placoderms:Origins of sex discovered?

A profound new discovery announced in Nature today by palaeontologist, Flinders University Professor John Long, reveals how the intimate act of sexual intercourse first evolved in our deep distant ancestors.

In one of the biggest discoveries in the evolutionary history of sexual reproduction, Professor Long has found that internal fertilisation and copulation appeared in ancient armoured fishes, called placoderms, about 385 million years ago in what is now Scotland.

Placoderms, the most primitive jawed vertebrates, are the earliest vertebrate ancestors of humans.

Published in Nature,  the discovery shows that male fossils of the Microbrachius dicki, which belong to the antiarch group of placoderms, developed bony L-shaped genital limbs called claspers to transfer sperm to females; and females developed small paired bones to lock the male organs in place for mating.

Artist's impression of the first act of copulation in our distant ancestors. Credit: Image courtesy of Flinders University

Artist’s impression of the first act of copulation in our distant ancestors.
Credit: Image courtesy of Flinders University

Measuring about 8cm long, Microbrachius lived in ancient lake habitats in Scotland, as well as parts of Estonia and China.

As the paper’s lead author, Professor Long, who is the Strategic Professor in Palaeontology at Flinders University in South Australia, discovered the ancient fishes mating abilities when he stumbled across a single fossil bone in the collections of the University of Technology in Tallinn, Estonia, last year.

The fossils, he said, symbolise the most primitive known vertebrate sexual organ ever found, demonstrating the first use of internal fertilisation and copulation as a reproductive strategy known in the fossil record.

Microbrachius means little arms but scientists have been baffled for centuries by what these bony paired arms were actually there for. We’ve solved this great mystery because they were there for mating, so that the male could position his claspers into the female genital area,” Professor Long said.

“It was previously thought that reproduction spawned externally in water, and much later down the track in the history of vertebrate evolution,” he said.

“Our earlier discoveries published in Nature in 2008 and 2009 of live birth and copulation in placoderms concerned more advanced placoderm groups. Our new discovery now pushes the origin of copulation back even further down the evolutionary ladder, to the most basal of all jawed animals.

“Basically it’s the first branch off the evolutionary tree where these reproductive strategies started.”

In one of the more bizarre findings of his research, Professor Long said the fishes probably copulated from a sideways position with their bony jointed arms locked together.

“This enabled the males to manoeuvre their genital organs into the right position for mating.

“With their arms interlocked, these fish looked more like they are square dancing the do-se-do rather than mating.”

Flinders Postdoctoral Research Fellow Dr Brian Choo, a co-author on the paper, said the discovery signifies the first time in evolutionary history that males and females showed distinct differences in their physical appearance.

“Until this point in evolution, the skeletons of jawed vertebrates couldn’t be distinguished because males and females had the same skeletal structures,” Dr Choo said.

“This is the first time in vertebrate evolution that males and females developed separate reproductive structures, with males developing claspers, and females developing fixed plates to lock the claspers in for mating,” he said.

The discovery highlights the importance of placoderms in the evolution of vertebrate animals, including humans, Professor Long said.

“Placoderms were once thought to be a dead-end group with no live relatives but recent studies show that our own evolution is deeply rooted in placoderms, and that many of the features we have, such as jaws, teeth and paired limbs, first originated with this group of fishes.

“Now, we reveal they gave us the intimate act of sexual intercourse as well.”

Dr Matt Friedman, a palaeobiologist from the University of Oxford, UK, described the discovery as “nothing short of remarkable.”

“Claspers in these fishes demand one of two alternative, but equally provocative, scenarios: either an unprecedented loss of internal fertilisation in vertebrates, or the coherence of the armoured placoderms as a single branch in the tree of life,” Dr Friedman, who was not involved in the study, said.

“Both conclusions fly in the face of received wisdom, and suggest that there is still much to discover about this critical episode in our own extended evolutionary history.”

The research involved a team of collaborators from Australia, Estonia, the UK, Sweden and China, who scrutinised a vast number of fossil specimens held in museum collections across the world.

Fossil specimens of male and female Microbrachius fossils will be placed on public display in the foyer of the South Australian Museum from today (October 20).

A Flinders Creations video documenting the discovery, as well as an animation portraying the earliest known copulation, can be viewed here and here.

