The ancient mollusk, from an extinct and wildly diverse group referred to as rudist clams, grew fast, laying down daily growth rings. The new study used lasers to sample minute slices of shell and count the expansion rings more accurately than human researchers with microscopes.
The growth rings allowed the researchers to work out the number of days during a year and more accurately calculate the length of each day 70 million years ago. The new measurement informs models of how the Moon formed and the way on the brink of Earth it’s been over the 4.5-billion-year history of the Earth-Moon gravitational dance.
The new study also found evidence that the mollusks harbored photosynthetic symbionts which will have fueled reef-building on the size of modern-day corals.
The high resolution obtained within the new study combined with the fast rate of growth of the traditional bivalves revealed unprecedented detail about how the animal lived and therefore the water conditions it grew in, right down to a fraction of each day.
“We have about four to 5 data points per day, and this is often something that you simply almost never get in geological history. we will basically check out each day 70 million years ago. It’s pretty amazing,” said Niels de Winter, an analytical geochemist at Vrije Universiteit Brussel and therefore the lead author of the new study.
Climate reconstructions of the deep past typically describe future changes that occur on the size of tens of thousands of years. Studies like this one provide 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 within 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 hi-fi 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.
The new study analyzed one person who lived for over nine years during a shallow seabed within the tropics — a location which is now, 70-million-years later, land within the mountains of Oman.
Torreites sanchezi mollusks appear as if tall pint glasses with lids shaped like bear claw pastries. the traditional mollusks had two shells, or valves, that met during 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 within the same event that killed the non-avian dinosaurs 66 million years ago.
“Rudists are quite special bivalves. There’s nothing love it living today,” de Winter said. “In the late Cretaceous especially, worldwide most of the reef builders are these bivalves. in order that 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 corpuscle . 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 also as seasonal patterns. The researchers used differences due to the season within the fossilized shell to spot years.
The new study found the composition of the shell changed more over the course of each 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 in the dark
“This bivalve had a really strong dependence on this daily cycle, which suggests that it had photosymbionts,” de Winter said. “You have the day-night rhythm of the sunshine being recorded within the shell.”
This result suggests daylight was more important to the life-style of the traditional mollusk than could be expected if it fed itself primarily by filtering food from the water, like modern-day clams and oysters, consistent with the authors. De Winter said the mollusks likely had a relationship with an indwelling symbiotic species that ate up sunlight, almost like living giant clams, which harbor symbiotic algae.
“Until now, all published arguments for photosymbiosis in rudists are essentially speculative, supported merely suggestive morphological traits, and in some cases were demonstrably erroneous. This paper is that the first to supply convincing evidence in favor of the hypothesis,” Skelton said, but cautioned that the new study’s conclusion was specific to Torreites and will not be generalized to other rudists.
De Winter’s careful count of the amount of daily layers found 372 for every yearly interval. This wasn’t a surprise, because scientists know days were shorter within the past. The result’s , however, the foremost accurate now available for the late Cretaceous, and features 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 round the Sun doesn’t change. But the amount of days within a year has been shortening over time because days are growing longer. The length of each day has been growing steadily longer as friction from ocean tides, caused by the Moon’s gravity, slows Earth’s rotation.