Jaw myology and bite force of the monk parakeet (Aves, Psittaciformes)

Abstract

Psittaciform birds exhibit novelties in jaw bone structure and musculature that are associated with strong bite forces. These features include an ossified arcus suborbitalis and the muscles ethmomandibularis and pseudomasseter. We analyse the jaw musculature of the monk parakeet (Myiopsitta monachus) to enable future studies aimed at understanding craniofacial development, morphology, function and evolution. We estimate bite force based on muscle dissections, physiological cross‐sectional area and skull biomechanical modelling. We also compare our results with available data for other birds and traced the evolutionary origin of the three novel diagnostic traits. Our results indicate that, in Myiopsitta, (i) the arcus suborbitalis is absent and the orbit is ventrally closed by an elongate processus orbitalis and a short ligamentum suborbitale; (ii) the ethmomandibularis muscle is a conspicuous muscle with two bellies, with its origin on the anterior portion of the septum interorbitale and insertion on the medial aspect of the mandible; (iii) the pseudomasseter muscle consists of some fibers arising from the m. adductor mandibulae externus superficialis, covering the lateral surface of the arcus jugalis and attaches by an aponeurotic sheet on the processus orbitalis; (iv) a well‐developed adductor mandibulae complex is present; (v) the bite force estimation relative to body mass is higher than that calculated for other non‐psittaciform species; and (vi) character evolution analysis revealed that the absence of the arcus suborbitalis and the presence of the m. pseudomassseter are the ancestral conditions, and mapping is inconclusive about presence of one or two bellies of the m. ethmomandibularis.

The uropygial gland of the monk parakeet Myiopsitta monachus: Histology, morphogenesis, and evolution within Psittaciformes (Aves)

“…With a phylogenetic tree and the character states data in the observed (terminal) taxa, character states at ancestral nodes can be reconstructed. Character mapping onto an established phylogeny represents a useful tool to test evolutionary hypotheses and understand the evolution of organism traits (e.g., Carril & Tambussi, ; Carril, Degrange, & Tambussi, ; Carril, Tambussi et al, ). The UG is an exclusive organ of the clade Aves that evolved only once in their phylogeny (Jacob & Ziswiler, ).…”

Skeletogenesis of Myiopsitta monachus (Psittaciformes) and sequence heterochronies in Aves

“…These bones form the rostral portion of the orbit and contribute to the formation of the septum inteorbitale, which lacks of foramen in Psittaciformes. Also, they provide the origin site of the Psittaciformes’ novel adductor muscle ethmomandibularis associated with strong bite forces (Tokita ; Carril et al ), and its early appearance may correspond to the functional importance hypothesis. In addition, based on the functional and size hypothesis, M. monachus shows the acceleration of the hyoid bones basihyale, urohyale, and epibranchiale (characters 30, 31 and 33; Fig.…”

“…For example, according to the size hypothesis, acceleration of the paraglossum and os palatinum would be expected, because they are distinctly large in Psittaciformes. Likewise, an acceleration of the os lacrimale and os squamosum would be expected, as their processus orbitalis and processus postorbitalis, respectively, form the exclusive arcus suborbitalis in some Psittaciformes and its where the novel adductor m. pseudomasseter attaches (Carril et al ). It is notable that in M. monachus , the ossification center of the os lacrimale is located precisely in the processus orbitalis, which is elongated and surrounds ventrally the orbit.…”

Palatal Biomechanics and Its Significance for Cranial Kinesis in Tyrannosaurus rex

“…Muscle map colors follow same palate and hypotheses of homology as Holliday (2009). Tokita, 2004;Holliday, 2009;Carril et al, 2015; Fig. 3).…”