Zoology 2022 Paper I 50 marks Describe

Q4

(a) Give an account of the origin as well as adaptive radiation of reptiles. (20 marks) (b) Describe general structure of a mammalian tooth. Also, classify mammalian teeth based on their shape, attachment and succession. (15 marks) (c) Describe habitat, habits and general features of Herdmania. Write a note on its development. (15 marks)

हिंदी में प्रश्न पढ़ें

(a) सरीसृपों के उद्भव के साथ साथ उनके अनुकूली विकिरण के बारे में एक विवरण दीजिए । (20 अंक) (b) स्तनधारियों के दांत की सामान्य संरचना का वर्णन कीजिए । आकार, लगाव (अटैचमेंट) एवं उत्तराधिकार के आधार पर स्तनधारियों के दांतों का वर्गीकरण भी कीजिए । (15 अंक) (c) हर्डमेनिया के आवास, स्वभाव एवं सामान्य विशेषताओं का वर्णन कीजिए । इसके परिवर्धन पर एक टिप्पणी भी लिखिए । (15 अंक)

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Directive word: Describe

This question asks you to describe. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

The directive 'describe' demands detailed, factual exposition with structural clarity. Allocate approximately 40% of time/words to part (a) on reptile origin and adaptive radiation (20 marks), and roughly 30% each to part (b) on mammalian tooth structure and classification (15 marks) and part (c) on Herdmania biology and development (15 marks). Structure each part with clear sub-headings: for (a) cover ancestral forms → evolutionary innovations → radiation patterns; for (b) present tooth anatomy first, then systematic classifications; for (c) begin with ecological setting, proceed to morphology, and conclude with developmental stages including metamorphosis.

Key points expected

  • Part (a): Origin from cotylosaurs/captorhinomorphs; key synapsid-diapsid split; evolutionary innovations (amniotic egg, water-resistant skin, improved jaw articulation); adaptive radiation into Testudines, Squamata, Crocodilia, Rhynchocephalia with ecological correlates
  • Part (a): Mesozoic dominance; endothermy evolution in therapsid-mammal transition; extinction patterns and survival mechanisms
  • Part (b): Tooth structure—enamel, dentine, pulp cavity, cementum, periodontal ligament; anatomical zones (crown, neck, root)
  • Part (b): Classification by shape (incisor, canine, premolar, molar/thecodont, pleurodont, acrodont attachment); diphyodont/polyphyodont succession patterns with mammalian examples
  • Part (c): Herdmania habitat (subtidal, benthic, filter-feeding), colonial habit, general features—tunic, siphons, branchial and atrial chambers; hermaphroditism
  • Part (c): Development—ovoviviparity, tadpole larva with notochord and dorsal nerve cord, retrogressive metamorphosis, settlement and adult formation

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Demonstrates precise understanding across all three parts: correctly identifies captorhinomorphs as reptile ancestors, distinguishes synapsid from diapsid lineages accurately, describes tooth histology with correct layer functions, and explains Herdmania's retrogressive metamorphosis without confusing it with progressive developmentShows generally correct concepts but with minor errors—may confuse synapsid/sauropsid relationships, oversimplifies tooth attachment types, or presents incomplete metamorphosis descriptionContains fundamental conceptual errors—claims reptiles evolved from amphibians directly without amniote intermediates, confuses thecodont with acrodont attachment, or describes Herdmania as having free-swimming adult stage
Diagram / labelling18%9Provides three well-executed diagrams: amniotic egg structure with labelled extraembryonic membranes for (a); longitudinal section of mammalian tooth showing enamel, dentine, pulp cavity and cementum for (b); Herdmania external morphology with incurrent/excurrent siphons and tunic layers, plus tadpole larva with notochord for (c)—all with accurate, complete labellingIncludes two adequate diagrams with most key structures shown; labels may be incomplete or slightly misplaced; one part may lack visual representation entirelyDiagrams absent or poorly executed—unrecognizable structures, missing critical components (e.g., no amnion in egg diagram, no enamel in tooth section), or entirely text-dependent answer
Examples & nomenclature20%10Uses specific, accurate nomenclature throughout: cites Seymouria, Hylonomus, Archaeothyris for reptile origins; names representative genera for each reptilian order (e.g., Sphenodon, Gavialis, Varanus); provides mammalian dental formulae (e.g., human 2.1.2.3/2.1.2.3); identifies Herdmania species and cites Indian coastal distributionUses some correct examples but with gaps—may provide generic reptile names without specificity, gives mammal examples without dental formulae, or mentions Herdmania without geographic referenceExamples absent, incorrect, or confused—uses dinosaur genera for reptile origins, provides no mammalian species references, or misidentifies Herdmania as a fish or cnidarian
Process explanation22%11Explains processes with clear causal logic: for (a) how amniotic egg enabled terrestrial conquest and subsequent radiation mechanisms; for (b) how tooth development proceeds from bud to cap to bell stages, and functional implications of different attachment types; for (c) sequential developmental stages from fertilization through tadpole to settled adult with metamorphic tissue reorganizationDescribes processes in sequence but lacks mechanistic explanation—presents radiation as list rather than adaptive response, describes tooth types without developmental origin, or narrates Herdmania life cycle without explaining metamorphic significanceProcess descriptions absent or incoherent—presents static facts without temporal or causal connections, confuses developmental sequences, or fails to distinguish ontogenetic stages
Evolutionary / applied context18%9Synthesizes evolutionary significance across parts: for (a) discusses reptile-mammal transition via therapsids and reptile-bird link through archosaurs; for (b) relates heterodont dentition to dietary diversification and mammalian success; for (c) interprets Herdmania's retrogressive metamorphosis as degenerative adaptation to sessile life, noting phylogenetic position of UrochordataMentions some evolutionary connections but superficially—notes reptile dominance without explaining why, states tooth diversity without linking to adaptive radiation, or describes Herdmania development without evolutionary interpretationEvolutionary context entirely absent—treats all content as disconnected factual lists with no synthesis, or presents misconceptions such as teleological explanations for adaptations

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