FOSSILS & DINOSAURS

Tracing Earth’s past in prehistoric rock deposits

INDIAN INSTITUTE OF SCIENCE (IISC)

Outcrop of the Palaeoproterozoic section in the Cuddapah basin — IMAGE: OUTCROP OF THE PALAEOPROTEROZOIC SECTION IN THE CUDDAPAH BASIN view more
CREDIT: YOGARAJ BANERJEE

What did the Earth look like about two billion years ago, when the planet’s atmosphere was being oxygenated?

By analysing ancient dolomite (carbonate) deposits found in Vempalle, in the Cuddapah district of Andhra Pradesh, researchers at the Indian Institute of Science (IISc) and the University of Tennessee have estimated the temperature and composition of a shallow, inland sea that most likely existed back in that time, called the Palaeoproterozoic era.

Their findings provide insight into how the conditions during that time provided just the right ambience for the emergence and bloom of photosynthetic algae. It also shows how a wealth of data about our planet’s past remains hidden inside ancient rocks.

“The story of our planet is written in the different strata of rocks,” explains Prosenjit Ghosh, Professor at the Centre for Earth Science (CEaS), IISc, and corresponding author of the study published in Chemical Geology.

Planet Earth hasn’t always been this hospitable for life. It has been through different phases of climatic extremes, including periods when carbon dioxide levels were almost too toxic for living creatures, just like our neighbour, Venus. However, various studies of fossils from the Palaeoproterozoic era have shown that some life might have existed even under these harsh conditions.

The large amounts of CO2 in the atmosphere were absorbed by the sea and trapped as carbonates in dolomites, says Yogaraj Banerjee, a former PhD student from CEaS and one of the authors.

“[Dolomite] is a direct precipitate from seawater. It provides a signal not only of seawater chemistry but also of seawater temperature,” explains Robert Riding, Research Professor at the Department of Earth and Planetary Sciences, University of Tennessee, USA, and another author of the study.

The team of researchers collected dolomite samples from chert – hard rocks formed by the interaction of microbes with seawater – as well as deposits underneath them called dolomitic lime-mud. Having first identified the strata of rock where the dolomitic mud could be found, the researchers extracted and transported them back to the lab. Then, they used a state-of-the-art technique known as clumped isotope thermometry to analyse them. The technique allows scientists to narrow down the temperature and composition of the deposits by looking at the arrangement of the carbon and oxygen bonds.

After two years of intense analysis, the team was able to figure out from the dolomitic mud that the temperature of the seawater during its original time period was about 20°C. This is in contrast to previous studies that analysed only chert samples from around the same period, and had estimated that the temperature was higher, around 50°C. The lower temperature estimate from the current study agrees more closely with the theory that the conditions were ideal for supporting lifeforms.

During the Palaeoproterozoic era, the type of water present was earlier believed to be only heavy water, containing a specific set of isotopes or forms of hydrogen. However, in the current study, the team showed that light water – the regular form of water found even today – was also present back then.

Taken together, these insights – the lower seawater temperature and the presence of light water – strongly support the hypothesis that the conditions around two billion years ago were just right for photosynthetic algae to emerge. These algae were mainly responsible for pumping oxygen into the atmosphere, and making way for other lifeforms to evolve and populate the planet.

The team now plans to search for similar lime-mud deposits in other places around the world to gather additional insights about the Palaeoproterozoic era.

Palaeoproterozoic (around 2 billion years-old) stromatolite fossils studied in this project

CREDIT

Yogaraj Banerjee

JOURNAL

Chemical Geology

DOI

10.1016/j.chemgeo.2023.121356

ARTICLE TITLE

Oxygen isotopic composition of Paleoproterozoic seawater revealed by clumped isotope analysis of dolomite, Vempalle Formation, Cuddapah, India

New details of Tully monster revealed

3D scanning of enigmatic fossil may have brought an end to debate about whether it is a vertebrate or invertebrate

Peer-Reviewed Publication

UNIVERSITY OF TOKYO

For more than half a century, the Tully monster (Tullimonstrum gregarium), an enigmatic animal that lived about 300 million years ago, has confounded paleontologists, with its strange anatomy making it difficult to classify. Recently, a group of researchers proposed a hypothesis that Tullimonstrum was a vertebrate similar to cyclostomes (jawless fish like lamprey and hagfish). If it was, then the Tully monster would potentially fill a gap in the evolutionary history of early vertebrates. Studies so far have both supported and rejected this hypothesis. Now, using 3D imaging technology, a team in Japan believes it has found the answer after uncovering detailed characteristics of the Tully monster which strongly suggest that it was not a vertebrate. However, its exact classification and what type of invertebrate it was is still to be decided.

