Question: the atlantoaxial joint is an example of what type of joint
[{'answer': 'a pivot joint', 'provenance': [{'wikipedia_id': '5032405', 'title': 'Atlanto-axial joint', 'start_paragraph_id': 1, 'start_character': 139, 'end_paragraph_id': 1, 'end_character': 152, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '5032405', 'title': 'Atlanto-axial joint', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 152, 'bleu_score': 0.9321022168949711, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10835746507103806015}, 'section': 'Section::::Abstract.'}]}]