Research press release


Scientific Reports

Palaeontology: No supersonic boom for dinosaur tails

ディプロドクス科恐竜(長い首と尾を持つ大型草食恐竜)の尾をモデル化して調べたところ、その尾を牛追い鞭のように動かす際の最高速度が秒速33メートル(時速100キロメートル以上)だった可能性が明らかになったと報告する論文が、Scientific Reportsに掲載される。しかし、この知見は、ディプロドクス科恐竜の尾の先端に付いていたという仮説上の構造(牛追い鞭の先端の房に似た構造)が音速(秒速340メートル)よりも速く動いて、小さな衝撃波を発生させたかもしれないという考えを示した以前の結果と矛盾している。

今回、Simone Contiたちは、ディプロドクス科恐竜の化石標本(5点)をもとに作成したモデルを用いて、ディプロドクス科恐竜の尾の動きのシミュレーションを行った。この尾のモデルは、長さが12メートル以上、重さが1446キログラムで、椎骨を模した82本の円柱体で構成され、動かすことのできない寛骨の付け根に取り付けられた。尾の付け根が弧を描くように動かした時には、鞭のような動きが生じ、最高速度が秒速33メートルに達した。これは、標準大気での音速の10分の1に満たず、遅すぎて衝撃波は発生しない。



Diplodocids – large herbivorous dinosaurs with long necks and tails – may have been able to move their tails like bullwhips at speeds of up to 33 metres per second (more than 100 kilometres per hour), according to a modelling study published in Scientific Reports. However, these findings contradict those of a previous study, which proposed that a hypothetical structure attached to the end of a diplodocid tail – similar to a tuft at the end of a bullwhip – could move faster than the speed of sound (340 metres per second) and create a small supersonic boom.

Simone Conti and colleagues simulated diplodocid tail movements using a model based on five fossilised diplodocid specimens. The model tail is over 12 metres long, weighs 1,446 kilograms and consists of 82 cylinders – representing vertebrae – attached to an unmovable hip bone base. When the tail base moves in an arc, it generates a whip-like movement with a maximum speed of 33 metres per second – more than ten times slower than the speed of sound in standard air and too slow to create a supersonic boom.

The authors tested whether their model tail would be able to withstand the stress of moving fast enough to create a supersonic boom. They found that the thin whip-like tail could not move at a maximum speed of 340 metres per second without breaking. The authors then assessed whether adding three different one metre-long hypothetical structures – mimicking the end of a bullwhip – to the end of the model tail could allow it to travel at the speed of sound without rupturing. The first structure consisted of three segments made of skin and keratin, the second consisted of braided keratin filaments, and the third had a flail-like structure composed of soft tissues. None of the structures was able to withstand the stress of moving at 340 metres per second without the tail breaking.

Together, the findings suggest that diplodocid tails may not have been able to move fast enough to create a small supersonic boom. However, the authors speculate that diplodocids may have still been able to move their tails fast enough to use them as defensive weapons or for combat with other diplodocids.

doi: 10.1038/s41598-022-21633-2


メールマガジンリストの「Nature 関連誌今週のハイライト」にチェックをいれていただきますと、毎週各ジャーナルからの最新の「注目のハイライト」をまとめて皆様にお届けいたします。