In the 1950s, Francis Tully was enjoying his hobby fossil hunting in a site known as Mazon Creek Lagerstätte in the U.S. state of Illinois, when he discovered what would later become known as the Tully monster. This 15-centimeter (on average), 300-million-year-old marine “monster” turned out to be an enigma, as ever since its discovery researchers have debated where it fits in the classification of living things (its taxonomic position). Unlike dinosaur bones and hard-shelled creatures that are often found as fossils, the Tully monster was soft-bodied. The Mazon Creek Lagerstätte is one of the few places in the world where the conditions were just right for imprints of these marine animals to be captured in detail in the underwater mud, before they could decay. In 2016, a group of scientists in the US proposed a hypothesis that the Tully monster was a vertebrate. If this was the case, then it could be a missing piece of the puzzle on how vertebrates evolved.

Despite considerable effort, studies both supporting and rejecting this hypothesis have been published in recent years, and so a consensus had not been reached. However, new research by a team from the University of Tokyo and Nagoya University may have finally brought an end to the debate. “We believe that the mystery of it being an invertebrate or vertebrate has been solved,” said Tomoyuki Mikami, a doctoral student in the Graduate School of Science at the University of Tokyo at the time of the study and currently a researcher at the National Museum of Nature and Science. “Based on multiple lines of evidence, the vertebrate hypothesis of the Tully monster is untenable. The most important point is that the Tully monster had segmentation in its head region that extended from its body. This characteristic is not known in any vertebrate lineage, suggesting a nonvertebrate affinity.”

The team studied more than 150 fossilized Tully monsters and over 70 other varied animal fossils from Mazon Creek. With the aid of a 3D laser scanner, they created color-coded, three-dimensional maps of the fossils which showed the tiny irregularities which existed on their surface through color variation. X-ray micro-computed tomography (which uses X-rays to create cross sections of an object so that a 3D model can be created), was also used to look at its proboscis (an elongated organ located in the head). This 3D data showed that features previously used to identify the Tully monster as a vertebrate were not actually consistent with those of vertebrates.

Although the researchers are confident from this study that the Tully monster was not a vertebrate, the next step of the investigation will be to answer what group of organisms it does belong to, possibly a nonvertebrate chordate (like a fishlike animal known as a lancelet) or some sort of protostome (a diverse group of animals containing, for example, insects, roundworms, earthworms and snails) with radically modified morphology.

Problematic fossils like the Tully monster highlight the challenge of piecing together the dynamic history of Earth and the diverse organisms that have inhabited it. “There were many interesting animals that were never preserved as fossils,” Mikami said. “In this sense, research on the fossils from Mazon Creek is important because it provides paleontological evidence that cannot be obtained from other sites. More and more research is needed to extract important clues from Mazon Creek fossils to understand the evolutionary history of life.”

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Paper Title:

Tomoyuki Mikami, Takafumi Ikeda, Yusuke Muramiya, Tatsuya Hirasawa, Wataru Iwasaki. Three-dimensional anatomy of the Tully monster casts doubt on its presumed vertebrate affinities Palaeontology 2023. DOI: 10.1111/pala.12646

Funding:

This research was supported by the Masason Foundation, Fujiwara Natural History Foundation, JSPS KAKENHI (grant numbers 18J21859 and 22J01214), and the World-Leading Innovative Graduate Study Program for Life Science and Technology.

Useful Links:

Graduate School of Science: https://www.s.u-tokyo.ac.jp/en/

Graduate School of Frontier Sciences: https://www.k.u-tokyo.ac.jp/en/index.html

Often used to study dinosaur footprints, these color-coded depth maps enabled the researchers to thoroughly investigate the structure of the Tully monster and other fossils from Mazon Creek.
CREDIT
Mikami, 2022.

