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, 8 (1), 14217

Exceptional Dinosaur Fossils Reveal Early Origin of Avian-Style Digestion

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Exceptional Dinosaur Fossils Reveal Early Origin of Avian-Style Digestion

Xiaoting Zheng et al. Sci Rep.

Abstract

Birds have a highly specialized and efficient digestive system, but when this system originated remains uncertain. Here we report six gastric pellets attributable to the recently discovered 160-million-year-old troodontid dinosaur Anchiornis, which is among the key taxa for understanding the transition to birds. The gastric pellets contain lightly acid-etched lizard bones or fish scales, and some are associated with Anchiornis skeletons or even situated within the oesophagus. Anchiornis is the earliest and most basal theropod known to have produced gastric pellets. In combination with other lines of evidence, the pellets suggest that a digestive system resembling that of modern birds was already present in basal members of the Paraves, a clade including troodontids, dromaeosaurids, and birds, and that the evolution of modern avian digestion may have been related to the appearance of aerial locomotion in this lineage.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
The troodontid Anchiornis STM0-179, with a gastric pellet comprising lizard bones preserved in the oesophageal area. (a) Photograph of the cranial and cervical region of the STM0-179 slab. (b) Photograph of the same portion of the counter slab. (c) Line-drawing of the cranial and cervical region of the STM0-179 slab, with the preserved pellet shaded in light blue. (d) Close-up photograph of the lizard bones preserved in STM0-179. In the pellet, at least three or four humeri and four or five femora are identifiable, and one of the femora is significantly smaller than the others. This suggests that the pellet contains bones from at least two relatively large lizards and one small lizard. Abbreviations: 1–4, sampling locations for the EDS analyses; den, dentary; fe1–5, femora 1–5; hu1–4, humeri 1–4; max, maxilla; ti, tibia; fi, fibula. Scale bar, 10 mm.
Figure 2
Figure 2
EDS results for the troodontid Anchiornis STM0-179. EDS spectra derived from the matrix surrounding the pellet (a), the pellet cement (b,c), and a lizard bone contained in the pellet (d).
Figure 3
Figure 3
Gastric pellets produced by the troodontid Anchiornis, containing fish scales and bones. (a) Photograph of Anchiornis STMA0-4, with red rectangle framing pellet. (b) Close-up of pellet preserved in STMA0-4. (c) Photograph of Anchiornis STM0-224, with red rectangle framing pellet. (d) Close-up of pellet preserved in STM0-224. (e) Photograph of isolated pellet STM0-227. (f) Close-up of isolated pellet STM0-227. Scale bar, 50 mm for (a,c), 5 mm for (b,df).
Figure 4
Figure 4
Evolution of digestive features in theropod dinosaurs. A two-chambered stomach with muscular gizzard, possibly highly acidic anterior stomach chamber, and relatively long gastric residence time might have characterized most theropods, including basal coelurosaurians; a digestive system with relatively short residence time and efficient antiperistalsis to expel indigestible material orally might have originated at the base of Paraves; and some highly specialized digestive structures such as the crop might have originated at the base of the Pygostylia.

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