Chapter 27 - The Rise of Animal Diversity

Animals (and how they are dangerous feeding machines)

• heterotrophs that ingest their food

• make life dangerous for the organisms around them

• most are mobile and can detect, capture, and eat other organisms

• have specialized muscle and nerve cells that allow them to move and respond rapidly

fossil and molecule evidence of animals

in sediments dating back to the Proterozoic

• first macoscopic fossils of large animals date back to the Ediacaran

Early diverging animal groups

• sponges

• cnidarians

• other animal groups

Phylum Porifera

AKA sponges

• live in both fresh and marine waters

• lack true tissues and organs

• suspension feeders - they capture food particles suspended in the water that pass through their body

• Choanocytes, which are flagellated collar cells, generate a water current through the sponge to ingest suspended food

• Spongocoel - cavity with pores that draws water in

• Osculum - opening where water comes out

Phylum Cnidaria

• one of the oldest groups in the clade Eumetazoa (animals with true tissues)

• originated before the Ediacaran

• wide range of both sessile and motile forms like jellies, corals, and hydras

• simple radial body plan and are diploblastic

• basic body plan contains a sac with a central digestive compartment ( the gastrovascular cavity)

• single opening functions as a mouth and anus

Jellyfish blooms

massive increase in jellyfish in one area due to overfishing

Cambrian Explosion

• happened during the Paleozoic Era

• marks the earliest fossil appearance of many major groups of living animals

• diversity of animals increased dramatically

• 3 hypotheses on what caused Cambrian explosion:

  • new predator-prey relationships

  • rise in atmospheric oxygen

  • evolution of the Hox gene complex

Origin of Bilaterians

bilaterians evolved by 670 million years ago

• which was 135 million years before the Cambrian explosion

• prior to the Ediacaran, eukaryote fossils were microscopic and smooth-walled

how was eukaryote life changed in the Ediacaran

• animals are dangerous feeding machines because of mobility, nervous system, and efficient digestive tract

• the rise of predators

Animal body plans

set of morphological and developmental traits

• 3 elements of body plans:

  • symmetry

  • tissues

  • body cavities

Symmetry (and types of symmetry)

animals categorized according to symmetry or lack of symmetry of their bodies

• Radial symmetry - identical body parts divided around a central axis

  • ex. starfish

• Bilateral symmetry - two-sided symmetry

  • divided into two mirror-halves along one plane

  • bilaterally symmetrical animals have:

    • dorsal (top) side and ventral (bottom) side

    • anterior (head) and posterior (tail)

    • cephalization - development of a head

tissues

collections of specialized cells isolated from other tissues by membranous layers

• during development, 3 germ layers give rise to the tissues and organs of the animal embryp

3 germ layers

• ectoderm - covers the embryo’s surface

• endoderm - innermost germ layers give rise and lines the developing digestive tube (the archenteron)

• mesoderm - found between ectoderm and endoderm

  • found ONLY in triploblastic animals

diploblastic vs. triploblastic

• diploblastic - animals that have have an ectoderm and endoderm

  • includes cnidarians and ctenophores

• triploblastic - animals have a mesoderm layer between the ectoderm and endoderm

  • includes all bilaterians

tissue layers in bilaterians

• body cavity

• body covering (from ectoderm)

• digestive tract (from endoderm)

• tissue layer lining body cavity and suspending internal organs (from mesoderm)

Body cavitiy

• most triploblastic animals have a body cavity called a coelom

  • its fluid cushions internal organs

5 Points reflected in the animal phylogeny

1. Animals share a common ancestor

2. sponges are basal animals

3. Eumetazoa is a clade of animals (eumetazoans) with true tissues

4. most animal phyla belong to the clade Bilateria and are called bilaterians

5. most animals are invertebrates

groups of Bilateria

1. Lophotrochozoa

2. Ecdysozoa

3. Deuterostomia

Lophotrochozoa

• include roughly 18 phyla

• ex. mollusks, annelids, rotifers, ectoprocts

• some have a feeding structure called lophophore

• other go through distinct developmental stage called the trocophore larva

mollusks

• include snails and slugs, oysters and clams, and octopuses and squids

• most are marine but can live in fresh water or are terrestrial

• soft-bodies animals, but most are protected by a hard shell

• many have a water-filled mantle cavity and feed using rasp-like radula

• body plan contains 3 main parts:

  • muscular foot

  • visceral mass

  • mantle

4 major groups of mollusks

1. chitons

2. gastropods - snails and slugs

3. bivalves - clams, oysters, and other bivalves

4. cephalopods - squid, octopus, cuttlefish, nautilus

chitons

• oval-shaped marine animals encased in an armor of eight dorsal plates

gastropods

• make up ¾ of mollusks

• most are marine but many are freshwater and terrestrial

• have a single, spiraled shell

• slugs lack a shell or have a reduced shell

bivalves

• include clams, oysters, mussels, and scallops

• have a shell divided into two halves

cephalopods

• includes squids and octopuses

• carnivores with beak-like jaws surrounded by tentacles of their modified foot

• most octopuses creep along sea floor in search of prey

• squids use their siphon to fire a jet of water allowing them to swim very fast

annelids

• body is composed of a series of fused rings

• some are predators and many are parasites

• earthworms are the most familiar, but this phylum consists mainly of marine and freshwater species

• leeches secrete a chemical called hirudin to prevent blood from coagulating

Ecdysozoan

• most species-rich animal group

• cuticle - tough coat that covers Ecdysozoans

  • ecdysis - process where the cuticle is shed or molted

• 2 largest phyla of Ecdysozoans

  • nematodes

  • arthropods

Nematodes (Phylum nematoda)

• AKA roundworms

• found in most aquatic habitats, in the soil, in moist tissues of plants, and in body fluids and tissues of animals

Athropoda

• found in nearly all habitats in the biosphere

• body plan consists of segmented body, hard exoskeleton, and jointed appendages

• origin dates back to the Cambrian explosion

4 arthropod lineages

1. Chelicerates - spiders, horseshoe crabs, scorpians, ticks, mites

2. Myriapods - centipedes and millipedes

3. insects

4. crustaceans - crabs, lobsters, shrimps, barnacles, and many others

Millipedes

• herbivores, eat decaying leaves and other plant matter

• may have been among the earliest terrestrial animals

• two pairs of legs per trunk segment

centipede

• carnivores

• one pair of legs per trunk segment

• have poison claws on their foremost trunk segment

insects

• there are more species of insects than all other forms combined

• live in almost every terrestrial habitat and in fresh water

Crustaceans (and the 2 types)

• live in marine and freshwater

• have branched appendages that are specialized for feeding and locomotion

• most have separate males and females

• ex. lobsters, crabs

• 2 types of crustaceans

  • isopods

  • decapods

isopods

small, terrestrial, freshwater, and marine species

• ex. pill bugs

decapods

large crustaceans

• ex. lobsters, crabs, crayfish, and shrimp

Deuterostomia: Phylum Echinoderms

• have a water vascular system

  • network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange

• ex. sea stars, urchins, sea cucumbers, brittle stars

Vertebrates

• have vertebrae - series of bones that make up the backbone

• includes the largest organisms ever to live on Earth

4 key characters of chordates

1. notochord

2. dorsal, hollow nerve cord

3. pharyngeal slits or clefts

4. muscular, post-anal tail

Lancelets

AKA cephalocordata

• bladelike shape

• marine suspension feeders that retain characteristics of the chordate body plan as adults

Tunicates

AKA urochordata, AKA sea squirts

• marine suspension feeders

• as an adult, they draw in water through an incurrent siphon which filters food particles

• more closely related to other chordates than lancelets are

Rise of vertebrates

originated in the Cambrian

• some of the earliest vertebrates were conodonts

• had mineralized skeletal elements in mouth and pharynx

Myllokunmingia and why it’s not considered a vertabrate

• had a skull but didn’t have vertebral column, so it’s not considered a vertebrate

Fossils of early vertebrates

• other armored, jawless, vertebrates had defensive plates of bone on their skin

• many emerged in the Ordovician, Silurian, and Devonian

Cyclostomes (and 2 types)

jawless vertebrates

• two groups

• Myxini (hagfish) - have a cartilaginous skull and axial rod of cartilage derived from the notochord

  • but lack jaws and vertebrae

• Lampreys (Petromyzontida) - have cartiliginous segments surrounding the notochord and arching partly over the nerve cord

  • oldest living lineage of vertebrates

Gnathostomes

jawed vertebrates

placoderms

the earliest gnathostomes that are extinct and have armored vertebrates

Chondrichthyans

• sharks, rays, and relatives

• skeleton composed mostly of cartilage

traits of sharks

• streamlined body and are swift swimmers

• carnivores

• short digestive tract

  • spiral valve - ridge that increases the digestive surface area

  • acute senses

Osteichthyes and its 2 clades

• ossified (bony) endoskeleton

• includes bony fish and tetrapods

• 2 clades

  • Ray-finned fishes (Actinopterygii) - make up most vertebrates

  • lobe-fins - lungfishes and coelacanths

lateral line

pressure sensitive organ that allows fish to feel vibrations in water

3 surviving lineages of lobe-fins

1. lungfishes

2. coelacanths

3. tetrapods

dipnoi

AKA lungfishes

• inhabit stagnant ponds and swamps

• are homologous to lungs of tetrapods

• have to surface to breathe air, otherwise they will drown

pros and challenges of life on land for early animals

pros:

• higher oxygen concentrations in the atmosphere than in the aquatic environment

• new food sources

• few competitors

challenges:

• scarce water

• temperature fluctuations

• no support against gravity

who were the first animals to colonize land (and who followed after)

arthropods (in the Ordovician)

• millipedes, centipedes, spiders, and wingless insects colonized land (early Devonian)

• vertebrates colonized land and forests formed (late Devonian)

• by the late devonian, terrestrial animal communities were similar to those today

arthropods characteristics

• appendages modified for walking, feeding, sensory reception, reproduction, and defense

• appendages are jointed and come in pairs

• cuticle - exoskeleton built from layers of protein and chitin that covers the body

  • helped arthropods colonize the land

gas exchange in arthropods

• aquatic arthropods - use gills for gas exchange

• terrestrial arthropods - have evolved specialized gas exchange structures

• insects - tracheal systems with branched air ducts

  • not as efficient as lungs

Rise of the insects (and adaptations that helped them survive)

Origin dates back to the Devonian

• explosion of insect diversity occurred in the Carboniferous and Permian periods

  • flight helped them escape predators and find food and mates, and disperse to new habitats

  • wings are extensions of the cuticle, so insects don’t have to sacrifice walking legs just to fly

3 Orders of insects

• Lepidoterans - btterflies and moths

• Hymenopterans - ants, bees, and wasps

• Hemipterans - bugs

Origin of Tetrapods

• many lobefins during the Devonian

• one lineage of lobe-fins had their fins become progressively more like limbs while the rest of the body retained adaptations for aquatic life

Fish vs. Tetrapod characteristics

Fish

• scales

• fins

• gills and lungs

Tetrapods

• neck

• ribs

• fin skeleton

• flat skull

• eyes on top of skull

3 clades of amphibians

1. Urodela (salamanders)

2. Anura (frogs and toads)

3. apoda (caecilians)

Caecilians (Apodans)

• legless and resemble worms but have backbones

• live in moist soils and tropical habitats

• some practice matriphagy

matriphagy

when embryos eat mother’s skin that she regrows

amphibians

• go through metamorphosis of an aquatic larva into a terrestrial adult

  • “amphibian” means “both ways of life”

• most have moist skin that complements lungs in gas exchange

• external fertilization in most species and eggs require a moist environment

amniotes and the amniotic egg

• characterized for the derived character of the clade, the amniotic egg

  • egg that contains membranes that protect the embryo

• group of tetrapods whose living members are reptiles, birds, and mammals

• other terrestrial adaptations include relatively impereable skin and ability to use rib cage to ventilate lungs

extraembryonic membranes

1. amnion - protects embryo in a fluid-filled cavity that cushions against mechanical shock

2. allantois - disposal sac for certain metabolic wastes produced by the embryo

3. chorion - this alongwith allantois membrane exchange gases between the embryo and the air

4. yolk sac - contains the yolk, a stockpile of nutrients

• other nutrients are stored in the albumen (the egg white)

origin and radiation of amniotes

• most recent common ancestor of amphibians and amniotes lived during the Carboniferous (350 mya)

• early amniotes resembled small lizards with sharp teeth

  • indicates that they were predators

reptiles (and how they maintain body heat)

clade that includes tuataras, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs

• have scales that create a waterproof barrier

• lay shelled eggs on land

• most reptiles are ectothermic

  • absorb external heat as main source of body heat

• birds are endothermic

  • can keep body warm through metabolism

Lineages of reptiles

• Tuatara - one surviving lineage of lepidosaurs

  • have a third (parietal) eye

• Squamates - lizards and snakes

• legless lepidosaurs that evolved from lizards

turtles and tortoises

• turtles are the most distinctive group of reptiles alive today

  • boxlike shell made of upper and lower shields that are fused to the vertebrate, clavicles, and ribs

  • some have adapted to desserts and others live entirely in ponds and rivers

Crocodilians

alligators and crocodiles

• belong to an archosaur lineage that dates back to the late Triassic

• more than 2 dozen species

Birds

are archosaurs, but almost every feature of their reptilian anatomy has gone through modification for flight adaptation

