Scientists Explore how Psittacosaurus Changed as it Grew

Commenting on his painstaking research work, the now qualified Dr Zhao stated:

“Some of the bones from baby Psittacosaurus were only a few millimetres across, so I had to handle them extremely carefully to be able to make useful bone sections.  I also had to be sure to cause as little damage to these valuable specimens as possible.”

Special Permission from the IVPP

With special permission from the IVPP,  the student sectioned two arm and two leg bones from sixteen individual dinosaurs, ranging in age from less than one year to ten years old, a fully grown adult animal.  He did the intricate sectioning work in a special palaeo-histology laboratory in Bonn, Germany, with the assistance and support of Professor Martin Sander of Bonn University.

The youngest specimens, those representing individuals around twelve months in age had long arms and relatively short back legs.  This suggest that these dinosaurs would have walked on all fours.  Analysis of the bone sections indicated that the arm bones were growing at their fastest when these reptiles were between one and three years of age.  From then on, the arm growth slowed and the hind legs showed a massive growth spurt, resulting in the hind limbs growing to nearly twice the length of the fore limbs.  The hind legs took over the role of locomotion, the adults could have ambled about on all fours if they wanted to (facultative quadrupeds).

A Change in Locomotion as these Dinosaurs Matured

Picture credit: Institute of Vertebrate Palaeontology and Palaeoanthropology

Professor Xing Xu of the Beijing Institute, one of Dr Zhao’s thesis supervisors, stated:

“This is a remarkable study, the first of its kind, it shows how much information is locked in the bones of dinosaurs.  We are delighted the study worked so well, and see many ways to use these new methods to understand even more about the astonishing lives of the dinosaurs.”

Professor Mike Benton of the University of Bristol, whom team members at Everything Dinosaur have met on several occasions, and Dr Zhao’s other PhD supervisor, added:

“These kinds of studies can also throw light on the evolution of a dinosaur like Psittacosaurus.   Having four-legged babies and juveniles suggests that at some time in their ancestry, both juveniles and adults were also four-legged, and Psittacosaurus and dinosaurs in general became secondarily bipedal.”

Asking Intriguing Questions

This study does ask a number of intriguing questions.  Psittacosaurus is regarded as a basal member of the Marginocephalia, a group of ornithischian dinosaurs that would give rise to the pachycephalosaurs and the ceratopsians.  Many of the early horned dinosaurs (dinosaurs that were ancestral to giants such as Styracosaurus and Triceratops), were lithe, agile, bipedal dinosaurs, animals like Archaeoceratops and Liaoceratops.

It was only as larger genera evolved that these animals became quadrupeds.  If Psittacosaurus evolved from a type of ornithopod then it is worth noting that ornithopods such as iguanodonts suggest that these animals as youngsters were bipedal, as they matured, they adopted a four-footed stance, the opposite of what is being seen with the psittacosaur fossil material.

The exact taxonomic relationship between Early Cretaceous ornithischian dinosaurs remains unclear, perhaps fossil material ascribed to the Barremian faunal stage of the Early Cretaceous and believed to represent a new genus of iguanodontid with some advanced skull characteristics could provide further clues.

Evidence of Baby Dinosaurs – Pachyrhinosaurus perotorum

Over the last few years a number of dinosaur discoveries from Upper Cretaceous sediments from well inside the Arctic Circle have provided palaeontologists with some remarkable data regarding dinosaurs living at high latitudes.

When asked to conjure up images of dinosaur fossil discoveries, most people might think of the Badlands of the western United States or the dusty, arid, inland areas of Mongolia, the frozen, bitterly cold wastes of Alaska do not readily spring to mind.  However, a team of researchers from the Perot Museum of Nature and Science (Dallas, Texas), have been busy working their way through over ten tonnes of fossil material excavated from a site more than two hundred miles inside the Arctic Circle and they have been rewarded with the discovery of evidence of a juvenile dinosaur.

Juvenile Pachyrhinosaurus

A new species of Pachyrhinosaurus was named and described by Perot Museum scientists back in 2011 from a bone bed consisting of at least eleven individual specimens excavated from a quarry associated with the Prince Creek Formation (Upper Cretaceous).  This new type of horned dinosaur was named Pachyrhinosaurus perotorum, the third species to be assigned to the Pachyrhinosaurus genus.

To read more about this discovery: New Species of Pachyrhinosaurus Announced.

