It is known that crossopterygians evolved into elpistostegids which would then become the first tetrapods (=four legged land animals; specifically the amphibians). However, our understanding of the fossil record is incomplete and what we find need not necessarily reflect the timing of evolution. The earliest body fossils of tetrapods are known from the Upper Devonian of Scotland, Greenland, Belgium, and several other places. However, trackways (=footprints) from what some consider to be from tetrapods are known from the Middle Devonian of Poland, Ireland, and Australia. These trackways suggest a Middle-Devonian origin of tetrapods. However, there is disagreement regarding the identification of these trackways. These trackways do not appear to show indisputable evidence of digits. What is also missing is a Middle Devonian tetrapod body. However, the object seen below bears a strong resemblance to a tetrapod skull. It is of Middle Devonian age. It is evident that it is quite dissimilar from the crocodile-like Upper Devonian tetrapods, and instead bears a closer resemblance to the early Carboniferous temnospondyli (also shown below), whose sudden appearance in the fossil record is also unexplained. If this is a tetrapod it would make this the oldest known body fossil. However, it is uncertain whether it really is a tetrapod skull. An alternative explanation is that this is the snout of a Glyptolepis paucidens which has been split down the middle in such a way as to create the illusion of a tetrapod skull. As this skull has yet to be scanned in high resolution, we regard this as a fossil of uncertain affinity.
