Trackways found in South Australia Hint at Polar Ornithomimids

The Ornithomimidae (Ostrich mimics), so called as their skeletons superficially resemble modern, ground living birds are known from extensive fossil material from the Northern Hemisphere.  However, the discovery of a set of dinosaur tracks, in South Australia indicates that theropods such as members of the Ornithomimidae may have roamed Gondwanaland too.  These trackways support body fossil evidence that suggest that these dinosaurs were indeed common in the Southern Hemisphere.  Indeed, the tracks made during the Cretaceous Period provide evidence of such dinosaurs living in polar regions in the southern hemisphere.  Scientists have speculated that with these trace fossils, plus evidence from dig sites in northern latitudes, the “Ostrich mimics” may have been warm-blooded.

Fossil Material

As the dinosaurs roamed the southern polar regions, they left a series of distinctive three-toed prints in the wet, sandy soil as they crossed a flood plain.  Over time, these trace fossils became compacted into cliffs and it was Anthony Martin  (Emory University) who discovered them in what is now Victoria, (Australia).

All together he found twenty-four complete prints, their different sizes perhaps representing different species or may be juveniles and adults of a single type of dinosaur.

A single three-toed print can be made out in pictures, the ruler helps to provide scale.

The tracks are all of three-toed animals (that is, three toes to walk on – digitgrade stance).  The narrow toes and their overall size indicate the bird-like prints of a type of bipedal dinosaur belonging to the theropod group – ornithomimids.  These light, cursorial dinosaurs had compact bodies, long tails, long necks and very long legs. They were swift runners and palaeontologists believe that some of the larger species such as the four-metre-long Struthiomimus (Struthiomimus sedens), that lived in North America during the Late Cretaceous (Campanian faunal stage), could have reached speeds in excess of sixty kilometres an hour.

The tracks indicated that the theropods were of three different sizes, ranging from the size of a chicken to around the size of a crane.  Their size and fossil bones found at other locations in Victoria, suggest to the researchers that these tracks represent evidence of “Ostrich mimics”.

From the Milanesia Beach

The slabs of sandstone were found along the rocky and remote Milanesia Beach in Otways National Park, west of Melbourne.  The rough surf pounds the coastal cliffs, frequently fracturing slabs and breaking them away from the cliff face.  When the tracks were made, Australia was connected to Antarctica and was located much closer to the South Pole, as a part of the ancient continent of Gondwanaland.  It is thanks to amazing fossil sites such as the famous Dinosaur Cove and East Gippsland locations (Victoria, Australia) that scientists have learnt about the incredible fauna and flora of the Cretaceous polar regions.

Martin set off on the trail toward the footprints among the ragged slabs scattering the shore after he noticed ripple marks and trace fossils of insect burrows.

He commented: “The ripples and burrows indicate a floodplain, which is the most likely area to find polar dinosaur tracks.”

Researchers cannot determine the species of the theropods from the tracks.  It’s possible they were all of the same species (possibly even a theropod family), or they could have been different species travelling in the same area at roughly the same time.  Ichnologists (scientists who study trace fossils including tracks and prints), are always reluctant to name a specific species based on the trackway evidence, however, a recent, remarkable examination of a fossil of a Protoceratops unearthed in 1965 provided ichnologists with a “holy grail” of dinosaur fossils – a body fossil of a dinosaur adjacent to a footprint from the same dinosaur species (Protoceratops).

To read more about this remarkable discovery: Stopping a Dinosaur Dead in its Tracks.

Theropod Trace Fossils

When the tracks were laid down between 115 million to 105 million years ago, (Late Aptian and Albian faunal stages) the Earth was experiencing global warming, with the average temperature of the area at 68 degrees Fahrenheit (20 degrees Celsius) — about 10 F (6 C) higher than current temperatures recorded in Victoria.  The Cretaceous is one of the warmest periods in the Earth’s recent history.  However, although the area would not have been as cold as polar regions today, dinosaurs would have had to have been tough to survive the low temperatures (it would have been cold enough to permit water to freeze at certain times of the year) and the prolonged period of darkness when the sun dipped below the horizon and the region was plunged into darkness for several months.

These harsh conditions would have dramatically affected the planet’s biology and ecology.

