Cordylus tropidosternum (Cope, 1869)
鎧と隙間で身を守るトカゲ
Protected by Armor and Crevices
全長約15～18cm。東アフリカからアフリカ南東部に分布するヨロイトカゲ科のトカゲで、「ネッタイヨロイトカゲ」の名でも知られています。ヨロイトカゲ類は、全身を覆う硬い鱗と棘状の尾を備え、爬虫類の中でも特に防御能力に優れたグループです。共通して頑丈な「鎧」をまとっていますが、その生かし方は種によって異なります。本種は比較的小型で、岩場だけでなく樹木も利用するなど環境への適応の幅が広く、体色は褐色から黄褐色を基調とし、暗色の帯やまだら模様によって岩肌や樹皮に溶け込む優れた保護色となっています。
ヨロイトカゲ類には、尾を口でくわえて体を丸めるアルマジロトカゲや、体をこわばらせて棘を外側へ向けることで捕食者に対抗する種など、多様な防御方法が見られます。一方、本種は危険を察知すると素早く岩の割れ目や樹皮の隙間へ逃げ込み、四肢を突っ張って体を隙間に押し付けることで、外敵に引き出されにくい姿勢をとります。頑丈な鱗と棘のある尾は、この防御行動を支える重要な役割を果たしており、隙間を巧みに利用することが本種最大の特徴です。昼行性で、昆虫やクモなどの小型無脊椎動物を捕食します。
トカゲ類の多くが卵を産むのに対し、本種は卵胎生で、雌は卵を体内で育てた後、4～6頭ほどの幼体を直接産みます。比較的小型で飼育下繁殖例も多いことから、ヨロイトカゲ類を代表する飼育種の一つとして広く親しまれています。現在は比較的広い分布域をもち、IUCNレッドリストでは「軽度懸念（LC）」に分類されています。鎧のような姿だけでなく、多様な防御戦略を進化させたヨロイトカゲ類の魅力を知る入口として、本種は格好の存在といえるでしょう。
Reaching a total length of about 15–18 cm, the Tropical Girdled Lizard is a member of the girdled lizard family distributed from East Africa to southeastern Africa. In Japanese, it is also known as the “Nettai Yoroi Tokage.” Girdled lizards are renowned for their exceptional defensive adaptations, characterized by their heavily armored scales and spiny tails. Although all members of the group share this living “armor,” they employ it in different ways. This relatively small species inhabits rocky areas as well as trees, demonstrating a broad ecological adaptability. Its brown to yellowish-brown body, often marked with dark bands or mottled patterns, provides excellent camouflage against rocks and tree bark.
Girdled lizards display a remarkable variety of defensive strategies. Some species, such as the Armadillo Girdled Lizard, curl into a tight ring while gripping the tip of the tail in the mouth. Others stiffen their bodies and present their spiny scales to discourage predators. In contrast, the Tropical Girdled Lizard relies on narrow crevices for protection. When threatened, it quickly retreats into cracks in rocks or beneath loose bark, then braces itself by extending its limbs and pressing its body firmly against the surrounding surfaces, making it extremely difficult for predators to pull it free. Its robust scales and spiny tail are essential to this strategy. The species is diurnal and feeds mainly on small invertebrates such as insects and spiders.
Unlike most lizards, which lay eggs, this species is viviparous, giving birth to approximately four to six fully developed young after retaining the eggs within the mother’s body. Because of its relatively small size and the success of captive breeding, it has become one of the best-known and most widely kept girdled lizards among reptile enthusiasts. Owing to its broad distribution, it is currently classified as Least Concern (LC) on the IUCN Red List. With its armored appearance and distinctive defensive behavior, this species offers an excellent introduction to the fascinating world of girdled lizards.
参考文献
All About 趣味 | ヒナタヨロイトカゲの基本情報と飼育方法！ 海外のトカゲの魅力 | 星野 一三雄 (2023年11月26日) 2026年7月18日閲覧
ANIMALIA | East African spiny-tailed lizard 2026年7月18日閲覧