paleobiology

Baby Dinosaur Skeleton Unearthed In Canada

The tiny, intact skeleton of a baby rhinoceroslike dinosaur has been unearthed in Canada.

The toddler was just 3 years old and 5 feet (1.5 meters) long when it wandered into a river near Alberta, Canada, and drowned about 70 million years ago. The beast was so well-preserved that some of its skin left impressions in the nearby rock.

The fossil is the smallest intact skeleton ever found from a group of horned, plant-eating dinosaurs known as ceratopsids, a group that includes the iconic Triceratops

Rare find

Finding intact baby dinosaurs is incredibly rare.

“The big ones just preserve better: They don’t get eaten, they don’t get destroyed by animals,” said study co-author Philip Currie, a paleobiologist at the University of Alberta. “You always hope you’re going to find something small and that it will turn out to be a dinosaur.”

Paleontologists had unearthed a few individual bones from smaller ceratopsids in the past. But without intact juvenile skeletons, such bones aren’t very useful, as scientists don’t really know how each bone changes during each stage of the animals’ lives, Currie said.

The team was bone-hunting in Dinosaur Provincial Park in Alberta when Currie came upon what looked like a turtle shell sticking out from a hillside. Upon closer inspection, the fossil turned out to be a frill, the bony decorative headgear that surrounds the back of the head in ceratopsids.

When the team excavated, they found the fossilized skeleton of a tiny dinosaur they identified as a Chasmosaurus belli, a species commonly found in the area.

Researchers finally figured out how the famous “Lucy” died. Her fossil was found in 1974, but a recent analysis of her fractures shows that she fell from a tree with her arms outstretched, which suggests that not only were she and her relatives more than just ground-walkers but they’d likely reached an evolutionary point where they were no longer very good tree-climbers. Source

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A hypothesized mechanism for the origin of life, an event called abiogenesis.  In this version, called RNA world, small molecules called nucleotides formed in the waters of the early Earth during the Hadean Eon, and polymerized on the surface of clay minerals.  These simple chains of RNA could replicate themselves in solution, but only slowly and inaccurately.  An RNA molecule developed which would fold into a structure that catalyzed RNA polymerization; a ribozyme.  The first ribozymes would replicate their sister strands, and produce copies of themselves and other RNA molecules. 

     In the same environment, long chains of carbon molecules called phospholipids were formed.  These molecules have two parts, the tail, which is hydrophobic, and the head, which is hydrophillic.  Because of these properties phospholipids will stick together and form micelles and vesicles in water.  Vesicles can absorb RNA nucleotides, concentrating them and creating a space where they can replicate, mutate and evolve.  At some point a ribozyme became enclosed within a vesicle, starting a chain reaction that evolved into the multitude of biological forms that we see today.

   Because this event occurred more than 3.8 billion years ago, theories about how and where it happened are highly speculative.  Possible environments for abiogensis include hydrothermal vents on the ocean floor, hyper saline bubbles of water trapped in ice, radioactive lakes or lagoons on earths surface, and even in space or on another planet, brought to earth through a panspermia event.  We have very little molecular evidence of the first cells, but ribozymes and catalytic RNA molecules are embedded in the DNA replication machinery of all life.  Because evidence of this event has almost certainly been lost to time, the true mechanisms of the origin of life may remain a mystery to science.

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I wanted to do a few portraits of women in paleontology so here’s Mary Anning and Professor Anusuya Chinsamy-Turan. 

Mary Anning discovered the first plesiosaur skeleton and one of the first ictheosaurs and also played a key role in the discovery of coprolites (dino poo). 

Anusuya Chinsamy-Turan is a South African vertebrate paleontologist known for her expertise in the study of the microstructure of fossil teeth and bones. She’s currently the head of the department of biological sciences at the University of Cape Town. 