Martin went on to add: “These tracks provide us with a direct indicator of how these dinosaurs were interacting with the polar ecosystems during an important time in geological history.”

The discovery of potential ornithomimid tracks in what would have been a polar environment adds credence to the study carried out by researchers at Canada’s Royal Tyrrell Museum (Alberta, Canada) who proposed that pits and marks preserved in fossilised Ornithomimidae arm bones suggest these dinosaurs may have been covered in proto-feathers.

A Model of an Ornithomimid Dinosaur (Struthiomimus)

A Struthiomimus dinosaur model, part of the CollectA Age of Dinosaurs Popular range.

The model shown above is a CollectA Age of Dinosaurs Popular Struthiomimus replica, to view CollectA prehistoric animal models: CollectA Ornithomimid and Other Theropod Figures.

A spokesperson for Everything Dinosaur commented about these tracks that hint at dinosaurs from polar regions:

“‘These trackways are certainly an exciting discovery and indicate that fleet-footed theropods were living in the polar regions.  However, it is impossible to tell whether these animals were residents or seasonal migrants.  Finding such trace fossils so far south adds support to the theory that these theropods may have been feathered to help insulate them and keep them warm.  This in turn suggests that these dinosaurs may have been warm-blooded.”

The report of the footprints was published on line in the journal of Australian palaeontology “Alcheringa”.

Marine Reptile Fossil Exposed at Low Tide

It is an apt location to find the fossilised remains of a 220-million-year-old marine reptile, in the inter-tidal zone of a rock strewn beach  After all, marine reptiles were very much at home in the sea, although many types did return to the land to lay eggs, to bask in the sun and so forth.  However, for one team of dedicated researchers having to extract what could be the best preserved fossil of a thalattosaur ever found in North America meant a tricky job with time and tides against them.

Marine Reptile Fossil

Thalattosaurs were a group of diapsid, marine reptiles known from Middle and Upper Triassic aged strata. These animals superficially resembled monitor lizards, but they were not closely related to modern lizards (Order Squamata).  Their fossilised remains have been found all over the world – North America, Europe and China, a number of families have been identified although their taxonomic relationship to other marine reptiles such as the ichthyosaurs remains uncertain.

Some of thalattosaurs (the name means “ocean lizards”) grew to lengths in excess of 4 metres.  Finding an almost complete fossil skeleton of such a creature is an extremely rare event.

Scientists believe that the thalattosaurs evolved from terrestrial reptiles, but adapted to an aquatic life style.  Gradually the skulls become longer and the chests deeper as these creatures evolved.

Working in very difficult conditions, Ken Olson (Museum of the Rockies) realised that he and his colleagues would need some more expert help if fossils of rare marine reptiles were to be recovered from the intertidal zone.  He turned to Patrick Druckenmiller, (Earth Sciences Curator at the University of Alaska Museum of the North), who had recently been involved in a project to excavate plesiosaur fossils in Norway.

In May of this year, an intriguing vertebrate fossil had been noticed partly exposed out of rock, but to excavate this specimen would be difficult due to the fact that for most of the time the fossil was covered in sea water, the site only being exposed at very low tides.

Tongass National Forest geologist Jim Baichtal immediately sent photographs to University of Alaska Museum of the North Earth Sciences Curator Patrick, who went through the process of eliminating what it could be:

Patrick stated:

“We know the rocks are about 220 million years old.  Based on the age of the rocks and what I could see in the picture, I was 99 percent sure that’s what it was.

Triassic Fossil

Druckenmiller and his museum colleague, Kevin May, travelled to the site in mid-June to collect the specimen from the semi-exposed outcrop near the small Alaskan town of Kake. The location lies in the intertidal zone, the tide problem meant they needed to excavate during a two-day window and would only have four hours each day, when the tide was at its lowest, (Spring tide) to retrieve the fossil.

If they missed their chance, the outcrop wouldn’t be exposed again until October (the next period of extremely low tides at which the fossil would be exposed again).

The team used rock saws to hack a series of steps down to the layer of rock surrounding the fossil.  On the first day, they were able to complete the excavation just five minutes before the site was submerged.  Druckenmiller spotted more bone penetrating the rock, so the team removed an even larger section on the second day, hoping it would contain the rest of the skeleton.

