Under the Noses of Dinosaurs, a New Species of Early Cretaceous Amphibian is Described

A small, fragmentary fossil found in an outcrop of the Kuwajima Formation, in western Central Japan has been identified as a new species of albanerpetontid amphibian.  This tiny animal, measuring just six centimetres in length inhabited a wide floodplain, that was crossed by meandering rivers in a humid environment some 130 million years ago.  The fossils represent the oldest example of this type of Tetrapod found in Asia, they predate the only other specimens known from Asia (Uzbekistan), by tens of millions of years.

A Life Reconstruction of the Little Albanerpetontid Amphibian (S. isajii)

An illustration of Shirerpeton – an Early Cretaceous amphibian.

Picture Credit: Takumi Yamamoto

The Ancient Albanerpetontidae Family

Superficially resembling modern-day Salamanders, these ancient amphibians are only distantly related to their modern counterparts.  They evolved in the Middle Jurassic and persisted until very recently, finally becoming extinct during the Pleistocene Epoch.  Several genera are known and they are characterised by their unique skulls and the presence of bony scales on their skin.  The tiny specimen consists of a partial skull, vertebrae and elements from a hind limb, a total of forty-three bones.  The only Asian examples of this clade of amphibian have been found in Uzbekistan.  These fossils date from the very end of the Cretaceous, so the Japanese specimen is some sixty million years older.

High resolution X-ray computed microtomography was used to identify the shape of the bones which remain partially buried in the part-prepared fossil.

The Rock Containing the Partially Exposed Fossil Bones Along with a Computer Image Tracing the Outline of the Individual Bones

A new Early Cretaceous amphibian from Japan (Shirerpeton).

Picture Credit: The Education Board of the city of Hakusan, (Ishikawa Prefecture, Japan)

Tiny Fossil

The picture (above) shows the holotype fossil of the new albanerpetontid amphibian, which has been named Shirerpeton isajii.  Image (A) shows the fossils in the 2.5 by 1.5 cm square slab of rock, whilst image (B), is a digital photograph with various bones from the skull highlighted.  Abbreviations: Br, braincase elements; Fr, frontal; L.La, left lacrimal; L.Mx, left maxilla; L.N, left nasal; L.Pa, left parietal; LPf, left prefrontal; L.Sm, left septomaxilla; L.Sq, left squamosal; R.La, right lacrimal; R.Pa, right parietal; R.Pf, right prefrontal; R.Sq, right squamosal; ?, unidentified element. Scale bars in both images = 5 mm.

Writing in the open-access academic journal PLOS One, the researchers, Susan Evans, a professor of vertebrate morphology and palaeontology (University College London) and Ryoko Matsumoto, a curator with the Kanagawa Prefectural Museum of Natural History were able to identify the specimen as a member of the Albanerpetontidae from the shape of the lower jaw.  The distinctive frontal bone of the skull, along with several other identified autapomorphies (unique traits), enabled the scientists to erect a new species.

Shirerpeton isajii

The scientists named the species in honour of Shinji Isaji, the head of the Tetori Group fossil investigation commission, a body under the Hakusan city government in charge of studying the Kuwajima fossil location where the fossil was found.

A spokesperson from Everything Dinosaur commented:

“There are about twenty of these amphibians known in the fossil record, currently assigned to five genera.  They were globally widespread during the Mesozoic, but this is the first time an albanerpetontid has been recorded from East Asia.  Their fragmentary record makes understanding their evolution and their phylogeny very difficult, scientists are not even sure how closely related these ancient lissamphibians are to extant amphibians.  Small animals like Shirerpeton are just as important as larger animals like dinosaurs when it comes to considering ancient environments and habitats.  In fact, this amphibian is probably more important than larger vertebrates in helping scientists to understand the localised climate in the Barremian of Japan.”

Middle Jurassic Dinosaur Tracks Put Skye Firmly on the Map

More evidence of Middle Jurassic dinosaurs on the Isle of Skye has emerged.  In a paper published in the Scottish Journal of Geology, a team of international scientists including researchers from the University of Edinburgh and the Chinese Academy of Sciences, report on a series of dinosaur prints and tracks from the Lealt Shale Formation (Bathonian faunal stage) of the Great Estuarine Group at Rubha nam Brathairean (Brothers’ Point), on the Trotternish peninsula (Isle of Skye).  Evidence of Middle Jurassic dinosaurs is globally rare, there are just a few fossil sites that provide information about terrestrial fauna that existed around 168 million years ago.  Trace fossils from the Isle of Skye are playing an increasingly significant role as palaeontologists seek to better understand the evolution and distribution of different types of dinosaur.

