Reptilia: Overview | Zoology Optional Notes for UPSC PDF Download

Reptilia: Characteristics and Classification of Cold-Blooded Vertebrates

Evolutionary Separation and Classification

1. Anapsida — Without any opening in the temporal region.
2. Parapsida — The skull possesses an upper opening where post-orbital and squamosal meet below.
3. Diapsida — Characterized by two openings on each side, separated by postorbital and squamosal bones.
4. Synapsida — Featuring a single opening with postorbital and squamosal meeting above.

General Characteristics of Reptiles

1. They inhabit both terrestrial and aquatic environments, including marine and freshwater habitats.
2. The skin is dry, cornified, and often covered by epidermal scales or scutes, with integumentary scent glands for pheromone secretion during breeding.
3. A single external nasal opening is present on the snout, with slightly depressed ear drums.
4. Two pairs of pentadactyl limbs ending in clawed digits.
5. Cloacal opening is either transverse or longitudinal.
6. A post-anal tail is a characteristic feature.
7. The heart comprises two auricles and a partially divided ventricle, with right and left systemic arches.
8. Kidneys exhibit a metanephric type.
9. Reproductive organs, including Mullerian and Wolffian ducts, reflect sexual dimorphism.
10. Twelve pairs of cranial nerves.
11. Well-developed vomero-nasal organ (Organ of Jacobson).
12. Procoelous vertebrae, a greatly developed sternum, and cleidoic eggs with calcareous shells for protection against desiccation.

Subclass — Anapsida: Unveiling the Characteristics

1. The skull in Anapsida features a solid roof.
2. The skull lacks fossae behind the eyes.

Order — Chelonia (Tortoises and Turtles): Insights into Their Traits

1. Dorsoventrally flattened bodies with a shield-like carapace and ventral plastron.
2. Retractile neck, limbs, and tails, with pentadactyle limbs modified in some marine forms.
3. Absence of teeth in adults, replaced by sharp horny plates.
4. Longitudinal cloacal opening and presence of a copulatory organ in males.
5. Oviparous nature with hibernation in temperate regions.
6. Immovable quadrate bone in the skull.

Subclass — Lepidosauria: A Closer Look

1. Diapsid skull structure.
2. Lizard-like reptiles with scaled skin.
3. Includes three orders: Eusuchia, Rhynchocephalia, and Squamata.

Order — Rhynchocephalia: Unraveling Distinctive Features

1. Dull olive green dorsal skin and whitish ventral coloration.
2. Bilaterally compressed, crested tail with regenerative capabilities.
3. Erective spines (frill) along the dorsal side.
4. Large eyes with vertical pupils.
5. Transverse slit cloacal aperture.
6. Simple brain with a well-developed parietal organ (third eye).

Order — Squamata: Exploring the Diversity of Lizards and Snakes

1. Skull with superior temporal fossa.
2. Immovably articulated maxilla, palatine, and pterygoid with a movable quadrate.
3. Procoelous vertebrae with chevron bone.
4. Transverse slit cloacal aperture and reversible copulatory sacs in males.
5. Well-developed Organ of Jacobson.
6. Global distribution, including distinct suborders: Lacertilia, Ophidia, and Amphisbaenia.

Suborder — Lacertilia: Studying Lizards in Detail

1. Elongated body with two pairs of limbs and a long tail.
2. Movable upper and lower eyelids.
3. Slightly movable quadrate.
4. Distinct T-shaped episternum on the sternum.
5. Presence of a tympanum, broad tongue, and urinary bladder.

Table 1: Examples of Lacertilia

Suborder — Ophidia (Serpentes): Understanding the World of Snakes

1. Typically scaly, limbless creatures with transparent spectacles protecting their eyes.
2. Absence of temporal fossae due to secondary adaptation.
3. Highly developed Vomero-nasal organ (Organ of Jacobson).
4. Freely movable maxillae, palatines, and pterygoids.
5. Flexible quadrate and reduction/absence of tympanic structures.
6. Additional intervertebral articulations known as zygantra and zygosphenes.

Table 2: Examples of Ophidia

Suborder — Amphisbaenia: Discovering Worm-like Lizards

1. Limbless, worm-like lizards with a compact and highly ossified skull.
2. Soft skin with numerous rings divided into little squares.
3. Concealed eyes and ears under the skin.
4. Short tail with the ability to crawl in both backward and forward directions.

Table 3: Examples of Amphisbaenia

Subclass — Archosauria: A Glimpse into the Diapsid Skull

1. Diapsid skull lacking inter-parietal and parietal foramina.
2. Variable tooth presence in different forms.
3. Lower jaw with vacuities between dentary and angular.

Order — Crocodilia/Loricata: Insights into Ferocious Freshwater Reptiles

1. Freshwater, carnivorous reptiles with powerful laterally compressed tails.
2. Pentadactyle limbs with webbed digits.
3. Epidermal scales supported by dermal bones or scutes.
4. Longitudinal cloacal aperture with erectile copulatory organs.
5. Thecodont teeth on premaxillae, maxillae, and dentaries.

Table 4: Examples of Crocodilia

Conclusion: A Glimpse into Reptilian Evolution
Reptiles, the pioneers of terrestrial vertebrates, have evolved diverse adaptations that have allowed them to thrive on Earth. From the distinct characteristics of different orders and suborders to the captivating examples of species, this article serves as a comprehensive guide to understanding the fascinating world of reptiles. As remnants of ancient lineages, reptiles continue to capture the imagination of scientists and nature enthusiasts alike