Journey to the center of the Earth:Isotope Study

A UC Santa Barbara geochemist studying Samoan volcanoes has found evidence of the planet’s early formation still trapped inside the Earth. Known as hotspots, volcanic island chains such as Samoa can ancient primordial signatures from the early solar system that have somehow survived billions of years.

Matthew Jackson, an associate professor in UCSB’s Department of Earth Science, and colleagues utilized high-precision lead and helium isotope measurements to unravel the chemical composition and geometry of the deep mantle plume feeding Samoa’s volcanoes. Their findings appear today in the journal Nature.

In most cases, volcanoes are located at the point where two tectonic plates meet, and are created when those plates collide or diverge. Hotspot volcanoes, however, are not located at plate boundaries but rather represent the anomalous melting in the interior of the plates.

Such intraplate volcanoes form above a plume-fed hotspot where the Earth’s mantle is melting. The plate moves over time — at approximately the rate human fingernails grow (3 inches a year) — and eventually the volcano moves off the hotspot and becomes extinct. Another volcano forms in its place over the hotspot and the process repeats itself until a string of volcanoes evolves.

“So you end up with this linear trend of age-progressive volcanoes,” Jackson said. “On the Pacific plate, the youngest is in the east and as you go to the west, the volcanoes are older and more deeply eroded. Hawaii has two linear trends of volcanoes — most underwater — which are parallel to each other. There’s a southern trend and a northern trend.”

This map of the Samoan hotspot shows its division into three parallel volcanic lineaments. Credit: UCSB

This map of the Samoan hotspot shows its division into three parallel volcanic lineaments.
Credit: UCSB

Because the volcanic composition of parallel Hawaiian trends is fundamentally different, Jackson and his team decided to look for evidence of this in other hotspots. In Samoa, they found three volcanic trends exhibiting three different chemical configurations as well as a fourth group of a late-stage eruption on top of the third trend of volcanoes. These different groups exhibit distinct compositions.

“Our goal was to figure out how we could use this distribution of volcano compositions at the surface to reverse-engineer how these components are distributed inside this upwelling mantle plume at depth,” Jackson said.

Each of the four distinct geochemical compositions, or endmembers, that the scientists identified in Samoan lavas contained low Helium-3 (He-3) and Helium-4 (He-4) ratios. The surprising discovery was that they all exhibited evidence for mixing with a fifth, rare primordial component consisting of high levels of He-3 and He-4.

“We have really strong evidence that the bulk of the plume is made of the high Helium-3, -4 component,” Jackson said. “That tells us that most of this plume is primordial material and there are other materials hosted inside of this plume with low Helium-3, -4, and these are likely crustal materials sent into the mantle at ancient subduction zones.”

The unique isotopic topology revealed by the researchers’ analysis showed that the four low-helium endmembers do not mix efficiently with one another. However, each of them mixes with the high He-3 and He-4 component.

“This unique set of mixing relationships requires a specific geometry for the four geochemical flavors within the upwelling plume: They must be hosted within a matrix that is composed of the rare fifth component with high He-3,” Jackson explained. “This new constraint on plume structure has important implications for how deep mantle material is entrained in plumes, and it gives us the clearest picture yet for the chemical structure of an upwelling mantle plume.”

Co-authors of the paper include Stanley R. Hart, Jerzy S. Blusztajn and Mark D. Kurz of the Woods Hole Oceanographic Institution, Jasper G. Konter of the University of Hawaii and Kenneth A. Farley of the California Institute of Technology. This research was funded by the National Science Foundation.

Mysterious Midcontinent Rift is a geological hybrid

An international team of geologists has a new explanation for how the Midwest’s biggest geological feature — an ancient and giant 2,000-mile-long underground crack that starts in Lake Superior and runs south to Oklahoma and to Alabama — evolved.

Scientists from Northwestern University, the University of Illinois at Chicago (UIC), the University of Gottingen in Germany and the University of Oklahoma report that the 1.1 billion-year-old Midcontinent Rift is a geological hybrid, having formed in three stages: it started as an enormous narrow crack in the Earth’s crust; that space then filled with an unusually large amount of volcanic rock; and, finally, the igneous rocks were forced to the surface, forming the beautiful scenery seen today in the Lake Superior area of the Upper Midwest.

