Dinosaurs took 30 million years to become dominant

28/11/2024 6:08

        The way the dinosaurs relinquished
        their long dominance is well known. An asteroid struck Earth 66
        million years ago, triggering a horrific mass extinction. But
        the way the dinosaurs - modest creatures initially - came to
        supremacy is less well understood.
        
        New research that relied heavily on fossilized feces and
        vomit - evidence of who is eating what and who is eating whom -
        provides new clarity on how dinosaurs bested the competition
        during the Triassic Period. The study focused on a region in
        Poland with extensive fossils from this pivotal time.
        
        First appearing roughly 230 million years ago, dinosaurs
        were at first overshadowed by other animals including large
        crocodile relatives - both terrestrial and semi-aquatic - and
        various plant-eaters including elephant-sized ones related to
        mammals and four-legged armored reptiles. By about 200 million
        years ago, dinosaurs reigned, their main competitors extinct.
        
        "We approached the rise of dinosaurs in a completely novel
        way. We analyzed feeding evidence to deduce the ecological role
        of dinosaurs across their first 30 million years of evolution,"
        said paleontologist Martin Qvarnström of Uppsala University in
        Sweden, lead author of the study published on Wednesday in the
        journal Nature.
        
        The earliest dinosaurs and close relatives were
        opportunists, eating foods including bugs, fish and insects.
        Subsequently, larger and more specialized dinosaur predators
        evolved along with herbivorous dinosaurs apparently better
        adapted than competitors to exploit new plants that arose when
        the climate became more humid.
        
        Feces fossils are called coprolites. Vomit fossils are
        called regurgitates. Together they are called bromalites. So why
        study this stuff? By examining undigested food - plants and prey
        - in bromalites, researchers can discern feeding patterns of
        various species and reconstruct an ecosystem's food webs.
        
        Hundreds of bromalites were examined, primarily coprolites.
        
        "We studied over 100 kilograms (220 pounds) of fossilized
        feces," said study senior author Grzegorz Niedźwiedzki, a
        paleontologist and geologist at Uppsala University and the
        Polish Geological Institute.
        
        How can researchers tell who left the feces or vomit?
        Skeletal fossils and footprints showed what animals were present
        at a given time. And the researchers deduced who produced a
        given coprolite based on factors including its size and shape,
        the type of undigested food and the nature of the digestive
        systems of living relatives of these extinct animals.
        
        Take, for example, the 20-foot-long (6-meter) four-legged
        meat-eater Polonosuchus, a type of reptile called a rauisuchian
        that was related to crocs and was an apex predator alongside the
        early dinosaurs.
        
        "We know that today's crocodiles and alligators digest food
        for a long time and thoroughly. In their feces, undigested bones
        are very rarely found. Such coprolites - large, sausage-shaped,
        with highly digested mass - we found in a site where bones of
        Polonosuchus were also found," Niedźwiedzki said.
        
        "In contrast, in sites where there were bones and tracks of
        predatory dinosaurs, we found coprolites containing a lot of
        undigested remains. Some of them are full of pieces of bones,
        fish remains, and there are also teeth. You can see that all
        this passed through the digestive tract quickly and was not
        digested in the crocodile way," Niedźwiedzki added.
        
        Early members of the dinosaur evolutionary lineage were
        omnivorous, like 7-foot-long (2-meter) Silesaurus.
        
        "The first dinosaur relative in the area, Silesaurus, was an
        opportunistic little thing that ate bugs, fish and plants. Some
        of the insects were amazingly well preserved," Qvarnström said.
        
        Big herbivorous and carnivorous dinosaurs began appearing
        late in the Triassic, which ended 201 million years ago.
        
        Environmental changes linked to Earth's increased volcanic
        activity precipitated a wider range of plants that ever-larger
        herbivorous dinosaurs exploited. This proliferation of big
        plant-eating dinosaurs encouraged the evolution of larger
        carnivorous dinosaurs.
        
        The large non-dinosaur meat-eaters disappeared before the
        start of the subsequent Jurassic Period, completing the
        transition to dinosaur dominion. By 200 million years ago,
        meat-eating dinosaurs 26 feet (8 meters) long were present,
        alongside plant-eating dinosaurs 33 feet (10 meters) long.
        
        Smok, a 20-foot-long (6-meter) strong-jawed carnivorous
        dinosaur relative, lived about 210 million years ago. Coprolites
        showed Smok's predilection for bone-crushing, obtaining
        nutritious marrow in a feeding trait associated with much later
        dinosaurs such as Tyrannosaurus.
        
        The coprolites of herbivorous dinosaurs offered surprises.
        
        "Another interesting and very mysterious discovery was the
        finding of geochemical signals in the coprolites from burnt
        plant remains, as well as pieces of charcoal. Did the dinosaurs
        eat charcoal from burnt plants? Ferns, whose remains are in
        coprolites, may be toxic, and the charcoal may have neutralized
        these toxins," Niedzwiedzki added.