Two Ancient Trackways Discovered in Arizona

A fortuitous rock fall on the Bright Angel Trail in the Grand Canyon National Park (Arizona), has revealed two ancient trace fossils that have been interpreted as the trackways created by small vertebrates as they climbed a steep sand dune.  The sandstone blocks containing the fossilised trackways from the Manakacha Formation, a sub-unit of the extensive Supai Group, are the subject of a scientific paper published in the academic, on-line, open-access journal PLOS One.

Estimated to be around 313 million years old (Moscovian Age of the Pennsylvanian Epoch – Late Carboniferous), the fossilised trackways are thought to have been made by either basal diapsid reptile or a basal synapsid and are the first tetrapod tracks reported from the Manakacha Formation and the oldest known from the Grand Canyon region.

An Artist’s Reconstruction of the Tetrapod Ascending the Sand Dune

Picture credit: Emily Waldman

Ascending Sand Dunes

The rocks in this region are aeolian sandstones and the discovery of the two trackways document the earliest known occurrence of dunefield-dwelling amniotes.  Lead author of the scientific paper, Steve Rowland (professor emeritus of geology at the University of Nevada), commented that these fossils demonstrate that by the Late Carboniferous, the first vertebrates capable of laying eggs out of water had adapted to desert habitats.

The Main Trackway, Line Drawing, Site of Rock Fall and Counterpart Slab

Picture credit: Rowland et al (PLOS One)

Side-stepping Ascent of a Steep Dune Revealed by Fossilised Trackways

The rock fall occurred close to a popular hiking trail and they were first spotted during a geology field trip to the Grand Canyon in 2016.  The leader of that trip, professor Allan Krill sent a photograph of the tracks to the Department of Geology at the University of Nevada and Professor Rowland decided to investigate further.  The tracks have been interpreted as showing the ascent of a dune slope at an angle of approximately 20 degrees, thus reducing the steepness of the climb.

The second trackway, a series of small rounded depressions in the rock suggest claw marks.  It has been postulated that these marks are a deeper undertrackway, made some hours or days after the first track was produced, possibly by an animal of the same species as the first trackmaker.

Line Drawing of Main Trackway (1) with a Plotted Three-dimensional Track Interpretation

Picture credit: Rowland et al (PLOS One)

The scientists conclude that to traverse over the steep slope the little animal was moving, laterally one step at a time so that it always had its three other legs to support its body and to grip the surface.  The transition across the dune may not have been particularly elegant but the 28 impressions that have been preserved may help to shed further light on the evolution of early amniotes, which are scarce in the Carboniferous/Early Permian fossil record of North America.

A Controversial Interpretation

Not everyone is convinced of the interpretation of the fossils by the research team which included Mario Caputo (Society for Sedimentary Geology) and Zachary Jensen (College of Southern Nevada).

A spokesperson representing the palaeontology programme at the Grand Canyon commented that there was a lot of disagreement amongst the scientific community when it came to interpreting fossil tracks and inferring animal behaviours from them.  During the Late Carboniferous, this part of Arizona was a coastal-plain on the western edge of the super-continent of Pangaea.  There were extensive dunefields in close proximity, the dunes being formed by the action of the wind (aeolian), occasionally exceptional tidal conditions, storms or other flooding events interrupted the aeolian deposition burying parts of the dunefield in fine mud.

The scientific paper: “Early adaptation to eolian sand dunes by basal amniotes is documented in two Pennsylvanian Grand Canyon trackways” by Stephen M. Rowland, Mario V. Caputo and Zachary A. Jensen published in the open-access, on-line journal PLOS One.

The Everything Dinosaur website: Everything Dinosaur.

Jurassic Fossils from the Isle of Skye Globally Significant

The filming might have resumed for the next instalment in the “Jurassic Park/World” franchise last week, but in the scientific community there has been an important development in the study and protection of Scotland’s very own “Jurassic Park”.

Significant Jurassic Fossils

Scientists from the University of Oxford, University College London, Birmingham University the University of Edinburgh and the National Museum of Scotland have published a new scientific paper that emphasises the importance of vertebrate fossils from the Isle of Skye.

