A small dinosaur that lived in what is now North America during the Late Cretaceous is offering new clues to how some theropods ate. The newly described species, Infernogallus jamesi, had a toothless beak and an unusual jaw structure that may have allowed it to process soft plant foods, including the fleshy parts of fruit. The study was published in Nature Communications.
The fossil comes from the Hell Creek Formation in the United States and includes the first known intact skull of a member of the caenagnathid family. The partial skeleton belonged to an animal estimated to have weighed about 12 kilograms. Microscopic examination of its bones suggests it had reached skeletal maturity.
Unlike many theropods, whose jaw muscles were mainly suited to forceful biting, I. jamesi appears to have had muscles that supported horizontal movement. Its lower jaw could shift forward and backward by as much as 15 millimeters, although the researchers note that soft tissues may have restricted its actual range of motion. The dinosaur’s relatively weak vertical bite suggests it was better suited to handling soft foods than to crushing hard or fibrous material.
The jaws and palate also had ridges and grooves that may have helped crush and shred food as the lower jaw moved, in a mechanism the researchers liken to a mortar. Features of the skull may also indicate a mobile tongue that helped position food in the mouth.
Comparisons with living birds and turtles that have toothless beaks pointed to parrots as the closest functional match. The researchers highlight the Pesquet’s parrot, which eats fruit pulp and discards seeds. The similarities suggest a possible way I. jamesi processed food, but do not establish that the dinosaur had the same diet. The team proposes that it may have eaten fruit pulp alongside other soft plant material. No fruit remains have been found in its digestive tract.
The study also considers whether the evolution of caenagnathids overlapped with the diversification of flowering plants and their fruits. The group’s origins are placed in the Aptian-Albian, shortly after the first fruits appeared, while its diversification and geographic expansion occurred later in the Cretaceous. The researchers say this timing, together with the jaw anatomy, is consistent with partial fruit-eating, but does not prove that fruits drove the group’s diversification.
Anatomical features in the older caenagnathid Microvenator celer suggest that adaptations for processing soft foods may have emerged early in the group’s history and became more developed over time. The researchers say fossilized stomach contents and further biomechanical comparisons could help test the dietary hypothesis.
The study also raises, but does not resolve, questions about the group’s disappearance at the end of the Cretaceous. The authors suggest that reliance on fruit pulp may have become a disadvantage when food webs were disrupted and more persistent resources, such as seeds, were important. They stress that this remains a hypothesis and does not by itself explain the extinction of caenagnathids.
Sources: elDiario.es.