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Adaptations for Digging & Burrowing. Ch. 17. Digging/Burrowing. Common widespread behavior For finding food, storing food, hiding eggs/young, temporary/long-term shelter Performed with hands, feet, head or some combination; occasionally with the mouth or neck ( Pituophis sp.). Salamanders.

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digging burrowing
Digging/Burrowing
  • Common widespread behavior
    • For finding food, storing food, hiding eggs/young, temporary/long-term shelter
  • Performed with hands, feet, head or some combination; occasionally with the mouth or neck (Pituophis sp.)
salamanders
Salamanders
  • Least specialized diggers of amphibians
    • Many use pre-existing burrows or
    • Enlarge natural crevasses w/ shovel-like head motions or lateral undulations
  • Tiger salamanders apparently best diggers
    • Survival in arid environments
    • Dig w/ muscular forelimbs, alternating every 3-10 strokes
    • No apparent morphological adaptations
feet first burrowing fogs
Feet-First Burrowing Fogs
  • Vast majority of frogs burrow hindfeet first
  • Head raised, 1 leg fully flexed, then soil immediately beneath & behind feet thrown posteriorly or onto frog’s back
  • Enlargement of inner metatarsal tubercle (integumentary projection on ventromedial surface of foot)
  • Increased size & robusticity of prehallux (skeletal support of inner metatarsal tubercle)
feet first burrowing frogs
Feet-First Burrowing Frogs
  • Relatively short hindlimbs where tibiofibula is shorter than femur
  • Mexican burrowing frogs (Rhinophrynus dorsalis)
    • loses a phalanx from 1st digit & remaining phalanx morphologically converges on distal prehallux
    • Thickened, rasp-like skin beneath spade-like elements
  • No apparent burrowing-morphologies of pelvises
head first burrowing frogs
Head-First Burrowing Frogs
  • Most information comes from Hemisus marmoratus & Arenophryne rotunda
  • Frog thrust snout into ground, then uses forelimbs to excavate around head
    • Forelimbs may be used alternately, synchronously, or unilaterally
    • Once buried, hindlimbs may be used to propel frog forward
head first burrowing frogs7
Head-First Burrowing Frogs
  • Humerus, radioulna, & fingers short & robust
  • Increased area of attachment for muscles on humerus (ventral humeral crest)
  • Decreased mobility in finger due to changes in shape & number of phalanges & intercalary cartilage (where present)
  • Coracoids longer & more robust (provide greater surface area for muscle attachment), and are more obliquely positioned relative to long axis of body
caecilians
Caecilians
  • Most highly adapted amphibian burrowers, but are poorly studied
  • All lack limbs (facilitates burrowing)
  • Fossorial taxa burrow w/ their heads
    • Rigid, heavily ossified skulls
turtles
Turtles
  • Digging is common among turtles especially tortoises, also underwater
    • Daily shelter, hibernation, nesting
  • Burrows usually dug w/ forelimbs, egg pits dug w/ alternating scooping w/ hindlimbs
  • Body pits prior to egg pits dug w/ forelimbs (alternating or synchronous), hindlimbs (alternating), all 4 limbs (diagonally alternating) or some sequential combination
turtles10
Turtles
  • Following based on Gopherus, an extensive tunneler
  • Distal phalanges enlarged to support large, flat nails
  • Forefeet short, broad & stiff
    • Reduced length & number of phalanges except distal phalanges
    • Close-packed, cuboidal carpal elements
crocodilians
Crocodilians
  • All bury eggs on land & some dig young out upon hatching, some burrow underground during extreme cold or drought, & one (Crocodylus palustris) may bury surplus food
  • May dig w/ hindlimbs (main method for egg chambers), forelimbs (main method for excavating hatchlings), snout, & jaws (in grassy areas)
  • No obvious morphological adaptations
    • All features seem plesiomorphic or evolved for other purposes
lepidosauria
Lepidosauria
  • More digging & burrowing taxa than any other major clade of vertebrates, & almost all at least somewhat capable of digging
  • Most quadrupedal species scratch w/ forelimbs alternating after several strokes
    • Some may use head (weak forelimbs or burrowing into soft sand)
lepidosauria13
Lepidosauria
  • Morphological specializations for limb-digging rare
  • Most specialized species: Palmatogecko rangei
  • Strongly webbed hand/feet
    • Likely evolved for locomotion over loose sand
  • Cartilaginous paraphalanges strengthen webbing more proximal than non-burrowing species
lepidosauria amphisbaenians
Lepidosauria: Amphisbaenians
  • Head-burrowers; all but 3 species of Bipes completely limbless
  • Limbed species use large forelimbs (no external hindlimbs) to dig when initially entering ground; afterwards burrow w/ head
lepidosauria amphisbaenians15
Lepidosauria: Amphisbaenians
  • Forelimbs are short, wide, & large relative to body
  • Zeugopodium short relative to stylopodium
  • Digits stout & roughly same length
    • Loss of phalanges + gain of phalanx in 1st digit for some sp.
