A recently published paper highlights Australia’s oldest known crocodilian eggshells.  The study is helping researchers from the University of New South Wales to unlock clues to an ancient ecosystem that thrived before Australia became an island continent.  The eggshell fragments have been assigned to the oospecies Wakkaoolithus godthelpi.

The fossilised fragments of eggshell are approximately fifty-five million years old (Eocene Epoch).  The come from mekosuchine crocodiles.  These now extinct crocodiles dominated inland waters during the Eocene.  Modern saltwater and freshwater crocodiles only arrived in Australia around 3.8 million years ago.

Electron microscope scans of the eggshell fragments. Picture credit: Xavier Panadès.

Picture credit: Xavier Panadès

Field teams have been working in clay pit close to the small town of Murgon in southeast Queensland. The clay layers preserve evidence of when Australia was still connected to South America and Antarctica.  It is one of the oldest fossil sites in Australia.  An international research team led by the Institut Català de Paleontologia Miquel Crusafont (ICP) in collaboration with researchers from University New South Wales (UNSW) identified the mekosuchine fossil eggshells.

Commenting on the significance of the fossil finds, lead author of the study Xavier Panadès i Blas (El Museu de la Conca Dellà, Isona, Spain), stated:

“These eggshells have given us a glimpse of the intimate life history of mekosuchines. We can now investigate not only the strange anatomy of these crocs, but also how they reproduced and adapted to changing environments.”

A virtual reconstruction of the Murgon palaeoecosystem during the Early Eocene, featuring the oospecies Wakkaoolithus godthelpi. Also shown is one of the abundant giant soft-shell turtles, Murgonomys braithwaitei, an archaic marsupial, Djarthia murgonensis, and an unnamed ancestral songbird. The clays that form the fossil deposit were accumulated in this ancient lake. Image: generated with Google Gemini AI.

Picture credit: Google Gemini AI

Swimming and Tree Climbing Crocodiles

Unlike Australia’s crocodiles today, mekosuchines filled much more varied ecological niches.  For example, some species were almost entirely terrestrial and inhabited forests.  Others were at home in the river systems and grew to at least five metres in length.  Co-author of the paper, Professor Michael Archer (UNSW) has postulated that some species were at least partly arboreal, and these animals have been termed “drop crocs.”

Professor Archer added:

“They were perhaps hunting like leopards – dropping out of trees on any unsuspecting thing they fancied for dinner.”

The palaeontological team from UNSW excavating the Tingamarra fossil deposit at Murgon, Queensland, Australia. The hard clay is quarried, dried and then soaked in water to release the fossils it contains. Photo credit: Mina Bassarova.

Picture credit: Mina Bassarova

Delicate Time Capsules

The authors state that tiny, fossilised eggshells are an underused resource in vertebrate palaeontology.  They preserve microstructural and geochemical signals that provide information on the kinds of creatures that laid them but also where they nested and how they bred.

Xavier Panadès i Blas explained:

“Our study shows just how powerful these fragments can be.  Eggshells should be a routine, standard component of palaeontological research – collected curated and analysed alongside bones and teeth.”

The shell fragments from the clay pit were examined under optical and electron microscopes.  Their microstructure indicates that they were laid on the margins of a lake, with the reproductive strategy adapting to fluctuating conditions.

Co-author of the study, Dr Michael Stein (UNSW), commented that mekosuchine crocs may have lost much of their inland territory because of encroaching dry land.  These crocodiles eventually had to compete in the shrinking waterways not only with new crocodilian rivals arriving in Australia but also with dwindling numbers of prey.  As the climate became much drier, many of the large prey animals that these crocodiles hunted became rarer.

The researchers think that the lake was surrounded by a lush, tropical forest.

Dr Stein said:

“This forest was also home to the world’s oldest-known songbirds, Australia’s earliest frogs and snakes, a wide range of small mammals with South American links, as well as one of the world’s oldest bats.”

Wakkaoolithus godthelpi eggshell fragments shown in high magnification. Picture credit: Xavier Panadès.

Picture credit: Xavier Panadès

A Study with Teeth

The research into the Tingamarra deposits at Murgon is just part of a much bigger story.  Professor Archer recalls finding a bizarre crocodilian jaw fragment in 1975 in the Texas Caves of southeastern Queensland.  This jaw fossil has been confirmed to represent a mekosuchine crocodile.  The large teeth in situ were linked to another type of extinct crocodile known from South America.  This was the first evidence of crocodiles related to South American crocodiles being present in Australia during the Eocene.

Discoveries like this are more than just a glimpse into ancient history. They are reminders that Australia’s fossil record can provide important clues to help save today’s threatened species. For example, scientists have been working to help bring a small possum – Burramys parvus back from the brink of extinction.  Researchers discovered that the possum’s prehistoric relatives, evolving over the past twenty-five million years, have always thrived in temperate lowland rainforests.

This led to the theory that the immediate ancestors of B. parvus likely followed the rainforests as they moved up into the alpine areas during a warm, wet interval during the Pleistocene Epoch. However, when the climate in the alpine zone changed and became cooler, these small marsupials had to evolve evasive behaviours such as hibernation to escape the increasingly hostile conditions.

Based on the findings from the fossil record a breeding facility in an area of non-alpine rainforest was set up.  As a result, the numbers of Burramys parvus have increased.  The possums are flourishing in a non-alpine sanctuary, just as the fossil record predicted.

Wakkaoolithus godthelpi Fossils Provide Guidance to Conservationists

As climate change threatens Australia’s fauna today, the fossil record can provide important indicators to assist with the conservation of species.

