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Full Research Article

Osteological Insights into the Malayan Sun Bear (Helarctos malayanus) Femur

T
Tolly Bora1
P
P.C. Kalita1
0000-0002-9711-9707
S
Swarup Debroy2,*
0000-0002-8845-8010
A
Arup Kalita1
P
P.J. Doley1
M
Mayura Moitrayee1
M
Manish Gautom1
1Department of Veterinary Anatomy and Histology, College of Veterinary Sciences and Animal Husbandry, Central Agricultural University, Selesih, Aizawl-796 014, Mizoram, India.
2Department of Veterinary Anatomy, College of Veterinary and Animal Sciences, Banda University of Agriculture and Technology, Banda-210 001, Uttar Pradesh, India.

ABSTRACT

Background: The Malayan sun bear (Helarctos malayanus) is the smallest member of the family ursidae and exhibits unique skeletal adaptations to its arboreal and omnivorous lifestyle. Detailed morphometric studies of its femur are scarce, particularly from the Indian subcontinent.

Methods: An adult female H. malayanus from Aizawl Zoological Park, Government of Mizoram, was examined postmortem. Twenty-one morphometric parameters were measured using a digital caliper.

Result: The femur measured 23.7 cm in length with a robust, slightly curved shaft and a hemispherical head bearing a distinct fovea capitis. The trochanter major was prominent, the trochanter minor was conical and medially directed and the distal extremity displayed large, rounded condyles separated by a deep fossa intercondylaris. This study provides the first detailed gross and morphometric description of the femur of H. malayanus from India. The data serve as a baseline for comparative anatomy, veterinary orthopedics and wildlife forensic applications and contribute to understanding the species’ morphological adaptations for locomotion and weight bearing.

INTRODUCTION

The Malayan sun bear (Helarctos malayanus) was initially listed as “Data deficient” (DD) in the 1996 IUCN Red List, reflecting a lack of adequate knowledge on its distribution, population trends and habitat range. With subsequent advances in ecological understanding and species monitoring, it was reclassified as “Vulnerable” (VU) in 2008 (Nazeri et al., 2012). Despite numerous ecological and behavioural studies covering aspects such as population density, reproductive cycles, home range, movement patterns, feeding ecology and niche preferences, there remains a paucity of detailed information on the species’ habitat requirements and geographic distribution.
       
The Malayan sun bear is the only ursid species adapted to life in equatorial lowland rainforests (Servheen et al., 1999). Among the eight extant bear species, it is the smallest, with adults typically measuring 120-150 cm in length and weighing between 27-65 kg (Stirling, 1993). In India, populations are largely restricted to the hilly terrains of the Patkai hill range, where they share habitat with species such as the clouded leopard (Neofelis nebulosa) (Doley et al., 2017), wild pig (Sus scrofa) (Doley et al., 2018), crested serpent eagle (Spilornis cheela) (Choudhary et al., 2021), Indian elephant (Elephas maximus indicus) (Kapadnis et al., 2025) and sloth bear (Melursus ursinus) (Kalita et al., 2002).
       
Malayan sun bears are characterized by a stocky body, large paws equipped with sharply curved claws, small rounded ears and a short, broad snout.
               
The present study addresses this gap by providing the first detailed gross anatomical and morphometric description of the femur of H. malayanus from India. Such data not only contribute to the species’ osteological reference but also hold value for comparative anatomy, veterinary orthopedics and wildlife forensic applications.

MATERIALS AND METHODS

The present research focused on the gross, morphological and morphometric analysis of the femur of the malayan sun bear. The specimen was obtained from Aizawl Zoological Park, Government of Mizoram, with due permission from the Department of Environment, Forest and Climate Change, Government of Mizoram. The collected femur sample was processed for skeletal preparation using the boiling maceration method (Simoens et al., 1994; Choudhary et al., 2020). The morphometrical data were recorded with the help of non-stretchable thread (Tomar et al., 2018) and digital caliper having calibration in centimetre.
       
Different morphometrical parameters measured for this study were selected in accordance with the studies carried out by Phatsara et al. (2016); Sarma et al. (2020).

