Читать книгу Oceans For Dummies - Joseph Kraynak - Страница 53

The Silurian period (from 443.8 to 419.4 million years ago) was a time of stable climate (well, relative to earlier periods), but warmer, causing sea levels to rise again. So fun. During this period:

 Early vascular plants appear, and fungi move onto land. This is also possibly when spiders and centipedes show up.

 Fish split into bony fish and cartilaginous fish. The cartilaginous fish eventually become sharks and rays.

 The bony fish split into two groups — lobe-finned and ray-finned. The ray-finned fish give rise to modern fish, while the lobe-finned fish evolve into tetrapods (generally four-limbed creatures), which later evolve into amphibians, reptiles, mammals, and birds.

 The first evidence appears showing coral reefs expanding and developing.

 Brachiopods (like oysters) are very common, but other organisms continue to thrive, including trilobites, echinoderms, cephalopods, and gastropods.

 Ostracoderms (jawless fish) diversify, and the first freshwater species evolves.

 Sea scorpions called eurypterids (sort of like horseshoe crabs) evolve, and holy moly are they ever terrifying! (See Figure 3-3.)

 Fish get jaws, although it will be about 430 million more years before Jaws, the book and movie, become popular entertainment.

Photo by Obsidian Soul with background by Dimitris Siskopoulos. Licensed under the CC BY 4.0.

FIGURE 3-3: Artist rendition of a sea scorpion (eurypterid).

The Silurian period ended in a series of smaller extinction events, likely caused by a drop in sea-level, which the bottom-dwellers couldn’t handle; mostly cephalopods went extinct.