1. ARTHROPODS

2. Arthropods Most diverse phylum - > 85% of all species
All habitats – esp. extremes
Segmented body w jointed appendages
Chitin (polysaccharide) exoskeleton
good protection
requires molting
prohibits large size

3. Phylum Arthropoda
Subphylum Trilobitomorpha – Trilobites (Camb-Perm)
Subphylum Chelicerata – Arachnids, Horseshoe crabs, Eurypterids (Ord-R)
Subphylum Crustacea – Lobsters, crabs, shrimp, barnacles, ostracodes (Camb–R)
Subphylum Tracheata (Unirama) – Insects (Dev–R)

4. Trilobites
Cranidium = cephalon missing free cheeks

5. Sutures
Opisthoparian
Proparian
Gonatoparian
underside

6. Biramous legs

7. A. compound (holochroal) eyes B. schizochroal eyes
Trilobite eyes
A. compound (holochroal) eyes
B. schizochroal eyes
Huygens lens
corrects spherical aberration

8. Subphylum Trilobitomorpha Class Trilobita Order Agnostida (Camb-O)
Phylum Arthropoda
Subphylum Trilobitomorpha
Class Trilobita
Order Agnostida (Camb-O)
Order Redlichiida (Camb)
Order Corynexochida (Camb)
Order Ptychopariida (Camb-O)
Order Asaphida (Camb-O)
Order Illaenida (O-D)
Order Trinucleida (O-S)
Order Harpida (Camb-D)
Order Phacopida (O-D)
Order Lichida (O-D)
Order Odontopleurida (O-D)
Order Proetida (Camb-P)

9. Agnostid – Peronopsis
small, isopygous,
2-3 thoracic segs, most blind
Redlichiida – Olenellus & Paradoxides
v. primitive,
pygidium may not be fused,
long genal spines,
telson, O. sutures

10. Corynexochid – Basidechenella
O. sutures, 7-8 thorax,
Ptychoparid – Elrathia
diverse, glabella tapers forward,
straight g. furrows,
many thorax.,
small pygidium

11. Asaphid – Isotelus
snowplow shape,
6-9 thorax
Illaenid – Illaenus
smooth ceph & pyg,
isopygous

12. Trinulceid – Cryptolithus
small pyg and thorax,
broad ornamented ceph brim,
long genal spines
(burrowing? Pelagic?)
Harpid – Harpes
broad smooth ceph,
eyes on stems,
many thoracic segs

13. Phacopids – Flexicalymene & Phacops
P sutures, prominent eyes, enroll

14. Lichid – Amphilichas
glabella to front of ceph,
large pyg w 3 pairs spiny pleurae
Odontopleurid – Dicranurus
spines everywhere

15. Proetid – Anisopyge & Kaskia
O. suture,
large holochroal eyes,
conservative

16. Trilobite ontogeny
proaspid – A, B
meraspid – C,D
holaspid - E

17. Marine – swimmers, crawlers, burrowers, probably ate detritus
Trilobite Ecology
Marine – swimmers, crawlers, burrowers, probably ate detritus
Trilobite Evolution
Responded to most extinctions, conservative forms, burrowers survive best
Late Ordovician extinctions wiped out many groups.
Frasnian-Fammenian almost ended them, rare afterwards
Good examples of iterative evolution

18. Phylum Arthropoda
Subphylum Chelicerata
Class Merostomata
Subclass Eurypterida
“Sea Scorpions” – largest known early Paleozoic predators (up to 2.5m)
Subclass Xiphosura
Horseshoe crabs

19. Varied forms
compound eyes, telson
Name refers to paddle legs
swim and walk
marine to brackish (fresh?)

20. Xiphosurans – “living fossil” Limulus
Larvae called “trilobite larvae”

21. Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Order Decapoda – crabs, lobsters, crayfish, shrimp
Class Maxillopoda
Subclass Cirripeda – barnacles
Subclass Ostracoda - ostracodes

22. Malacostraca - Decapods

23. Maxillopoda - Barnacles

24. Ostracodes – most small (Leperditids get up to several cm’s)
Most benthic, v small planktonic
Good environmental info