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I just wanted to share two amazing artists I discovered today while I was trying to draw maniraptors. The first five images are from Julio Lacerda and the last five are from Mark Witton. They are just AMAZING – I am absolutely blown away by not just the artwork but also the designs, the interaction between animals and their environments, composition, the incredible detail, and storytelling within each piece. It’s just phenomenal work. Witton also has a PhD in paleobiology and is an active researcher, and his blog is full of not just artwork but research and recent discoveries and discussions and is just fabulous.

sciencedaily.com
Seeing dinosaur feathers in a new light - Science Daily

External image
Feathers close up (stock image). The researchers’ hypothesis: The evolution of feathers made dinosaurs more colorful, which in turn had a profoundly positive impact on communication, the selection of mates and on dinosaurs’ procreation. Credit: © thawats / Fotolia [Click to enlarge image]

Why were dinosaurs covered in a cloak of feathers long before the early bird species Archaeopteryx first attempted flight? Researchers from the University of Bonn and the University of Göttingen attempt to answer precisely that question in their article “Beyond the Rainbow” in the latest issue of the journal Science. The research team postulates that these ancient reptiles had a highly developed ability to discern color. Their hypothesis: The evolution of feathers made dinosaurs more colorful, which in turn had a profoundly positive impact on communication, the selection of mates and on dinosaurs’ procreation.

The suggestion that birds and dinosaurs are close relatives dates back to the 19th century, the time when the father of evolutionary theory, Charles Darwin, was hard at work. But it took over 130 years for the first real proof to come to light with numerous discoveries of the remains of feathered dinosaurs, primarily in fossil sites in China. Thanks to these fossil finds, we now know that birds descend from a branch of medium-sized predatory dinosaurs, the so-called theropods. Tyrannosaurus rex and also velociraptors, made famous by the film Jurassic Park, are representative of these two-legged meat eaters. Just like later birds, these predatory dinosaurs had feathers – long before Archaeopteryx lifted itself off the ground. But why was this, particularly when dinosaurs could not fly?

Dinosaurs’ color vision

“Up until now, the evolution of feathers was mainly considered to be an adaptation related to flight or to warm-bloodedness, seasoned with a few speculations about display capabilities” says the article’s first author, Marie-Claire Koschowitz of the Steinmann Institute for Geology, Mineralogy and Paleontology at the University of Bonn. “I was never really convinced by any of these theories. There has to be some particularly important feature attached to feathers that makes them so unique and caused them to spread so rapidly amongst the ancestors of the birds we know today,” explains Koschowitz. She now suggests that this feature is found in dinosaurs’ color vision. After analyzing dinosaurs’ genetic relationships to reptiles and birds, the researcher determined that dinosaurs not only possessed the three color receptors for red, green and blue that the human eye possesses, but that they, like their closest living relatives, crocodiles and birds, were probably also able to see extremely short-wave and ultraviolet light by means of an additional receptor. “Based on the phylogenetic relationships and the presence of tetrachromacy in recent tetrapods it is most likely that the stem species-of all terrestrial vertebrates had photo receptors to detect blue, green, red and uv,” says Dr. Christian Fischer of the University of Göttingen.

This makes the world much more colorful for most animals than it is for human beings and other mammals. Mammals generally have rather poor color vision or even no color vision at all because they tended to be nocturnal during the early stages of their evolution. In contrast, numerous studies on the social behavior and choice of mates among reptiles and birds, which are active during the day, have shown that information transmitted via color exerts an enormous influence on those animals’ ability to communicate and procreate successfully.

Feathers allowed for more visible signals than did fur

We know from dinosaur fossil finds that the precursors to feathers resembled hairs similar to mammals’ fur. They served primarily to protect the smaller predatory dinosaurs – which would eventually give rise to birds – from losing too much body heat. The problem with these hair-like forerunners of feathers and with fur is that neither allow for much color, but tend instead to come in basic patterns of brown and yellow tones as well as in black and white. Large flat feathers solved this shortcoming by providing for the display of color and heat insulation at the same time. Their broad surface area, created by interlocked strands of keratin, allows for the constant refraction of light, which consequently produces what is referred to as structural coloration. This refraction of light is absolutely necessary to produce colors such as blue and green, the effect of metallic-like shimmering or even colors in the UV spectrum. “Feathers enable a much more noticeable optical signaling than fur would allow. Iridescent birds of paradise and hummingbirds are just two among a wealth of examples,” explains Koschowitz.

This work means we must see the evolution of feathers in a whole new light. They provided for a nearly infinite variety of colors and patterns while simultaneously providing heat insulation. Prof. Dr. Martin Sander of the University of Bonn’s Steinmann Institute summarizes the implications of this development: “This allowed dinosaurs to not only show off their colorful feathery attire, but to be warm-blooded animals at the same time – something mammals never managed.”


Story Source:

The above story is based on materials provided by Universität Bonn. Note: Materials may be edited for content and length.