In addition to finding fossils of adults, the scientists have identified portions of the skull from a juvenile.  The presence of such a young dinosaur so far north suggests that far from migrating north each year to take advantage of the long days and good feeding opportunities the extra daylight brought, some dinosaurs may have been permanent residents coping with the harsh, cold winters at high latitudes.

Horned Dinosaur Fossil

Elements from the skull of the juvenile came from the same bone bed where the adult material was found.  The site is known as the Kikak-Tegoseak Quarry and the rocks in this area represent material deposited by rivers, the strata has been dated to approximately 69 million years of age (Early Maastrichtian faunal stage).

North Alaska today is approximately 1,500 miles from the North Pole, however, back in the Late Cretaceous it was much closer, about 350 miles away, although the temperature was much warmer than today.  Snow would have fallen occasionally but the landscape was dominated by extensive conifer forests with an understorey of hardy flowering plants and ferns.  During that part of the year, when the North Pole faces the sun there would have been constant daylight.  However, when the North Pole tilts away from the sun, northern Alaska would have endured the best part of four months in total darkness.

A Museum Quality Reconstruction of a Pachyrhinosaurus Specimen

PNSO Brian the Pachyrhinosaurus dinosaur model.

To view models and replicas of Pachyrhinosaurus and other ceratopsians: PNSO Age of Dinosaurs Figures.

The field team organised the removal and transport of the large amount of fossil material, transporting it by air and road to the preparation laboratory at the Dallas-based museum.  Dr Tykoski, the member of staff responsible for the fossil preparation work and his colleagues set about removing the fossils from the surrounding rock.  The discovery of the juvenile dinosaur fossil material was made last  year, when Dr Tykoski was working on a block of sediment about the size of a football.

Skull Elements

The fossils represent elements from the skull, an incomplete nasal bone.  Fortunately, one of the key diagnostic features of this species of Pachyrhinosaurus is the area of skull represented by the nasal bone.  The immature, juvenile specimen has a small, narrow, hardened patch on its snout, whilst in mature animals this area of the skull thickens into a large and bumpy boss.  It has been suggested that these hardened and very thick parts of the skull were used in intra-specific head-butting contests between adults.

This newly described specimen, reported in a paper published in the online academic journal “PLoS One”, shows a mix of features in the nasal bone that helps palaeontologists to assess how skull characteristics of Ceratopsian dinosaurs changed as the animal grew.  The specimen consists of an incomplete nasal bone that includes the rearward part of the nasal horn, the dorsal surface between the horn and the left-side contacts for the prefrontal and frontal bones, and some of the left side of the rostrum behind and slightly underneath in relation to the nasal horn.

The combination of morphologies in the new specimen suggests either an additional stage of development should be recognized in the ontogeny (growth and development) of the nasal boss of Pachyrhinosaurus, or that the ontogenetic pathway of nasal boss development in P. perotorum was notably different from that of other species within the Pachyrhinosaurus genus.

How the Skull Features of P. perotorum Grew and Developed

How a baby P. perotorum grew up.

Picture credit: Perot Museum of Nature and Science

Pachyrhinosaurus perotorum

A series of Pachyrhinosaurus perotorum skulls (on the left) and stylized life reconstructions (on the right) at three (of a proposed six) different life stages.  Stage 2 skull is based on juveniles of the closely related species Pachyrhinosaurus lakustai from southern Alberta.  The Stage 4 skull represents a ‘partially grown’ or ‘early adolescent’ individual, based on the new specimen (DMNH 21460) discovered in 2012 by the museum preparation team.  The Stage 6 skull is that of a mature adult, based on DMNH 22558, a nearly complete Pachyrhinosaurus perotorum skull described by Fiorillo and Tykoski in 2012 and currently on public exhibit in the Perot Museum of Nature and Science.

The ‘fleshed-out’ reconstructions are based on previously published ideas of Pachyrhinosaurus skin structures, but modified to reflect new information revealed by the new specimen (DMNH 21460).  Light tan indicates ‘normal’ skin, while dark brown indicates cornified (= thickened, hardened, horn-tissue-covered) scales, horns, sheaths, or other cornified tissue.  Scale bar equals 50 cm.