 

The volcanic rocks of the 1.1 billion-year-old Midcontinent Rift play a prominent role in the natural beauty of Isle Royale National Park in Lake Superior. Credit: Image courtesy of Northwestern University


The volcanic rocks of the 1.1 billion-year-old Midcontinent Rift play a prominent role in the natural beauty of Isle Royale National Park in Lake Superior.
Credit: Image courtesy of Northwestern University

The rift produced some of the Midwest’s most interesting geology and scenery, but there has never been a good explanation for what caused it. Inspired by vacations to Lake Superior, Seth and Carol A. Stein, a husband-and-wife team from Northwestern and UIC, have been determined to learn more in recent years.

Their study, which utilized cutting-edge geologic software and seismic images of rock located below the Earth’s surface in areas of the rift, will be presented Oct. 20 at the Geological Society of America annual meeting in Vancouver.

“The Midcontinent Rift is a very strange beast,” said the study’s lead author, Carol Stein, professor of Earth and Environmental Sciences at UIC. “Rifts are long, narrow cracks splitting the Earth’s crust, with some volcanic rocks in them that rise to fill the cracks. Large igneous provinces, or LIPs, are huge pools of volcanic rocks poured out at the Earth’s surface. The Midcontinent Rift is both of these — like a hybrid animal.”

“Geologists call it a rift because it’s long and narrow,” explained Seth Stein, a co-author of the study, “but it’s got much more volcanic rock inside it than any other rift on a continent, so it’s also a LIP. We’ve been wondering for a long time how this could have happened.” He is the William Deering Professor of Geological Sciences at the Weinberg College of Arts and Sciences.

 

This question is one of those that EarthScope, a major National Science Foundation program involving geologists from across the U.S., seeks to answer. In this case, the team used images of the Earth at depth from seismic experiments across Lake Superior and EarthScope surveys of other parts of the Midcontinent Rift. The images show the rock layers at depth, much as X-ray photos show the bones in people’s bodies.

In reviewing the images, the researchers found the Midcontinent Rift appeared to evolve in three stages.

“First, the rocks were pulled apart, forming a rift valley,” Carol Stein said. “As the rift was pulling apart, magma flowed into the developing crack. After about 10 million years, the crack stopped growing, but more magma kept pouring out on top. Older magma layers sunk under the weight of new magma, so the hole kept deepening. Eventually the magma ran out, leaving a large igneous province — a 20-mile-thick pile of volcanic rocks. Millions of years later, the rift got squeezed as a new supercontinent reassembled, which made the Earth’s crust under the rift thicker.”

To test this idea, the Steins turned to Jonas Kley, professor of geology at Germany’s Gottingen University, their host during a research year in Germany sponsored by the Alexander von Humboldt Foundation.

Kley used software that allows geologic time to run backwards. “We start with the rocks as they are today,” Kley explained, “and then undo movement on faults and vertical movements. It’s like reconstructing a car crash. When we’re done we have a picture of what happened and when. This lets us test ideas and see if they work.”

Kley’s analysis showed that the three-stage history made sense — the Midcontinent Rift started as a rift and then evolved into a large igneous province. The last stage brought rocks in the Lake Superior area to the surface.

Other parts of the picture fit together nicely, the Steins said. David Hindle, also from Gottingen University, used a computer model to show that the rift’s shape seen in the seismic images results from the crust bending under weight of magma.

Randy Keller, a professor and director of the Oklahoma Geological Survey, found that the weight of the dense magma filling the rift explains the stronger pull of gravity measured above the rift. He points out that these variations in the gravity field are the major evidence used to map the extent of the rift.

“It’s funny,” Seth Stein mused. “Carol and I have been living in Chicago for more than 30 years. We often have gone up to Lake Superior for vacations but didn’t think much about the geology. It’s only in the past few years that we realized there’s a great story there and started working on it. There are many studies going on today, which will give more results in the next few years.”

The Steins now are working with other geologists to help park rangers and teachers tell this story to the public. For example, a good way to think about how rifts work is to observe what happens if you pull both ends of a Mars candy bar: the top chocolate layer breaks, and the inside stretches.

“Sometimes people think that exciting geology only happens in places like California,” Seth Stein said. “We hope results like this will encourage young Midwesterners to study geology and make even further advances.”

Microfossils reveal warm oceans had less oxygen

Researchers in Syracuse University’s College of Arts and Sciences are pairing chemical analyses with micropaleontology — the study of tiny fossilized organisms — to better understand how global marine life was affected by a rapid warming event more than 55 million years ago.

Their findings are the subject of an article in the journal Paleoceanography.