  • Hand is broad w/ large claws
  • Pectoral girdle positioned unusually close to head
  • Loss of limbs helpful for burrowing, but apparently evolved as a result of body elongation
mammalian scratch diggers
Mammalian Scratch-Diggers
  • Most common form of digging in mammals
  • Variable degrees of morphological adaptations (many have none)
  • Rapid, alternating strokes of clawed forelimbs in predominantly parasagittal plane
  • Many rodents use large incisors to help loosen soil, & some may use head & feet to move loosened soil
mammalian scratch diggers17
Mammalian Scratch-Diggers
  • Enlarged sites of attachment for forelimb muscles used in digging
    • posteroventral portion of scapula, acromion process long?, deltoid tubercle of humerus, median epicondyle, long olecranon process
  • Sites of attachment shifted, length of elements changed to increase mechanical advantage
    • Deltoid tubercle of humerus positioned far from shoulder, long olecranon process (sometimes accompanied by shortening of radius), shortened manus
  • Articulations may be altered to stabilize joints
    • Long acromion may limit lateral rotation of humerus, vertically oriented keel-&-groove articulations in digits limit lateral movements
  • Some bones shorter/stouter/more robust
    • Short & stout humerus w/ thicker cortical bone around diaphysis, shortened metacarpals & phalanges, large & robust distal phalanges/claws
mammalian scratch diggers18
Mammalian Scratch-Diggers
  • Burrowers may brace themselves by pushing hindlegs out laterally against burrow walls
  • Pelvis roughly horizontally oriented, nearly parallel w/ vertebral column, & acetabula positioned high – prevents torsion when bracing
  • Elongated sacrum – increased stability for pelvis = greater forces generated by hindlimbs?
hook pull diggers
Hook-&-Pull Diggers
  • Used exclusively by anteaters to open ant/termite nest during foraging
  • Large claws on 2nd & 3rd digits hooked into crack/hole, then fingers are strongly flexed & the arm is pulled towards body
hook pull diggers20
Hook-&-Pull Diggers
  • Sites of muscle attachment enlarged to accommodate larger muscles: postscapular fossa (limb retractor), median epicondyle (3rd digit flexor)
  • Distal tendon of largest head of the triceps muscle merges w/ tendon of M. flexor digitorum profundus, changing function to flex the 3rd digit
  • Shape of bones changed to provide mechanical advantage: larger median epicondyle, notch in median epicondyle acts as a pulley for medial triceps tendon
  • Hooking digits large & robust
  • Keel-&-groove articulations in digits limit lateral & torsional movement
possible theropod analog
Possible Theropod Analog
  • Mononykus Cretaceous Mongolia
  • Single large functional claw
  • Palms face ventrally
  • Joints of manus limit movement to parasagittal plane
  • All apparently convergent w/ mammalian hook-&-pull diggers
  • Senter (2005)
humeral rotation diggers
Humeral Rotation Diggers
  • Best known in moles & shrew moles, may also be used by monotremes
  • Lateral thrusts of forefeet almost entirely through long-axis rotational movements of humeri
  • Both arms may be used synchronously (loose soil) or one at a time
humeral rotation diggers23
Humeral Rotation Diggers
  • Scapula oriented almost horizontally = anterior displacement of forelimbs, and humerus oriented obliquely = forefoot positioned laterally