RESULTS AN DISCUSSION

The femur of malayan sun bear with a maximum length of 23.7 cm (Table 2) was found to be the largest and most massive bone of the appendicular skeleton, as reported by Garvin (2023) in the femur of black bear and brown bear was the largest bone of the hindlimb measuring 28.1-39.2 cm and 26.7-51.5 cm respectively.
       
The shaft of the femur in the malayan sun bear was slightly flattened and curved anteriorly in its distal half, which was consistent with the observations of Darshan (2015) in the Sloth Bear and Onwuama et al. (2021) in the African lion, where the femoral shaft was described as nearly semicylindrical. In the Malayan Sun bear, the femoral shaft exhibited two surfaces separated by two thick, rounded borders. The cranial surface (Fig 1) was narrow and transversely rounded at the centre but became flat, wide and smooth at the extremities. Comparable findings were reported by Getty (1975) in dogs, where the femoral shaft was described as wider and compressed craniocaudally. However, Sinha et al. (2017) stated that in the asian palm civet, the proximal cranial surface was rough. The caudal surface (Fig 1) of the femoral shaft was flat and narrow in the centre. Its proximal two-thirds were occupied by the facies aspera (FA) (Fig 1), while the smooth distal one-third was traversed by an oblique vascular groove. Distally, the labium mediale and labium laterale were absent, resulting in the facies poplitei being undermarketed. The nutrient foramen was inconsistent and, when present, appeared as a small opening near the lateral border of the midshaft, a finding similar to that of Darshan (2015) in sloth bears and Tomar et al. (2019) in royal bengal tiger. Podhade et al., (2013) reported that the caudal surface of the femur in Leopards was rough in the upper third but smooth and expanded in the lower third, whereas Ray et al. (1996) observed it to be flat and smooth in leopards. The supracondyloid fossa and supracondyloid crest were absent in the femur of malayan sun bear, instead two deep prominent nonarticular depression were present above each condyle. Similar findings were also reported by Darshan (2015) in Sloth Bears. In Malayan Sun Bear, greatest and least circumference of the shaft was found to be 8.6cm and 6.4 cm respectively (Table 2) whereas Darshan (2015) in Sloth Bear found the width at mid shaft was 2.65±0.05 cm.

Fig 1: Cranial (A) and caudal (B) view of femur of malayan sun bear.


       
The proximal extremity (Fig 1) of femur was comprised of caput femoris (CpF), collum (Cuf), trochanter major (TMj), trochanter minor (TMn), trochanter tertius (TTr), trochanteric ridge (TR) and trochanteric fossa (TF). The length of proximal extremity which was measured as an oblique line between the fovea capitis (FC) and trochanter tertius (TTr) (Table 1) and was found to be 5.2 cm (Table 2) while its maximum width which was measured as the distance between fovea capitis (FC) and trochanter major (TMj) (Table 1) was found to be 5.4cm (Table 2). Similar studies were carried in blackbear, brown bear where maximum width of the proximal extremities was measured to be 6 cm and 7 cm respectively (Garvin, 2023).

Table 1: Morphometrical parameters and corresponding anatomical landmarks.



Table 2: Morphometrical parameters and their measurements (cm).


       
The medially placed hemispherical caput femoris (CpF) (Fig 1) formed the highest point of the bone which was in accordance to the finding of Darshan (2015) in Sloth Bear which according to him was a likely adaptation for a bipedal posture.The fovea capitis (FC) (Fig 2) was deep, presented one or two nutrient foramens at its base and was slightly towards the caudo-ventral aspect of the caput femoris (CpF). Almost similar finding was reported in jaguar by Belu et al. (2012) and in red panda by Makungu et al. (2015) where they stated that fovea capitis was more profound and was placed towards the edge of the articular surface. The articular surface of the caput femoris (CpF) was notched below the fovea capitis (FC) and was separated from the collum femoris (Cuf) (Fig 1) by a prominent crest except at its dorsal aspect where it blended smoothly with the dorsal margin of the collum femoris (Cuf).

