Paleontology: New light on cichlid evolution in Africa

Cichlids (Cichlidae) are a group of small to medium-sized fish that are ubiquitous in freshwater habitats in the tropics. They are particularly notable in exhibiting a wide range of morphological and behavioral specializations, such as various modes of parental care, including mouthbrooding. Some species (mainly members of the genus Tilapia) have achieved fame as culinary delicacies and are of considerable economic significance. Cichlids have undergone rapid diversification in Africa, which is home to at least 1100 species. This process has been especially prominent in the Great Lakes in East Africa’s Rift Valley (Lakes Tanganyika, Malawi and Victoria), where it is referred to as the East African Radiation.

“Cichlid diversification in East Africa has become a central paradigm in evolutionary biology. As a consequence, dating the onset of the process and understanding the mechanisms that drive it are issues of great interest to evolutionary biologists and paleobiologists,” says LMU paleontologist Professor Bettina Reichenbacher, who is also member of the GeoBio-Center at LMU. Fossils from the area provide the sole source of direct evidence that would allow one to determine the timing and trace the course of lineage diversification within the group. However, the search for cichlid fossils has proven to be both arduous and extremely time- consuming. Indeed, only about 20 fossil species of cichlids from Africa have yet been formally described.

In a study that appears in the online journal Scientific Reports, a team of researchers led by Bettina Reichenbacher now describes a new fossil cichlid, which the authors assign to the new genus Oreochromimos. The name derives from the fact that the specimens, which the team discovered in Central Kenya, show similarities to members of the Tribe Oreochromini (hence the element ‘mimos’, meaning ‘mimic’, in the genus name), which are widely distributed in Africa today. “Determining whether or not the fossils could be assigned to any of the extant cichlid lineages was particularly challenging,” says Stefanie Penk, first author of the study and a doctoral student in Reichenbacher’s group. The difficulties are rooted in the great diversity of the modern cichlid fauna in Africa, and the fact that even distantly related species may be morphologically very similar to each other. “The architecture of the skeleton in cichlids is pretty conservative. All of them have a similar basic form, which undergoes very little change during speciation,” Reichenbacher explains. In collaboration with Dr. Ulrich K. Schliewen, co-author of the new paper, Curator of Fishes at the Bavarian State Collection for Zoology in Munich (SNSB-ZSM) and also a member of the GeoBio-Center at LMU, the team adopted the ‘best-fit approach’ to the classification of the fossil specimens. This requires comparison of the fossil material with all the relevant modern lineages of cichlids. In light of their contemporary diversity, that might seem an impossible task. But thanks to Schliewen’s knowledge — and the range of comparative material represented in the collection under his care — the strategy succeeded.

A unique glimpse of the past

Reichenbacher and colleagues recovered the Oreochromimosmaterial from a fossil-fish Lagerstätte in Kenya’s Tugen Hills, which lie within the Eastern Branch of the East African Rift System. This site provides a unique window into the region’s past. The volcanic and sedimentary rocks deposited here date back 5-20 million years. They were overlain by younger material and subsequently uplifted to altitudes of as much as 2000 m by tectonic forces. As a result, the fossil-bearing rocks exposed in the Tugen Hills are either inaccessible to exploration or have been lost to erosion in other parts of Africa. Consequently, the strata here contain a unique assemblage of fossils. Undoubtedly the best known finds so far excavated are the 6-million-year-old remains of a hominin species, which has been named Orrorin tugenensis (orrorin means ‘original man’ in the local language). But cichlid fossils are also among the paleontological treasures preserved in these sedimentary formations — and they are at the heart of Reichenbacher’s Kenya Project, which began in 2011. The material collected so far was recovered in cooperation with Kenya’s Egerton University, and is now on loan to LMU’s Department of Earth and Environmental Sciences for further study.

The Oreochromimos specimens are about 12.5 million years old, which makes this genus the oldest known fossil representative of the Tribe Oreochromini. It therefore qualifies as the oldest fossil clade yet assigned to the Haplotilapiini, the lineage which gave rise not only to most of the species that constitute the present-day diversity of African cichlids, but also to the East African Cichlid Radiation in the Great Lakes of the Rift Valley. With their use of an innovative approach to comparative systematics, the authors of the new study have provided a basis for the taxonomic assignment of future finds of fossil cichlid material. “With the aid of this dataset, it will be possible to classify fossil cichlids much more reliably than before and thus to shed new light on their evolutionary history,” says Bettina Reichenbacher.