Druckenmiller added:

“We couldn’t see anything that day, we thought, ‘it’s probably here and the animal is probably this long, so we’ll take out a slab about that big.”

The two slabs of rock, weighing over 200 kilogrammes between them were transported by boat to Thorne Bay, from there, they went onto to the fossil preparation laboratory at the museum.  It will take many months to reveal the rest of the skeleton but the researchers are optimistic that they have recovered an large portion of the fossil, including skull material.

Patrick went on to state:

“It’s reasonably complete and once we reveal more of the skeleton, we will be able to compare it to other thalattosaurs to see if it is a new species.”

Even if it is a known species, it will be one of the best specimens ever found in North America and possibly anywhere else in the world.  The thalattosaur is currently one of Alaska’s most compete fossil vertebrates.

After the specimen has been prepared and formally studied and the results published, the fossil will be available for display at the museum.

For models and replicas of prehistoric animals including marine reptile figures: Marine Reptiles and Prehistoric Animal Replicas.

New Jersey Mine Could Show Exact Moment of Cretaceous Mass Extinction Event

A team of researchers are busily exploring a fifteen-metre-deep hole in New Jersey in a bid to find the exact moment when the Mesozoic ended and the Cenozoic began.  The site, part of a greensand mine is one of the last locations on the eastern seaboard of the United States where Cretaceous strata can be studied,  The scientists are in a race against time as the site is due to be developed and to disappear under concrete as new houses are built.

The Mesozoic

Palaeontologist Kenneth Lacovara is one of the research team members looking deep into the mine with a view to pinpointing for the exact moment, 66 million years ago, when all dinosaurs, marine reptiles and Pterosaurs perished. That secret could be harder to uncover if the fossil material at this location can no longer be unearthed after a housing and retail development is built on this open cast pit.

Lacovara, an associate professor of biology at Drexel University in Philadelphia, looks at this 40-foot plus deep hole at the end of a dirt road and sees a line in the sand where the Cretaceous period ends. Below that line are dinosaurs, above it, not a single fossil bone belonging to a dinosaur can be found.

He thinks that the creatures his team has been uncovering here all died en masse when an extra-terrestrial body struck the Earth and changed the course of the history of life on our planet. If his theory proves correct, it would be the only burial ground of its kind and provide scientists with a living laboratory to study how the dinosaurs and their cousins the marine reptiles and pterosaurs became extinct.

New Jersey as a state has a special place in the hearts of American palaeontologists.  The first nearly complete dinosaur skeleton ever discovered was a Hadrosaurus (H foulkii) found in Haddonfield (New Jersey) in 1858.   This dinosaur was named and described by the famous American anatomist Joseph Leidy.  But over the years, the numerous silt mines that made for great dinosaur digging were replaced with housing developments and shopping malls.

Today, this site in a southwestern corner of the state is the only remaining mine for greensand, a silt used for fertiliser and water softener.  It’s also the only access to the Late Cretaceous Period on the entire eastern seaboard of the United States.

Commenting on the importance of this fossil location Lacovara stated:

“This site is the last existing window into the ancient Cretaceous period in the eastern half of the United States. It’s extraordinary.”

But the township of Mantua, a community of 15,000 people, has other plans for the site.  Township officials would like to see the mine closed and a retail and lower cost housing development built in its place.  A developer has drawn up plans that include shops and affordable housing.  The fate of this location will be decided at a municipal meeting scheduled for July 15th

Inversand, the mine’s owner, has been operating the site since 1926, digging greensand.  For years, the company has had a close relationship with palaeontologists, alerting them when they came across large fossils.

Inversand President Alan Davies commented:

“If we find something beyond the routine shark tooth or clam, we call them up.”

The biggest find he recalls happened in the 1960s, when workers came across the skull of a Mosasaurus, a giant marine reptile, that now resides at the New Jersey State Museum in Trenton.  Mining for greensand is no longer economically viable for Inversand and the company would like to end operations.  If the mine were to shut down and the pump that continuously clears groundwater out of the area were to turn off, the hole would completely fill with water in a matter of weeks, transforming it into a lake. Davis says the mine could shut within three years.

