Deuterostome Animals

Lecture 12 - Deuterostome Animals

Outline

  • Introduction

  • What is an Echinoderm?
      - Lineages   - Hemichordates

  • What is a Chordate?
      - Cephalochordates
      - Urochordates

  • What is a Vertebrate?
      - Jawless fishes
      - Jawed fishes
      - Tetrapods
        - Amphibians
        - Amniotes
        - Mammals
        - Reptiles
        - Birds
        - Primates & Homo sapiens

Introduction

  • Deuterostomes include some of the largest-bodied and morphologically complex animals.

  • Traditionally, considered monophyletic due to:
      - Gut development occurs in a posterior-to-anterior direction (anus develops first).
      - Coelom develops from out-pocketing of mesoderm.

  • This monophyly is supported by molecular studies.

Echinodermata

  • Characteristic of "spiny skin" and exclusively marine.

  • Main synapomorphies:
      - Radial symmetry (pentaradial) in adults; however, larvae exhibit bilateral symmetry.
      - Endoskeleton made of calcium carbonate.
      - Water vascular system with tube feet.

Endoskeleton & Water Vascular System

  • Endoskeleton:
      - A protective and supportive structure located internally beneath a thin layer of epidermal tissue.
      - Forms via the secretion of calcium carbonate plates within the skin.
        - These plates can either fuse to form rigid structures or remain independent, creating flexible support.

  • Water vascular system:
      - A network of branching, fluid-filled tubes and chambers forming a hydrostatic skeleton.
      - Tube feet:
        - Elongated, fluid-filled appendages that play a role in locomotion and feeding.

Class Crinoidea

  • Includes feather stars and sea lilies.
      - Approximately 600 species exist, primarily sessile filter feeders.
      - Most abundant during the Paleozoic era, around 488 million years ago with over 5000 species.
      - 80 stalked species notably inhabit deep waters, whereas 540 stalk-less species are widespread.

Class Asteroidea

  • Comprising sea stars and sea daisies, with around 1,900 species that are primarily predators and scavengers.
      - Sea daisies (3 species) are unique as they reside on submerged wood and absorb nutrients through a membrane encompassing their bodies.
      - Notable species include Pisaster sp., Asterias sp., and the Crown of Thorns (Acanthaster planci).

Class Ophiuroidea

  • Includes brittle and basket stars with approximately 2,100 species recognized as predators, scavengers, and detritivores.
      - Move using their arms; most organs are located in a centralized disk.

Class Echinoidea

  • Comprised of sea urchins and sand dollars, with around 1,000 species.
      - Sea urchins predominantly act as herbivores, while sand dollars are deposit feeders.
      - They possess a jaw-like structure in their mouths, known as Aristotle’s lantern, formed by five calcium carbonate teeth meeting in the center, operated by muscles capable of extension and retraction during feeding.

Class Holothuroidea

  • Sea cucumbers account for about 1,250 species engaging in suspension or deposit feeding.
      - They feature reduced or completely absent internal skeletons.
      - A notable species includes Scotoplanes known as the sea pig.

Phylum Hemichordata

  • Comprising acorn worms with 111 marine species.
      - Possess a stomochord instead of a notochord for support.
      - Lacking a postanal tail, these organisms can burrow, deposit feed, or suspension feed.

Phylum Chordata

  • Chordates exhibit four key morphological features at some life stage:
      1. Pharyngeal gill slits as openings in the throat.
      2. A dorsal hollow nerve cord extending the length of the body formed from neuronal projections.
      3. A notochord that is a stiff yet flexible supportive rod running the body’s length.
      4. A muscular post-anal tail.

Chordata Phylogeny

  • Based on key features:
      - Openings in the throat called pharyngeal gill slits.
      - Dorsal hollow nerve cord, notochord, and muscular post-anal tail.
      - Inclusive of various subdivisions and evolutionary progressions stemming from early Chordata.

Subphylum Cephalochordata

  • Commonly referred to as lancelets with about 25 marine species.
      - Small, averaging 6 cm in length, they are mobile suspension feeders displaying fish-like movement.
      - Important features include pharyngeal slits or pouches, a dorsal hollow nerve cord, a notochord, muscular post-anal tail, and a mouth.

