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Thread: Fossils can define a whole ecosystem in the Cretaceous

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    tWebber shunyadragon's Avatar
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    Fossils can define a whole ecosystem in the Cretaceous

    Most often there are limited fossils to describe some animals and plants, but now they have enough fossils to define a whole ecosystem in the late Cretaceous.

    Source: https://www.newswise.com/articles/late-cretaceous-dinosaur-dominated-ecosystem.



    Late Cretaceous dinosaur-dominated ecosystem
    New study published in Geology

    Newswise — Boulder, Colo., USA: A topic of considerable interest to paleontologists is how dinosaur-dominated ecosystems were structured, how dinosaurs and co-occurring animals were distributed across the landscape, how they interacted with one another, and how these systems compared to ecosystems today. In the Late Cretaceous (~100-66 million years ago), North America was bisected into western and eastern landmasses by a shallow inland sea. The western landmass (Laramidia) contained a relatively thin stretch of land running north-south, which was bordered by that inland sea to the east and the rising Rocky Mountains to the west. Along this ancient landscape of warm and wet coastal plains comes an extremely rich fossil record of dinosaurs and other extinct animals.

    Yet, from this record, an unexpected pattern has been identified: Most individual basins preserve an abundant and diverse assemblage of dinosaur species, often with multiple groups of co-occurring large (moose- to elephant-sized) herbivorous species, yet few individual species occur across multiple putatively contemporaneous geological formations (despite them often being less than a few hundred kilometers apart). This is in fairly stark contrast to the pattern seen in modern terrestrial mammal communities, where large-bodied species often have very extensive, often continent-spanning ranges. It has therefore been suggested that dinosaurs (and specifically large herbivorous dinosaurs) were particularly sensitive to environmental differences over relatively small geographic distances (particularly with respect to distance from sea level), and may have even segregated their use of the landscape between more coastal and inland sub-habitats within their local ranges.

    In their new study published in Geology, Thomas Cullen and colleagues sought to test some of these hypotheses as part of their broader research reconstructing the paleoecology of Late Cretaceous systems.

    One of the methods they're using to do that is stable isotope analysis. This process measures differences in the compositions of non-decaying (hence, "stable") isotopes of various common elements, as the degree of difference in these compositions in animal tissues and in the environment have known relationships to various factors such as diet, habitat use, water source, and temperature. So the team applied these methods to fossilized teeth and scales from a range of animals, including dinosaurs, crocodilians, mammals, bony fish, and rays, all preserved together from a relatively small region over a geologically short period of time in sites called vertebrate microfossil bonebeds.

    By analyzing the stable carbon and oxygen isotope compositions of these fossils they were able to reconstruct their isotopic distributions in this ecosystem--a proxy for their diets and habitat use. They found evidence of expected predator-prey dietary relationships among the carnivorous and herbivorous dinosaurs and among aquatic reptiles like crocodilians and co-occurring fish species.

    Critically, says Cullen, "What we didn't see was evidence for large herbivorous dinosaurs segregating their habitats, as the hadrosaurs, ceratopsians, and ankylosaurs we sample all had strongly overlapping stable carbon and oxygen ranges. If some of those groups were making near-exclusive use of certain parts of the broader landscape, such as ceratopsians sticking to coastal environments and hadrosaurs sticking to more inland areas, then we should see them grouping distinctly from each other. Since we didn't see that, that suggests they weren't segregating their resource use in this manner. It's possible they were doing so in different ways though, such as by feeding height segregation, or shifting where in the landscape they go seasonally, and our ongoing research is investigating some of these possibilities."

    Another important part of their study was comparing the fossil results to an environmentally similar modern environment in order to examine how similar they are ecologically. For a modern comparison, they examined the animal communities of the Atchafalaya River Basin of Louisiana, the largest contiguous wetland area in the continental U.S. The landscape of this area is very similar to their Cretaceous system, as are many elements of the plant and animal communities (not including the non-avian dinosaurs, of course).

