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Ancient shrimp-like animals had 'modern' hearts and blood vessels

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Ancient shrimp-like animals had 'modern' hearts and blood vessels

An international team of researchers from the University of Arizona, China and the United Kingdom has discovered the earliest known cardiovascular system, and the first to clearly show a sophisticated system complete with heart and blood vessels, in fossilized remains of an extinct marine creature that lived over half a billion years ago. The finding sheds new light on the evolution of body organization in the animal kingdom and shows that even the earliest creatures had internal organizational systems that strongly resemble those found in their modern descendants.

"This is the first preserved vascular system that we know of," said Nicholas Strausfeld, a Regents' Professor of Neuroscience at the University of Arizona's Department of Neuroscience, who helped analyze the find.

Being one of the world's foremost experts in arthropod morphology and neuroanatomy, Strausfeld is no stranger to finding meaningful and unexpected answers to long-standing mysteries in the remains of creatures that went extinct so long ago scientists still argue over where to place them in the evolutionary tree.

The 3-inch-long fossil was entombed in fine dustlike particles – now preserved as fine-grain mudstone - during the Cambrian Period 520 million years ago in what today is the Yunnan province in China. Found by co-author Peiyun Cong near Kunming, it belongs to the species Fuxianhuia protensa, an extinct lineage of arthropods combining advanced internal anatomy with a primitive body plan.

"Fuxianhuia is relatively abundant, but only extremely few specimens provide evidence of even a small part of an organ system, not even to speak of an entire organ system," said Strausfeld, who directs the UA Center for Insect Science. "The animal looks simple, but its internal organization is quite elaborate. For example, the brain received many arteries, a pattern that appears very much like a modern crustacean."

In fact, Strausfeld pointed out, Fuxianhuia's vascular system is more complex than what is found in many modern crustaceans.

"It appears to be the ground pattern from which others have evolved," he said. "Different groups of crustaceans have vascular systems that have evolved into a variety of arrangements but they all refer back to what we see in Fuxianhuia."

"Over the course of evolution, certain segments of the animals' body became specialized for certain things, while others became less important and, correspondingly, certain parts of the vascular system became less elaborate," Strausfeld said.
Ancient shrimp-like animals had 'modern' hearts and blood vessels
This image shows a schematic reconstruction of the animal, outlining the cardiovascular system in red, the brain and central nervous system in blue and the gut in green. Credit: Nicholas Strausfeld

Strausfeld helped identify the oldest known fossilized brain in a different specimen of the same fossil species, as well as the first evidence of a completely preserved nervous system similar to that of a modern chelicerates, such as a horseshoe crab or a scorpion.

"This is another remarkable example of the preservation of an organ system that nobody would have thought could become fossilized," he said.

In addition to the exquisitely preserved heart and blood vessels, outlined as traces of carbon embedded in the surrounding mineralized remains of the fossil, it also features the eyes, antennae and external morphology of the animal.

Using a clever imaging technique that selectively reveals different structures in the fossil based on their chemical composition, collaborator Xiaoya Ma at London's Natural History Museum was able to identify the heart, which extended along the main part of the body, and its many lateral arteries corresponding to each segment. Its arteries were composed of carbon-rich deposits and gave rise to long channels, which presumably took blood to limbs and other organs.

"With that, we can now start speculating about behavior," Strausfeld explained. "Because of well-supplied blood vessels to its brain, we can assume this was a very active animal capable of making many different behavioral choices."

Researchers can only speculate as to why the chemical reactions that occurred during the process of fossilization allowed for this unusual and rare kind of preservation, and as to why only select tissues were preserved between a few rare and different specimen.

"Presumably the conditions had to be just right," Strausfeld said. "We believe that these animals were preserved because they were entombed quickly under very fine-grained deposits during some kind of catastrophic event, and were then permeated by certain chemicals in the water while they were squashed flat. It is an invertebrate version of Pompeii."
Ancient shrimp-like animals had 'modern' hearts and blood vessels
This is an image of the animal's whole cardiovascular system. Credit: Xiaoya Ma

Possibly, only one in thousands of fossils might have such a well-preserved organ system, Strausfeld said.