• about 10,000 species

derived characteristics of birds

many are adaptations for flight

• flight enhances hunting and scavenging, escape from predators, and migration

  • requires a great amount of energy, acute vision, and fine muscle control

• wings with keratin feathers

• other adaptations: lack of urinary bladder, females only having one ovary, small gonads, and loss of teeth

the feather

useful in flight

• consists of a central air-filled shaft that radiates the vanes

• vanes are made up of barbs with small branches called barbules

origin of birds

probably descended from small theropods, which are a group of carnivorous dinosaurs

• feathered theropods evolved into birds by 150 mya

• Archaeopteryx

Archaeopteryx

oldest bird known (~150 mya)

• even though there is an even older known bird-like feathered dinosaur fossil called Xiaotingia (155 mya)

Order Passeriformes

songbirds

• most diverse group of living birds

mammals

amniotes tha have hair and produce milk via mammary glands

derived characters of mammals

1. mammary glands that produce milk

2. differentiated theeth

3. efficient respiratory circulatory systems

4. relatively large brain

5. hair

Early Evolution of Mammals

mammals and reptiles are sister groups that have been separated for more than 300 million years

• mammals evolved from synapsids in the late Triassic

• non-mammalian synapsids lacked hair and laid eggs

3 living lineages of mammals in the early Cretaceous

monotremes, marsupials, and eutherians

Monotremes

small group of egg-laying mammals consisting of chidnas and platypus

Marsupials

includes opossums, kangaroos, and koalas

• embryo develops within a placenta in mother’s uterus

• born very early in its development

  • completes its embryonic development while in a maternal pouch called marsupium

• most species found in Australia

what threatens Tasmanian devil populations

populations threatened by devil facial tumour disease, a transmissible form of cancer

Eutherians (placental mammals)

have a longer period of pregnancy compared to marsupials

• young eutherians complete their embryonic development within a uterus, connected to the mother by the placenta

• ex. ground squirrels and red foxes

Primates

Mammalian order that includes lemurs, tarsiers, monkeys, and apes

• humans are members of the ape group

• earliest primates were tree-dwellers

derived characteristics of primates

most have hands and feet adapted for grasping

• monkeys and apes have an opposable thumb

• large brain and short jaws

• forward-looking eyes close together on the face providing depth perception

• complex social behaviour and parental car

Hominins

• ancestor of humans

• humans diverged from other apes during the Miocene (6-7 mya)

• Hominins are more closely related to humans than to chimps

• oldest hominin fossils are from Sahelanthropus tchadensis (6.5 mya)

Hominin evolution

• early had a small brain but probably walked up right

• - Ardipithecus (4.4 mya) was bipedal but had a smaller brain than Homo sapiens

Australopiths

paraphyletic assemblage of hominins that lived between 2-4 mya

• some species walked fullly erect

Homo habilis

earliest fossils in genus Homo are from Homo habilis (1.6-2.4 mya)

• brain 675 cm³

• stone tools have been found with their fossils

  • which is why they’re named “handy man”

Homo erectus

left africa 1.8 mya

• first hominin to leave Africa

• became extinct 50,000-200,000 years ago

Homo bodoensis

lived in Africa and southeastern Europe 126,000-770,000 years ago

• suggested that it was the direct ancestor of Homo sapiens

neanderthals (Homo neanderthalensis)

• lived in Europe and Near East from 28,000-200,000 years ago

• thick-boned with a larger brain than H. sapiens

• buried their dead

• made hunting tools

• interbred with Homo sapiens

Homo sapiens

• emerged 195,000 years ago or earlier

• all living humans are descended from these African ancestors

• Humans spread beyond Africa in one or more waves

• reached Australia 50,000-70,000 years ago

• first arrived in the New World roughly 15,000 years ago or 21,000-23,000 years ago

Ecological effects of animals on Marine ecosystems

abundance of cyanobacteria decreased in the early Cambrian

• this may have been caused by activities of crustaceans and others with suspension feeding mouthparts

• this causes algae (that require more light for photosynthesis than cyanobacteria) increased in population and moved to deeper water

ecological effects of animals on terrestrial ecosystems

terrestrial ecosystems had a simple structure before animals emerged

• early plants harnessed energy from the sun and drew nutrients from the soil while decomposers returned nutrients to the soil

• by 410 mya, plants were consumed by herbivores which were eaten by predators

  • detritivores consumed organic debris

• ecosystems now have a complex network of interactions

example of ecological effects of animals

• geese feed on grasses and other marsh plants

• lesser snow geese breed in marshlands in Hudson bay

• at low population numbers, this improves marsh plant growth

• at high numbers, geese can destroy the marsh