e390-11 Siliceo.qxd 30/1/12 14:20 Página 277 Estudios Geológicos, 67(2) julio-diciembre 2011, 277-290 ISSN: 0367-0449 doi:10.3989/egeol.40605.189 Comparative anatomy of the frontal sinuses in the primitive sabre-toothed felid Promegantereon ogygia (Felidae, Machairodontinae) and similarly sized extant felines Anatomía comparada de los senos frontales en el félido dientes de sable primitivo Promegantereon ogygia (Felidae, Machairodontinae) y felinos actuales de tamaño similar G. Siliceo1, M.J. Salesa1, M. Antón1, J.F. Pastor2, J. Morales1 ABSTRACT In the present work, the frontal sinuses of the sabre-toothed felid Promegantereon ogygia are analysed, in comparison to those of the extant felines Acinonyx jubatus, Puma conocolor and Panthera pardus, of similar body weight. The study was carried out using 3D virtual models obtained from CT Scan images, a non-destructive technique that has revealed as a powerful tool for accessing to all kind of intracranial information. Our study shows that the frontal sinuses of P. ogygia were more similar to those of P. concolor, both in the presence of several struts reinforcing the dorsal part, and in the devel- opment of a remarkable caudal expansion. This caudal expansion would act as a thermal insulator of the brain, and would indicate a more open environment than previously supposed for this species, whereas the struts would be related to biomechanical stresses produced during the “canine shear-bite”, the killing method of the machairodontines. Keywords: frontal sinus, pneumatisation, skull, Felidae, Felinae, Machairodontinae. RESUMEN En el presente trabajo, se analizan los senos frontales del félido dientes de sable Promegantereon ogy- gia, en comparación con los de los felinos actuales Acinonyx jubatus, Puma conocolor y Panthera pardus, de similar peso corporal. El estudio se llevó a cabo utilizando modelos virtuales 3D obtenidos por tomogra- fía axial computerizada, una técnica no destructiva que se ha revelado como una poderosa herramienta para acceder a todo tipo de información intracraneal. Nuestro estudio muestra que los senos frontales de P. ogygia eran más similares a los de P. concolor, tanto en la presencia de varios puntales óseos de refuerzo de la parte dorsal, y en el desarrollo de una notable expansión caudal. Esta expansión caudal actuaría como un aislante térmico del cerebro, y podría indicar un entorno más abierto de lo que se supo- ne para esta especie, mientras que los puntales óseos se relacionarían con tensiones biomecánicas pro- ducidas durante el mordisco típico de los macairodontinos, el método de ataque de los machairodontinos. Palabras clave: seno frontal, pneumatización, cráneo, Felidae, Felinae, Machairodontinae. Introduction groups. The study of these structures is very inter- esting for the analysis of cranial morphology and The cranial sinuses are air-filled spaces located functional anatomy, but their functionality has been within the skull of Vertebrates, highly variable in widely debated and several hypotheses have been shape and development among the different proposed (Blanton & Biggs, 1968; Blaney, 1990; 1 Departamento de Paleobiología, Museo Nacional de Ciencias Naturales - CSIC, C/ José Gutiérrez Abascal 2, 28006. Madrid, Spain. Email: [email protected], [email protected], [email protected], [email protected] 2 Departamento de Anatomía, Facultad de Medicina, Universidad de Valladolid, C/ Ramón y Cajal 7, 47005 Valladolid, Spain. Email: [email protected] e390-11 Siliceo.qxd 30/1/12 14:20 Página 278 278 G. Siliceo, M.J. Salesa, M. Antón, J.F. Pastor, J. Morales Witmer, 1997). Frontal sinuses are included in a Paulli, 1900; Nemours, 1931; Shea, 1936; Buhler, complex system of cranial cavities (pneumatisa- 1972; Davis et al., 1996), increasing surface area of tions) called paranasal sinuses, which include, olfactory mucosa (Braune & Clasen, 1877; Negus, besides the frontal sinuses, all the sinuses located 1957, 1958), humidifying and warming the inspired within the ethmoidal, maxilar and sphenoidal bones air (Proetz, 1922, 1938; O’Malley, 1924; Gannon et (Barone, 2010; Evans, 1993; Joeckel, 1998; al., 1997), thermoregulation of the brain (Bignon, Edinger, 1950). These cavities may extend to adja- 1889; Bremer, 1940; Proetz, 1953; Verheyen, 1953; cent bones, such as the temporal bone (Sherwood, Dyce et al., 2002), or producing nitric oxide gas 1999). In Mammals, the paranasal sinuses derive (Lundberg et al., 1994). Nevertheless, no one of from diverticula of the nasal cavity formed by these hypotheses is completely satisfactory or wide- means of a pneumatisation process. Thus, these ly applicable. For example, a function related to res- sinuses are connected with the nasal cavity, and piratory physiology (humidifying and warming the