Missing Link Between Crestless, Crested Duck-Billed Dinosaurs

Summary: The missing link between crestless and crested duck-billed dinosaurs is nicknamed Superduck, according to a study published Nov. 11, 2015, in PLOS ONE.

illustration of Probrachylophosaurus bergei by paleoartist John Conway: Mostly Mammoths @MostlyMammoths, via Twitter Nov. 13, 2015

A new hadrosaurid acquires a long scientific name, a transitional evolutionary role between crestless and crested duck-billed dinosaurs and a trendy common name, according to a study published Nov. 11, 2015, in the open-access, peer-reviewed journal PLOS ONE.

The bones belong to a 14-year-old adult, according to tree ring-like growth lines in the specimen’s tibia.

The specimen carries the non-scientific designation Superduck and the scientific name Probrachylophosaurus bergei ("Sam Berge’s pre-short-crested lizard"). The nickname describes the fossil’s 30-foot (9.14-meter) looks. The Late Cretaceous skeleton from the Kennedy Coulee exposure of the Judith River Formation in north-central Montana’s Hill County of 79.5 million years ago emerges since 2007 as big, but not as the largest hadrosaurid ever.

Co-authors Elizabeth A. Freedman Fowler, Great Plains Dinosaur Museum director of paleontology in Malta, Montana, and John R. Horner, Montana State University Department of Earth Sciences Regent’s Professor and Museum of the Rockies curator of paleontology in Bozeman, fit Superduck into paleontology’s missing link niche.

Superduck gives evidence of heterochrony, of different timing in the growth rate of body parts. Heterochrony handles the earlier crest development or the faster cranial growth in Superduck’s bigger-crested successors.

It involves the uncrested Acristavus gaglarsoni of Montana’s lower Two Medicine Formation 81.4 million years ago, the mini-crested Probrachylophosaurus bergei and the maxi-crested Brachylophosaurus canadensis of the Judith River Formation of Montana and the Oldman Formation of Alberta 77.76 million years ago.

The two co-authors judge eight kinds of skull bones as most useful in comparing the three duck-beaked dinosaurs in question: “Probrachylophosaurus exhibits a unique combination of characters that make it morphologically intermediate between Acristavus and Brachylophosaurus. Probrachylophosaurus is most similar to Acristavus in overall morphology of the jugal [cheek] and lacrimal [front eye-socket rim]. The morphologies of the frontal, quadrate [jaw joint], and squamosal [cranial side] are more similar to Acristavus in some attributes, but more similar to Brachylophosaurus in others. The braincase of Probrachylophosaurus is most similar to Brachylophosaurus. The presence of a posteriorly-oriented nasal crest also unites Probrachylophosaurus with Brachylophosaurus. The dentary [lower jaw bones] is more similar to that of Acristavus than to Brachylophosaurus."

Dr. Freedman Fower knows of age-specific breeding joining with age-specific cresting to restrict mating to sexually mature hadrosaurids. She links size subtleties to adults and juveniles: “We think that the crests of dinosaurs were visual signals so that they could recognize members of their own species, and also tell whether the animal was mature or not.”

Growth lines mark arrested growth at ages 6 and 7, spurts at age 8 and maturity at age 10. The co-authors note old injuries to calf bones, foot bones, lower jaw bones, shinbones and six tail vertebrae.

The co-researchers observe that the foraging-, mating- or predation-related injuries to Superduck, a plant-eater preyed upon by Tyrannosaurus rex, require further investigations and publications.

visual abstract of Probrachylophosaurus bergei vs. Brachylophosaurus canadensis: Elizabeth Freedman Fowler, CC BY 2.0 Generic, via EurekAlert!

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

illustration of Probrachylophosaurus bergei by paleoartist John Conway: Mostly Mammoths @MostlyMammoths, via Twitter Nov. 13, 2015, @ https://twitter.com/MostlyMammoths/status/665214805100228608

visual abstract of Probrachylophosaurus vs Brachylophosaurus; credit Elizabeth Freedman Fowler: CC BY 2.0 Generic; "All figures and photographic images will be published under a Creative Commons Attribution License (CCAL), which allows them to be freely used, distributed, and built upon as long as proper attribution is given.", via EurekAlert! @ https://www.eurekalert.org/multimedia/692052; (EurekAlert! news release URL @ https://www.eurekalert.org/news-releases/760583); (former URL @ http://www.eurekalert.org/multimedia/pub/102772.php?from=311062)

For further information:

AB Wire. 13 November 2015. "Discovery of New Dinosaur Species Reveals Evolutionary Link." American Bazaar Online.
Available @ http://www.americanbazaaronline.com/2015/11/13/discovery-of-new-dinosaur-species-reveals-evolutionary-link/

Freedman Fowler, Elizabeth A., and John R. Horner. 11 November 2015. "A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana." PLOS ONE. DOI: 10.1371/journal.pone.0141304
Available @ http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141304

GeoBeats News. 16 November 2015. "New Duck-Billed Dinosaur Species Discovered in Montana." YouTube.
Available @ http://www.youtube.com/watch?v=WZwkISrDxdc

Mostly Mammoths @MostlyMammoths. 13 November 2015. "#FossilFriday @montanastate Dr. Liz Freedman Fowler finds new dinosaur." Twitter.
Available @ https://twitter.com/MostlyMammoths/status/665214805100228608