“Global warming impacts marine life in complex ways, of which the loss of dissolved oxygen [a condition known as hypoxia] is a growing concern” says Zunli Lu, assistant professor of Earth sciences and a member of Syracuse’s Water Science and Engineering Initiative. “Moreover, it’s difficult to predict future deoxygenation that is induced by carbon emissions, without a good understanding of our geologic past.”

Lu says this type of deoxygenation leads to larger and thicker oxygen minimum zones (OMZs) in the world’s oceans. An OMZ is the layer of water in an ocean where oxygen saturation is at its lowest.

Assistant Professor of Earth Sciences Zunli Lu was among the researchers to release these findings. Credit: Syracuse University

Assistant Professor of Earth Sciences Zunli Lu was among the researchers to release these findings.
Credit: Syracuse University

Much of Lu’s work revolves around the Paleocene-Eocene Thermal Maximum (PETM), a well-studied analogue for modern climate warming. Documenting the expansion of OMZs during the PETM is difficult because of the lack of a sensitive, widely applicable indicator of dissolved oxygen.

To address the problem, Lu and his colleagues have begun working with iodate, a type of iodine that exists only in oxygenated waters. By analyzing the iodine-to-calcium ratios in microfossils, they are able to estimate the oxygen levels of ambient seawater, where microorganisms once lived.

Fossil skeletons of a group of protists known as foraminiferas have long been used for paleo-environmental reconstructions. Developing an oxygenation proxy for foraminifera is important to Lu because it could enable him study the extent of OMZs “in 3-D,” since these popcorn-like organisms have been abundant in ancient and modern oceans.

“By comparing our fossil data with oxygen levels simulated in climate models, we think OMZs were much more prevalent 55 million years ago than they are today,” he says, adding that OMZs likely expanded during the PETM. “Deoxygenation, along with warming and acidification, had a dramatic effect on marine life during the PETM, prompting mass extinction on the seafloor.”

Lu thinks analytical facilities that combine climate modeling with micropaleontology will help scientists anticipate trends in ocean deoxygenation. Already, it’s been reported that modern-day OMZs, such as ones in the Eastern Pacific Ocean, are beginning to expand. “They’re natural laboratories for research,” he says, regarding the interactions between oceanic oxygen levels and climate changes.”

Earliest-known lamprey larva fossils discovered

Few people devote time to pondering the ancient origins of the eel-like lamprey, yet the evolutionary saga of the bloodsucker holds essential clues to the biological roots of humanity.

Today, the Proceedings of the National Academy of Sciences published a description of fossilized lamprey larvae that date back to the Lower Cretaceous — at least 125 million years ago.

They’re the oldest identified fossils displaying the creature in stages of pre-metamorphosis and metamorphosis.

“Among animals with backbones, everything, including us, evolved from jawless fishes,” said Desui Miao, University of Kansas Biodiversity Institute collection manager, who co-authored today’s PNAS paper. “To understand the whole arc of vertebrate evolution, we need to know these animals. The biology of the lamprey holds a molecular clock to date when many evolutionary events occurred.”

(A) This is a photograph of fossil transformer in left view. (B) Photograph of fossil transformer in left view. (C) Box area in B in higher magnification, showing the radials. (D) Photograph and (E) drawing of the head and anterior part of the body of A. (F) Photograph and (G) drawing of the head and anterior part of the body of B. Credit: Proceedings of the National Academy of Sciences

(A) This is a photograph of fossil transformer in left view. (B) Photograph of fossil transformer in left view. (C) Box area in B in higher magnification, showing the radials. (D) Photograph and (E) drawing of the head and anterior part of the body of A. (F) Photograph and (G) drawing of the head and anterior part of the body of B.
Credit: Proceedings of the National Academy of Sciences

Miao said features of the human body come from the jawless fishes, such as the lamprey, a slowly evolving organism — often parasitic — which has inhabited Earth at least since the Devonian, about 400 million years ago.

“For example, a jawless fish such as a lamprey has seven pairs of gill arches, and the anterior pair of these gill arches evolved into our upper and lower jaws,” he said. “Our middle ear bones? They come from the same pair of gill arches.”

Indeed, lamprey evolution sheds light on the development of all animals with a backbone. Because of this, scientists have yearned to discover more history about the stages of the aquatic creature’s three-phased life cycle.

