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EOS223 Introduction to Palaeontology and Evolution. Trilobites. Massive increase in:. Early Cambrian:. Soft bodied creatures. Creatures with skeletons. Early Cambrian:. (1) Small Shelly Fossils. Latouchella. Hyolithellus. (1) Small Shelly Fossils. Tommotia. Early Cambrian :.

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Presentation Transcript
slide1

EOS223

Introduction to

Palaeontology

and

Evolution

Trilobites

slide2

Massive increase in:

Early Cambrian:

Soft bodied creatures

Creatures with skeletons

slide3

Early Cambrian:

(1)Small Shelly Fossils

slide4

Latouchella

Hyolithellus

(1)Small Shelly Fossils

Tommotia

slide5

Early Cambrian:

(2) Archaeocyatha

(1)Small Shelly Fossils

slide7

Archaeocyatha

Incertae sedis

slide8

Archaeocyatha

Incertae sedis

Lower Cambrian reef community

slide9

Early Cambrian:

(3)Trilobites

(2) Archaeocyatha

(1)Small Shelly Fossils

slide10

CambrianFauna

TRILOBITES I

slide11

Trilobites

  • Among the first arthropods
  • Phylum (Class?) Trilobita
  • Range: L.Cam - U.Perm
  • Hard-shelled with multiple body segments & jointed legs
  • 15,000+ described species

Huntonia sp.

slide12

Trilobites

  • Single most diverse group of extinct organisms
  • Enormous variety of sizes & shapes:

Smallest: just under 1mm

Largest: 30-70 cm

  • Exclusively marine
slide15

Trilobites

Basic Morphology:

CEPHALON

THORAX

PYGIDIUM

Acaste downingiae (Silurian)

slide16

Trilobites

Basic Morphology:

Axial lobe

Left Pleural Lobe

Right Pleural Lobe

Acaste downingiae (Silurian)

slide17

Trilobites

Basic Morphology:

CEPHALON

PYGIDIUM

Acaste downingiae (Silurian)

slide18

Trilobites

Basic Morphology:

Pygidium size relative to cephalon :

Micropygous

Heteropygous

Macropygous

Isopygous

slide20

Trilobite

Dorsal Morphology:

Glabella

Anterior

Anterior border

Glabellar furrows

Eye

Lateral border

Axial furrow

Palpebral lobe

Occipital ring

Posterior border

Acaste downingiae (Silurian)

Posterior

slide21

Trilobite

Eyes:

(1)

Holochroal

  • One of first advanced visual systems
  • Compound eyes with lenses made out of calcite
  • Compound eyes in living arthropods very sensitive to motion - probably similarly as NB for predator detection in trilobites
  • 3 Types seen in Trilobites:

(2)

Schizochroal

(3)

Abathochroal

slide22

Huge variation of size & form among trilobite eyes:

Trilobite

Related to particular ecological lifestyles

Many of the earliest trilobite eyes were crescentic

Phacops (Devonian, Morocco)

Olenellus (Lower Cambrian)

Schizochroal eyes gave species such as Phacops an excellent field of vision

slide23

Huge variation of size & form among trilobite eyes:

Trilobite

Related to particular ecological lifestyles

Free-swimming pelagic trilobite Opipeuter:

Eyes dominate cephalon & provide 360 visual field

slide24

Free-swimming pelagic trilobite Opipeuter:

Eyes dominate cephalon & provide 360 visual field

slide26

Huge variation of size & form among trilobite eyes:

Trilobite

Related to particular ecological lifestyles

Russian Asaphoid Neoasaphus:

Eyes on stalks!

slide27

Huge variation of size & form among trilobite eyes:

Trilobite

Related to particular ecological lifestyles

Cryptolithus:

Specialised bottom feeder with large pitted sensory fringe & eyes reduced or lost.