    From their comparisons, the team found that the Cretaceous system was similar to the Louisiana one in having a very large amount of resource interchange between the aquatic and terrestrial components of the ecosystem, suggesting that fairly diverse/mixed diets were common, and food being obtained from both terrestrial and aquatic sources was the norm. They also found that habitat use differences among the herbivorous mammals in the Louisiana system was more distinct than among those large herbivorous dinosaurs in the Cretaceous system, lending further evidence to their results about their lack of strict habitat use preferences.

    Lastly, the team used modified oxygen stable isotope temperature equations to estimate mean annual temperature ranges for both systems (with the Louisiana one being a test of the accuracy of the method, as they could compare their results to directly measured water and air temperatures). The team found that in their Late Cretaceous ecosystem in Alberta, mean annual temperature was about 16-20 degrees C, a bit cooler than modern day Louisiana, but much warmer than Alberta today, reflecting the hotter greenhouse climate that existed globally about 76 million years ago.

    Characterizing how these ecosystems were structured during this time, and how these systems changed across time and space, particularly with respect to how they responded to changes in environmental conditions, may be of great importance for understanding and predicting future ecosystem responses under global climate change. The team's research continues and should reveal much more about the food webs and ecology of the dinosaurs and other organisms that inhabited these ancient landscapes.



    FEATURED ARTICLE

    Large-scale stable isotope characterization of a Late Cretaceous dinosaur-dominated ecosystem

    Thomas Cullen, tcullen@fieldmuseum.org; David Evans; Fred Longstaffe; Ulrich Wortmann; Li Huang; Federico Fanti; Mark Goodwin; Michael Ryan.
    URL: https://pubs.geoscienceworld.org/gsa...erization-of-a

    GEOLOGY articles are online at http://geology.geoscienceworld.org/content/early/recent. Representatives of the media may obtain complimentary articles by contacting Kea Giles at the e-mail address above. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY in articles published. Non-media requests for articles may be directed to GSA Sales and Service, gsaservice@geosociety.org.

    https://www.geosociety.org.

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    Evolution is God's ID rogue06's Avatar
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    Until relatively recently paleontologists have concentrated largely on the fossils at a site and pretty much ignored the sedimentary rock they were found in. This has changed and as a result we are learning a great deal more about the environment and ecosystems that the organisms inhabited.

    Still I gotta wonder how much data could we have acquired if this was something we had been doing for numerous decades and not just the past two to two and a half.

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    tWebber shunyadragon's Avatar
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    Interesting times the volume of discoveries and research results has never been this high in a very long time. Even the research in older fossils is increasing.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

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    tWebber shunyadragon's Avatar
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    . . . just a few million years after the asteroid impact they found . . .

    Source: https://gazette.com/cheyenneedition/paleontologists-talk-about-game-changing-mammal-skull-find-at-corral/article_00ee6ce0-63c9-11ea-b7fc-174f094658c3.html



    Paleontologists talk about game-changing mammal skull find at Corral Bluffs Open Space

    The scientists talked about their discovery of a full mammal skull from the period following the asteroid impact that supposedly caused the dinosaurs’ extinction as well as the discovery’s importance to society.

    Mammals first appeared on the planet during the Triassic Period starting about 252 million years ago and existed with dinosaurs throughout the Mesozoic Era ending about 65 million years ago. That’s when the dinosaurs went extinct, ushering in the Cenozoic Era when mammals flourished and diversified.

    Lyson and Miller first visited Corral Bluffs in September 2016. According to Lyson, scientists have studied this fossil-rich area since the early 1900s but never found complete fossils. Lyson, who led the research team, split open one of the areas’ white concretion rocks and unearthed an entire mammal skull dating back to the period after an asteroid slammed into the Earth.

    “All of the fossils we found, including numerous mammals skulls, are 65 to 66 million years old. Our search image of looking for fossils is what ‘cracked’ the case for finding complete fossils from this interval of time,” Lyson said.