Professor Archer stated:

“Clues from the fossil record matter.  Not just to understand the past, but also to help secure the future”.

The new crocodile species’ name, Wakkaoolithus godthelpi, acknowledges, with permission, the Wakka Wakka First Nations people, on whose Country the fossils were found. The second part of the name recognises Henk Godthelp, who was part of the UNSW palaeontologist crew along with Professor Archer, Professor Sue Hand and many other research staff and students.

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

The scientific paper: “Australia’s oldest crocodylian eggshell: insights into the reproductive paleoecology of mekosuchines” by Xavier Panadès I Blas, Àngel Galobart, Michael Archer, Michael Stein, Suzanne Hand and Albert Sellés published in the Journal of Vertebrate Paleontology.

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A recently published scientific paper lends weight to the theory that Nanotyrannus is a valid taxon.  Writing in the journal “Science” a team of scientists, including researchers from the Cleveland Museum of Natural History used a novel approach to confirm that a skull does indeed represent skeletally mature adult.  Their evidence confirms that the fossil specimen, known as the “Cleveland skull” does not represent a juvenile Tyrannosaurus rex.  An often-overlooked bone helped make the breakthrough.  The Nanotyrannus hyoid bone provided the vital information.

Whether Nanotyrannus lancensis represents a distinct taxon or an immature T. rex is a decades-long controversy.  This new study comes shortly after a paper that concluded that Nanotyrannus was a valid taxon.  Indeed, this study claimed that there were two species of Nanotyrannus in the known fossil record.

To read Everything Dinosaur’s blog post about this earlier study: Nanotyrannus – A New Chapter in Tyrannosaur Evolution.

The “Cleveland skull” – Nanotyrannus lancensis fossil material. Picture credit: Cleveland Museum of Natural History.

Picture credit: Cleveland Museum of Natural History

The Cleveland Skull

The Cleveland skull lies at the heart of this long-running controversy. Discovered in 1942, the specimen consists almost entirely of a skull, with no associated postcranial bones. As a result, palaeontologists found it difficult to determine whether these fossils represented a juvenile tyrannosaur or an adult animal. If the fossil skull represented an adult, then this would indicate a new tyrannosaur genus present in Hell Creek. Hence, the erection of a new tyrannosaur species (Gorgosaurus lancensis) in a paper published posthumously in 1946 by the American palaeontologist Charles Whitney Gilmore.

Dr Caitlin Colleary (Department of Earth Sciences, Cleveland Museum of Natural History), examining the Nanotyrannus skull material. Picture credit: Cleveland Museum of Natural History.

Picture credit: Cleveland Museum of Natural History

The Nanotyrannus Hyoid Bone

One small bone proved vital when trying to assess the skull material. The Nanotyrannus hyoid bone had detached from the skull and was stored separately in the museum collection. This slender throat bone had gone largely unnoticed until a visiting researcher recognised its potential importance. The hyoid supports the tongue and airway in living animals. Crucially, it also records growth in a measurable way. The researchers were able to demonstrate that the histology preserved in this bone was useful for assessing the ontogeny of the fossils. The research team therefore applied histological analysis to the hyoid, an approach never used on this bone before.

Before examining the Cleveland specimen, the scientists validated their method. They studied hyoids from birds and crocodilians, which represent living dinosaur relatives. They then compared the Nanotyrannus hyoid bone with those from theropod dinosaurs including Tyrannosaurus rex, Allosaurus, and Coelophysis.

Thin sections viewed under a microscope revealed clear growth patterns. Most importantly, the hyoid contained an external fundamental system. This structure forms when growth has ceased. The team demonstrated that hyoid bone histology is useful for ontogenetic assessment in extant and extinct archosaur.

Senior author of the paper, Dr Caitlin Colleary (Department of Earth Sciences, Cleveland Museum of Natural History), explained:

“By applying a new technique to a specimen that’s been in the collection for nearly 80 years, we unlocked information that’s been there all along.”

The Cleveland Skull Material Represents a Fully Grown Animal

The presence of this feature confirms that the Cleveland skull fossils belonged to a fully grown individual. It did not represent a juvenile Tyrannosaurus rex. Instead, it supports the interpretation of Nanotyrannus lancensis as a distinct taxon coeval with T. rex.

A Nanotyrannus (N. lancensis) left, competes for food with a juvenile Tyrannosaurus rex, whilst an adult T. rex watches in the background. Picture credit: Andrey Atuchin.

Picture credit: Andrey Atuchin

Nanotyrannus Hyoid Bone Study – The Implications

This study has significant implications for tyrannosaur research. The holotype defines the species. Demonstrating adult status strengthens the case for Nanotyrannus beyond reasonable doubt. The study also highlights the enduring value of museum collections. A single overlooked bone provided the decisive evidence. Sometimes, the most important discoveries wait quietly in storage.

For the moment, the debate has shifted decisively. The Nanotyrannus hyoid bone offers direct proof of skeletal maturity. As a result, this small tyrannosaur finally steps out from the shadow of Tyrannosaurus rex.  This study and the earlier Nanotyrannus paper, indicate that the Hell Creek ecosystem was home to a wide assemblage of predatory dinosaurs.

Everything Dinosaur acknowledges the assistance of a media release from the Cleveland Museum of Natural History in the compilation of this article.

The scientific paper: “A diminutive tyrannosaur lived alongside Tyrannosaurus rex” by Christopher T. Griffin, Jeb Bugos, Ashley W. Poust, Zachary S. Morris, Riley S. Sombathy, Michael D. D’Emic, Patrick M. O’Connor, Holger Petermann, Matteo Fabbri and Caitlin Colleary published in the journal Science.

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