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21
The Jurassic Giants
What conditions allowed some animals to grow to the largest sizes ever seen on Earth?

Picture Earth at its most lush and abundant, that's the Jurassic Period. This is when dinosaurs reached their most spectacular sizes, when the climate was warm and wet, and when vast oceans teemed with giant marine reptiles. Your learner will explore how the planet's conditions and food sources allowed some animals to grow to absolutely enormous proportions, and how all these creatures fit together in complex food webs that supported this incredible diversity of life.

S2S_Lesson21 by Selene

Key Ideas

  • Some dinosaurs grew very, very large during the Jurassic Period.
  • Plants were everywhere, giving herbivore dinosaurs lots of food.
  • Many different animals lived on land, in the air, and in the oceans.
  • Warm global temperatures and high plant growth allowed ecosystems to support enormous sauropods.
  • Long-necked dinosaurs (sauropods) could reach food that other animals could not, reducing competition.
  • Jurassic ecosystems included complex food webs linking plants, herbivores, and predators.
  • Oceans were filled with large marine reptiles, while pterosaurs occupied the skies, showing how life adapted to many different environments.

Spines
  • DK's Science as You've Never Seen it Before: Food Chains pg. 188-189
  • Mammoth Science: Food Chains pg. 48
✏️  Notebooking Activity
Label the energy pyramid with examples from the Jurassic Period. Include producers, primary consumers, and secondary consumers. Add where the original energy is coming from.

Vocabulary
  • Jurassic — The middle period of the Mesozoic Era (about 201-145 million years ago) when dinosaurs grew to their largest sizes.
  • Sauropod — A group of enormous, long-necked, plant-eating dinosaurs — the largest land animals that ever lived.
  • Herbivore — An animal that eats only plants; giant sauropods were herbivores that needed vast amounts of vegetation.
  • Carnivore — An animal that eats other animals; Jurassic carnivores like Allosaurus hunted sauropods and other dinosaurs.
  • Food Web — A network of feeding relationships in an ecosystem showing who eats whom.
  • Pterosaur — Flying reptiles of the Mesozoic Era; not dinosaurs, but close relatives that evolved powered flight.
  • Warm-Blooded — Able to generate and maintain body heat internally; evidence suggests many dinosaurs may have been warm-blooded.

Cosmic CalendarWhere we are: December 25 to 26
The Jurassic covers Christmas and the day after on the Cosmic Calendar. Read the script below before the lesson.

Read aloud: December 25th and 26th on our Cosmic Calendar. The Jurassic Period, roughly 201 to 145 million years ago. Dinosaurs are now the dominant land animals on Earth. The giants we picture when we think of dinosaurs, the long-necked sauropods, the large predators, they’re out there right now on our calendar. The skies are beginning to fill with flying reptiles and the first birds. Look at how little time is left on the calendar. Six days until December 31st. And within those six days, mammals will rise, modern birds will spread, and eventually humans will appear in the final seconds. But right now, December 25th and 26th belong to the dinosaurs, and they are spectacular.

Timeline EntriesLabel the next page in your timeline “The Jurassic Giants: 201 Million Years Ago”. The workbook prompt asks learners to draw a massive Brachiosaurus stretching its neck into the treetops of a lush Jurassic forest, with a tiny Archaeopteryx gliding between the branches above.

Discussion Questions
  1. What do you notice about how big some Jurassic dinosaurs were?
    Sample answer: Some dinosaurs were much bigger than animals we see today.
  1. Why do animals need plants to survive?
    Sample answer: Plants are food for plant-eaters and help other animals get food too.
  2. What happens to animals if there is plenty of food?
    Sample answer: They can grow, stay healthy, and have babies.
Digging Deeper
  • How might long necks and large bodies reduce competition among herbivorous dinosaurs? 
    Sample answer: Different body sizes and neck lengths allowed dinosaurs to eat plants at different heights, so they weren't all competing for the same food.)
  • Why are food webs more useful than food chains when studying ecosystems
    Sample answer: Food webs show many connections and energy paths, not just one linear relationship.

Species to ResearchThe Jurassic Period is packed with iconic species. Here are some learners can choose to research:
  • Brachiosaurus— A truly enormous long-necked sauropod; one of the tallest animals to ever live.
  • Stegosaurus— The plated herbivore with distinctive back plates; likely used for temperature regulation or display.
  • Allosaurus— The apex predator of the Jurassic; a large theropod and a distant cousin of T. rex.
  • Archaeopteryx— The famous “first bird,” showing a mix of feathered bird traits and dinosaur features.
  • Diplodocus— A long, whip-tailed sauropod; one of the longest dinosaurs ever discovered.
  • Pterodactylus— A flying pterosaur (not a dinosaur, but a close relative) that soared over Jurassic seas.

SCIENTIST SPOTLIGHT: Mary AnningMary Anning was an English fossil hunter and self-taught paleontologist from Lyme Regis who made some of the most significant fossil discoveries of the nineteenth century. She found the first complete ichthyosaur skeleton, the first two plesiosaur skeletons ever identified, and an early pterosaur, among many other specimens. She came from a working-class family and had almost no formal education, yet her eye for fossils and her understanding of the rocks was extraordinary. Male scientists regularly bought her specimens, published papers about them, and did not give her credit. She was barred from the Geological Society of London because she was a woman. She died in poverty at the age of 47. Today she is recognized as one of the most important figures in the history of paleontology.

Videos:
Books:
Digging Deeper Activity:
Ichthyosaurs and plesiosaurs were not dinosaurs. Research what group of animals they belong to and how they were adapted for life in the sea. What do their body shapes tell us about how they swam and hunted? Draw and label one of the animals Mary Anning discovered.

Sources and More Information:

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