  • Increased area of attachment for enlarged muscles
    • Area of origin on scapula for M. teres major
    • Manubrium long & ventrally keeled for pectoral muscles
  • Processes & articulations reoriented for mechanical advantage & passive flexion/rotation
    • Increased distance between humeral head & teres tubercle
    • Deflection of tendon of M. biceps brachii through tunnel = passive rotation of humerus during recovery
    • Fossa at distal end of medial epicondyle far lateral to axis of rotation = passive flexion of manus
humeral rotation diggers24
Humeral Rotation Diggers
  • Glenoid has elliptical articulation w/ humerus to stabilize joint
  • Radius, ulna, metacarpals, & proximal phalanges shortened (mechanical advantage) & robust
  • Distal phalanges enlarged to support large broad claws
  • Large radial “sesamoid” on inner edge of forefoot increases width of hand
humeral rotation diggers25
Humeral Rotation Diggers
  • Hindlimbs used for kicking back loose soil in deep burrows & for bracing against burrow walls as in scratch-diggers
  • Pelvis elongated & nearly parallel to vertebral column, acetabula raised
  • Pelvis fused to sacrum in up to 3 places
  • Hindlimbs shorter (shorter tibiofibula & pes) = increased force generated + presumed increased efficiency in tunnel locomotion
aquatic amphibious amniotes
Aquatic/Amphibious Amniotes
  • Many different taxa independently evolved aquatic or semi-aquatic lifestyles
  • Multiple types of land-to-water transitions are easy to make & readily advantageous (as opposed to land-to-air transition)
  • Many animals may be good swimmers &/or spend much of their time in the water & have little/no aquatic adaptations
mammals
Mammals
  • May primarily wade or swim
  • May swim w/ forelimbs, hindlimbs/tail, or both
  • Limbs/tail may move in vertical plane or horizontal plane
  • Limbs may provide forward thrust through drag-based paddling or by generating lift (fin shaped like hydrofoil)
mammals few swimming adaptations
Mammals: Few Swimming Adaptations
  • Shallow waders: walk in shallows, generally w/o submerging
    • Tapirs, moose, etc.
    • Little or no limb adaptations
  • Deep waders: walk on substrate beneath surface of water
    • Hippopotamus
    • May have larger &/or denser bones to counter buoyancy
  • Quadrupedal paddlers
    • Most terrestrial species
    • May have webbed feet
mammals pelvic swimming i
Mammals: Pelvic Swimming I
  • Alternating pelvic paddling (beaver): alternating flexion & extension of hindlimbs in vertical plane
  • Alternate pelvic rowing (muskrat): alternating flexion & extension of hindlimbs in horizontal plane
  • Both may have large feet w/ webbing (or long hairs)
    • Muskrat also has feet shifted to be perpendicular to plane of motion
  • Lateral pelvic & caudal undulation (giant otter shrew)
    • propelled mainly by sinuous movements of tail & adjacent vertebra
    • Hindfeet play secondary role
    • Fewer limb specializations than rowers/paddlers; tail may be mediolaterally flattened
mammals pelvic swimming ii
Mammals: Pelvic Swimming II
  • Pelvic oscillation (phocids): Feet move in horizontal plane w/ plane of feet held vertically, & most power provided by vertebral column
  • Ilium is short & anterior part is laterally deflected where propulsive muscles in back attach; ischium & pubis are long
  • Femur is short, but robust where muscles attach
