Chordate & Vertebrate Characteristics: Zoo 102

• Study notes on the Characteristics of Chordates and Vertebrates
• Prepared by Dr. Lorelie Burgos-Nuñeza, Division of Biological Sciences
• Zoo 102 Comparative Anatomy of Vertebrates

Topics Covered

• Review of evolution
• Definition of terms related to comparative anatomy
• Chordate characteristics
• Vertebrate characteristics – main and satellite features
• Concepts relevant to modern vertebrate morphology

Evolution Overview

• Charles Darwin is associated with the theory of evolution

Descent with Modification

• Species adapt to different environments

Accumulation of Differences

• Differences arise from species' ancestors over time

Natural Selection

• Natural selection is a key element in descent with modification
• Natural environment influences the propagation of specific traits observed in populations

Natural Selection Example

• A population of both black and tan mice moves into an area where the rocks are very dark

Predation

• Tan mice are more visible to predators
• Tan mice are therefore eaten at a higher frequency than black mice

Surviving Mice

• Only surviving mice reach reproductive age and leave offspring

Result

• The next generation has a higher fraction of black mice

Evidence of Evolution

• Fossils- Remains of organisms that lived in the past

Fossils Show Extinct Species

• Fossils show the existence of extinct species that may be related to extant species

Embryology

• Embryology studies of the embryos
• Shows similar structures found in different taxa that are only found in embryos
• Embryos of fish, birds, mammals & reptiles all have gills & tails

Fish Embryos

• All but fish lose their gill slits as adults
• Some species lose their tails

Comparative Anatomy

• Comparative anatomy studies anatomical structures to find similarities and differences

Homologous Structures

• Structures are anatomically similar, but have different functions

Divergent Evolution

• Divergent evolution indicates similar origin

Vestigial Structures

• Vestigial structures are features present in modern animals that are no longer used

Vestigial Structures Function

• Give hints as to the organism evolution.

Vestigial Structures Examples

• Examples of vestigial structures include the human tailbone, whale pelvis, and appendix.

Rate of Evolution

• How rapidly a species evolves can vary

Evolutionary Speed

• Evolution can happen at different rates
• Can be gradual and over a long period of time
• It can also happen relatively quickly
• It can be affected by many factors

Comparative Vertebrate Anatomy

• Descriptive Morphology studies the structure of vertebrates
• Functional Morphology studies functional significance of the structure
• Variation occurs in structure and function in geological time
• Structure is a product of the development of the individual (ONTOGENESIS) and of the species/group (PHYLOGENESIS)

Study of Living Species

• Reveals similarities & differences among animals today

Study of Extinct Species

• Reveals what vertebrates were like in the past
• Assembling data in geological time frame shows a panorama of changes through time

Taxonomic Classification

• Kingdom: Animalia
• Phylum: Chordata

Chordata Subphylums

• Subphylum Urochordata
• Subphylum Cephalochordata
• Subphylum Vertebrata (=Craniata) which includes Vertebrata (craniates with vertebrae) and Hagfish and lamprey* (craniates without jaws)

Chordates

• Chordates have a notochord in embryo, at least

Craniates

• Craniates are chordates with neurocranium (braincase)

Cladogram of Chordates

• Displays the evolutionary relationships among different chordate groups starting from Echinodermata

Chordates share a set of derived characters

• Can exhibit these traits only during embryonic development

Chordate Traits

• Notochord
• Dorsal, hollow nerve cord
• Pharyngeal slits or clefts
• Muscular, post-anal tail

Phylogenetic Tree of Vertebrates

• Shows the evolutionary relationships among vertebrate groups, from sharks to mammals, based on shared characteristics like vertebrae, jaws, bony skeleton, four limbs, amniotic egg, hair, and two post-orbital fenestrae

Vertebrate Characteristics

• Notochord
• Pharynx: pouches, slits & arches
• Dorsal hollow central nervous system
• Vertebral column

