Download geologic history

Fossil History
EEB 286
Silurian
- bryophyte and lichen fauna well established on land
- likely tiny herbivores, detritivores and predators
- late Silurian: putative excreta from millipedes
Devonian:
Middle Devonian:
Rhynie Chert from Scotland
- ca 395-400 mybp: Collembola
- other Devonian arthropods: spiders, mites, scorpions, and pseudoscorpions (Roberta),
millipedes, & centipedes, but only one true insect:
- ca. 390 mybp: Archaeognatha
- assoc. with zysterophylls and lycopsids
Carboniferous:
Lower Carboniferous (Mississippian):
- myriopods predominate over insects in desposits
- few insect fossils (little freshwater for preservation)
Upper Carboniferous (Pennsylvanian):
* insects numerically abundant, especially in coal-forming swamps
-upper Carboniferous has been called the “Age of Insects”
* origin of wings
- Paleoptera and Neoptera appear at same time
- some gigantism
e.g., some Ephemeroptera with wingspans upward of 45 cm (18”)
e.g. some Paleodictyophora with wingspans of 52 cm
e.g., some Protodonata with 60-70 cm wingspans! (28”)
* good representation of paleopterous and hemipteroid orders: 13 insect orders present
e.g., Ephemeroptera, Orthoptera; several extinct orders
* origin of Holometabola
* in essence looking at origins of our modern insect fauna
* insect-plant coevolution already well underway...the evidence based on form
- feed on seed ferns, lycopods, and cordaites
1. mouthparts of Paleodictyoptera (70 genera in 21 families) had
long piercing beaks + trough-like labium = evidence of plant feeding
2. plants all of a sudden with closed strobili, hardened seed coats, and protected
micropyles
Permian:
* another spike of evolution
* +/-30 orders were likely present (+/-30 present today)(See Figure 8.1 in your text)
* 15 of our extant orders present, e.g., Plecoptera, Coleoptera, and Hemiptera
* all major (speciose) orders present except Hymenoptera and Lepidoptera
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hence decidedly modern at the ordinal level
* much drying during the Permian; coal-forming swamps with lycopsids disappear
* end of Permian:
- major glaciation; worldwide extinction; possibly another meteor impact
- marine taxa lost 96% of their diversity
- single greatest extinction event in Earth’s history (e.g., hasta la vista Trilobitomorpha)
Triassic and Jurassic:
* time of rebuilding
* modern families appear
* important radiations of Coleoptera, Diptera, and Hymenoptera (not Lepidoptera)
* blood sucking Diptera have been identified
Cretaceous:
* explosive radiation of the flowering plants ("Darwin's abominable mystery")
* appearance of bees
* radiation of Lepidoptera and many other phytophagous groups
* excellent insect fossils in amber
* some modern plant-insect associations still present: leaf mine in sycamore kin
Cenozoic
* by end of Cretaceous fauna looks rather modern with some insects falling into extant genera
Taxic Diversity Through Geologic Time:
* ordinal diversity was pretty much in place by Permian/Jurassic
* most modern orders by Jurassic (see Figure 8.1 in your text)
* half of extant insect species diversity is associated with angiosperms, therefore most of our
insect diversity had to have come after the radiation of angiosperms in the Cretaceous
About insect fossils:
1. Hard-bodied things and freshwater taxa have better fossil records
2. Amber insects
- detailed preservation
even cellular details
- blood-sucking flies in Mesozoic deposits
- many forest and other terrestrial taxa that are otherwise rare in fossil record in amber
- unfortunately not many plants producing (sap) amber before the Cretaceous radiation of
angiosperms
3. DNA preservation in amber!
- DNA is highly degraded--very short fragments out of amber insects
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