Subphylum Urochordata

  • Encompasses tunicates and sea squirts comprising about 2,000 marine species primarily engaging in suspension feeding.
      - The excurrent siphon serves as a defense mechanism expelling jets of water at attackers.
      - Notably, tunicates have reduced Hox genes—only nine compared to thirteen in other vertebrates.

Subphylum Vertebrata

  • Distinguishing features include the spinal cord evolved from dorsal hollow nerve cords and the vertebral column, which replaces the notochord for support.

  • Key synapomorphies include:
      - Vertebrae: structures forming a column of cartilage or bone.
      - Cranium: a protective casing for the brain composed of bone, cartilage, or fibrous material.

  • The functions of these features revolve around safeguarding the central nervous system.

Phylogenetic Diversity of Vertebrata

  • Includes classification across diverse vertebrate classes:
      - Ray-finned fishes, amphibians, turtles, sharks, rays, skates, mammals, and representatives such as hagfishes and lampreys.
      - Progressive evolutionary traits such as loss of vertebrae, development of jaw structures; and adaptation for diverse environments are featured in various lineages.

Myxinoidea

  • Hagfishes consist of approximately 78 marine species that are scavengers and predators.
      - They possess a cranium but lack vertebrae, jaws, and paired appendages; the notochord serves as supportive structure.
      - Noteworthy defense mechanism includes slime excretion.
      - Following reproductive cycles, eggs hatch into juvenile forms.

Petromyzontoidea

  • Lampreys encompass around 46 species of ectoparasites that inhabit marine and freshwater environments.
      - They utilize suckers to feed on blood and other bodily fluids.
      - Their anatomy includes a cartilage structure along the nerve cord, but they lack jaws or paired appendages.
      - Life cycle involves hatching into lancelet-like larvae.

Jawed Fishes

  • The appearance of jawed fishes is noted in the fossil record as early as 430 million years ago.

  • Innovations with jaws improved predatory capabilities and biting actions.
      - Synapomorphies of gnathostomes (jawed vertebrates) include:
        - Paired fins, internal fertilization, and presence of a neck.
        - Genome duplication resulting in four sets of Hox genes.
        - Enlarged forebrain enhancing olfactory and visual senses.
        - Development of the lateral line system in aquatic species with rows of sensory organs detecting vibrations along the body sides.

Other Synapomorphies of Jawed Fishes

  • Endoskeleton: Initially cartilaginous, becomes stiffened by the deposition of bone.

  • Bone Formation:
      - Early dermal bone is ectodermally derived; bony endoskeleton originates from mesoderm.

  • Swim Bladder Origin:
      - First appeared in ancient types of fishes (placoderms). Originated as auxiliary respiratory structures from esophageal outpocketings, lost in cartilaginous fishes while evolving into swim bladders in ray-finned fishes.

  • Origin-of-lung Hypothesis:
      - Early fish acquired lung functionality by gulping air or secreting oxygen from internal tissues.

Gill-Arch Hypothesis

  • Gill arches are curved tissue regions situated between gills.

  • The anterior arch evolved, showing size enhancement and a change in orientation.
      - Evidences indicate:
        - Both gill arches and jaws consist of similar bars of bony or cartilaginous tissue that hinge and can flex forward, with developmental backgrounds from the same embryonic cell populations (neural crest cells).
        - Developmental regulatory genes, such as Hox and Dlx, exhibit comparable expression patterns in both structures.

Chondrichthyes

  • Including sharks, rays, and skates, amounting to 1,200 marine species (some extending into freshwater).
      - Display a cartilaginous skeleton equipped with jaws and paired lateral fins.
      - Predatory lifestyle and some employ filter-feeding mechanisms.
      - Absence of swim bladders compensated by an oily liver, possessing placoid scales and 5-7 gill openings.
      - Cloaca: serves as a single outlet for waste and reproductive functions.

Local Chondrichthyan Species

  • Common species include Horn Shark (Heterodontus francisci), Great White Shark, and Common Thresher (Alopias vulpinus).

Size Comparison

  • The Great White Shark (Carchardon carcharias) has varying sizes, while the now-extinct Carcharodon megalodon demonstrated significant size disparities around 1.5 million years ago.

