Dinosaur fossils are well-known from Alaska, most famously from areas like Denali National Park and the North Slope, but there are very few records of dinosaurs from the Alaskan Peninsula in the southwest part of the state. In this study, Fiorillo and colleagues document abundant dinosaur trackways from Aniakchak National Monument, around 670km southwest of Anchorage.

The trackways were preserved in the Chignik Formation, a series of coastal sediment deposits dating back to the Late Cretaceous Period around 66 million years ago. Survey work from 2001-2002 and 2016-2018 identified more than 75 trackway sites including dozens of dinosaur footprints. Based on the anatomy of the prints, the authors identified two footprints of armored dinosaurs, one of a large predatory tyrannosaur, and a few footprints attributable to two types of birds. The remaining 93% of the trackways belonged to hadrosaurs, highly successful herbivores which are typically the most common dinosaurs in high-latitude fossil ecosystems.

Previous research on skeletal dinosaur remains in northern Alaska has found that hadrosaurs were most abundant in coastal habitats. The trackways documented in this study reveal that the same trend was true in southern Alaska. The authors suggest that understanding habitat preferences in these animals will contribute to understanding of how ecosystems changed through time as environmental conditions shifted and dinosaurs migrated across northern corridors between continents.

Fiorillo adds, “Our study shows us something about habitat preferences for some dinosaurs and also that duck-billed dinosaurs were incredibly abundant. Duck-billed dinosaurs were as commonplace as cows, though given we are working in Alaska, perhaps it is better to consider them the caribou of the Cretaceous.”

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Ötzi the Iceman is a remarkable 5,300-year-old human specimen found frozen in ice approximately 3,200 meters above sea level in the Italian Alps. He was frozen alongside his clothing and gear as well as an abundant assemblage of plants and fungi. In this study, Dickson and colleagues aimed to identify the mosses and liverworts preserved alongside the Iceman.

Today, 23 bryophyte species live the area near where Ötzi was found, but inside the ice the researchers identified thousands of preserved bryophyte fragments representing at least 75 species. It is the only site of such high altitude with bryophytes preserved over thousands of years. Notably, the assemblage includes a variety of mosses ranging from low-elevation to high-elevation species, as well as 10 species of liverworts, which are very rarely preserved in archaeological sites. Only 30% of the identified bryophytes appear to have been local species, with the rest having been transported to the spot in Ötzi’s gut or clothing or by large mammalian herbivores whose droppings ended up frozen alongside the Iceman.

From these remains, the researchers infer that the bryophyte community in the Alps around 5,000 years ago was generally similar to that of today. Furthermore, the non-local species help to confirm the path Ötzi took to his final resting place. Several of the identified moss species thrive today in the lower Schnalstal valley, suggesting that Ötzi traveled along the valley during his ascent. This conclusion is corroborated by previous pollen research, which also pinpointed Schnalstal as the Iceman’s likely route of ascent.

Dickson adds, “Most members of the public are unlikely to be knowledgeable about bryophytes (mosses and liverworts). However, no fewer than 75 species of these important investigative clues were found when the Iceman (aka Ötzi) was removed from the ice. They were recovered as mostly small scraps from the ice around him, from his clothes and gear, and even from his alimentary tract. Those findings prompted the questions: Where did the fragments come from? How precisely did they get there? How do they help our understanding of the Iceman?”

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Surprisingly, the planets with the highest masses tend to be those with the highest eccentricities, even though the inertia of a larger mass should make it harder to budge from its initial orbit. This counter-intuitive observation prompted astronomers at UC Santa Cruz to explore the evolution of planetary systems using computer simulations. Their results, reported in a paper published in Astrophysical Journal Letters, suggest a crucial role for a giant-impacts phase in the evolution of high-mass planetary systems, leading to collisional growth of multiple giant planets with close-in orbits.

“A giant planet is not as easily scattered into an eccentric orbit as a smaller planet, but if there are multiple giant planets close to the host star, their gravitational interactions are more likely scatter them into eccentric orbits,” explained first author Renata Frelikh, a graduate student in astronomy and astrophysics at UC Santa Cruz.

Frelikh performed hundreds of simulations of planetary systems, starting each one with 10 planets in circular orbits and varying the initial total mass of the system and the masses of individual planets. As the systems evolved for 20 million simulated years, dynamical instabilities led to collisions and mergers to form larger planets as well as gravitational interactions that ejected some planets and scattered others into eccentric orbits.

Analyzing the results of these simulations collectively, the researchers found that the planetary systems with the most initial total mass produced the biggest planets and the planets with the highest eccentricities.

“Our model naturally explains the counter-intuitive correlation of mass and eccentricity,” Frelikh said.

Coauthor Ruth Murray-Clay, the Gunderson professor of theoretical astrophysics at UC Santa Cruz, said the only non-standard assumption in their model is that there can be several gas giant planets in the inner part of a planetary system. “If you make that assumption, all the other behavior follows,” she said.

According to the classic model of planet formation, based on our own solar system, there is not enough material in the inner part of the protoplanetary disk around a star to make gas giant planets, so only small rocky planets form in the inner part of the system and giant planets form farther out. Yet astronomers have detected many gas giants orbiting close to their host stars. Because they are relatively easy to detect, these “hot Jupiters” accounted for the majority of early exoplanet discoveries, but they may be an uncommon outcome of planet formation.

“This may be an unusual process,” Murray-Clay said. “We’re suggesting that it is more likely to happen when the initial mass in the disk is high, and that high-mass giant planets are produced during a phase of giant impacts.”