Fig 2: Proximal extremity of femur of malayan sun bear (MSB).


       
The collum femoris (Cuf) was long and flattened craniocaudally. Its cranial surface was rough and slightly concave while its caudal surface presented a small tubercle. Its dorsal border was straight and short while its ventral border was concave and long.
       
The trochanter major (TMj) (Fig 1) was at the level of the collum femoris (Cuf) and appeared as a large pyramidal process with rough lateral surface. Similar finding was also observed by Makungu et al., (2015) in red panda where they reported that the trochanter major was placed lower than the caput femoris. Its proximal and lateral surface was rough and presented a prominent crest, the cervical tubercle (CTb) (Fig 1) on its anterior margin. Similar finding was also reported by Darshan (2015) where they observed that the trochanter major of Sloth Bear was in the form of a rough quadrangular projection at the level of the collum femoris with a slightly anterio-dorsal over hang. Whereas the trochanter major was made up of a small cranial and large caudal portion in African lion (Onwuama et al., 2021). 

The trochanter minor (TMn) (Fig 2) was observed as a rough, medially directed prominent tuberosity. Similar observations were reported by Taylor (1976), who noted that the medially directed trochanter minor in african carnivores allowed greater femoral rotation and was linked to climbing ability. Comparable findings were also recorded by, Tomar et al., (2019) in royal bengal tiger, Sinha et al. (2017) in asian palm civet and Podhade et al. (2013) in leopard.
       
The trochanter tertius (TTr) (Fig 1) was in the form of a rough area on the caudomedial aspect of the distal end of proximal extremity. It was connected to the cervical tubercle of the trochanter major by a curved crest running along the craniolateral margin of the proximal extremity of the femur.                          

Trochanteric ridge (TR) (Fig 1) was straight, extended between the trochanter major (TMj)and trochanter tertius (TTr) which was similar to that of red panda (Makungu et al., 2015), royal bengal tiger (Tomar et al., 2019), Ring-tailed lemurs (Makungu et al., 2014). But in leopard (Podhade et al., 2013), asian palm civet (Sinha et al., 2017) and tiger (Pandit, 1994) trochanteric ridge was oblique and connected the trochanter major to the trochanter minor. Its lateral surface was slightly convex and rough while its medial surface was excavated to form a part of the trochanteric fossa (TF) (Fig 2).
       
The trochanteric fossa (TF) (Fig 2) was elliptical, deep and had a maximum depth of 1.5 cm (Table 2). Whereas mean depth of the trochanteric fossa (TF) was found to be 1.60±0.03 cm in leopard (Podhade et al., 2013) and 2.08+0.07 cm in royal bengal tiger (Tomar et al., 2019).
       
