A research paper published this week in the journal “Nature” has revealed that early mammals may have lived much longer than their modern-day counterparts.  The study describes two Krusatodon kirtlingtonensis fossil specimens.  These mouse-sized mammals lived approximately 166 million years ago (Bathonian faunal stage of the Middle Jurassic).  The fossils come from the remarkable Jurassic strata found on the Isle of Skye.

The research led by National Museums Scotland describes the fossilised remains of one adult and one juvenile.  The adult K. kirtlingtonensis is thought to have been around seven years old when it perished.  The juvenile is thought to have been between seven to twenty-four months old when it died.  It was still in the process of replacing its deciduous dentition (milk teeth) with its final, adult set of teeth.

National Museums Scotland’s Dr Elsa Panciroli with enlarged, 3D printed models of Krusatodon kirtlingtonensis skeletons. Picture credit: Duncan Mc Glynn.

Picture credit: Duncan Mc Glynn

The scientists conclude that early diverging mammaliaforms did not experience the same life histories as extant small-bodied mammals. Furthermore, the fundamental shift to faster growth over a shorter lifespan may not have taken place in mammaliaforms until during or after the Middle Jurassic.

Two Krusatodon kirtlingtonensis Fossil Specimens

These two Krusatodon kirtlingtonensis fossils are extremely significant.  The adult specimen represents one of the earliest fossil discoveries from the Isle of Skye.  It was found in the 1970s.  This specimen is one of the most complete Jurassic mammaliaform skeletons known to science.  The juvenile fossil was found more recently (2016).  It is the only known skeleton of an immature Jurassic mammaliaform. Indeed, there is no other record of an adult and juvenile from the same Jurassic mammaliaform taxon.

The Isle of Skye is one of the most important locations in the world for Middle Jurassic fossils.  Vertebrate body and trace fossils confirm the presence of a rich biota of dinosaurs, pterosaurs and early mammals. This new study focusing on K. kirtlingtonensis underscores the significance of the Scottish island to palaeontology.

An article about the discovery of a large, new species of pterosaur (Dearc sgiathanach): Fantastic Pterosaur from the Isle of Skye.

Dr Elsa Panciroli examines the barnacle encrusted fossil which contained Krusatodon kirtlingtonensis material. Picture credit: Duncan Mc Glynn.

Picture credit: Duncan Mc Glynn

X-ray Computed Tomography Employed

The discovery of a juvenile and adult of the same species of Jurassic mammaliaform is unique.  As a result, a ground-breaking comparative analysis into their growth and life history (ontogeny) was undertaken. The ages of the specimens at death were determined using X-ray imaging to count the growth rings in their teeth.  Therefore, the age of each animal at the time they died could be established.  The X-ray computed tomography was carried out in several laboratories, including the European Synchrotron (ESRF) located in Grenoble, France.

Extant small mammals have much shorter lifespans.  Many live for less than a year.  They mature quickly, losing their milk teeth and weaning within months of birth.  In addition, most small mammals living today rapidly reach sexual maturity and breeding age. The Krusatodon fossils reveal for the first time that the earliest mammals didn’t finish replacing their milk teeth until well into their second year of life, possibly later.  The researchers conclude that mammals grew more slowly in the Jurassic than they do today.  This suggests a fundamental shift in the growth patterns and life expectancy of mammals must have taken place during or after the Middle Jurassic.

An adult and young Krusatodon kirtlingtonensis life reconstruction. A stegosaur can be seen in the background. Fossilised tracks found on the Isle of Skye indicate the presence of stegosaurs in the ecosystem.  Picture credit Maija Karala.

Picture credit: Maija Karala

Dr Elsa Panciroli, lead author and Associate Researcher of Palaeobiology at National Museums Scotland, commented:

“These fossils are among the most complete mammals from this time period in the world. They give us unprecedented insights into the lives of the first mammals in the time of dinosaurs. Although on the outside Krusatodon looked like a shrew or mouse, on the inside it was quite different; it grew more slowly and lived much longer than small mammals do today. As a result, it probably had quite a different physiology and life history as well. Skye’s fossils are really putting Scotland firmly on the map when it comes to understanding mammal evolution. This is just the tip of the iceberg in terms of what they can tell us.”

National Museums Scotland’s Dr Elsa Panciroli pointing out details on a high-resolution scan of the Krusatodon kirtlingtonensis fossils. Picture credit: Duncan Mc Glynn.