JOURNAL

Palaeontology

DOI

10.1111/pala.12646

METHOD OF RESEARCH

Imaging analysis

SUBJECT OF RESEARCH

Animals

ARTICLE PUBLICATION DATE

17-Apr-2023

Fossils reveal the long-term relationship between feathered dinosaurs and feather-feeding beetles

Amber fragments preserve remains of feathers and larvae related to modern feather-feeding beetles in intimate contact

Peer-Reviewed Publication

UNIVERSITY OF OXFORD

Moult remains of feather-feeding beetle larvae among feather portions in Spanish amber — IMAGE: MOULT REMAINS OF FEATHER-FEEDING BEETLE LARVAE INTIMATELY ASSOCIATED WITH DOWNY FEATHER PORTIONS FROM AN UNIDENTIFIED THEROPOD DINOSAUR IN EARLY CRETACEOUS AMBER OF SPAIN. INSETS SHOW THE HEAD WITH POWERFUL MANDIBLES OF ONE OF THE LARVAL MOULTS (TOP) AND THE PIGMENTATION PATTERN OF FEATHER SECOND ORDER BRANCHES (BOTTOM), WITH THE MAIN STEM OF ONE FEATHER AT THE RIGHT OF THE AMBER FRAGMENT. AMBER FRAGMENT IS ONLY 6 MILLIMETRES ACROSS. view more
CREDIT: CN IGME-CSIC

New fossils in amber have revealed that beetles fed on the feathers of dinosaurs about 105 million years ago, showing a symbiotic relationship of one-sided or mutual benefit, according to an article published in Proceedings of the National Academy of Sciences of the United States of America today*.

The main amber fragments studied, from the Spanish locality of San Just (Teruel), contain larval moults of small beetle larvae tightly surrounded by portions of downy feathers. The feathers belonged to an unknown theropod dinosaur, either avian (a term referring to “birds” in wide sense) or non-avian, as both types of theropods lived during the Early Cretaceous and shared often indistinguishable feather types. However, the studied feathers did not belong to modern birds since the group appeared about 30 million years later in the fossil record, during the Late Cretaceous.

When looking at modern ecosystems, we see how ticks infest cattle, frogs capture insects with acrobatic tongues, or some barnacles grow on the skin of whales. These are just a few of the diverse and complex ecological relationships between vertebrates and arthropods, which have coexisted for more than 500 million years. The way that these two groups have interacted throughout deep time is thought to have critically shaped their evolutionary history, leading to coevolution. Nevertheless, evidence of arthropod-vertebrate relationships is extremely rare in the fossil record.

The larval moults preserved in the amber were identified as related to modern skin beetles, or dermestids. Dermestid beetles are infamous pests of stored products or dried museum collections, feeding on organic materials that are hard for other organisms to decay such as natural fibres. However, dermestids also play a key role in the recycling of organic matter in the natural environment, commonly inhabiting nests of birds and mammals, where feathers, hair, or skin accumulate.

“In our samples, some of the feather portions and other remains – including minute fossil faeces, or coprolites – are in intimate contact with the moults attributed to dermestid beetles and show occasional damage and/or signs of decay. This is hard evidence that the fossil beetles almost certainly fed on the feathers and that these were detached from its host,” explains Dr Enrique Peñalver, from the Geological and Mining Institute of Spain of the Spanish National Research Council (CN IGME-CSIC) and lead author of the study.

“The beetle larvae lived −feeding, defecating, moulting− in accumulated feathers on or close to a resin-producing tree, probably in a nest setting. A flow of resin serendipitously captured that association and preserved it for millions of years.”

“Three additional amber pieces each containing an isolated beetle moult of a different maturity stage but assigned to the same species were also studied, allowing a better understanding of these minute insects than what is usually possible in palaeontology,” says Dr David Peris, from the Botanical Institute of Barcelona (CSIC-Barcelona City Council) and co-author of the study. The most impressive, complete specimen was found in the amber deposit of Rábago/El Soplao in the northern Spain, roughly of the same age as San Just.

“It is unclear whether the feathered theropod host also benefitted from the beetle larvae feeding on its detached feathers in this plausible nest setting,” says Dr Ricardo Pérez-de la Fuente, from Oxford University Museum of Natural History and co-lead author of the study. “However, the theropod was most likely unharmed by the activity of the larvae since our data show these did not feed on living plumage and lacked defensive structures which among modern dermestids can irritate the skin of nest hosts, even killing them.”

Isolated moult of the feather-feeding beetle larva found in the Spanish amber outcrop of Rábago/El Soplao, with detail of its powerful mandibles (left). Length of the moult is less than two millimetres.