Evolutionary convergence is a phenomenon whereby different species living in and adapted to similar environments evolve similar morphological and functional characteristics that make them look very similar despite not having any kinship in common.

One of the most debated questions among scholars is to reliably determine which traits are most likely to converge between species and the causes.

Many hypotheses are still unexplored, not only ecological but also behavioural and phylogenetic. The ecological factor most frequently assumed to have produced morphological convergence in carnivores, specifically in their craniomandibular complex, is diet.

Why is it important to shed light on this aspect? Because if similar diets produced converging tooth morphologies, palaeoecologists might be able to define the ecological conditions of a specific geographical area in the past.

While the number of documented cases of evolutionary convergence has so far been lower than expected, there have been many cases based on purely qualitative considerations that have not allowed us to understand the frequency of the phenomenon, making it challenging to identify recurrent evolutionary trends, both between and within taxonomic groups.

Today, a new study published in the journal Evolution and coordinated by Luigi Maiorano of the Charles Darwin Department of Biology and Biotechnology at Sapienza University of Rome, in collaboration with Sapienza's Museum of Zoology, Liverpool John Moores University and the University of Naples Federico II, presents the largest ever quantitative assessment of craniomandibular evolutionary convergence in the mammalian order Carnivora.

"This study," says Davide Tamagnini of the Charles Darwin Department of Biology and Biotechnology, and the study's first name, "is part of a growing trend in research, which employs innovative methods (phylogenetic comparative method) to investigate phenomena traditionally described only qualitatively. The work also uses simple morphological data, extracted from a large number of taxa of the order Carnivora, to clarify whether diet causes convergence in their craniomandibular complex."

The evidence supports the rarity of evolutionary convergence within broad ecological categories but instead shows a greater frequency of this evolutionary phenomenon in isolated cases of unrelated species that play the same role in their environment.

That is the case of the giant panda and the red panda, which belong to two different families: the former to the ursid family (like bears), and the latter to the ailuridae family (like raccoons), which share a bamboo-based diet, the typical black spots around the eyes and the so-called "false thumb". 

While convergence in pandas can be found in two species living in the same habitat and region, there are frequent examples of convergent morphological adaptations among carnivores, even in species that evolved on different continents. These species pairs are commonly considered 'ecologically equivalent' because they live in different geographical regions but occupy similar ecological niches.

"In this research, we studied morphological convergence by grouping species according to the type of food prevalent in their diet. Then, we considered several cases of potential morphological convergence by focusing on ecologically equivalent species of similar body size, or taxa that are very similar for diet and habitat, but with large differences in size."

"Our results," says Luigi Maiorano, study coordinator, "hardly support the occurrence of convergent evolution in the food categories of living carnivores: convergent evolution in this clade seems to be a rare phenomenon."

Therefore, the phenomenon of convergence is less frequent than expected, and this result is probably due to complex interactions between morphology, ecology, and biomechanics.

This research also highlights the importance of the taxonomic scale considered in macroevolutionary studies.

References:

Testing the occurrence of convergence in the craniomandibular shape evolution of living carnivorans - Davide Tamagnini, Carlo Meloro, Pasquale Raia, Luigi Maiorano - Evolution, 75(7): 1738-1752. DOI: https://doi.org/10.1111/evo.14229

Further Information

Luigi Maiorano
Department of Biology and Biotechnology "Charles Darwin"
luigi.maiorano@uniroma1.it

Davide Tamagnini
Department of Biology and Biotechnology "Charles Darwin"
davide.tamagnini@uniroma1.it