Common ancestor identified – Researchers decode ancient origins of horns, antlers and ossicones

A diverse range of mammal headgear is on display at the Museum's Richard Gilder Center for Science, Education and Innovation as part of the Louis V. Gerstner, Jr. collections. Credit: Alvaro Keding/AMNH

A genomic study supports the hypothesis that the evolution of ruminant horns and antlers was not independent.

From the small ossicones of a giraffe to the gigantic antlers of a bull elk, which can reach the width of a car, the headgear of ruminant hoofed mammals is extremely diverse, and new research suggests that despite physical differences, the fundamental aspects of these bony animals are extremely varied. the adaptations likely evolved from a common ancestor.

This discovery is published in the journal Communication biology by researchers from the American Museum of Natural History, Baruch College and the CUNY Graduate Center.

“Horns and antlers are incredibly diverse structures, and scientists have long debated their evolutionary origins,” said Zachary Calamari, assistant professor at Baruch College and the CUNY Graduate Center and a research associate at the Museum. “This genomic research not only brings us closer to solving an evolutionary mystery, but also helps us better understand how bones form in all mammals.”

Study of modern ruminant species

There are approximately 170 modern ruminant ungulate mammals species with headgear, and many others in the fossil record. The headgear we see today comes in four types: antlers, horns, ossicones, and pronghorns—and they are used in a variety of ways, including for defense, recognizing other members of the species, and mating . Until recently, scientists did not know whether these different bony head coverings evolved independently in each ruminant group or from a shared common ancestor.

Study author Zachary Calamari scans a moose skull at the American Museum of Natural History. Credit: Matt Shanley/AMNH

As a Ph.D. in Comparative Biology. A student at the Museum's Richard Gilder Graduate School, Calamari began studying this question using genomic and computerized analysis of 3D shapes. Working with John Flynn, the Museum's curator of fossil mammals, Calamari focused on sequencing transcriptomes, the genes expressed in a tissue at a specific time, for the helmets. Their research supports the idea that all forms of ruminant headgear evolved from a common ancestor as paired bony outgrowths originating from the animals' “forehead,” the area near the frontal bones of the skull.

Insights from Genetic Research

“Our results provide more evidence that horns form from the cranial neural crest, a layer of embryonic cells that forms the face, rather than from the cells that form the bones on the sides and back of the head,” Flynn said. “It is striking to note that these are the same cells that form the antlers. And the distinctive patterns of gene expression in bovine horns and deer antlers, compared to other bone and skin tissue “controls,” provide compelling evidence for the common origin of fundamental aspects of these bone structures. spectacular in an ancient ancestor. »

By comparing their newly sequenced bovine horn transcriptome to deer antler and pigskin transcriptomes, Calamari and Flynn confirmed for the first time with transcriptomes that family-specific headgear differences likely evolved under the form of elaborations on a general bone structure inherited from a common ancestor.

“In addition to gene expression patterns that support a unique origin of horns and antlers, our results also show that the regulation of gene expression patterns in these structures may differ from that of other bones,” Calamari said. “These results help us understand the evolutionary history of horns and antlers and could suggest that differences in other cranial appendages of ruminants, such as ossicones and pronghorns, are also elaborations on a shared ancestral cranial appendage.”

Reference: “Gene expression supports a unique origin of horns and antlers in hoofed mammals” by Zachary T. Calamari and John J. Flynn, May 20, 2024, Communication biology.
DOI: 10.1038/s42003-024-06134-4

This study was supported in part by the Richard Gilder Graduate School and the National Science Foundation, grant nos. DGE-0966166 and DDIG DEB-1601299.