Evolutionary Innovations of the Paleozoic
Why a Fossil Record?
- Improves with biomineralization
- First occurrence in latest Precambrian (Yudomian stage)
and earliest Cambrian (Tommotian stage)
- Skeletal elements may have been more of a
support-function in early organisms rather than protection
from predation.
- Early Invertebrates
- Mineralized organisms include gastropods (snails),
sponges (spicules as skeletal wall elements), and variety of
organisms with unknown systematic affinities.
- Abundant trilobites and brachiopods & a wide diversity of
soft-bodied animals.
- Burgess Shale - A Fossil Lagerstätten
- Shelf-slope mass movement deposit
- Animals buried in an underwater avalanche of fine mud
that preserved amazingly fine details of the structure of
their soft parts.
- Burgess Shale Diversity
- Organisms represent an early snapshot of the complexity
of evolving life systems.
- The Burgess Shale fossils as a group have already
developed into a variety of sizes and shapes from the
much simpler, pre-Cambrian life forms.
- Amiskwia sagittiformis
- Three body segments: a head with two prominent
tentacles, unsegmented trunk with stubby side fins, and a
flattened tail; Up to 1 inch.
- Fins and tail suggest this was an active swimmer
- Amiskwia has no obvious relationship (affinity) to any
other living or extinct group.
- Anomalocaris canadensis
- Largest Burgess Shale animal up 6 ' length!
- Front limbs captured and held prey; Mouth on the
undersurface with sharp teeth
- Large eyes and a body half flanked with a series of
swimming lobes
- An active predator.
- Asheyaia pendunculata
- Unusual assembly of spines and grasping arms at the head
end. Mouth lies in the center of that ring of six finger-like
projections.
- Limbs are not jointed, but tapered, ten pairs of lobe-like
appendages
- 2+ inches in length
- Canadapsis perfecta
- Early ancestor of the crustaceans
- A lobster-like creature with a segmented "tail" and a
number of walking legs with associated gill flaps tucked
under.
- Details in the head appendages conclusively relate these
animals to crustaceans.
- Canadia spinosa
- Annelids, about 1 to 2 inches in length
- Head with pair of slender tentacles
- Body covered with setae (short bristles).
- Sediment has never been found in the gut, may have been
a carnivore or scavenger.
- Choia carteri - Sponge
- Small, thin disk with radiating spines, resembles a spiny
sand dollar
- Habit: laid on the substrate and filtered food from water.
- Lying with its convex side up, it was less likely to be
overturned by wave action.
- Size: about 1" diameter.
- Hallucenogenia sparsa
- Invertebrate Life Strategies
- Diversification in body plan and behavior
- Epifaunal
- Infaunal habits
- Boreres and burrowers
- Attached and mobile forms
- Filter-feeders, sediment-feeders, and grazers.
- Possible Earliest Chordate?
- Pikaia exhibits:
- Dorsal, longitudinal notochord
- Musculature arranged in a series of v- shaped
segments reminiscent of fish.
- Chordates have a notochord and dorsal nerve chord.
- Ordovician Mass Extinction
- Two Phases of Extinction
- Planktonic graptolites & trilobites & brachs
- More trilobite groups
- Conodonts, corals & bryozoans reduced
- Invertebrate biogeographies compressed towards equator
- Lowered sea-level resulted in loss of shallow marine
environments
- Reefs Through the Paleozoic
- Archaeocyathids in Cambrian
- Ordovician modernization
- Silurian and Devonian reefs inhabited by organisms that
survived the catastrophic Mass Extinction in latest
Ordovician oceans.
- Vertebrates Diversify
- Vertebrates are chordates having:
- Dorsal, central nerve cord; gill slits; blood
circulation away from the heart in a main ventral
vessel and return to the heart in a dorsal vessel
- Earliest records are external plates of "fish" found in
Upper Cambrian (Wyoming).
- Morphology and structure indicate these are plates of
armoured jawless fish (Agnatha).
- What are Phishies
- Agnatha (jawless fish) - C to Rec
- Ostracoderms - Ord to Dev (EXTINCT)
- Acanthodii - Late Sil to Perm (EXTINCT)
- Placodermi - Late Sil to Perm (EXTINCT)
- Chondrichthyes - Dev to Rec
- Osteichthyes (bony fish) -Dev to Rec
- Early Ostracoderms
- Armored or unarmored
- Gills protected by bony plates.
- Tail morphologies provide evidence for variety of life
habits
- Lateral small eyes, dorsal nostrils ending in blind sac
- Most lacked paired appendages.
- Heterocercal or Reverse Heterocercal tail
- Acanthodians
- Oldest jawed fish in Late Silurian terrestrial deposits
- Fusiform body with head covered by mosaic of bony
plates
- Several pairs of fins in addition to pelvic & pectoral fins.
- Devonian radiation & diversification.
- Placoderms
- Non-paired and paired appendages (fins) present
- Flattened ray-types and fusiform types
- Heavily armoured, freshwater jawed fish
- Late Devonian found in marine deposits
- Captain D's Fish Appear
- Modern fish (cartilagenous [sharks, rays, skates] & bony)
appear in the late Silurian
- Undergo radiation in the Devonian
- Higher vertebrates (amphibians) evolved from bony fish.
- Osteichthyes - The Bony Fish
- Actinopterygians (ray-finned fish) dominate modern world
- Lack muscular base to their paired fins
- Lack nasal passages that open into the throat
- Sarcopterygians (lobe-finned fish)
- Possess sturdy, fleshy lobe-fins
- Pair of openings in roof of mouth to external
nostrils.
- Sarcopterygian Diversity
- Order Dipnoi ("Lung-fish"): Dev to Rec
- Modern forms capable of breathing air by means of
lungs during dry seasons.
- Crossopterygii (amphibian ancestors by homology)
- Paired short muscular fins
- Articulation of bones in same arrangement in
subsequent tetrapods.
- Crossopterygians
- Coelocanthii (modern day Latimeria)
- Rhipidistia - freshwater predators with internal nostrils.
(EXTINCT)
- Late Devonian Mass Extinction
- Loss of extensive Devonian reef communities
- Reduction in tabulate corals and stromatoporoids
- Few rugose corals survive
- Occurs over 20 MY interval
- Ecological crisis brought about by change in terrestrial
ecosystem
- Mid-Paleozoic Major Events
- Silurian recovery biota
- Diversification of Fish
- First Ammonoids
- First Insects
- First Amphibians
- Terrestrial vegetation
- Advent of Forests
- The End of an Era - The Mother of All Mass Extinctions
- >90% biodiversity lost
- Terrestrial ecosystem disruption with onset of Greenhouse
vegetation
- Tropical marine invertebrates suffer