Jurassic Period: The Age of Giants and Evolutionary Radiations

The Jurassic Period represents a pivotal chapter in Earth's history, spanning from approximately 201.4 to 143.1 million years ago. Nestled within the Mesozoic Era, this period witnessed profound shifts in continental geography, dramatic climatic changes, and the spectacular radiation of life forms that would define the prehistoric world. From the rise of iconic dinosaurs to the diversification of marine reptiles and early mammals, the Jurassic was a time of immense biological innovation.

alt=A realistic black-and-white portrait of Brongniart, who is clean shaven with a full head of hair. He is dressed in a formal jacket — Portrait of Alexandre Brongniart, who coined the term "Jurassic"

Key Facts

Middle Jurassic strata in Neuquén Province, Argentina

Time Span: Approximately 201.4 ± 0.2 to 143.1 ± 0.6 million years ago.
Geologic Era: Part of the Mesozoic Era, following the Triassic.
Subdivisions: Divided into three stages: Early (Lower), Middle, and Late (Upper) Jurassic.
Major Life Forms: Characterized by the dominance of dinosaurs, ichthyosaurs, plesiosaurs, and various gymnosperms.
Geological Context: Marked by significant tectonic activity and the breakup of the supercontinent Pangea.

Chronology and Stratigraphy

Tidwell Member of the Morrison Formation (Upper Jurassic), Colorado

The Jurassic is scientifically organized into three distinct stages. The Early Jurassic begins with the Hettangian stage, following the Triassic–Jurassic extinction event. The Middle Jurassic follows, and the period concludes with the Late Jurassic, transitioning into the Cretaceous Period.

Folded Lower Jurassic limestone layers of the Doldenhorn nappe at Gasteretal, Switzerland

The Three Stages of the Jurassic

To understand the progression of this era, geologists divide it into specific ages:

Early Jurassic: Includes the Hettangian, Sinemurian, Pliensbachian, and Toarcian stages.
Middle Jurassic: Comprises the Aalenian, Bajocian, Bathonian, and Callovian stages.
Late Jurassic: Consists of the Oxfordian, Kimmeridgian, and Tithonian stages.

Chronological Breakdown of the Jurassic Period
Jurassic Subdivision	Stages/Ages Included	Approximate Time Range (Ma)
Early Jurassic	Hettangian to Toarcian	201.4 – 184.2
Middle Jurassic	Aalenian to Callovian	174.7 – 165.3
Late Jurassic	Oxfordian to Tithonian	161.5 – 145.0

Paleogeography and Tectonics

Kimmeridge Clay at Egmont Bight in the Jurassic Coast, southern England

During the Jurassic, the Earth's surface underwent massive transformations. The supercontinent Pangea began to fragment, leading to the formation of new ocean basins. This tectonic movement significantly influenced global climate patterns and marine ecosystems.

Map of geography during the Early Jurassic, around 190 million years ago

The movement of tectonic plates, such as the formation of the Pacific Plate during the Early Jurassic, reshaped the coastlines and created diverse habitats ranging from shallow seas to vast inland basins. These changes are visible in the fossil record through varying sedimentary layers found globally, from Argentina to China.

Flora: The Green World of the Jurassic

The landscape of the Jurassic was dominated by gymnosperms—plants that produce "naked" seeds, not enclosed in an ovary. This era saw the flourishing of conifers, Ginkgoales (relatives of the modern Ginkgo), and Bennettitales (an extinct group of seed plants).

Black fossils of leaves on yellow coloured rock — Leaves of Ginkgo huttonii from the Middle Jurassic of England

Ferns and other lower plants also played a vital role in the ecosystem, providing the foundational energy for the food webs of the time. The presence of diverse flora supported a wide array of herbivores, from small insects to massive dinosaurs.

Life restoration of the stem and leaves of a member of the extinct seed plant order Caytoniales, a group which reached its apex of abundance during the Jurassic, and which may be closely related to living flowering plants.

Fauna: A Diverse Biological Explosion

Map of global geography during the Late Jurassic, around 155 million years ago

The Jurassic is perhaps most famous for its incredible animal life. The period saw the rise of several major groups that dominated different ecological niches.

