Arrange the following poikilothermic vertebrate groups in increasing order of structural complexity and separation of oxygenated and deoxygenated blood in their cardiac chambers.
- 1Pisces (e.g., *Tilapia zillii*), possessing a two-chambered heart consisting of one atrium and one ventricle.
- 2Amphibia (e.g., *Bufo regularis*), possessing a three-chambered heart with two atria and a single undivided ventricle.
- 3Non-crocodilian Reptilia (e.g., *Agama agama*), possessing a three-chambered heart with a partially divided ventricle.
- 4Crocodilian Reptilia (e.g., *Crocodylus niloticus*), possessing a four-chambered heart with a completely divided ventricle.
Answer
The correct sequence from lowest to highest cardiac chamber complexity and separation of blood streams is: Pisces (two-chambered heart) → Amphibia (three-chambered heart with undivided ventricle) → Non-crocodilian Reptilia (three-chambered heart with partially divided ventricle) → Crocodilian Reptilia (four-chambered heart with completely divided ventricle).
The structural evolutionary sequence of heart chambers in poikilothermic vertebrates begins with Pisces, which possess a single-circuit, two-chambered heart (one atrium and one ventricle). Amphibians follow with a double-circuit, three-chambered heart (two atria and one undivided ventricle). Non-crocodilian reptiles feature a three-chambered heart with a partial inter-ventricular septum that reduces mixing of oxygenated and deoxygenated blood. Crocodilians represent the most structurally advanced poikilothermic heart with four distinct chambers (two atria and two completely separated ventricles).
Step-by-Step Solution
Key Concept
Evolutionary progression of heart chamber structures in poikilothermic vertebrates