WHAT IS IT
You’ve probably seen sand dollars used as beach décor, but what you’re holding is a little more extraordinary. This Holeclypus fossil would have buried itself in the low-tide mud of the Jurassic period 145–200 million years ago, sharing the same waters as the plesiosaur and ichthyosaur. Notice the fivefold symmetrical “flower” shape on its skeleton—the “petals” being the imprint of tube feet the creature uses for respiration.
INTERESTING PROPERTIES
• When alive, this sand dollar would be covered in colorful, velvety spines that it uses for mobility.
• Sand dollars are closely related to sea urchins and this fossil would have lived around the time when the two genera diverged.
USES
• Add this fossil from Madagascar to your collection and use it to upstage all your friends who return from their boring beach vacations. They have a sunburn. You have a fossil.
This table contains the geological time periods of the past 2.5 billion years on Earth to aid in understanding age immense age of these fossils.
(Ma = Mega-annum = 1,000,000 years)| EON | ERA | PERIOD | EXTENT (Ma) | DURATION (Ma) |
|---|---|---|---|---|
| Phanerozoic | Cenozoic | Quaternary | 2.588–Present | 2.588+ |
| Neogene | 23.03–2.588 | 20.4 | ||
| Paleogene | 66.0–23.03 | 42.9 | ||
| Mesozoic | Cretaceous | 145.5–66.0 | 79.5 | |
| Jurassic | 201.3–145.0 | 56.3 | ||
| Triassic | 252.17–201.3 | 50.9 | ||
| Paleozoic | Permian | 298.9–252.17 | 46.7 | |
| Carboniferous | 358.9–298.9 | 60 | ||
| Devonian | 419.2–358.9 | 60.3 | ||
| Silurian | 443.4–419.2 | 24.2 | ||
| Ordovician | 485.4–443.4 | 42 | ||
| Cambrian | 541.0–485.4 | 55.6 | ||
| Proterozoic | Neoproterozoic | Ediacaran | 635.0–541.0 | 94 |
| Cryogenian | 850–635 | 215 | ||
| Tonian | 1,000–850 | 150 | ||
| Mesoproterozoic | Stenian | 1,200–1,000 | 200 | |
| Ectasian | 1,400–1,200 | 200 | ||
| Calymmian | 1,600–1,400 | 200 | ||
| Paleoproterozoic | Statherian | 1,800–1,600 | 200 | |
| Orosirian | 2,050–1,800 | 250 | ||
| Rhyacian | 2,300–2,050 | 250 | ||
| Siderian | 2,500–2,300 | 200 | ||