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World’s smallest fossil monkey found in Amazon jungle

A team of Peruvian and American scientists have uncovered the 18-million-year-old remains of the smallest fossil monkey ever found.

A fossilized tooth found in Peru’s Amazon jungle has been identified as belonging to a new species of tiny monkey no heavier than a hamster.

The specimen is important because it helps bridge a 15-million-year gap in the fossil record for New World monkeys, says a team led by Duke University and the National University of Piura in Peru.

The new fossil was unearthed from an exposed river bank along the Río Alto Madre de Dios in southeastern Peru. There, researchers dug up chunks of sandstone and gravel, put them in bags, and hauled them away to be soaked in water and then strained through sieves to filter out the fossilized teeth, jaws, and bone fragments buried within.

The team searched through some 2,000 pounds of sediment containing hundreds of fossils of rodents, bats and other animals before they spotted the lone monkey tooth.

“Primate fossils are as rare as hen’s teeth,” said first author Richard Kay, a professor of evolutionary anthropology at Duke who has been doing paleontological research in South America for nearly four decades.

A single upper molar, the specimen was just “double the size of the head of a pin” and “could fall through a window screen,” Kay said.

Paleontologists can tell a lot from monkey teeth, particularly molars. Based on the tooth’s relative size and shape, the researchers think the animal likely dined on energy-rich fruits and insects, and weighed in at less than half a pound — only slightly heavier than a baseball. Some of South America’s larger monkeys, such as howlers and muriquis, can grow to 50 times that heft.

“It’s by far the smallest fossil monkey that’s ever been found worldwide,” Kay said. Only one monkey species alive today, the teacup-sized pygmy marmoset, is smaller, “but barely,” Kay said.

In a paper published online July 23 in the Journal of Human Evolution, the team dubbed the animal Parvimico materdei, or “tiny monkey from the Mother of God River.”

Now stored in the permanent collections of the Institute of Paleontology at Peru’s National University of Piura, the find is important because it’s one of the few clues scientists have from a key missing chapter in monkey evolution.

Monkeys are thought to have arrived in South America from Africa some 40 million years ago, quickly diversifying into the 150-plus New World species we know today, most of which inhabit the Amazon rainforest. Yet exactly how that process unfolded is a bit of a mystery, in large part because of a gap in the monkey fossil record between 13 and 31 million years ago with only a few fragments.

In that gap lies Parvimico. The new fossil dates back 17 to 19 million years, which puts it “smack dab in the time and place when we would have expected diversification to have occurred in the New World monkeys,” Kay said.

The team is currently on another fossil collecting expedition in the Peruvian Amazon that will wrap up in August, concentrating their efforts in remote river sites with 30-million-year-old sediments.

“If we find a primate there, that would really be pay dirt,” Kay said.

Other authors include Jean-Nöel Martinez and Luis Angel Valdivia of the National University of Piura, Lauren Gonzales of the University of South Carolina, Wout Salenbien and Paul Baker of Duke’s Nicholas School of the Environment, Siobhán Cooke of the Johns Hopkins University School of Medicine, and Catherine Rigsby of East Carolina University.

This research was supported by the National Science Foundation (EAR 1338694, DDIG 0726134) and the National Geographic Society (Young Explorers Grant 9920-16 and Waitt Grant W449-16).

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Oldest completely preserved lily discovered

Botanist Dr. Clement Coiffard of the Museum für Naturkunde Berlin discovered the oldest, completely preserved lily in the research collection: Cratolirion bognerianum was found in calcareous sediments of a former freshwater lake in Crato in northeastern Brazil. With an age of about 115 million years, Cratolirion is one of the oldest known monocotyledonous plants. These include orchids, sweet grasses, lilies and lilies of the valley.

Cratolirion is extraordinarily well preserved, with all roots, the flower and even the individual cells are fossilised. With a length of almost 40 centimetres, the specimen is not only extremely huge, but also shows almost all the typical characteristics of monocotyledonous plants, including parallel-veined, narrow leaves with a leaf sheath, a fibrous root system and triple flowers.

