Haramiyids

An intrusion is always younger than the rock layers around and beneath it. A fault is always younger than the rock it cuts through. The surface where new rock layers meet a much older rock surface beneath them is called an unconformity. An unconformity is a gap in the geologic record.

The principle of cross-cutting relationships states that a fault or intrusion is younger than the rocks that it cuts through. The fault cuts through all three sedimentary rock layers (A, B, and C) and also the intrusion (D). So the fault must be the youngest feature.

Answer: Recent prosauropods from Madagascar are the oldest, about 230 million years old. Until recently, the oldest dinosaur found was Eoraptor (from Argentina) – it is about 228 million years old.

Megalosaurus

Trilobites existed for nearly 270 million years. Actually, not only did they exist… for the majority of their lengthy stay on Planet Earth, they thrived.

They died out at the end of the Permian, 251 million years ago, killed by the end Permian mass extinction event that removed over 90% of all species on Earth. They were very diverse for much of the Palaeozoic, and today trilobite fossils are found all over the world.

Trilobites have been extinct since before the age of Dinosaurs (about 251 million years ago), but some living creatures bear such close superficial resemblance to trilobites that they cause great excitement when encountered. Alas, no living trilobite has ever truly been documented.

On the contrary, the trilobites survived for more than 250 million years (longer than the dinosaurs), and dominated seafloor ecosystems for much of this time. Pick up a piece of rock from the Cambrian period, over 500 million years ago, and most of the fossils you ll see are trilobites.

Trilobites had compound eyes, akin to those of today’s insects and crustaceans. We know that because trilobites’ lenses were made of calcite, so they often fossilized along with the rest of the trilobite’s exoskeleton. The findings indicate that trilobites had apposition eyes.

The microbes, spanning 10 major and numerous minor groups of bacteria, may be the planet’s oldest-known organisms. Up to 99 percent of the microbes, dating back to the age of dinosaurs, that were found encased in the sediment survived despite having essentially no nutrients for all that time.

The earliest trilobites known from the fossil record are redlichiids and ptychopariid bigotinids dated to some 540 to 520 million years ago.

When danger struck, some trilobites could ball themselves up like underwater pill bugs, with their rear end flexed under their head.