The distal extremity (Fig 3) of the femur of malayan sun bear measuring 4.4 cm (Table 2) width was found to be smaller than its proximal extremity. It was craniocaudally flattened and made up of a trochlea in front and two condyles (Fig 3) separated by a wide fossa intercondylaris (Fln Cy) (Fig 3) behind. In similar studies conducted on the femur of various species, the width of the distal extremity was found to be 4.61±0.06 cm in the leopard (Podhade et al., 2013), 1.61±0.06 cm in the Asian Palm Civet (Sinha et al., 2017) and 7.84±0.09 cm in the royal bengal tiger (Tomar et al., 2019). The trochlear ridges (LTr, MTr) (Fig 3) were sagittal, similar in height and wide apart.In the asian palm civet, the lateral ridge was longer and positioned higher than the medial one (Sinha et al., 2017), while in the Rhesus Monkey (Sarma et al., 2020) and ring-tailed lemur (Makungu et al., 2014), it was observed to be thicker and more elevated than its counterpart. In contrast medial ridge was more prominent in sloth bear (Darshan, 2015) and chital (Yadav et al., 2012), sambar deer (Rajani et al., 2012), indian muntjac (Rajani et al., 2013) and marshdeer (Schimming et al., 2015). The width of the trochlea was 2.4 cm (Table 2) which was found to be much smaller than that of the royal bengal tiger (Tomar et al., 2019) measuring 4.04±0.26 cm but comparatively larger than Rhesus Monkey (Sarma et al., 2020) measuring 1.45 cm. The condylus lateralis (CyL) (Fig 3) was slightly smaller and showed a notch on it medial margin which was similar to that of rhesus monkey (Sarma et al., 2020), chital (Yadav, 2012), marshdeer (Schimming et al., 2015). Indian muntjac (Rajani et al., 2013) where they reported that the condylus medialis, was smaller than the lateral one. The condylus medialis (CyM) (Fig 3) was pyramidal in shape and was at a lower level. But in royal bengal tiger (Tomar et al., 2019), leopard (Podhade et al., 2013), asian palm civet (Sinha et al., 2017) and Indian elephant (Lakshmishree et al., 2017), the condylus lateralis, was at lower lower level than medial one. The epicondylus lateralis (EpCyL) (Fig 1) was in the form of a nodule while epicondylus medialis (EpCyM) (Fig 1) was more prominent and ridge like. Whereas in Marshdeer (Schimming et al., 2015) epicondyles lateralis was more prominent. The caudal surface of both the epicondyles dorsal to the condyles presented a deep fossa for muscular attachment. The fossa extensoria (FE) (Fig 3) and fossa musculipoplitei (FMP) (Fig 3) were in the form of two deep depression separated by a ridge located below the epicondylus lateralis (EpCyL) near the junction between the lateral trochlear ridge (LTr) (Fig 3) and the condylus lateralis (CyL) (Fig 3). Though the fossa extensoria (FE) and fossa musculipoplitei (FMP) were at the same level but fossa extensoria (FE) was deeper and anterior to the fossa musculipoplitei (FMP). Similar finding was also reported by Darshan (2015) in sloth bear, Schimming et al., (2015) in Marsh deer. However, the fossa extensoria found to be shallow in Indian elephant (Lakshmishree et al., 2017) and absent in ring-tailed lemurs (Makungu et al., 2014).

Fig 3: Distal extremity of femur of malayan sun bear (MSB).


       
The fossa intercondylaris (Fln Cy) (Fig 3) was wide, rough and presented many nutrient foramens (NF) (Fig 3) which was similar with asian palm civet (Sinha et al., 2017), african lion (Onwuama et al., 2021) and marsh deer (Schimming et al., 2015). However, quadrangular fossa intercondylaris was observed by Tomar et al. (2019) in royal bengal tiger. Deep fossa intercondylaris was reported by Sarma et al. (2020) in rhesus monkey. The maximum length, width and depth of fossa intercondylaris (Fln Cy) was measured to be 2.2 cm,1.4 cm and 1.12 cm (Table 2) respectively,while the mean depth of fossa intercondylaris in asian palm civet, leopard and royal bengal tiger was measured to be 0.37±0.04 cm,1.47±0.04 cm and 2.14±0.09 cm respectively (Sinha et al., 2017; Podhade et al., 2013; Tomar et al., 2019).

CONCLUSION

The present study provides the first detailed gross anatomical and morphometric description of the femur in the Malayan sun bear (Helarctos malayanus) from India. The femur displayed robust structural adaptations, including a well-developed proximal extremity, prominent trochanters and enlarged distal condyles, features consistent with the species’ climbing ability and weight-bearing demands. The morphometric data generated here establish a valuable baseline for comparative anatomical research, veterinary orthopedic reference and forensic identification of skeletal remains in wildlife conservation contexts. These findings contribute to the limited osteological database of H. malayanus and underscore the importance of detailed skeletal studies in understanding species-specific adaptations and supporting conservation strategies.

ACKNOWLEDGEMENT

The authors express their sincere gratitude to the authorities of Aizawl Zoological Park, Government of Mizoramfor granting permission and logistical support for sample collection. No external financial grant was received for the conduct of this study.
 
Data availability statement
 
The data that support the findings of this study are available from the corresponding author upon reasonable request.

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest concerning this article.