However, it was not trivial to examine the fossilised object, as it consisted of iron oxides associated with the stone. In order to see details here, Coiffard collaborated with the HZB physicist Dr. Nikolay Kardjilov, who is an expert in 3D analysis with X-rays and neutrons. At the HZB he also built up a 3D computed x-ray tomography and refined the data analysis in such a way that hardly any disturbing artefacts arise during the investigation of large, flat objects. This made it possible to analyse the details of the inflorescence hidden in the stone. A colour coding in the CT scan makes these details visible: the main axis is marked in turquoise, the supporting leaves in dark green, the pistils in light green and the remains of the actual petals can still be seen in orange.

Many early dicotyledonous flowering plants have already been described from the same sediments of the former freshwater lake in Crato. These include water lilies, aron rods, drought-resistant magnolias and relatives of pepper and laurel. In contrast to other flowering plants of the same age from the USA, Portugal, China and Argentina, the flowering plants of the Crato-Flora are unusually diverse. This could be due to the fact that Lake Crato was in the lower latitudes, but all other fossils of early flowering plants come from the middle latitudes.

From this newly described plant Cratolirion bognerianum and the species of Crato flora mentioned above, it can be deduced that the tropical flowering plants were already very diverse. “It is probable that flowering plants originated in the tropics, but only very few fossils have been described to date,” explains Coiffard. This study thus provides new insights into the role of the tropics in the development of early flowering plants and their rise to global supremacy.

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Bird with unusually long toes found fossilized in amber

Meet the ancient bird that had toes longer than its lower legs. Researchers have discovered a bird foot from 99 million years ago preserved in amber that had a hyper-elongated third toe. The study, published in the journal Current Biology on July 11, suggests that this bird might have used its toes to hook food out of tree trucks. This is the first time such a foot structure has been observed in birds, either extinct or living.

“I was very surprised when I saw the amber,” says first author Lida Xing at China University of Geosciences (Beijing). “It shows that ancient birds were way more diverse than we thought. They had evolved many different features to adapt to their environments.”

To study the Cretaceous period fossil, Xing and his colleagues scanned the amber with micro-CT and created a 3D reconstruction of the foot. They found that the bird’s third toe, measuring 9.8 millimeters, is 41 percent longer than its second toe and 20 percent longer than its tarsometatarsus, which is a bone in the lower legs of birds. The team compared the ratios with those of 20 other extinct birds from the same era and 62 living birds. No bird has a foot that resembles this one.

The researchers named it Elektorornis chenguangi. Elektorornis means “amber bird,” and it belongs to a group of extinct birds called Enantiornithes, the most abundant type of bird known from the Mesozoic era. It is thought that Enantiornithines became extinct during the Cretaceous-Paleogene extinction event about 66 million years ago, along with dinosaurs. They have no living descendants.

Based on the fossil, the team estimates that the Elektorornis was smaller than a sparrow, and it was arboreal, meaning it spent most of its time in trees as opposed to on the ground or in water.

“Elongated toes are something you commonly see in arboreal animals because they need to be able to grip these branches and wrap their toes around them,” says co-author Jingmai O’Connor at the Chinese Academy of Sciences. “But this extreme difference in toe lengths, as far as we know, has never been seen before.”

The amber the foot was found in, measuring 3.5 centimeters long and weighing 5.5 grams, was discovered around 2014 in the Hukawng Valley of Myanmar. During the Mesozoic era, the valley was full of trees that produced resin, a gooey substance that oozes out of the tree bark. Plants and small animals, such as geckos and spiders, often get trapped in the resin and become fossilized with the amber after millions of years. Scientists have discovered many extinct animals, including the oldest known bee and a feathered dinosaur tail, in amber from this valley.

Xing obtained the amber from a local amber trader, who didn’t know what animal this weird foot belonged to.

“Some traders thought it’s a lizard foot, because lizards tend to have long toes,” Xing says. “Although I’ve never seen a bird claw that looks like this before, I know it’s a bird. Like most birds, this foot has four toes, while lizards have five.”

