New research suggests that various headgear in ungulates evolved from a common ancestor

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A diverse array of mammalian 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 Core. Credit: Alvaro Keding/AMNH

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A diverse array of mammalian 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 Core. Credit: Alvaro Keding/AMNH

From the tiny ear bones of a giraffe to the gigantic antlers of a male moose – which can grow as wide as a car – the headgear of ruminant ungulate mammals is extremely diverse, and new research suggests that despite the physical differences, fundamental aspects of these bony adaptations probably evolved from a common ancestor.

This finding is published today in the journal Communication Biology by researchers from the American Museum of Natural History and Baruch College and the CUNY Graduate Center.

“Horns and antlers are incredibly diverse structures, and scientists have long debated their evolutionary origins,” says Zachary Calamari, an 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 bone forms in all mammals.”

There are approximately 170 modern species of headgeared and ruminant mammals, and many more in the fossil record. The headgear we see today comes in four types: antlers, horns, ossicles, and pronghorns, and they are used in a variety of ways, including for defense, recognition of other members of the species, and mating. Until recently, scientists were unsure whether these different bony headgear evolved independently in each group of ruminants or from a shared common ancestor.

As a comparative biology Ph.D. student at the museum’s Richard Gilder Graduate School, Calamari began investigating this question using genomic and computer-based 3D shape analysis. Working with the museum’s Frick Curator of Fossil Mammals, John Flynn, Calamari focused on sequencing transcriptomes, the genes expressed in a tissue at a specific time, for headgear.

Their research supports the idea that all forms of ruminant headgear evolved from a common ancestor as paired bony outgrowths of the animals’ “forehead,” the area near the frontal bones of the skull.

“Our results provide more evidence that horns arise from the cranial neural crest, an embryonic cell layer 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 that these are the same cells that form antlers. And the distinctive patterns of gene expression in bovine horns and deer antlers, compared to other ‘control mechanisms’ of bone and skin tissue, provide compelling evidence of the shared origin of fundamental aspects of these. spectacular bony structures in an ancient ancestor.”


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

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

By comparing their newly sequenced transcriptome from cattle horns with transcriptomes from deer antlers and pig skins, Calamari and Flynn confirmed for the first time with transcriptomes that family-specific differences in headgear likely evolved as elaborations of a common bony structure inherited from a common ancestor.

“In addition to gene expression patterns supporting a single origin of horns and antlers, our results also show that the regulation of gene expression patterns in these structures may differ from other bones,” Calamari said.

“These results help us understand the evolutionary history of horns and antlers and could suggest that differences in other ruminant cranial appendages, such as ossicles and pronghorns, are also elaborations of a shared ancestral cranial appendage.”

More information:
Zachary T. Calamari et al., Gene expression supports a single origin of horns and antlers in ungulates, Communication Biology (2024). DOI: 10.1038/s42003-024-06134-4

Magazine information:
Communication Biology

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