However, lamprey larvae are small and soft, thus seldom fossilized.

“They just don’t have hard parts,” Miao said. “Even fully developed fossil lampreys are rare because they lack skeletons. Most fossil fishes are bony fishes — fish we eat and leave bones on the plate. But lampreys don’t have bones or teeth that can be preserved as fossils.”

Fortunately, during the lush Lower Cretaceous era, freshwater lakes covered Inner Mongolia. These waters were chock-full with the ancestors of today’s lampreys, and many fossils became beautifully preserved in a layer of late-Cretaceous shale, including larvae.

“This type of rock preserves very fine details of fossils,” Miao said. “The same rock preserved evidence of dinosaur feathers from this era. The lamprey larvae were found by local people and some by our Chinese colleagues who specialize in early fishes.”

According to the KU researcher and fellow authors Meemann Chang, Feixiang Wu and Jiangyong Zhang of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in Beijing, the larval fossils show the life cycle of the lamprey “emerged essentially in its present mode no later than the Early Cretaceous.”

This cycle consists of a long-lasting larval stage, a metamorphosis and a comparatively brief adulthood with a markedly different anatomy, according to the PNAS paper. The larvae come from the fossil lamprey species Mesomyzon mangae.

“Our larvae look modern,” Miao said. “The developmental stage is almost identical to today’s lamprey. Before this, we didn’t know how long lampreys have developed via metamorphosis. Now, we know it goes back 125 million years at least. In other words, lampreys haven’t changed much — and that’s very interesting.”

Then, like today, lampreys lived in both freshwater and saltwater. At the larval stage, they’d have dwelled in the sand or mud and drawn nutrients from micro-organisms in the water. Then, as mature lampreys, some of them would have subsisted by fastening themselves to host organisms and swigging their blood — often killing their host in the end.

“They attach to larger fish or whales,” Miao said. “They hold on forever.”

The National Basic Research Program of China, the Asian-Swedish Research Partnership Program of the Swedish Research Council and KU Endowment supported this research.

The unexamined diversity in the ‘Coral Triangle’

Research on zoantharians, a group of animals related to corals and anemones, by researchers James Reimer of the University of the Ryukyusin Okinawa, Japan, Angelo Poliseno of Universita Politecnica delle Marchein Italy, and Bert Hoeksema from Naturalis Biodiversity Center, Netherlands, has demonstrated how little we know about marine diversity in the so-called “center of marine biodiversity” located in the central Indo-Pacific Ocean.

The researchers utilized previously collected specimens from Indonesia, the Philippines, Malaysia, and Papua New Guinea, combined with field images from Dr. Hoeksema to examine species of Zoantharia, marine cnidarians commonly found in shallow subtropical and tropical oceans throughout the world. The study was published in the open access journal ZooKeys.

“The central Indo-Pacific is commonly called the “Coral Triangle” due to its high hard coral diversity, in fact the highest in the world” said Reimer, “but in fact for many groups of marine animals we really have little concrete information on diversity, or numbers of species, in this region.”

Previous research included brief reports on a few species of Zoantharia, but until now no formal attempts had been made to list species from this region. Surprisingly, of the 24 potential species identified by the researchers, at least 9 are undescribed.

Much of the work was performed by Dr. Reimer in the Netherlands in 2012, when he visited the Naturalis Museum and Dr. Hoeksema to examine their Zoantharia collection. “What struck me as particularly amazing was the fact that Naturalis housed over 600 Zoantharia specimens collected over the years, and in many cases, even specimens from 1930 had not yet been formally examined,” stated Reimer. “This research demonstrates the real importance of museum collections, as well as the lack of expert researchers for many taxonomic groups.”

“Unfortunately, for many regions of the world, we are only just beginning to examine diversity, despite some of these areas being among the most threatened,” added Reimer. It is hoped future specimen collections will allow further analyses and formal descriptions of these previously unreported species.

Physics determined ammonite shell shape

Ammonites are a group of extinct cephalopod mollusks with ribbed spiral shells. They are exceptionally diverse and well known to fossil lovers. Régis Chirat, researcher at the Laboratoire de Géologie de Lyon: Terre, Planètes et Environnement (CNRS/Université Claude Bernard Lyon 1/ENS de Lyon), and two colleagues from the Mathematical Institute at the University of Oxford have developed the first biomechanical model explaining how these shells form and why they are so diverse. Their approach provides new paths for interpreting the evolution of ammonites and nautili, their smooth-shelled distant “cousins” that still populate the Indian and Pacific oceans. This work has just been published on the website of the Journal of Theoretical Biology.