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    Full Research Article

    Osteological Insights into the Malayan Sun Bear (Helarctos malayanus) Femur

    T
    Tolly Bora1
    P
    P.C. Kalita1
    0000-0002-9711-9707
    S
    Swarup Debroy2,*
    0000-0002-8845-8010
    A
    Arup Kalita1
    P
    P.J. Doley1
    M
    Mayura Moitrayee1
    M
    Manish Gautom1
    1Department of Veterinary Anatomy and Histology, College of Veterinary Sciences and Animal Husbandry, Central Agricultural University, Selesih, Aizawl-796 014, Mizoram, India.
    2Department of Veterinary Anatomy, College of Veterinary and Animal Sciences, Banda University of Agriculture and Technology, Banda-210 001, Uttar Pradesh, India.

    ABSTRACT

    Background: The Malayan sun bear (Helarctos malayanus) is the smallest member of the family ursidae and exhibits unique skeletal adaptations to its arboreal and omnivorous lifestyle. Detailed morphometric studies of its femur are scarce, particularly from the Indian subcontinent.

    Methods: An adult female H. malayanus from Aizawl Zoological Park, Government of Mizoram, was examined postmortem. Twenty-one morphometric parameters were measured using a digital caliper.

    Result: The femur measured 23.7 cm in length with a robust, slightly curved shaft and a hemispherical head bearing a distinct fovea capitis. The trochanter major was prominent, the trochanter minor was conical and medially directed and the distal extremity displayed large, rounded condyles separated by a deep fossa intercondylaris. This study provides the first detailed gross and morphometric description of the femur of H. malayanus from India. The data serve as a baseline for comparative anatomy, veterinary orthopedics and wildlife forensic applications and contribute to understanding the species’ morphological adaptations for locomotion and weight bearing.

    INTRODUCTION

    The Malayan sun bear (Helarctos malayanus) was initially listed as “Data deficient” (DD) in the 1996 IUCN Red List, reflecting a lack of adequate knowledge on its distribution, population trends and habitat range. With subsequent advances in ecological understanding and species monitoring, it was reclassified as “Vulnerable” (VU) in 2008 (Nazeri et al., 2012). Despite numerous ecological and behavioural studies covering aspects such as population density, reproductive cycles, home range, movement patterns, feeding ecology and niche preferences, there remains a paucity of detailed information on the species’ habitat requirements and geographic distribution.
           
    The Malayan sun bear is the only ursid species adapted to life in equatorial lowland rainforests (Servheen et al., 1999). Among the eight extant bear species, it is the smallest, with adults typically measuring 120-150 cm in length and weighing between 27-65 kg (Stirling, 1993). In India, populations are largely restricted to the hilly terrains of the Patkai hill range, where they share habitat with species such as the clouded leopard (Neofelis nebulosa) (Doley et al., 2017), wild pig (Sus scrofa) (Doley et al., 2018), crested serpent eagle (Spilornis cheela) (Choudhary et al., 2021), Indian elephant (Elephas maximus indicus) (Kapadnis et al., 2025) and sloth bear (Melursus ursinus) (Kalita et al., 2002).
           
    Malayan sun bears are characterized by a stocky body, large paws equipped with sharply curved claws, small rounded ears and a short, broad snout.
                   
    The present study addresses this gap by providing the first detailed gross anatomical and morphometric description of the femur of H. malayanus from India. Such data not only contribute to the species’ osteological reference but also hold value for comparative anatomy, veterinary orthopedics and wildlife forensic applications.

    MATERIALS AND METHODS

    The present research focused on the gross, morphological and morphometric analysis of the femur of the malayan sun bear. The specimen was obtained from Aizawl Zoological Park, Government of Mizoram, with due permission from the Department of Environment, Forest and Climate Change, Government of Mizoram. The collected femur sample was processed for skeletal preparation using the boiling maceration method (Simoens et al., 1994; Choudhary et al., 2020). The morphometrical data were recorded with the help of non-stretchable thread (Tomar et al., 2018) and digital caliper having calibration in centimetre.
           
    Different morphometrical parameters measured for this study were selected in accordance with the studies carried out by Phatsara et al. (2016); Sarma et al. (2020).