The Isle of Skye is Heralded as One of the Most Important Places in the World for Middle Jurassic Vertebrate Fossils

Picture credit: Jon Hoad

The Kilmaluag Formation

Outcrops of the Bathonian-aged Kilmaluag Formation on the Trotternish peninsula on the Isle of Skye hold vital information on how vertebrate life was evolving and changing around 167 million years ago.  The strata contain both body and trace fossils of numerous tetrapods including dinosaurs.  Since there are not that many highly fossiliferous sites around the world providing evidence of terrestrial ecosystems and biota from back in the Middle Jurassic, the Isle of Skye has long been recognised as a hugely significant.

The area was given greater legal protection last year, when the Scottish Government signed a Nature Conservation Order (NCO), to assist in the protection of the rare vertebrate fossils found in the area and to deter irresponsible fossil collecting on the island.

To read about the provision of the Nature Conservation Order: Legal Protection for Isle of Skye Fossil Sites.

In this new study, the researchers which include Scottish palaeontologist Elsa Panciroli, a research assistant in the department of Evolution and Palaeobiology at the University of Oxford, conclude that unlike other contemporaneous fossil localities from England, the strata of the Kilmaluag Formation provides partial skeletons, providing unprecedented insights and new data.

An Abundant Assemblage of Jurassic Fossils

The research team state that this location has yielded predominantly small-bodied tetrapods including amphibians, many types of reptiles (including pterosaurs and dinosaurs) and non-mammalian cynodonts as well as early mammals.  An abundant fossil fish and invertebrate assemblage is also reported.

A Sauropod Track from the Isle of Skye

Picture credit: Jon Hoad

The researchers provide a comprehensive overview of the Kilmaluag Formation, outlining the importance of its geology and the fossil discoveries made to date.  They also present evidence of several species that are being reported from the Isle of Skye for the first time.   The review places the vertebrate faunal assemblage in an international context and confirms the global significance of the region.

Insights into Early Mammal Evolution

Although the dinosaurs grab all the headlines, the Kilmaluag Formation is most likely to provide important information with regards to the evolutionary history of early mammals, the Squamata (lizards and snakes) along with amphibians.

To read Everything Dinosaur’s blog post about damage to dinosaur footprints being reported: Dinosaur Footprints Damaged on the Isle of Skye.

The link between the fossil sites in Wyoming and the Isle of Skye: What have Wyoming and the Isle of Skye got in Common?

Evidence of Scottish Stegosaurs: Scottish Stegosaurs.

The scientific paper: “Diverse vertebrate assemblage of the Kilmaluag Formation (Bathonian, Middle Jurassic) of Skye, Scotland” by Elsa Panciroli, Roger B. J. Benson, Stig Walsh, Richard J. Butler, Tiago Andrade Castro, Marc E. H. Jones and Susan E. Evans published by The Royal Society of Edinburgh/Cambridge University Press.

The Everything Dinosaur website: Everything Dinosaur.

Dinosaur Eggs Provide a View on a “Hidden Ecosystem”

Not all the dinosaurs that ever existed are likely to be named and described by scientists.  Identifying these long extinct creatures relies on there being a fossil record of some sort to study.  A team of researchers writing in the journal “Cretaceous Research”, report on a new Lower Cretaceous fossil egg locality in Hyogo Prefecture, Japan, that provides a tantalising glimpse into a hidden dinosaur dominated ecosystem.

The researchers, which include Kohei Tanaka (University of Tsukuba, Japan) and Darla Zelenitsky (University of Calgary, Canada), describe eggs and eggshell fragments associated with four ootaxa, two of which are new to science.  The site reveals a hidden diversity of small dinosaurs, particularly non-avian theropods, in the Hyogo region and indicates the area was utilised for nesting by various small dinosaur species in the Early Cretaceous.

