Animal Diversity and Evolution

Chapter 6: Animal Diversity and Evolution

• Animals existed on Earth before humans and play a crucial role for the environment and people.
• Animal diversity has caused changes that impact people positively and negatively.
• Differences among animal function exist, but similarities can also occur.
• Evolution began in oceans with species unlike those present.
• Scientists are still discovering approximately 8.7 million species globally.
• Adaptation became common allowing organisms to keep up with a changing environment.
• Animals are multicellular eukaryotes with tissues/structures for specific functions.
• Animals are heterotrophic and require food.
• Animals undergo life cycle stages to reach maturity.

Learning Outcomes

• Understanding of animal life variety is needed.
• Animals use descriptive terminology of morphology, anatomy, embryology, and reproductive biology.
• Need to identify animal species' distribution, habitat, ecology, and value.
• Appreciation for organisms that are uniquely and similarly related is important.
• Discussion and description of animal's major classification is key.
• Features that distinguish Kingdom Animalia from other kingdoms must be listed.
• Processes of animal reproduction and embryonic development should be explained.
• Differences in animal body plans that support basic animal classification has to be explained.
• Comparison and contrast between protostome and deuterostome embryonic development is essential.

Kingdom of animal overview

• 1.3 million living animal species are identified.
• There are more animal species than estimates show.
• There is a large range of morphological diversity.
• Animals are multicellular, heterotrophic eukaryotes that develop tissues from embryonic layers.
• Nearly every criterion distinguishing animals vary.
• Animals are multicellular, ingestive heterotrophs unlike fungi.
• Animals ingest food and use enzymes to digest it in their bodies
• Plants are autotrophic eukaryotes, generating organic molecules by photosynthesis.
• Fungi are absorptive heterotrophs.
• Animal cells lack cell walls, which provide structural support for plants and fungi.
• Animal bodies are held by extracellular structural proteins, especially collagen.
• Nerve cells for impulse conduction and muscle cells for movement are two specialized cells only found in animals.
• These cells are organized into nervous and muscle tissue.
• Most animals reproduce sexually, with a dominant diploid stage.
• Sperm fertilizes a nonmotile egg in most animals.
• The zygote cleaves through mitotic divisions, forming a multicellular blastula, which in many species is shaped like a hollow ball.
• The embryonic tissues that develop into adult body parts are produced during the gastrulation phase. A gastrula is the resulting development phase.
• Most animals have a distinct larval stage/stages however some develop directly through transient stages into adults.
• The larva is a sexually immature stage that differs morphologically from an adult.
• Larva eat different foods and may live in habitat unlike adults.
• Metamorphosis transforms animal larvae into adults.
• Hox genes are a homeobox-containing family of genes that animals share.
• Hox genes influence animal morphology by controlling the expression of other genes in animal embryos.
• Sponges, among simplest living animals, lack Hox genes but possess other homeobox genes, which influence their shape by formation of water channels in the body wall.
• The Hox gene family arose via duplication of homeobox genes with the ancestors of advanced animals.
• Over time the Hox gene family underwent a series of duplications.
• Hox genes regulate anterior-posterior (front-to-back) axis formation and other development elements in vertebrates, insects, and most animals.
• Despite differences and millions of years of divergent evolution, similar sets of conserved genes govern a fly and a human’s development.

History of Animals

• The history of animals spans more than half a billion year.
• Paleontologists estimate that over 99% of all animal species have become extinct.
• Studies suggest that animal diversity originated over the last billion years.
• Molecular clocks estimates the divergence between animal and fungi ancestors happened about a billion years ago.
• Studies propose that living animal's common ancestor may has lived 675-800 million years ago.
• Combined morphological and molecular studies indicate living animals' common ancestors may have been suspension feeders similar to current day choanoflagellates.