Picture credit: Duncan Mc Glynn

Analysis of Teeth Growth Patterns Yields Surprising Results

Co-author Dr Elis Newham, a Postdoctoral Research Associate at Queen Mary University of London explained:

“Our study benefited greatly from a new technique we developed using synchrotron X-ray technology. This allowed us to analyse growth patterns in the teeth of these fossils, much like counting tree rings. It was surprising to discover that Krusatodon, while showing a similar development pattern to modern mammals, grew much slower and lived longer. This research emphasises the value of studying juvenile fossils, and the X-ray cementochronology technique offers a powerful tool for unlocking these secrets from the past.”

Dr Stig Walsh, Senior Curator of Vertebrate Palaeobiology at National Museums Scotland and fellow co-author on the research, said:

“Even in the context of the amazing palaeontological finds on Skye in recent years, these fossils are remarkable. Mammal fossils of this age are exceptionally rare worldwide, and most are just single teeth found by sieving sediment. To find two such rare fossil skeletons of the same species at different growth stages has rewritten our understanding of the lives of the very earliest mammals. We’re thrilled they are both now part of Scotland’s National Collection, an important part of the global fossil record, and will be preserved for generations of researchers to come.”

National Museums Scotland’s Dr Elsa Panciroli examines two Krusatodon kirtlingtonensis fossils. Picture credit: Duncan Mc Glynn.

Picture credit: Duncan Mc Glynn

International Collaboration

In addition to National Museums Scotland, the study also involved researchers from the American Museum of Natural History (New York), the University of Chicago, the European Synchrotron Radiation Facility, and Queen Mary University of London.

Co-author Professor Roger Benson (American Museum of Natural History), described the juvenile fossil material:

“When we found the tiny juvenile skull, I didn’t realise what we’d found right away. The part of the fossil that was sticking out of the rock was blasted by erosion, surrounded by barnacles, and looked just like a piece of ash. I used micro-CT scanning, a form of 3D X-ray imaging, and was very surprised to see a whole skull in the rock. For science, it’s really remarkable to have this fossil and it told us a lot about growth and life history in some of the earliest mammals.”

To read a blog post from 2019 about greater legal protection for Scottish fossil sites: Legal Protection for Isle of Skye Fossils.

Everything Dinosaur acknowledges the assistance of a media release from National Museums Scotland in the compilation of this article.

The scientific paper: “Jurassic fossil juvenile reveals prolonged life history in early mammals” by Elsa Panciroli, Roger B. J. Benson, Vincent Fernandez, Nicholas C. Fraser, Matt Humpage, Zhe-Xi Luo, Elis Newham and Stig Walsh published in the journal Nature.

The Everything Dinosaur website: Prehistoric Animal Models and Toys.

And so, the hammer came down and bidding ended on a remarkable Stegosaurus fossil skeleton that had been offered for sale at the auction house Sotheby’s (New York).  The Stegosaurus specimen, nicknamed “Apex” sold for a whopping $44.6 million USD (£34.5 million GBP).  This is a world record amount for a dinosaur fossil.  It had an estimated value of between $4 million and $6 million USD.  However, as the bidding started this was soon exceeded.

Seven bidders wanted this Stegosaurus, and they were prepared to pay big bucks to get it.  After fifteen minutes of frantic excitement lot thirteen was sold.  Unsurprisingly, given the sums involved, the Stegosaurus fossil skeleton was purchased by an anonymous bidder.  The buyer is believed to be a billionaire hedge fund owner (Kenneth Griffin).

The stunning Stegosaurus skeleton “Apex” sold for a world record amount of $44.6 million USD at Sotheby’s New York. Picture credit: Matthew Sherman.

Picture credit: Matthew Sherman

“Apex” A Stunning Stegosaurus Fossil Skeleton

“Apex” was discovered on privately owned land in Moffat County, Colorado.  The land is owned by a commercial palaeontologist called Jason Cooper.  It is ironic, that the dig site was close to the small town of Dinosaur. The material, representing a single animal, consists of 254 fossil bones. This represents nearly eighty percent of the entire skeleton. The estimated number of bones in a Stegosaurus skeleton is 319, give or take the odd chevron.

Not only is it one of the most complete large dinosaur skeletons discovered, the bones bear witness to some remarkable pathology that helps tell the tale of this iconic Late Jurassic herbivore. The mounted skeleton measures over 8.2 metres long.

