Week 12 Flashcards
Stem Reptiles
The most primitive reptile group … small, lizard-like forms that evolved from amphibians.
How Did Posture Influence Dinosaur Success?
Early reptiles had a sprawling posture with limited mobility & breathing.
Thecodonts evolved a semi-upright stance with improved movement.
Dinosaurs developed a full upright posture… legs directly beneath body = efficient mobility & breathing → key to their evolutionary success.
Saurichian (“lizard-hipped”) dinosaurs
had a backward facing ischium
And foreward-facing pubis. Both meat-eating and plant-eating forms are
known
Ornithischian (“bird-hipped”) dinosaurs
had a backward facing ischium
and pubis. All ornithischians were plant eaters (the backward rotation of
the pubis may have allowed for a bigger stomach).
Oldest known dinosaurs
Earliest: meat-eating saurischians (theropods)
Later: plant-eating saurischians (sauropods) by Late Triassic
Ornithischians (plant-eaters) appeared by Early Jurassic
Common dinosaur myths
1) Dinosaurs were slow, tail-dragging brutes
2) Dinosaurs had scaly skin like lizards
3) Dinosaurs were dumb
4) Pterosaurs were flying dinosaurs
5) The Loch Ness Monster is a dinosaur
6) Dinosaurs were cold-blooded like lizards
7) Dinosaurs were dull-coloured
8) Dinosaurs were unsuccessful (that’s why they went extinct)
Mother of Pearl
common term for the shiny, iridescent material forming the inner surface of seashells.
Nacre
The material comprising mother of pearl, largely composed of aragonite crystals
Mantle
a fleshy membrane that surrounds the visceral mass
Function of the mantle
The mantle secretes calcium carbonate prisms to grow the shell. It also secretes aragonite nacre (mother of pearl) over the prismatic layer.
When not secreting shell material, the mantle separates from the shell
characteristics of the internal layer of a mollusc shell
Prismatic layer: Blocky crystals (calcite or aragonite), opaque or weakly translucent.
Nacreous layer: Plate-like aragonite, shiny, colourful, and translucent.
Smooth nacre surface lets mantle slide without damage.
What determines the lustre of nacre (mother of pearl)?
1) Surface reflection – Aragonite tablets act like mirrors, enhancing brilliance.
2) Internal reflection – Tablets transmit light and reflect it internally, creating a warm glow.
Orient
The iridescent play of colours in nacre
What causes the “orient” (iridescence) in nacre?
Surface grooves/ridges split light into colours (diffraction).
At certain angles, colours reinforce each other (constructive interference), creating brilliant iridescence.
How do refraction and reflection contribute to nacre’s orient (rainbow-like colour)?
Tiny aragonite crystals act like prisms, refracting light into rainbow colours.
Light bouncing off multiple crystal layers creates constructive interference, enhancing the colourful effect.
What is ammolite and how does it form?
Ammolite is fossilized ammonite nacre, used as a gemstone.
It’s rare because aragonite usually dissolves or alters to calcite.
Ammonites had chambered shells for buoyancy.
What makes the color play (orient) in ammolite special, and how is it used in jewelry?
Ammolite’s intense color play is likely due to slight deformation of aragonite crystals. It’s soft and fragile, so jewelry often uses a thin layer of ammolite backed for durability.
Difference of pearl VS edible oysters
Pearl oysters produce nacreous pearls (precious), while edible oysters can also produce pearls, but these are porcelaneous, not nacreous, as they don’t secrete nacre.
How a pearl forms
When a foreign body irritates the mantle, and the mollusc surrounds it with layers of nacre. The pearl’s colour and lustre match the nacreous layer of the shell. Sand rarely forms the nucleus, as oysters expel most sediment.
Blister pearls
form when an irritant, like a parasite, gets trapped between the shell and mantle. The mollusc covers it with nacre, creating a blister-like pearl attached to the shell.
Free pearls
Form when an irritant is completely surrounded by nacre-secreting mantle cells, held away from the shell. In the wild, only 1 in 10,000 oysters produces a pearl
Properties of pearls
lustre, colour and orient
Fossil pearls
can retain their nacreous lustre due to exceptional preservation, mainly the lack of dissolution.