Neoproterozoic Era

• Neoproterozoic Era (1 billion–542 million years ago).
• The oldest accepted animal fossils date 565-550 million years old, despite molecular data indicates an earlier animal origin.
• Ediacara Hills of Australia gave the fossils the name Ediacara biota.
• Ediacara fauna includes sponges, and other organisms like living cnidarians.
• Some organisms are not linked to any living algae or animal.
• Neoproterozoic rocks showed microscopic signs of early animals.
• 575-million-year-old microfossils found in China displayed current-day animal embryos' structural organization.
• Debate continues whether the fossil embryos found and examined are animals or other closely related extinct species.

Paleozoic Era

• Paleozoic Era (542–251 million years ago)
• Animals rapidly diversified between 535 - 525 million years ago in the Cambrian period, known as the Cambrian explosion
• About half of extant animal phyla, like arthropods, chordates, and echinoderms, arose during this Cambrian explosion.
• Fossils of Cambrian animals contained the first hard, mineralized skeletons.
• Diversification of bilaterian phyla occurred during Cambrian alongside the decline in Ediacaran life.
• Several hypotheses for the reason for the Cambrian explosion involves new predator-prey relationships, atmospheric changes, and developmental flexibility.
• Predators gained adaptations during Cambrian enabling them to catch prey and the prey acquired protective shells to deter the predators.
• New predator-prey relationships emerged causing the natural selection and decline of some groups and rise of others.
• Increased atmospheric oxygen levels existed before Cambrian explosion, which provided opportunities for animals with higher metabolic rates and larger body sizes.
• Hox genes and other genetic changes emerged affecting the regulation of developmental genes led to new body forms and development flexibility.
• These hypotheses are not mutually exclusive and likely played a role.
• Animal diversity continued to increase during the Ordovician, Silurian, and Devonian periods and mass extinction punctuated it.
• Vertebrates (fishes) rose to the top of predators in marine food webs.
• About 460 million years ago, arthropods started adapting to terrestrial habitats as millipedes and centipedes appeared on land.
• Fern galls date back to 302 million years ago and were enlarged cavities that resident insects stimulate fern plants to form, which suggests that insects and plants were influencing each other's evolution.

Mesozoic Era

• Mesozoic Era (251–65.5 million years ago)
• Animal phyla began to spread into new ecological habitats.
• In the oceans coral reefs were first formed and providing marine animals with new habitats.
• Some reptiles succeeded as large aquatic predators with the return to the water.
• On land, flight evolved in pterosaurs and birds.
• The evolution of herbivorous and carnivorous dinosaurs of all sizes evolved.
• The first mammals-tiny nocturnal insect-eaters-arose.
• During the late Mesozoic, insects and flowering plants underwent dramatic radiations.

Cenozoic Era

• Cenozoic Era (65.5 million years ago to the present)
• This era had mass extinctions of terrestrial and marine animals occurred.
• Some species that disappeared were large, nonflying dinosaurs and marine reptiles.
• Mammalian herbivores and carnivores were diversified as mammals filled vacated ecological niches. African primate species adapted to woodlands and savannas' open spaces as global climates cooled.
• Those primates were the ancestors of humans.

Body Plans

• Animals can be categorized by “body plans".
• Animal species displays incredible amount of morphological variation which can be arranged into relatively small number of major "body plans."
• Functional whole-the living animal-integrates set of morphological and developmental traits as a body plan.
• Evolutionary development examines how body plans evolved.
• Animal body plans have evolved and changed drastically over time.
• For example, A key step in molecular control of gastrulation has remained unchanged for over 500 million years, the innovation of which helps explain why most animals are not a hollow ball of cells.
• As lineages evolved and diversified in nature other aspects of animal body plans diversified.
• Similar body forms have sometimes evolved independently in two different lineages.

Symmetry

• Animals can be categorized by the symmetry (or absence of symmetry) of their bodies.
• Many sponges like symmetry.
• Sea anemone like creatures display radial symmetry with a top (mouth) and bottom side but with no left/right sides.
• Bilateral symmetry seen in many animals, display two axes of orientation that is front to back and top to bottom.
• Bilateral symmetrical animals feature dorsal (top) and ventral (bottom) sides, left and right sides, and anterior(front) and posterior (back) end.
• Cephalization is tied to bilateral symmetry which concentrates nervous and sensory equipment on anterior animal’s end.
• The symmetry of animal reflects its daily function and lifestyle
• Planktonic/sessile radial animals need to meet environment equally well coming at them from all sides.
• Animals active in movement are usually bilaterally symmetrical, with a central nervous system that supports movement involved in crawling, burrowing, flying, and swimming.
• Radial and bilateral symmetry has existed for at least for 550 million years.