  • Tibia & fibula are long often w/ a synostosis proximally
  • Feet are symmetrical w/ 1st & 5th toes relatively large
  • Forelimb morphology reflect terrestrial locomotion
mammals pelvic swimming iii
Mammals: Pelvic Swimming III
  • Simultaneous pelvic paddling (otters)
    • Synchronous movement of hindlimbs in vertical plane
    • Similar limb morphology to APP: large, webbed feet
    • Tail & back muscles also participate
  • Dorsoventral pelvic undulation (sea otter)
    • Feet are asymmetrical hydrofoils (digit 5 longest) thrust provided during upstroke & downstroke
    • Femur, tibia, & fibula short
  • Dorsoventral caudal undulation (giant otter)
    • Flattened tail + webbed fingers/toes
    • Limbs generalized since tail is used to swim
mammals pelvic swimming iv
Mammals: Pelvic Swimming IV
  • Caudal oscillation (Cetacea & Sirenia)
  • All propulsion by paddle/fluke shaped tails, no external hindlimbs
  • Forelimbs in cetaceans used for steering & stabilizing
    • Elbow, wrist, & fingers immobile
    • Fingers asymmetrical w/ leading edge longest, displaying hyperphalangy
mammals pectoral swimming i
Mammals: Pectoral Swimming I
  • Alternating pectoral paddling (polar bears)
    • Alternating movement of forelimbs in vertical plane
    • Morphology same as for terrestrial bears
  • Alternating pectoral rowing (platypus)
    • Alternating movement of forelimbs in horizontal plane
    • Presumably swim by humeral rotation as in walking
    • Forelimb of Ornithorhynchus resembles that of moles (humeral rotation diggers) w/ webbed feet
mammals pectoral swimming ii
Mammals: Pectoral Swimming II
  • Pectoral oscillation (Otariidae)
  • Forelimbs provide lift during upstroke & downstroke
  • Forelimbs are powerful & far back on body
  • Humerus, radius, & ulna short
  • Hand long, asymmetrical (thumb longer & more robust) flipper
    • Cartilaginous elements on distal phalanges lengthen fingers beyond nails
  • Hindlimbs used in steering & terrestrial locomotion
    • Femurs are short
    • Feet are long, symmetrical (large 1st & 5th digits) & webbed
birds
Birds
  • Many species of birds evolved to live in & around water
  • Three functionally distinct regions (“locomotor modules”): pectoral, pelvic, & caudal
  • Aquatic adaptations involve either pelvic or pectoral regions w/out significantly affecting the other region
bird pelvic swimming i
Bird: Pelvic Swimming I
  • Wading
    • A large number of birds live in close association w/ water, but don’t swim
    • May have longer, broader toes to distribute weight &/or long legs to wade deeper
  • Alternating pelvic surface paddling (ducks)
    • Float on surface & paddle w/ webbed feet
    • Some may do limited diving – short, laterally held femur, tibiotarsus long & parallel to vertebra, knee extensions limited, & ankle joint at level of tail
birds pelvic swimming ii
Birds: Pelvic Swimming II
  • Alternating pelvic submerged paddling (loons, hesperornithiformes)
    • Paddle backwards underwater
    • Webbed feet are reoriented far back on body
  • Lateral pelvic undulation (grebes)
    • Feet provide lift; toes are asymmetric & each has a hydrofoil cross-section
  • Quadrupedal surface paddling (flightless steamer ducks)
    • Combine simultaneous beats of wings w/ alternating beats of hindlimbs on the surface
birds pectoral swimming
Birds: Pectoral Swimming
  • Simultaneous pectoral undulation (auks, penguins, etc.)