  • Whale Shark (Rhincodon typus), ranging from 26 to 72 feet in length, and species such as Tiger Shark (Galeocerdo cuvier) reflect diverse sizes within the Chondrichthyes.

Actinopterygii

  • Known as ray-finned fishes, accounting for over 32,200 marine and freshwater species.
      - Characterized by a bony (calcium carbonate) skeleton where fins are supported by long bony rods structured in ray patterns.
      - First appearances record around 430 million years ago.

External Anatomy of Actinopterygii

  • Most species exhibit oviparity, with external fertilization.

  • Gills are guard by a bony flap known as operculum.

  • Skin is covered by bony scales, with mucous secretions aiding in reducing hydrodynamic drag.

Internal Anatomy of Actinopterygii

  • Possess a gas-filled swim bladder that aids in buoyancy.

  • The lateral line system, appearing as a series of tiny pits along the body, serves to detect movements and vibrations in the water.

Sarcopterygii

  • Referring to lobe-finned fishes and tetrapods, emerged in the Silurian period, around 430 million years ago.
      - Pectoral and pelvic fins feature rod-shaped bones encompassed by thick muscular layers, facilitating mobility across substrates in aquatic habitats.

Classes of Sarcopterygii

  • Actinistia (Coelacanths):
      - Recognized with 2 known marine species, showcasing four fleshy lobed fins backed by bones with a unique skull hinge allowing wide jaw openings. Rediscovered in 1938, previously thought extinct for 65 million years.

  • Dipnoi (Lungfishes):
      - Contains 6 known freshwater species that inhale air into lungs attached to their pharynx or gills.
      - Notably have four lobed fins and can utilize swimming and crawling in shallow pools.
      - Exhibit omnivorous feeding habits.

Tetrapod Deuterostome Animals

  • Synapomorphies that characterize tetrapods include:
      - Development of four limbs and feet with digits.
      - Adaptation of a neck allowing head movement independence.
      - Pelvic girdle integration with the vertebral column.
      - Absence of gills in all but certain aquatic species.
      - Functionality of ears adapted for airborne sound detection.

Origin of Tetrapod Limbs

  • Approximately 365 million years ago (late Devonian), vertebrates transitioned to terrestrial environments.

  • The Limbs-from-Fins hypothesis posits that shared regulatory proteins dictate the development of limbs in both fishes and tetrapods, supported by fossil records revealing transitional forms.

Transitional Forms

  • Key transitional species include Tiktaalik rosaea, Eusthenopteron, and Panderichthys, each displaying limb structures that arise from fin anatomy, offering vital insight into the evolution of terrestrial locomotion.

Amphibia

  • Amphibians represent the first tetrapods to inhabit terrestrial zones.
      - Adult stages predominantly engage in terrestrial feeding but reproduce in aquatic environments.
      - Most undergo metamorphosis, and gas exchange occurs through moist skin as well as lungs.

Orders of Amphibia

  • Order Anura:
      - Encompasses around 7,600 species such as frogs and toads, with adult forms lacking tails and employing sit-and-wait predatory strategies, utilizing extensible tongues.
      - Exhibit vocalizations for territory defense and mating attraction; reproduction is typically external with a noticeable metamorphosis from herbivorous tadpoles.

  • Order Urodela:
      - Salamanders account for 800 species retaining tails in both larval and adult stages, featuring carnivorous feeding habits using extensible tongues for terrestrial varieties and jaws for aquatic types.
      - Internal fertilization is common during reproduction.

  • Order Gymnophiona (Apoda):
      - Consists of 220 species that are limbless, snake-like amphibians preying on earthworms in soil or aquatic invertebrates.
      - Predominantly exhibit internal fertilization with a majority being viviparous.

New Findings in Caecilians

  • Some caecilian species have shown milk provisioning behaviors towards hatchlings, evolving more complex parental care methods that resemble lactation, observed in maternal feeding patterns.

Origin of Amniotes

  • The amniotic egg is a significant synapomorphy, offering protective encasements that mitigate dehydration rates, facilitating life beyond aquatic environments.

Amniote Phylogeny

  • Early amniotes diverged from a common ancestor with amphibians around 350 million years ago.

  • Initially, they thrived in warm, moist environments (during the Carboniferous) and were small lizard-like predators, with herbivores appearing in later evolutionary stages.

