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evidence of connective link // example and detail explanation - science info
A connective link demonstrates the characteristics of more than one group of organisms (taxonomically). Such organisms establish continuity in the series by proving that one group has evolved from the other.
VIRUSES
A connective link between non-living and living is any virus-like bacteriophage (the virus that infects bacteria)
the genetic material of the virus is basically RNA ( ribonucleic acid)
viruses are non-living organism
Affinity with the non-living organism
(1) Theas can be crystallized like inorganic and organic compounds.
(2) These are unable to respond to external stimuli.
(3) Cell organelles are absent.
(4) Lack of growth and metabolism.
Affinity with a living organism
(1) These under mutation.
(2) These reproduce in the living cells.
(3) These show recombination and heritability.
Euglena
A connecting link between the animals and plant,
reason-based to the connective link between the animals and plant a euglena present the chloroplast basically animals has heterotropic hence animals do not present the chloroplast, but euglena present the chloroplast hence, euglena called the connective link between the animals and plant.
Affinities with animals
(1) Body is covered by a pellicle.
(2) reproduction is like animals.
(3) some characters are matched with animals.
Affinities with plants
(1) It has chloroplast containing chlorophyll.
(2) Nutrition is holotypic or autotrophic.
(3) It may synthesize food through photosynthesis.
proterosongia
It shares the characters of the group protozoa and Porifera.
Affinities with protozoan and sponges
(1) protozoan characters: Colonial behaviour.
(2) Spong's characters: Its cells are similar to choanocytes or collar cells of sponges.
peripatus
A connective link between the Annelida and Arthropoda.
Affinity with annelids
(1) Presence of thick cuticle.
(2) Present of simple eyes.
(3) Body is pseudosegmented and worm-like appearance.
(4) Excretory organ is nephridia.
Affinities with arthropods
(1) Presence of antennae.
(2) Respiratory organ is the trachea.
(3) Presence of clawed and pseudosegmented walking legs.
Neopilina
A connecting link between Annelida and Mollusca.
Affinities with annelids:
(1) Presence of trochophore larva.
(2) Egg divides by spiral cleavage as in polychaetes.
(3) presence of 5-6 pairs of ctenidia, 6 pairs of nephridia, 8 pairs of retracted muscles and two pairs of auricles.
Affinities with molluscs:
(1) Presence of shell and mantle.
(2) Presence of flat muscular fool as found in a chiton.
(3) Presence of soft and dorsoventrally flattened body.
Balanoglossus
A connective link between non-chordates and chordates.
Affinities with chordates.
(1) Presence of notochord.
(2) Presence of a dorsal hollow nerve cord.
(3) Presence of pharyngeal gill slits.
Affinities with non-chordates.
(1) Burrowing habit and tubicolous life.
(2) Dorsal position of the heart.
(3) Nervous system is poorly developed and forms epidermal nerve plexus.
Chimaera
A connecting link between bony fishes and cartilaginous fishes.
Affinities with bony fish.
(1) Presence of four pairs of gills.
(2) Presence of smallmouth with flesh lips.
(3) cloaca remains absent.
(4) Anus and urinogenital apertures are separate.
(5) Presence of operculum.
Affinities with cartilaginous fish
(1) Presence of ventral mouth.
(2) Presence of cartilaginous endoskeleton.
(3) Pelvic claspers presence in males.
(4) Presence of 2 dorsal fins.
(5) Placoid scales presence in young ones.
Lung fishes
Lung fishes are the connective link between the fishes and amphibian.
Affinities with fish
(1) Fish like appearance.
(2) Presence of paired fins.
(3) Presence of dermal scales.
(4) Presence of gills.
(5) Presence of lateral line sense organ.
(6) Ear is represented by internal air only.
Affinities with amphibian
(1) Presence of internal nostrils.
(2) Presence of lung, i.e. modified air bladder.
(3) Heart with imperfectly divided auricle.
Prototheria
Echidna (spiny anteater) and Ornithorhynchus (platypus) are connecting link between reptile and mammals.
Affinities with reptiles.
(1) Presence of cloaca.
(2) They lay eggs, which are reptile in structure and development.
(3) Egg contain enough yolk to nourish in structure and development.
(4) Embryonic development is similar to reptiles.
Affinities with mammals.
(1) Presence of hairs.
(2) They produce milk and nourish their children.
(3) They have mammary glands.
Archaeopteryx
It is a connective link between reptiles and birds. Archaeopteryx is also considered as a missing link because it is a fossil organism. it was found in the rock of cretaceous period by Andreas Wagner (1861) in Germany.
Some reptile characters of Archaeopteryx are given below
(1) Jaw are provided with homodont (similar) teeth.
(2)
(3) Bone are not pneumatic.
(4) Cervical vertebrae are fewer, 9-19.
(5) Amphicoelus vertebrae.
(6) Cervical and abdominal ribs are present.
(7) Sternum is weak or absent.
(8) Scales are present.
(9) Carpals and metacarpal are free.
(10) Pelvic girdle has an elongated ilium and backwardly directed pubis.
Some avian characters of Archaeopteryx are given below
