Paleontology Exam 3

Phylum Mollusca

• second largest animal phylum, most common marine animals today.

• Includes slugs, snails, squids, cuttlefish, octopus, clams, mussels, oysters

• unsegmented, soft-bodied animals

• live in marine, freshwater, and terrestrial habitats

• highly diverse

Mollusk Body Plan Features

1. Radula: rasping feeding organ, composed of chitin and designed to scrape and drill

2. Foot: sole-like structure on which the animal crawls, but is very modified usually

3. Visceral mass: internal digestive, excretory, reproductive, and circulatory organs enclosed in the celomic cavity

4. Mantle: sheet of tissue lying dorsally over the visceral mass that is responsible for secreting the shell

Mollusk Shells

• mollusk shells are secreted as calcium carbonate, mainly aragonite

3 Classes of Mollusk

Bivalvia, Gastropoda, Cephalopoda

Bivalvia

• consisting of two hinged parts/valves

• includes clams, oysters, mussels, scallops, etc

• majority are filter feeders

• shells are composed of calcium carbonate

• typically bilaterally symmetrical

• pearls are a valuable byproduct

Bivalve Morphology

important ones to remember: dorsal v ventral, adductor muscles, foot, beak, siphon

Bivalve Classification

• based primarily on gill structure

• protobranch, filibranch, eulamellibranch, septibranch

Bivalve Life Modes

a) shallow and deep burrowers into soft to firm substrates

b) epifaunal swimming, attached, or resting on soft to firm substrates

c) boring into hard substrates

Bivalve Reproduction

• sexual reproduction, separate sexes

• external fertilization — sperm and egg released into the water

• larva hatches and develops in the water

History of the Bivalve

• Early Cambrian to recent

• they were hit hard by the Permian-Triassic extinction but didn’t reestablish themselves like the brachiopods

• being able to burrow may have been a major factor in their success

Bivalve vs. Brachiopod

• superficially resemble brachiopods

• Bivalvia valves are mirror images of each other

• brachiopod valve made up of calcium phosphate and carbonate, while bivalves are just calcium carbonate

Gastropoda

• stomach foot

• snails and slugs

Gastropod Life Modes

• mostly benthic

• have adapted to almost every marine environment

• creeping, floating, free-swimming

• feeding: grazing, predatory, or parasitic

Gastropod Reproduction

• separate sexes or hermaphroditic

• reproductive modes are highly diverse

• most gastropods have internal fertilization, but some are external

Torsion

• the rotation of the visceral mass, mantle, and shell 180 degrees with respect to the head and the foot

• most gastropods have torsion

• mantle cavity, gills, anus, excretory and reproductive openings come to lie above the head

• advantages of this arrangement are unclear, torsion seems to be distinctly disadvantageous

• coiling of the shell is unrelated to the rotation of the soft parts

Gastropod Shell

• usually composed of aragonite

• usually conical in shape

• whorl: each revolution of the shell

• spire: whorls comprised together

• columella: central pillar caused by tight coiling about the vertical axis

• also know suture, operculum, aperture

• normally oriented with the aperture (opening) facing forward and the apex facing upwards

• if the aperture is on the right-handside, the shell is coiled clockwise in dextral mode, while sinistral shells have opposite sense of coiling

• shell surface is commonly modified by strong growth lines, ribs, tubercles

• variety of shell shapes (patelliform, convolute, discoidal, biconical, digitate, turbinate, turreted, pupiform)

Limpet

• group of aquatic snails that exhibit a conical shell shape and a strong, muscular foot

• patelliform

Gastropod Classification

• divided into 3 subclasses largely based on information from their soft parts

• traditionally defined based on the radula and their respiratory and nervous systems

• Prosobranchia, Opisthobranchia, Pulmonata

Prosobranchia

• mostly marine

• fully torted with one or two gills, an anteriro mantle cavity and cap-shaded or consipiral shells

• euomphalus, patella, turritella

Opistobrachia

• untorted with the shell reduced or absent and the mantle cavity posterior or absent

• untorsion: they have gone through torsion followed by detorsion

• pteropods: wing-foot, specialized free swimming pelagic sea snails

• sea slugs: unshelled snail

Pulmonata

• untorted with the mantle cavity modified as an air-breathing lung, and the shells are usually conspiral

