a clade is a taxonomic group of closely related species.
Afropithecus and kenyapithecus (and related ilk) are taxa of non-bipedal primates who lived during the miocene, which was a time of a huge expansion of african primates, particularly apes (a primate without a tail). There has been some speculation that those taxa did not lead to hominids (bipedal apes), but are closely related to one/s that did later in the pliocene.
A synapomorphy is a shared derived characteristic, that is, a character that a species has that is more "advanced" than ancestral species and is shared with later related species. Cladistics would put species that have synapomorphies as more closely related than those that don't. This european fossil has synapomorphies that would put it into a clade with african apes thought to be closely-related to pliocene hominids, such as a flatter face, which is a synapomorphy of hominids in relation to, say, monkeys. It is, however extremely fragmentary (although a lot can be told from the right bit of fragment!).
The authors are claiming this one find posits a euro-asian origin for the pliocene emergence of hominids--a huge claim because it is thought that the first hominids led to...us. Conversely they say that perhaps there was parallel evolution going on whereby bipedality evolved both in europe and in africa.
I haven't seen this fossil, but i am skeptical...contrarary to the abstract, there is a mountain of fossil evidence from miocene/pliocene africa that indicates that the earliest hominids came out of an african clade of apes to roam the savannah as the climate changed and started to dry up the vast jungles they lived in. Which one is not known, due to the difficulty of finding fossils where there is or used to be rainforests (animals don't fossilize in jungles), which is what most of africa was during the miocene. But one fossil from spain? Let's see more fossils, not just one newly-named species
does that help?
Oh yeah, and since this is a mead forum, eventually those african apes evolved into us--mead brewing bipedal apes. The pinnacle of the evolutionary process.