UPPER CRETACEOUS TOOTHED BIRDS IN SOUTH AMERICA

70-Million-Year-Old Toothed Enantiornithes Bird Beak

Teeth and jaws, beaks and claws — all species adapt and change over time based on survival. One of the key features of being alive is needing to eat. Depending on what is on the menu, we adapt accordingly. 

I had been thinking about this from a very mammal-centric perspective, but it is true for all animals — birds included.

When we think of our feathered friends, we think of beaks and feathers. True, birds descend from the mighty lineage of dinosaurs, but our experience of them is of their modern forms. 

This modern viewpoint of their characteristics makes beaks with teeth seemingly more fantasy than reality — except this has not always been the case. 70 million years ago, birds flying our Cretaceous skies in what would become South America, Europe and Asia had teeth embedded in their beaks.

The discovery of polyphyodonty and dental replacement in toothed stem birds dates back to the nineteenth century. Marsh reported replacement teeth inside resorption pits in the Late Cretaceous Hesperornis and Ichthyornis.

Enantiornithine Birds & Cladogram

The birds that inhabit the current biomes do not have teeth, but the primitive birds found as fossils in the Upper Cretaceous of Brazil certainly did. 

These ancient relatives to our modern fauna had teeth embedded in their jaw-beaks, clawed fingers and a long tail. 

Both these ancient birds and their modern cousins are descended from the dinosaurs, more specifically the Maniraptora, that clade of coelurosaurian dinosaurs characterized by long arms and three-fingered hands — reduced or fused in some lineages — and semi-lunate or half-moon shaped bone in their wrists you will know as the carpus. 

As with all the dinosaurs in this clad, they had teeth and lots of them.

William Nava, head of the Marília Museum of Paleontology, São Paulo, Brazil, uncovered an outcrop in the city of Presidente Prudente with abundant fossilized bird bones. 

Bird bones are a rare thing as they are delicate, often scavenged before burial and hollow, making them poor candidates for preservation. While bird bones preserved as fossils are generally rare, this was not the case at William's Quarry. The site was a smorgasbord of bones from a number of primitive bird species that lived at the end of the Cretaceous. 

The birds belong to the group of Enantiornithes who looked very much like our modern birds on the outside, but internally they had clawed fingers on each wing and teeth which they replaced in a similar fashion to most reptiles. 

Two other sites have exceptionally preserved Enantiornithes bones. Since most Enantiornithes bones are fragmentary, some species are only known from a piece of a single bone. We are luckier at some sites than others. Almost all complete, fully articulated fossil specimens with soft tissue preserved were known from Las Hoyas in Cuenca, Spain and the Jehol group in Liaoning, China. But the fossil outcrops in the Adamantina Formation, Bauru Group of Brazil can now be added to that very short list.  

If you fancy a read, check out their publication, Dental replacement in Mesozoic birds: evidence from newly discovered Brazilian enantiornithines.” The team included Yun-Hsin Wu and Luis M. Chiappe of the Natural History Museum of Los Angeles County, David J. Bottjer of the University of Southern California, William Nava from the Marília Museum of Paleontology, and Agustín G. Martinelli from the Vertebrate Paleontology Section of the Bernardino Rivadavia Argentine Museum of Natural Sciences.

Publication link: https://www.nature.com/articles/s41598-021-98335-8

Images: Photographs of the enantiornithine specimens MPM-90, MPM-373, and MPM-351, and a simplified cladogram highlighting the stem avian taxa discussed in this study. MPM-373: (a) dorsal view; (b) right lateral view; (c) left lateral view. MPM-90: (d) dorsal view; (e) right lateral view. MPM-351: (f) left lateral view. En external nares, Fp frontal process. With an embedded illustration of a reconstruction of Sinornis santensis by McBlackneck. There is some mice type used so feel free to click the image to see if full size.

The studied specimens consist of two sets of premaxillae (MPM-90 and MPM-373) and an incomplete left dentary (MPM-351) exquisitely preserved in three dimensions. These specimens are housed at the Museu de Paleontologia de Marília (MPM), São Paulo State, Brazil.