The impressive “thagomizer” on “Apex” the Stegosaurus fossil skeleton. Picture credit: Matthew Sherman.

Picture credit: Matthew Sherman

Auction House and Commercial Palaeontologist Co-operating Closely

Cassandra Hatton, Sotheby’s Global Head of Science & Popular Culture worked closely with Jason Cooper from the day of discovery onwards.  The fossils were carefully documented and excavated.  The material was prepared and mounted and at each stage the highest standards of transparency were adhered to.  The aim being to preserve as much information about the fossils as possible.  Skin impressions were noted and three, tiny ossicles representing throat armour were carefully extracted from the Morrison Formation matrix.  These also ended up as part of the Stegosaurus lot.

This is the first time an auction house has been so intimately involved with a dinosaur skeleton.

Cassandra stated:

“This sale has been years in the making, and at every turn, we have worked closely with Jason Cooper, from the moment of its discovery in Dinosaur, Colorado, to its sale in New York.  I am thrilled that such an important specimen has now taken its place in history, some 150 million years since it roamed the planet.  This remarkable result underscores our unwavering commitment to preserving these ancient treasures.”

Following the sale, the anonymous buyer is believed to have remarked:

“Apex was born in America and is going to stay in America!”

An Amazing Specimen

The fossil was preserved in hard sandstone and the black colour is typical of Morrison Formation specimens.  The fossils represent a fully-grown, robust adult and the fossilisation is described as “superb”, with little or no distortion.  Along with the skin impressions, fragile cervical plates and elements of the pebbly throat armour have been preserved.  Some fossil bones indicate the presence of arthritis.  This suggests “Apex” lived to an old age.  There are no signs of combat injuries or trauma on the bones.  In addition, there is no evidence of post-mortem scavenging by theropod dinosaurs.

A spokesperson from Everything Dinosaur commented that it was hoped that this remarkable Stegosaurus fossil skeleton would be made available to science for further study.

The spokesperson added:

“Commercial palaeontologists play an important role as they excavate specimens that could have been lost to science through erosion and weathering.  To excavate, clean and prepare such a remarkable specimen would have probably cost hundreds of thousands of dollars. Whilst we understand the importance of financial gain in these situations, and we suspect a portion of the money will be reinvested in further field work and research, hopefully, this specimen will be made available to the scientific community for further analysis and study.”

Sotheby’s Natural History Auction

The auction featured numerous amazing fossil specimens as well as meteorites, minerals, gogottes and for the first time, Palaeolithic tools including tools made by Neanderthals.  The Neanderthal tools sold for $22,800 USD, much higher than the pre-auction estimate.  A large iridescent ammonite fetched an eye-watering $72,000 USD.

Other fossils in the auction included mass mortality trilobite fossils from Morocco, Megalodon otodus teeth, fossil eurypterids from New York and beautiful fossilised fish. The natural history themed auction also featured meteorites and rare minerals including a large lapiz lazuli tower from Afghanistan.

The auction also included numerous dinosaur fossils such as a Tyrannosaurus rex femur, two T. rex teeth and an Edmontosaurus (E. annectens) skull.

Lot 26 the Edmontosaurus skull with an estimated value of between $40,000 and $60,000 USD. Picture credit: Sotheby’s New York.

Picture credit: Sotheby’s New York

Auctions of fossils and other rare objects can be controversial.  For example, Everything Dinosaur has previously reported upon the seizure of a Tarbosaurus specimen after evidence emerged that it had been illegally smuggled out of Mongolia.

To read more about this: Tyrannosaur Skeleton Smuggled out of Mongolia.

Sadly, there is a lot of illegal fossil collecting taking place. Many of these specimens are sold on the black market and find their way into Europe and America.  However, the authorities in many countries are cracking down on this illegal trade and some perpetrators have been jailed.

Fossil dealer incarcerated: American Fossil Dealer is Jailed.

The spokesperson from Everything Dinosaur commented:

“It is worrying to read of other rare items being offered for auction, particularly the Palaeolithic tools.  The large sums of money these lots are sold for could incentivise unscrupulous parties to exploit archaeological sites as well as fossil quarries.  Let us hope that sales such as this leads to closer regulation and greater co-operation between countries.”

Everything Dinosaur acknowledges the assistance of a media release from Sotheby’s New York “The most valuable fossil ever sold at auction “apex” achieves $44.6m at Sotheby’s”.  This media release was available to download from the Sotheby’s New York website on 18th July 2024.