Organization in Animal Tissues

• Animal body plans depend upon organization of the animal's tissues.
• True tissues are collections of specialized cells that membranous layers isolated to.
• Sponges and some other groups lack True tissues.
• The embryo becomes layered via gastrulation in all other animals.
• The development then progresses and creates concentric layers of embryonic tissue form various tissues and organs from Germ layers.
• Ectoderm is the outer germ layer covering embryo surface, which creates outer surface/central nervous system in some phyla.
• The innermost germ layer is endoderm, which lines the pouch during gastrulation that will give rise to the lining of digestive trace or cavity/organs derived from them.
• Animals that are diploblastic contain only two layers of germ such as cnidarians and comb jellies.
• The presence of Triploblastic animals are those that consist of three germ layers.
• In these animals, the Mesoderm Is the third germ layer that lies between endoderm and ectoderm. This will further later develop most organs and muscles that lie in-between digestive tube and outer covering.
• Triploblasts consist of vertebrates and anthropoids

Body Cavities

• Most triploblastic animals possess a body cavity (a fluid filled/air space between the digestive tract and body wall that is known as a coelom.
• “True” coelom forms from tissue derived from mesoderm
• The outer/inner layers of tissue that surround the coelom connect and create structures to suspend internal organs of any animal. Animals with a true coelom are coelomates. The creation of cavity from endoderm and mesoderm exist in some triploblastic animals which is called a "pseudocoelom," and animals with one would be pseudocoelomates . A pseudocoelom functions as a fully functional cavity unlike some which lack body cavity. These are known as acoelomates and have solid body that without the cavity. A cavity has many functions with fluid that cushions organs prevent internal injuries The noncompressible fluid of soft bodied coeleomates can work as a hydrostatic skeleton against which muscles can work. The presence of the body cavity creates means for internal organs to move and grow independently from body wall. The group containing any organisms that have similar body forms are part of the same grade

Developmental Modes

• Developmental modes of animals vary. There are two categories in which animal developmental modes are classified being The protostome or deuterostome developments. The center of differences involves cleavage collem form/blastopore fate with patterns on development.

Protostomes experiences spiral cleavage were the cell divisions are diagonal to vertical access of the embryos. Determent cleavage is found in Most protostomes that means each embryonic sale has a determined date. Deuterostomes most radial cleavage means claims are perpendicular to the vertical access of the embryo in development, Indeterminate cleavage in most deuterostomes means each in early embracement can still develop into embryos. the possible identical twins may be created from fertilization. in general The digestive is created as the blind pouch called the archenteron that becomes the gut and gastrulation process has ended, Then initially solid messes of mesoderm form and slits create collem for protostomes. The mesoderm was able to both away from the archenterons and hollow mesoderm walls with collem and Duterostomes forming walls Difference in fate of blastopore comes in the time of protostome versus deuterostomes development were first leads to the formation of the Archenter. Most bilaterians form a second opening that is opposite from the Archenter

Recent Phylogenetic Shifts

• Views of animal phylogeny keep evolving and are now often shaped by new molecular and morphological data Boundaries/relationship between phylas are always debated which often come down zoologist comparing phylogeny using molecular data. New studies of fossil data and phylas that are less known provide clarification of key traits among groups that came about during that time. There is a seek in trying to place all organisms into clades to better understand ancestors that include all its descendants. Trees are often shaped using hierarchy and all clades are placed in it based on methods that derive shared information Clades that emerge or derived through sharing unique characteristics make it for it one its members for instances anatomical traits that are found related and in embryo logical manner are put togetether by researchers for homolougous Molecular and data sequences can provide other details and insights of ancestries