Tag Archives: gondwana

Tarantulas are *everywhere* and now researchers know why

Image in Creative Commons.

Tarantulas are among the most infamous spiders, in large part due to their size and appearance — with hairy legs, big jaws, and vibrant colors, tarantulas tend to make a splash every time they appear. But one thing puzzled researchers about tarantulas: why are they so widespread around the globe?

Tarantulas are found on all continents (outside of Antarctica), and they are dispersed in many parts of the world. This is especially surprising since individual tarantulas don’t really like to move around much.

“They are quite widespread and are found throughout the subtropical regions of every continent,” a research team led by bioinformatician Saoirse Foley from Carnegie Mellon University explains in a new study.

“[Their] behaviors do not portend that tarantulas would be successful dispersers, yet they have spread across the globe and have colonized strikingly different ecological niches.”

Females and juveniles rarely if ever go out of their burrows, and males usually venture just to look for mates. So how are they so widespread?

Primordial tarantula ranges. Image credits: Foley et al (2021).

To answer this question, Foley and colleagues followed two different trails: the biogeographic dispersion patterns of tarantulas throughout history, as well as their genetic history (from transcriptome databases). They then modeled how tarantulas could have dispersed over their evolutionary history, building an evolutionary tree of tarantulas and calibrating it with known fossil evidence.

They found that tarantulas likely emerged some 120 million years ago during the Cretaceous period, when Tyrannosaurs, velociraptors, and others dinosaurs roamed the planet. This lead researchers to an interesting conclusion: geology did a lot of dispersion work for the tarantulas.

“Previous studies estimate that tarantulas emerged between 150 Ma-71 Ma or ~107 Ma, which is compatible with a Gondwanan origin,” the researchers explain. “Indeed, some tarantulas (Selenocosmiinae) are suggested to be North Gondwanan taxa.”

Dispersion of tarantulas through Asia. Image credits: Foley et al.

At the time, many of the world’s current continents were huddled together in a supercontinent called Gondwana, which included Antarctica, South America, Africa, Madagascar, and Australasia, as well as the Arabian Peninsula and the Indian subcontinent. However, some tarantulas also seem to be surprisingly proficient dispersers.

Some tarantulas from India stayed local, but others moved and diversified across Asia, diverging while the Indian tectonic plate was still isolated and drifting towards Asia. These two lineages colonized Asia 20 million years apart.

“Our results indicate that both of these Asian lineages diverged while the Indian Plate was still rafting towards Asia… Interestingly, the two lineages also appear to be ecologically divergent,” the researchers note.

There are currently around 1,000 tarantula species, ranging in size from smaller than a coin to as big as a dinner plate. Their exhibit remarkable variety, and since their fossil record is so sparse, there is still much we don’t know about their evolution and diversification — which is why studies like this one are so important.

Tarantula range. Tarantulas of various species occur throughout the United States, Mexico, in Central America, and throughout South America. Other species occur variously throughout Africa, much of Asia (including the Ryukyu Islands in southern Japan), and all of Australia. In Europe, some species occur in Spain, Portugal, Turkey, southern Italy, and Cyprus.

Ultimately, the study suggests that geology gave tarantulas a helping hand in spreading across the globe, but could also lead researchers to reconsider tarantulas’ dispersion and adaptability capacity.

“Previously, we did not consider tarantulas to be good dispersers. While continental drift certainly played its part in their history, the two Asian colonization events encourage us to reconsider this narrative. The microhabitat differences between those two lineages also suggest that tarantulas are experts at exploiting ecological niches, while simultaneously displaying signs of niche conservation,” said Foley.

Journal Reference: Saoirse Foley, Henrik Krehenwinkel, Dong-Qiang Cheng, William H. Piel. Phylogenomic analyses reveal a Gondwanan origin and repeated out of India colonizations into Asia by tarantulas (Araneae: Theraphosidae). PeerJ, 2021; 9: e11162 DOI: 10.7717/peerj.11162

An artist's impression of a New Zealand burrowing bat, Mystacina robusta, that went extinct last century. Credit: Gavin Mouldey.