Journal Reference:

  1. M.-C. Koschowitz, C. Fischer, M. Sander. Beyond the rainbow. Science, 2014; 346 (6208): 416 DOI: 10.1126/science.1258957

Fascinating!  Really, this got me thinking big time.

The Evolutionary Origins of Eusocial Insects

The extreme altruism exhibited by euso­cial insects was one of the Darwin’s dilemmas when developing his theory of natural selection. In The Origin of Species, Darwin described sterile worker castes in the social insects as “the one special difficulty, which at first appeared to me insuperable and actually fatal to my whole theory”.

The Scientist (January 1, 2015) has an article titled “The Genetics of Society” , summarizing how some researchers aim to unravel the molecular mechanisms by which a single genotype gives rise to diverse castes in eusocial organisms. See the article here: Feature: The Genetics of Society .

The cited research is yet another example of how modern molecular science is unraveling the fine details of the history of life on earth, as Darwin’s Dilemma long ago ceased being a dilemma.

How can nature select for a worker (bee or ant, for example) phenotype that solely exists to help others reproduce, when it does not have any offspring of its own? We now understand that worker behavior can evolve because workers still pass on their genes through the related offspring they help raise.

Above: A GIANT MOTHER: A queen Texas leafcutter ant (Atta texana) is many times larger than her worker daughters — who are, importantly,  all genetic sisters.

Recent research has applied genomics (gene expression transcriptomics), proteomics, phylogenomics and epigenomics, many of the various “omics” technologies that have matured and become inexpensive over the past decade.

Some of the notable findings/hypotheses supported by evidence that has emerged in recent years, as summarized in the article:

1) Each eusocial lineage evolved from a solitary ancestor—a species in which a single genome produced a single adult phenotype, as is the case for the majority of insects alive today. Based on the morphology of both extant and extinct species, it was long believed that bees represented the most ancestral of the hymenopteran lineages. However, recent high-throughput sequencing of transcriptomes indicates that wasps may in fact be the more ancient group, with bees and ants having diverged from the wasp lineage around 145 million years ago, in the lower Cretaceous Period.

2) Moreover, recent investigations of division of labor in eusocial insects with simpler societies have highlighted many of the same toolkit genes associated with castes found in the highly eusocial honeybee.

3) Some “old” genes have adopted new functions in certain species. The ancestral function of juvenile hormone (JH), for example, was to produce yolk for egg development. And in all eusocial insects studied to date, JH is upregulated in queens (i.e., the gene is expressed more), suggesting they retain the gene’s ancestral function. However, JH has also evolved a new function—regulating foraging behavior in workers of several eusocial species.

The first social insects are believed to have evolved in the upper Jurassic, and separately and independently in Insect Order Hymenoptera (bees, ants and wasps) and Infraorder Isoptera (termites). and that, among these, wasps were likely first.

Below is a detailed Cretaceous wasp insect fossil from Brazil, preserved as if in flight:

Class Insecta, Order Hymenoptera indet.
Geological Time: Lower Cretaceous Late Aptian-Cenomanian (108-92 million years ago)
Size: 14 mm long with 20 mm wingspan
Fossil Site: Crato Formation, Nova Olinda Member, Ceara, Brazil

Image credit: Virtual Fossil Museum (CC BY-NC 4.0)

Below is a lower Cretaceous termite from the Crato Formation in Brazil:

Image Credit: Fossil Mall Science (CC BY-NC 4.0)

Below is a winged ant in Miocene Dominican fossil amber:

Image Credit: Fossil Mall Science (CC BY-NC 4.0)

The final image is of an Alate, the sexual form of termites that swarm from the colony in huge numbers to fly weakly to a new site to form another colony, Soon they shed their wings and set up housekeeping. Modern-day termites time the emergence of all colonies in a region to swamp the predators, giving at least a few the opportunity to found new colonies.

Image credit: Virtual Fossil Museum (CC BY-NC 4.0)

Latest Paleo illustration from Nobu Tamura:
THE OLDEST NORTH AMERICAN VERTEBRATE
Astraspids: Jawless armored fish from the Ordovician 
455 million years ago

Source: Nobu Tamura / Spinops

Astraspis (‘star shield’) is an extinct genus of primitive jawless fish from the Ordovician of Central North America and Bolivia (Astraspis - Wikipedia)

Astraspis desiderata Walcott, 1892
Chordata → Craniata → Agnatha → †Pteraspidimorpha → †Astraspida

Late Ordovician  //  Harding Fm  //  Colorado, US
Length: 20 cm

The headshield of Astraspis was made of hundreds of small bony plates called tesserae. With Eriptychius, they constitute the earliest known definite vertebrates from North America. 

