A diverse array of mammalian headgear is on display in the museum’s Richard Gilder Center for Science, Education and Innovation as part of the Louis V. Gerstner, Jr. Collections. Author: Alvaro Keding/AMNH
A genomic study supports the hypothesis that the evolution of horns and ruminant horns was not independent.
From the tiny ossicones of a giraffe to the huge antlers of a moose, which can reach the width of a car, the headgear of ruminant ungulates is extremely diverse, and new research suggests that despite the physical differences, the fundamental aspects of these bony animals are very diverse. the adaptations probably evolved from a common ancestor.
This discovery was published in the journal Communication biology by researchers from the American Museum of Natural History, Baruch College and the CUNY Graduate Center.
“Deer 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 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 are formed in all mammals. »
Study of modern ruminant species
There are about 170 modern ungulate ruminant mammals species with headdresses and many others in the fossil record. The headgear we see today comes in four types: horns, antlers, ossicones, and pronghorns—and is used in a variety of ways, including defense, recognizing other members of the species, and mating. Until recently, scientists did not know whether these different headdresses evolved independently in each group of ruminants or from a common ancestor.
Study author Zachary Calamari scans a moose skull at the American Museum of Natural History. Credit: Matt Shanley/AMNH
As a PhD in comparative biology. A student at the museum’s Richard Gilder Graduate School, Calamari began studying this question using genomics and computerized 3D shape analysis. Working with John Flynn, the museum’s curator of mammalian fossils, Calamari focused on sequencing the transcriptomes, the genes expressed in tissue at specific times, 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 animal’s “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 shape the face, rather than from cells that form the bones at the sides and back of the head,” Flynn said. “It is striking to note that these are the same cells that form horns. And the distinctive patterns of gene expression in bovine antlers and deer antlers, compared to other “controls” of bone and skin tissue, provide compelling evidence for the common origin of fundamental aspects of these spectacular bone structures in an ancient ancestor. »
By comparing their newly sequenced bovine horn transcriptome with that of deer antler and pigskin, Calamari and Flynn confirmed for the first time with transcriptomes that family-specific headgear differences likely evolved as elaborations of a general bone structure inherited from a common ancestor.
“In addition to the gene expression patterns that support the unique origin of antlers and deer, our results also show that the regulation of gene expression patterns in these structures may differ from that in other bones,” Calamari said. “These results help us understand the evolutionary history of antlers and deer and could suggest that differences in other ruminant cranial appendages, such as ossicones and tusks, are also elaborations of a shared ancestral cranial appendage. »
This research was supported in part by the Richard Gilder Graduate School and the National Science Foundation, grant no. DGE-0966166 and DDIG DEB-1601299.