CT Scan of Ancient Whale Reveals Evolution of Echolocation

There are many different types of dolphins, porpoises and toothed whales around today.  These sleek, marine mammals are characterised by their superb adaptations to their environment, social behaviours, their intelligence and also their ability to use a complex sensory system to make sense of their underwater world.

Echolocation in Whales

Modern toothed whales (Odontocetes), use sonar frequencies (echolocation) to communicate with each other, for navigation and to locate and capture prey.  These are the only marine mammals to have evolved the ability to hear and make sense of such high frequency sounds.  But how did this super sensitive system evolve?  This is a question that we are part way to solving thanks to a remarkable piece of research carried out by scientists at Monash University and  Museum Victoria (Australia).

An Illustration of a Prehistoric Whale – Dorudon

Fossils of ancient whales trace their evolution, but when did echolocation evolve?

Picture credit:  Julius Csotonyi.

CT Scan of Ancient Whale Inner Ear Bone

In a paper published in the Royal Society’s journal “Biology Letters”, the researchers which included PhD student Travis Park (School of Biological Sciences, Monash University and Geosciences, Museum Victoria, both in Melbourne, Australia) explain how they borrowed a fossilised inner ear (cochlea) from the vertebrate fossil collection of the Smithsonian Institute and subjected the object to a CT scan (computerised tomography) to see inside and reveal the intricate structures that made up the hearing mechanism.

Student Travis Park Compares the Fossil Bone to the Inner Ear of an Extant Dolphin

The fossil cochlea (left) compared to the cochlea of a modern dolphin (right). Study suggests ancient toothed whales had echolocation.

Picture credit: Ben Healley

Comparing Extant with Extinct

Today’s dolphins and toothed whales produce high frequency sounds in their nasal passages.  These are transmitted through air sinuses and a specialised organ, the melon, which consists of a mass of fatty tissue.  It is the melon that propagates these sounds into the surrounding environment.  These sounds “bounce” of objects in the animal’s surroundings and the reflected signals reach the inner ear (cochlea) via acoustic fat pads that are located at the end of the lower jaw bone and the middle ear.

The CT scan produced a three-dimensional image of the cochlea and an assessment of the ancient creature’s hearing abilities could then be made using the cochlea of modern, extant dolphin as a benchmark.

Ancient Whale Fossil Ear Bone

The 26-million-year-old fossil ear bone from a xenorophid (one of the earliest Odontocetes known) revealed internal structures that were remarkably similar to those found in extant toothed whales.  The team concluded that ancient Oligocene whales had ears tuned for hearing high frequency sounds and therefore the ability to use echolocation.

A Computer Model Generated from the CT Scan Reveals the Intricate Structure

CT scan shows sophisticated cochlea of Oligocene fossil whale.

Picture credit: Biology Letters

The picture above shows (a) the fossil bone with the inner ear structure superimposed on the transparent image, (b) a cross-sectional element from the CT scan showing key features of the inner ear.  Images (c) and (d) are computer models created from the CT scan that shows the shape and structure of the ancient cochlea.  From an assessment of the morphology and the structure of this cochlea, scientists have been able to determine the likely hearing abilities of the long extinct animal.

Commenting on the outcomes of the research, Travis Park stated:

“When I first looked at the inner ear of the xenorophid, I was blown away by just how similar this incredibly old toothed whale was to a modern echolocating dolphin.”

Intriguing Questions Remain

This means that even the most ancient ancestors of today’s toothed whales and dolphins had ears tuned for hearing high frequency sound, and therefore the ability to echolocate like their living relatives.  It is likely that echolocation evolved in the ancestral Odontocetes but the fossil record is incomplete and a number of tantalising questions remain, as explained by co-author of the study Dr. Erich Fitzgerald (Museum Victoria):

“Our paper shows even the earliest known fossil Odontocetes have all the tools for echolocation seen in living dolphins.  But they must have evolved from something that didn’t quite have all the tricks of the Odontocete trade.  What were those animals like and how did they start down the path to sonic super senses?  The quest for the origins of this extraordinary group of creatures continues.”

Plotting the Evolution of Echolocation in the Toothed Whales

Plotting the evolution of whale echolocation using a 26 million-year-old fossil inner ear bone.

Picture credit: Biology Letters

Charting the Evolution of the Inner Ear of Cetaceans

The diagram above charts the evolution of the inner ear in cetaceans (whales).  The fossil bone used in the study has been assigned to the Xenorophidae family (fossil specimen used in the study is USNM-534010).  The researchers suggest that over millions of years, the inner ear of these creatures evolved into organs more capable of hearing high frequency sounds.