    RESULTS AN DISCUSSION

    The femur of malayan sun bear with a maximum length of 23.7 cm (Table 2) was found to be the largest and most massive bone of the appendicular skeleton, as reported by Garvin (2023) in the femur of black bear and brown bear was the largest bone of the hindlimb measuring 28.1-39.2 cm and 26.7-51.5 cm respectively.
           
    The shaft of the femur in the malayan sun bear was slightly flattened and curved anteriorly in its distal half, which was consistent with the observations of Darshan (2015) in the Sloth Bear and Onwuama et al. (2021) in the African lion, where the femoral shaft was described as nearly semicylindrical. In the Malayan Sun bear, the femoral shaft exhibited two surfaces separated by two thick, rounded borders. The cranial surface (Fig 1) was narrow and transversely rounded at the centre but became flat, wide and smooth at the extremities. Comparable findings were reported by Getty (1975) in dogs, where the femoral shaft was described as wider and compressed craniocaudally. However, Sinha et al. (2017) stated that in the asian palm civet, the proximal cranial surface was rough. The caudal surface (Fig 1) of the femoral shaft was flat and narrow in the centre. Its proximal two-thirds were occupied by the facies aspera (FA) (Fig 1), while the smooth distal one-third was traversed by an oblique vascular groove. Distally, the labium mediale and labium laterale were absent, resulting in the facies poplitei being undermarketed. The nutrient foramen was inconsistent and, when present, appeared as a small opening near the lateral border of the midshaft, a finding similar to that of Darshan (2015) in sloth bears and Tomar et al. (2019) in royal bengal tiger. Podhade et al., (2013) reported that the caudal surface of the femur in Leopards was rough in the upper third but smooth and expanded in the lower third, whereas Ray et al. (1996) observed it to be flat and smooth in leopards. The supracondyloid fossa and supracondyloid crest were absent in the femur of malayan sun bear, instead two deep prominent nonarticular depression were present above each condyle. Similar findings were also reported by Darshan (2015) in Sloth Bears. In Malayan Sun Bear, greatest and least circumference of the shaft was found to be 8.6cm and 6.4 cm respectively (Table 2) whereas Darshan (2015) in Sloth Bear found the width at mid shaft was 2.65±0.05 cm.

    Fig 1: Cranial (A) and caudal (B) view of femur of malayan sun bear.


           
    The proximal extremity (Fig 1) of femur was comprised of caput femoris (CpF), collum (Cuf), trochanter major (TMj), trochanter minor (TMn), trochanter tertius (TTr), trochanteric ridge (TR) and trochanteric fossa (TF). The length of proximal extremity which was measured as an oblique line between the fovea capitis (FC) and trochanter tertius (TTr) (Table 1) and was found to be 5.2 cm (Table 2) while its maximum width which was measured as the distance between fovea capitis (FC) and trochanter major (TMj) (Table 1) was found to be 5.4cm (Table 2). Similar studies were carried in blackbear, brown bear where maximum width of the proximal extremities was measured to be 6 cm and 7 cm respectively (Garvin, 2023).

    Table 1: Morphometrical parameters and corresponding anatomical landmarks.



    Table 2: Morphometrical parameters and their measurements (cm).


           
    The medially placed hemispherical caput femoris (CpF) (Fig 1) formed the highest point of the bone which was in accordance to the finding of Darshan (2015) in Sloth Bear which according to him was a likely adaptation for a bipedal posture.The fovea capitis (FC) (Fig 2) was deep, presented one or two nutrient foramens at its base and was slightly towards the caudo-ventral aspect of the caput femoris (CpF). Almost similar finding was reported in jaguar by Belu et al. (2012) and in red panda by Makungu et al. (2015) where they stated that fovea capitis was more profound and was placed towards the edge of the articular surface. The articular surface of the caput femoris (CpF) was notched below the fovea capitis (FC) and was separated from the collum femoris (Cuf) (Fig 1) by a prominent crest except at its dorsal aspect where it blended smoothly with the dorsal margin of the collum femoris (Cuf).