April 20, 2014 // Copyright © Nobu Tamura under Creative Commons 3.0 Unported 

More information at Tamura's Paleo Exhibit …

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Feathers for Tyrannosaurs

Feathery dinosaurs can be an acquired taste. Not everyone likes seeing animals that have traditionally been wrapped in scales begin to sprout brightly-colored plumage, especially when such changes threaten to dispel the menacing appearance of Hollywood dinosaur villains like Jurassic Park‘sVelociraptor. Of course, alterations to some dinosaurs raise the dander of fossil aficionados more than others. A fluffy Siats will stir debate among experts, but, simply by dint of the dinosaur’s celebrity, the prospect of a fuzzy tyrannosaur is a pop culture flashpoint in the tussle between dinosaurs of our childhood and the animals science is uncovering.

The impending release of Walking With Dinosaurs 3D has put tyrannosaur feathers on my mind again. The Land Before Time it ain’t, but the gorgeously-rendered animated film will undoubtedly excite the latest generation of young dinosaur fans. That’s why many paleontologists and dinosaur fans are disappointed that CGI docudrama’s villains, a gaggle of iridescent Gorgosaurus, are devoid of any fluff or fuzz.

In the grand scheme of the tyrannosaur family tree, Gorgosaurus was a large, sleek, and agile member of a subgroup called tyrannosaurids. This is the category of the most famous tyrant dinosaurs, including Tyrannosaurusitself. Yet we know relatively little about what the outside of these dinosaurs looked like. There are some rumored skin impressions – some lost, others frustratingly unpublished – that show tyrannosaurids had pebbly scales, at the very least. Befitting the traditional view of dinosaurs as scabrous reptiles, the filmmakers decided to go the conservative route and reviveGorgosaurus sans fluff.

Body size has played into the argument for scaly tyrannosaurids, too. If a 30 foot long, two ton plus Gorgosaurus had an active, hot-running metabolism, then wouldn’t an insulating coat of fluff cause the predator to overheat? Scale supporters could concede that small tyrannosaurs, and maybe even tyrannosaurid chicks, had fluff, but the prospect of a heat-addledTyrannosaurus has helped keep large tyrannosaurs scaly.

Enter Yutyrannus. Not long after the Walking With Dinosaurs 3D settled on their scaly Gorgosaurus, paleontologist Xu Xing and colleagues described a roughly 30 foot long, one and a half ton tyrannosauroid that wore an expansive coat of protofeathers. Yutyrannus, along with some experimental work on how large animals shed body heat, suggest that body size was not a barrier to being a fluffy dinosaur.

Yutyrannus was described too late to change the look of Hollywood’s latest take on Gorgosaurus. And fans of the scaly-skinned model are often quick to point out a relational barrier between the two dinosaurs. The 125 million year old Yutyrannus was an archaic from categorized as a tyrannosauroid, while Gorgosaurus was a later and more derived member within the tyrannosaurid subgroup. Since the only tyrannosaurs so far discovered with protofeathers are the tyrannosauroids Yutyrannus and the comparatively tiny Dilong, and tyrannosaurids only left behind scaly skin, then maybe tyrannosaurs shed their simple plumage over evolutionary time.

Read More

smithsonianscience.si.edu
New horse-sized tyrannosaur reveals how T. rex became top predator

Tyrannosaurs had to get smart before they got big. 

Introducing Timurlengia euotica who, with its big brain and sharp hearing, fills in a 20 million-year gap in the fossil record and explains how T. rex got to be king. 

Get to know this new (and by new, we mean 90 million years old) dinosaur, a discovery published today and coauthored by a paleontologist from our National Museum of Natural History.

youtube

Scientific Artist Reimagines The Good Dinosaur

In this full length episode, paleoartist Josh Cotton digitally re-sculpts the main character of Disney-Pixar’s The Good Dinosaur while critiquing the science of the film!

(It’s finally up! Thank you all for your patience!)

