Against your impression, first true mammals had appeared in very early period of the evolutionary history of Vertebrate, the Triassic (about 200 million years ago).
"Mammalian evolution is a tale told by teeth mating to produce slightly altered descendant teeth.", a famous paleontologist S. J. Gould said, as a paleontological joke. It means: "The majority of fossil mammals are known only by their teeth."
（ancestral horse, lower jawbone）
(ancestral horse, lower jawbone)
Shark teeth are constantly replaced throughout their lifetime, we human cannot do that.
One shark sometimes spends over 30,000 teeth until the end of life, so fossilized shark teeth are easily found out.
Worms in amber
Fossilized tree resin is called Amber, a kind of jewel. Ancient bugs and worms sometimes trapped in resin, turned into fossils together.
Their figures are mostly still alive. Please see the 30-million-year-ago-worms.
They are a kind of marine animal, close relative of octopuses and squids. But unfortunately, they completely extincted 65 million years ago, so nowadays we can see them as fossils in the rocks.
They had Nautilus-like spiral shells that separated by some walls into chambers. Each chamber maybe contained some gases, so reserchers guess the animals were able to move up-and-down in the water.
partial fossil Baculites sp.
partial fossil Lamberticeras lamberti
One group of extincted echinoderms.
Like other echinoderms (starfishes, sea urchins etc.) , their main bodies ( = theca) were protected by a set of interlocking plates of calcium carbonate. The theca had a
stalk to attach the sea floor.
For more information, please see our Scientific Column page
, almost text are Japanese but you can see some illustrations and references.
Also, please visit our other page: CT-scanned Echinodermata 3D Library
Star sands are one of the famous souvenir of southern Japanese islands. Against the name, they are not real sands but animal's shell, a species of benthic foraminifera, Baculogypsina sphaerulata
Most foraminiferas have microscopic scale, but fortunately, Star Sands are large enough to see with the naked eye. Although, enlarged movies are also beautiful.
Baculogypsina sphaerulata 1
Baculogypsina sphaerulata 2
Benthic foraminifera, a large group of unicellular organisms living on the bottom of water. They have calcium carbonate shells like molluscs.
Their fossils are used as an index of the past environment. Microfossils.
Also belonging to foraminifera group, floating in the water.
Their fossils are very common and found in large quantities, therefore used as a marker of rock's age, and as an index of past environmental changes. Microfossils.
A group of planktonic unicellular organisms, distinguished by their siliceous (glass) skeletons.
Their fossils are used as a marker of rock's age, and as an index of past environmental changes. Microfossils.
Very small multicelular organisms, mostly within 2-3 mm length, but they are relatives of shrimps and crabs.
They have two shells that made of calcium carbonate. Microfossils.