MORPHOMETRICS OF FLIGHTLESSNESS IN THE ALCIDAE BRADLEY C. LIVEZEY Museumof Natural History,University of Kansas,Lawrence, Kansas 66045 USA ABSTRACT.--Datacollected from skin specimensof the 23 Recentspecies of Alcidae,skeletal material for Recentand fossilalcids, and publisheddata on body massand wing area were usedto describethe morphometriccharacteristics of flightlessnessin the GreatAuk (Pinguinus impennis)and the fossil mancallineauks. A regressionequation confirmed a body-masses- timate (5 kg) for P. impennis(Bfidard 1969). The size and relatively small wings produced wing-loadingsof roughly 22 g.cm-2, comparableto thoseof medium-sizedpenguins. Multi- variate analysisof external measurementsunderscored the uniquely large size, relatively short wings, and moderatelydeep bill of Pinguinuscompared to other Recentalcids. Analysis of skeletal measurementsrevealed that the genera of flightlessAlcidae (Pinguinus,Mancalla, Praemancalla,and Alcodes)were characterizedby relatively short distal wing elementsand dorsoventralflattening of all majorwing elements,in combinationwith relatively large core and pelvic dimensions.These differenceswere most pronouncedin Mancalla,moderately developedin Praemancalla,and smallestin Pinguinus.Estimated body mass (1-4 kg) for selected fossil mancallinesexceeded the largest flighted alcids (Uria) but was lessthan for Pinguinus. Pinguinuswas a comparativelylarge piscivoresharing many morphologicalfeatures with the Razorbill (Alca torda)and tourres (Uria spp.). Its flightlessnessevidently was a consequence of extremespecialization for pursuit diving, convergentwith that of the Spheniscidae.Loss of flight imposedsignificant requirements on breeding sites and foraging habitatsof the GreatAuk and presumablythe mancallines,and renderedPinguinus exceptionally vulnerable to human exploitation.Received 30 December1987, accepted 23 May 1988. THE Great Auk (Pinguinusirnpennis), a flight- Blanc 1927, Storer 1945, Miller and Howard 1949, less alcid of the North Atlantic, is remembered Verheyen 1958).Even compilationsof standard most for its extinction in the 19th century. This external measurements for the Great Auk are is understandable, for the demise of the Great not available (cf. Coues 1868, Forbush 1912). Auk remains one of the most dramatic extir- The situationis relatedto the rarity of skin spec- pations in historicaltimes, one related to hu- imens and the variable distribution of the abun- man exploitationfor food (Grieve 1885,Nettle- dant skeletal material of Pinguinusin museums. ship and Evans1985) and possiblyto long-term The fossil flightless mancalline alcids of climatic trends (Bengtson 1984). Superstition coastalCalifornia are morphologically similar also took a toll: the last Great Auk taken in Great but less well known. Hundreds of elements of Britain reportedly was killed as a tempest-con- the group have been recovered,and 8 species juring witch (Ley 1935, Greenway 1967). The in 3 generaare recognizedfrom the late Mio- extermination of the specieswas complete by cene through the early Pleistocene:Praeman- 1844 (Greenway 1967), despite the prediction callalagunensis, P. wetrnorei, Mancalla californiensis, of this eventuality in the late 18th century(Net- M. diegensis,M. rnillerLM. cedrosensis,M. ernlongL tleship and Evans 1985). and Alcodes ulnulus (Lucas 1901; Miller 1933; Flightlessnessof the Great Auk, traditionally Howard 1947, 1966, 1968, 1970, 1971, 1976, 1978, less compelling to ornithologiststhan the de- 1982, 1983; Miller and Howard 1949; Olson 1981; mise of the species,is of comparableimportance Howard and Barnes1987). The Miocene genus to evolutionarybiology. Although the flightless Praemancallais considered to be a possible conditionof Pinguinuswas noted frequentlyby ancestorof the largely Pliocenegenus Mancalla early naturalists,particularly with respectto its (Howard 1966, 1976.) Neither genus is thought vulnerability to