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Yanornis specimen shows fish diet

From: Ben Creisler

New in PLoS ONE:

Xiaoting Zheng, Jingmai K. O'Connor, Fritz Huchzermeyer, Xiaoli Wang,
Yan Wang, Xiaomei Zhang, Zhonghe Zhou (2014)
New Specimens of Yanornis Indicate a Piscivorous Diet and Modern
Alimentary Canal.
PLoS ONE 9(4): e95036.

A crop adapted for an herbivorous diet of seeds has previously been
documented in the Early Cretaceous birds Sapeornis and Hongshanornis.
Here we report on several specimens of Yanornis that preserve a crop
containing fish. One specimen preserves two whole fish in the
oesophagus, indicating that Early Cretaceous birds shared trophic
specializations with Neornithes for the increased energetic demands of
flight – namely the storing of food for later consumption when the
stomach is full. Whole fish also indicate that despite their presence,
teeth were not used to orally process food, suggesting the
hypertrophied dentition in this taxon were utilized in prey capture.
The presence of macerated fish bones in the crop of other specimens
indicates the highly efficient advanced muscular system of peristalsis
responsible for moving ingested items between different segments of
the alimentary canal was also in place. Despite the fact many features
of the modern avian alimentary canal are inferred to compensate for
the absence of teeth in birds (expandable oesophagus, grinding
gizzard), the derived alimentary canal was apparently present in
toothed Cretaceous birds. Although Yanornis was considered to have
switched their diet from piscivorous to herbivorous, based on position
and morphology we reinterpret the gastroliths reported in one specimen
as sand impacted in the intestines, and reconstruct the taxon as
primarily piscivorous. This is a novel interpretation for fossilized
gastroliths, and the first documentation of this condition in the
fossil record.