At the time Fuxianhuia crawled on the seafloor or swam through water, life had not yet conquered land.

"Terrible sand storms must have occurred because there were probably no plants that could hold the soils," Strausfeld said. "The habitats of these creatures must have been inundated with massive fallouts from huge storms."

Tsunamis may also be the cause for the exceptional preservation.

"As the water withdraws, animals on the seafloor dry," Strausfeld said. "When the water rushed back in, they might become inundated with mud. Under normal circumstances, when animals die and are left to rot on the seafloor, they become unrecognizable. What happened to provide the kinds of fossils we are seeing must have been very different."

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Complex brains evolved much earlier than previously thought,


Complex brains evolved much earlier than previously thought, as evidenced by a 520-million year old fossilized arthropod with remarkably well-preserved brain structures. Representing the earliest specimen to show a brain, the fossil provides a "missing link" that sheds light on the evolutionary history of arthropods, the taxonomic group that comprises crustaceans, arachnids and insects.

The remarkably well-preserved fossil of an extinct arthropod shows that anatomically complex brains evolved earlier than previously thought and have changed little over the course of evolution. According to University of Arizona neurobiologist Nicholas Strausfeld, who co-authored the study describing the specimen, the fossil is the earliest known to show a brain.

The discovery will be published in the Oct. 11 issue of the journal Nature.

Embedded in mudstones deposited during the Cambrian period 520 million years ago in what today is the Yunnan Province in China, the approximately 3-inch-long fossil, which belongs to the species Fuxianhuia protensa, represents an extinct lineage of arthropods combining an advanced brain anatomy with a primitive body plan.

The fossil provides a "missing link" that sheds light on the evolutionary history of arthropods, the taxonomic group that comprises crustaceans, arachnids and insects.

The researchers call their find "a transformative discovery" that could resolve a long-standing debate about how and when complex brains evolved.

"No one expected such an advanced brain would have evolved so early in the history of multicellular animals," said Strausfeld, a Regents Professor in the UA department of neuroscience.

According to Strausfeld, paleontologists and evolutionary biologists have yet to agree on exactly how arthropods evolved, especially on what the common ancestor looked like that gave rise to insects.

"There has been a very long debate about the origin of insects," Strausfeld said, adding that until now, scientists have favored one of two scenarios.

Some believe that insects evolved from the an ancestor that gave rise to the malacostracans, a group of crustaceans that include crabs and shrimp, while others point to a lineage of less commonly known crustaceans called branchiopods, which include, for example, brine shrimp.
Complex brains evolved much earlier than previously thought, 520-million-year-old fossilized arthropod confirms
A reconstruction of the brain of the 520 million-year-old fossil Fuxianhuia protensa (left), which has a very simple body shape, yet shows unexpected similarity to the complex brain of a modern crustacean, such as the land hermit crab …more

Because the brain anatomy of branchiopods is much simpler than that of malacostracans, they have been regarded as the more likely ancestors of the arthropod lineage that would give rise to insects.

However, the discovery of a complex brain anatomy in an otherwise primitive organism such as Fuxianhuia makes this scenario unlikely. "The shape [of the fossilized brain] matches that of a comparable sized modern malacostracan," the authors write in Nature. They argue the fossil supports the hypothesis that branchiopod brains evolved from a previously complex to a more simple architecture instead of the other way around.

This hypothesis arose from neurocladistics, a field pioneered by Strausfeld that attempts to reconstruct the evolutionary relationships among organisms based on the anatomy of their nervous system. Conventional cladistics, on the other hand, usually look to an organism's overall morphology or molecular data such as DNA sequences.

Strausfeld, who holds appointments in other UA departments including evolutionary biology and entomology, has catalogued about 140 character traits detailing the neural anatomies of almost 40 arthropod groups.