Everything Dinosaur has written a number of articles that feature the research of Dr Fitzgerald (Senior Curator of Vertebrate Palaeontology at the Museum Victoria), he has certainly been involved in an eclectic range of studies including mapping Australia’s dinosaur diversity, looking at the origins of seals and examining the fossilised bones of a bird with “pseudo teeth” in its beak.

Australia’s diverse dinosaurs: Australia – A Dinosaur Melting Pot

The first seals of Australia: Australia’s First Seal – A Pliocene Pinniped

Giant bird with a toothy grin: Giant “Toothed” Birds Once Soared Over Australia

Triassic Fossil Study Suggests Fossil Size a Poor Predictor of Maturity in Ancient Reptiles

Scientists at the Department of Geosciences at Virginia Tech (Blacksburg, Virginia, USA), have published a paper in the “Journal of Vertebrate Palaeontology”, that challenges some of the long-held assumptions about the growth of ancient reptiles.  Using an analysis of muscle tissue scars preserved on limb bones of Triassic fossils combined with cross-sectional bone studies to examine growth and the age of individuals, the researchers conclude that dinosaurs and their close relatives within the Archosauria had much more variation in growth patterns than expected.  The growth variation does not seem to be linked to gender.

Triassic Fossils

Size of the Fossil Bone May Not be Directly Linked to the Maturity of the Animal

A study of the bones of the Triassic reptile Asilisaurus.

Picture credit: Virginia Tech

Lead author of the scientific paper Christopher Griffin is pictured above holding two differently sized leg bones (femora) of Asilisaurus kongwe the study suggests that bone size is not a good indicator of animal maturity.

Asilisaurus kongwe – On the Road to the Dinosaurs

Fossils of the silesaurid Asilisaurus kongwe were used in the study.  Sufficient fossil material had been excavated over the course of nearly ten years of field trips to the Middle Triassic sediments of Tanzania to provide a suitable sample set and this little carnivore was, most likely an ancestor of the Dinosauria.  It has been assigned to the Dinosauriforms, a clade of archosaurs that gave rise to the dinosaurs and the birds.

The researchers found that when they examined the large number of bones associated with this species, they found that mature, adult bone size did not uniformly split into two distinct groups (male and female).  Instead, they found much more variation in bone size.  It might be difficult to apply this research to the whole of the Dinosauria, but as co-author Professor Sterling Nesbitt states:

“The earliest dinosaurs grew just like their closest relatives, and there are very few features that make dinosaurs unique from their closest relatives.”

If this is the case, then the Asilisaurus study could shed light on the growth habits (ontogeny), of the dinosaurs, at least the first types of dinosaur that evolved a few million years after Asilisaurus roamed Africa.

An Illustration of Asilisaurus kongwe

Depicted as a lithe, agile, active animal.

Picture credit: Andrey Atuchin

The large sample size (most silesaurids and early dinosaurs for that matter are known from highly fragmentary fossil material), permitted the scientists to study several individual specimens that appeared to be more mature than larger specimens and individuals of the same approximate size that appeared to be a different stages of growth.

Analysis of Muscle Scars

Analysis of the scars found on the surface of the bones where tendons and muscles once attached and cross-sectional studies showing the internal structure of the bone itself, allowed the scientists to plot changes in the anatomy and bone tissue.  The researchers found that although the sample set lived roughly at the same time and in the same location, they grew differently from each other.

Think of the analogy of a modern family with siblings and cousins of different heights and weights.

The more mature an individual was at death, the larger its bone scars appeared.  As with any animal or person, an individual skeleton goes from possessing few scars to possessing many during life, with scars appearing in a particular order as the age of the individual increases.

Size is Probably a Poor Predictor of Skeletal Maturity in Silesaurids

The researchers conclude that except for the smallest and largest individuals in the study (the least and most mature respectively), size of bones is probably a poor predictor of skeletal maturity in Asilisaurus and therefore, probably in other silesaurids and ultimately the early members of the Dinosauria as well.

Commenting on the implications for this research, Master’s student Christopher Griffin explained:

“Our study includes more individuals and more bone scars and with this increase in sample size we found that individuals fall on a trajectory that is more similar to maturity difference.  This suggests that similar variation in bone scars in early dinosaurs is variation in growth not male and female difference.  Because this variation appears to be widespread among early dinosaurs and their closest relatives, it is likely that high variation in growth between individuals characterised the most recent common ancestor of Asilisaurus and all dinosaurs.”