    Fig 2: Proximal extremity of femur of malayan sun bear (MSB).


           
    The collum femoris (Cuf) was long and flattened craniocaudally. Its cranial surface was rough and slightly concave while its caudal surface presented a small tubercle. Its dorsal border was straight and short while its ventral border was concave and long.
           
    The trochanter major (TMj) (Fig 1) was at the level of the collum femoris (Cuf) and appeared as a large pyramidal process with rough lateral surface. Similar finding was also observed by Makungu et al., (2015) in red panda where they reported that the trochanter major was placed lower than the caput femoris. Its proximal and lateral surface was rough and presented a prominent crest, the cervical tubercle (CTb) (Fig 1) on its anterior margin. Similar finding was also reported by Darshan (2015) where they observed that the trochanter major of Sloth Bear was in the form of a rough quadrangular projection at the level of the collum femoris with a slightly anterio-dorsal over hang. Whereas the trochanter major was made up of a small cranial and large caudal portion in African lion (Onwuama et al., 2021). 

    The trochanter minor (TMn) (Fig 2) was observed as a rough, medially directed prominent tuberosity. Similar observations were reported by Taylor (1976), who noted that the medially directed trochanter minor in african carnivores allowed greater femoral rotation and was linked to climbing ability. Comparable findings were also recorded by, Tomar et al., (2019) in royal bengal tiger, Sinha et al. (2017) in asian palm civet and Podhade et al. (2013) in leopard.
           
    The trochanter tertius (TTr) (Fig 1) was in the form of a rough area on the caudomedial aspect of the distal end of proximal extremity. It was connected to the cervical tubercle of the trochanter major by a curved crest running along the craniolateral margin of the proximal extremity of the femur.                          

    Trochanteric ridge (TR) (Fig 1) was straight, extended between the trochanter major (TMj)and trochanter tertius (TTr) which was similar to that of red panda (Makungu et al., 2015), royal bengal tiger (Tomar et al., 2019), Ring-tailed lemurs (Makungu et al., 2014). But in leopard (Podhade et al., 2013), asian palm civet (Sinha et al., 2017) and tiger (Pandit, 1994) trochanteric ridge was oblique and connected the trochanter major to the trochanter minor. Its lateral surface was slightly convex and rough while its medial surface was excavated to form a part of the trochanteric fossa (TF) (Fig 2).
           
    The trochanteric fossa (TF) (Fig 2) was elliptical, deep and had a maximum depth of 1.5 cm (Table 2). Whereas mean depth of the trochanteric fossa (TF) was found to be 1.60±0.03 cm in leopard (Podhade et al., 2013) and 2.08+0.07 cm in royal bengal tiger (Tomar et al., 2019).
           
