Echinodermata: Deuterostome Phylogeny

Deuterostomes

• Echinodermata and Chordata are the two phyla of deuterostomes.

Echinoderm Phylogeny

• Echinodermata is classified under Deuterostomes phylogenetically.
• Deuterostomes are a superphylum of animals.
• Protostomes are broken up into 2 groups: Lophotrochozoa and Ecdysozoa

Phylum Echinodermata

• These are exclusively marine animals.
• They are deuterostomes characterized by an endoskeleton made of calcium carbonate plates covered by living tissue.
• They exhibit pentaradial symmetry as adults but have bilateral symmetry as larvae.
• Members include sea stars, brittle stars, sea urchins, sand dollars, and sea cucumbers.
• Echinodermata’s precise origin is unknown but thought to have evolved from bilaterally symmetrical ancestors given the larvae symmetry.
• The free-swimming larva of the common sea star, Asterias rubens is bilateral.
• Adult sea stars display pentaradial symmetry.

Echinoderm Body Plan

• Have a hydraulic system aiding movement or feeding.
• This fluid-filled water-vascular system consists of a central ring canal from which radial canals extend.
• The madreporite is the opening/entrance to the water vascular system.
• Radial canals transport liquid to the tube feet.
• The tube foot extends and attaches to the substrate when the ampulla contracts.
• The tube foot bends and pulls the animal forward when muscles in tube feet contract.

Symmetry

• Echinoderms are pentaradial as adults, bilateral as larvae.
• The mouth defines the oral surface.
• Systems are organized with branches radiating from the center.
• The nervous system is a nerve ring with branches and no centralization of function.

Phylum Chordata

• Chordate endoskeletons differ greatly from echinoderm endoskeletons.
• Chordate endoskeletons are truly internal.
• However, echinoderm endoskeletons are functionally comparable to arthropod exoskeletons.
• Fish, amphibians, reptiles, birds, and mammals are chordates.

Chordate Characteristics

• All chordates possess four key characteristics at some point:
  • Nerve cord
  • Notochord, which may be replaced by a vertebral column
  • Pharyngeal slits, which become gills or pharyngeal pouches in terrestrial vertebrates
  • Postanal tail (nearly all other animals have a terminal anus)
• Chordate muscles are arranged in segmented blocks known as somites.
• Most chordates also have an internal skeleton which the muscles work against.
• Chordata are split into 3 subphyla
  • Urochordata (~Tunicata): Larvae have notochord and nerve cord, but adults typically lose the tail, notochord and nerve cord; sea squirts
  • Cephalochordata: Notochord persists throughout the life of the animal
  • Vertebrata

Characteristics Of Chordates

• Vertebrates, tunicates, and lancelets are chordates and coelomate animals.
• Chordates have a flexible notochord that provides resistance to muscle contraction which permits rapid lateral body movements.
• Chordates have pharyngeal pouches or slits reflecting aquatic ancestry and present habitat and a hollow dorsal nerve cord.
• The notochord gets replaced during embryonic development by the vertebral column in vertebrates.

Subphylum Vertebrata

• Vertebrates are chordates with a spinal column.
• Vertebrates are distinguished from nonvertebrates by:
  • Vertebral column encloses and protects the dorsal nerve cord.
  • Head is distinct and well-differentiated possessing sensory organs.
• Vertebrates also have:
  • Neural crest: unique group of embryonic cells forming vertebrate structures
  • Internal organs: liver, kidneys, endocrine glands, heart, and closed circulatory system
  • Endoskeleton: made of cartilage or bone and enables great size and extraordinary movement

History Of The Vertebrates

• They first appeared in the oceans and had mouths at one end and fins at the other 545 MYA.
• Jawed fish later became dominant.
• Amphibians then invaded the land.
• Reptiles then replaced them as the dominant land vertebrates.
• Birds and mammals then became dominant after the Cretaceous mass extinction (~65 MYA) when the dinosaurs disappeared.

Phylogeny of the Living Vertebrates

• A phylogeny of the living vertebrate groups shows key evolving characteristics, including:
  • Rayed & Lobed fins
  • Jaws, internal bony skeleton
  • Mammary glands, 4-chamber heart, hair

Fishes

• The most diverse vertebrate group which includes many different species across classes.
• Over half of all vertebrates are fishes.
• Fishes provided the evolutionary base for amphibians' land invasion.
• Distinguishing features include:
  • Vertebral column
  • Jaws and paired appendages
  • Internal gills
  • Single-loop blood circulation
  • Nutritional deficiencies

History Of Fish

• The first fish had mouths with no jaws.
  • Agnatha (class Myxini) as hagfish and lampreys (class Cephalaspidomorphi), are extant.
  • Ostracoderms are now extinct.
• The development of jaws occurred in the late Silurian period.
• Jaws evolved from the anterior gill arches made of cartilage.

