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Flashcards in Fossils Practical Deck (15):
1

Symmetry?

o Bilaterians – one plane of symmetry
o Radiata (radial) – have a central axis about which a number of similar units are repeated
Orientation
o Anterior: head
o Posterior: feet (food towards this area)
o Dorsal: back or top fin
o Ventral: front or bottom fin

2

Sponges?

o A collar of microvilli around the flagellum captures food – filter feeding
o Likely the last common ancestor of animals was a sponge
o No differentiated tissue
• Sponge fossil
o Cross-section
• Top is where sponge emerges from the end of the fossil
• Water travels from bottom to top
o External
• Kind of like a fruit off a tree
• One end like the start of a stem and another is a confining cone with symmetrical markings
• Ostia (dots) around the whole exterior
• Grown by growing more cells between cells = expansion

3

Corals overview?

• The sister taxon to Bilaterian animals
• Differentiated tissue
• Reproduce sexually – all corals in a colony are clones
• Coral polyps are essentially upside-down jellyfish; their tentacles are used to pluck suspended organic matter from the water column

4

Rugose Corals?

• Bi-lateral symmetry
• Septa are the lines which are added as it grows – converge into the calyx to give a firmer grip for the animal – out of calyx comes polyps
• Vertical cross section
o Rectangular fossil
o Tabulae marks towards the bottom of the fossil – show where it has lived before
o Dissepiments that close upward at the top (small, upwardly closing convex plates)
• External
o Shell like-fossil: one end encloses to a point (calyx), one open as a circle and is cone shaped
o Ridges on the outside
o Septa in the circle
• Whole colonial rugose coral
o Zooid circles cover the surface
o Septa visible in the centre of the zooids
• Growth
o Grows upward towards the calyx, only lives in the last few sections of the calyx, tabulae number grows

5

Tabulate Corals


• Cambrian to Permian
• Tabulate corals form extremely interconnected colonies with small polyps; no solitary tabulates are known. Their colonies can resemble domes, often with shared coenenchyme between corallites, or chains of jewellery. Septa are typically reduced or absent, and corallite walls may be perforate or even absent; tabulae are usually prominent. New corallites were added either at the edge of the colony, or in between existing corallites, depending on the species and environmental conditions.
Structure
o 3D tabular structure, individual tubes can be seen on the cross-section with circular openings and small septa on the top
o Tabulae cut the tubes into a series of chambers – shows where the coral used to live
o Grew by budding and branching and then by just adding more corals

6

Scleractinian corals


• Their colonies can resemble domes, often with shared coenenchyme between corallites, or chains of jewellery. Septa are typically reduced or absent, and corallite walls may be perforate or even absent; tabulae are usually prominent. New corallites were added either at the edge of the colony, or in between existing corallites, depending on the species and environmental conditions.
Structure:
• Kind of like a flower
• Coral with circular parts where septa converge on the centre
• Can identify it as it is lighter than other corals (made of aragonite)

7

Bryozoans:


• Feeds using a tentacular organ – lophophore
• Small mounds which act as chimneys, shooting water away from the colonies
• Genetically identical
• Connection between organisms by tissue allows sharing of nutrients
• New zooids added at the frontiers
Structure:
• Zooid extends from muscular collar, where it filter feeds
• Mouth and anus here
• Has both ovary and testis
• Connection tissue at bottom – like a vase
• See the circular imprint on fossils
Fossil
• See little circular imprints – like small volcanos
• Can also be smaller – like the fossil has little eggs
• Connected by membranes

8

Dickinsonia


• One of most abundant edicarian fossils – hard to extract – need to make moulds
• Depositional setting = coarse grained = oxygen and air were present – allowed decay so only impression present

Fossil
• Impression:
o Circular
o Line from bottom to top which splits at top into two lines
o Lines (segements) converge off centre line to the sides
o Looks like imprint of millipede or shell
• Growth
o Grows more segments – babies had fewer segments

9

Bivalve:


o Dorsal is the cone part of shell
o Posterior where the food goes to
o Two symmetrical valves
Structure:
o Anterior
o Ligiment tissue (catch)
o Muscle scar below this, small semi-conical shape = only closed (always open)
o Syphen, longer base where it lived – outside of semi-conical areas
Lines are pallial lies + palatial sinus
o Don’t know how it fed as there is no organic matter and therefore no digestive system
o Posterior
o Hinge plate
o Growth lines – typical shell lines
Rely on elastic ligament to reopen the shells once closed – sometimes-on outside of shell –sometimes like a elastic band, sometimes like an elastic ball
Allows it to conserve energy as it needs to be open more than its closed to feed but can still protect against predation

10

Brachiopods:


Structure:
o Symmetrical from dorsal to ventral margin but not symmetrical shells
o Shell which has steeper sides and is taller
o Does not have a ligiment, contract their diductor muscles to open the shell
o Bi-valve has more energetic efficiency when opening to feed but is more susceptible to predation than brachiopod and brachiopod has more efficiency when closing as it is not fighting against elastic

11

Trilobites:


o Extinct group of arthropods
o Modern day representatives: lobsters, spiders and insects
o Mineralised skeleton
Structure:
o Have three body regions: from front to back the head (cephalon), body (thorax) and tail (pygidium). These regions comprise a number of segments, each of which bore a pair of appendages: either legs (each with a gill branch) or antennae
o Face:
o Compound eyes
o Surrounded by facial sutures
o Nose like glabella
o Grid shows that the lateral border has elongated – growth vector

12

Graptolites

Fossils:
o Planktic – floaters
o Ordovician
o Leg fossil – pendent
o Leaf shape
o Theca inside – like teeth that dip toward the end

o Benthic (bottom dwelling)
o Originated in the mid-Cambrian – disappeared in the Carboniferous
o Lines of dissepiments
o Where they taper off are the Rhabdosomes
o Hold fast where they converge - anchors

13

Nautiloids:


o Shell
o Split into chambers – last chamber is where the animal lives – mostly gas (air) in the previous areas
o Siphuncle from centre
o Difference from ammonoids: concave septa and a central siphuncle

14

Ammonoids:


o Coiled exoskeletons of late Devonian-Creatceous cephalopods
o Siphuncle on the outside
o Suture lines and growth lines
o Convex septa

Goniatites have smooth, simple suture lines;
o ceratites have simple saddles but crenelated lobes;
o ammonites have super- frilly suture lines with a fractal appearance
More complex = stronger = more pressure = living deeper (does take more energy however)

15

Echinoids?

Regular Echinoid:
o Round knobbly one
o Radial symmetry
o Half-cylindrical (cake like)
o Side on – holes/dots where spines would have come out
o Anterior is the bottom of the cake
o Top down – Abulacacra – stripes from the central Periproct that go down the sides (star fish looking) – general plate on top
o Posterior is the top of the cake
o Would have a feeding apparatus ‘Aristotle’s lantern’ – rarely mineralises
Irregular Echinoids:
o Heart shaped ones
o Bilateral symmetry
o Aboral surface – side with central circle connecting the ambulacra, mouth at the bottom where, between two ambulacra
o Oral surface, Anus at top of heart

Burrowers vs non burrowers:
o If burrowers = streamlined
o Position of mouth and anus differs
o Smaller spines of burrowers