David M. Alba, researcher at the ICP, has just published in the journal Evolutionary Anthropology an article that reviews the entire fossil record of the Vallès-Penedès hominoids and outlines its implications for the evolution of this group. Although there is still scientific debate about some elements, the Catalan hominids are increasingly seen as primitive forms of the family Hominidae (great apes and humans), although a closer relationship with orangutans than with African apes and humans is not excluded.
The more we learn about the fossil hominids of the Vallès-Penedès, the further is the hypothesis that these apes have a closer relationship with hominins (gorillas, chimpanzees, bonobos and us humans) than with orangutans. To some extent, this information is a bit disappointing for those who want to be close to the home origin of our species. But if everything is confirmed, we are once again faced with one of the challenges that the scientific study of evolution is getting us used to.
The hominids of the Vallès-Penedès, an amazing mixture of modern and primitive traits
The fossil specimen Pierolapithecus catalaunicus (Abocador de Can Mata, els Hostalets of Pierola, 11.9 My), known as Pau, shows the first unequivocal evidence of orthogrady (erect trunk) among the fossil hominids known worldwide. His face has the characteristics of modern facial morphology of extant great apes. But, Pierolapithecus also shows primitive adaptations for quadruped movement over the branches.
The facial remains of Dryopithecus fontani (Abocador de Can Mata in els Hostalets de Pierola and Castell de Barbera in Barberà del Vallès, 11.9-10.5 My) show a more modern morphology that, in some respects, recalls that of extant gorillas. Moreover, Dryopithecus had a thin enamel tooth, such as the African great apes. Other postcranial remains, however, show a mix of modern features, similar to modern hominids, and primitives, characteristic of the Miocene hominids.
The fossil remains of Hispanopithecus laietanus (Can Llobateres and Estació Depuradora d’Aigües Residuals in Sabadell, Can Feu in San Quirze del Vallès, among others, 10-9.5 My) show more derived facial, as well as the rest of the skeleton, characteristics than those of dryopithecines of the Middle Miocene (Pierolapithecus, Dryopithecus and Anoiapithecus), but it does not seem clear that these characteristics are more closely related to extant great apes. In any case, it is the first hominid showing adaptations for moving suspended under the branches, as shown by a study based on the specimen known as Jordi, while still preserving some adaptation to most primitive quadruped arboreal movements.
Neither the study of the remains of Anoiapithecus brevirostris (Abocador de Can Mata in els Hostalets Pierola, 11.9 My) nor of Hispanopithecus crusafonti (Teuleria del Firal in Seu d'Urgell and Can Poncic in San Quirze del Vallès, 10-10.5 My ) is conclusive on the position of the Catalan Miocene hominids in our lineage.
A captivating and exciting challenge
The information provided by the Vallès-Penedès hominids adds to that obtained with other fossil Hominoids in Africa, elsewhere in Europe and Asia. The first hominoids are found in Africa, about 23 million years ago, while the oldest hominid fossils (kenyapithecines) are found in Europe, Africa and Turkey about 15-14 My ago. About 13 My ago, in Europe, these forms would have led to dryopitecines (represented by Catalan Miocene hominids ), which would probably have ended extinct without descendants, while the evolution in Asia could have resulted in pongines (currently represented by orangutans). It is still to be understood, however, if the African hominins originated in this continent from African kenyapithecines or if they evolved from some Eurasian form who returned to Africa about 10 My ago.
If dryopithecines truly became extinct without originating any modern extant hominid form, and if pongines and hominins evolved independently from more primitive kenyapithecines, then ... How can Catalan dryopithecines, as Hispanopithecus, show more derived locomotor characteristics, similar to extant hominids?
The answer lies in what is known as homoplasy or fake homology , ie similar characters evolved independently in two different organisms, often due to similar adaptations. The more we delve into the study of the family Hominidae, the more we realize that homoplasy is everywhere, and particularly affects those characters involved in locomotion.
The Catalan Miocene hominids are now considered stem hominids, and contrary to what some researchers had argued in the past, they do not show any characteristic that allows us to relate them to hominins. This would support an evolution of hominins exclusively African, from African kenyapithecines instead of European dryopithecines. We still need to clarify, however, the phylogenetic relationships among the various European dryopithecines, and it is not ruled out that it could be brother group of pongines, rather than basals hominids earlier to the divergence between pongines and hominins.
In any case, the Miocene hominids play an important role in the study of the family Hominidae. In fact, given the high degree of homoplasy present in the evolution of this group, and the current decimated diversity, it is impossible to reconstruct the evolutionary history of our lineage exclusively from the few extant forms that have survived. To do that, we need to study the fossil record.