The mystery of Pliobates cataloniae

The Pliobates cataloniae is an extinct primate that lived in what is now Catalonia 11.6 million years ago.

The enigma began to be forged in 2015, when a partial skeleton with the associated skull of a small primate from the Abocador de Can Mata (a landfill located in the Catalan town of Hostalets de Pierola) was described as a new genus and species, Pliobates cataloniae. . Nicknamed “Laia” by the researchers, this partial skeleton corresponds to an adult female weighing about 5 kilograms that lived in the subtropical forests of the Vallès-Penedès basin about 11.6 million years ago.

The original study revealed that Laia consumed soft fruits and moved through the forest canopy by cautiously climbing, and combining this with hanging from branches.

In that study, phylogenetic analyzes were also carried out based on the morphological characteristics of the teeth, skull and the rest of the body, with the aim of deciphering the closest kinship relationships of Pliobates. The results suggested that Pliobates was a basal anthropomorph prior to the divergence between small anthropomorphic apes (gibbons and siamangs) and great anthropomorphic apes (orangutans, gorillas and chimpanzees).

However, subsequent phylogenetic analyzes by other research teams suggested that Pliobates is a pliopithecoid, that is, a more primitive ape, prior to the divergence between Old World monkeys and anthropomorphs.

The truth is that the skeleton of Pliobates shows a surprising mosaic, with a mixture of primitive characteristics like those of basal apes, along with others more similar to those presented by current anthropomorphs, which makes the interpretation of their kinship relationships difficult.

Now, the scientific description of new dental remains and the results of new phylogenetic analyzes of Pliobates have been presented.

The work has been carried out by an international team led by the Miquel Crusafont Catalan Institute of Paleontology (ICP) in Cerdanyola del Vallès and which is one of the NEAR institutions of the Generalitat of Catalonia.

The newly described teeth come from a different locality, but are about the same age as the “Laia” skeleton. The researchers used microcomputed tomography not only to examine the internal morphology of teeth (specifically focusing on the enamel-dentin junction, which is not affected by tooth wear), but also to digitally extract permanent teeth from juvenile individuals who had not yet erupted. “The lower first and second molars that we extracted from a child’s jaw were especially important,” explains Florian Bouchet, first author of this study, which is part of his doctoral thesis. “The shape of the lower molars has great diagnostic value for pliopithecoid primates, mainly due to the presence of a distinctive structure known as the ‘pliopitecine triangle’,” adds the researcher. It is a small valley bounded by two ridges (the ‘arms’ of the triangle), which distinguish pliopithecoids from other primates.

“The results of the study conclusively indicate that Pliobates is a derived crouzellid pliopithecoid, more closely related to little-known and also small-sized genera such as Plesiopliopithecus and Crouzelia, which have been recorded elsewhere in Europe,” explains the main senior author of the study and director of the ICP, David M. Alba.

Interestingly, phylogenetic analyzes integrating the new dental data unequivocally support the crouzelid consideration of Pliobates. However, they lead to very different results for pliopithecoids as a whole, depending on the anatomical region considered.

Therefore, craniodental characteristics place pliopithecoids as a basal catarrhine clade, that is, as a group that includes all descendants of a last common ancestor that diverged before the split between Old World monkeys and anthropomorphs. .

In contrast, when postcranial features are included in the analyses, it incorrectly places pliopithecoids as basal hominoids, more closely related to anthropomorphs and humans than to monkeys. This is because Pliobates exhibits multiple postcranial features convergent with those of modern anthropomorphs, reinforcing the view that such features could also have evolved independently among various lineages of anthropomorphs due to adaptation to climbing and/or suspension behaviors. .

In summary, the results show that Pliobates is a primitive pliopithecoid, a basal catarrhine that shows features convergent with extant hominoids. Despite this, Pliobates remains a very relevant element in elucidating the evolution of hominoids. On the one hand, it nicely illustrates the possibility that similar postcranial characteristics exist in groups that have evolved independently due to similar selection pressures. On the other hand, Pliobates has been reconstructed as a cautious arboreal climbing animal that also shows important quadrupedal and suspensor components in its locomotor repertoire. Consequently, it can be considered a suitable analogue model to understand the intermediate phases in the evolutionary transition from quadrupedal anthropomorphs to climbers/suspenders during hominoid evolution.

The study is titled “The Miocene primate Pliobates is a pliopithecoid.” And it has been published in the academic journal Nature Communications.

Recreation of the appearance in life of Pliobates cataloniae made by Quagga (currently on display at the ICP Museum in Sabadell), surrounded by the new infant jaw with the permanent molars in semi-transparency (right) and occlusal view of the digitally extracted first lower molar showing the distal arm of the pliopithecine triangle (left), without scale. (Photography by DM Alba and digital illustrations by Florian Bouchet, © ICP)

The exceptional paleontological macrosite of the Can Mata landfill

The macrodeposit of the Can Mata landfill, in the fossiliferous area of ​​Hostalets de Pierola (Catalonia, northeast of the Iberian Peninsula), is one of the most important in the world for the study of Miocene primates. The paleontological control carried out during the expansion of the landfill over the last two decades, under the scientific supervision of researchers linked to the ICP, has made it possible to recover thousands of fossil remains of vertebrates from between 12.6 million and 11.1 million years ago, including some extraordinary remains of primate skeletons. In addition to Pliobates, the skeleton of Pierolapithecus catalaunicus (known as “Pau”), found in 2002 and scientifically described in 2004, as well as the skull of Anoiapithecus brevirostris (“Lluc”), scientifically described in 2009, stand out.

During the late Middle Miocene and early Late Miocene, the area where the current landfill is located was a closed forest with a hot and humid climate, sporadically with permanent bodies of water nearby. This environment was home to considerable faunal diversity, including around 80 species of mammals that have been identified at the site, as well as amphibians, reptiles and birds. Thus, in addition to hominoid and pliopithecoid primates, small mammals (such as hedgehogs, shrews and rodents), ungulates (such as horses, rhinoceros and deer), many carnivores (including the false saber-toothed, currently extinct) and proboscideans distantly related to modern elephants. (Source: Catalan Institute of Paleontology Miquel Crusafont)