{"id":1885,"date":"2015-08-31T09:22:14","date_gmt":"2015-08-31T14:22:14","guid":{"rendered":"http:\/\/naturalsciences.org\/calendar\/?post_type=news&p=1885"},"modified":"2015-09-06T11:34:59","modified_gmt":"2015-09-06T16:34:59","slug":"tail-as-old-as-time-researchers-trace-ankylosaurs-tail-evolution","status":"publish","type":"news","link":"https:\/\/naturalsciences.org\/calendar\/news\/tail-as-old-as-time-researchers-trace-ankylosaurs-tail-evolution\/","title":{"rendered":"Tail As Old As Time \u2013 Researchers Trace Ankylosaur\u2019s Tail Evolution"},"content":{"rendered":"

How did the ankylosaur get its tail club? According to research from North Carolina State University and the North Carolina Museum of Natural Sciences that traces the evolution of the ankylosaur\u2019s distinctive tail, the handle arrived first on the scene, and the club followed.<\/p>\n

The typical ankylosaur had a wide armored body and a flexible tail. But one group of ankylosaurs \u2013 ankylosaurids \u2013 also had a tail club that could have served as a useful weapon. These \u201cweaponized\u201d ankylosaurids lived about 66 million years ago, during the Cretaceous period. But ankylosaurian dinosaurs were around well before that time \u2013 over 145 million years ago, during the Jurassic.<\/p>\n

Victoria Arbour, currently a postdoctoral researcher at NC State and the North Carolina Museum of Natural Sciences, formerly a Ph.D. candidate at the University of Alberta when she started the work, was interested in how the ankylosaur developed its unique tail. In a paper published in the Journal of Anatomy<\/em>, Arbour compared Jurassic ankylosaur specimens to those from the early and late Cretaceous period, tracing the tail\u2019s evolution from flexible to fearsome.<\/p>\n

An ankylosaur\u2019s tail is composed of a handle and a knob. The knob is made up of osteoderms, a special kind of bone formed in the skin, or dermis, that are unique to armored dinosaurs. The handle is the lower portion of the tail which supports the knob.<\/p>\n

\u201cIn order for an ankylosaur to be able to support the weight of a knob and swing it effectively, the tail needs to be stiff, like an axe handle,\u201d says Arbour. \u201cFor that to occur, the vertebrae along the tail had to become less flexible, otherwise the momentum generated by the knob\u2019s weight could tear muscle or dislocate vertebrae.\u201d<\/p>\n

Arbour looked at a number of early ankylosaurids including Liaoningosaurus<\/em> which lived 122 million years ago, Gobisaurus<\/em>, which lived 90 million years ago, and Pinacosaurus<\/em>, which lived 75 million years ago and is the earliest specimen with a complete tail club, to determine which of three possible evolutionary paths was most likely.<\/p>\n

\u201cThere are three ways the tail could have evolved,\u201d Arbour says. \u201cThe knob could have evolved first, in which case you\u2019d see ankylosaurids with osteoderms enveloping the end of the tail, but with the tail remaining flexible. The handle could have evolved first, meaning you would see early ankylosaurids with overlapping or fused tail vertebrae. Or the knob and handle could have evolved in tandem, in which case you\u2019d see ankylosaurids with both structures, but there could have been other differences like shorter handles or smaller knobs\u201d<\/p>\n

By comparing the tails of the specimens, Arbour saw that by the early Cretaceous, ankylosaurs had begun to develop stiff tails with fused vertebrae. The knob appeared in the late Cretaceous.<\/p>\n

\u201cWhile it\u2019s possible that some of the species could still have developed the handle and knob in tandem,\u201d says Arbour, \u201cit seems most likely that the tail stiffened prior to the growth of the osteoderm knob, in order to maximize the tail\u2019s effectiveness as a weapon.\u201d<\/p>\n

Philip Currie, professor and research chair in dinosaur paleobiology at the University of Alberta, Canada, contributed to the work. The research was funded by the National Sciences and Engineering Research Council, the Killam Trusts, and the Dinosaur Research Institute<\/p>\n

Note to editors<\/strong>: Abstract follows<\/p>\n

\"A<\/a>

A timeline showing the steps in the evolution of ankylosaur tail clubs. Diagram by Victoria Arbour.<\/p><\/div>\n

\u201cAnkylosaurid dinosaur tail clubs evolved through stepwise acquisition of key features\u201d<\/strong><\/p>\n

Authors<\/em>: <\/strong>Victoria Arbour, NC State University, North Carolina Museum of Natural Sciences, and the University of Alberta, Canada; Philip Currie, University of Alberta, Canada<\/p>\n

Published:<\/em> Journal of Anatomy<\/em><\/p>\n

Abstract:<\/strong><\/p>\n

Ankylosaurid ankylosaurs were quadrupedal, herbivorous dinosaurs with abundant dermal ossifications. They are best known for their distinctive tail club composed of stiff, interlocking vertebrae (the handle) and large, bulbous osteoderms (the knob), which may have been used as a weapon. However, tail clubs appear relatively late in the evolution of ankylosaurids, and seemed to have been present only in a derived clade of ankylosaurids during the last 20 million years of the Mesozoic Era. New evidence from mid Cretaceous fossils from China suggests that the evolution of the tail club occurred at least 40 million years earlier, and in a stepwise manner, with early ankylosaurids evolving handle-like vertebrae before the distal osteoderms enlarged and coossified to form a knob.<\/p>\n