"There have been all sorts of implications why branchiopods shouldn't be the ancestors of insects," he said. "Many of us thought the proof in the pudding would be a fossil that would show a malacostracan-like brain in a creature that lived long before the origin of the branchiopods; and bingo! – this is what this is."

Strausfeld traveled to the Yunnan Key Laboratory for Palaeobiology at Yunnan University in Kunming, China, to join his collaborator, Xiaoya Ma, a postdoctoral fellow at London's Natural History Museum, in studying the brain anatomies of various fossil specimens. In the institute's collection, they came across the fossil of Fuxianhuia protensa described in the paper.

"I spent a frenetic five hours at the dissecting microscope, the last hours of my visit there, photographing, photographing, photographing," he said. "And I realized that this brain actually comprises three successive neuropils in the optic regions, which is a trait of malacostracans, not branchiopods."

Neuropils are portions of the arthropod brain that serve particular functions, such as collecting and processing input from sensory organs. For example, scent receptors in the antennae are wired to the olfactory neuropils, while the eyes connect to neuropils in the optic lobes.

When Strausfeld traced the fossilized outlines of Fuxianhuia's brain, he realized it had three optic neuropils on each side that once were probably connected by nerve fibers in crosswise pattern as occurs in insects and malacostracans. The brain was also composed of three fused segments, whereas in branchiopods only two segments are fused.

"In branchiopods, there are always only two visual neuropils and they are not linked by crossing fibers," Strausfeld said. "In principle, Fuxianhuia's is a very modern brain in an ancient animal."

The fossil supports the idea that once a basic brain design had evolved, it changed little over time, he explained. Instead, peripheral components such as the eyes, the antennae and other appendages, sensory organs, etc., underwent great diversification and specialized in different tasks but all plugged into the same basic circuitry.

"It is remarkable how constant the ground pattern of the nervous system has remained for probably more than 550 million years," Strausfeld added. "The basic organization of the computational circuitry that deals, say, with smelling, appears to be the same as the one that deals with vision, or mechanical sensation."

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Extinct 'mega claw' creature had spider-like brain 520 million years ago

Research led by University of Arizona Regents' Professor Nick Strausfeld and London Natural History Museum's Greg Edgecombe has revealed 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.

The team discovered the earliest known complete nervous system exquisitely preserved in the fossilized remains of a never-before described creature that crawled or swam in the ocean 520 million years ago.

Described in the current issue of the journal Nature, the find belongs to an extinct group of marine arthropods known as megacheirans (Greek for "large claws") and solves the long-standing mystery of where this group fits in the tree of life.

"We now know that the megacheirans had central nervous systems very similar to today's horseshoe crabs and scorpions," said the senior author of the study, Nicholas Strausfeld, a Regents' Professor in the University of Arizona's department of neuroscience. "This means the ancestors of spiders and their kin lived side by side with the ancestors of crustaceans in the Lower Cambrian."

The scientists identified the 3-centimeter-long creature (a little over an inch) unearthed from the famous Chengjiang formation near Kunming in southwest China, as a representative of the extinct genus Alalcomenaeus. Animals in this group had an elongated, segmented body equipped with about a dozen pairs of body appendages enabling the animal to swim or crawl or both. All featured a pair of long, scissor-like appendages attached to the head, most likely for grasping or sensory purposes, which gave them their collective name, megacheirans.

Co-author Greg Edgecombe said that some paleontologists had used the external appearance of the so-called great appendage to infer that the megacheirans were related to chelicerates, based on the fact that the great appendage and the fangs of a spider or scorpion both have an "elbow joint" between their basal part and their pincer-like tip.

"However, this wasn't rock solid because others lined up the great appendage either a segment in front of spider fangs or one segment behind them," Edgecombe said. "We have now managed to add direct evidence from which segment the brain sends nerves into the great appendage. It's the second one, the same as in the fangs, or chelicerae. For the first time we can analyze how the segments of these fossil arthropods line up with each other the same way as we do with living species – using their nervous systems".

