First macroscopic animal fossils: Neoproterozoic Era (1 Billion–542 Million Years Ago) Early members of the animal fossil record include the Ediacaran biota (from Ediacara Hills of Australia), which dates from 565 to 550 million years ago.

Paleozoic Era (542–251 Million Years Ago) The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals (about half of all extant phyla arose in Cambrian) There are several hypotheses regarding the cause of the Cambrian explosion and decline of Ediacaran biota New predator-prey relationships A rise in atmospheric oxygen The evolution of the Hox gene complex

Pangea 300mya

Animal diversity continued to increase through the Paleozoic, but was disrupted by mass extinctions. Animals began to make an impact on land by 460 million years ago. Vertebrates made the transition to land around 365 million years ago.

Mesozoic Era (251–65.5 Million Years Ago) Coral reefs emerged, becoming important marine ecological niches for other organisms. During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates. The first mammals emerged Flowering plants and insects diversified

Cenozoic Era (65.5 mya - Present) The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals. These extinctions included the large, nonflying dinosaurs and the marine reptiles. Mammals increased in size and exploited vacated ecological niches. The global climate cooled. Chicxulub asteroid

Cambrian Explosion Chicxulub meteor, K-PG extinction – end of dinos Triassic – appearance of dinosaurs and mammals. Pangea starts to breatk into Gondwana and Lurasia PT Extinction – 90% of all marine and 70% of all terrestrial species go extinct Pangea 1st Vertebrates on land “Age of Fish” (Devonian) Cambrian Explosion

Shocked quartz 110mi wide, 12mi deep Irridium dust cloud layer. Meteorites can contain as much as 470ppb, most crust has ~0.4ppb. The clay layer on the K-PG boundary around the world has 6ppm

Percent of marine species to go extinct in a given time.

“Spindle diagram” showing the numbers of families of major vertebrate clades since the Cambrian.

Body plan and symmetry Animals can be categorized according to the symmetry of their bodies, or lack of it Some animals have radial symmetry, with no front and back, or left and right Two-sided symmetry is called bilateral symmetry

Body plan and symmetry Bilaterally symmetrical animals have A dorsal (top) side and a ventral (bottom) side A right and left side Anterior (head) and posterior (tail) ends Cephalization, the development of a head Radial animals are often sessile or planktonic (drifting or weakly swimming) Bilateral animals often move actively and have a central nervous system

Body plan and symmetry

Tissues Animal body plans also vary according to the organization of the animal’s tissues Tissues are collections of specialized cells isolated from other tissues by membranous layers During development, three germ layers give rise to the tissues and organs of the animal embryo

Sponges and a few other groups lack true tissues Diploblastic animals have ectoderm and endoderm These include cnidarians and ctenophora Triploblastic animals also have an intervening mesoderm layer; these include all bilateria: flatworms, arthropods, vertebrates, and others Endoderm – develops into GI tract (except mouth, pharynx, anus), glands of GI tract including liver, lungs, thyroid, and thymus, urinary bladder, urethra Ectoderm – develops into epidermis, nervous tissue, nephridia Mesoderm – other organs and structures (muscle, cartlidge, bone,kidneys, gonads, heart, blood vessels, blood cells, etc

Radial symmetry animals have 2 Germ layers Ectoderm is the germ layer covering the embryo’s surface Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron

Bilateral symmetry animals have 3 Germ layers Ectoderm is the germ layer covering the embryo’s surface Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron Mesoderm is the middle germ layer

Body cavities Most triploblastic animals possess a body cavity (deuterostomes and protostomes) A true body cavity is called a coelom and is derived from mesoderm Coelomates are animals that possess a true coelom

Body cavity formed from mesoderm Body cavity formed from mesoderm and endoderm NO body cavity

Coelomates and pseudocoelomates belong to the same grade A grade is a group whose members share key biological features A grade is not necessarily a clade, an ancestor and all of its descendants

Protostome and Deuterostome development Based on early development, many animals can be categorized as having protostome development or deuterostome development

Protostome and Deuterostome development Protostomes are all other bilateria Deuterostomes are echinoderms and chordates

Protostome and Deuterostome development Distinguished based upon differences in… Cleavage Coelom formation And the fate of the blastophore

archenteron archenteron

Animal phylogeny Phylogenies can be constructed using molecular, morphological and fossil data. The book attempts to discuss the differences of morphological and molecular data phylogenies.

Major molecular and morphological data points of agreement All animals share a common ancestor Sponges are basal animals Eumetazoa is a clade of animals (eumetazoans) with true tissues Most animal phyla belong to the clade Bilateria, and are called bilaterians