The last common ancestor of all animals was probably a:

• A. flagellated protist similar to modern choanoflagellates
• B. photosynthetic cyanobacterium
• C. unicellular amoeba
• D. multicellular green alga

Answer: (A)

Verified step by step guidance

1. Understand the question: The problem is asking about the last common ancestor of all animals. This requires knowledge of evolutionary biology and the characteristics of early life forms.
2. Recall the characteristics of animals: Animals are multicellular, heterotrophic organisms that lack cell walls and are capable of movement at some stage in their life cycle. Their ancestors would likely share some of these traits.
3. Review the options: Analyze each option provided: (1) flagellated protist similar to modern choanoflagellates, (2) photosynthetic cyanobacterium, (3) unicellular amoeba, and (4) multicellular green alga. Consider which of these aligns with the evolutionary traits of animals.
4. Focus on choanoflagellates: Modern choanoflagellates are flagellated protists that share structural and genetic similarities with animals. They are considered the closest living relatives of animals and provide clues about the characteristics of the last common ancestor.
5. Conclude based on evidence: The last common ancestor of all animals was likely a flagellated protist similar to modern choanoflagellates, as this aligns with the evolutionary evidence and the traits shared between animals and their closest relatives.