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Let us learn about the comparison between ratites and carinates.
Comparison # Ratites: (Palaeognathae):
1. Distribution:
Discontinuous, except Ostrich, they are confined to southern continents and islands.
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2. Habitat:
Terrestrial—usually living in desert.
3. Size:
Usually large
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Exoskeleton:
4. Tail:
Functionless.
5. Feathers:
Devoid of hooks and hooklets. The barbs are free.
6. After shaft:
Usually well-developed.
7. Rectrices:
Absent or irregularly arranged. These are never fan-shaped.
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8. Down feathers:
Absent
9. Pterylosis:
The apteria is usually absent adult, but distinct in young’s.
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10. Wings:
Reduced in size, may be vestigial or absent.
11. Uropygial gland:
Absent except in Kiwi
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12. Rhamphotheca (Horny sheath to the beak):
Compound, composed of several separate pieces.
Hard Parts:
A. Skull
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13. Nature of skull:
Large and strongly built.
14. Type of skull:
Dromaeogathous
15. Sutures of skull:
Persistent
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16. Quadrate:
Y-shaped bone, articulates with the squamosal by a single or partly divided facet.
17. Vomer:
Large, broad and separates the palatines.
18. Palatines:
Do not articulate with therostrum
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19. Maxillopalatine process:
Small, do not articulate with one another.
20. Basipterygoid process:
Large and developed from the basisphenoid.
B. Vertebrae
21. Sacral vertebrae:
Not firmly ankylosed
22. Pygostyle:
Undeveloped
C. Sternum & Uncinate process
23. Sternum:
Plate-like without keel. No trace of carinal ossification in young.
24. Uncinate process:
Absent
D. Pectoral girdle
25. Scapula:
Plant-Like
26. Coracoid:
Plant-like
27. Coracoid and scapula:
Comparatively smaller arid completely ankylosed.
28. Coracoscapular angle:
Approaches two right (obtuse) angles.
29. Furcula:
Absent
30. Acromion and Acrocoracoid processes:
Absent or vestigial.
E. Pelvic girdle
31. Ilium and Ischium:
Loose and not fused posteriorly.
32. Pelvic symphysis:
Pubic symphysis is present in Ostrich and ischiatic symphysis is found in Rhea.
F. Limbs
33. Limb-bones:
Not much pneumatic.
34. Digits in forelimbs:
Usually three digits are present, two with claws.
35. Hind limbs:
Usually elongated—adapted to cursorial life.
Soft Parts
36. Tongue:
Usually small.
37. Caecum:
Very large.
38. Flight muscles:
Completely reduced.
A. Respiratory System
39. Syrinx:
Absent except Rhea.
40. Air-sacs:
ill-developed or absent
B. Blood Vascular System
41. R.B.C:
Smaller in size
42. Heart:
Smaller in size
43. Ovary:
Smaller in size
C. Reproductive Sys/tem
44. Penis:
Present
45. Egg-shell:
Thick and hard.
46. Pore-canal:
Branched.
47. Young’s:
Usually precocial, i.e., independent.
48. Examples:
Ostriches, rheas, emus, cassowary, kiwi and tinamous among living birds.
Comparison # Carinates (Neognathae):
1. Distribution:
Cosmopolitan
2. Habitat:
In all spheres.
3. Size:
Variable—but smaller in size.
Exoskeleton
4. Tail:
Functional, actively helps in steering during flight.
5. Feathers:
Barbs are united by hooks and hooklets, i.e., barbs are united.
6. After shaft:
Usually ill-developed except Heron.
7. Rectrices:
Present, regularly arranged round the uropodium. These are fan-shaped.
8. Down feathers:
Present
9. Pterylosis:
Apteria is well –marked.
10. Wings:
Well-developed and constitute the principal organs for flight.
11. Uropygial gland:
Present
12. Rhamphotheca (Horny sheath to the beak):
Never dromaeognathous, may be schizognathous or aegithognathous or desmognathous.
Hard Parts
A. Skull
13. Nature of skull:
Small, light and fragile.
14. Type of skull:
Never dromaeognathous, may be schizognathous or aegithognathous or desmognathous.
15. Sutures of skull:
Absent in adult.
16. Quadrate:
Never Y-shaped , articulates by two facets.
17. Vomer:
Small, narrow and may be truncated.
18. Palatines:
Converge together behind and movably attached to vomer by a cup-and-ball joint
19. Maxillopalatine process.
Unite with one another to form large secondary palate.
20. Basipterygoid process:
May be sent, if present , hangs from the base of the rostrum.
B. Vertebrae
21. Sacral vertebrae:
Most of them are firmly ankylosed.
22. Pygostyle:
Well-developed.
C. Sternum & Uncinate process
23. Sternum:
Well- developed with a prominent well – ossified mid-ventral keel or carina.
24. Uncinate process:
Present
D. Pectoral girdle
25. Scapula:
Sabre-shaped
26. Coracoid:
Pillar- Like
27. Coracoid and scapula:
Both are well – developed and not ankylosed.
28. Coracoscapular angle:
Less than 90° (acute), exceeds 90° in Albatross.
29. Furcula:
Present and well-developed.
30. Acromion and Acrocoracoid processes:
Well- developed
E. Pelvic girdle
31. Ilium and Ischium:
Completely fused posteriorly.
32. Pelvic symphysis:
Absent.
F. Limbs
33. Limb-bones:
Highly pneumatic
34. Digits in forelimbs:
Usually three digits are found and claws are absent in adult.
35. Hind limbs:
Usually adapted for cursorial/arboreal/aquatic life.
Soft Parts
36. Tongue:
Prominent and pointed at the tip.
37. Caecum:
Usually small.
38. Flight muscles:
Well-developed. May be slightly reduced in flightless members.
A. Respiratory System
39. Syrinx:
Present
40. Air-sacs:
Highly developed and play an important role in aerial life.
B. Blood Vascular System
41. R.B.C:
Larger in size
42. Heart:
Larger in size
43. Ovary:
Usually right ovary is absent.
C. Reproductive System
44. Penis:
Absent excepted in duck
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45. Egg-shell:
Thin and fragile
46. Pore-canal:
Un-branched
47. Young’s:
Altricial, dependents and helpless.
48. Examples:
All other living groups of both birds including penguin
Phylogenetic Relationship:
Opinions differ as regards the phylogenetic relationship between the ‘ratites’ and ‘carinates’. It is claimed that the ratites are primitive than carinates.
This contention is untenable today because the condition of the cerebellum indicates their emergence from Volant ancestors and many carinates have been recorded to have lost many carinate features specially the conversion from keeled to raft-like sternum due to their loss of flight.
Many workers, particularly de Beer, (1956) suggested that the so-called primitive features of the ratites, viz., the condition of the feathers with free barbs without hooks, arrangement of palate bones, retention of sutures in the skull are essentially neotenous characters and not primitive as advocated by earlier workers.
Many neognathous birds pass through palaeognathous condition during development and the latter is possibly an arrested development of neognathous condition as suggested by McDowell (1948). The above evidences suggest that the ratites have been evolved from flying ancestors.
They do not form a natural group, but represent a heterogeneous assemblage of several evolutionary lines. E, R. Lowe (1935) and Holmgren (1955) are in favour that ‘ratites’ are monophyletic and have originated from dinosaurs independently.
