Tag: Argentinosaurus

When Did the Dinosaurs Live?

This blog is the first in a series that will explore the timeline of Earth’s history, from the formation of the planet to the dominance and eventual extinction of dinosaurs.

           This blog is about dinosaurs in time; that is, dinosaurs in the timeline of Earth’s history. Not dinosaurs on time, because dinosaurs were hardly ever on time seeing they didn’t have clocks.

           Scientists say the Earth was formed 4.6 billion years ago. At first it was just molten lava, hundreds of miles deep. Over millions of years the Earth cooled and a crust appeared.

Artist’s impression of the Hadean Eon.
Tim Bertelink, CC BY-SA 4.0, via Wikimedia Commons

            The first lifeform that existed was a sort of blue-green algae. Then other lifeforms appeared, including shellfish. That whole time period of more than four billion years is called the Precambrian Eon. From 542 million years ago to the present age is the Phanerozoic Eon. It’s divided into three eras, the Paleozoic, the Mesozoic, and the Cenozoic. During the Paleozoic (from 541 to 252 million years ago) life began to bloom. The first fish, first amphibians, and the first reptiles appeared. The first plants also began to grow. But then a massive extinction wiped out 90% of life on Earth. Its cause is not known, but it ended the Paleozoic Era making way for the Mesozoic Era (from 252 to 66 million years ago).

           That’s when we get to the good stuff: Dinosaurs! The Mesozoic is divided into three time periods: the Triassic, the Jurassic, and the Cretaceous. And about halfway through the Triassic Period a new kind of animal evolved: a dinosaur.

Timeline of Earth (MYA means millions years ago))
Thanaben, CC BY-SA 3.0, via Wikimedia Commons

           During the Triassic the Earth was warm and fairly dry, with ice at the north and south poles. (Although Santa Claus hadn’t moved in yet.) Most of the large island masses gathered together in a supercontinent called Pangaea. Conifers, cycads (which looked like mutant pineapples), and ferns were the most common plants, and reptiles ruled the planet. It was about 240 million years ago that the first dinosaurs appeared. They were small and walked on two legs. Over millions of years, they began to change, and many varieties of dinosaurs appeared. Some were meat eaters; others, plant eaters. Some grew to large sizes. These included Riojasaurus and Lessemsaurus. But then 201 million years ago, another mass extinction took place, probably caused by volcanic action in the Atlantic Ocean, rising sea levels, and climate change.

Pangaea breaking up
Public Domain U.S. Dept. of the Interior

           Some dinosaurs survived and moved into the Jurassic Period. Pangaea broke apart and, over millions of years, formed the continents we know today. Their environment ranged from arid deserts to lush tropical forests. Conifers and ferns were the main plants. Most importantly, dinosaurs dominated each new continent. Some of the largest of all dinosaurs evolved during this time, including Alamosaurus, Argentinosaurus, and Dreadnaughtus. The fierce predator Allosaurus also lived in this time period. And the earliest known bird, Archaeopteryx, emerged in the late Jurassic.

USGS; Diarama by Masato Hattori. Map courtesy of Colorado Plateau Geosystems Inc., Public domain, via Wikimedia Commons

           About 140 million years ago, life on Earth began to change dramatically. Many new life forms emerged while others went extinct. There doesn’t seem to have been any big extinction event, but scientists date this as the beginning of the Cretaceous Period (my favorite time period!). Flowering plants appeared, but there were still a lot of the familiar conifers and ferns. Many new, strange-looking dinosaurs dominated the environment. Tyrannosaurus became an apex predator and weird dinosaurs, such as Parasaurolophus, Ankylosaurus, Triceratops and Pachycephalosaurus roamed around.

           Dinosaurs were so abundant it seemed they would rule Earth forever – but an asteroid colliding with Earth 66 million years ago brought their world to an end. The Cenozoic Era began, with an opening for mammals to dominate the world. The asteroid collision will be the subject of my next blog.

Sources (Click Me!)

Davis, Josh. “The Triassic Period: The Rise of the Dinosaurs.” London Natural History Museum, n.d., https://www.nhm.ac.uk/discover/the-triassic-period-the-rise-of-the-dinosaurs.html

“Hadean Eon: The Formation of Earth (4.6 to 4.0 billion years ago).” EarthHow, 2024. https://earthhow.com/hadean-eon/

“Mesozoic.” U.S. Dept. of the Interior. https://www.usgs.gov/youth-and-education-in-science/mesozoic

Title Image of Triceratops facing Tyrannosaurus
Marcin Chady, CC BY 2.0, via Wikimedia Commons

What Was the Biggest Dinosaur?