A Juvenile Specimen

Commenting on the discovery of juvenile Pachyrhinosaurus mateial Dr Tykoski stated:

“After a couple weeks of working on it, our question was ‘what on earth is this?’  It had features on it that looked like the big adult skull of the Pachyrhinosaurus perotorum that we had originally found, yet it was very narrow and skinny and didn’t have the big expanded nose of the adult.  After ruling out all of the possibilities through the process of elimination, we realised this was a juvenile specimen.  This provided us a snapshot in the development of the species – and that’s not common – so this was a very exciting moment for us.”

The finding of this juvenile specimen in and amongst the fossils of several adult animals has important ramifications.  This suggests that either very young animals migrated northwards, or perhaps they may have been born somewhere on route to the feeding grounds.  It also opens up the possibility that at least one species of large, herbivorous dinosaur was so at home in the harsh Alaskan environment that they were able to breed there and that they were perhaps permanent residents.

The Perot Museum of Nature and Science has already organised a number of return expeditions to North Alaska and the team have plans to study other likely fossil-bearing sites in a bid to learn more about these Late Cretaceous dinosaurs.

Three Different Species

At present, there are three different species of pachyrhinosaurs known, the last to be described was the Perot Museum’s North Alaskan discovery in 2011.  The species are differentiated by different morphologies on the skull.

An Illustration Showing the Differences in Skull Morphology of Pachyrhinosaurus species.

Three species of pachyrhinosaur have been described to date.

Picture credit: Perto Museum of Science and Nature

Everything Dinosaur acknowledges the help of the Perot Museum of Nature and Science in the compilation of this article.

Ancient Horse Bone Yields Oldest Sequence of DNA Known to Science

A team of international researchers have been able to sequence a substantial portion of the genome of an ancestral horse from a leg bone of a horse that roamed about in Canada some 700,000 years ago.  This research sheds light on the evolution of the Equine family and dramatically extends the known limit of DNA survival.  DNA material has been recovered from other Pleistocene aged fossils, those of Cave Bears (Ursus spelaeus), Mastodons and Mammoths but this DNA recovery is from a sample more than half a million years older than other material successfully studied to date.

Ancient Horse Bone

The study has just been published in the academic journal “Nature” the fossilised leg bone was part of a collection of horse fossils preserved in the Canadian permafrost of the Yukon.  The fossils were found at a location known as Thistle Creek (west-central Yukon Territory)

The fossils are estimated to be around 735,000 years old (Mid Pleistocene), and the fifteen centimetre long leg bone which was used in the DNA study, is part of a collection excavated out of the cold, hard permafrost back in 2003.  Leg bones, being relatively thick and robust have a greater potential for preserving organic material within them than smaller more fragile bone material.

Ancient Genetic Material Recovered from a Horse Fossil

Picture credit: D.G. Froese/Nature Journal

Extracting DNA

In a recent study, the leg bones of 158 Moas (extinct, giant flightless birds), were used to develop a framework for estimating the half-life of DNA.  This controversial research from New Zealand suggested a half-life of DNA at just 521 years.  The scientists involved with this study programme calculated that fragments of DNA could survive in perfect preservation conditions for perhaps as long as 6.8 million years, but analysis of this highly unstable, ancient material would probably prove impossible.  This new study of DNA related to Equus (horses), may not be 6.8 million years old but the ancient horse leg bone has yielded the most ancient DNA sequence know to science thus far.

To read more about the study of genetic material in Moa bones: Controversial Research Proposes a Half-Life for DNA.

Finding Organic Molecules

Ludovic Orlando, an evolutionary biologist at the University of Copenhagen and one of the co-authors of the scientific paper, explained that the team wanted to determine whether there might be any biological molecules left in this sample.  The first step was to try to identify any evidence of amino acids that would have constituted any collagen (protein found in bone), within the specimens studied.  Once the team had established that there were these proteins present, the researchers moved on in their analysis with the aim of trying to extract DNA from the ancient horse’s leg bone.

Recently, a team of scientists from Manchester University were able to identify an animal from fragments of tibia (leg bone) found in the Yukon.  The fossil bone fragments, much older than the horse fossils (dated to around 3.5 million years ago), were found to belong to a type of ancient camel.

The Manchester-based team were able to make this conclusion by tracing minute amounts of collagen in the fossilised bone and then de-coding it to see how closely it resembled the collagen found in living species.  The technique is referred to as “collagen fingerprinting”.  However, Ludovic Orlando and his colleagues were able to go further and to identify a quantity of genetic material within their sample, allowing them to sequence about seventy percent of this ancient horse’s genome.