Giant, ancient bat discovered in New Zealand could walk on all fours

Fossils of a giant burrowing bat, about three times larger than today’s average bat, were discovered by paleontologists in New Zealand. The ancient species belongs to a lineage that used to flourish in the southern landmasses of Australia, New Zealand, South America and possibly Antarctica.

An artist's impression of a New Zealand burrowing bat, Mystacina robusta, that went extinct last century. Credit: Gavin Mouldey.

An artist’s impression of a New Zealand burrowing bat, Mystacina robusta, that went extinct last century. Credit: Gavin Mouldey.

Judging from its teeth and bones, Vulcanops jennyworthyae — named so after researcher Jenny Worthy who found the fossils — likely weighed an estimated 40 grams. Even at this modest weight, it’s the biggest burrowing bat that we know of.

Burrowing bats not only fly but also scurry about on all fours. It’s common to see them foraging for animal and plant food on the forest floor and along tree branches. Although they also lived in Australia, nowadays, burrowing bats can only be found in New Zealand.

If it was anything like today’s burrowing bats, Vulcanops j. must have had a broad diet comprising of both plants and animals. Burrowing bats commonly chase down insects and other invertebrates like weta and spiders, but also consume fruit, flowers, and nectar. Due to its large size and specialized teeth, Vulcanops j. should have been capable of eating even more plant food as well as small vertebrates — a diet more like that of its South American cousins.

Vulcanops jennyworthyae

Vulcanops jennyworthyae likely enabled the giant extinct bat to eat a broader diet than its cousins. Perhaps it also munched on small vertebrates. Credit: Scientific Reports.

“Burrowing bats are more closely related to bats living in South America than to others in the southwest Pacific,” says study first author and University of New South Wales Professor Sue Hand.

“They are related to vampire bats, ghost-faced bats, fishing and frog-eating bats, and nectar-feeding bats, and belong to a bat superfamily that once spanned the southern landmasses of Australia, New Zealand, South America and possibly Antarctica.”

Around 50 million years ago, all of these landmasses were part of the same giant continent called Gondwana. The climate was also wildly different with average global temperatures up to 12 degrees Celsius higher than today. Antarctica, for instance, was covered in lush forests and was ice-free. After tectonic activity fragmented these landmasses, Australasia’s burrowing bats became isolated from their South American relatives.

“The fossils of this spectacular bat and several others in the St Bathans Fauna show that the prehistoric aviary that was New Zealand also included a surprising diversity of furry critters alongside the birds,” said study co-author, Associate Professor Trevor Worthy of Flinders University.

The fossil dig site at St Bathans in New Zealand. Credit: Trevor Worthy.

The fossil dig site at St Bathans in New Zealand. Credit: Trevor Worthy.

Vulcanops’ lineage became extinct not long after the early Miocene, when the climate in New Zealand took a sudden swing, becoming far colder and drier. The environmental changes left many species vulnerable — and Vulcanops was not alone. Numerous species couldn’t adapt, including crocodiles, terrestrial turtles, flamingo-like palaelodids, swiftlets, several pigeon, and non-flying mammals.

Today, only two bat species comprise the entire native land mammal fauna in New Zealand. All other land mammals in the country have been introduced by humans over the past 800 years.

The findings appeared in the journal Scientific Reports. 

What is Gondwana: the supercontinent

Gondwana used to be a supercontinent, from around 550 million years ago to approximately 180 million years ago, alongside Laurasia. Gondwana incorporated present-day South America, Africa, Arabia, Madagascar, India, Australia, and Antarctica.

The Earth is a planet alive.

That shouldn’t surprise anyone — after all, our planet is bustling with life on the surface. But it goes deeper than that, literally. The atmosphere, the magnetic field that prevents solar radiation from frying us alive, the terrain on which we live — these are all the product of lively processes taking place under the surface.

For most people, the world around us seems like a very stable place. Its shape seems, pardon the pun, set in stone. But the continents we know today are only a temporary arrangement, and they looked very different in Earth’s earlier history.

Be patient enough, and you’ll see the earth itself spring to life — it moves, breaking apart or coming together all over the planet. This is the story of the last in a breed of geological titans, a supercontinent we named Gondwana.

