🌍 Have you ever imagined what life was like on Earth millions of years ago? Do you know how different the planet, the oceans and the creatures that lived there were from what we know today? To give you a glimpse of this distant period, today we're going to explore the Ordovician era. This is a fascinating and mysterious period in the planet's history, which has only recently begun to reveal some of its previously deeply buried secrets.
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💥 Ordovician:
- Brachiopods were extremely abundant during this phase of evolution still largely dominated by invertebrates. Brachiopods are animals with shells whose soft parts are contained between two valves. Although they resemble bivalves like clams, the body parts inside the shell are very different. What's more, their valves have a different symmetry to that of clams. A pedicle emerges from the larger of the two valves, enabling this brachiopod to attach itself to the seabed. Brachiopods are protostomans, one of two existing groups of bilaterians, along with Bryozoans. Bryozoans are mossy animals that live in colonies. They take a variety of forms, including arborescence or lace fan. Although they strangely resemble corals, they are not corals.
Each individual secretes an arborescent calcium carbonate skeleton attached to a hard surface. Each specimen, called a zooid, usually measures less than 1 millimetre in length and lives in its own little lodge. All interconnected, they form colonies containing millions of zooids, which can grow to several meters in size. Within the same colony, each individual plays a distinct role. Some gather food, others help to strengthen the group. Finally, some of these individuals contribute to cleaning. To feed, bryozoans create a water current that brings tiny creatures to their mouths. Most of the time, these are plant-like organisms such as phytoplankton. Bryozoans gradually colonize certain areas of the seabed, eventually building up into extensive reefs.
Trilobites make up a large part of the Ordovician fauna. These crustaceans, which secreted an easily identifiable segmented exoskeleton, reached their peak during the Ordovician. In fact, they are the most famous prehistoric animals after the dinosaurs. Over 18,000 species have been recorded. They ranged in size from 1 to 70 cm in length, and their way of life covered the whole range of Thalassic environments. Some were detritus feeders, grazers or even predators. While a few species mastered swimming, the majority of trilobites moved along the seabed, burrowing into the sediment to escape predators. Trilobites also developed the first advanced visual system. All trilobites had a head, called the cephalon, a thorax and a tail, as well as pairs of biramed legs on the ventral side. As with crustaceans, these legs had two branches, one serving as a gill for respiration, the other for locomotion and feeding. The most common trilobites include Cryptolithus, which measured around 1.5 cm in length, and Acidaspis, nearly 2 cm. But there were also specimens of far more spectacular dimensions. These included the Calymene, between 2 and 5 cm long, and above all, the Isoletus, which could commonly reach up to 38 cm in length. However, the world's largest trilobite species ever discovered is Isoletus rex. Its complete fossil measures no less than 72 cm long and 40 cm wide.
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🎬 Today's program:
- 00:00 - Introduction
- 01:54 - After the Cambrian-Ordovician extinction
- 06:57 - The continents in Ordovician times
- 10:39 - Climate in Ordovician times
- 14:40 - Life spreads in the oceans
- 17:00 - Life on the continents
- 18:51 - First known Lagerstätten
- 22:16 - Fezouata in Morocco
- 24:48 - Taichoute site
- 27:29 - Recent discovery in England
- 30:19 - Incredible creatures of the Ordovician period
- 49:46 - Evolution of species
- 51:51 - Ordovician crisis
- 01:20:15 - What's next?
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15 июн 2024
