September 30, 2022

Strange Animals That Lived Before the Dinosaurs Reveal the Evolutionary Origin of Tusks

In a brand-new study in Proceedings of the Royal Society B, paleontologists traced the very first tusks back to ancient mammal loved ones that lived before the dinosaurs, and to do so, they had to specify what makes a tusk a tusk in the very first place.
The researchers decided that for a tooth to be a tusk, it has to extend out past the mouth, it has to keep growing throughout the animals life, and unlike the majority of mammals teeth (consisting of ours), tusks surface areas are made of dentine rather than hard enamel.
To study whether dicynodonts tusks actually were tusks, the scientists cut paper-thin pieces out of the fossilized teeth of 19 dicynodont specimens, representing ten different species, and analyzed their structure with a microscope. It wasnt a stringent development from non-tusks to tusks, however– different members of the dicynodont household evolved tusks individually.
” Dicynodont tusks can inform us a lot about mammalian tusk development in general,” states Angielczyk.

Life restoration of the dicynodont Dicynodon. Aside from the tusks in the upper jaw, many dicynodonts possessed a turtle-like beak that they utilized to chew their food.
A variety of animals have tusks, from elephants and walruses to five-pound, guinea pig-looking animals called hyraxes. But something tusked animals have in typical is that theyre all mammals– there are no known fish, reptiles, or birds with tusks. In a brand-new study in Proceedings of the Royal Society B, paleontologists traced the first tusks back to ancient mammal relatives that lived prior to the dinosaurs, and to do so, they had to define what makes a tusk a tusk in the very first place.
” Tusks are this really famous anatomy, however till I began dealing with this study, I never actually thought of how tusks are limited to mammals,” states Megan Whitney, a researcher at Harvard University and the lead author of the research study.
” We had the ability to reveal that the first tusks belonged to animals that came before modern-day mammals, called dicynodonts,” says Ken Angielczyk, a curator at Chicagos Field Museum and an author of the paper. “Theyre really weird animals.”

Left side of the skull of the dicynodont Dolichuranus (NMT RB554) from Tanzania. The big tusk is visible at the lower left of the specimen. Credit: Ken Angielczyk
The dicynodonts mostly lived prior to the time of the dinosaurs, from about 270 to 201 million years earlier, and they varied from rat-sized to elephant-sized. Modern mammals are their closest living loved ones, but they looked more reptilian, with turtle-like beaks. And since their discovery 176 years earlier, one of their specifying features has been the pair of protruding tusks in their upper jaws. The name dicynodont even means “2 canine teeth.”
The scientists understood to study the origin of tusks while taking a lunch break on a paleontological dig. “We were being in the field in Zambia, and there were dicynodont teeth all over,” remembers Whitney. “I keep in mind Ken selecting them up and asking how come they were called tusks, because they had features that tusks dont have.”
Angielczyk had hit upon an important difference: not all protruding teeth are technically tusks, and the teeths makeup and development patterns inform us whether they count. “For this paper, we needed to define a tusk, since its a surprisingly ambiguous term,” says Whitney. The scientists chose that for a tooth to be a tusk, it has to extend out past the mouth, it has to keep growing throughout the animals life, and unlike the majority of mammals teeth (including ours), tusks surface areas are made of dentine instead of difficult enamel.
Separated tusk fragments found in Zambia by field groups in 2018. Credit: Ken Angielczyk
Under these criteria, elephants, walruses, warthogs, and hyraxes all have tusks. Other big teeth in the animal kingdom do not make the cut. Rodent teeth, even though they in some cases stick out and are ever-growing, have an enamel band on the front of the tooth, so they dont count.
Some of the dicynodont tusks that the group observed in Zambia didnt appear to fit the definition of a tusk either– they were coated in enamel instead of dentine.
The different makeup of teeth versus tusks likewise gives researchers insights into an animals life. “Enamel-coated teeth are a different evolutionary method than dentine-coated tusks, its a trade-off,” states Whitney. Enamel teeth are harder than dentine, but due to the fact that of the geometry of how teeth grow in the jaw, if you desire teeth that keep growing throughout your life, you cant have a total enamel covering.
Animals like human beings made an evolutionary financial investment in long lasting but hard-to-fix teeth– once our adult teeth grow in, were out of luck if they get broken. Tusks are less durable than our enamel-coated teeth, but they grow continually, even if they get damaged. Its like the compromise of getting a vehicle thats very trusted but really challenging to get fixed when it does have trouble, versus driving a beater that needs regular repairs but is a model thats inexpensive and simple for any mechanic to repair.
The different sort of teeth animals have developed can tell researchers about the pressures those animals dealt with that might have produced those teeth. Animals with tusks might utilize them for battling or for rooting in the ground, exposing them to little injuries that would be risky for enamel teeth that do not grow continuously.
To study whether dicynodonts tusks truly were tusks, the scientists cut paper-thin slices out of the fossilized teeth of 19 dicynodont specimens, representing ten different species, and analyzed their structure with a microscope. It wasnt a strict progression from non-tusks to tusks, however– various members of the dicynodont household progressed tusks individually.
Whitney says she was surprised by the finding. “I sort of expected there to be one point in the family tree where all the dicynodonts began having tusks, so I believed it was quite stunning that we really see tusks develop convergently,” she states.
” Dicynodont tusks can tell us a lot about mammalian tusk development in general,” says Angielczyk. “For instance, this study reveals that reduced rates of tooth replacement and a flexible ligament attaching the tooth to the jaw are required for true tusks to progress. Everything ladders as much as giving us a much better understanding of the tusks we see in mammals today.”
” Dicynodonts were the most varied and plentiful vertebrates on land prior to dinosaur times, and theyre popular for their tusks. The reality that in truth just a few have true tusks, and the rest have huge teeth, is a lovely example of development we can document. We can see how to build a tusk!” says Brandon Peecook, a curator at the Idaho Museum of Natural History and one of the papers authors.
The scientists say that the research study, which shows the earliest known instance of true tusks, might help researchers better comprehend how evolution works.
” Tusks have evolved a variety of times, which makes you question how– and why? We now have good data on the physiological modifications that required to occur for dicynodonts to evolve tusks. For other groups, like warthogs or walruses, the jury is still out,” says Christian Sidor, a curator at the University of Washington Burke Museum and among the papers authors.
” Despite being extremely odd animals, there are some things about dicynodonts, like the evolution of tusks, that notify us about the mammals around us today,” says Angielczyk. “Plus, anytime you can say mammals arent that special, dicynodonts did it first, thats a good day.”
For more on this research, read Fossil Dental Exams Reveal How Tusks Evolved– Originated in “Very Weird Animals” Called Dicynodonts.
Referral: “The evolution of the synapsid tusk: insights from dicynodont therapsid tusk histology” by M. R. Whitney, K. D. Angielczyk, B. R. Peecook and C. A. Sidor,27 October 2021, Proceedings of the Royal Society B.DOI: 10.1098/ rspb.2021.1670.

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