaur fossils push back oceanic reptile origins” by Kear, B.P., Engelschiøn, V.S., Hammer, Ø., Roberts, A.J. and Hurum, J.H. published in Current Biology.

New research suggests maniraptoran theropod dinosaurs possessed a propatagium. The propatagium (pronounced pro-pah-ta-gee-um), is a soft tissue structure that joins the wrists and shoulders of volant birds. It helps with the wing flapping motion and provides a leading edge to the wing. Without this structure, birds could not fly.

Propatagia in Maniraptoran Dinosaurs

If members of the Maniraptora, such as Therizinosaurus, Velociraptor, Oviraptor and troodontids had a propatagium on each arm, this would change how these dinosaurs are depicted. Many existing models and replicas would not be accurate and these figures would require updating.

The Propatagium

Modern volant birds have a propatagium. A specialised wing structure, without which they would not be able to fly. The evolutionary origins of the propatagium remain uncertain, but new research led by scientists at the University of Tokyo (Japan), is helping to fill some of the gaps. By conducting a statistical analysis of the arm joints associated with the fossilised remains of some dinosaurs, the researchers have concluded that a propatagium was present in certain theropod dinosaurs on the dinosaur/bird evolutionary lineage.

Propatagia are also known in other volant vertebrates – the bats and pterosaurs. These structures are examples of convergent evolution. Anatomical traits arising as animals adapt in similar ways to similar selective pressures.

Birds Evolved from Dinosaurs

Most scientists agree that birds evolved from maniraptoran dinosaurs. It therefore seems appropriate to look for avian traits within the Dinosauria, such as the presence of feathers, strong but light bones, and inner ears that help with balance and spatial awareness.

The University of Tokyo’s Department of Earth and Planetary Science wanted to try to see if evidence for the propatagium could be found in the non-avian dinosaur fossil record. The propatagium contains a muscle which connects the wrist to the shoulder and the research team set about trying to find evidence for this soft tissue structure in the fossilised remains of maniraptoran dinosaurs.

Co-author of the paper, published in the journal “Zoological Letters”, Associate Professor Tatsuya Hirasawa explained:

“It [the propatagium] is not found in other vertebrates, and it’s also found to have disappeared or lost its function in flightless birds, one of the reasons we know it’s essential for flight. So, in order to understand how flight evolved in birds, we must know how the propatagium evolved. This is what prompted us to explore some distant ancestors of modern birds, theropod dinosaurs.”

Studying Theropod Dinosaurs

Theropod dinosaurs such as Giganotosaurus, Tyrannosaurus rex and Velociraptor had arms, not wings, although some theropods such as the dromaeosaurid Microraptor were capable of flight. If the researchers could find evidence of early examples of the propatagium within non-avian dinosaurs, they would gain a better understanding of how some Dinosauria gradually transitioned from having arms to evolving wings.

Unfortunately, a soft tissue structure such as a propatagium would only be preserved in exceptional circumstances. Hard, mineralised parts of the body such as bones have a far greater fossilisation potential. Perhaps the bones of fossilised dinosaurs could provide a clue?

Co-author of the study, Yurika Uno (University of Tokyo) explained:

“The solution we came up with to assess the presence of a propatagium was to collect data about the angles of joints along the arm, or wing, of a dinosaur or bird.”

Studying Joint Angles

The presence or lack of a propatagium could be inferred by examining the angles of the joints in the arm in articulated fossil specimens. The way arm joints are articulated in fossils gives away the presence or absence of the propatagium structure. Thus the researchers could provide indirect evidence demonstrating the evolution of the avian wing structure.

The graduate student added:

“In modern birds, the wings cannot fully extend due to the propatagium, constraining the range of angles possible between connecting sections. If we could find a similarly specific set of angles between joints in dinosaur specimens, we can be fairly sure they too possessed a propatagium. And through quantitative analyses of the fossilised postures of birds and nondinosaurs, we found the tell-tale ranges of joint angles we hoped to.”

A Focus on the Maniraptora

The researchers postulate that the propatagium likely evolved in a group of dinosaurs known as the maniraptoran theropods. The Maniraptora clade is composed of coelurosaurian dinosaurs and is defined as including all birds and the non-avian dinosaurs that were more closely related to birds than they were to Ornithomimus velox.

Close examination of the fossilised remains of the oviraptorosaurian Caudipteryx and the winged dromaeosaurian Microraptor indicate the presence of propatagia. The researchers suggest that they have found evidence for the presence of a propatagium in dinosaurs that existed prior to the evolution of flight in the maniraptoran lineage.

Why Did the Propatagium Evolve?