It remains unknown why the amber bird evolved such an unusual feature. The only known animal with disproportionally long digits is the aye-aye. The aye-aye is a lemur that uses its long middle fingers to fish larvae and insects out of tree trunks for food. Therefore, the researchers suggest Elektorornis might have used its toe for the same purpose.

“This is the best guess we have,” O’Connor says. “There is no bird with a similar morphology that could be considered a modern analog for this fossil bird. A lot of ancient birds were probably doing completely different things than living birds. This fossil exposes a different ecological niche that these early birds were experimenting as they evolved.”

Moving forward, the team hopes to extract the proteins and pigments from some feathers exposed on the surface of the amber. Xing says such data could help them better understand the bird’s adaptation to the environment, such as whether it had camouflage plumage.

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Bird three times larger than ostrich discovered in Crimean cave

A surprise discovery in a Crimean cave suggests that early Europeans lived alongside some of the largest ever known birds, according to new research published in the Journal of Vertebrate Paleontology.

It was previously thought that such gigantism in birds only ever existed on the islands of Madagascar and New Zealand as well as Australia. The newly-discovered specimen, discovered in the Taurida Cave on the northern coast of the Black Sea, suggests a bird as giant as the Madagascan elephant bird or New Zealand moa. It may have been a source of meat, bones, feathers and eggshell for early humans.

“When I first felt the weight of the bird whose thigh bone I was holding in my hand, I thought it must be a Malagasy elephant bird fossil because no birds of this size have ever been reported from Europe. However, the structure of the bone unexpectedly told a different story,” says lead author Dr Nikita Zelenkov from the Russian Academy of Sciences.

“We don’t have enough data yet to say whether it was most closely related to ostriches or to other birds, but we estimate it weighed about 450kg. This formidable weight is nearly double the largest moa, three times the largest living bird, the common ostrich, and nearly as much as an adult polar bear.”

It is the first time a bird of such size has been reported from anywhere in the northern hemisphere. Although the species was previously known, no one ever tried to calculate the size of this animal. The flightless bird, attributed to the species Pachystruthio dmanisensis, was probably at least 3.5 metres tall and would have towered above early humans. It may have been flightless but it was also fast.

While elephant birds were hampered by their great size when it came to speed, the femur of the current bird was relatively long and slim, suggesting it was a better runner. The femur is comparable to modern ostriches as well as smaller species of moa and terror birds. Speed may have been essential to the bird’s survival. Alongside its bones, palaeontologists found fossils of highly-specialised, massive carnivores from the Ice Age. They included giant cheetah, giant hyenas and sabre-toothed cats, which were able to prey on mammoths.

Other fossils discovered alongside the specimen, such as bison, help date it to 1.5 to 2 million years ago. A similar range of fossils was discovered at an archaeological site in the town of Dmanisi in Georgia, the oldest hominin site outside Africa. Although previously neglected by science, this suggests the giant bird may have been typical of the animals found at the time when the first hominins arrived in Europe. The authors suggest it reached the Black Sea region via the Southern Caucasus and Turkey.

The body mass of the bird was reconstructed using calculations from several formulae, based on measurements from the femur bone. Applying these formulae, the body mass of the bird was estimated to be around 450kg. Such gigantism may have originally evolved in response to the environment, which was increasingly arid as the Pleistocene epoch approached. Animals with a larger body mass have lower metabolic demands and can therefore make use of less nutritious food growing in open steppes.

“The Taurida cave network was only discovered last summer when a new motorway was being built. Last year, mammoth remains were unearthed and there may be much more to that the site will teach us about Europe’s distant past,” says Zelenkov.

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Antarctic marine life recovery following the dinosaurs’ extinction

A new study shows how marine life around Antarctica returned after the extinction event that wiped out the dinosaurs.

A team led by British Antarctic Survey studied just under 3000 marine fossils collected from Antarctica to understand how life on the sea floor recovered after the Cretaceous-Paleogene (K-Pg) mass extinction 66 million years ago. They reveal it took one million years for the marine ecosystem to return to pre-extinction levels. The results are published today (19 June 2019) in the journal Palaeontology.

The K-Pg extinction wiped out around 60% of the marine species around Antarctica, and 75% of species around the world. Victims of the extinction included the dinosaurs and the ammonites. It was caused by the impact of a 10 km asteroid on the Yucatán Peninsula, Mexico, and occurred during a time period when the Earth was experiencing environmental instability from a major volcanic episode. Rapid climate change, global darkness, and the collapse of food chains affected life all over the globe.