—Josh

Mesozoic moose by Hyrotrioskjan
I
’ve taken the liberty of editing this description by the artist (who is not a native speaker of English):

Therizinosaurs are said to be found in non-arid strata. They have huge feet which are perfect to cross swamps. The long neck could be used to grab water plants. Some modern birds have closable nostrils… maybe a feature which is older than we think.

I don’t mean to say Therizinosaurs were semiaquatic; I suggest instead a lifestyle  similar to the modern moose, often seen grazing in the water.

Therizinosaurs may have carried their young on their backs. The thorax was very wide, as far as know, and together with muscles, skin and feathers it was maybe a nice place to rest when Mum was searching for food.

ERAS OF THE EARTH

It wasn’t long ago that our Earth was thought to be only a few thousand years old and having been created in a matter of days. However during the scientific revolution that was taking place in the 18th and 19th centuries, minds like Darwin, Hutton and Lyell were challenging these age old theories. It was Charles Lyell that pioneered the theory that the forces of physics have remained the same throughout history, James Hutton also expressed that we can interpret the ancient past by studying modern day natural processes because the past and present are governed by the same laws. His findings reported that layers of sediment accumulated at around 2cm per year, he deduced that since mountains are sedimentary formations and thousands of metres high that the planet is more than a few thousand years old, but hundreds of millions. 

Our Earth is actually 4600 million years old, this staggeringly long time is almost impossible for the human mind to comprehend. As far as we know, life emerged as single celled organisms around 3800 million years ago, for the next 3 billion years it would remain as these minute unicellular organisms. This is the Precambrian, 4600 - 570 million years ago. 

To help us grasp the immense history of the Earth, a geological timescale was developed with each period marking a milestone in evolution and life.

CAMBRIAN 540 - 488 million years ago
Named after Cambria, an ancient name for Wales where rocks of this age are greatly exposed.
The Cambrian period sees explosive development of multicellular life with all the main modern phyla being established. Complex eyes and food chains evolve as well as active predation. Life is confined to the sea.

See Hallucigenia Opabinia Anomalocaris  

ORDOVICIAN 488 - 440 million years ago
Named for an ancient welsh tribe, the ordovices who lived in areas where rocks of this age are well exposed. Th oceans flourish with huge diversity of jawless fish, trilobites and gastropods and arthropods begin to dominate. The period ends with arthropods taking the first steps onto land. The end of the ordovician is marked by the first of the five major mass extinctions to hit the planet.

See Pterygotus Cameroceras 

SILURIAN 444 - 416 million years ago
Named for another welsh tribe, the silures, who inhabited areas where rocks of this age are abundant. Life in the oceans recovered from extinctions, magnificent coral reefs thrive in warm seas. Small plants begin to colonise the land and jawed fishes evolve.

DEVONIAN 416 - 359 million years ago
Named after the English county of Devon which is rich in Devonian age rocks and fossils. The Devonian period is also known as the age of the fishes. Jawed fish and placoderm fish rule the oceans, trilobites still thrive. Plants move from the coastal areas deep into land and the first forests spring up. Shark species increase in numbers and early forms of amphibian begin to spend more time on land.

See Dunkleosteus 

CARBONIFEROUS 359 - 299 million years ago
Known as the age of amphibians and named for the ancient coal deposits which were laid down during this time. The land is overrun with lush forests and swamps, The two main continents of the time, Eurasia and Gondwana are colliding to form the supercontinent Pangea. Winged insects take over the skies, oxygen content is much higher that today allowing insects to reach great sizes and the first true reptiles evolve, these are the first truly terrestrial vertebrates.

PERMIAN 299 - 251 million years ago
Named after Perm in Russia where rocks of the age are well exposed. Pangea is covered in harsh deserts, the number of species goes into decline, eventually 95% of them are wiped out in the worst mass extinction ever seen. Mammal like reptiles evolve. The first dinosaurs evolve towards the end of the Permian, they start as a few isolated groups and begin to increase rapidly in numbers.

See Scutosaurus Helicoprion Dimetrodon Gorgonops 

TRIASSIC 251 - 200 million years ago
Named after the word “Trias” referring to 3 rock divisions in Germany called bunter, muschelkalk and keuper. The climate of Pangea is warm and dry and dinosaurs have gradually assumed dominance in the land, skies and oceans. Mammals only exist as a few small species. Ichthyosaurs and plesiosaurs reign in the sea and reach phenomenal size.

