~ Nigerian Veterinary Journal ~ Vol3S (3) 1026·1037 -----ARTIClE------------------------------------------------ Morphometric Study of the Skull of the Greater Cane Rat (Thryonomys swinderianus, Temmnick) OlUDE. M.A.'.'. MUSTAPHA. O.A.".'. SONUBI. A.C.'. FALADE. lE.'. OGUNBUNMI. lK.'. ADEBAYO. A.O.',' and AKINlOYE. AK ' 'Department of Vetennary Anatomy. Coltege of Veterinary Medicine, Federat University of Agricutture. AIleokuta, Ogun State, Nigeria, 'Department of Veterinary Anatomy, FaCIlity of Veterinary Medicine, University of lbadan, Ibadan, Oyo State, Nigeria, 'Department of Veterinary Surgery and Theriogenology. FaC1JJtyofVeterinary Medicine. University of tbadan, Ibadan, Oyo State, Nigeria. 'Corresponding author Email:[email protected], Tel:+2348035915275 SUMMARY INTRODUCTION This study was designed to investigate The Greater cane rat (GCR) (Thryonomys some morphometric characteristics of the swinderianus), popularly known as skull of the Greater cane rat (GCR) grasscutter, is one ofthe wildrodents that is involving 30 morphometric parameters. A currently undergoing domestication and total of 10 adult GCR were used for this captive rearing in parts of Africa and is study comprising of both sexes (5 males regarded as the continent's number one and 5 females). Student t-test was used to "micro-rodents" (Ajayi, 1974; Asibey and analyze the values obtained and to Addo, 2000). It belongs to the sub-order determine differences between the sexes. Hystricomorpha because they have their Morphological features were found in the medial masseter muscles spread through zygomatic bone which occurred as a large the infra-orbital foramen while the lateral and thick bone on both ends. From 30 masseter muscles are attached to the parameters analyzed, 12 were statistically zygomatic arches as in primitive rodents significant (p s 0.05) between both sexes, (Allaby,1999). The GCRis sturdy-looking, confirming the presence of sexual with a stockybody and short brown, bristly, dimorphism in the skull of this rodent. This scaly tail; it measures up to 60 em in length study provided baseline research data on and 7.2 kg in weight (Onadeko, 1996). The the typologyof the skull ofthe GCR. body is covered by coarse, thick and pointed hairthat varies in colour and can be KEYWORDS: Greater cane rat, ofany shade between grayish and yellowish morphometry, skull, sexual dimorphism, brown (Dorst and Oandelot, 1969). The craniometry. GCR has received increasing attention from researchers who have documented works on the reproductive system (Adjanohoun, 1993; Adu and Yeboah, 2000; Addo et aJ., 2002; Addo, 2002; Adebayo et al., 2009; Adebayo and Olurode, 2010), urinary system (Olukole, 2009), circulatory system (Opara et aI., 2006) and nervous system (Dwarika et aI., 2008; Spruston, 2008; Byanet et al., 2009; Elston and Manger, 2014). In the past, morphological studies were restricted to 1026 Oluda at al ISSN 0331 • 3026 qualitative description of tissue structures biologyof the GCR.Itwill also be useful to and therefore, they are essentially breeders, clinicians and researchers. subjective. In recent years, the applications of morphometric and stereological MATERIALSandMETHODS techniques have increased in biomedical Investigation was carried out on 10 adult research and have been well recognized as GCR(5 males and 5 females). The animals a new approach in morphological study were purchased from Pavemgo grasscutter (Mukerjee and Rajan, 2006). Farm at Badagry, Lagos State, Nigeria. Morphometric studies particularly of the Their live weights were recorded and skull are very important in arthrology examined to exclude skeletal deformities, (Bokonyi, 1974), regional anaesthesio!ogy after which they were anaesthesized using (Olopade and Onwuka, 2005), taxonomy chloroform. The animals were then and comparative anatomy within and slaughtered and decapitated at the between breeds (Van der Merwe, 2007). In occipitoatlantal joint, rapidly bled and the rodent taxonomy, morphometric analysis skulls were prepared using the skull especially of the skulls has longbeen one of maceration process (Olude et al., 2009). the fundamental techniques for The form (shape, size and position) of the characterizing, defining and discerning the entire skull and individual bones of the identity of individual specimens (Olayemi, skull were studied using information from 2007; Bezerra and de Oliveira, 2010; Olude et al., (2009), Hebel and Stromberg Olayemi et al., 2012; Reisser et al., 2012). (1976) as guides. The live weight of the Since the head contains the brain, major animals and the decapitated heads were sensory organs and the feeding apparatus, determined using an electronic weighing skull morphometry can also reveal a lot of machine (Mettler Toledo@). Thirty