Reptilia

  • Distinct synapomorphies include:
      - Scales composed of keratin that protect against desiccation.   - Majority birth through laying shelled eggs on land, offering drying protection.
      - Internal fertilization occurs before shell secretion in egg-laying processes.
      - Mostly ectothermic, with the exception of birds, and have well-developed lungs.

Testudinia

  • Specifically refers to turtles, constituting about 360 species shielded by bony shells.
      - Predation varies; marine and freshwater forms are typically carnivorous, while terrestrial tortoises are herbivorous.
      - All are oviparous, lacking parental care, with two lineages emerging concerning head retraction capabilities—side-necked and vertical-necked turtles.

Lepidosauria

  • Contains approximately 11,500 ectothermic species, with smaller lizards generally being carnivorous and larger ones herbivorous.
      - Primary reproduction methods are oviparous or ovoviviparous, with unique species such as tuataras endemic to specific island locales off New Zealand.

Crocodilia

  • Comprised of 27 species of ambush predators, featuring eyes and nostrils positioned high on their heads.
      - Lays eggs and engages in complex parental care behaviors, with a lineage traceable to the Triassic period originating from small terrestrial quadrupeds.

Aves

  • Derived traits include absence of urinary bladders, singular ovarian presence in females, small gonad sizes in both sexes, lack of teeth, and air-filled bones characterized by honeycombed internal structures.

  • Feathers are formed from β-keratin, evolved as adaptations for insulation, camouflage, or courtship prior to the advent of powered flight.

Origin & Characteristics of Birds

  • The evolution of feathers is hypothesized to predate powered flight, and by 160 million years ago, feathered theropods had evolved into birds, such as Archaeopteryx, which marks the oldest known bird.

  • Neornithines include extant birds, encompassing 28 orders with over 11,200 species, showing characteristics optimized for flight, social behaviors, and reproductive strategies.

Early Synapsids

  • Early non-mammalian synapsids displayed characteristics such as absence of hair, sprawling gaits, and egg-laying reproductive strategies rooted in the Permian period.
      - Synapsid evolution reflected gradual jaw modifications leading to complex structures supporting mammal-like ear bones emerging by the end of the Triassic, with true mammals first appearing during the Jurassic era.

Mammalia

  • Mammals display a number of derived traits such as mammary glands for lactation, presence of hair, and adaptations for improved metabolic rates and thermoregulation.
      - Notable traits include a larger brain-to-body-size ratio, extensive parental care, and specialized dentition suited to diverse diets.

Phylogeny of Mammalia

  • Organizational distinctions include:
      - Monotremes: Egg-laying mammals (5 species) native to Australia and New Guinea.
        - Notable for lower metabolic rates and unique feeding methods.   - Marsupials: Emphasize live young birth with extensive care, including development in pouches (spanning 387 species).
        - Diverse nutrition strategies correlate with ecological conditions across different habitats.   - Eutherians: Representing 6,150 species, they possess complex placental structures with extended gestation methods across various feeding types and ecological adaptations.

Primates

  • Characterized by derived traits including adaptations for grasping and increased brain capacity.
      - Two principal groups include prosimians and anthropoids, exhibiting diverse behaviors and social structures.

Evolution of Anthropoids

  • Monkeys diversify under different ecological pressures in the Old World and the New World.
      - Apes are less arboreal than their monkey relatives and show complex social behaviors.

Hominids & Hominins

  • Notably, leveraging tools and chronicling evolution to understand the lineage leading to modern humans, including significant transitions such as bipedalism and dietary adaptations.

Early Hominins

  • Early hominins reveal substantial morphological distinctions compared to contemporary humans, marking the evolutionary path leading to advanced species such as Homo ergaster and Homo erectus, who exhibited novel behaviors and adaptations that enabled survival across diverse environments.

Recent Discoveries

  • Fossils of earlier human relatives, including Homo floresiensis (nicknamed "Hobbit") and Homo naledi, reveal nuances in evolutionary history and adaptations.

Homo sapiens

  • Fossils dating as far back as 300,000 years elucidate the evolution of Homo sapiens, showcasing significant cognitive and social complexities.
      - The out-of-Africa hypothesis posits origins in Africa with subsequent global dispersibility evidenced through varied genetic lineages leading to contemporary human diversity.