The mechanical model predicts the correlations observed between rib frequency and amplitude and the shell's general shape in ammonites (blue morphological space) and nautili (red morphological space) The 3D-views produced by the model are juxtaposed with fossil specimens, ammonites and nautili, that have a similar shape. The ribs tend to disappear for the broadly open shell shapes that have characterized nautili for almost 200 million years. W = expansion rate D = coiling tightness Credit: Copyright: © Derek Moulton, Alain Goriely and Régis Chirat

The mechanical model predicts the correlations observed between rib frequency and amplitude and the shell’s general shape in ammonites (blue morphological space) and nautili (red morphological space) The 3D-views produced by the model are juxtaposed with fossil specimens, ammonites and nautili, that have a similar shape. The ribs tend to disappear for the broadly open shell shapes that have characterized nautili for almost 200 million years. W = expansion rate D = coiling tightness
Credit: Copyright: © Derek Moulton, Alain Goriely and Régis Chirat

The shape of living organisms evolves over time. The questions raised by this transformation have led to the emergence of theories of evolution. To understand how biological shapes change over a geological time scale, researchers have recently begun to investigate how they are generated during an individual’s development and growth: this is known as morphogenesis. Due to the exceptional diversity of their shell shapes and patterns (particularly the ribs), ammonites have been widely studied from the point of view of evolution but the mechanisms underlying the coiled spirals were unknown until now. Researchers therefore attempted to elucidate the evolution of these shapes without knowing how they had emerged.

Régis Chirat and his team have developed a model that explains the morphogenesis of these shells. By using mathematical equations to describe how the shell is secreted by ammonite and grows, they have demonstrated the existence of mechanical forces specific to developing mollusks. These forces depend on the physical properties of the biological tissues and on the geometry of the shell. They cause mechanical oscillations at the edge of the shell that generate ribs, a sort of ornamental pattern on the spiral.

By examining various fossil specimens in light of the simulations produced by the model, the researchers observed that the latter can predict the number and shape of ribs in several ammonites. The model shows that the ornamentation of the shell evolves as a function of variables such as tissue elasticity and shell expansion rate (the rate at which the diameter of the opening increases with each spiral coil).

By providing a biophysical explanation for how these ornamentations form, this theoretical approach explains the diversity existing within and between species. It thus opens new perspectives for the study of the morphological evolution of ammonites, which seems to be largely governed by mechanical and geometric constraints. This new tool also sheds light on an old mystery. For almost 200 million years, the shells of nautili, distant “cousins” of ammonites, have remained essentially smooth and free of distinctive ornamentation. The model shows that having maintained this shell shape does not mean that nautili — wrongly referred to as “living fossils” — have not evolved, but is due to a high expansion rate, leading to the formation of smooth shells that are difficult to distinguish from one another.

More generally, this work highlights the value of studying the physical bases of biological development: understanding the “construction rules” underlying the morphological diversity of organisms makes it possible to partially predict how their shape evolves.

How dinosaur arms turned into bird wings

Although we now appreciate that birds evolved from a branch of the dinosaur family tree, a crucial adaptation for flight has continued to puzzle evolutionary biologists. During the millions of years that elapsed, wrists went from straight to bent and hyperflexible, allowing birds to fold their wings neatly against their bodies when not flying.

How this happened has been the subject of much debate, with substantial disagreement between developmental biologists, who study how the wings of modern birds develop in the growing embryo, and palaeontologists who study the bones of dinosaurs and early birds. A resolution to this impasse is now provided by an exciting new study publishing on September 30 in PLOS Biology.

(A) Whole-mount alcian blue staining confirms the ulnare is the first carpal formed in avian embryos, distal to the ulna. Thereafter, a distal carpal 3 (referred to as “element x” in previous embryological descriptions) is formed distal to the ulnare, coexisting with it. Finally, the ulnare disappears, whereas dc3 persists. Credit: J. Botelho et al.; DOI: 10.1371/journal.pbio.1001957

(A) Whole-mount alcian blue staining confirms the ulnare is the first carpal formed in avian embryos, distal to the ulna. Thereafter, a distal carpal 3 (referred to as “element x” in previous embryological descriptions) is formed distal to the ulnare, coexisting with it. Finally, the ulnare disappears, whereas dc3 persists.
Credit: J. Botelho et al.; DOI: 10.1371/journal.pbio.1001957

Underlying this striking evolutionary transformation change is a halving in the number of wrist bones, but developmental biologists and palaeontologists have different names for most of them, and seldom agree on the correspondence between specific dinosaur bones and those of their bird descendants. Indeed, each field has radically different data sources, methods, and research objectives, talking little to each other.