  • Underwater flying: movement of wings similar in air & water
  • Combining aquatic & aerial flight reduces efficiency for both
    • Reduced wing area (shorter) = high wing loading
  • Flightless birds maximize efficiency for swimming
    • Reduced range of motion in joints; reduced internal wing musculature
    • Wing bones are short, stiff, flattened, & skeleton is dense
    • Wings positioned near midbody
    • Head, tail, & feet used for steering = feet placed more posteriorly
reptiles
Reptiles
  • Nonmammalian & nonavian amniotes
  • Most obligatorily aquatic taxa are extinct & have relatively poorly understood evolutionary histories
  • Most extant taxa & probably basal amniotes are/were facultatively aquatic
reptiles primitive aquatic locomotion
Reptiles: Primitive Aquatic Locomotion
  • Wading/bottom walking: many reptiles wade into water to feed w/o swimming
    • Some species w/ dense bodies may walk underwater such as some freshwater chelonians & apparently some placodonts
  • Lateral axial undulation & oscillation (crocodiles & squamates)
    • Propulsion provided by tail & to a lesser extent body
    • In slow swimming limbs are mainly used for maneuvering; fast swimming limbs are generally held immobile against body
    • More amphibious forms (crocodilians, phytosaurs) may have shorter, broader limbs
reptiles obligatorily aquatic taxa
Reptiles: Obligatorily Aquatic Taxa
  • Lateral axial undulation & oscillation
  • Mosasaur & ichthyosaur limbs evolved into fins w/ shortened long bones, reduced flexibility & hyperphalangy
  • Ichthyosaurs caudal fins convergent w/ cetaceans & sharks
    • limbs may show change in number of digits & loss of digit distinction
    • bones lightweight = buoyancy control or energy conservation (less inertia)
  • Sea snakes live entire lives in water
    • Limblessness advantageous for streamlining
    • Evidence that snakes evolved from aquatic taxa: fossils w/ aquatic morphologies (pachyostotic ribs, flattened tail), presumed close relatives that are aquatic (mosasaurs)
reptiles limb propulsion i
Reptiles: Limb-Propulsion I
  • Rowing
  • Freshwater turtles row w/ 4 limbs w/ webbed feet in alternating diagonal strokes
  • Pachypleurosaurs also apparently used this method & added tail undulations
  • Nothosaurs had relatively long (hyperphalangy), broad (long bones widened, space between radius & ulna), & stiffened forelimbs
reptiles limb propulsion ii
Reptiles: Limb-Propulsion II
  • Quadrupedal undulation (plesiosaurs)
    • Lift-based thrust of all limbs w/ comparable size & structure
    • Laterally projecting hydrofoil limbs
    • Massive femur/humerus; reduced zeugopod & wrist/ankle elements, loss of elbow/knee & wrist/ankle joints, & hyperphalangy
  • Pectoral undulation (sea turtles)
    • Lift-based propulsion w/ strong synchronous beats of long hydrofoil forelimbs
    • Hindlimbs used for steering & locomotion on land
sesamoids ossicles
Sesamoids & Ossicles
  • Ossicles: any overlooked appendicular skeletal elements
  • Highly variable size, shape, & position within & between taxa
  • Often overlooked by anatomists, but important for pathology & biomechanical issues
  • Intratendinous element: initially develop within a tendon or ligament (including sesamoids)
  • Periarticular element: adjacent to a joint/articulation but not initially within a tendon or ligament
sesamoids
Sesamoids
  • ‘Sesamoid’ often used as a wastebasket for any small & unusual skeletal elements
  • Sesamoid: skeletal elements that develop within tendon or ligament adjacent to an articulation or joint
  • Relatively small & ovoid in shape
  • Frequently have an inconstant distribution
sesamoid diversity distribution
Sesamoid Diversity & Distribution
  • Oldest known example (Permian) next to digit joints on palmar side of manus in captorhinids
  • Oldest example (late Triassic) on a turtle (generally extant taxa don’t have them) on dorsal side of manus & pes
  • Similar sesamoids also known in pterosaurs, a dinosaur (Saichania), lizards, birds, mammals & some anurans
  • Ulnar patellas found in some pipid anurans, birds, mammals & most squamates
    • Tends to replace olecranon process in birds & lateral epicondyle in tree shrews & a bat (Rousettus)
  • Oldest knee sesamoid (mid-Triassic) found in Macrocnemius bassanii
    • Also found in an anuran, some lizards, mammals & birds
  • Tarsal sesamoids found in anurans, birds, lizards & primates
patella patelloid
Patella & Patelloid
  • Patella: relatively large, well-ossified sesamoid cranially adjacent to distal end of femur
    • Predominant sesamoid for study: biomechanical, orthopedic, pathological & evolutionary
