Redefining the simplicity of the craniomandibular complex of nightjars: The case of Systellura longirostris (Aves: Caprimulgidae) by means of anatomical network analysis.

To study morphological evolution, it is necessary to combine information from multiple intersecting research fields. Here, we report on the structure of the bony and muscular elements of the craniomandibular complex of birds, highlighting its morphological architecture and complexity (or simplification) in the context of anatomical networks of the Band-winged Nightjar Systellura longirostris (Caprimulgiformes, Caprimulgidae). This species has skull osteology and jaw myology that departs from the general structural plan of the craniomandibular complex of Neornithes and is considered morphologically simple. Our goal is to test if its simplification is also reflected in its anatomical network, particularly in those parameters that measure complexity and to explore if the distribution of the networks in a phylomorphospace is conditioned by their evolutionary history or by convergence. Our results show that S. longirostris clusters with other Strisores and momotids and is segregated from the other bird species analyzed when plotted in the phylomorphospace, as a consequence of convergence in the network parameters. Systellura has a craniomandibular complex consisting of fewer muscles connecting more bones than the model species (e.g., the rock pigeon or the guira cuckoo). In this sense, Systellura is actually more complex regarding the number of integrative bony parts, while its craniomandibular complex is simpler. According to its anatomical network, Systellura also can be interpreted as less complex, particularly compared with other Strisores and taxa that reflect the general structure of the craniomandibular complex in Neornithes.