Turtle ant soldiers evolution, new research


This September 2019 video is called Turtle Ants, Cephalotes atratus from Ecuador.

From Rockefeller University in the USA:

Soldier ants reveal that evolution can go in reverse

March 9, 2020

Turtle ant soldiers look like real-life creatures straight out of a Japanese anime film. These tree-dwelling insects scuttle to and fro sporting shiny, adorably oversized heads, which they use to block the entrances of their nests — essentially acting as living doors.

Not all heads are shaped alike: some soldiers have ones that resemble manhole covers and perfectly seal tunnel entrances. Others have square heads, which they assemble into multi-member blockades reminiscent of a Spartan army’s overlapping shields. This variety in head shapes reveals more than just another of nature’s quirky oddities: it can also shine a light on how species evolve to fill ecological niches. And that evolution, new research published in the Proceedings of the National Academy of Sciences shows, is not always a one-way street toward increasing specialization. Occasionally, it can take a species back to a more-generalist stage.

“Usually, you would think that once a species is specialized, it’s stuck in that very narrow niche,” says Daniel Kronauer, head of Rockefeller’s Laboratory of Social Evolution and Behavior. “But turtle ants are an interesting case of a very dynamic evolutionary trajectory, with a lot of back and forth.”

A match made in evolution

Like many other social insects living in colonies, turtle ants specialize for different functions, often evolving exaggerated features suited to their job. For the soldiers, this process has resulted in large heads that come in a variety of shapes.

“There’s a whopping four-fold difference between the smallest and largest turtle ant soldier heads,” says Scott Powell, a biologist at George Washington University and lead author of the new study. “To help people picture this, I often say that the smallest species is able to sit comfortably on the head of the largest species.”

The shape and size of a turtle-ant soldier’s head is dictated by the type of tunnel the species in question occupies. The ants don’t dig the tunnels themselves, but move into those excavated by wood-boring beetles. And since a hand-me-down tunnel might be too big or too small, Kronauer says, the ants diversify rapidly to be able to occupy it.

The relationship between turtle-ant heads and tunnels can hence offer a uniquely clear insight into natural selection. Researchers can easily compare a trait — head circumference — with the ecological feature it’s evolved to adapt to: the nest-entrance size. As Kronauer says, “It’s a 1:1 match on the exact same scale.”

A dynamic process

To examine the evolutionary journey of various head shapes, the researchers grouped 89 species of turtle ants based on whether soldiers sported a square, dome, disc, or dish-shaped head. They also included a group of turtle-ant species that don’t have soldiers. They then examined the evolutionary relationships among these groups using the species’ genetic information, which they had previously gathered.

If evolution was a one-way path, the first turtle ants that appeared some 45 million years ago should have lacked soldiers altogether, then gradually evolved toward specialization — starting with the generalist, square-headed soldiers, all the way to those with highly-tailored dish heads.

But the new analysis suggests that this was not the case. Instead, the oldest common ancestor the researchers could trace likely had a square head. That ancestor went on to form a range of species, from ones with no soldiers at all to others with different levels of specialization. In some cases, more specialist species reversed direction over time, evolving back into more generalist head shapes.

The finding nicely shows just how surprisingly flexible nature can be in fitting the shape of an organism to the context of the environment they occupy, Powell says.

“The space that evolution has to play with is actually quite a bit larger than previously thought,” Kronauer adds.

Dinosaur age days were shorter, mollusks show


This 1 July 2016 video from England says about itself:

New insights for the rudist phylogeny (Bivalvia, Hippuritida)

By Valentin Rineau.

Recorded at Progressive Palaeontology 2016, Oxford.

From the American Geophysical Union in the USA:

Ancient shell shows days were half-hour shorter 70 million years ago

Beer stein-shaped distant relative of modern clams captured snapshots of hot days in the late Cretaceous

March 9, 2020

Earth turned faster at the end of the time of the dinosaurs than it does today, rotating 372 times a year, compared to the current 365, according to a new study of fossil mollusk shells from the late Cretaceous. This means a day lasted only 23 and a half hours, according to the new study in AGU’s journal Paleoceanography and Paleoclimatology.

The ancient mollusk, from an extinct and wildly diverse group known as rudist clams, grew fast, laying down daily growth rings. The new study used lasers to sample minute slices of shell and count the growth rings more accurately than human researchers with microscopes.

The growth rings allowed the researchers to determine the number of days in a year and more accurately calculate the length of a day 70 million years ago. The new measurement informs models of how the Moon formed and how close to Earth it has been over the 4.5-billion-year history of the Earth-Moon gravitational dance.

The new study also found corroborating evidence that the mollusks harbored photosynthetic symbionts that may have fueled reef-building on the scale of modern-day corals.

The high resolution obtained in the new study combined with the fast growth rate of the ancient bivalves revealed unprecedented detail about how the animal lived and the water conditions it grew in, down to a fraction of a day.

“We have about four to five datapoints per day, and this is something that you almost never get in geological history. We can basically look at a day 70 million years ago. It’s pretty amazing,” said Niels de Winter, an analytical geochemist at Vrije Universiteit Brussel and the lead author of the new study.

Climate reconstructions of the deep past typically describe long term changes that occur on the scale of tens of thousands of years. Studies like this one give a glimpse of change on the timescale of living things and have the potential to bridge the gap between climate and weather models.

Chemical analysis of the shell indicates ocean temperatures were warmer in the Late Cretaceous than previously appreciated, reaching 40 degrees Celsius (104 degrees Fahrenheit) in summer and exceeding 30 degrees Celsius (86 degrees Fahrenheit) in winter. The summer high temperatures likely approached the physiological limits for mollusks, de Winter said.

