About
When you travel along National Route 299, which weaves through the mountains of Kanna Town in Gunma Prefecture, you will come across an impressive rock wall known as the Sebayashi Ripple Marks (“Sazanami Iwa”), standing 15 meters high and 11 meters wide. On the surface of this rock are traces of waves formed about 120 million years ago, during the Cretaceous period. Back then, this area was a sea, and the waves that washed up on the sandy shore created patterns in the sand, which over time fossilized. These ripple marks were designated as a Natural Monument of Gunma Prefecture in 1965 (Showa 40).
However, this rock wall held an even more astonishing secret. In 1985 (Showa 60), researchers discovered that the depressions on the upper part of the ripple marks were actually dinosaur footprints. This was the first confirmation of fossilized dinosaur footprints in Japan, leading the then-Nakazato Village (now Kanna Town) to declare itself the “Dinosaur Kingdom.” On the upper left portion of the rock wall are two large footprints of a bipedal dinosaur, and from the upper right to lower left, there are a series of footprints from a smaller dinosaur. These footprints are proof that dinosaurs once walked in this land.
The geological strata here form part of a 40-kilometer-long and 2-4 kilometer-wide mountain graben zone that extends along National Route 299 from Ogano Town in Saitama Prefecture, over the Shigasaka Pass, through Kanna Town and Ueno Village in Gunma Prefecture, across the Jukkoku Pass at the Gunma-Nagano border, and finally to Sakuho Town in Nagano Prefecture. This graben zone is an area where Early Cretaceous strata spread widely, and many dinosaur footprints and fossils have been found here.
Near the Sebayashi Ripple Marks is the Kanna Town Dinosaur Center, where dinosaur fossils and models are on display. Events such as hands-on fossil excavation experiences are also held, offering visitors a chance to feel the romance of ancient times. A visit to this place will let you sense the breath of dinosaurs from over 100 million years ago.
群马县神流町的山间，沿着国道299号线前行，就会见到被称为“濑林漣痕（波纹岩）”的岩壁，高15米，宽11米。在这块岩壁表面，刻有大约1亿2千万年前白垩纪时期形成的波浪痕迹。当时，这一带被海洋覆盖，海浪拍打沙滩，在沙面上留下了波纹，这些波纹经过漫长岁月沉积为化石。1965年（昭和40年），这种漣痕被指定为群马县的天然纪念物。
然而，这块岩壁还隐藏着更为惊人的秘密。1985年（昭和60年），研究人员发现，在波纹岩上部的凹陷实际上是恐龙的足迹。这是日本首次被确认的恐龙足迹化石，因此，当时的中里村（现神流町）宣布自己为“恐龙王国”。岩壁左上有两枚大型二足行走恐龙的足迹，从右上到左下则排列着小型恐龙的足迹。这些足迹证明恐龙曾在这片土地上行走。
这一地层属于一条全长40公里、宽2至4公里、沿国道299号延伸的山地地堑带，这条地堑从埼玉县小鹿野町出发，越过志贺坂峠，经群马县神流町、上野村，再越过上信国境的十石峠，抵达长野县佐久穗町。这条地堑带内广泛分布着白垩纪前期的地层，恐龙足迹和化石在此多有发现。
濑林漣痕附近建有神流町恐龙中心，馆内展示有恐龙化石和模型，并定期举办化石发掘体验等活动，让到访者感受太古时代的浪漫。来到这里，你将有机会亲身感受到1亿多年前恐龙的气息。