Equus Genetic Material

Although for the majority of their 700,000 years of incarceration the horse fossils were protected from liquid water (ground water present in a fossil matrix can speed up the breakdown of organic material) and biological contaminants, the scientists were able to identify from climate change studies that the area in which the fossils had been found had thawed out on several occasions.  However, some of the Equus genetic material had still been preserved.

Of the twelve billion or so DNA molecules identified most were from bacteria that had populated the bone after the horse had died.  However, using DNA from the modern horse species as reference markers, the researchers were able to identify “endogenous DNA”, genetic material from the ancient horse itself.

From the detailed analysis of the organic material, the scientists were able to identify about 3% of the total “pool of organic data” as being horse DNA, that’s about 40 million DNA molecules.

Dr Orlando described this finding as:

“A bit of horse DNA in an ocean of microbial DNA.”

Multi-national Team of Researchers

The multi-national team of researchers pulverised a fragment of the bone to recover its DNA, then subjected it to high-throughput, next-generation gene sequencing to unravel the blueprint of this ancient horse, which team members at Everything Dinosaur have nick-named “Old Ned”, a reference to the theme to the television series “Steptoe and Son”, father and son rag and bone men who owned a horse.

A survey of the recovered DNA sequence looking for specific material in the genes known as single nucleotide polymorphisms (SNPs) has enabled the scientists to estimate past population sizes.  It seems that over the last two million years or so, the horse family has experienced a number of significant population declines and then population explosions.  Analysis of climate change data shows that there is a close match between rising horse numbers and improving (warmer) climate.

The location of the genetic differences between the ancient and modern horses also provided tantalising clues into some of the possible consequences of these genetic differences, Dr Orlando went onto explain:

“Once you have the genome, one thing you can do is to actually look at different genes that we know today are important for different traits.  What we’ve learned for example is the alleles that prime to the racing performance in domestics were not present at that time.”

Commenting on the wider implications of the study, co-author Eske Willerslev of the University of Copenhagen stated:

“Pushing back the time barrier is important because it has implications for our evolutionary understanding of anything from Hominins to other animals, because we can look further back in time than people have done previously.”

Everything Dinosaur Comments

A spokesperson from Everything Dinosaur stated:

“Ten years ago, such developments in extracting viable genetic material from such fossil material was simply not possible, next generation sequencing technology has completely revised our expectations.  If DNA can be identified from fossil material more than 700,000 years old, then this widens the net for scientists as they seek to retrieve more genetic data from fossils.”

This branch of genetics is certainly leading to a whole range of new and exciting developments, not least of which is a more complete understanding of the evolution of extant types of horse – all 4 million years of it.  The fossil material from the Yukon is an example of a “rocking horse” that could well have “rocked” our understanding of the ability of organic material to survive fossilisation.

Study of Homo erectus Fossils Suggest that Early Hominins Had the Ability to Use Projectile Weapons

Our shoulder joints are effectively a loose fitting “ball and socket” joint.  The shoulder joints in humans have given our arms great manoeuvrability and mobility.  However, as a relatively loose fitting joint with a large degree of motion, injuries can occur.

The Shoulder Joint

The ability to use our arms and shoulders to throw an object, something like a roughly shaped spear, could have enhanced our ancestor’s ability to hunt game.  The addition of more meat into their diet would have enabled them to grow larger bodies, develop bigger brains and to raise more offspring, thanks to better, protein rich nutrition.  Research by a team of scientists from George Washington and Harvard universities (United States), suggests that shoulders capable of hurling an object at speed evolved some two million years ago.

The research paper, published in the academic journal “Nature” proposes that Homo erectus evolved the ability to throw.

Homo erectus

H. erectus was a long-lived species of hominid.  It evolved around two million years ago and survived at least until about 300,000 years ago, this makes it the longest surviving species of hominid known to science.  These ancient hominids evolved in Africa but spread into south-eastern Europe and Asia.  Although very different looking to modern humans with their long, low skulls and distinctive brow ridges they used fire and made sophisticated stone tools.  Intriguingly, they were the first species along the human branch of the hominid family tree to live environments outside their African savannah homelands.  Their brains were also considerably bigger than earlier human ancestors.

Could the ability to hunt using throwing spears have enabled Homo erectus to master new environments?

Homo erectus – The First Hominid Species to be Able to Throw a Projectile?

