Finished saber teeth in three years

The canines of Szechelium tigers were only fully mature despite rapid growth

Upper jaw of the saber-toothed tiger Smilodon fatalis with full-blown fangs © American Museum of Natural History / J. Tseng
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Fast and yet slower: The large canine teeth of saber-toothed tigers grew twice as fast as today's lions - and yet were fully grown at the age of three due to their enormous size. Using fossils, US researchers have researched growth and development of saber teeth in juveniles. Pronounced timing was important so that the teeth were ready in time for the hunt, the researchers write in the journal "PLOS ONE".

The most impressive feature of the extinct saber-toothed tiger are its giant canines: like daggers protrude up to 18 inches long from the upper jaw. The so armed animals of the genus Smilodon were in their time in North and South America at the top of the food chain. But about 10, 000 years ago disappeared the big cats, which are related in spite of the common name as Säbelzahntiger but little with today's tigers.

Few cub in the tar pits

At what stage of development and especially how fast the big cats their trademark grew, was previously unexplored. However, because the pronounced canines were a key feature of Smilodon's hunting behavior, they are important for a complete understanding of its lifestyle. Scientists led by Aleksander Wysocki of Clemson University, South Carolina, have studied the growth of saber teeth more closely.

They compared smilodon fossils from the La Brea tar pits in Los Angeles and paid special attention to the young animals' bits. However, these are relatively rare there: "Given the large number of predators around the tar pits, young animals would have been in danger of becoming prey themselves, " explains Wysocki. While other robbers hunted for animals caught in the tar and often got themselves stuck, the young cats therefore kept back.

Teeth of a juvenile: In addition to the larger milk tooth, the permanent saber tooth grows already. © American Museum of Natural History / J. Tseng

Sick teeth with rapid growth

In the rich fossil collections from the tar pits, the researchers still found enough material. Using isotope analysis and micro-computed tomography, they calculated the growth rate of the canines. They came to an impressive speed of six millimeters per month. This is about twice as fast as living lions today, and human fingernails grow about 3.4 millimeters per month. display

Despite this rapid growth, it took about three years for the saxophone offspring to have the full-grown dentition of an adult animal. Because just like humans and many other mammals also Smilodon had a first "Milchgebiss". The kittens initially grew a set of milk teeth, which had grown to about one and a half years.

Decisive timing

At this age, the skull bones finally grew together, which had previously been loosely attached, as well as in human infants. This happens about eight months later for lions cubs living today. However, the timing is crucial: the jaw muscles are attached to two of these skull bones. In order to be able to use the teeth effectively, they must not only be fully grown, but also a stable bone structure is necessary.

At about 20 months, the young cats lost their milk teeth. But that did not stop them toothless: The permanent teeth broke through towards the end of the growth phase of the milk teeth and were ready for use when they were dropped. For almost a year, a double set of teeth could be seen in the teeth of the young animals: the milk teeth and behind them the already growing permanent teeth. "Although his canines were more than twice as long as those of a lion, Smilodon needed less than twice as much time to grow them, " Wysocki concludes. (PLOS ONE, 2015; doi: 10.1371 / journal.pone.0129847)

(American Museum of Natural History, 02.07.2015 - AKR)