• lived in terrestrial environments

Gastropod Evolution

• no general agreement on the origin of gastropods

• it is thought to have been derived from a monoplacophoran-type (bearing one plate) ancestor by torsion and development of an exogastric condition

Cephalopod

• head footed

• examples are cuttlefish, squids, octopus

• they are named because their head is situated directly on top of the foot — the foot is divided into tentacles

• most complex mollusks

• mantle encloses everything except head and tentacles, and acts as pump to bring large quantities of water into the cavity

Cephalopod Anatomy

• exclusively marine

• prominent head

• arms for feeding, propulsion, reproduction

• many can expel ink to discourage predators

• very well developed eyes

• gills for respiration

• jet propulsion by squeezing body together quickly

• bilateral symmetry

Cephalopod Habitat

• benthic

• highly motile

• live on seafloor

• have adapted to almost every marine environment

Cephalopod Feeding

• most are predators using arms, tentacles, suckers to capture then their beaks rip prey apart

Cephalopod Reproduction

• separate sexes

• distinct egg cases

• many types die after reproduction, mostly only living 1-2 years

Cephalopod Evolution

• cambrian to present

• cephalopods also though to be have been derived from the “bearing one plate” ancestor

• early cephalopods likely predators near the top of the food chain

• most ancient varieties had protective shells, which were at first conical but developed in to nautiloid

• competition with fish is thought to have forced cephalopods into deeper water, pressuring them to lose their shells

Ammonoidea

• ammonites

• group of extinct mollusks

• more closely related to living octopus, squids, and cuttlefish

Nautilus

• easily visible foot, divided into many tentacles

• leathery cover that works somewhat like an operculum, closing the aperture when the animal is at rest or in danger

Squids and Cuttlefish

• earliest cuttlefish from cretaceous

• earliest squids from devonian

• squids and cuttlefish have an internal shell that is made of 3 layers with gas-filled spaces between each layer, helps with buoyancy

Octopus

• eight arms, all with powerful suckers

• good eye sight

• eyes are elevated and capable of excellent vision in the dark

• suckers on the ventral surface of arms are used to grip and capture food

Arthropoda

• joint + foot or leg

• lobsters, spiders, beetles, trilobites, etc

• common and very diverse, accounts for a majority of all species today

• adapted to marine and terrestrial environments

• several arthropod-like animals in Ediacara biota suggest an ancient origin for Arthropoda

Arthropod Body Plan

• segmented body plan

• jointed appendages

• hard external skeleton

• 3 parts - head, thorax, and abdomen

• exoskeleton is hard, made of chitin

• bilateral symmetry

Molting

shed old exoskeleton and secrete a larger one, very vulnerable after molting

Arthropod Anatomy

• complete digestive tract with a dorsal heart and a ventral nervous system

• mandible for chewing and proboscis for sucking

• respiration through gills, trachea, book lungs, or body surface

• sensory organs include antennae and hairs, simple and compound eyes

Compound Eye

• has many lenses for increased eye sight for arthropods

• they bulge out for more surface area and able to expand field of vision

Arthropoda Sub Phylums

• trilobitomorpha: trilobites

• chelicerata: spiders, horseshoe crabs, scorpions

• myriapoda: centipedes, millipedes

• crustacea: shrimp, lobsters

• hexapoda: insects

Sub Phylum Crustacea

• shrimps, crabs, lobsters, barnacles, pill bugs

• two pairs of antennae

• mandibles for chewing

• pair of appendages on each body segment

• gills for oxygenand a hard exoskeleton for protection.

Sub Phylum Chelicerata

• horseshoe crabs, spiders, mites, scorpions

• pincer-like appendages

• small pinchers to venomous fangs

• eurypterids, NY state fossil

Sub Phylum Myripoda

• flexible centipedes and millipedes

• first animals to colonize the land

• came through the late Carboniferous forests

Sub Phylum Hexapoda

• insects

• highly diverse group, divided into two groups

  • pterygotes: wings

  • apterygotes: without wings

• ants, beetles, dragonflies, flies, cockroaches, wasps

• developed coevolutionary relationships with plants, especially between flowering plants

