The Evolution Of The Modern Avian Digestive System (1 Viewer)

JINGMAI K. O’CONNOR & ZHONGHE ZHOU, 2020

THE EVOLUTION OF THE MODERN AVIAN DIGESTIVE SYSTEM: INSIGHTS FROM PARAVIAN FOSSILS FROM THE YANLIAO AND JEHOL BIOTAS

[Palaeontology, Vol. 63, Part 1, 2020, pp. 13–27

Free pdf: https://onlinelibrary.wiley.com/doi/pdf/10.1111/pala.12453

Abstract:

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 of 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 either strong homoplasy or that diet in each lineage of non-ornithuromorph birds was highly specialized. Regardless, modern digestive capabilities appear to be limited to the Ornithuromorpha, although the complete set of derived feeding related characters is restricted to the Neornithes.

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Fred

FIG 1. A, simplified cladogram of pennaraptoran relationships indicating where direct evidence regarding diet is available. Red indicates general carnivory; orange, piscivory; yellow, an invertebrate diet; and green, generalized herbivory. Dashed lines indicate either unconfirmed ingested remains or ingested remains that do not conclusively indicate diet (gastroliths). Open circles indicate dental reduction, closed circles indicate the element is edentulous, and a grey line indicates skull material is unknown. B–C, simplified diagrams of the gastrointestinal tract in: B, crocodilians; C, Neornithes; note that although crocodilians do not have a true two-chambered stomach, the tissue is still regionally specialized into glandular and muscular regions; blue lines indicate bi-directional peristalsis. Abbreviations: cec, ceca; cr, crop; d, dentary; eo, oesophagus; int, intestines; m, maxilla; p, premaxilla; prv, proventriculus; py, pylorus; ven, ventriculus. Modified from O’Connor (2019).

Fred

Ingested remains in non-avian paravians. A, Yanliao troodontid Anchiornis STM0-179 (main slab) preserving lizard bones in the oesophagus (image: X.-L. Wang). B, Jehol dromaeosaurid Microraptor STM5-32 preserving the articulated remains of a lizard (indicated by dashed oval). Scale bars represent 1 cm.

Fred