Meaning: 'Previously' means 'at an earlier time' or 'before now,' indicating that the belief about the dinosaurs' diet has changed based on new evidence.

Wrong options:

• prior: 'Prior' is a more formal term that can mean 'before,' but it does not fit as smoothly in this context as 'previously' does, which is more commonly used in this type of narrative.
• beforehand: 'Beforehand' implies something done in advance, which does not fit the context of discussing past beliefs about the dinosaurs' diet.
• earlier: 'Earlier' is a comparative term that suggests a specific point in time, but it lacks the clarity and common usage of 'previously' in this context.

Correct answer: by

Explanation: The preposition 'by' correctly indicates the agent performing the action of producing the coprolites, aligning with the passive construction of the sentence. It fits grammatically and contextually, as it shows that the coprolites were produced by the hadrosaurs.

Meaning: 'By' is used to indicate the doer of an action, in this case, the hadrosaurs that produced the coprolites.

Wrong options:

• with: 'With' suggests the means or instrument used, which does not fit here as we are discussing who produced the coprolites, not how they were produced.
• for: 'For' implies purpose or benefit, which does not align with the context of indicating the agent of the action.
• of: 'Of' indicates possession or relation, which is incorrect in this context where we need to specify who produced the coprolites.

Correct answer: had been eating

Explanation: The phrase 'had been eating' fits grammatically as it uses the past perfect continuous tense, indicating an action that was ongoing in the past before another past event. This aligns with the context of discussing the dinosaurs' diet prior to the findings about crustaceans.

Meaning: 'Had been eating' refers to an action that was happening over a period of time in the past, suggesting that the dinosaurs regularly consumed rotten wood before the new evidence was discovered.

Wrong options:

• have been eating: 'Have been eating' is present perfect continuous, which does not fit the past context of the sentence as it suggests an ongoing action up to the present.
• were eating: 'Were eating' is past continuous but does not convey the ongoing nature of the action leading up to another past event as effectively as 'had been eating.'
• have eaten: 'Have eaten' is present perfect, indicating a completed action, which does not align with the ongoing nature of their diet in the past.

Correct answer: also

Explanation: The word 'also' appropriately indicates an addition to the previous statement about the hadrosaurs' diet, fitting grammatically and contextually as it connects the idea of eating wood with the new information about consuming sea animals.

Meaning: 'Also' means 'in addition' or 'too,' indicating that the hadrosaurs not only ate wood but also included small sea animals in their diet.

Wrong options:

• too: 'Too' implies excess or is often used at the end of a clause, which does not fit well in this context where we need a conjunction to connect ideas.
• as well as: 'As well as' is a phrase that can indicate addition but is more complex and less direct than 'also,' making it less suitable for this sentence structure.
• besides: 'Besides' suggests an additional point but carries a slightly different connotation, often implying a contrast, which does not fit the context of simply adding information.

Correct answer: have proposed

Explanation: The phrase 'have proposed' fits grammatically as it uses the present perfect tense, indicating that the action of proposing is relevant to the present context. This aligns with the ongoing nature of scientific inquiry and findings.

Meaning: 'Have proposed' means that the palaeontologists have put forward a suggestion or theory that is still considered valid or relevant now.

Wrong options:

• proposing: 'Proposing' is a gerund and does not fit as it lacks the necessary auxiliary verb to indicate the completed action in the present context.
• to propose: 'To propose' is an infinitive form that does not fit grammatically in this context where we need a completed action that has relevance to the present.
• will propose: 'Will propose' indicates a future action, which does not align with the context of discussing a current theory based on past findings.