The K-Pg extinction fundamentally changed the evolutionary history of life on Earth. Most groups of animals that dominate modern ecosystems today, such as mammals, can trace the roots of their current success back to the aftermath of this extinction event.

A team of scientists from British Antarctic Survey, the University of New Mexico and the Geological Survey of Denmark & Greenland show that in Antarctica, for over 320,000 years after the extinction, only burrowing clams and snails dominated the Antarctic sea floor environment. It then took up to one million years for the number of species to recover to pre-extinction levels.

Author Dr Rowan Whittle, a palaeontologist at British Antarctic Survey says:

“This study gives us further evidence of how rapid environmental change can affect the evolution of life. Our results show a clear link in the timing of animal recovery and the recovery of Earth systems.”

Author Dr James Witts, a palaeontologist at University of New Mexico says:

“Our discovery shows the effects of the K-Pg extinction were truly global, and that even Antarctic ecosystems, where animals were adapted to environmental changes at high latitudes like seasonal changes in light and food supply, were affected for hundreds of thousands of years after the extinction event.”

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Plate tectonics may have driven ‘Cambrian Explosion’

The quest to discover what drove one of the most important evolutionary events in the history of life on Earth has taken a new, fascinating twist.

A team of scientists have given a fresh insight into what may have driven the “Cambrian Explosion” — a period of rapid expansion of different forms of animal life that occurred over 500 million years ago.

While a number of theories have been put forward to explain this landmark period, the most credible is that it was fuelled by a significant rise in oxygen levels which allowed a wide variety of animals to thrive.

The new study suggests that such a rise in oxygen levels was the result of extraordinary changes in global plate tectonics.

During the formation of the supercontinent ‘Gondwana’, there was a major increase in continental arc volcanism — chains of volcanoes often thousands of miles long formed where continental and oceanic tectonic plates collided. This in turn led to increased ‘degassing’ of CO2 from ancient, subducted sedimentary rocks.

This, the team calculated, led to an increase in atmospheric CO2and warming of the planet, which in turn amplified the weathering of continental rocks, which supplied the nutrient phosphorus to the ocean to drive photosynthesis and oxygen production.

The study was led by Josh Williams, who began the research as an MSc student at the University of Exeter and is now studying for a PhD at the University of Edinburgh.

During his MSc project he used a sophisticated biogeochemical model to make the first quantification of changes in atmospheric oxygen levels just prior to this explosion of life.

Co-author and project supervisor Professor Tim Lenton, from the University of Exeter’s Global Systems Institute said: “One of the great dilemmas originally recognised by Darwin is why complex life, in the form of fossil animals, appeared so abruptly in what is now known as the Cambrian explosion.

“Many studies have suggested this was linked to a rise in oxygen levels — but without a clear cause for such a rise, or any attempt to quantify it.”

Not only did the model predict a marked rise in oxygen levels due to changes in plate tectonic activity, but that rise in oxygen — to about a quarter of the level in today’s atmosphere — crossed the critical levels estimated to be needed by the animals seen in the Cambrian explosion.

Williams added: “What is particularly compelling about this research is that not only does the model predict a rise in oxygen to levels estimated to be necessary to support the large, mobile, predatory animal life of the Cambrian, but the model predictions also show strong agreement with existing geochemical evidence.”

“It is remarkable to think that our oldest animal ancestors — and therefore all of us — may owe our existence, in part, to an unusual episode of plate tectonics over half a billion years ago” said Professor Lenton.

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Neanderthals and modern humans diverged at least 800,000 years ago, research on teeth shows

Neanderthals and modern humans diverged at least 800,000 years ago, substantially earlier than indicated by most DNA-based estimates, according to new research by a UCL academic.

The research, published in Science Advances, analysed dental evolutionary rates across different hominin species, focusing on early Neanderthals. It shows that the teeth of hominins from Sima de los Huesos, Spain — ancestors of the Neanderthals — diverged from the modern human lineage earlier than previously assumed.