One of the Sauropod Prints at Rubha nam Brathairean

Sauropod track from the Isle of Skye.

Picture Credit: Jon Hoad

In 2015, Everything Dinosaur published an article featuring the discovery of a series of Sauropod prints and tracks found on northern Skye, at a locality close to Duntulm Castle (Duntulm Formation).

To read this article: Isle of Skye Sauropods and their Water World

Although, the Duntulm Castle site is just a few miles from the newly described trace fossils at Brothers’ Point and the strata in which the footprints and tracks were found are part of the Great Estuarine Group sequence of Middle Jurassic rocks, the two fossil sites represent different sub-units of strata.  The Lealt Shale Formation is geologically older than the fossiliferous rocks found at the Duntulm Castle site (Duntulm Formation).  Both locations represent a sequence of deposits made in brackish, lagoonal environments.  The fact that a second series of Sauropod tracks and prints have been found preserved in rocks laid down in a lagoon, strengthens the idea that Middle Jurassic Sauropods habitually spent time in these environments.  Could this indicate that at least some Middle Jurassic Sauropods were semi aquatic?

Did Middle Jurassic Sauropods Habitually Hang Out in Lagoons?

The Isle of Skye (Bathonian faunal stage).

Picture Credit: Jon Hoad

Around Fifty Footprints Measured and Studied

The researchers measured, photographed and analysed around fifty footprints in a tidal area.  Working conditions on the rugged headland were difficult, due to the tidal environment and the often, inclement weather for which, the Trotternish peninsula is famed.  Despite the harsh conditions, the scientists were able to identify two trackways and many examples of isolated prints.

The location preserves numerous small Sauropod manus (hand) and pes (foot) prints along with several isolated and broken medium-to-large tridactyl prints.  The three-toed (tridactyl) prints indicate the presence of Theropods (most probably carnivorous dinosaurs).  Measurements of the Sauropod tracks and stride lengths indicate that these trace fossils were made by relatively small members of the Sauropoda, the tracks indicate individuals around two metres high at the shoulders.  The Sauropod tracks, with their characteristic narrow gauge and toe morphology, have been tentatively assigned to the ichnotaxon Breviparopus.  The Theropod trackmaker remains equally enigmatic, however, some of the three-toed prints are reminiscent of the tracks associated with the ichnotaxon Eubrontes.

One of the Sauropod prints from the Lealt Shale Formation

Sauropod footprint from the Isle of Skye.  The geological hammer and the pen provide scale (as do the copious gastropods).

Picture Credit: Paige dePolo (University of Edinburgh)

Commenting on the significance of this discovery, one of the authors of the scientific paper, Paige E. dePolo (University of Edinburgh) stated:

“This tracksite is the second discovery of Sauropod footprints on Skye.  It was found in rocks that were slightly older than those previously found at Duntulm on the island and demonstrates the presence of Sauropods in this part of the world through a longer timescale than previously known.  This site is a useful building block for us to continue fleshing out a picture of what dinosaurs were like on Skye in the Middle Jurassic.”

Co-author Dr Stephen Brusatte (University of Edinburgh), added:

“The more we look on the Isle of Skye, the more dinosaur footprints we find.  This new site records two different types of dinosaurs — long-necked cousins of Brontosaurus and sharp-toothed cousins of T. rex — hanging around a shallow lagoon, back when Scotland was much warmer and dinosaurs were beginning their march to global dominance.”

A Fossil Bias?

Although the discovery of a second site, demonstrating Sauropod tracks in a lagoonal depositional environment, raises the intriguing idea that these large, long-necked herbivores spent time in such environments, palaeontologists have to be careful what they infer from such data.  Sauropods may have spent much of their time in different habitats, such as forests, or perhaps, in more open environments such as fern prairies, however, in such environments the fossil preservation potential for things like tracks and footprints are that much lower.  Hence, the evidence for such behaviour may not exist, there could be a preservational bias in favour of recording Sauropod activity in brackish lagoons.  Thanks to this dedicated research team, more information has been obtained with regards to the Middle Jurassic palaeofauna of Scotland.  We look forward to future discoveries and fossil finds that will continue to inform the debate.