    • Constant in most lizards, birds, & mammals
    • Absent in nonavian archosaurs, turtles & most marsupials
  • Patelloid: more proximally positioned sesamoid of fibrocartilage
    • Found in some marsupials, various placental mammals, a crocodilian & a turtle
    • May co-occur w/ patella
patella patelloid histology
Patella/Patelloid Histology
  • Mature patella consists of lamellar cortex and a trabeculated core w/ hyaline cartilage lined articular surfaces
  • Chondrocyte-like cells of patelloid more disorderly than in the patella
patella development
Patella Development
  • Most true sesamoids develop through endochondral ossification
  • The patella presumably starts as a cluster of cells w/in quadriceps-patellar tendon, then undergoes chondrification to form hyaline cartilage mass
  • Unlike other sesamoids, patellas ossify early in ontogeny and develop in absence of mechanical stimuli
    • Though mechanical stimuli necessary for regeneration (dogs) & to stimulate underdeveloped patellas in humans
  • Recent research suggest LMXIB plays a role in patella development & dorso-ventral limb patterning
  • Hoxa9/Hoxd9 and Hoxd9/Hoxd10 mutants result in misshapen & displaced patellas
traction epiphyses
Traction Epiphyses
  • Bony projections of insertion for a tendon/ligament that develop independently of the limb element
  • Proposed to be sesamoids incorporated into long bones, or sesamoids are disarticulated traction epiphyses, or that both ossicles are completely separate
  • Evidence in favor of the 1st hypothesis:
    • In some mammals & birds the tibial tuberosity is derived from an independent condensation originating from w/in patellar ligament
    • In some birds the patella is also incorporated into the hypertrophic cnemial crest
mineralized tendons ligaments
Mineralized Tendons & Ligaments
  • Found in various tetrapods, most notably birds
  • Tend to be slender, elongate & terminate in advance of joints
  • Development based off of studies of the domestic turkey
  • Tenocytes (fibroblasts) of tendons hypertrophy & adopt a stellate morphology followed by hypertrophic tenocytes producing vesicles containing calcium & phosphorus = associated w/ earliest appearance of mineralization
lunulae
Lunulae
  • Periarticular ossicles of the knee & other synovial joints, nested within the menisci
  • They form osseous wedges w/ a crescentic morphology
  • May serve protective & biomechanical roles, such as resisting compressive forces or acting as a fulcrum
lunulae diversity distribution
Lunulae Diversity & Distribution
  • Best known in knee, though also found in other joints such as the wrist & ankle
  • Reported in lissamphibians, squamates, birds, & a variety of mammals
  • Very common in nonophidian squamates; up to 5 elements in an individual
  • Knee lunulae very common in rodents
lunulae development histology
Lunulae Development & Histology
  • All exists as hyaline cartilaginous precursors & ossify after birth/hatching
  • In humans, lunulae most often a result of injury or pathology
  • Experiments w/ chick embryos suggest that development of menisci (& therefore lunulae) is dependent on movement of limbs & may result from biomechanical induction
  • Haines (1942) hypothesized that lunulae form when menisci reach surpass a threshold size
  • Outer layer made of lamellar bone & inner layer is cancellous bone with or without marrow
problematic sesamoids ossicles
Problematic Sesamoids & Ossicles
  • Definitions of sesamoid & lunulae require knowledge of where the elements form during skeletogenesis; many ossicles only known from mature individuals
  • The panda’s “thumb” may be a true sesamoid, a remodeled periarticular ossicle, or a neomorphic derivitive of the carpal series
  • Other examples include:
    • the “panda’s toe” (enlarged tibial “sesamoid”)
    • “sesamoids” associated w/ digits in human manus (tendons & ligaments attach secondarily)
    • Rods & extensions that support wings/membranes of bats, gliding mammals & pterosaurs (pteroid)
biomechanics
Biomechanics
  • Most explanations for sesamoids emphasis potential current or past biomechanical function
  • Sesamoids & ossicles are most common in areas subject to friction, compression or torsion
  • Known to sometimes occur in response to injury
  • Connective tissue known to respond to compression/tension by altering ECM composition, fiber orientation, cellular morphology & cellular orientation
  • Osteogenic index developed to predict the likelihood & position of sesamoid formation under different stress regimes
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