“The high fidelity of this data-set has allowed the authors to draw two particularly interesting inferences that help to sharpen our understanding of both Cretaceous astrochronology and rudist palaeobiology,” said Peter Skelton, a retired lecturer of palaeobiology at The Open University and a rudist expert unaffiliated with the new study.

Ancient reef-builders

The new study analyzed a single individual that lived for over nine years in a shallow seabed in the tropics — a location which is now, 70-million-years later, dry land in the mountains of Oman.

Torreites sanchezi mollusks look like tall pint glasses with lids shaped like bear claw pastries. The ancient mollusks had two shells, or valves, that met in a hinge, like asymmetrical clams, and grew in dense reefs, like modern oysters. They thrived in water several degrees warmer worldwide than modern oceans.

In the late Cretaceous, rudists like T. sanchezi dominated the reef-building niche in tropical waters around the world, filling the role held by corals today. They disappeared in the same event that killed the non-avian dinosaurs 66 million years ago.

“Rudists are quite special bivalves. There’s nothing like it living today,” de Winter said. “In the late Cretaceous especially, worldwide most of the reef builders are these bivalves. So they really took on the ecosystem building role that the corals have nowadays.”

The new method focused a laser on small bits of shell, making holes 10 micrometers in diameter, or about as wide as a red blood cell. Trace elements in these tiny samples reveal information about the temperature and chemistry of the water at the time the shell formed. The analysis provided accurate measurements of the width and number of daily growth rings as well as seasonal patterns. The researchers used seasonal variations in the fossilized shell to identify years.

The new study found the composition of the shell changed more over the course of a day than over seasons, or with the cycles of ocean tides. The fine-scale resolution of the daily layers shows the shell grew much faster during the day than at night

“This bivalve had a very strong dependence on this daily cycle, which suggests that it had photosymbionts,” de Winter said. “You have the day-night rhythm of the light being recorded in the shell.”

This result suggests daylight was more important to the lifestyle of the ancient mollusk than might be expected if it fed itself primarily by filtering food from the water, like modern-day clams and oysters, according to the authors. De Winter said the mollusks likely had a relationship with an indwelling symbiotic species that fed on sunlight, similar to living giant clams, which harbor symbiotic algae.

“Until now, all published arguments for photosymbiosis in rudists have been essentially speculative, based on merely suggestive morphological traits, and in some cases were demonstrably erroneous. This paper is the first to provide convincing evidence in favor of the hypothesis,” Skelton said, but cautioned that the new study’s conclusion was specific to Torreites and could not be generalized to other rudists.

Moon retreat

De Winter’s careful count of the number of daily layers found 372 for each yearly interval. This was not a surprise, because scientists know days were shorter in the past. The result is, however, the most accurate now available for the late Cretaceous, and has a surprising application to modeling the evolution of the Earth-Moon system.

The length of a year has been constant over Earth’s history, because Earth’s orbit around the Sun does not change. But the number of days within a year has been shortening over time because days have been growing longer. The length of a day has been growing steadily longer as friction from ocean tides, caused by the Moon’s gravity, slows Earth’s rotation.

The pull of the tides accelerates the Moon a little in its orbit, so as Earth’s spin slows, the Moon moves farther away. The moon is pulling away from Earth at 3.82 centimeters (1.5 inches) per year. Precise laser measurements of distance to the Moon from Earth have demonstrated this increasing distance since the Apollo program left helpful reflectors on the Moon’s surface.

But scientists conclude the Moon could not have been receding at this rate throughout its history, because projecting its progress linearly back in time would put the Moon inside the Earth only 1.4 billion years ago. Scientists know from other evidence that the Moon has been with us much longer, most likely coalescing in the wake of a massive collision early in Earth’s history, over 4.5 billion years ago. So the Moon’s rate of retreat has changed over time, and information from the past, like a year in the life of an ancient clam, helps researchers reconstruct that history and model of the formation of the moon.

Because in the history of the Moon, 70 million years is a blink in time, de Winter and his colleagues hope to apply their new method to older fossils and catch snapshots of days even deeper in time.

North American extinct Carolina parakeets


This 9 March 2020 video from the USA says about itself:

When you picture a parrot, you probably don’t picture Denver, but up until about a century ago, the United States was home to its very own species of parrot: the Carolina parakeet. What happened to this endemic bird?

Hosted by Michael Aranda.

Belemnites and dinosaur age global warming


This 2006 video says about itself:

A short video introducing belemnites which were extinct cousins of the squid, octopus and cuttlefish.

From the University of Erlangen-Nuremberg in Germany:

Why organisms shrink in a warming world

March 9, 2020

Everyone is talking about global warming. A team of palaeontologists at GeoZentrum Nordbayern at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) has recently investigated how prehistoric organisms reacted to climate change, basing their research on belemnites.

These shrunk significantly when the water temperature rose as a result of volcanic activity approximately 183 million years ago, during the period known as the Toarcian. The FAU research team published their results in the online publication Royal Society Open Science.

‘Belemnites are particularly interesting, as they were very widespread for a long time and are closely related to the squid of today,’ explains palaeontologist Dr. Patricia Rita. ‘Their fossilised remains, for example the rostrum, can be used to make reliable observations.’ Within the context of the DFG-funded research project ‘Temperature-related stresses as a unifying principle in ancient extinctions,’ the hypothesis was confirmed that climate has a significant influence on the morphology of adult aquatic organisms. The body size of dominant species fell by an average of up to 40 percent.

The team of researchers believe that this Lilliput effect was a precursor to the later extinction of the animals. It is still unclear whether rises in temperature influenced the organisms’ metabolism directly or indirectly, for example due to a shortage of food sources.