Evolution of the Jaw

• Jaws evolved from the anterior gill arches of ancient, jawless fishes.

Groups of Bony Fish

• Ray-finned fishes (class Actinopterygii): Parallel bony rays support and stiffen fins without intrinsic muscles.
• Lobe-finned fishes (class Sarcopterygii): Fins consist of a long fleshy muscular lobe supported by a central bone core with fully articulated joints.
  • They are almost certainty amphibian ancestors.

Class Amphibia

• First vertebrates to walk on land.
• Direct descendants of fishes.
• Three orders of Amphibians exist:
  • Anura: Frogs and Toads
  • Caudata: Salamanders and Newts
  • Apoda: Caecillians
• There are 5 Distinguishing Amphibian Features
  • Legs - adaptation to life on land
  • Lungs
  • Cutaneous respiration – supplement lungs
  • Pulmonary veins - separate pulmonary circuit which allows higher pressure blood to tissues
  • Partially divided heart – improves separation of pulmonary and systemic circuits
  • Lungs to extract oxygen from air
  • Redesigned heart and circulatory system to drive larger muscles
  • Reproduction still in water to prevent egg drying.
  • System to prevent whole body desiccation.

Successful Invasion Of Land By Vertebrates Require

• Legs to support body's weight.
• Lungs to extract oxygen from air.
• Redesigned heart and circulatory system to drive larger muscles.
• Reproduction still in water to prevent egg drying.
• System to prevent whole body desiccation.
• Ichthyostega was one of the first amphibians evolving from lobe-finned fish.
• Ichthyostega had sturdy forelegs, flipper-shaped hindlimbs and are thought to move like a seal.
• Long, broad, overlapping ribs form a solid cage for lungs and heart.
• Tiktaalik was a transitional fossil found in 2006 between fish and Ichthyostega.
• Tiktaalik also had gills and scales like a fish and a neck like an amphibian.
• Its shoulder, forearm, and wrist bones were like those of amphibians, but the end of the limb was a lobed fin instead of toes.

Class Reptilia

• Reptilia has over 10,000 living species.
• All living reptiles have three features:
  • Amniotic eggs are watertight.
  • Dry skin covers the body and prevents water loss.
  • Thoracic breathing increases lung capacity.

Amniotic Eggs

• Reptiles, birds, and mammals are amniotes.
• The amniotic egg has the following 4 membranes:
  • Chorion: Outermost layer for gas exchange
  • Amnion: Encases embryo in fluid-filled cavity
  • Yolk sac: Provides food
  • Allantois: Contains excreted wastes from embryo
• Reptiles are categorized by skull type:
  • Anapsids
  • Synapsids
  • Diapsids

Reptile Orders

• Include:
  • Lizards
  • Snakes
  • Tuataras
  • Turtles
  • Crocodiles
  • Stegosaur
  • Tyrannosaurus
  • Pterosaur
  • Plesiosaur
  • Ichthyosaur
• Reptiles are divided into Amniotic, Diapsid and Synapsid classifications.

Anapsids, Synapsids, and Diapsids

• Reptiles dominated earth for 250 million years.
• They are distinguished by the number of holes on the side of the skull behind the eye orbit:
  • 0 (anapsids)
  • 1 (synapsids): dominate first but mostly extinct except mammals
  • 2 (diapsids): include largest animals to that point and gave rise to dinosaurs, crocodiles, and birds
  • Dinosaurs dominated for over 150 million years and became extinct 65 MYA due to an asteroid impact.
  • The only descendants are birds.
• Modern reptiles have two important characteristics:
  • Internal fertilization: Sperm fertilizes egg before protective membranes form.
  • Improved circulation: Oxygen is provided more efficiently, with the septum in the heart improved to extend a partial wall and crocodiles, birds, and mammals have fully divided 4-chambered hearts.

Birds

• Birds (Class Aves) are the most diverse of all terrestrial vertebrates, with over 10,000 species.
• Success lies in unique feather structure — feathers developed from reptile scales.
• Birds retain reptilian traits: amniotic eggs and scales on legs.
• Their distinguishing traits include:
  • Feathers: provide lift for flight and conserve heat, are modified scales of keratin
  • Flight skeleton: Bones are thin and hollow and many are fused for rigidity anchoring strong flight muscles, while the keeled breastbone provides attachment for flight muscles.
• Feathers developed reptile scales.
• Linked structures provide continuous surface and a sturdy but flexible shape.
• Archaeopteryx are first known bird species
• Had skull with teeth and are long-reptilian-tailed.
• Feathers attached to wings and at the tail.
• Exhibit one theropod line which evolved to become the bird.
• Forelimbs are almost identical to those of theropods (“beast-footed” dinosaurs).
• They likely have an evolved feather for insulation.
• Birds Are the Direct Descendants of Theropod Dinosaurs which were the most fearsome land predators the Earth has ever seen!, a clade that includes T-rex.