A different Earth

Some 500 million years ago, during the late Ediacaran period, tectonic motions brought today’s Africa, South America, Australia, Antarctica, India, the Arabian Peninsula and Madagascar into a single, massive piece of land. This was the early version Gondwana, stretching from the Equator almost to the south pole. Its climate was mild, however, as the world was a warmer place back then. Multicellular organisms had developed by this time, but they were primitive. The few fossils we’ve found from this period show a biota consisting of segmented worms, round creatures resembling modern jellyfish, and frond-like organisms.

More continents collided with this early Gondwana over time to form Pangaea, the “whole Earth,” roughly 300 million years ago. It was immense by any stretch of the imagination, all of the planet’s landmass was fused into one block dominating the southern hemisphere, surrounded by the biggest ocean in history. Then, 20 to 70 million years later, magma plumes from the Earth’s core started burning through the crust like a blowtorch, creating a rift between what we know today as Africa, South America, and North America.

Pangea’s breaking-up stages.
Image credits U.S. Geological Service.

Convection cells associated with these plumes widened the fissure into a fully fledged Tethys ocean, separating a northern supercontinent called Laurasia — today’s North America, Europe, and Asia — from a southern one, our fully formed Gondwana. It has lost some of its original bits to Laurasia — such as Florida and parts of Georgia — but still contains all the landmasses we see today in the southern hemisphere. We’re now in the Jurassic period. Dinosaurs are roaming about, most of the world is covered in lush rainforests, and the last supercontinents are poised to break up.

It’s not you, it’s tectonics

The break-up didn’t happen at once, however. Gondwana fragmented in stages. Sometime between 170 million and 180 million years ago, modern Africa and South America began breaking apart from the rest of Gondwana. They stayed fused for about 30 to 40 million years until the South Atlantic Rift broke them up, opening the ocean (with the same name) between them.

That’s why South America’s eastern coast and Africa’s western coast look like they’d fit together snugly — at one point, they actually did.

South America and Africa with the approximate location of their Mesoproterozoic (older than 1.3 Ga) cratons (old and stable parts of the crust.)
Image credits Woudloper / Wikimedia.

At about the same time as the South Atlantic Rift was opening up, the easternmost part of the continent, Madagascar and India, split from the rest, opening the central Indian Ocean. The two stayed fused together until the Late Cretaceous period, after which India made a beeline for Eurasia —  50 million years ago, the collision between the two was so violent it raised the Himalayas.

At this point basically all that’s left of former Gondwana is Australia and Antarctica — too little to be counted as a supercontinent. They did stay fused together until around 45 million years ago, though. After that, Antarctica moved south and froze over (due to a combination of the climate cooling down and shifting ocean currents around the new landmasses) and Australia went adrift towards the north, colliding with southern Asia. The collision is still taking place today, as the Australian plate is advancing north at a rate of about 3 centimeters (1.2 inches) a year.

Today’s tectonic plates. Red arrows indicate primary direction of movement.
Image credits U.S. Geological Survey.

We still don’t know exactly what caused the continent to break apart. One theory holds that hot spots formed beneath it, creating rifts that broke the supercontinent apart. In 2008, however, University of London researchers suggested that Gondwana instead split into two tectonic plates, which then were then further fragmented.

How we figured all of this out

The uncanny resemblance between the shape of western Africa and eastern South America was first officially noted by Sir Francis Bacon in 1620 as accurate maps of the two continents became available. In 1912, Alfred Wegener, a German meteorologist, proposed that the two continents formed a single body at one point — in fact, he was the first to envision the great supercontinent Pangaea. However, geologists at the time strongly criticised his theory, citing his lack of formal training in the field. Geologists then couldn’t believe that something as huge as a continent could move; they simply lacked knowledge of a system that would explain how this could happen; they had no known way to reliably recreate the movements.

Alexander Du Toit, a South African geologist, further elaborated on the theory in his 1937 book Our Wandering Continents. Seeing the opposition Wegener’s theory encountered, he carefully amassed evidence of the two continents’ past link — the occurrence of glacial deposits (or tillites) and rock strata on both sides of the Atlantic, as well as similar fossil flora and fauna found exclusively on southern continents, especially the fern species Glossopteris. His theory gained traction with scientists from the southern hemisphere but was still widely criticised by geologists in the northern hemisphere. They envisioned land bridges spanning from continent to continent to explain how one species could be found on both sides of an ocean, even to the point where these bridges would circle whole continents.