The Newly Erected Ootaxa Himeoolithus murakamii the Most Abundant Ootaxa from the Quarry Site

Picture credit: University of Tsukuba and Museum of Nature and Human Activities Hyogo Prefecture with life reconstruction by Ayaka Nagate

The Kamitaki Locality

The fossil site, known as the Kamitaki locality lies close to the  Sasayama River in Kamitaki, Sannan-cho, Tamba City,  Hyogo Prefecture.  One horizon has yielded a variety of small vertebrate fossils including frogs and lizards, plus a partial tail from a titanosaur that was formally named and described in 2014 (Tambatitanis amicitiae).  Eggshell fragments are also associated with this part of the site.  However, a horizon some 5.5 to 6.75 metres above the bonebed layer has yielded an astonishing quantity of egg fossils, including a nearly complete egg, several partial eggs and hundreds of eggshell fragments.

The researchers conclude that this horizon represents a nesting area in which a variety of small theropods raised their young.

As a result of this research, two new theropod egg taxa have been named – Himeoolithus murakamii and Subtiliolithus hyogoensis.  Although no skeletal remains of these little dinosaurs have been found, the presence of all the egg fossils suggests that there were numerous different types of small theropod co-existing in this ancient ecosystem.

The Location of the Fossil Site within Hyogo Prefecture

Picture credit: University of Tsukuba and Museum of Nature and Human Activities Hyogo Prefecture/Cretaceous Research with additional annotation by Everything Dinosaur

Examining the Mudstone Deposits

The mudstone deposits are thought to have been laid down around 110 million years ago (Albian faunal stage of the Lower Cretaceous) and the palaeoenvironment has been described as floodplain which was subjected to a extremes of seasonality with long periods of very dry conditions punctuated by a very wet season that led to flood events.

The most abundant ootaxon at the quarry, Himeoolithus, is represented by four eggs and over 1300 scattered eggshell fragments. Himeoolithus accounts for over 96% of all the egg fossils associated with this site.  Himeoolithus is the smallest non-avian theropod egg known to date, the scientists estimate that the egg probably weighed about as much as a quail egg (around 9.9 grammes).  It is also a very unusual shape, being elongate with its length 2.25 times its width (length : width ratio 2.25).

The new egg fossil horizon was discovered in 2015 and was mapped and intensively excavated in the winter of 2019.  In total, the egg fossil horizon and the lower Kamitaki Bonebed (Ohyamashimo Formation), have yielded six small theropod ootaxa.

The Stratigraphy of the Kamitaki Locality and Examples of Associated Ootaxa

Picture credit: University of Tsukuba and Museum of Nature and Human Activities Hyogo Prefecture/Cretaceous Research

Notable Biodiversity

The ootaxa demonstrate that this ancient habitat was home to a variety of small theropod dinosaurs.  It is likely that many other palaeoenvironments associated with the Lower Cretaceous were also home to a diverse variety of small theropods too, these animals being currently under-represented in the fossil record.

Lead author of the paper, Professor Kohei Tanaka, confirmed that the research team thought that the new egg fossil horizon was a nesting site and the deposit was not the result of a transportation and subsequent burial of egg material from another location:

“Our taphonomic analysis indicated that the nest we found was in situ, not transported and redeposited, because most of the eggshell fragments were positioned concave-up, not concave-down like we see when eggshells are transported.”

Commenting About the Dinosaur Eggs

The professor added:

“The high diversity of these small theropod eggs makes this one of the most diverse Early Cretaceous egg localities known.  Small theropod skeletal fossils are quite scarce in this area.  Therefore, these fossil eggs provide a useful window into the hidden ecological diversity of dinosaurs in the Early Cretaceous of south-western Japan, as well as into the nesting behaviour of small non-avian theropods.”

Everything Dinosaur acknowledges the assistance of a media release from the University of Tsukuba (Japan), in the compilation of this article.

The scientific paper: “Exceptionally small theropod eggs from the Lower Cretaceous Ohyamashimo Formation of Tamba, Hyogo Prefecture, Japan” by
Kohei Tanaka, Darla K. Zelenitsky, François Therrien, Tadahiro Ikeda, Katsuhiro Kubota, Haruo Saegusa, Tomonori Tanaka and Kenji Ikuno published in the journal Cretaceous Research.

The Everything Dinosaur website: Everything Dinosaur.