Early hominid with a strong throwing arm?

Picture credit: Everything Dinosaur

For models and replicas of prehistoric animals and early hominids: Bullyland Prehistoric Life Models.

Use of Stop-motion Photography

The American research team used stop-motion photography to capture the range of movement and muscle action when college athletes were involved in throwing activities.  They then compared their studies with the anatomy of chimpanzees.  The team discovered that humans have the ability to throw at very high speeds, much faster than our closest living relative, the chimpanzee.   Professional athletes can reach speeds in excess of ninety miles per hour, whilst chimps, although with stronger arms and superior grip strength, they can only reach throwing speeds of twenty miles per hour.

The bio-mechanics of the throw action was analysed and it was observed that the shoulder performs like a sling-shot as the arm rotates backwards.

The Evolution of Our Ability to Throw

The shoulder joint, our most mobile joint.

Picture credit: Neil Roach

The picture above shows that the maximum shoulder rotation (pictured middle) is when elastic energy is able to power the throw.

Store Elastic Energy

The ligaments and tendons surrounding the shoulder then stretch and store elastic energy, which powers the forward throw.  When this energy is released it generates what scientists found was the fastest motion the human body produces.

Neil Roach, (George Washington University) who led the study, stated that the changes in the anatomy of early humans enabled energy storage in the shoulder that permitted fast throwing.  From this evidence it could be implied that more effective hunting methods could have come about.

He went onto add:

“Success at hunting allowed our ancestors to become part-time carnivores, eating more calorie-rich meat and fat and dramatically improving the quality of their diet.  This dietary change led to seismic shifts in our ancestors’ biology, allowing them to grow larger bodies, larger brains, and to have more children, and it also did interesting things to our social structure.  We start to see the origins of divisions of labour around that time, where some would be hunting, others would be gathering new foods.  It probably also allowed us to move to new environments, such as areas that did not have vegetation to support us before we had the ability to hunt.”

The Throwing Action

Professor Daniel Lieberman, (Harvard University) declared that for him the most fascinating aspect of this research was that half the power the humans generate from the throwing action comes from elastic energy stored in the shoulder muscles.

He commented:

“That’s not a by-product of evolution for something else, it’s clearly an adaptation.  There were shifts in our anatomy that enabled us to throw accurately, so we want to understand better just what those early hunting challenges were.”

With no evidence of spears having been found in the earliest fossils of H. erectus, this interpretation of fossil material by the American team has raised a few eyebrows (or should that be brow ridges).  Other scientists, including those that specialise in studying human and other primate anatomies have suggested that a more holistic approach to comparative anatomy be used.

Comparing Human Anatomy with that of a Chimpanzee

Chimp chest (pictured left) compared with human chest (pictured right)

Picture credit: Brian Roach/Neil Roach

Professor Susan Larson from Stony Brook University, (United States), a scientist not involved in the study, has queried the conclusions drawn from this research.  Her work also focuses on the shoulder anatomies of primates and humans in order to study their evolution.  She said it could be easy to over interpret what was significant from a fossil.

“We’re looking at the same fossils, it’s a question about how you interpret the anatomy that you see in those fossils.  Homo erectus was not necessarily such a proficient thrower.  I think [Dr Roach and colleagues] are discounting the combination of features of how the shoulder as a whole has to work.”

The few fossils of Homo erectus arms and shoulders suggest that they had an extensive range of movement.  Their hands too, were very capable of manipulating objects and showing great dexterity, however, more work is required before such conclusions can be made.

Professor Larson added:

“You cannot look at just one thing and say how a complicated piece of anatomy works, especially something like the shoulder.  You have to understand how all parts work together to bring about a broad range of motion.”

One interesting point to note, if ancient hominids like H. erectus were throwing spears, chances are they would favour either the left or right hand.  The paper has been regarded as an interesting hypothetical model rather than a definitive explanation of fossil evidence by many scientists working in this field.  For example, the humeral torsion, the angle at which the head of the humerus (funny bone) articulates with the scapula (shoulder bone) in H. erectus specimens does not fall within the range of modern throwing athletes.

There is also no evidence of asymmetry in the humeral torsion angle in H. erectus fossils that one would expect if one limb was preferred over the other for throwing.

Interesting thought, those ball tosses at Wimbledon by today’s tennis players may have a very ancient evolutionary lineage.