The critical advance made in the new study involved combining these two strands of research. Using an interdisciplinary approach, the lab run by Alexander Vargas at the University of Chile has re-examined fossils stored at several museum collections, while at the same time collecting new developmental data from seven different species of modern birds. Joao Botelho, a Brazilian student in Vargas’ lab, developed a revolutionary new technique that allows him to study specific proteins in 3D embryonic skeletons. By combining these data from both fossils and embryos, the research team has made a major step forward in clarifying how the bird wrist evolved.

From early dinosaur ancestors with as many as nine wrist bones, birds have only kept four during the course of evolution, but which of the original bones are they? The identity of each of these bones was debated. For instance, the late Yale professor John Ostrom famously pointed out in the 1970’s that the wrists of both birds and bird-like dinosaurs possess a very similar, half-moon shaped bone called the semilunate, and that this bone resulted from the merging of two bones present in dinosaurs. This formed part of Ostrom’s then-controversial argument that birds descended from dinosaurs. However, the failure of developmental biologists to confirm this raised doubts that it was the same bone, and even that birds came from dinosaurs.

Now, the new data obtained by the Vargas lab has revealed the first developmental evidence that the bird semilunate was formed by the fusion of the two dinosaur bones. They go on to show that another bone — the pisiform — was lost in bird-like dinosaurs, but then re-acquired in the early evolution of birds, probably as an adaptation for flight, where it allows transmission of force on the downstroke while restricting flexibility on the upstroke. Combined, the fossil and developmental data provide a compelling scenario for a rare case of evolutionary reversal.

The study by the Vargas lab also settled the identity of the other two bones of the bird wrist, which were commonly misidentified in both fields. This emphasizes the downsides of not integrating all data sources, and reveals a situation perhaps akin to that of astronomy and experimental physics in the pursuit of cosmology: Together, palaeontology and development can come much closer to telling the whole story of evolution — this integrative approach resolves previous disparities that have challenged the support for the dinosaur-bird link and reveals previously undetected processes, including loss of bones, fusion of bones, and re-evolution of a transiently lost bone.

Fossil of ancient multicellular life sets evolutionary timeline back 60 million years

A Virginia Tech geobiologist with collaborators from the Chinese Academy of Sciences have found evidence in the fossil record that complex multicellularity appeared in living things about 600 million years ago — nearly 60 million years before skeletal animals appeared during a huge growth spurt of new life on Earth known as the Cambrian Explosion.

A fossil of a 600 million-year-old multicellular organism displays unexpected evidence of complexity. Credit: Virginia Tech

A fossil of a 600 million-year-old multicellular organism displays unexpected evidence of complexity.
Credit: Virginia Tech

The discovery published online Wednesday in the journal Nature contradicts several longstanding interpretations of multicellular fossils from at least 600 million years ago.

“This opens up a new door for us to shine some light on the timing and evolutionary steps that were taken by multicellular organisms that would eventually go on to dominate the Earth in a very visible way,” said Shuhai Xiao, a professor of geobiology in the Virginia Tech College of Science. “Fossils similar to these have been interpreted as bacteria, single-cell eukaryotes, algae, and transitional forms related to modern animals such as sponges, sea anemones, or bilaterally symmetrical animals. This paper lets us put aside some of those interpretations.”

In an effort to determine how, why, and when multicellularity arose from single-celled ancestors, Xiao and his collaborators looked at phosphorite rocks from the Doushantuo Formation in central Guizhou Province of South China, recovering three-dimensionally preserved multicellular fossils that showed signs of cell-to-cell adhesion, differentiation, and programmed cell death — qualities of complex multicellular eukaryotes such as animals and plants.

The discovery sheds light on how and when solo cells began to cooperate with other cells to make a single, cohesive life form.

The complex multicellularity evident in the fossils is inconsistent with the simpler forms such as bacteria and single-celled life typically expected 600 million years ago.