Sub Phylum Trilobitomorpha

• trilobites

• lack specialized mouthparts

• some of the earliest arthropods

• exoskeleton is divided into three lobes

  • axial lobe protects digestive system

  • two pleural lobes cover appendages

  • it is composed of calcite

• grows by molting

• morphology greatly varied and have a broad range of adaptations

• benthic, leaving tracks in marine sediments

• diet of microscopic organisms

Trilobite Abnormalities and Injuries

• since there are many trilobite fossils, we can learn a lot about them

• abnormalities:

  • injuries sustained during molting

  • pathological conditions resulting fro disease or infection

  • teratological effects arising from embryological or genetic malfunctions

• many fossils show signs of predation that show an asymmetric distribution

• predation scars are 3x as likely to be present on the right side

  • could indicate a lateralization of nervous system OR

  • scarred specimens were survivors and predators preferred to attack the left side and we never see those victims

Trace fossils

the product of an organism interacting with a substrate in an environment that generates a three-dimensional physical structure

Ichnology

study of trace fossils / a powerful tool for understanding past sedimentary environments and one of the major clues to the behavior of animals

What do trace fossils give evidence about?

1. the behavior of organisms

2. sedimentary environments

What can cause trace fossils?

dwelling, feeding, crawling, hiding, resting, grazing, cultivating, reproducing, escaping

Examples of trace fossils

burrows, footprints, boreholes, bite marks, feeding

Facts about trace fossils

• most traces are largely facies dependent

• no secondary displacement or transport

• trace fossils are common in rocks that are otherwise unfossiliferous

• non-preservation of the causative organism

3 Principles of Ichnology

1. the same individual can produce different structures corresponding to different behavior

2. identical structures may be produced by the activity of systematically different organisms where behavior is similar

3. the same individual may produce different structures corresponding with identical behavior but in different substrates

abundance

one animal, especially if mobile, can make many traces during its lifetime, whereas it may or may not have its body preserved in the fossil record

Facts about trace fossil preservation

1. preserved in rocks where body fossils are rare

2. diagenesis (heat and pressure) may destroy body fossils but has little effect on trace fossils

3. not subject to post-mortem transport, are automatically in situ

Types of trace fossil preservation

• full relief: 3 dimensional relief, all sides of the trace exposed

• semi relief: concave troughs or depressions on the top or bottom surface of a bed

  • epirelief: top trail on the surface

  • hyporelief: traces on the underside of the underlying bed

• semireliefs are easier to understand and get information

Trace fossil morphological classification

• tracks/trails on bedding plane

• radially symmetrical horizontal markings

• tunnels and shafts

• arbitrary and not objective

Classifications of Trace Fossils

1. morphological and preservational

2. behavioral

3. phylogenetic

Repichnia

• locomotion or crawling traces

• tracks of moving surface dwellers

• usually continuous

Cubichnia

• resting traces

• impressions caused when the animal interrupted its locomotion for rest and refuge

• often reflects the anatomy of the undersurface of the organism

Pascichnia

• grazing or surface feeder traces

• series of parallel loops demonstrates a feeder moving along the sediment surface to eat bacteria

Fodinichnia

• feeding traces/burrows

• excavations made my deposits feeders, eating the sediment to digest the food within it

• can be simple or complex branched

Domichnia

• dwelling traces/structures

• permanent burrows and borings of suspension feeders

• can be subcylindrical tubes or u-shaped

Fugichnia

• escape structures

• showing signs of forced escape

• animal digs out to escape or digs burrow upward to continue suspension feeding

What are trace fossils used to understand?

• distribution and activity of organisms

• depositional energy

• sedimentation rate

• oxygenation of bottom water and the substrate (defined by the amount of sediment reworking by burrowing organisms)

Importance of trace fossils in geology

• long time range: similar taxa occur in present day environments

• narrow facies range: certain traces are found in close association with certain substrates

• no reworking: traces are a part of the rock, so they are destroyed by erosion rather than reworked like body fossils

• occurrence in nonfossiliferous rocks: good for studies in hostile rock and poorly population environments

• creation by soft-bodied taxa: trace fossils can give info about organisms that are not found in the fossil record

• burrows and trails can help distinguish if sedimentary beds have been overturned

• observing burrows that were circular cross-sections can determine stress that rocks have undergone