However, the theory of plate tectonics became widely embraced by the 1960s when the Vine–Matthews–Morley hypothesis was formed following paleomagnetism (or fossil magnetism) measurements of the ocean’s floor. These measurements recorded the magnetic properties stored in ocean-bottom rocks as they formed over time, proving that rift areas add new material to oceanic plates, pushing continents apart.

This cemented the theory of tectonic plates, and furthermore helped us understand how these imense landmasses moved in the past — including how Gondwana came to be and ultimately broke up.

How magnetic stripes form on the sea floor.
Image credits Chmee2 / Wikimedia.

Gone-dwana

Gondwana is the last of the supercontinents the world has seen — so far. Plates are being formed and consumed today, just as they have been since the Earth’s crust cooled down to a solid. The same tectonic processes that made and shattered Gondwana and the supercontinents before it functions just the same, powered by the huge quantity of heat trapped in the depths of the Earth. They will keep on mashing continents together, so it’s almost guaranteed that a new supercontinent will form in the future.

But considering the timeframes geology works with, we’re probably not going to be around any longer to see it happen.

 

Scientists find Permian fauna from Gondwana

Some 270 million years ago, the world was entirely a different place, and even with numerous paleontological findings, we’re still finding more and more evidence of the fauna that inhabited the world. Now, researchers have found new fauna in northern Brazil, in what used to be the continent of Gondwana.

Image via Cisneros et al, 2015.

“Almost all of our knowledge about land animals from this time, comes from a handful of regions in North America and western Europe, which were located near the equator. Now we finally have information about what kinds of animals were present in areas farther to the south, and their similarities and differences to the animals living near the equator,” said Dr Kenneth Angielczyk from the Field Museum of Natural History, a team member and a co-author of a paper in the journal Nature Communications.

 

During the late Paleozoic and early Mesozoic eras, Pangaea was the place to be; well, technically speaking, it was the only place to be, because it was the only supercontinent – all the continents were merged into it. But some 300 million years ago, it started to split, initially into two parts: Laurasia and Gondwana. Gondwana formed prior to Pangaea, then became part of Pangaea, and finally broke up after the breakup of Pangaea. Gondwana is believed to have sutured between about 570 and 510 Mya, thus joining East Gondwana to West Gondwana. But just like the tectonic structure of the planet was different, so too were the ecosystems that populated the continents.

Juan Cisneros from the Universidade Federal do Piauí and his team found a new early Permian continental tetrapod fauna from South America in tropical Western Gondwana that sheds new light on patterns of tetrapod distribution. Based on the characteristics of the animals they found, north-eastern Brazil was a lacustrine system inhabited by a unique community of amphibians and reptiles.

“Our findings demonstrate that tetrapod groups common in later Permian and Triassic temperate communities were already present in tropical Gondwana by the early Permian (Cisuralian). This new fauna constitutes a new biogeographic province with North American affinities and clearly demonstrates that tetrapod dispersal into Gondwana was already underway at the beginning of the Permian,” they write in their article.

These new findings provide unparalleled window into tropical wetland faunas of Gondwana at the time – the fact that we can indirectly know so much about an environment so far away in time is absolutely amazing to me.

Journal Reference.

America’s invasive species – 450 million years ago

Land clearing and human habitation put significant pressure on local species – combine this with globalization and a general recklessness of the population, and you get a big, negative impact (both environmental and economic) from invasive plants.

invasive-species-laurentia-450-million-years invasive-species-laurentia-450-million-years

But invasive plants aren’t something new – they’ve been around for hundreds of millions of years. Scientists have now analyzed 450-million-year-old fossils of marine creatures that once dwelled in Laurentia, the continent North America once was part of. You may recall the article we posted yesterday about the 350 million year old scorpion, which included a discussion about Laurentia and Gondwana – the only two existing continents on the face of the Earth in that period.