Articulating the Fossils of an Individual (Asilisaurus kongwe)

Fossil material laid out to represent Asilisaurus (femora labelled).

Picture credit: Virginia Tech with additional annotation by Everything Dinosaur (note the skull to the left of the picture is a model)

Growth Rates Not Well Understood

The growth rates of early, rapidly diverging ancestral dinosaurs is very poorly understood.  This study that assessed the thigh bones (femora) of Asilisaurus kongwe provides an opportunity to examine in detail the ontogeny of one of the closest known relatives of the Dinosauria.

Everything Dinosaur has written about the discovery of Asilisaurus, to read the article: Dinosaurs Around Ten Million Years Earlier than Previously Thought

Everything Dinosaur recognises the help of Virginia Tech in the compilation of this article.

Looted Dinosaur Fossils Returned Home to Mongolia

This week saw another success in the fight against illegal fossil smuggling and the black market in rare artefacts such as prehistoric animal fossils.  Officials from the U.S. Immigration and Customs returned a number of dinosaur skeletons and other fossils to the Mongolian government.  In a ceremony held in New York, investigators from the U.S. Immigration and Customs Enforcement’s (ICE) Homeland Security Investigations (HSI) handed over fossils that had been recovered from Wyoming and the “big apple”.

Dinosaur Fossils

An Articulated Psittacosaurus Dinosaur Skeleton on Display

Psittacosaurus fossils on display at the Senckenberg Naturmuseum (Frankfurt).

Picture credit: Everything Dinosaur

The Removal of Fossils from Mongolia

A law passed in the 1920s forbids the removal of artefacts deemed to be of significant cultural value from Mongolia, the returned items include nearly complete skeletons of the basal horned dinosaurs Protoceratops and Psittacosaurus, along with a beautifully preserved nest of Protoceratops eggs.  In addition, the fossils of the duck-billed dinosaur Bactrosaurus and the skull of a tyrannosaurid Alioramus as well as the skull of Psittacosaurus were returned.

Commenting on the significance of the returns, Peter Edge, (HSI’s Executive Associate Director) stated:

“Today’s ceremony is an excellent demonstration of the co-operation between HSI, our colleagues at the Department of Justice and our foreign counterparts with the Government of Mongolia.  A successful repatriation requires extensive co-operation among all parties involved, which is rewarded by the knowledge that we’ve returned what rightfully belongs to the people of Mongolia.”

Building on the Success of the Tarbosaurus bataar Repatriation

U.S. customs most noteworthy success came in 2013 with the high profile repatriation of a mounted Tarbosaurus bataar skeleton that had originally been put up for auction in New York the year before.  Tarbosaurus, like Alioramus was a member of the Tyrannosauridae family, this case resulted in the prosecution and eventual jailing of Florida fossil dealer Eric Prokopi.

To read more about this:  American Fossil Dealer Jailed for Dinosaur Smuggling

The Tarbosaurus case brought to the world’s attention the problem of illegal fossil dealing, it laid the foundation for much greater co-operation between governments and other federal bodies and sent a very clear message to the unscrupulous dealers and their middle men.  In this latest ceremony, a total of twenty-three dinosaur fossils were handed over to the Mongolian government.

A spokesperson from Everything Dinosaur commented:

“We would like to take this opportunity to congratulate all the parties involved in achieving such a successful conclusion.  These efforts will further strengthen cross-border co-operation and bilateral ties between nations as authorities attempt to reduce the level of fossil smuggling and the illegal removal and export of rare artefacts from Asia.”

An Almost Complete Protoceratops Skeleton

Picture credit: Everything Dinosaur

For models and replicas of Protoceratops and other horned dinosaurs (whilst stocks last): Beasts of the Mesozoic Figures.

Trained Investigators

HSI’s specially trained investigators, assigned to both domestic and international offices, partner with governments, agencies and experts to protect cultural antiquities.  They also train investigators from other nations and agencies to investigate crimes involving stolen property and art, and how to best enforce the law to recover these items when they emerge in the marketplace.  Those involved in the illicit trafficking of cultural property, art and antiquities can face prison terms of up to twenty years, fines and possible restitution to the purchasers of the items.

This is just the latest success for the HSI, since 2007 this American organisation has repatriated more than 8,000 items to more than thirty countries.

Everything Dinosaur acknowledges the help of the U.S. Immigration and Customs Enforcement media team for the compilation of this article.

Visit Everything Dinosaur’s website: Everything Dinosaur.