Data from: The evolution of the modern avian digestive system – insights from paravian fossils from the Yanliao and Jehol biotas

The avian digestive system, like other aspects of avian biology, is highly
modified relative to other reptiles. Together these modifications have
imparted the great success of Neornithes, the most diverse clade of
amniotes alive today. It is important to understand when and how aspects
of the modern avian digestive system evolved among neornithine ancestors
in order to elucidate the evolutionary success of this important clade and
to understand the biology of stem birds and their closest dinosaurian
relatives – Mesozoic Paraves. Although direct preservation of the soft
tissue of the digestive system has not yet been reported, ingested remains
and their anatomical location preserved in articulated fossils hint at the
structure of the digestive system and its abilities. Almost all data
concerning direct evidence of diet in Paraves comes from either the Upper
Jurassic Yanliao Biota or the Lower Cretaceous Jehol Biota, both which are
known from deposits in north-eastern China. Here, the sum of the data
gleaned from the thousands of exceptionally well-preserved fossils of
paravians is interpreted with regards to the structure and evolution of
the highly modified avian digestive system and feeding apparatus. This
information suggests intrinsic differences between closely related stem
lineages implying strong homoplasy and that the modern digestive system is
limited to the crownward lineage.