Comparison of the musculoskeletal forelimb anatomy of the Saimaa ( Pusa hispida saimensis ) and Baltic ringed seals ( Pusa hispida botnica )

Species or subspecies that are difficult to distinguish based on morphological characters common in all major marine groups and habitats (Churchill & Uhen, 2019; Knowlton, 1993). Ringed seals form a particularly interesting group this respect, consisting of both widespread populations as well small local inhabiting fresh brackish water environments. The unique evolutionary history the Saimaa ringed seal offers an excellent opportunity for comparative anatomical studies with other adapted different habitats, but such also challenging due endangered status seal. population consisted less than 200 individuals from 1950s 1980s, estimated size is now circa 400 (Metsähallitus, 2019). Low-to-moderate genetic differentiation between Baltic Sea Arctic Seas reported contrast high these (Martinez-Bakker et al., 2013; Savriama 2018; Valtonen 2012), which became landlocked about 9,500 years ago (Ukkonen 2014; 2012). Subtle distinct differences have been mainly skull jaw muscles (Amano 2002; Endo 1998, Hyvärinen Nieminen, 1990; Laakkonen Jernvall, 2020; Nordqvist, 1899) lungs (Laakkonen 2016). Most studies, however, compare only few each subspecies, prevents elimination intraspecific age-specific variation subspecies. Furthermore, recent study cautions against use postcranial anatomy below level subfamily taxonomy Phocids retained archaic features like mobile phalanges sizeable claws allowing prey processing forelimbs (Böhmer Hocking Quakenbush, 1991). Besides steering during swimming used when moving ice land molting breeding (Backhouse, 1961; Berta 2015). Quakenbush (1991) observed captive holding large fish its teeth slapping it flipper until piece enough swallow had torn off, relatively small-sized (Auttila 2015; Kunnasranta 1999; Sinisalo 2008) do not require manual handling oral food (Jernvall 2000; Jones Kienle Berta, 2016; 2020). Both studied here, routinely their digging, excavate lairs (Helle 1984; McLaren, 1958; Smith, 1987), scraping breathing holes (Stirling, 1977). There several reports literature describing limb bones (Bryden, 1971; Bryden Felts, 1974), including members genus Pusa (Howell, 1929; King, 1969; Miller, 1888; Murie, 1870, 1872, 1874; Piérard, 1991; Turner, 1888) muscle freshwater has apart examination thoracic Baikal seal, sibirica (Koster 1990). As part our research aiming understand seals, we cadaver dissections forelimb (Pusa hispida saimensis) botnica). All found dead collected by staff Parks Wildlife Finland, unit Metsähallitus (a state enterprise administers state-owned areas), stored at ?20°C necropsy. Specimens usually various stages decomposition, 2018 2019 one individual was good condition, enabling more detailed examination. These were shipped frozen Veterinary Faculty University Helsinki dissection June 2020. examined bycaught gill nets. One subadult (30–42 kg) pup (?30 kg). In addition, two legally shot hunter (outside community) Bothnian Bay (the northernmost Sea) via Oulu carried out summer adults (?42 We weighed just prior (Table 1). After removal body, soaked intrinsic located within itself) attached 24 hr remove blood tissues (Figure dissected four specimens, 26 specific, muscle–tendon units (see Table 1 names) being identified systematically removed. terminology accordance International Committee Gross Anatomical Nomenclature (ICVGAN, 2017). Of architectural measurements, measured mass (tendon removed) electronic balance (Pesola PTS3000, division 0.1 g). muscles, joint architecture possible ligaments Finally, boiled cleaned general bone anatomy, especially surfaces attachment sites (Figures 2-5; specimen number 846 chosen model figures because represents adult). insertions metacarpal phalanxes visualized there considerable exact attachments. Koster al. (1990) extrinsic joining trunk) P. did examine damage caused hunting seals) sampling seals). specimens display any pathology. similar, no corresponding Statistical weight comparisons sample sizes age/body difference specimens. Individual grouped functional joint, noted those previously findings briefly discussed. A protuberance spina scapulae, similar (1990), visible botnica 2) minor seen saimensis, probably young age. Interestingly, lacked protuberance. relation infraspinous fossa, supraspinous fossa considerably reduced phocids (Wyss, 