Dinosaurs and Land Vertebrates

Dinosaurs reached new heights of diversity during this time. Theropods (bipedal carnivores), Sauropodomorphs (long-necked herbivores), and Ornithischians (bird-hipped dinosaurs) occupied various roles. Notable examples include the massive Mamenchisaurus and the early bird-like Archaeopteryx.

Fossil of complete Archaeopteryx, including indentations of feathers on wings and tail — Archaeopteryx lithographica from the Late Jurassic (Tithonian) of Germany

Skeleton of Mamenchisaurus sinocanadorum from the Middle-Late Jurassic of China

Beyond dinosaurs, the Jurassic hosted early mammals (mammaliaformes), various amphibians, and reptiles such as crocodylomorphs and turtles. Small, agile creatures like Henkelotherium suggest that even early mammalian relatives were adapting to diverse environments, including arboreal (tree-dwelling) lifestyles.

Henkelotherium, a likely arboreal dyolestoid from the Late Jurassic of Portugal

Marine and Aerial Life

The oceans were teeming with life. Ichthyosaurs and plesiosaurs were the apex predators of the seas, while various fish, including early sharks (Chondrichthyes) and bony fish (Actinopterygii), filled the waters. Marine invertebrates like ammonites and various molluscs were also abundant.

Skeleton of an icthyosaur in side view — Fossil of Ichthyosaurus somersetensis at the Natural History Museum, London

Rhomaleosaurus cramptoni at the Natural History Museum, London

In the skies, pterosaurs—flying reptiles—navigated the Jurassic atmosphere, representing one of the earliest successful groups of vertebrates to achieve powered flight.

Skeleton of Rhamphorhynchus muensteri at Teylers Museum, Haarlem

Frequently Asked Questions

Grainstone with calcitic ooids and sparry calcite cement; Carmel Formation, Middle Jurassic, of southern Utah, US

Two images of a round conifer cone, the left one is in cross-section — Petrified Araucaria mirabilis cone from the Middle Jurassic of Argentina

Restoration of a member of Bennettitales belonging to Williamsoniaceae.

Skeleton of Heterodontosaurus, a primitive ornithischian from the Early Jurassic of South Africa

Holotype specimen of Platysuchus, a telosaurid thalattosuchian

Thalassemys, a thalassochelydian sea turtle known from the Late Jurassic of Germany

Topside view of a salamander skeleton — Skeleton of Karaurus sharovi, a stem-group salamander from the Middle to Late Jurassic of Kazakhstan

Fossils and life restorations of the two species of Yanliaomyzon , a lamprey known from the Middle Jurassic of China

Fossil of Thrissops, an ichthyodectid stem-group teleost from the Late Jurassic Solnhofen Limestone of Germany, showing preserved colouration

Fossil of Pseudorhina from the Late Jurassic of Germany, a close relative of modern angelsharks.

Lichnomesopsyche daohugouensis, an extinct mesopsychid scorpionfly from the Late Jurassic of China

Mongolarachne from the Late Jurassic of China

Eryon, a polychelidan decapod crustacean from the Late Jurassic of Germany.

Fossil specimen of Proteroctopus from the Middle Jurassic of France, formerly thought to be world's oldest known octopus

What defines the start of the Jurassic Period?

The Jurassic begins approximately 201.4 million years ago, following the Triassic–Jurassic mass extinction event. It is formally marked by the Hettangian stage.

Which animals were most dominant during the Jurassic?

Dinosaurs were the dominant land animals, particularly sauropods and theropods. In the oceans, marine reptiles like ichthyosaurs and plesiosaurs were highly successful.

What kind of plants grew during this time?

The Jurassic landscape was dominated by gymnosperms, including conifers, cycads, and Ginkgoales, along with various ferns.

How did the Earth's geography change during the Jurassic?

The supercontinent Pangea began to break apart, leading to the formation of new oceans and changing the global climate and sea levels.

Is the Jurassic Period the same as the "Age of Dinosaurs"?

While the Jurassic is a major part of the Mesozoic Era (often called the Age of Dinosaurs), the dinosaur era actually spans the Triassic, Jurassic, and Cretaceous periods.