Conocoryphe(secondarily lost eyes)

Species living on bottom in deeper waters would have little or no need for eyes at all….

slide28

Trilobite

Dorsal Morphology:

Anterior

Pleuron

Axial ring

Axial furrow

Pleural furrow

Acaste downingiae (Silurian)

Posterior

slide29

Trilobite

Dorsal Morphology:

Anterior

Posterior

Articulating facet

  • Trilobite Enrollment:
  • Defensive ball
  • Flexible articulation of segments
  • Lock mechanism
  • Soft parts safe inside
  • Trilobite couldwatch & wait until coast was clear!
slide30

Trilobite

Dorsal Morphology:

Anterior

Posterior

Articulating facet

  • Trilobite Enrollment:
  • Defensive ball
  • Flexible articulation of segments
  • Lock mechanism
  • Soft parts safe inside
  • Trilobite could watch & wait until coast was clear!
slide31

Trilobite

Dorsal Morphology:

Anterior

Pleuron

Axial ring

Axial furrow

Pleural furrow

Acaste downingiae (Silurian)

Pleural rib

Pleural field

Terminal axial piece

Posterior

slide32

Trilobite

Dorsal Morphology:

Anterior

Facial suture

Genal angle

Acaste downingiae (Silurian)

Posterior

slide33

Proparian

Opistho-parian

Gonatoparian

Trilobite

Facial Suture Morphology:

3 types defined by where suture ends, relative to genal angle:

slide34

Proparian

Opistho-parian

Gonatoparian

Trilobite

Facial Suture Morphology:

3 types defined by where suture ends, relative to genal angle:

slide35

Trilobite

Dorsal Morphology:

Anterior

Librigena (Free Cheek)

Facial suture

Genal angle

Fixigena(Fixed Cheek)

Acaste downingiae (Silurian)

Posterior

slide36

Trilobite

Growth:

  • Trilobites grew by ecdysis (moulting)
  • Librigena split away along facial sutures & allow trilobite to exit old exoskelton:
slide37

Trilobite

Growth:

Fossil evidence of the molting sequence

Example of the consequence of molting: the displaced cranidium and librigenae of the Canadian trilobite Pseudogygites latimarginalis in the photographs is explained by the reconstruction of the molting sequence shown under the photographs:

…the facial sutures separate, allowing the molting trilobite (purple) an opening through which it emerges from its old exoskeleton (white).

slide38

Trilobite

Ontogeny:

  • After hatching & development of hard exoskeleton, moulting leaves record of developmental stages…..
  • 3 larval stages are recognised:

Ontogeny of Dimeropyge:

Protaspid period

Meraspidperiod

Holaspidperiod

Adult number of segments attained

Now just  in size

Early stage:larva lacks segments

Middle stage:larva bears fewer segments than in adult form

slide41

Trilobite

Ventral Morphology:

Anterior

Hypostome

Doublure

Axial furrow

Acaste downingiae (Silurian)

Posterior

slide42

Trilobite

Ventral Morphology:

  • Calcified ventral structure
  • Thought to be mouthpart
  • 3 types distinguished:

Hypostome:

slide43

Trilobite

Ventral Morphology:

  • Calcified ventral structure
  • Thought to be mouthpart
  • 3 types distinguished:

Hypostome:

Natant

Conterminant

Impendent

Thought to be related to feeding strategy

slide44

Trilobite

Ventral Morphology:

Anterior

Hypostome

Doublure

Axial furrow

Apodeme

Acaste downingiae (Silurian)

Posterior

slide45

Trilobite

Limb Morphology:

Antennae

Walking leg

Gill

slide46

Trilobite

Limb Morphology:

  • Limbs & antennae usually not preserved
  • Very rare examples though:

An example of the olenid trilobite Triarthrus eatoni (Ordovician; Beecher’s Trilobite Bed) showing preserved antennae, legs & gill filaments.

slide47

Trilobite

Limb Morphology:

  • Limbs & antennae usually not preserved
  • Very rare examples though:

Burgess Shale trilobites Olenoides serratus (Mid Cambrian) showing antennae, limbs & anal cerci

slide48

Trilobite

Limb Morphology:

Antenna

Gill branch

Food passed forwards to mouth

1 pair of Biramus limbs per segment of thorax

Walking leg

Reconstruction of Olenoides serratus

Anal cerci

(Unspecialised limbs)

slide49

Trilobite

Mode of Life:

Trilobites occupied huge set of habitats & paleolatitudes:

Tropical shallows & reefs

Many habitats in between

Polar depths

Diversity of form suggests a complex ecology with many modes of life…..

slide50

Trilobite

Mode of Life:

1

Predator-scavengers

  • The majority of early trilobites
  • Expanded & spiny gnathobases on legs

Olenoides sp.

slide51

Trilobite

Mode of Life:

1

Predator-scavengers

  • The majority of early trilobites
  • Expanded & spiny gnathobases on legs

Olenoides sp.