Back then, the forerunners of the Appalachian Mountains may have opened the gates for invasive species to storm Laurentia (or Laurasia). The Taconic mountains, as they were called, left a depression behind the mountain range, flooding the area with cool, nutrient-rich water. In order to better understand how these tectonic processes affected existing life, paleontologists investigated the remains of brachiopods – clam like creatures which dominated the waters during that time.

journal.pone.0068353.g001

“Our data show a very clear shift in evolutionary processes that coincides with a shift in Earth systems dynamics,” researcher Alycia Stigall, a paleontologist at Ohio University, explained.” In particular, these results shed light on the Earth system controls on how new species form, or speciation.”

As geological changes slowly took their toll in Laurentia, the fossils highlight two different patterns of evolution: vicariance and dispersal. Vicariance occurs following large-scale geophysical events such as the uplift of a mountain chain, or the separation of continents; through it, new species appear, each better suited for their new habitats.

Dispersal on the other hand involves directly invading habitats for which you are suited. Although initially biodiversity increases, in the long run, this is a very negative process, following which only a few aggressive plants dominate, thus greatly reducing biodiversity.

These findings could provide valuable insight into what drives dispersal today – as a great number of plants are threatened by invasive species.

“Only one out of 10 invaders truly become invasive species,” Stigall said in a statement. “Understanding the process can help determine where to put conservation resources.”

It’s also valuable data in the attempt to understand the emergence of new species:

“Scientists, both biologists and paleontologists, have spent a lot of time and effort studying extinction — the process by which the Earth loses species,” Stigall said. “We understand many of those controls very well — (meteor) impact, volcanism, ocean acidification, habitat destruction. It is relatively easy to envision ways to reduce a population size to zero and thereby cause a species to go extinct. “Understanding speciation is much more complex,” Stigall continued. “Species form by breakdown of gene flow between populations. This is much harder to study on short timescales and the process is explicitly tied to a geographic place and ancestors, which requires understanding both geography and evolutionary history.”

Journal Reference: PLoS ONE. David F. Wright, Alycia L. Stigall: Geologic Drivers of Late Ordovician Faunal Change in Laurentia: Investigating Links between Tectonics, Speciation, and Biotic Invasions.

Gardiners-Seychelles-frog

This frog hears through its mouth

One of the smallest amphibians in the world, the  Gardiner’s Seychelles frog, is also one of the most eccentric. The frog doesn’t stand out through an over-glamorous coloring or some unique, wild mating call, but rather as a result of one of its weird biological features. This frog doesn’t have ears – yet it can hear. How? By receiving sound waves through its mouth.

Gardiners-Seychelles-frogAll frogs actually hear in a different way from all the other animals, in the sense they don’t have  an external cartilaginous sounding board – instead frogs have eardrums placed directly under the skin. But Seychelles frogs don’t even have this. Can it hear in the first place? Well, a team of researchers from a variety of French universities tested the Seychelles hearing range. They placed a frog in a room where they played recorded calls from other frogs through a speaker. The frog responded to these calls, signifying it could hear them.

Talk with your ears, listen with your mouth

The mystery deepened even further after the scientists had the frogs X-rayed and saw that their bones didn’t conduct sound, like human jawbones do for instance. So scientists made a wild guess: what if the frog could hear through its mouth by directing sound to its inner ear – a cavity within the frog’s skull that hosts reverberated noises?They performed a simulation  and, indeed, it showed that the frog was indeed capable of hearing through this method. This doesn’t mean it hears in this manner though – it just demonstrates that it could.

The Seychelles frog can only be found on a few islands in the Seychelles, off the coast of Madagascar. Scientists suspect that due to its isolation, the species’ hearing has evolved very little. Advanced hearing, characterized by the evolution of eardrums, dates back from the time of  the separation of Gondwana, an ancient supercontinent. Studying Sechelles frogs, researchers hope not only to unravel how this peculiar animal performs basic biological functions, but also how Gondwana animals might had looked and behaved like.

via PopSci

 

350-million-year-old former inhabitant of Gondwana found

A 350 million year old fossilized scorpion has become the world’s oldest known land animal to have ever walked the supercontinent Gondwana.

Ancient history

laurasia gondwana

It’s 350 million years ago – take a moment to ponder that. Take a long human lifespan of 100 years, and multiply it by 100, and again by 100 – now you have a million years. Multiply it again by 350, and you get to the life of this now fossilized scorpion! It blows my mind just to think about that; it was so long ago, that the face of the Earth looked nothing like it does now.