Subphylum Features

• The first three characteristics are also chordate features
• The fourth is unique to Subphylum Vertebrata

Notochord

• Notochord is the 1st skeletal structure to appear
• Located ventral to the central nervous system (CNS) & dorsal to alimentary tract
• Made of a rod of living cells

Notochord Development

• Head region: incorporated in the floor of the skull
• Trunk and Tail: surrounded by cartilaginous vertebrae (excepts for Agnathans)
• Provides support around the body

Notochord in Fish and Amphibians

• Persists but constricted within the centrum of each vertebrae

Notochord in Cartilaginous Fish

• Retained in adulthood, surrounded by cartilaginous vertebrae

Notochord in Reptiles, Birds, Mammals

• Visible in early embryos
• Eventually obliterated during development

Pulpy Nucleus

• The Pulpy nucleus is a vestige in mammals, within intervertebral disc; not found in modern birds & reptiles

Clarification on Notochord in Lampreys

• Notochord grows along with the animals with paired lateral neural cartilages
• The cartilages rest in the notochord lateral to the spinal cord

Pharynx

• Pharyngeal Pouches: Arise as diverticula of pharyngeal endoderm which grow towards the surface

Pharyngeal Slits

• Formed in pouch met by ingrowing ectodermal groove

Pharyngeal Slits Outcome

• Fishes’ become permanent gills
• Amphibians become temporary larval gills
• Reptiles, birds, and mammals’ are absent in adulthood

In tetrapods

• 1st pharyngeal slit becomes the auditory tube and middle ear cavity.
• 2nd persists as the pouch of the palatine tonsil

Pharyngeal Arches

• Tissue column that separates each pharyngeal pouch or slit

Component of the Pharyngeal Arches

• Skeletal elements become Visceral skeleton
• Striated muscle becomes branchiomeric muscles
• Cranial nerves become 5th, 6th, 9th or 10th
• Aortic Arches connect the dorsal and ventral aortas

Fates of Pharyngeal Arches

• 7 total
• 1st: mandibular arch
• 2nd: Hyoid arch
• 3rd to 7th : branchial arches

Dorsal Hollow Central Nervous System

• Develops into the central nervous system: brain and spinal cords
• Develops from a plate of ectoderm that rolls into a tube dorsal to notochord

Post Anal Tail

• The Posterior elongation of the body extending beyond the anus
• In some species, like humans, this feature is only present during the embryonic stage or become a vestigial structure

General Body Plan of Vertebrates

• Regional differentiation (Head, Trunk & Tail)
• Bilateral symmetry and anatomical planes
• Metamerism

General Plan of Craniate Body

• Regional differentiation
• Head consists of special sense organs to monitor env.
• Brain to receive & process incoming info
• Jaws for food intake
• Gills for respiration
• Trunk has a coelom housing the viscera; neck (narrow extension of trunk, no coelom)
• The Postanal tail starts at the anus
• Caudal continuation of body wall muscles, axial skeleton, nerves & blood vessels
• 2 pairs of appendages (pectoral and pelvic girdles)

Bilateral Symmetry & Anatomical Planes

• 3 principal body axes: longitudinal (anteroposterior) axis, dorsoventral axis, and left-right axis which has identical structures

Metamerism

• Metamerism consist of repeated segments

Principal Anatomical Planes

• Cross section/transverse cut thru transverse plane formed by the left- right & dorso-ventral
• Frontal section cut thru frontal plane formed by left-right & longitudinal axes
• Sagittal section cut thru sagittal plane formed by longitudinal & dorsoventral axes

Satellite Characteristics of Vertebrates

• Integument consists of 2 layers of epidermis (multilayered) & dermis
• Digestive contains complete; ventral & specialized regions; ceca or diverticula, liver & pancreas; ends in cloaca; opens in anus
• Coelom consist of pericardial & pleuroperitonial (pleural & abdominal) and scrotal cavities
• Respiratory consists of gills and lungs
• Circulatory consists of a closed circulatory system with a heart, blood vessels, and blood