The scientific paper: “A Sauropod-dominated Tracksite from Rubha nam Brathairean (Brothers’ Point), Isle of Skye, Scotland” by Paige E. dePolo, Stephen L. Brusatte, Thomas J. Challands, Davide Foffa, Dugald A. Ross, Mark Wilkinson and Hong-yu Yi published in the Scottish Journal of Geology

“The Rise and Fall of the Dinosaurs” by Dr Steve Brusatte

One of the authors of this scientific paper (indeed one of the authors of the 2015, Duntulm Formation tracks research), Dr Steve Brusatte (School of Geosciences at Edinburgh University), has a new dinosaur book out next month.  Look out for the excellent “The Rise and Fall of the Dinosaurs” coming into shops in May.

New Dinosaur Book Out Very Soon

“The Rise and Fall of the Dinosaurs” by Steve Brusatte.

Picture Credit: Pan Macmillan

To read Everything Dinosaur’s recent book review: A Review of “The Rise and Fall of the Dinosaurs”

Updating Arkansaurus fridayi

A few days ago, Everything Dinosaur published an article about the newly described basal ornithomimosaur called Arkansaurus fridayi.  Although the fossil bones were found nearly fifty years ago, the scientific paper describing the fossils and officially naming this dinosaur has only just been published (Journal of Vertebrate Palaeontology).  Lead author of the paper, ReBecca Hunt-Foster of the Bureau of Land Management, emailed us so that we could post up more images of this significant fossil discovery.

A Life Restoration of the Basal Ornithomimosaur Arkansaurus fridayi

Arkansaurus fridayi life restoration.

Picture Credit: Brian Engh

To read Everything Dinosaur’s earlier article on the formal description of Arkansaurus: “Arkansas Reptile” – A Rare Insight into Appalachian Dinosaurs

More Primitive Than Asian Ornithomimosaurs That Lived at the Same Time

Ornithomimosaurs (the ostrich-mimic dinosaurs) are quite well known from the Early Cretaceous of Asia, however, very little is known about North American ornithomimosaurs from this time in Earth’s history, hence the importance of the Arkansaurus fossils.  The dinosaur has been named from a single, partial right foot, recovered from the Lower Cretaceous (Albian to Aptian faunal stages) of the Trinity Group of Arkansas.

A Cast of the Fossil Foot Bones (Anterior View)

Arkansaurus fridayi foot bones (cast).

Picture Credit: R. Hunt-Foster

Contemporaneous with the likes of Beishanlong (B. grandis) from Gansu Province (north-west China), living around 113 million years ago, Arkansaurus fridayi can be distinguished from other ornithomimosaurs based on differences in the toe claws (pedal unguals) and the presence of a laterally compressed third metatarsal (toe bone) that is ovoid in shape when looked at in proximal view.  Other anatomical differences are cited by the researchers including a distal ungual with a very weak flexor tubercle, lacking spurs.

Two Views of the Metatarsal Bones of Arkansaurus

Views of the metatarsals of Arkansaurus.

Picture Credit: R. Hunt-Foster

The picture above shows two views of the toe bones (metatarsals)  of Arkansaurus (a) in proximal view, that is viewed from the top of the bone closest to the ankle looking down onto the bones and (b) anterior view, viewed from the front.  The third metatarsal is actually the bone in the middle.  The scientists conclude that the condition of the third toe bone suggests that Arkansaurus fridayi is more basal than Asian ornithomimosaurs of similar age, but consistent with older North American forms.

A Cast of the Fossil Toe and Claw Bones

A view of a cast of the foot bones of Arkansaurus fridayi.

Picture Credit: R. Hunt-Foster

This specimen provides knowledge of a poorly understood radiation of ornithomimosaurs in the Cretaceous landmass known as Appalachia and is the only known Saurischian dinosaur fossil found to date in the state of Arkansas.

ReBecca Hunt-Foster Has Worked on These Fossils for Several Years

ReBecca Hunt-Foster examining limb bones (2003).

Picture Credit: R. Hunt-Foster