There were only two major continents back then, called Laurasia and Gondwana, separated by the Tethys sea. Gondwana included most of the landmasses in today’s Southern Hemisphere, including Antarctica, South America, Africa, Madagascar and the Australian continent, as well as the Arabian Peninsula and the Indian subcontinent, which are now a part of the Northern hemisphere.

Paleozoic Era

We’re in a period called Carboniferous – when amphibians were dominant land vertebrates and were almost starting to evolve into reptiles, arthropods are extremely common, and vast swaths of forest cover almost every inch of land; these forests will lie down and eventually become coal – thus giving the name of the period (Carboniferous = coal bearing).

The oldest land walking Gondwanese

scorpion gondwana

Ok, Gondwanese isn’t a real word, I just made it up. But this new species, Gondwanascorpio emzantsiensis is the oldest we know that walked on Gondwana. Its discovery brings some tantalizing clues about the development of life before Earth’s continents broke apart to form the continents as we see them today.

“There has been no evidence that Gondwana was inhabited by land living invertebrate animals at that time,” said Robert Gess who is based at the Evolutionary Studies Institute at Wits University.

Gess uncovered the scorpion fragments—with a pincer and a sting clearly showing in the rock in South Africa, near the Eastern Cape. The implications this finding has are quite significant.

“For the first time we know for certain that not just scorpions, but whatever they were preying on were already present in the Devonian,” added Gess.

“We now know that by the end the Devonian period Gondwana also, like Laurasia, had a complex terrestrial ecosystem, comprising invertebrates and plants which had all the elements to sustain terrestrial vertebrate life that emerged around this time or slightly later,” said Gess.

scorpion 2

The first real land vertebrates, from which ultimately even humans evolved appeared some 350 million years ago.

Journal reference: The earliest record of terrestrial animals in Gondwana: A scorpion from the Famennian (Late Devonian) Witpoort Formation of South Africa.

Next supercontinent will be called Amasia, and will be centered around the North Pole

Based on how the tectonic plates are moving now, no later than one hundred million years, Asia and the Americas will merge into one huge supercontinent, named Amasia. Geophysicists have long theoretized this, but a team of researchers from Yale University offered a new view on how Amasia will be formed.

Continental drift

Continental drift was proposed by Alfred Wegener in 1912, and it was proven right soon afterwards. Basically, it states that the Earth’s continents are in a state of relative motion, a theory which was improved in the 60s with the tectonic plates theory. Basically, the whole crust on our planet can be split into ten major tectonic plates which moves as the seafloor spreads.

As almost always with geology, in order to understand something taking place now, we have to take a look into our planet’s past. The Earth’s first supercontinent, Rodinia, was formed 1.1 billion years ago and lasted until 750 million years ago, and was surrounded by a huge planetary ocean called Mirovia.

However, tectonic plates didn’t stop moving, so the continent split and reformed again and 250 million years ago, Pangaea, the next supercontinent was formed, surrounded by an ocean called Panthalassa. However, this didn’t last forever either, and continents started to rescramble into pretty much what we see today.

Next stop: Amasia

A great part of the information we have about these supercontinents comes from geopaleomagnetic measurements (‘geo‘ means ‘earth’, ‘paleo‘ means ‘old’). When certain minerals are formed, they ‘lock’ in a record of the intensity and direction of the magnetic field when they formed. This record can be analyzed hundreds of millions later and still hold highly accurate indications about the tectonic plates they were formed in.

Yale University geology and geophysics professor David Evans, along with graduate students Taylor Kilian and Ross N. Mitchell, studied the magnetism in some ancient rocks to figure out when they were positioned when they formed and how they moved as the years passed.

“The Americas will remain in the Pacific ‘ring of fire’ girdle of post-Pangaean subduction, closing the Arctic Ocean and Caribbean Sea,” the Yale geophysicists wrote in a Nature journal article published today. In other words, they think Amasia will form over the Arctic, 90 degrees away from the original Pangea.

To geologists, this geophysical idea sounds perfect, as previous supercontinents appear to have formed successively at 90 degrees to each other. After all, Asia and the Americas are already tied together by economic and social issues – and 100 million years from now, they will be literally tied.