Only a Few Locations in the World Have the Geology to Highlight the End of the Mesozoic

A warm and humid Earth back in the early Mesozoic. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Facing a looming deadline, Lacovara and his team have stepped up their efforts to dig, applying for grants and enlisting students and amateur palaeontologists to shovel the grey, muddy sand for pieces of natural history.

The scientists worry that without this pit, they’ll lose a historic treasure trove.  We at Everything Dinosaur, hope that a solution can be found and at least some part of the site can be kept as open access to palaeontologists to allow them to continue their studies.

For models and replicas of North American, Late Cretaeous dinosaurs and other prehistoric animals: Wild Safari Prehistoric World Figures.

New Study Suggest Pachycephalosaurs may have Clashed Heads After All

The pachycephalosaurs (the name means “thick-headed lizards”) are often referred to as the “Bone-heads” as the most striking feature about these bird-hipped dinosaurs was their incredibly thick skulls, which in many cases were adorned with bony nodules.  Related to the ceratopsians, scientists believe that these bipeds evolved in the Early Cretaceous and survived up to the very end of the Age of Reptiles.

Pachycephalosaurs

Most of what we know about this particular group of dinosaurs comes from skull material as many genera have been named and described on the basis of the discovery of skull bones.  This is in stark contrast to other types of dinosaur, the sauropods for example, where bones relating to the head are exceptionally rare.  The thickened skulls with their solid bone domes had excellent fossil preservation potential.  Such thick bones could withstand the stresses of the fossilisation process.

Perhaps the most famous of the pachycephalosaurids is Pachycephalosaurus wyomingensis, (from which this group of dinosaurs was named).  P. wyomingensis is known from just skull material but it has been estimated to have reached lengths in excess of 8 metres, making it the largest pachycephalosaur dinosaur discovered to date.

An Illustration of Pachycephalosaurus (P. wyomingensis)

Picture credit: Everything Dinosaur

To read more about Pachycephalosaurus: Pachycephalosaurus – The “Bone-headed” Dinosaur.

Why did these dinosaurs have such thick skulls?  It was not to protect a particularly large brain, these dinosaurs had brains no bigger than any other comparable sized ornithischian, perhaps these animals evolved well-protected heads as they engaged in head-butting contests just like some sheep and antelope do today.  The ideas of pachycephalosaurs indulging in such behaviour was first put forward by the American palaeontologist Ed Colbert in 1954.

Debating the Theory

This theory has been debated ever since.  Perhaps the most famous challenge to the theory of intra-specific conflict amongst pachycephalosaurs came in 2004 when the head-butting activities of these dinosaurs was examined by two American researchers, Mark Goodwin and John “Jack” Horner.  These researchers discovered that the radiating bone structure that was thought to provide strength to the dome of the skull was only present in juvenile specimens, and not in mature adults.  It was assumed, just like in extant animals the adults would have indulged in any head-butting, not young dinosaurs.

However, new research from the University of Calgary published in the online scientific journal “PloS One” suggests that these Cretaceous dinosaurs may indeed have used their thick heads for head butting contests.  The Canadian based research team compared the fossilised skulls of two types of pachycephalosaur with the skulls of modern herbivores some of which were known to be “head-bangers”.

Bio-mechanical Studies

They concluded that previous bio-mechanical studies may have suggested that these dinosaurs butted heads, but this had been challenged by studies on how the skull bones grew and developed as the animals matured.  However, new computer analysis and modelling using advanced statistical methodologies do support the theory first put forward by Colbert, back in 1954 – that the skulls of these dinosaurs could have withstood the impact from a clash of heads.  These dinosaurs could have been head-butters after all.

The two pachycephalosaurs involved in the study were Stegoceras validum and Prenocephale prenes.  The fossil skulls of these two dinosaurs were compared to ten skulls of artiodactyls (even-toed ungulates), known to indulge in various forms of intra-specific combat including head butting.  The team found that the bony anatomy of some pachycephalosaur domes are better at protecting the brain than in any modern head-butter.

Co-author Dr Eric Snively commented:

“Pachycephalosaur domes are weird structures not exactly like anything in modern animals. We wanted to test the controversial idea that the domes were good for head-butting.  Finding out brings us closer to their social lives: were pachycephalosaurs more likely just showing off their domes like peacocks with their tails, or were they also cracking their heads together like musk oxen?”