            It’s almost impossible to declare that one dinosaur was the biggest of them all. Do you mean longest, heaviest, or tallest? Also, it’s very unlikely that paleontologists have actually found the biggest specimen of a dinosaur type. Millions and millions of dinosaurs once lived on Earth, and we’ve found only a small percent of them. We do know that all of the biggest dinosaurs are plant eaters. They come from the group of dinosaurs called sauropods, the long-necked dinosaurs – and most of the very biggest ones have been found in Argentina.

            So, how do paleontologists figure out how long or tall a dinosaur was? They need to look at the spine. Put your fingers on the back of your neck. The little bones you feel there that are part of your spine are called vertebrae. When a dinosaur skeleton is found, usually many of the vertebrae are missing. When there is a gap, paleontologists have to guess how many are missing. One way they do this is by comparing the bones they have to other, similar dinosaurs. If a similar dinosaur had, say, 80 vertebrae in its tail, paleontologists would assume that a closely related dinosaur had 80, too. But that might not be true. And it’s hard to know how big those missing vertebrae would be. Scientists have to make the best estimate they can, but they often don’t agree with one another. However, they have provided some great contenders for biggest dinosaur!

Longest:

Danny Cicchetti, CC BY-SA 3.0, via Wikimedia Commons

            This might be Barosaurus (BARE-uh-sore-us). It was discovered in 1889 in South Dakota. Its name means slow, heavy lizard, and it must have been. Scientists think it was probably 82-89 feet long. That’s long, but that’s not what put it in contention for longest. Scientists have found a huge vertebra that they think belonged to Barosaurus. From the size of it, the creature it came from was likely about 157 feet long! That’s almost as long as three eighteen-wheeler trucks set end to end.

Nobu Tamura (http://spinops.blogspot.com), CC BY 3.0, via Wikimedia Commons

            Another contender is Argentinosaurus (are-juhn-tee-nuh-SORE-us). Scientists have only found 13 of its bones: a few ribs, some vertebrae, and a five-foot-long femur (thigh bone). This isn’t much to try to figure out  how big this dinosaur was, but the sizes of those bones have led scientists to estimate that Argentinosaurus was between 75 and 100 feet long. If that top limit is right, Argentinosaurus is definitely among the very biggest dinosaurs.

Heaviest:

User:Mariolanzas, CC BY-SA 4.0, via Wikimedia Commons

            Argentinosaurus is also a contender for the heaviest dinosaur, but because estimates of its weight are based on so few bones, some scientists discount it. However, paleontologists have unearthed more than 200 bones of Patagotitan (PAT-ah-go-TIE-ton). These  bones were found in Argentina in 2012 and cause scientists to estimate that it weighed about 76 tons. The largest land animal today is the African elephant. Its top weight is seven tons. That means that Patagotitan weighed nearly as much as 11 elephants. And some scientists think at its biggest it weighed as much as 14 elephants.  

Nobu Tamura email:nobu.tamura@yahoo.com http://spinops.blogspot.com/,
CC BY-SA 4.0, via Wikimedia Commons

            Dreadnoughtus (dred-NOHR-tus) is a definite contender in weight. Its name means fearing nothing. And it’s hard to imagine any creature that it would have to be afraid of. It was discovered in Argentina in 2005.  Scientists have recovered almost half of its bones, so they are able to be fairly accurate in their estimates. They place its weight between 54 and 65 tons (though some scientists say that’s too high). It was also about 85 feet long and as tall as a two-story building.   

Tallest:

Levi bernardo, CC BY-SA 3.0, via Wikimedia Commons

            Two stories, however, is not a contender for height.  The tallest dinosaurs reached close to the height of a six-story building, though again, it’s tricky to know for sure. Scientists don’t agree on how high up long-necked dinosaurs could lift their heads. Sauroposeidon  (Sore-uh-ps-SY-don) is certainly one of the tallest.
            It was found in Oklahoma in 1994 and named for the Greek god Poseidon. Poseidon could cause earthquakes, and it probably felt like this dinosaur could do that, too – just by walking. It probably stood just over 55 feet tall, which is, as it says above, almost the height of a six-story building.

            Patagotitan shows up again here. Depending on how it carried its long neck, it might have been as tall as a seven-story building. If it carried its head and neck low to the ground, straight out from its body, it’s a contender for longest dinosaur at 122-130 feet. The picture at the right shows Patagotitan at the Field Museum in Chicago

            Scientist do not agree which one was the biggest dinosaur. Other lists would include such dinosaurs as Mamenchisaurus (mah-MUN-chi-SORE-us), a creature whose neck was longer than the rest of its body, or Giraffatitan (ji-RAF-ah-TIE-tan), which had the same general build as a gigantic giraffe. We may never know which dinosaur was the biggest. But we can all agree that they were awesome!

            Which dinosaur do you vote for as biggest? Do you know a big dinosaur that isn’t in this list? Please leave your answers in the comment section.