This document discusses the evolutionary relationships between chordates, hemichordates, and echinoderms. It notes that chordates and hemichordates share some characteristics like a dorsal nerve cord and pharyngeal slits, though it is unclear if these are homologous. Chordates are distinguished by features like a tadpole larva, notochord, post-anal tail, and endostyle. The document suggests that hemichordates, chordates, and echinoderms had a common ancestor and that early echinoderms were sessile filter feeders. Through paedomorphosis, chordates evolved from these sessile ancestors into a larval form that was mobile and fish-like,

1. Phylogenetic relationship
of Protochordates

2. Common characteristics between
chordates and hemichordates.
1. Dorsal tubular nerve cord
2. Pharyngeal slits of hemichordates
• These characteristics are evidence of
evolutionary ties between these two phla.
• But it is not cleared that these are
homologous structures or not.

3. Different characteristics
It differentiate chordates from hemichordata.
1. Tadpole larvae
2. Notochord
3. Post anal tail
4. Endostyle

5. EVOLUTION
• Hemichordata, chordata and echinodermata are
deuterostomes.
• Zoologist believe that they have common triploblastic
ancestor.
• But this fossil could not be discovered.

6.  Evolution of chordates from sessile
ancestors
• Earlier echinoderms were sessile filter feeders.
• Evolution of motile chordates occur by development of a
tadpole like larva.
• Larval mobility is an adaptation for sedentary species take
place by paedomorphosis.
 Paedomorphosis is sexual maturity at larval stages.
• Paedomorphosis produced a fish like chordates which is a
ancestor of higher chordates.

7.  Evolution of vertebrates

8. HEAD
• Anterior end of the nerve cord is changed into a
brain.
• They have developed specialized sense organs on
the head.
• These are evidence of a high degree of
cephalization.
 Cephalization is the concentration of all sense
organs in the head.

9. SKELETON
• Skeleton is modified anteriorly into a skull or cranium.
• Vertebrates and chordates have bony endoskeleton.

10. Fossil record
• Vertebrates have left an abundant fossil record.
• About 500 million years ago,jawless fishes were common
in ordovician period.
• Over a period of 100 million years ago, fishes became
dominant vertebrates.
• At the end of devonian period , terrestrial vertebrates
appeared on earth' s habitat.