The trophic habits of early birds

The number of teeth is reduced from 14 maxillary and 16 dentary teeth in Anchiornis to 8-10 maxillary and 11-13 dentary teeth in Archaeopteryx.

“The number of teeth is reduced from 14 maxillary and 16 dentary teeth in Anchiornis , a taxon documented to be at least partially vertivorous [84], to 8-10 maxillary and 11-13 dentary teeth in Archaeopteryx [13, 81].”

Most closely related non-avian theropods were carnivorous vertivores and targeted larger food items, which were ingested whole or largely unprocessed.

“In contrast, most closely related non-avian theropods were carnivorous vertivores and targeted larger food items, which were ingested whole or largely unprocessed [84, 92, 93].”

The disparities between Archaeopteryx and Anchiornis likely reflect differences in diet, with Anchiornis being relatively more predatorial.

“Together, these disparities likely reflect differences in diet, with Anchiornis being relatively more predatorial, consistent with the documented remains of a lizard in the esophagus of one specimen preegestion [84].”

The morphology of the foot, lacking the hyperextensible second digit present in most non-avian deinonychosaurs except for Anchiornis, and features of the skull associated with increased dexterity, suggest adaptations for feeding on small food items, as opposed to the hypercarnivory typical of deinonychosaurs.

“The morphology of the foot, lacking the hyperextensible second digit present in most non-avian deinonychosaurs except for Anchiornis [36], and features of the skull associated with increased dexterity, suggest adaptations for feeding on small food items, as opposed to the hypercarnivory typical of deinonychosaurs [84, 93, 118] (Fig.4).”