This giant-impacts phase is analogous to the final stage in the assembly of our own solar system, when the moon was formed in the aftermath of a collision between Earth and another planet. “Because of our solar system bias, we tend to think of impacts as happening to rocky planets and ejection as happening to giant planets, but there is a whole spectrum of possible outcomes in the evolution of planetary systems,” Murray-Clay said.

According to Frelikh, collisional growth of high-mass giant planets should be most efficient in the inner regions, because encounters between planets in the outer parts of the system are more likely to lead to ejections than mergers. Mergers producing high-mass planets should peak at a distance from the host star of around 3 astronomical units (AU, the distance from Earth to the sun), she said.

“We predict that the highest-mass giant planets will be produced by mergers of smaller gas giants between 1 to 8 AU from their host stars,” Frelikh said. “Exoplanet surveys have detected some extremely large exoplanets, approaching 20 times the mass of Jupiter. It may take a lot of collisions to produce those, so it’s interesting that we see this giant-impacts phase in our simulations.”

Research from James Cook University, Lancaster University, the University of Copenhagen and Queensland University of Technology, published in Biology Letters, reveals neither energy availability alone, nor in combination with other local factors, accounts for differences in the diversity of coral species across depth.

The research, funded by the Australian Research Council Centre of Excellence Programme, generated an unprecedented dataset of 8,460 coral colonies across six reefs in Kimbe Bay, Papua New Guinea.

This allowed the team to conduct a robust test of the drivers that underlie how corals are distributed over depth for the first time, enabling them to test the theory that there will be a greater species diversity where there is greater available energy.

For corals, the highest diversity was expected in the shallows because they depend on energy from sunlight. To test this idea, researchers surveyed diversity at depths of between 0 and 45 metres, reaching significantly deeper than most previous surveys, and covering 98 per cent of the light gradient.

In contrast to the expectations based on the theory, the research revealed that coral diversity among the team’s samples was highest at depths of between 15 and 20 metres.

Lead author Dr Edward Roberts, of James Cook University, said: “Our understanding of how coral diversity varies across depth has been limited by a lack of high quality data due to the difficulty of deeper surveys.

“We were able to overcome that in our survey in Kimbe Bay. This allowed us to test the classic Species Energy hypothesis that proposes the greater the energy available, the greater the diversity, as theoretically more energy allows more individuals to co-exist. This in turn allows more species to maintain large enough populations to avoid local extinction.

“Our results do not agree with this classic explanation of how diversity changes with energy. Instead, the shallowest depths had fewer species, a pattern also poorly explained by alternative explanations such as competition between corals or environmental disturbance.”

The results of the research provide cause to find new theories about diversity distribution.

Co-author Dr Sally Keith, of Lancaster Environment Centre, said: “Hyper-diverse corals reefs are ideal ecosystems to test theories about how diversity is distributed in nature, so it is really interesting that our results do not support the classic hypotheses.”

“More broadly, our analyses cast doubt on the suitability of these hypotheses more generally across terrestrial, marine and freshwater systems, suggesting that ecologists might need to rethink the underlying causes of these fundamental patterns of diversity.”

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Egg fungi — oomycetes — are known to cause many dangerous diseases in plants and animals. They also infest fish and algae, but the relationship between these microorganisms and algae is still poorly understood. Up to now, why some species first massively reproduce in the oceans and then disappear again has been unclear. One hypothesis is that microorganisms produce chemical signaling substances which are regulating the interactions, such as defense, mating and communication, between living organisms. In order to identify such substances, the team of scientists established a laboratory system in which the egg fungus Lagenisma coscinodisci infects a marine diatom under controlled conditions.

Researchers found that during the infection process, two new substances were formed: both were so-called carbolines from the class of alkaloids which also includes nicotine and caffeine. Large amounts of these compounds accumulate after oomycete infection. “The identity of the substances surprised us, as it has been described in diatoms for the first time and their induction during infection was conserved in the whole population of cells,” explains Marine Vallet, one of the two main authors of the new study. Interestingly, although these two substances benefited the oomycete, they were detrimental to the algae, ultimately killing it.

It is not easy to investigate such a system, because these fungal pests kill their host within just a few hours. “Oomycetes are known to take various forms: They are often found only as tiny spores in their host. Sometimes they do not cause any harm at all and are ‘asleep’ in their host, at other occasions they can cause mass killing of the cells. These processes result in highly dynamic fluctuation of dominant species in the oceans,” says Tim Baumeister, another main author, describing the initial challenges that the researchers faced.

Using high-resolution mass spectrometric methods to separate and identify small substances from complex mixtures, combined with microscopic techniques, scientists were able to identify the active compounds produced by a single algal cell. “One has to bear in mind that a single cell is 30 times smaller than a pinhead and that the concentrations of all substances are very low — to show the chemistry in one single cell is a major technical achievement,” explains Georg Pohnert, head of the Max Planck Fellow Group Interactions in Plankton Communities and Chair of Instrumental Analytics at Friedrich Schiller University Jena.

Not all diatoms are equally vulnerable to attack, so how do certain diatoms defend themselves? These and many other unresolved questions remain to be addressed in follow-up studies The team is especially interested in identifying signaling substances involved in diatom interactions with their environment. “Our ocean is a treasure to protect, there are still so many fantastic discoveries awaiting us there,” concludes Marine Vallet. [KG/AO]

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