Question 1

How do you say Hettangian?

Accepted Answer

Hettangian is pronounced heh-TAN-jee-un. Break it into four parts: heh, TAN, jee, and un, with the strongest stress on the TAN syllable in the middle. Say it out loud a few times and it starts to flow naturally. The word comes from a French place name, Hettange-Grande, which is why it has that slightly unusual spelling.

Question 2

What does Hettangian mean?

Accepted Answer

Hettangian is named after Hettange-Grande, a small town in northeastern France near the borders of Luxembourg and Germany. Geologists in the 1800s named this age of the Jurassic after rock outcrops near that town where the period's characteristic layers were first studied. The suffix 'ian' is a standard Latin-style ending used in geology to mean 'of' or 'belonging to' a particular place.

Question 3

When did the Hettangian period start and end?

Accepted Answer

The Hettangian began approximately 201.3 million years ago and ended around 199.3 million years ago. That makes it only about 2 million years long, which is quite short compared to many other geologic stages. It marks the very beginning of the Jurassic Period and comes right after the catastrophic End-Triassic Mass Extinction.

Question 4

What dinosaurs lived during the Hettangian?

Accepted Answer

Early sauropodomorphs, the ancestors of giant long-necked dinosaurs like Brachiosaurus, were already spreading across the continents during the Hettangian. Small theropod dinosaurs also roamed the land as predators. Because the End-Triassic Extinction had just wiped out so many competing animals, dinosaurs were rapidly expanding into new ecological roles during this time.

Question 5

What caused the Hettangian period to start?

Accepted Answer

The Hettangian began right after the End-Triassic Mass Extinction, one of the five biggest extinctions in Earth's history. Scientists believe massive volcanic eruptions from the Central Atlantic Magmatic Province triggered this extinction by flooding the atmosphere with carbon dioxide and sulfur, causing rapid climate change and ocean acidification. About 76% of all species went extinct, and the Hettangian marks the beginning of life's recovery and the dawn of the Jurassic world.

Question 6

Is the Hettangian part of the Jurassic Period?

Accepted Answer

Yes, the Hettangian is actually the very first age and stage of the entire Jurassic Period. The Jurassic Period starts at the same moment the Hettangian starts, 201.3 million years ago. It is followed by the Sinemurian stage, and together these early Jurassic stages represent the world rebuilding after a devastating extinction event.

Question 7

Where was the Hettangian boundary officially defined?

Accepted Answer

The official starting point of the Hettangian, called a GSSP or Global Boundary Stratotype Section and Point, is located at Kuhjoch in the Karwendel Mountains of Austria. This site has an exceptionally well-preserved sequence of marine limestone rocks that record the exact boundary between the Triassic and Jurassic Periods. The International Commission on Stratigraphy officially ratified this location in 2010.

Question 8

What was the climate like during the Hettangian?

Accepted Answer

The Hettangian was a warm, humid period with no polar ice caps and elevated levels of carbon dioxide in the atmosphere. Temperatures were significantly higher than today, partly as a result of the massive volcanic eruptions that had just triggered the End-Triassic Extinction. Shallow tropical seas covered much of what is now Europe, and warm lowland forests and fern prairies spread across the continents.

Question 9

What came before and after the Hettangian?

Accepted Answer

The Hettangian follows the Rhaetian stage, which was the final stage of the Triassic Period. The Hettangian is then followed by the Sinemurian stage, the second age of the Early Jurassic. The boundary between the Rhaetian and the Hettangian is also the boundary between the Triassic and Jurassic Periods, marked by one of Earth's five major mass extinctions.

Question 10

How do geologists know where the Hettangian starts in rock layers?

Accepted Answer

Geologists identify the start of the Hettangian using a combination of fossil evidence and chemical signatures in rock layers. The most important markers are ammonite fossils: specific species of these coiled shell creatures appear and disappear at very precise moments in time, allowing scientists to match rock layers from different parts of the world. The base of the Hettangian is specifically marked by the first appearance of the ammonite species Psiloceras spelae tirolicum at the Kuhjoch site in Austria.

Question 11

How long did the Hettangian last?

Accepted Answer

The Hettangian lasted approximately 2 million years, from about 201.3 million years ago to 199.3 million years ago. In geological terms, this is actually quite a short span of time. Many other stages of the Jurassic Period lasted three to five times longer. Despite its brief duration, the Hettangian was enormously important as the opening chapter of the Age of Dinosaurs.

Question 12

What happened to the oceans during the Hettangian?

Accepted Answer

Hettangian seas were warm but were still recovering from the devastating ocean acidification that came with the End-Triassic Extinction. Ammonites diversified quickly and became the dominant shelled invertebrates of these seas. Ichthyosaurs, the dolphin-like marine reptiles, also survived the extinction and cruised Hettangian oceans. True coral reefs were largely absent early in this period because the acidification had destroyed reef ecosystems, and they took millions of years to fully recover.

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