information on the ontogeny, phylogeny craniometric parameters apart from and adaptation of rodents. Several weights were determined as adapted from morphometric studies of the skull have Olude et aI., (2009), Fernandeset al., been documented in many domestic (2008), and \.vysocki(1985)(see Table 1). animals and rodents such as the dog, cat Measurements were taken using ruler, (Kunzelet al., 2003), pig (Endo et a!., vernier calipers, measuring cylinder, pair 2002), West African dwarf goat (Olopade, of dividers, plasticine and twines. The 2006), African giant rat (Olude et al., parameters were recorded in centimetre 2009). Skull morphometry is scarce in (em), mililitre (mL) and percentage (%). rodents undergoing captive rearing and Data obtained were analyzed using the domestication. 'Webbet al., (1979)sparsely student t-test (p s 0.05) and all analyses described the morphology ofthe GCRskull were done using the SPSSversion 15. and Van der Mer-we(2007) reported the distinguishing features for differentiating the skulls of Thryonomys swinderianus and Thryo nomys gregor ianus. Little information exists however,on the detailed morphometry of the skull of the GCR.The present study, therefore seeks to document the morphometric data of various skull bone measurements in the GCR (Thryonomys swin der ia n u s). The information obtained will essentially add to the ongoing attempts to understand the 1027 Oluda at al ISSN 0331 • 3026 Table 1: Parameters and the definitions of dimensions used in morphometric analysis FEATURES DIMENSION TAKEN FRONTAL BONE LENGTH (FBL) Total length of frontal bone from the fronto nasal suture io the suture Ironto -inter parieta I suture NASAL LENGTH (NSL) Overall length of the nasal bone from the rostral end of the frontal bone to the rostral tip of the nasal bone. FRONTOPARIETAL TO NUCHAL Length from the frontoparietal suture to the EMINENCE (FNE) nuchal eminence INTERPARIETAL TO NUCHAL Length from the interparietal bone to the tip of CREST(JNC) the nuchal crest. RJGHT INFRAORBITAL LENGTH Greatest length across the right infraorbital (RIOL) foramen. LEFT INFRAORBITAL LENGTH Greatest length across the left infraorbital (LJOL). foramen INTERPARACONDYLAR WIDTH The greatest breadth of the ventromedial ends (IPCW) of the jugular processes INTERCONDYLAR WIDTH (lCW) Width between the lateral ends of the occipital condyles BASAL SPHENOID LENGTH Length of the basisphenoid (BSL) BASAL OCCIPITAL LENGTH Length of the basioccipital portion of the (BOL) occipital bone from the tip of the foramen magnum to the suture formed between the basioccipital and the basispbeniod bones. MAXIMUM MANDIBULAR From the base of the mandible to the highest HEIOTfJ CMlYffJ) level of the coronoid process HEIGTH FROM CON DYLlOD From tbe condyloid fossa to base of the FOSSA TO MANDmLE BASE mandible (CFMB) CONDYLOID FOSSA TO HEIGHT From the maximum height of mandible to the OF MANDIBLE (CFMH) condyloid fossa. MANDIBULAR SYMPHYSEAL Length from rostral to caudal limit of the LENGTH (MSL) mandibular symphysis. DJASTEMAL GAP LENGTH (DGL) Length of the lower diastemal gap from the lateral end of the alveolus of the lateral incisor (on the bony ridge to the cranial border of the alveolus of tile J"llJolar). 1028 Oluda at al ISSN 0331 • 3026 DIASTEMAL CURVE LENGTH Length of the diastemal curve from the lateral (DCL) end of the alveolus of the lateral incisor (on the bony ridge to the cranial border of the alveolus of tbe first molar) UPPER DlASTEMAL GAP Maximum length of the upper diastemal gap. LENGTH (UDG) LEFT ORBITAL LENGTH (LOL) Maximum circumference of the left orbit from rim to rim (includes maximum horizontal and maximum vertical diameters). RIGHT ORBITAL LENGTH (ROL) Maximum length of the right orbit from rim to rim (includes maximum horizontal and maximum vertical diameters). LEFT ORBITAL Maximum circumference of the left orbit from CIRCUMFERENCE (LOC) rim to rim. RIGHT ORBITAL Maximum circumference of the right orbit CIRCUMFERENCE (ROC) from rim to rim LEFT ORBITAL HEIGHT (LOH) Maximum height of the left orbit from the dorsal tip of the orbital rim to the ventral tip of the orbital rim RIGHT ORBITAL HEIGHT (ROH) Maximum height of the right orbit from the dorsal tip of the orbital rim to the ventral tip of the orbital rim ZYGOMATIC WIDTH (ZGW) Maximum width across the zygomatic arches lNTERCANTHl WiDTH Minimum distance between the medial margins DISTANCE (lCD) of the orbits RIGHT ORBITAL INDEX (ROI) ROHIROLxlOO LEFT ORBITAL INDEX (LOI) LOHILOL x 100 UPPER DIASTEMAL LENGTH Length of the gap diastema! gap from the (UDL) lateral end of the alveolus of the lateral incisor on the bony ridge to the cranial border of tbe alveolus of the I" molar). RIGHT INFRAORBITAL Maximum breadth of the right infraorbital BREADTH (RIOB) foramen