Using CT scanning and the new statistical method for diagnosing behaviour in fossil animals, the researchers compared the bony-headed dinosaurs with modern ungulates (hoofed animals) that engage in different kinds of combat.

Dr Snively stated:

“Our analyses are the closest we can get to observing their behaviour.  In a way, we can get inside their heads by colliding them together virtually.  We combined anatomical and engineering analyses of all these animals for a pretty thorough approach.  We looked at the actual tissue types in the skulls and heads of the animals.”

Co-author and fellow researcher Dr Jessica Theodor (Associate Professor in the Biological Sciences Dept. at the University of Calgary said:

“Head-butting is a form of male-to-male competition for access to females.  It’s pretty clear that although the bones are arranged differently in the Stegoceras, it could easily withstand the kinds of forces that have been measured for the living animals that engage in head-butting.”

Studying the Skulls

Describing the skulls of animals known to crack heads as “like a good motorcycle helmet”, the team stated that the skull of a typical head-butter was hard on the outside with a sort of spongy impact absorbing material just beneath the outer surface and then a stiff, really dense coat of hardened material to protect the brain.

Images show sections through the skulls of the dinosaur Stegoceras validum, the small African antelope known as a Duiker (Cephalophus leucogaster), regarded as morphologically close to this type of pachycephalosaur and a Bighorn sheep (Ovis canadensis).

The CT scans reveal similar dome structure. A. In the Stegoceras specimen, compact bone (z1 and z3: zones 1 and 3), occurs deep and superficial to a cancellous region (z2: zone 2:). Moderately dense compact bone shows as a green band at the base of zone 3 (white line); note cancellous bone (blue) above the line in the anterior portion of this zone. B. Cephalophus. C. Similar stratification is evident in the sectioned Ovis cranium, with nearly identical zones of cancellous and compact bone broken by a ventral sinus.

The Stegoceras had an extra layer of dense bone in the middle.  Stegoceras was a small pachycephalosaur approximately three metres long, that lived in north America during the Late Cretaceous.

The researchers concluded that Llamas would crack their skulls if they indulged in head-butting.  Giraffes would not be very good at head-banging contests – their skulls could not withstand the force of too many collisions.  Musk ox and Big Horn Sheep have the sort of adaptations to help them cope with bouts of head-butting.  In this way they have similar skulls to Stegoceras, so this could be evidence to support head-banging pachycephalosaurs.

Perhaps, Colbert was onto something after all.

To view models and replicas of pachycephalosaurs and other dinosaurs: Papo Dinosaur and Prehistoric Animal Models.

Seven Hundred Million-Year-Old Fossils Pose a Puzzle

Microscopic fossils of marine organisms that lived in the Precambrian may represent the first type of life on Earth to develop the ability to secrete their own mineral coating, perhaps as protection against predators or maybe as a floatation device to help these bizarre micro-organisms remain stable in the water column.

Precambrian Fossils

The Proterozoic Eon is the name given to the period of Earth’s history that lasted from approximately 2.5 billion years ago until the start of the Palaeozoic Eon some 550 million years ago and the Cambrian geological period.  The world was very different from today, the atmosphere was probably toxic although during this immense expanse of time photosynthetic microbes began to transform the planet releasing oxygen into the atmosphere.

The continents that we know today, were not present Earth was a very alien world indeed.  However, although for much of the Proterozoic life was entirely microscopic and single-celled, by the end of this eon large, soft-bodied organisms the ancestors of plants, fungi and animals were beginning to colonise the sea bed.

It was during the Proterozoic that perhaps the most fundamental evolutionary development for life on Earth occurred – the evolution of complex cells (eukaryotes).  The first living organisms on the planet had very simple cell structures.  These organisms, most of which consisted of just one cell, had a structure that lacked a nucleus.

Over the course of this eon, cell structures gradually become more complicated with the evolution of nuclei and a cell membrane.   Now a team of U.S. based scientists have published a paper showing evidence of phosphate biomineralisation in micro-organisms dating from more than 700 million years ago – this evidence of a biochemical relationship within organisms helps support earlier published data and helps to shed light on the diversity and early evolution of eukaryotes.

Extracting Minerals from the Environment

The ability to extract minerals from the environment and use it to build a protective shell or external skeleton can be seen in a number of Phyla today.  For example, Cnidaria (corals) create exoskeletons formed from a form of calcium (argonite), more primitive corals used calcite.  Phosphates can also be used to create an exoskeleton and it is evidence of phosphate biomineralisation discovered in micro-organism fossils from rocks found in Canada that has got the researchers all excited.

Mineralised exoskeletons appear in the fossil record in abundance at the start of the Cambrian geological period, scientists believe the evolution of a mineralised exoskeleton was a key driving force in the Cambrian faunal explosion that led to a huge diversification of animal life.  Indeed, the origins of all the Phyla alive today can be traced to this period in Earth’s history.

The micro-fossils were actually discovered four years ago by a research team working on the Fifteenmile Group of strata in Yukon Province (Canada).  However, the paper detailing the research has only just been published in the scientific journal “Geology”.

Paper Published in the Academic Paper “Geology”

Images produced by scanning electron microscopes show in high resolution to plate-like structures and tiny spikes, the microfossil (Characodictyon) is approximately 20 microns long, about the fifth of a width of a human hair.

Phoebe Cohen, a postdoctoral researcher in MIT’s department of earth, atmospheric and planetary sciences, and Francis Macdonald, an assistant professor of geology at Harvard University, removed a number of candidate rocks from the remote site on the Alaskan/Canadian border and when back in the laboratory, microscopic analysis began to reveal the well-preserved fossils with their tiny shield-like plates, some even had minute spikes and points sticking out them.

Strange Organisms

These strange organisms have been identified as being members of the Characodictyon genus, lived sometime between 717 million and 812 million years ago, a time period in which single-cell organisms thrived just before the first “Snowball Earth” event, when the planet plunged into a deep freeze and became covered in vast ice sheets.

Cohen suspects the deep freeze killed off these spiny micro-organisms as no trace of such creatures have been found in younger strata.  Using scanning electron microscopy, Cohen and Macdonald, along with collaborators at UCLA, created three-dimensional images of the fossils.  The images revealed the animal was covered in plates, each about 20 microns wide (one-fifth the width of a human hair) and arranged in a honeycomb pattern, with teeth-like spines jutting out and rimming the perimeter.

The plates had patterns similar to those on modern-day Coccolithophores — spherical, single-celled algae found in enormous blooms throughout the ocean.  These algae produce their mineralised plates within vacuoles (sacs that play a role in digestion and release of waste) and ultimately extrude the plates to the surface to form protective coverings.

X-Ray Analysis

Analysis of the plate composition by X-Rays indicates that the lattice work of the plate-like structure was composed of a number of elements, shown in the images released as organic carbon (red), calcium (purple) and phosphorus (green).

The researchers think the newly discovered organisms may have formed their spiny coats similarly as these ancient creatures also lived in a water column environment.

Exactly why such a complex biomineralisation process evolved in such a simple organism remains a mystery.

Commenting on the discovery Cohen said:

“It takes a lot of effort, energy and just sheer biomass to create these.”

The researchers speculate, that the spines and plates helped the small organisms stay afloat, sort of biomineralised, phosphate based life jackets – helping to keep these sun loving creatures stable in the water column.  Today, Coccolithophores reside in the ocean’s photic zone, which extends from the surface to just above the depth at which light can no longer reach.  Maintaining the most light efficient place in this zone allows such plankton to grow and thrive — an advantage their ancient counterparts also may have developed, the researchers say.

Neoproterozoic Fossils

Intriguingly, pointing at some pre-Snowball Earth arms race, the plates may also have served as armour, discouraging other organisms from attacking them.  If this is the case then this is further evidence for more complex food chains in the Precambrian than previously thought.

Associate professor of geological sciences at the University of California, Susannah Porter stated:

“It’s a good possibility that these fossil plates functioned in defence against predators.  This would be significant if true, for it would be some of the earliest evidence for complex food webs that consist not only of primary producers … but also organisms that actively prey on other living organisms.”

The American based research team hopes that their discovery will encourage other scientists to study strata dating from a roughly similar time in the Proterozoic to search for other evidence of complex life.  This discovery provides a unique window into the diversity of early eukaryotes – the ancestors of complex celled organisms on our planet, including humans.