If maniraptoran dinosaurs had propatagia prior to the evolution of powered flight, then this raises an intriguing question. Why did the propatagium evolve? Why did these particular theropods evolve such a structure?

The University of Tokyo researchers are optimistic that by studying more fossils as well as embryonic development within extant vertebrates they might be able to provide some answers.

The team thinks some theropods might have evolved the propatagium not because of any pressure to learn to fly, as their forelimbs were made for grasping objects and not for flying. The propatagium originally had another purpose. It could be speculated that this “leading edge” of the arm evolved to help amplify visual intraspecific communication. Perhaps it evolved as a soft tissue structure used in display to demonstrate fitness for breeding and to win mates.

An enlarged surface area of the forelimb might have played a role in helping to shade eggs or perhaps play some other role in the brooding process.

Finding fossil evidence to support these suggestions is likely to prove difficult. However, if further studies demonstrate the presence of propatagia in the Maniraptora, it will change the way these types of dinosaurs are depicted.

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

The scientific paper “Origin of the propatagium in non-avian dinosaurs” by Yurika Uno and Tatsuya Hirasawa published in Zoological Letters

Carboniferous chimaeras were suction feeders unlike their modern relatives such as the rat fish which are durophagous (feed on hard-shelled prey such as crabs, snails and molluscs). That is the conclusion of new research published this week in the academic journal The Proceedings of the National Academy of Sciences (PNAS).

An Exceptional Three-dimensional Fossil

The research led by the Muséum national d’histoire naturelle (MNHN) located in Paris, and the University of Birmingham has shown that an ancient relative of chimaeras, jawed vertebrates that are related to cartilaginous fishes (sharks and rays), fed by sucking in prey animals underwater.

An exceptional three-dimensional fossil of an ancient chimaera (Iniopera genus), has revealed new clues about the diversity of these creatures during the Carboniferous period.

Carboniferous Chimaera

The fossil, from a genus called Iniopera, is the only suction feeder to be identified among chimaeras, and quite different from living chimaeras, which generally feed by crushing molluscs and other hard-shelled prey between their teeth.

Chimaeriformes are an ancient order of cartilaginous fish (Chondrichthyes) that are thought to have evolved in the Devonian. Most extant species are found at depths greater than two hundred metres, and some chimaera fish are restricted to extremely deep water (Bathypelagic Zone).

Most fossil and extant chimaeras are quite small, very few specimens exceed one metre in length. However, other prehistoric, cartilaginous fish that were distantly related to Iniopera grew much larger. For example, the Permian genus Helicoprion with its bizarre tooth-whorl jaw, which has been estimated to have grown to around eight metres in length.

Picture credit: Everything Dinosaur

Although models of prehistoric fish from the Chondrichthyes Class are rare, PNSO have included two prehistoric shark figures (O. megalodon and Cretoxyrhina) and a replica of Helicoprion.

To view the PNSO prehistoric animal model range in stock at Everything Dinosaur: PNSO Age of Dinosaurs Models and Figures.

Identifying a Suction Feeder

Commenting on the significance of this study, lead researcher Dr Richard Dearden (University of Birmingham) stated:

“Being able to identify Iniopera as a suction feeder sheds light on the diverse role of chimaeras in these early ecosystems. In particular, it suggests that in their early evolutionary history, some chimaeras were inhabiting ecological niches that are now monopolised by ray finned fishes – a far cry from their modern life as specialised shell-crushers.”

The cartilage skeleton of these fish are rarely fossilised and the Chondrichthyes tend to be underrepresented in the fossil record. The skeletons that are preserved tend to be crushed flat and distorted so interpreting them is notoriously difficult. However, by studying the tooth shapes and diverse body plans, palaeontologists were already aware that extinct forms were far more varied than their living counterparts.

3-D Imaging Techniques

Using advanced 3-D imaging techniques, the researchers reconstructed the head, shoulder and throat skeleton of the Iniopera fossil. They then estimated the location of major muscles and found the anatomy was poorly suited to durophagous feeding. Instead, the researchers believe the animal was more likely to have used the muscle arrangement to expand the throat to take in water and a forward-pointing mouth to orient towards prey.

Suction feeding is a technique used by many animals that live underwater. It involves generating low pressures in the throat to pull in water and prey. To do this effectively, the animal needs to be able to rapidly expand its throat, and point its mouth forward towards prey items. Numerous different aquatic jawed vertebrates, such as ray-finned fishes and some turtles have evolved specialised anatomies to help them feed in this manner more effectively.

The suction feeding theory is also supported by fossilised Chimaeriformes that have preserved stomach contents. Small arthropods have been found in association with the body cavity of several specimens and their relatively entire state suggests suction feeding as the method of prey capture.

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