Sima de los Huesos is a cave site in Atapuerca Mountains, Spain, where archaeologists have recovered fossils of almost 30 people. Previous studies date the site to around 430,000 years ago (Middle Pleistocene), making it one of the oldest and largest collections of human remains discovered to date.

Dr Aida Gomez-Robles (UCL Anthropology), said: “Any divergence time between Neanderthals and modern humans younger than 800,000 years ago would have entailed an unexpectedly fast dental evolution in the early Neanderthals from Sima de los Huesos.”

“There are different factors that could potentially explain these results, including strong selection to change the teeth of these hominins or their isolation from other Neanderthals found in mainland Europe. However, the simplest explanation is that the divergence between Neanderthals and modern humans was older than 800,000 years. This would make the evolutionary rates of the early Neanderthals from Sima de los Huesos roughly comparable to those found in other species.”

Modern humans share a common ancestor with Neanderthals, the extinct species that were our closest prehistoric relatives. However, the details on when and how they diverged are a matter of intense debate within the anthropological community.

Ancient DNA analyses have generally indicated that both lineages diverged around 300,000 to 500,000 years ago, which has strongly influenced the interpretation of the hominin fossil record.

This divergence time, however, is not compatible with the anatomical and genetic Neanderthal similarities observed in the hominins from Sima de los Huesos. The Sima fossils are considered likely Neanderthal ancestors based on both anatomical features and DNA analysis.

Dr Gomez-Robles said: “Sima de los Huesos hominins are characterised by very small posterior teeth (premolars and molars) that show multiple similarities with classic Neanderthals. It is likely that the small and Neanderthal-looking teeth of these hominins evolved from the larger and more primitive teeth present in the last common ancestor of Neanderthals and modern humans.”

Dental shape has evolved at very similar rates across all hominin species, including those with very expanded and very reduced teeth. This new study examined the time at which Neanderthals and modern humans should have diverged to make the evolutionary rate of the early Neanderthals from Sima de los Huesos similar to those observed in other hominins.

The research used quantitative data to measure the evolution of dental shape across hominin species assuming different divergent times between Neanderthals and modern humans, and accounting for the uncertainty about the evolutionary relationships between different hominin species.

“The Sima people’s teeth are very different from those that we would expect to find in their last common ancestral species with modern humans, suggesting that they evolved separately over a long period of time to develop such stark differences.”

The study has significant implications for the identification of Homo sapiens last common ancestral species with Neanderthals, as it allows ruling out all the groups postdating 800,000 year ago.

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Chewing gums reveal the oldest Scandinavian human DNA

The first humans who settled in Scandinavia more than 10,000 years ago left their DNA behind in ancient chewing gums, which are masticated lumps made from birch bark pitch. This is shown in a new study conducted at Stockholm University and published in Communications Biology.

There are few human bones of this age, close to 10,000 years old, in Scandinavia, and not all of them have preserved enough DNA for archaeogenetic studies. In fact, the DNA from these newly examined chewing gums is the oldest human DNA sequenced from this area so far. The DNA derived from three individuals, two females and one male, creates an exciting link between material culture and human genetics.

Ancient chewing gums are as of now an alternative source for human DNA and possibly a good proxy for human bones in archaeogenetic studies. The investigated pieces come from Huseby-Klev, an early Mesolithic hunter-fisher site on the Swedish west coast. The sites excavation was done in the early 1990’s, but at this time it was not possible to analyse ancient human DNA at all, let alone from non-human tissue. The masticates were made out of birch bark tar and used as glue in tool production and other types of technology during the Stone Age.

“When Per Persson and Mikael Maininen proposed to look for hunter-gatherer DNA in these chewing gums from Huseby Klev we were hesitant but really impressed that archaeologists took care during the excavations and preserved such fragile material,” says Natalija Kashuba, who was affiliated to The Museum of Cultural History in Oslo when she performed the experiments in cooperation with Stockholm University.

“It took some work before the results overwhelmed us, as we understood that we stumbled into this almost ‘forensic research’, sequencing DNA from these mastic lumps, which were spat out at the site some 10,000 years ago!” says Natalija Kashuba. Today Natalija is a Ph.D. student at Uppsala University.