1988; Figure 2). low caudal ridge (infraspinous 1991) separated musculus infraspinatus teres major, almost entirely lateral side articular surface scapula concave, humeral spheroidal. phocids, tuberculum minus elevated above head humerus 3), providing wide insertion area subscapularis (Bryden 1974; study). By lying proximal head, point provides greater moment arm rotator cuff musculature acting protractors rotators animals smaller tubercles (English, 1974, cited At distal end, possessed supracondylar foramen medial discernible shoulder slight thickening capsule Seven act joint. deltoideus originated scapulae fascial attachments adjacent muscles. It continued distally approximately along edge infraspinatus, former partly covered before deltoid crest find accessory described supraspinatus entire supraspinatus, extending over cranial scapula. showed varying degree partition (also Howell, 1929) inserting widely humerus, majus occupied infraspinata, aspect Its fused capsule. Although mostly laterally 2), acts 3). length inserted strong tendon slightly tuberosity tiny followed origin (scapula) (humerus) points This surface. Similar Howell (1929) fibers fusing humerus. except narrow parts near edges bone. Many tendons surrounding Also side, coracobrachialis biceps brachii, subscapulo-capsularis. Musculus (1990). olecranon process ulna many associated elbow flattened 4 5) very enlarged pinnipeds (Berta hinge-like end articulated concave 4). narrow, oriented articulation radius collateral ligament No separate could be distinguished thicker site. Eight action main extensors forearm triceps brachii. caput longum appeared attach fascia 5). accessorium brachii orientation close ends attachment. keep intact upon removal. mediale mediocaudal shaft base bone, craniomedial laterale (base humeri) 4), dorsocranial anconeus epicondyle caudomedial beneath sibirica. tensor fasciae antebrachii severing report hispida, some authors discuss complex processus coracoideus lay under intertubercular groove it. aponeurosis-like centimeters proximity brachialis humeri, passing third radioulnar origins flexors seems areas (radius, both). supinator epicondylus lateralis extended cover radius, while pronator dorsally latter teres. brachioradialis into eventual dorsal thickened, annular visible. forming carpal short ligaments. digits trochleated phalangeal articulations mobility digits. (Quakenbush, 1991), first digit phalanx media either here. arrangement contributes haulage grip (discussed below). reduction fifth intermediate manus 2015) study. Unlike otariids, webbed paw bearing sharp supported internally ungual processes, closely resembling terrestrial carnivores, employ clawed variety tasks (Hocking 2018). extensor digitorum communis carpi radialis, most went transverse carpus fingers thumb. tendons, fourth digits, proximalis tendons. radialis thinner ossa metacarpalia II III. originating ulnaris, thin terminating os metacarpale V. another branch ulna. abductor pollicis longus bone's laterocaudal crossing area. digiti I longus, m. metacarpi originate together previous 4) after remained already flexor ulnaris 5), long widened canal accessorium. numerous variations right left sides seals. superficialis half joined profundus 3) divided carpus: distalis digit. wider way rest 6). canal, three varied Strong flexion finger joints 6) results “haulage grip” 1961) whenever they locomotion mention quinti verified ICVGAN (2017), pars muscularis second suggested derived ulnaris. Comparison data mammals (adult) study), appears comparison well-studied felines (Cuff Viranta extends potential adduct forelimb, likely important streamline body swimming. should mammals, outside contour. result, axilla falls wrist. conclusion, musculoskeletal gross arctic wrist Because tightly connected function may able vary without significantly altering function. render reduce selection pressure specific matching phenotypic characteristic particular biomechanical function, requires analyses beyond alone. thank collection background information collaboration Jukka Jernvall his biology gratefully acknowledged. J.L. received funding Raija Ossi Tuuliainen Foundation. conflict interests declare. Juha Laakkonen: Conceptualization; curation; formal analysis; acquisition; investigation; methodology; project administration; resources; supervision; visualization; writing-original draft; writing-review editing. Heini Nihtilä: