Brain Development in Early Mammals Linked to Development of Sense of Smell

Whilst the Dinosauria came to prominence around 215 million years ago, primitive shrew-like creatures, the ancestors of today’s modern mammals were sniffing out a survival strategy that would lead to the development of larger brains.   In a study carried out on the fossilised skulls of some ancient ancestors of true mammals, natural selection for a keener sense of smell may have been the evolutionary driver leading to bigger brains.

Early Mammals

It is not the size of the brain that makes one animal more intelligent than another, more it is a case of how the various compartments of the brain responsible for certain functions compare and the overall ratio of brain volume and capacity to body size – known as the Encephalisation Quotient or EQ.

The Encephalisation Quotient is a very simple way of  measuring the intelligence of an animal.  It is a ratio of the brain weight of the animal being studied compared to the brain weight of a control animal of the same body mass.  This method for measuring intelligence relies on the assumption that smarter animals have larger brains to body ratios than less intelligent ones.  This helps determine the relative intelligence of extinct animals, if the brain volume using CAT scans and other technology can be applied to fossil material.  In general, warm-blooded animals (like mammals) have a higher EQ than cold-blooded ones (like reptiles such as snakes and crocodiles).

Birds and mammals have brains that are about 10 times bigger than those of bony fish, amphibians, and reptiles of the same body size, that are around today.  The Dinosauria, such a diverse Order, show a huge variation in Encephalisation Quotient.  For example, Apatosaurus (A. ajax), a Sauropod from the Late Jurassic had a body length in excess of 20 metres and weighed perhaps as much as 30 Tonnes but its brain was tiny, smaller than a cricket ball.  Even the “most intelligent” of all the known Dinosaurs – troodontids would have been about as “smart” as an Emu – a flightless bird from Australia not known for its intellect.

However, researchers have puzzled over the fact that mammals have such large brains, relative to other land vertebrates such as reptiles.  A new study co-authored by Zhe-Xi Luo, a palaeontologist at the Carnegie Museum of Natural History (Pittsburgh, Pennsylvania), suggests that it was the need to develop a super effective sense of smell that led to the evolution of larger brain size.

The palaeontologist stated:

“Mammals didn’t get our larger brains for thinking.  We got it for a more urgent and more basis need – our sense of smell was far more important.”

Brain Development

Some researchers have speculated that the early, nocturnal mammals evolved larger brains to boost their hearing, as vision was less important at night.  It is assumed that these small creatures such as the triconodont Morganucodon that was analysed in this study, were nocturnal creatures.  Choosing to live in the twilight world for fear of being eaten by the dinosaurs which were much more active during the day.  Other scientists have suggested that mammal’s brains are proportionately larger because as many early mammals evolved smaller bodies their brains failed to shrink to scale.

As an aside, the concept of having the dinosaurs roam during the day, and once dusk fell having the Dinosauria hand over to a night shift that included a number of ancestral mammals is quite an outdated concept.  True, many small mammals alive today are nocturnal, so it is likely small mammalian ancestors in the Mesozoic were also probably creatures of the night.  But many scientists now believe that there were plenty of hunters around at night, quite capable of snatching up an unwary, furry multituberculate or two.

Indeed, a recent study into the orbits (eye sockets) of some dinosaur fossil skulls, concluded that some members of the Theropoda may have been night-hunters, or at least hunters in low light levels.  The predation threat from dinosaurs may have led to the evolutionary “spur” that favoured small, mammalian ancestors with better senses and hence larger brains.

The research team reconstructed the oldest known skulls of proto-mammals, the 10 cm long, shrew-like Morganucodon and Hadrocodium.  Luo and colleagues found clues to how the mammalian brain may have begun to grow bigger.  Using CAT scanning technology the researchers created three-dimensional images of the brain endocasts,  based on the fossilised impressions of brain tissue and spaces left on the inside of the preserved fossil skulls.  This gave the team a detailed view of the surface of the brain and the nasal cavities.

The team then compared these endocasts with those for seven fossils of early cynodonts – synapsids just like mammals but primitive reptiles that were abundant during the Early Triassic.  It is the cynodonts, that scientists believe, are the ancestors of mammals.  The team also examined the endocasts of twenty-seven other primitive mammals from the Mesozoic and compared their results with an analysis of the brains of 2 two hundred and seventy living mammal species.

They found that the size of the mammalian brain evolved in three major stages. First, by the time Morganucodon was alive 190 million years ago, the brain was almost 50% larger than in cynodonts, and areas that process smell, such as the olfactory bulb, were distinctly larger. Then, a short time later in Hadrocodium, the closest known relative of living mammals, the brain had expanded another 50%, with parts involved in smell accounting for most of the increase.  Thirdly, by 65 million years ago when modern types of “crown” mammals arose, regions of the brain that control neuromuscular coordination by integrating different senses had enlarged.

Examples of Early Mammals

A selection of prehistoric animal models from the Mojo “Prehistoric and Extinct” range.  Models of early mammals. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

To view models and replicas of early prehistoric mammals: Mojo Fun Prehistoric and Extinct Figures.

Images released show the computer generated image of the brain (pink) and the swollen front section of the brain equating to the olfactory bulbs (part of brain attributed to detection and analysis of sense of smell.

Biologist R. Glenn Northcutt of the University of California (UC), stated:

“The paper provides the first evidence of the relative size of the brains and which parts were initially enlarging during critical stages in the evolution of modern mammalian brains.  Until now, we could only speculate what changes were occurring and at what rate. Now we have data and can infer what selective pressures were driving brain evolution in the radiation that led to mammals.”

Biological anthropologist Terrence Deacon of UC Berkeley also praises the descriptive work that shows the olfactory bulb was “unambiguously enlarged” compared with the structure in reptiles.  But he warns that just because it was larger when the brain began to expand doesn’t mean that the sense of smell drove the size increase, it could just correlate with enlargement caused by another adaptation.

Deacon commented that regardless of the trigger, though the fossils show that a:

“Mammalian pattern of brain organisation is apparent at this very early stage of proto-mammalian evolution.”

Crocodile/Bird Split Pushed Back in Time due to New Study

A re-examination of a Early Triassic vertebrate fossil found in China during the 1970s originally thought to be an ancestor of both crocodiles and Aves (birds)  has led to scientists concluding that this fossil represents an ancestor of crocodiles only.  This suggests that the crocodile/bird evolutionary split took place earlier than previously thought – perhaps as far back as in the Palaeozoic more than 250 million years ago.

The only known specimen of Xilousuchus sapingensis has been re-examined by a Washington University based researcher and it has been re-classified as a member of the Archosauria, characterised by skulls with long, narrow snouts and teeth set in sockets.  After the Permian mass extinction event, it was the archosaurs that quickly diversified to become one of the dominant types of land vertebrate on the planet.  The archosaurs gave rise to the crocodiles, birds and to the dinosaurs.

The new examination dates the fossil of . sapingensis to the very Early Triassic period (247 million to 252 million years) commented Sterling Nesbitt, the University of Washington postdoctoral researcher responsible for this new study.  The new study places this particular reptile on the crocodile side of the archosaur family tree.

Drawings show the skull and neck vertebrae from the fossil archosaur. The areas coloured “white” in the diagrams released show the portions of the illustration that represent actual fossils.  The extended neural spines from the neck vertebrae numbers six onwards, suggest a sail-like structure on the back, similar in form and function to the sail on a pelycosaur such as Dimetrodon.

The researcher Nesbitt stated:

“We are marching closer and closer to the Permian-Triassic boundary with the origin of the archosaurs, and today the archosaurs are still the dominant land vertebrate, when you look at the diversity of birds.”

This new study could sharpen the debate amongst palaeontologists as to the origins of the Archosauria.  Did they exist before the Permian mass extinction, surviving the extinction event or were only archosaur precursors around in the Late Permian geological period?

Nesbitt added:

“Archosaurs might have survived the extinction or they might have been a product of the recovery from the extinction.”

The research is published this week in the online journal “Earth and Environmental Science Transactions of the Royal Society of Edinburgh.

Co-authors are Jun Liu of the American Museum of Natural History (New York) and Chun Li of the Institute of Vertebrate Paleontology and Palaeoanthropology (Beijing, China). Nesbitt did most of his work on the project while a postdoctoral researcher at the University of Texas at Austin.

The X. sapingensisspecimen consisting of a skull and ten vertebrae, was found in the Heshanggou Formation in northern China, an area with deposits that date from the early and mid-Triassic period, from 252 million to 230 million years ago, and further back, before the mass extinction event that brought the Permian geological period to an end.

The fossil was originally classified as an archosauriform, a “cousin” of archosaurs, rather than a true archosaur, but that was before the discovery of more complete early archosaur specimens from other parts of the Triassic period. The researchers examined bones from the specimen in detail, comparing them to those from the closest relatives of archosaurs, and discovered that X. sapingensis differed from virtually every archosauriform.

Among their findings was that bones at the tip of the jaw that bear the teeth likely were not down-turned as much as originally thought when the specimen was first described in the 1980s. They also found that neural spines of the neck formed the forward part of a sail similar to that found on another ancient archosaur called Arizonasaurus, a very close relative of Xilousuchus found in Arizona.

An Picture of Arizonasaurus

Picture credit: Everything Dinosaur

The family trees of birds and crocodiles meet somewhere in the Early Triassic and archosauriforms are the closest cousin to those archosaurs, Nesbitt said. But the new research places X. sapingensis firmly within the archosaur family tree, providing evidence that the early members of the crocodile and bird family trees evolved earlier than previously thought.

Commenting on the appearance of this ancestral crocodile, Sterling said:

“This animal is closer to a crocodile, but it’s not a crocodile. If you saw it today you wouldn’t think it was a crocodile, especially not with a sail on its back.”

On the Crocodilian Side of the Archosauria (Smok wawelski)

Smok wawelski.

To view models of Triassic archosaurs: CollectA Deluxe Prehistoric Life Models.

Advanced Technology Clears up Blurry Amber Revealing Treasures Within

Researchers at the University of Manchester (England), have used advanced computer imaging techniques combined with three-dimensional X-ray scanning technology to reveal the face and details of an ancient spider that lived during the Palaeogene Period, some forty-nine million years ago.

Ancient Spider

The spider, known as a Huntsman Spider (Sparassidae), was preserved in tree resin that solidified and formed amber, trapping this little arthropod and enabling scientists nearly fifty million years later to study it in fine detail.  Amber is a sticky, resin produced by certain trees, especially conifers.  Insects and other organisms become trapped in this resin and fossilised when it hardens into amber.

Unfortunately, over time in the presence of oxygen the amber can become opaque, thus obscuring the tiny creatures that it might contain.  The use of sophisticated X-ray computer tomography enables scientists to lift the veil on the hidden treasures that amber might contain, enabling them to build up amazingly detailed pictures of pollen, plant debris and small creatures that were trapped and preserved.

This is not the first time that spider fossils have been revealed by close examination of amber.  Back in 2009 we reported on the discovery of the remains of spider’s silk threads being preserved in a lump of amber found in the UK that dated from the Cretaceous Period.

To read this article: World’s Oldest Spider’s Web Discovered.

Scientists from Manchester University, working with their colleagues from the Berlin Natural History Museum explored the amber nodule to reveal the facial features of this ancient spider.  Their work is being reported in the scientific journal “Naturwissenschaften”.  This team have demonstrated how opaque amber nodules can yield important scientific data, when X-ray computer tomography and other sophisticated research techniques are applied.

Commenting on the study, Dr David Penney, of Manchester University’s Faculty of Life Sciences stated:

“More than 1,000 species of fossil spider have been described, many of them from amber.  The best-known source is Baltic amber, which is about 49 million years old and that has been actively studied for more than 150 years.”

He went onto add:

“Indeed, some of the first fossil spiders to be described back in 1854 were from the historically significant collection of Georg Karl Berendt, which is held in the Berlin Natural History museum.  A problem here is that these old, historical amber pieces have reacted with oxygen over time and are now often dark or cracked, making it hard to see the animal specimens inside.”

The Manchester University team were surprised to find the oldest example known of a Huntsman spider preserved in amber.  These strong and quick spiders would have been unlikely candidates to get caught in slow moving tree resin – but apparently one spider forty-nine million years ago may have been unlucky enough to have been caught.  To test the theory that the spider’s remains were indeed that of a Huntsman, an international team of experts in the fields of fossils and living spiders, and in modern techniques of computer analysis decided to re-study Georg Berendt’s original specimen to determine what it was.

The Face of the Forty-Nine Million Year Old Huntsman

Picture credit: Manchester University

Dr Penny said:

“The results were surprising.  Computed tomography produced three-dimensional images and movies of astounding quality, which allowed us to compare the finest details of the amber fossil with similar-looking living spiders.  We were able to show that the fossil is unquestionably a Huntsman spider and belongs to a genus called Eusparassus, which lives in the tropics and also arid regions of southern Europe today, but evidently lived in central Europe fifty million years ago.”

Professor Philip Withers of  Manchester University concluded:

“Normally such fossils are really hard to detect because the contrast against the amber is low but with phase contrast imaging the spiders really jump out at you in three-dimensions.  Usually you have to go to a synchrotron X-ray facility to get good phase contrast, but we can get excellent phase contrast in the lab.  This is really exciting because it opens up the embedded fossil archive not just in ambers.”

For models and replicas of ancient invertebrates from the Palaeozoic and the Mesozoic: CollectA Prehistoric Life Models and Figures.

New Primate Genus Provides Evidence of Land Bridges between Old World and New

Texas, that vast state in the southern part of the United States may be synonymous with westerns, cattle and stetsons but forty-three million years ago the area was a tropical paradise, one of the last places in North America to suffer from global cooling as the world got drier and colder.  Flourishing in this verdant, tree covered world was a primate, an animal similar to a small, modern lemur in appearance.

A Primate

The fossil evidence was found in the Devil’s Graveyard area of the Badlands of western Texas, although not complete, remains of the jaw bone have been discovered providing an insight into the animal’s facial characteristics and diet.  The animal has been formally named Mescalerolemur horneri.

M. horneri lived during the Eocene Epoch about 43 million years ago.  It is a member of an extinct primate group –- the Adapiforms, that were found throughout the Northern Hemisphere in the Eocene.  However, just like Mahgarita stevensi, a younger fossil primate found in the same area in 1973, Mescalerolemur is more closely related to Eurasian and African Adapiforms than those from North America.

Mescalerolemur horneri

Chris Kirk, Associate Professor in the Dept. of Anthropology at the University of Texas commented:

“These Texas primates are unlike any other Eocene primate community that has ever been found in terms of the species that are represented.  The presence of both Mescalerolemur and Mahgarita, which are only found in the Big Bend region of Texas, comes after the more common Adapiforms from the Eocene of North America had already become extinct.  This is significant because it provides further evidence of faunal interchange between North America and East Asia during the Middle Eocene.”

By the end of the Eocene, primates and other tropically adapted species had all but disappeared from North America due to climatic cooling, so Kirk is sampling the last burst of diversity in North American primates.  With its lower latitudes and more equable climate, West Texas offered warm-adapted species a greater chance of survival after the cooling began, a sort of safe haven against the rigours of climate change.

Associate Professor Kirk stated that Marie Butcher, a then undergraduate who graduated with degrees in anthropology and biology from The University of Texas at Austin, found the first isolated tooth of Mescalerolemur in 2005.  Since that time, many more primate fossils have been recovered by Kirk and his team at a locality called “Purple Bench.”  This fossil locality is three to four million years older than the Devil’s Graveyard sediments that had previously produced Mahgarita stevensi.

Kirk stated:
“I initially thought that we had found a new, smaller species of Mahgarita.”

However, as more specimens were prepared at the Texas Memorial Museum’s Vertebrate Paleontology Lab, Kirk realised he had discovered not just a new species, but a new genus that was previously unknown to science.

Fossils of Mescalerolemur reveal it was a small primate, weighing only about 370 grams, less than an IPad. This body weight is similar to that of the living greater dwarf lemur.  Mescalerolemur’s dental anatomy reveals a close evolutionary relationship with Adapiform primates from Eurasia and Africa, including Darwinius masillae, a German fossil primate previously claimed (in a controversial paper) to be a human ancestor.

To read more about Darwinius: Debate over “Ida” Rumbles On.

However, the discovery of Mescalerolemur provides further evidence that Adapiform primates like Darwinius are more closely related to living lemurs and bush babies than they are to humans.

For example, the right and left halves of Mescalerolemur’s lower jaws were two separate bones with a joint along the mid-line, a common trait for lemurs and bush babies.  Mahgarita stevensi, the closest fossil relative of Mescalerolemur, had a completely fused jaw joint like that of humans.

For models and replicas of prehistoric mammals: Mojo Fun Prehistoric Life Models and Figures.

The pictures released shows Mescalerolemur horneri’s partial upper jaw (in two pieces, at left) and partial lower jaw (at right) (scales = 2 mm). Explaining the significance of the difference in jawbones, Kirk said:

“Because Mescalerolemur and Mahgarita are close relatives, fusion of the lower jaws in Mahgarita must have occurred independently from that observed in humans and their relatives, the monkeys and apes.”

The new genus is named after the Mescalero Apache, native Indians, who inhabited the Big Bend region of Texas from about 1700-1880.  The species name, horneri, honours Norman Horner, an entomologist and professor emeritus at Midwestern State University (MSU) in Wichita Falls, Texas.  Horner helped to establish MSU’s Dalquest Desert Research Site, where the new primate fossils were found.  The taxonomic relationship between the various types of Old World and New World Adapiforms suggest that faunal exchange was taking place over much of the Eocene Epoch, perhaps land bridges existed that permitted this exchange of genera.

New Study Extols the Virtue of Having a Long-Neck for Sauropods

A team of UK based researchers have calculated that sauropods such as Apatosaurus and Nigersaurus evolved long-necks so that they could reach a lot of plant food material without having to move very far.  This new study has calculated that the long necks of these herbivores enabled them to gather a great deal of food without having to expend a lot energy.  Think of a Diplodocus as a thirty metre long feeding platform.

Sauropods

The scientists have compared the long-necks of sauropods to the long, extension nozzle fitted to post war vacuum cleaners, devices to help housewives and their partners cope with having to lug a heavy machine around the house.

The long necks of these highly successful group of lizard-hipped dinosaurs, taken to extremes by the enormously long neck of the sauropod Mamenchisaurus for example, resemble the solution that designers came up with when they realised that early vacuum cleaners were too cumbersome to manoeuvre easily around a room.  The fitting of a long, extension hose permitted the user to reach more area of the carpet, without having to move the heavy suction machine and the bag.

In a study led by Professor Graeme Ruxton (Glasgow University) and Dr David Wilkinson at Liverpool John Moores University, animals such as the Late Jurassic Brachiosaurus would have used 80% less energy foraging for food when its neck reached nine metres from its torso than if the neck was only six metres long.

Long-necked Dinosaurs – Nature’s Vacuum Cleaners

Picture credit: Everything Dinosaur

With a 6-metre-long neck, the heavy Brachiosaurus could only have reached food immediately beneath or above it and would have had to move to reach more, but a longer neck gave the creature the ability to feed on vegetation further away while standing still.

Sauropod Models and Replicas

For models and replicas of sauropods such as Nigersaurus, Apatosaurus and Brachiosaurus, take a look at the Wild Safari Prehistoric World model range: Safari Ltd. Wild Safari Prehistoric World Models.

A lot of work has already been undertaken by researchers as they try to understand the anatomy of sauropods, creatures that were the largest type of land animal ever to evolve, with some species reaching lengths in excess of thirty metres.  In the study, published in the scientific journal “Biology Letters” the researchers state:

“We draw an analogy here with the cylinder vacuum cleaners that were commonplace in households in industrialised countries from the 1950s to the 1970s.  Because the machinery required to create suction was large and heavy, the main body of the vacuum cleaner was positioned by the user in a central location within a room.  The user then moved the light head-part at the end of a long tube across the surrounding carpet.”

This is certainly an interesting comparison, one that helps to explain the “feeding platform” concept favoured by many palaeontologists.  Over recent years more fossils of Jurassic and Cretaceous sauropods have been discovered, indicating just how diverse this basic long-necked body plan became.

For example, the bizarre sauropod Nigersaurus (from Niger in Africa) has been nicknamed the “Mesozoic Lawnmower”, to read more about this peculiar long-necked dinosaur click the link below:

Nigersaurus: Nigersaurus – the dinosaur that grazed like a cow.