covered with a thin epithelial tissue, which is a inspired air) has been refuted based on the evidence continuation of the nasal mucosa. The maxillary that the sinus epithelium is almost devoid of glan- sinus derives from the respiratory portion of the dular tissue and the sinus ostium (the opening that nasal cavity, whilst the ethmoidal, frontal and sphe- connects a sinus to the nasal cavity itself) is situated noidal sinuses, derive from the olfactory portion of out of the path of the respiratory currents (Proetz, the nasal cavity (Witmer, 1997, 1999). The most 1953; Blanton & Biggs, 1968; Witmer, 1997). The widely accepted hypothesis for the origin of the humidification and warming of the inspired air is cranial pneumatisation states that this process is provided by the epithelium of the maxilloturbinates, produced when the mucous epithelial tissue from which is placed in the line of the respiratory current the nasopharyngeal cavity expands into different (Hillenius, 1992). Besides this, for other authors the cranial bones, which are close to the nasal cavity; paranasal sinuses are simply functionless structures this mucosa is very rich in osteoclasts, which are resulting from a process of unnecessary bone tissue responsible for the resorption of the cranial bony removal, followed by deposition of necessary bone tissue (Witmer, 1997; Smith et al., 2005). This to maintain a strong structure that supports biome- process of bone remodelling is restricted by several chanical stress (Weidenreich, 1941; Edinger, 1950; structural and biomechanical constrains, which are Witmer, 1997). different depending on the bone in which the cavity Anyway, in order to assess the functionality of is being developed. Thus, in the case of frontal the paranasal pneumatisation, it is necessary to sinuses, they grow as separate left and right entities study the different groups of sinuses as separated from the middle nasal meatus, as their development entities, with similar formation processes, but with is confined laterally by the orbits, and rostro-cau- different structural constrains and physiological fea- dally by the inner and outer tables of the frontal tures. Thus, although primarily paranasal sinuses bone (Zollikofer & Weissmann, 2008). could have been formed as a result of a bone Besides, this process of pneumatisation requires remodeling process, they have probably developed certain equilibrium between bone resorption and a set of secondary functions, different in each group deposition, in order to keep the sinus biomechani- of vertebrates. cally stable (Sherwood, 1999; Witmer, 1997). This equilibrium results in a sinus structure with cham- bers and bony struts, the latter supporting the cavity, General morphology of the frontal sinuses in as they are located in areas of high biomechanical mammals demands (Witmer, 1997). Several hypotheses have been proposed to The frontal sinuses are located between the exter- explain the function of these cranial pneumatisa- nal and internal tables of the frontal bone. These tion, most of them related to physiology or architec- two tables contact by means of several struts devel- ture, development and biomechanics of the skull, oped along the sinus, forming an irregular trans- such as: imparting resonance to the voice (Cleland, verse partition; rostrally and medially, the naso- 1862; Bignon, 1889; Leakey & Walker, 1997; Dyce frontal opening connects the sinus with the nasal et al., 2002), protection of the brain from shocks cavity (Barone, 2010; Evans, 1993). The sinuses are (Rui et al., 1960; Schaffer & Reed, 1972; Davis et subdivided into a series of chambers by a variable al., 1996), reducing cranial weight (Cleland, 1862; number of bony struts, which can be from more or Estudios Geológicos, 67(2), 277-290, julio-diciembre 2011. ISSN: 0367-0449. doi:10.3989/egeol.40605.189 e390-11 Siliceo.qxd 30/1/12 14:20 Página 279 Comparative anatomy of the frontal sinuses in the primitive sabre-toothed felid Promegantereon ogygia 279 less cylindrical structures to bony sheets. Some the 3D morphology of these cavities, mostly species have relatively simple frontal sinuses, with because these structures usually have complex a low number of struts, such as felids; others devel- shapes, with prolongations and connections to other op complex frontal sinuses, such as some bovids, cavities. Also, the very nature of the destructive whose sinuses have a great number of struts and a techniques drastically reduces the available fossil complicated system of interconnected chambers skulls, so they were used only when relatively large (Farke, 2010). There are also intermediate mor- samples were available. phologies, such as that seen in canids, which show The development of non-invasive and non- frontal sinuses