本期Nature封面所示为Zachelmie 采石场的一块石板，其上有一个行迹和一个有四趾印的孤立足迹，这些印记用木炭凸显了出来。图片上的手是本文第一作者Grzegorz Niedzwiedzki的。
近4亿年前由四足陆地脊椎动物踩踏出的化石行迹的发现，将使人们对我们关于四足动物起源的认识进行较大重新评估。
由Per Ahlberg及其同事获得的这些发现来自波兰圣十字山中的Zachelmie 采石场。其中一些行迹保存非常完好，使人们可对足迹形态进行仔细研究，它们像是原始四足动物“鱼甲龙属”所留下来的。但使得这些行迹显得如此特殊的还是它们的年龄：它们比已知最早的四足动物身体化石要早1800万年，比最早的Elpistostegids（Tiktaalik、Panderichthys和它们的近亲，被看作是鱼类与四足动物之间的过渡形式）要早1000万年。这些发现表明，我们所知道的Elpistostegids是后来幸存下来的，而不是直接的过渡形式，它们反映了我们对于陆地脊椎动物最早历史的了解有多么少。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 463, 43-48 (7 January 2010) | doi:10.1038/nature08623
Tetrapod trackways from the early Middle Devonian period of Poland
Grzegorz Nied?wiedzki1, Piotr Szrek2,3, Katarzyna Narkiewicz3, Marek Narkiewicz3 & Per E. Ahlberg4
1 Department of Paleobiology and Evolution, Faculty of Biology, Warsaw University, 2S. Banacha Street, 02-097 Warsaw, Poland
2 Department of Paleontology, Faculty of Geology, Warsaw University, 93 ?wirki i Wigury Street, 02-089 Warsaw, Poland
3 Polish Geological Institute, 4 Rakowiecka Street, 00-975 Warsaw, Poland
4 Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Uppsala University, Norbyv?gen 18A, 752 36 Uppsala, Sweden
Correspondence to: Per E. Ahlberg4 Correspondence and requests for materials should be addressed to P.E.A.
The fossil record of the earliest tetrapods (vertebrates with limbs rather than paired fins) consists of body fossils and trackways. The earliest body fossils of tetrapods date to the Late Devonian period (late Frasnian stage) and are preceded by transitional elpistostegids such as Panderichthys and Tiktaalik that still have paired fins. Claims of tetrapod trackways predating these body fossils have remained controversial with regard to both age and the identity of the track makers. Here we present well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian (Eifelian stage) age that are approximately 18 million years older than the earliest tetrapod body fossils and 10 million years earlier than the oldest elpistostegids. They force a radical reassessment of the timing, ecology and environmental setting of the fish–tetrapod transition, as well as the completeness of the body fossil record.