Olenoides serratus: terror of the Burgess mudflats

Primary food processing conducted externally

slide52

Trilobite

Mode of Life:

1

Predator-scavengers

  • The majority of early trilobites
  • Expanded & spiny gnathobases on legs
  • Conterminant hypostomes (firmly attached)

Conterminant

Huge variety of CH seen suggests prey specialisation…..

slide53

Trilobite

Mode of Life:

Sizable digestive chamber for processing large chunks of prey

1

Predator-scavengers

  • The majority of early trilobites
  • Expanded & spiny gnathobases on legs
  • Conterminant hypostomes (firmly attached)
  • Inflated glabella

Reedops maurulus

slide54

Trilobite

Mode of Life:

1

Predator-scavengers

  • The majority of early trilobites
  • Expanded & spiny gnathobases on legs
  • Conterminant hypostomes (firmly attached to frontal doublure)
  • Inflated glabella
  • Larger species very likely predatory

Large trilobites like this foot-long paradoxidid make good candidates for a predatory lifestyle.

slide55

Trilobite

Mode of Life:

2

Deposit Feeders

  • (Large proportion of trilobites)
  • Close to base of food chain
  • Natant hypostomes

Natant

Consistency of shape:generalisedhabit with no need for specialised mouthparts.

slide56

Trilobite

Mode of Life:

2

Deposit Feeders

  • (Large proportion of trilobites)
  • Close to base of food chain
  • Natant hypostomes

grazing on beds of algae

scavenging for bits of benthic detritus

slide57

Trilobite

Mode of Life:

3

Filter Feeders

Long genal spines

Large cephalic shield to house filtering area

Thorax & pygidium elevated above substrate

In a few species:hypostome also elevated

Harpes (Devonian)

slide58

Trilobite

Mode of Life:

3

Filter Feeders

Suggestedfilter feeding position of Cryptolithus:

Cryptolithus tesselatus

slide59

Spinosity

Kettneraspis

Comura

Trilobite

Mode of Life:

Hoplolichas plautini

Other features to note in benthic forms:

slide60

Reduction or Loss of eyes

Trimerus

Spinosity

Conocoryphe

Living in deep, poorly-lit or aphotic habitats.

Kettneraspis

Comura

Bumastus

Cyclopyge

Trilobite

Mode of Life:

Other features to note in benthic forms:

Effacement

Swimming

Burrowing

slide61

Trilobite

Mode of Life:

4

Pelagic Planktivores

  • Swim freely in water column
  • Globally distributed

Smooth, streamlined body

Free-swimming pelagic trilobite Opipeuter:

Wide axial lobe

Large eyes

slide62

Trilobite

Mode of Life:

4

Pelagic Planktivores

  • Swim freely in water column
  • Globally distributed

Carolinites genacinaca (Proetida : Telephinidae), depicted swimming in a venter-up orientation.

slide63

Often found in huge numbers

Trilobite

Mode of Life:

?

5

Planktonic

  • Larvae

Agnostids:

  • Camb-Ord
  • Simple form & small size
  • Small-eyed or eyeless
  • Global distribution

Possibly benthic swimmer

Not visual hunters

Acadagnostus

slide64

Trilobite

Mode of Life:

6

Symbionts(?)

  • Oleninids:
  • Occupied deep benthic nearly anoxic substrates
  • High in sulphur compounds
  • Modern analogous crustaceans often havesymbioticsulphur-eating bacteria(housed in gill structures)

Huge surface areas

Olenoides serratus

(Mid Cambrian)

slide65

Trilobite

Mode of Life:

slide66

Trilobite

Evolution:

Cambrian:

High diversity

NB Biostratigraphically

Many blind forms

Many lack defence against predators

End Camb Extinction: Linked to rise of predators

slide67

Trilobite

Evolution:

Ordovician:

Diversification into wide range of niches

Greatest variety of body forms

Lots of new defensive strategies

End Ord Mass Extinction: Hit badly

slide68

Trilobite

Evolution:

Sil & Dev:

Very limited recovery

Variety & diversity subdued

End Dev Mass Extinctions

slide69

Trilobite

End Permian Mass Extinction

Evolution:

Carb & Perm:

Only 1 Order remains...

Extinct by Latest Permian