Exciting link between material culture and human genetics

The results show that, genetically, the individuals whose DNA was found share close genetic affinity to other hunter-gatherers in Sweden and to early Mesolithic populations from Ice Age Europe. However, the tools produced at the site were a part of lithic technology brought to Scandinavia from the East European Plain, modern day Russia. This scenario of a culture and genetic influx into Scandinavia from two routes was proposed in earlier studies, and these ancient chewing gums provides an exciting link directly between the tools and materials used and human genetics.

Emrah Kirdök at Stockholm University conducted the computational analyses of the DNA. “Demography analysis suggests that the genetic composition of Huseby Klev individuals show more similarity to western hunter-gatherer populations than eastern hunter-gatherers,” he says.

“DNA from these ancient chewing gums have an enormous potential not only for tracing the origin and movement of peoples long time ago, but also for providing insights in their social relations, diseases and food.,” says Per Persson at the Museum of Cultural History in Oslo. “Much of our history is visible in the DNA we carry with us, so we try to look for DNA where ever we believe we can find it,” says Anders Götherström, at the Archaeological Research Laboratory at Stockholm University, where the work was conducted. The study is published in Communications Biology.

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These beetles have successfully freeloaded for 100 million years

Almost 100 million years ago, a tiny and misfortunate beetle died after wandering into a sticky glob of resin leaking from a tree in a region near present-day Southeast Asia. Fossilized in amber, this beetle eventually made its way to the desk of entomologist Joe Parker, assistant professor of biology and biological engineering at Caltech. Parker and his colleagues have now determined that the perfectly preserved beetle fossil is the oldest-known example of an animal in a behaviorally symbiotic relationship.

A paper describing the work appears on April 16 in the journal eLife.

Symbiotic relationships between two species have arisen repeatedly during animal evolution. These relationships range from mutually beneficial associations, like humans and their pet dogs, to the parasitic, like a tapeworm and its host.

Some of the most complex examples of behavioral symbiosis occur between ants and other types of small insects called myrmecophiles — meaning “ant lovers.” Thanks to ants’ abilities to form complex social colonies, they are able to repel predators and amass food resources, making ant nests a highly desirable habitat. Myrmecophiles display elaborate social behaviors and chemical adaptations to deceive ants and live among them, reaping the benefits of a safe environment and plentiful food.

Ants’ social behaviors first appear in the fossil record 99 million years ago, during the Cretaceous period of the Mesozoic era, and are believed to have evolved not long before, in the Early Cretaceous. Now, the discovery of a Cretaceous myrmecophile fossil implies that the freeloading insects were already taking advantage of ants’ earliest societies. The finding means that myrmecophiles have been a constant presence among ant colonies from their earliest origins and that this socially parasitic lifestyle can persist over vast expanses of evolutionary time.

“This beetle-ant relationship is the most ancient behavioral symbiosis now known in the animal kingdom,” says Parker. “This fossil shows us that symbiosis can be a very successful long-term survival strategy for animal lineages.”

The fossilized beetle, named Promyrmister kistneri, belongs to a subfamily of “clown” beetles (Haeteriinae), all modern species of which are myrmecophiles. These modern beetles are so specialized for life among ants that they will die without their ant hosts and have evolved extreme adaptations for infiltrating colonies. The beetles are physically well protected by a thick tank-like body plan and robust appendages, and they can mimic their host ants’ nest pheromones, allowing them to disguise themselves in the colony. They also secrete compounds that are thought to be pacifying or attractive to ants, helping the beetles gain the acceptance of their aggressive hosts. The fossilized Promyrmister is a similarly sturdy insect, with thick legs, a shielded head, and glandular orifices that the researchers theorize exuded chemicals to appease its primitive ant hosts.

Depending on another species so heavily for survival has its risks; indeed, an extinction of the host species would be catastrophic for the symbiont. The similarities between the fossilized beetle and its modern relatives suggest that the particular adaptations of myrmecophile clown beetles first evolved inside colonies of early “stem group” ants, which are long extinct. Due to Promyrmister’s remarkable similarity to modern clown beetles, Parker and his collaborators infer that the beetles must have “host switched” to colonies of modern ants to avoid undergoing extinction themselves. This adaptability of symbiotic organisms to move between partner species during evolution may be essential for the long-term stability of these intricate interspecies relationships.

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