Viu algo para melhorar? Proponha uma alteração.
Sponges have no muscles, nerves or organs. They sit on the sea floor pumping water through their bodies to filter out food. Yet in the Paleozoic seas, these simple animals were among the dominant reef builders — and the reefs they built can be walked through today at Carlsbad Caverns and Guadalupe Mountains national parks.
What a sponge is
Sponges form the phylum Porifera, "pore bearers." They come in many shapes — cups, flasks, spheres, cauliflower forms, folded plates, crusts — and today live almost entirely in the sea, as they are assumed to have in the past.
Only sponges with hard parts fossilize. Most of those have spicules: slender, pointed elements of silica that form a supporting skeleton. "Glass sponges" have such well-developed silica frameworks that 90 percent of their dry weight is glass. A few have heavily calcified skeletons that resemble corals or form layers. Sponges have a fossil record reaching back to the Precambrian, and in places were abundant enough to form widespread rock formations. Several important groups are now extinct.
Sponges in national parks
Sponge fossils are known in place from at least 48 national park sites, most in Paleozoic rocks and mostly forms with strongly mineralized skeletons.
| Era | Sponges | Parks |
|---|---|---|
| Cambrian | archaeocyathids, the first reef builders, which flourished briefly before going extinct | Yukon-Charley Rivers National Preserve (Alaska), Mojave National Preserve (California) |
| middle Paleozoic | layered stromatoporoids, building reefs with corals | Delaware Water Gap National Recreation Area (New Jersey and Pennsylvania) |
| early Permian | sponges and algae building massive reefs | Carlsbad Caverns (New Mexico), Guadalupe Mountains (Texas) |
| Permian | sponges in the Kaibab Formation | the rim of Grand Canyon National Park and Grand Canyon-Parashant National Monument (Arizona) |
Sponge fossils in Carlsbad Caverns National Park; the scale bar has 1-cm squares. Credit: NPS photo by Rod Horrocks.
In Guadalupe Mountains, the sponge Lemonea was one of the most common builders of the Permian Reef.
The Permian sponge Actinocoelia maeandrina in the Kaibab Formation, Grand Canyon-Parashant National Monument: the outside of a concretion, and a broken surface showing the sponge. Scale bars 3 cm. Credit: NPS, 2020 field inventory.
Sponge fossils record how life in the oceans changed over time: sponges played a very different ecological role in Paleozoic seas than in modern ones.
Sources
Based on "Fossil Sponges," from the National Park Service series Invertebrate Fossils in National Parks, a work of the United States government in the public domain.
Nestas publicaçõesInvertebrate Fossils in National Parks
Licença: CC0 1.0 (domínio público) · Adaptado de www.nps.gov
1
0
0
0
Comentários