The team analyzed the fossil by applying different imaging and image processing techniques, taking advantage of iron deposits that had selectively accumulated in the nervous system during fossilization.

To make the neural structures visible, the researchers used computed tomography (CT), a technique that reconstructs 3-D features within in the specimen. However, "the CT scan didn't show the outline of the nervous systems unambiguously enough," Strausfeld said, "while a scanning laser technique mapping the distribution of chemical elements showed iron deposits outlining the nervous system almost as convincingly but with minor differences."
Extinct 'mega claw' creature had spider-like brain
This si an 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 …more

Next, the group applied advanced imaging techniques to the scans, first overlaying the magenta color of the iron deposit scan with the green color of the CT scan, then subtracting the two.

"We discarded any image data that were not present in both scans," Strausfeld explained. "Where the two overlapped, the magenta and the green added to each other, revealing the preserved nervous system as a white structure, which we then inverted."

This resulted in what resembled a negative X-ray photograph of the fossil.

"The white structures now showed up as black," Strausfeld said, "and out popped this beautiful nervous system in startling detail."

Comparing the outline of the fossil nervous system to nervous systems of horseshoe crabs and scorpions left no doubt that 520-million year–old Alalcomenaeus was a member of the chelicerates.

Specifically, the fossil shows the typical hallmarks of the brains found in scorpions and spiders: Three clusters of nerve cells known as ganglia fused together as a brain also fused with some of the animal's body ganglia. This differs from crustaceans where ganglia are further apart and connected by long nerves, like the rungs of a rope ladder.

Other diagnostic features 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, just like in horseshoe crabs.

To make the analysis more robust, the researchers then added these features to an existing catalog of about 150 characteristics used in constructing evolutionary relationships among arthropods based on neuroanatomical features.
Extinct 'mega claw' creature had spider-like brain
This is the fossil of the megacheiran Alalcomenaeus, a distant relative of scorpions and spiders. Credit: N. Strausfeld et al.

"Greg plugged these characteristics into a computer-based cladistic analysis to ask, 'where does this fossil appear in a relational tree?'" Strausfeld said. "Our fossil of Alalcomenaeus came out with the modern chelicerates."

But according to Strausfeld, the story doesn't end there.

"The prominent appendages that gave the megacheirans their name were clearly used for grasping and holding and probably for sensory inputs. The parts of the brain that provide the wiring for where these large appendages arise are very large in this fossil. Based on their location, we can now say that the biting mouthparts in spiders and their relatives evolved from these appendages."

Less than a year ago, the same research team published the discovery of a fossilized brain in the 520 million year-old fossil Fuxianhuia protensa, showing unexpected similarity to the complex brain of a modern crustacean.

"Our new find is exciting because it shows that mandibulates (to which crustaceans belong) and chelicerates were already present as two distinct evolutionary trajectories 520 million years ago, which means their common ancestor must have existed much deeper in time," Strausfeld said. "We expect to find fossils of animals that have persisted from more ancient times, and I'm hopeful we will one day find the ancestral type of both the mandibulate and chelicerate nervous system ground patterns. They had to come from somewhere. Now the search is on."

For this research project, Strausfeld teamed up with Gengo Tanaka of the Japan Agency for Marine-Earth Science and Technology in Yokosuka, Japan; Xianguang Hou, director of the Yunnan Key Laboratory for Paleobiology at Yunnan University in Kunming, China, and his colleague Xiaoya Ma who is presently working with Gregory Edgecombe in the paleontology department of the Natural History Museum, London.

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Half-Billion-Year-Old Heart Found More Complex than Today’s - April 24, 2014
Excerpt: "520 million years ago, the first known animal heart was formed.
It was the heart of an ancient shrimp, and quite a heart it was. For it, and its vascular system, have been found to be more complex than that of modern shrimp,"
http://www.biosciencetechnology.com/articles/2014/04/half-billion-year-old-heart-found-more-complex-today%E2%80%99s?et_cid=3902736&et_rid=653535995&type=cta

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