Class Mammalia

• There are only 5,000 species.
• Almost 4,000 species are rodents, bats, shrews, or moles.
• Mammals also boast:
  • Hair: Long, keratin-rich filaments that extend from hair follicles and provide insulation, camouflage, and sensory structure.
  • Mammary glands: Females possess mammary glands that secrete milk.

History Of Mammals

• They have been around since dinosaurs (~220 MYA).
• Tiny, shrewlike, insect-eating, tree-dwelling, and may have been nocturnal.
• Mammals reached maximum diversity in the Tertiary period (65 to 2 MYA) after the mass extinction of dinosaurs.
• The total number of mammalian species has declined over the last 15 million years.
• Mammalia is broken up into two subclasses
  • Prototheria: Characterized as the most primitive and includes monotremes that lay shelled eggs (oviparous) include.
  • Theria, characterized as Viviparous - young are born alive with two living groups that include:
    • Marsupials which have pouched mammals
    • Placental mammals which are the largest group.

Monotremes

• Lay shelled eggs like reptiles.
• They have a single opening (cloaca) for feces, urine, and reproduction.
• Lack well-developed nipples.
• Only three living species are left:
  • Duck-billed platypus (right)
  • Two echidna species (left)

Marsupials

• The major difference related to embryonic development is a short-lived placenta.
• Marsupials find the marsupial pouch after birth, latches onto nipple, and continues to develop
• Kangaroo and Opossum are examples of marsupials.
• Placental mammals produce a true placenta that nourishes an embryo throughout development.
• It forms from fetal and maternal tissues with developed young.

The Placenta

• Its a characteristic of placental mammals
• They evolved from membranes in the amniotic egg.
• Chorion, the outermost part of the amniotic egg which forms most of the placenta itself.
• It serves as the provisional lungs, intestine, and kidneys of the fetus but does not ever mix maternal and fetal blood.
• The umbilical cord evolved from the allantoisto

Evolution of Primates

• The primates are mammals that gave rise to people.
• Primates have evolved two features suited for an arboreal environment:
  • Grasping digits (fingers and toes)
  • Binocular vision to enable depth perception.
• Prosimians include lemurs, lorises, and tarsiers and are now considered to be paraphyletic.
• Anthropoids Monkeys, apes and humans nearly, all diurnal, have color vision, and live in social groups.

Anthropod History

• About 30 MYA:
  • New World monkeys migrated to South America, are arboreal, and have prehensile tails.
  • Old World monkeys and hominids remained in Africa.
• Hominoids Include:
  • Apes: gibbon, orangutan, gorilla, and chimpanzee with larger brains than monkeys and lack tails and may be more related to hominoids.
  • Hominids: humans, orangs, gorillas, and chimps and the common ancestor diverged from chimpanzees and began the evolution of humans.

Hominids vs Hominins

• The Hominid common ancestor (i.e. chimps + orangs + gorillas + hominins) is thought to have been an arboreal climber.
• Hominins Became Bipedal.
• Apes remained knuckle-walking.
• Differences Related to Bipedal Locomotion:
  • The human vertebral column is more curved.
  • Spinal cord exits the bottom of the skull.
  • Humans carry much of the body's weight on the lower limbs.
• Earliest of these Hominins include
  • Australopithecus, Genus with 7 older and smaller-brained species.
  • Homo
    • Genus with 3-7 species
    • Hallmark is that hominins are bipedal throughout all the lineages found so far.

Modern Humans

• Modern Humans first appeared in Africa about 600,000 years ago.
• Have Three evolved species:
  • Homo heidelbergensis (Oldest) - May have Coexisted with Homo Erectus.
  • Homo Neanderthalensis - Shorter, stockier than modern humans (homo sapiens).
  • Homo Sapiens (“Wise man”).
  • Lumped into Three Categories in total.
• There are different Human ‘Races’
• Human beings differentiated traits around the world. All these humans are capable of mating fertile offspring.
• Humans now rely on skin tone to define races due to visual cues.

Homo Sapiens

• As the only Surviving Hominin, they continue to present;
  • Progressive Increase, Effective Tool and Making Usage, Refined Conceptual Thought Usage.
• There are extensive amounts of cultural experiences exhibited.
• Humans now change and mold the world rather than evolutionary changes to survival of environment.
• Human groupings are different than skin and visual similarity.