Nicknamed the Napoleon of the dinosaur kingdom, N. Hoglundi seemed as

Hi brt

That's a valid question. However, grammatically speaking, "seems to have been" is absolutely correct. Whereas "seems" is undoubtedly referring back to the singular subject, "To have been" is used as an infinitive phrase that combines the infinitive form of the verb "have" with the past participle "been." In such a construct, it indicates an action or state that occurred in the past. It is not directly affected by subject-verb agreement.

Take for an example - She wanted to have a vacation after a strenuous year

Here, "wanted" is the verb and "to have" is used in the infinitive form of "having" to indicate what she wanted to "have".

That being said, "have" can be used in many ways, apart from a plural verb. Here are some of those cases:
Auxiliary verb for forming perfect tenses: "Have" is used as an auxiliary verb to form the perfect tenses in English. For example: "I have eaten," "She has written," "They have seen."

Possession: "Have" is used to indicate possession or ownership. For example: "I have a car", "They have a house."

Auxiliary verb for forming the passive voice: "Have" is used as an auxiliary verb to form the passive voice in English. For example: "The book has been read," "The project will have been completed."

Auxiliary verb for forming conditionals: "Have" can be used as an auxiliary verb to form conditionals, particularly in the subjunctive mood. For example: "If she had known, she would have come."

Hope this helps.

Thank you for the reply.....
It really helped me. Once I see it as infinitive it completely makes sense.

Posted from my mobile device