    Miller, a Colorado College graduate, co-led the research team and spearheaded collecting plant fossils from the Corral Bluffs area. He and colleagues analyzed more than 6,000 specimens to determine the relationship between plant and animal diversity following the asteroid impact.

    According to Miller, Carbon 14 dating is applicable only to organic materials newer than 50,000 years old, and therefore did not figure in determining the fossils’ age. “These fossils are ... way too old for carbon dating. In this case, we used paleomagnetism and uranium-lead dating to date the fossils,” Miller said.

    The discovery is regarded as a major scientific breakthrough because it paints a portrait of the million years period following the asteroid impact. The New York Times, Reuters, Science Magazine and Washington Post all published articles about the discovery.

    The discovery also was featured on an episode of NOVA, a Rocky Public Broadcasting Television program that focuses on frontline science and engineering stories. “We knew it was a once-in-a-lifetime discovery when it happened,” Miller said.

    It has changed science forever, according to Lyson. “For the first time, we were able to pull together the vertebrate and plant fossil record, along with time and temperature and put together a really cohesive story of what happened after Earth’s last mass extinction 66 million years ago. We found that life rebounded quite quickly,” Lyson said.

    Miller believes the discovery opens a new world into the study of how life emerged from the extinction of the dinosaurs. “We’re just on the cusp of learning so much about some of our earliest ancestors,” Miller said.

    Looking ahead, Lyson hopes this discovery inspires people to make others. “Many folks think everything has been found or is known, but that is far from the truth. We have only scratched the surface with this discovery. I’ll be working on the fossils from this discovery for the rest of my life. The discovery will keep lots of scientists busy for centuries to come.”

    © Copyright Original Source

    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

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    tWebber shunyadragon's Avatar
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    Quote Originally Posted by rogue06 View Post
    Until relatively recently paleontologists have concentrated largely on the fossils at a site and pretty much ignored the sedimentary rock they were found in. This has changed and as a result we are learning a great deal more about the environment and ecosystems that the organisms inhabited.

    Still I gotta wonder how much data could we have acquired if this was something we had been doing for numerous decades and not just the past two to two and a half.
    Some years ago I saw an article about paleontologists sorting through debri from dinosaur excavations in the Midwest and finding many small mammal bones, and other fossils.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

  6. #6
    Evolution is God's ID rogue06's Avatar
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    Quote Originally Posted by shunyadragon View Post
    Interesting times the volume of discoveries and research results has never been this high in a very long time. Even the research in older fossils is increasing.
    A number of big discoveries have been made by someone combing through old fossil collections stored in the drawers in back rooms of various museums.

    One that springs immediately to mind were the discovery of transitional "flatfish" dating from the Eocene at the Paris National Museum of Natural History and Britain’s Natural History Museum in London by Brian Friedman. Until then even the majority of scientists conceded that their asymmetrical, one-sided eye arrangement was a characteristic that arose suddenly in flatfish because they could not comprehend any benefit for the fish if it took millions of years for an eye to migrate from one side to the other. Many assumed that the flatfish’s anatomy was probably a result of a few chance mutations, a through a process called "saltation."

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  7. #7
    Evolution is God's ID rogue06's Avatar
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    Quote Originally Posted by shunyadragon View Post
    Some years ago I saw an article about paleontologists sorting through debri from dinosaur excavations in the Midwest and finding many small mammal bones, and other fossils.
    A dozen or so years ago in China they discovered a fossilized badger-sized mammal that actually ate dinosaurs, Repenomamus, which was still digesting the remains of a juvenile Psittacosaurus (an early ceratopsian dinosaur) when it died. Whether it was a predator, scavenger or both (very few predators turn down a free meal) is not known.

    I'm always still in trouble again

    "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
    "Of course, human life begins at fertilization that’s not the argument." --Tassman

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