Ancient DNA analysis has solved a key mystery in the family tree of crocodiles, researchers say, historically an incredibly diverse and rapidly evolving group of critters whose ancestry has proven tricky to unravel.
The extinct “horned” crocodile (Voay robustus), endemic to Madagascar, now has a secure spot in the branches of “true” crocodiles.
It would have been a sister to Crocodylus niloctus, the famous Nile croc, which is the only species remaining on the island. The discovery also supports notions that modern crocodile ancestry has its roots in Africa.
As the species’ “first molecular systematic characterisation”, the researchers say their study, published in the journal Communications Biology, challenges evolutionary trees that have grouped Voay with dwarf crocodiles (Osteolaemus tetraspis).
V. robustus is thought to have died out with other megafauna including elephant birds, giant tortoises, dwarf hippos and various lemur species following human settlement 9000 to 2500 years ago.
“This crocodile was hiding out on the island of Madagascar during the time when people were building the pyramids, and was probably still there when pirates were getting stranded on the island,” says lead author Evon Hekkala, from Fordham University, US.
“They blinked out just before we had the modern genomic tools available to make sense of the relationships of living things. And yet, they were the key to understanding the story of all the crocodiles alive today.”
Hekkala’s team conducted phylogenetic analysis of 1300–1400-year-old mitochondrial genomes from V. robustus fossil skulls preserved in the American Museum of Natural History, unearthed from Holocene deposits in the island’s southwestern corner.
Their results suggest the horned crocodile is the closest species to the common ancestor of today’s living crocodiles.
“This finding was surprising and also very informative to how we think about the origin of the true crocodiles found around the tropics today,” says co-author George Amato. “The placement of this individual suggests that true crocodiles originated in Africa and from there, some went to Asia and some went to the Caribbean and New World.”
Natalie Parletta is a freelance science writer based in Adelaide and an adjunct senior research fellow with the University of South Australia.
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