See Proterosuchus Tanystropheus 

JURASSIC 200 - 146 million years ago
Named for the Jura mountains. Dinosaurs still dominate the land and the oceans flourish with marine reptiles and ammonites. The first bird start to appear towards the end of the Jurassic.

See Liopleurodon Megalosaurus 

CRETACEOUS 146 - 65 million years ago
Named for the latin “creta” meaning chalk which is laid down during this period and found widely now. Dinosaurs continue to dominate, the first flowering plants evolve. Sea levels are up to 300m higher than today in some areas, much of the land is covered in shallow seas. Carbon dioxide concentrations rise, slowly choking the atmosphere. The end of the cretaceous is marked by the extinction of the dinosaurs due to possible meteor impact.

See Archelon Deinosuchus Ankylosaurus 

PALEOGENE 65 - 23 million years ago
The world begins to recover, mammals and birds begin to flourish and exploit the vacant niches left behind by the dinosaurs, in doing so they grow to incredible sizes. The climate is gradually cooling and will continue to do so bringing the earth into an ice age. In these cooler conditions the first grasses evolve.

See Gastornis Paraceratherium Entelodon Andrewsarchus Ambulocetus

NEOGENE 23 - 2.5 million years ago
The climate is still cooling, ice sheets begin to spread down from the poles, as a result sea levels slowly drop. The size of forests reduce and grasslands take over resulting in vast open planes. Mammals dominate the earth due to their ability to adapt to changing environments and harsh conditions. Towards the end of the period early hominids begin to appear.

See amphicyon Glyptodonts Megalodon

QUATERNARY 2.5 million years ago to present
With an enduring ice age much of the mammalian megafauna have become extinct. Hominids have continued to evolve, only the homo sapiens survive as they are able to adapt.

See Megatherium 

Newfound Giant Dinosaur Ruled Before T.Rex

Tyrannosaurs reign as the most famous of all meat-eating dinosaurs. But they didn’t always dominate, suggests the newly discovered bones of a massive carnivorous dinosaur that lived 98 million years ago.

Named Siats meekerorum (pronounced “See-atch”), the dinosaur discovered in eastern Utah by paleontologists was a previously unknown “apex,” or top, predator that ruled long before North America’s tyrannosaurs came to power.

In the Nature Communications study published today, Lindsay Zanno of North Carolina State University and Peter Makovicky of Chicago’s Field Museum of Natural History add to our knowledge of gigantic dinosaur predators prior to the days of Tyrannosaurus rex, which lived some 67 million years ago.

At full size, the two-legged carnivore may have weighed more than four tons and stretched nearly the length of a school bus.

The discoverers report that the dinosaur’s first (or genus) name is a tribute to its predatory prowess. In the legends of Utah’s native Ute tribe, “Siats” is the name of a voracious monster.

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EARLIEST KNOWN COMPLETE NERVOUS SYSTEM DISCOVERED
Extinct ‘Mega Claw’ Creature Had Spider-Like Brain  
October 16, 2013 - University of Arizona news release

A team of researchers led by University of Arizona Professor Nick Strausfeld and London Natural History Museum’s Greg Edgecombe have discovered the earliest known complete nervous system, exquisitely preserved in the fossilized remains of a never-before described arthropod that crawled or swam in the ocean 520 million years ago.

The find suggests that the ancestors of chelicerates – spiders, scorpions and their kin – branched off from the family tree of other arthropods – including insects, crustaceans and millipedes – more than half a billion years ago.

Continue reading
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IMAGES
Fossil of the megacheiran Alalcomenaeus, a distant relative of scorpions and spiders. (Photo: N. Strausfeld et al.)

Close-up of the head region of the Alalcomenaeus fossil specimen with superimposed colors, using a microscopy technique revealing the distribution of chemical elements in the fossil.  //  Copper shows up as blue, iron as magenta and the CT scans as green. The coincidence of iron and CT denote nervous system. The creature boasted two pairs of eyes (ball-shaped structures at the top). (Photo: N. Strausfeld/UA) 

Illustration of the nervous systems of the Alalcomenaeus fossil (left), a larval horseshoe crab (middle) and a scorpion (right). Diagnostic features revealing the evolutionary relationships among these animals include the forward position of the gut opening in the brain and the arrangement of optic centers outside and inside the brain supplied by two pairs of eyes. (Illustration: N. Strausfeld/UA) 

(via UANews)