Visit Everything Dinosaur’s website: Everything Dinosaur.

Ancient Hominin Females Moved from the Groups they were Born Into

A team of researchers from the Max Planck Institute for Evolutionary Anthropology (Leipzig), have utilised a new research technique involving the analysis of strontium isotopes in fossilised tooth enamel to suggest that it was the females that roamed whilst the males were stay-at-homes.

Ancient Hominins

So far ranging and residence patterns amongst early hominins have been indirectly inferred from morphology, stone tool sourcing, comparison to living primates and phylogenetic models.  An international team of researchers including Sandi Copeland, Vaughan Grimes and Michael Richards (Max Planck Institute for Evolutionary Anthropology) have now investigated landscape use in Australopithecus africanus (with fossils from sites dating between 2.8-2.0 million years ago) and Paranthropus robustus (with fossils from sites dating between 1.9-1.4 million years ago) from the Sterkfontein and Swartkrans cave sites in South Africa using strontium isotope analysis. This method helps identify the geological substrate on which an animal lived during tooth mineralisation, the paper has been published in the latest edition of the science journal “Nature”.

The researchers show that a high proportion of small, but not large, hominin teeth had non-local strontium isotope compositions.  Given the relatively high levels of sexual dimorphism in early hominins, the smaller teeth probably represent females, indicating that females were more likely than males to disperse from their natal (ie. where they were born) groups.  This is similar to the dispersal pattern found in chimpanzees, bonobos, and many human groups, but dissimilar to that of most gorillas and other primates.

Established palaeontological and archaeological techniques provide little tangible evidence for how early hominins used and moved across landscapes.  For example, home range size has been estimated based on a rough correlation with body mass, and models of early hominin dispersal have relied on behaviours common among hominoids and presumed to be present in a common ancestor.

Commenting on this Dr Copeland from the Institute’s department of Human Evolution stated:

“However, the highly uncertain nature of such reconstructions limits our understanding of early hominin ecology, biology, social structure, and evolution”.

Fossil Tooth Analysis

Copeland and colleagues have now used a geochemical proxy, strontium isotope analysis of tooth enamel, to investigate early hominin landscape use.  Strontium is ingested and incorporated in trace quantities into mammalian teeth.  First, the researchers determined strontium isotopes in plant specimens that were collected within a 50 kilometre radius of the Sterkfontein and Swartkrans caves in order to establish the background of biologically available strontium across the region.  They then sampled a series of hominin tooth crowns by employing a relatively new method for measuring strontium isotopes in teeth that is called laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS).

This method is almost non-destructive as it leaves only tiny traces on the enamel surface.  The researchers found that although there is no significant difference between the proportion of non-locals in P. robustus (36 %) and A. africanus (25 %), there are significant differences between subsets of hominins defined by tooth size.

Male and Female Neanderthal Models

A female and a male Neanderthal model.

To view Neanderthal models and other prehistoric figures (whilst stocks last): CollectA Prehistoric Life Models.

Explaining the results of the study, which was carried out with the co-operation from scientists from other universities including the University of Colorado and Oxford University, Dr Copeland said:

“The strontium isotope data suggest differences in landscape use between males and females.  Because strontium was incorporated into the teeth before adulthood, when the hominins were probably travelling with their mothers, the data are unlikely to reflect differences in foraging areas between adult males and adult females.  Rather, the strontium isotopes probably indicate that females preferentially moved away from residential groups”.

The hominins’ female but not male dispersal pattern is similar to the one found in chimpanzees, bonobos, and many human groups, but dissimilar to that of most gorillas and other primates.  This suggests that early hominin social structure was not like that of gorillas in which one or few males dominate groups of females.

The small proportion of non-local large hominins could indicate that male australopiths had small home ranges, which would be surprising given that the evolution of bipedalism is commonly attributed to the need to move over large distances.  The results could also imply that male australopiths preferred the types of resources found on dolomite landscapes.  This study was the first to apply this method to early fossil hominins, and lays the groundwork for future studies of other fossil species, including Australopithecus and Paranthropus in East Africa, and later hominins belonging to our genus Homo.