While some hypotheses can now be discarded, several interpretations may still exist, including the multicellular fossils being transitional forms related to animals or multicellular algae.

Xiao said future research will focus on a broader paleontological search to reconstruct the complete life cycle of the fossils.

Xiao earned his bachelor’s and master’s degrees from Beijing University in 1988 and 1991 and his doctoral degree from Harvard University in 1998. He worked for three years at Tulane University before arriving at Virginia Tech in 2003.

He is currently active in an editorial role for seven professional publications and has published more than 130 papers.

52-million-year-old amber preserves ‘ant-loving’ beetle

Scientists have uncovered the fossil of a 52-million-year old beetle that likely was able to live alongside ants — preying on their eggs and usurping resources — within the comfort of their nest. The fossil, encased in a piece of amber from India, is the oldest-known example of this kind of social parasitism, known as “myrmecophily.” Published today in the journal Current Biology, the research also shows that the diversification of these stealth beetles, which infiltrate ant nests around the world today, correlates with the ecological rise of modern ants.

Scientists have uncovered the fossil of a 52-million-year old beetle that likely was able to live alongside ants—preying on their eggs and usurping resources—within the comfort of their nest. Credit: © AMNH/J. Parker

Scientists have uncovered the fossil of a 52-million-year old beetle that likely was able to live alongside ants—preying on their eggs and usurping resources—within the comfort of their nest.
Credit: © AMNH/J. Parker

“Although ants are an integral part of most terrestrial ecosystems today, at the time that this beetle was walking the Earth, ants were just beginning to take off, and these beetles were right there inside the ant colonies, deceiving them and exploiting them,” said lead author Joseph Parker, a research associate at the American Museum of Natural History and postdoctoral researcher at Columbia University, who is a specialist on these beetles. “This tells us something not just about the beetles, but also about the ants — their nests were big enough and resource-rich enough to be worthy of exploitation by these super-specialized insects. And when ants exploded ecologically and began to dominate, these beetles exploded with them.”

Today, there are about 370 described species belonging to Clavigeritae, a group of myrmecophilous, or “ant-loving” beetles about 1-3 millimeters in length, and Parker estimates that several times this number of species still await discovery. Remarkable adaptations enable these beetles to bypass the fortresslike security of ant nests, which employ a pheromone code of recognition that ants use to identify, and then dismember and consume, intruders. Through ways that scientists are still trying to understand, Clavigeritae beetles pass through these defenses and integrate seamlessly into colony life.

“Adopting this lifestyle brings lots of benefits. These beetles live in a climate- controlled nest that is well protected against predators, and they have access to a great deal of food, including the ants’ eggs and brood, and, most remarkably, liquid food regurgitated directly to their mouths by the worker ants themselves,” Parker said. “But pulling off this way of life means undergoing drastic morphological changes.”

Clavigeritae beetles look quite different from their closest relatives, with fusions of segments within the abdomen and antennae — likely meant to provide additional protection from the ants, which often pick the beetles up and carry them around the nest — and mouthparts that are recessed inside the head in order to accept liquid food from worker ants. They also have glands that cover the body with oily secretions, and thick brushes of hair on top of their abdomens, called trichomes, which act as candlewicks and conduct chemical-containing secretions from nearby glands. The makeup of these chemicals is unknown, but they are thought to encourage ants to “adopt” rather than attack the beetles.

“If you watch one of these beetles interact inside an ant colony, you’ll see the ants running up to it and licking those brush-like structures,” Parker said.

Although Clavigeritae beetles are species-rich, they are quite rarely encountered in nature and so, unsurprisingly, the newly discovered specimen — brought to Parker’s attention by American Museum of Natural History curator David Grimaldi, who is an expert in amber fossils — is thought to be the first fossil of this group to be discovered. Named Protoclaviger trichodens by Parker and Grimaldi, the Eocene fossil is from an amber deposit in what was once a rain-forest environment in modern-day India. Although its body is very similar to modern Clavigeritae beetles, with two stark, hook-like trichomes, some of its characteristics are clearly more primitive. For example, Protoclaviger’s abdominal segments are still distinct, whereas in modern beetles they are fused together into a single shieldlike segment.

“Protoclaviger is a truly transitional fossil,” Parker said. “It marks a big step along the pathway that led to the highly modified social parasites we see today, and it helps us figure out the sequence of events that led to this sophisticated morphology.”