    The distal extremity (Fig 3) of the femur of malayan sun bear measuring 4.4 cm (Table 2) width was found to be smaller than its proximal extremity. It was craniocaudally flattened and made up of a trochlea in front and two condyles (Fig 3) separated by a wide fossa intercondylaris (Fln Cy) (Fig 3) behind. In similar studies conducted on the femur of various species, the width of the distal extremity was found to be 4.61±0.06 cm in the leopard (Podhade et al., 2013), 1.61±0.06 cm in the Asian Palm Civet (Sinha et al., 2017) and 7.84±0.09 cm in the royal bengal tiger (Tomar et al., 2019). The trochlear ridges (LTr, MTr) (Fig 3) were sagittal, similar in height and wide apart.In the asian palm civet, the lateral ridge was longer and positioned higher than the medial one (Sinha et al., 2017), while in the Rhesus Monkey (Sarma et al., 2020) and ring-tailed lemur (Makungu et al., 2014), it was observed to be thicker and more elevated than its counterpart. In contrast medial ridge was more prominent in sloth bear (Darshan, 2015) and chital (Yadav et al., 2012), sambar deer (Rajani et al., 2012), indian muntjac (Rajani et al., 2013) and marshdeer (Schimming et al., 2015). The width of the trochlea was 2.4 cm (Table 2) which was found to be much smaller than that of the royal bengal tiger (Tomar et al., 2019) measuring 4.04±0.26 cm but comparatively larger than Rhesus Monkey (Sarma et al., 2020) measuring 1.45 cm. The condylus lateralis (CyL) (Fig 3) was slightly smaller and showed a notch on it medial margin which was similar to that of rhesus monkey (Sarma et al., 2020), chital (Yadav, 2012), marshdeer (Schimming et al., 2015). Indian muntjac (Rajani et al., 2013) where they reported that the condylus medialis, was smaller than the lateral one. The condylus medialis (CyM) (Fig 3) was pyramidal in shape and was at a lower level. But in royal bengal tiger (Tomar et al., 2019), leopard (Podhade et al., 2013), asian palm civet (Sinha et al., 2017) and Indian elephant (Lakshmishree et al., 2017), the condylus lateralis, was at lower lower level than medial one. The epicondylus lateralis (EpCyL) (Fig 1) was in the form of a nodule while epicondylus medialis (EpCyM) (Fig 1) was more prominent and ridge like. Whereas in Marshdeer (Schimming et al., 2015) epicondyles lateralis was more prominent. The caudal surface of both the epicondyles dorsal to the condyles presented a deep fossa for muscular attachment. The fossa extensoria (FE) (Fig 3) and fossa musculipoplitei (FMP) (Fig 3) were in the form of two deep depression separated by a ridge located below the epicondylus lateralis (EpCyL) near the junction between the lateral trochlear ridge (LTr) (Fig 3) and the condylus lateralis (CyL) (Fig 3). Though the fossa extensoria (FE) and fossa musculipoplitei (FMP) were at the same level but fossa extensoria (FE) was deeper and anterior to the fossa musculipoplitei (FMP). Similar finding was also reported by Darshan (2015) in sloth bear, Schimming et al., (2015) in Marsh deer. However, the fossa extensoria found to be shallow in Indian elephant (Lakshmishree et al., 2017) and absent in ring-tailed lemurs (Makungu et al., 2014).

    Fig 3: Distal extremity of femur of malayan sun bear (MSB).


           
    The fossa intercondylaris (Fln Cy) (Fig 3) was wide, rough and presented many nutrient foramens (NF) (Fig 3) which was similar with asian palm civet (Sinha et al., 2017), african lion (Onwuama et al., 2021) and marsh deer (Schimming et al., 2015). However, quadrangular fossa intercondylaris was observed by Tomar et al. (2019) in royal bengal tiger. Deep fossa intercondylaris was reported by Sarma et al. (2020) in rhesus monkey. The maximum length, width and depth of fossa intercondylaris (Fln Cy) was measured to be 2.2 cm,1.4 cm and 1.12 cm (Table 2) respectively,while the mean depth of fossa intercondylaris in asian palm civet, leopard and royal bengal tiger was measured to be 0.37±0.04 cm,1.47±0.04 cm and 2.14±0.09 cm respectively (Sinha et al., 2017; Podhade et al., 2013; Tomar et al., 2019).

    CONCLUSION

    The present study provides the first detailed gross anatomical and morphometric description of the femur in the Malayan sun bear (Helarctos malayanus) from India. The femur displayed robust structural adaptations, including a well-developed proximal extremity, prominent trochanters and enlarged distal condyles, features consistent with the species’ climbing ability and weight-bearing demands. The morphometric data generated here establish a valuable baseline for comparative anatomical research, veterinary orthopedic reference and forensic identification of skeletal remains in wildlife conservation contexts. These findings contribute to the limited osteological database of H. malayanus and underscore the importance of detailed skeletal studies in understanding species-specific adaptations and supporting conservation strategies.

    ACKNOWLEDGEMENT

    The authors express their sincere gratitude to the authorities of Aizawl Zoological Park, Government of Mizoramfor granting permission and logistical support for sample collection. No external financial grant was received for the conduct of this study.
     
    Data availability statement
     
    The data that support the findings of this study are available from the corresponding author upon reasonable request.

    CONFLICT OF INTEREST

    The authors declare that they have no conflicts of interest concerning this article.

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