Arthropods and Trilobites Flashcards
What is the age range of phylum Arthropoda?
Cambrian to recent
What % of all animals described are Arthropods?
75%
What ranking debate is there concerning arthropods?
Whether phylum or superphylum
and
If they form a natural (monophyletic) group
What variety if there for arthropods?
Position, number and morphology of their limbs
Where do Arthropods fall on the group tree?
Metazoa, Bilateria, Protosomes, Ecdysozoa
What are phylum arthropoda united by?
Possession of a jointed exoskeleton which is often hard and inflexible
What are the advantages of exoskeletons?
Support for soft tissue
Firm site for muscle insertion
Protection (predators and environment change)
Division of skeleton into jointed sections
What is the advantage of exoskeletons dividing the skeleton into jointed sections?
Will act as a series of levers allowing for precision in locomotion, feeding etc
What are the limitations of exoskeletons?
To grow Ecdysis must occur (moulting) leaving the arthropod vulnerable
What % of arthropod mortality arises from Ecdysis?
70%
What can an exoskeleton allow to happen within a lifecycle?
allows animals to change morphology (metamorphosis)
What is the segmentation of Arthropoda like?
Segments = Metameres
Grouped into Tagmata
What does the grouping of segments into tagmata allow for?
feeding
locomotion
sensory systems
visceral elements (gut carrying)
What is a sister group of arthropods?
Phylum Onychophora (Cambrian - recent)
What is the closest relative to true (eu) arthropods from Onychophora?
Peripatus (recent)
What is a fossil record example of Onychophora?
Hallucigenia (Mid Cambrian), Burgess shale
What is a fossil record example of Chelicerata?
Sanctacaris (Mid Cambrian), Burgess Shale
What are some examples of present day Chelicerata?
Spiders
Mites
Scorpions
What is a group that branches from Chelicerata?
Merostomata
What is the present day and fossil record example of Merostomata?
Xiphosurids (Limulus) - present
Eurypterids - past
What was Eurypterid like in its environment?
In the middle paleozoic shallow water and terrestrial setting it was t
What are Chelicerata like at present day?
Predominantly terrestrial (being one of the first to transition to land)
What is the fossil record and recent example of Myriapoda?
Centipedes - present
Arthropleura from Carboniferous
What is characteristics about subphylum Hexapoda?
They have six legs (limbs) - insects
What species dominates the oligostraca group?
ostracods
What is the exoskeleton of ostracods like?
Produce bi-valve protective exoskeleton
What is the exoskeleton like for Subphylum Vericrustacea?
Folded (almost bi-valve) carapace
What is an example of Subphylum Vericrustacea?
Phyllocarids (Mid Cambrian, Burgess / Early Cambrian Chenjiang)
What are recent examples of Subphylum Vericrustacea?
Shrimps
Crabs
Lobsters
Barnacles
(predominantly marine)
What is the age range of subphylum Trilobitomorpha?
Cambrian to Permian
What is the environment of Trilobitomorpha
wholly marine
How many genera and species of Trilobitomorpha have been described?
> 4000 genera (40,000 species)
How is Trilobitomorpha’s body split?
Longitudinal (length ways “tip to tail”)
What is a burgess shale example of the sister group to Trilobita?
Marrella
Why are the appendages of Trilobitomorpha rarely preserved?
As the ventral side is organic and easily decays
While dorsal side heavily mineralised (calcite)
Where is an example of where Trilobitomorpha appendages have been preserved as Lagerstatte?
Burgess shale
What is the variation between Trilobitomorpha appendages like?
Minor
What do most appendages appear to be like in Trilobitomorpha
Biramous (2 projections) wit a 6 segment walking leg and gill branch for respiration
What are the upper and lower leg of Trilobitomorpha attached to?
The Coxa
What variation with Trilobitomorpha appendages has been identified to show behavioural changes?
Gnathobase- goes from smooth and chunky for Eoredlichia and then transition to Sharp edge Naraoia (predatory)
What are the “tails” at either end of Trilobitomorpha called?
At head - Antenna
Tail - Cerci
What is the hypostome?
hard mouth part of Trilobitomorpha
What are the 3 types of trilobite facial structures?
Proparian
Gonatoparian
Opisthoparian
What is used to make inferences about Trilobitomorpha mode of life?
Hard parts
Compared to recent forms
Distribution in sedimentary environment
Where can Opipeuterella be found in the fossil record?
Spitsbergen
Ireland
Sweden
Utah
Australia
What was the size of Opipeuterella?
1-2 cm length
What were the eyes of Opipeuterella like?
Large convex eye (2000 lenses) giving 360 view
What do the large eyes of Opipeuterella suggest?
It was pelagic (lived in water column)
What meant that Opipeuterella was not adapted to resting on the sediment?
cephalon steeply arched cheeks project down well below the pleurae with border
facing down
What did a wide convex axis exoskeleton allow for with Opipeuterella?
Provided for for powerful musculature (needed for swimming)
What is the length to width ratio like for Opipeuterella
3:1 (similar to modern day dimensions)
How do we know Opipeuterella was pelagic?
As it appears in both deep and shallow water sediments
What is the purpose of the types of facial suture?
important for mode of life
Proparian wider - shovel like
Gonatoparian - streamlined