hunterson land, the anatomical to be closely related to Pinguinus.The Pacific correlatesof flightlessnessin the GreatAuk have generagenerally are placedin a separatefamily received relatively little attention. Existingan- or subfamily (Howard 1966, 1983) and may be atomical studies consistof basicdescriptive os- relatedmost closely to the puffins(Fraterculini; teology(Owen 1879,Wiman and Hessland1942) R. M. Chandlerunpubl. data). Pinguinus isjudged and limited mensural comparisons(Lucas 1890, to be closelyrelated to the Razorbill (Alca torda) 681 The Auk 105: 681-698. October 1988 682 BRADLEYC. LIVEZE¾ [Auk,Vol. 105 and murres (Uria spp.) on behavioral and mor- Cullen !982; Murray et al. !983; Dunning !984). Wing phologicalgrounds (Storer 1945,Strauch 1985). areas were traced (Raikow !973), from fresh birds or Alcids are wing-propelled diving birds. thawed, fresh-frozen specimens, and the resultant Strokesof the partly folded wings provide vir- areaswere measuredwith a compensatingpolar pla- nimeter.Additional wing areaswere taken from Mag- tually all of the propulsion and much of the nan (!9!2, 1922),Poole (!938), Kuroda(!967), Spring maneuverability for submarine locomotion (!97!), Stempniewicz(!982), and Pennycuick(!987); (Townsend 1909, Kelso 1922, Storer 1945). several tracings were provided by R. M. Chandler. Structuralconvergences between the GreatAuk Wing-loadingwas calculated as the ratio of body mass and the similarly flightless, wing-propelled divided by total wing area (g.cm-2;Clark !97!). penguins (Spheniscidae)have receivedconsid- Associated skeletal material of the Great Auk is not erable attention (e.g. Owen 1879,Wiglesworth available. One possible exception is an apparently 1900,Storer 1945). Aerial flight and submarine complete,largely articulatedskeleton of an immature propulsion clearly impose different selective bird at the British Museum. Mounted skeletons of Pinguinusare compositesof unassociatedskeletal ele- pressureson alar structureand the morphology ments. Extensive series of disassociated skeletal ele- of Pinguinusreflects the evolutionary substitu- ments are held at the U.S. National Museum of Nat- tion of aerial flight for extreme specialization ural History, AmericanMuseum of Natural History, for diving (Wiglesworth 1900;Bent 1919;Storer and Museumof ComparativeZoology (Harvard Uni- 1960, 1971;B•dard 1969;Bengtson 1984). Man- versity). Anatomical nomenclature follows Baumel callawas probably at least as specializedosteo- (!979). logically for diving as Pinguinus(Wiman and I soughtto measureat least 40 unworn specimens Hessland 1942, Miller and Howard 1949, How- of eachmajor skeletal element of P. impennis.The more ard 1970). fragile scapula,furcula, and distal phalangeswere not I comparedflightless and flighted alcids,em- availablein suchnumbers. Comparable data were col- phasizingmultivariate morphometric analyses. lected from all available material of Mancalla, Prae- mancalla,and Alcodes.Limited mensural data also were Data from study skins and skeletonsof all 22 collected from a new speciesof Mancalla (here re- extant alcid species,the Great Auk, and the fos- ferred to as Mancallalg. sp.; Chandler unpubl. data) sil mancalline auks were included. My objec- and Australcasp. (Brodkorb !955, Olson !977). Pin- tives were: to describequantitatively the mor- guinusalfrednewtoni, a poorly represented Pliocene form phological characteristicsassociated with loss similar to P. impennisin its measurements(Olson !977), of flight in the Alcidae; to estimatethe body was excludedfrom study.I alsosampled !0 complete massof adequatelyrepresented mancalline auks; skeletons (5 of each sex) of each of the 22 extant and, using available ecological and biogeo- speciesof alcid, although completesamples were not graphicalinformation, to considerselected as- available for severalspecies (e.g. Cepphuscarbo, Syn- pectsof the evolutionof flightlessnessin alcids. thliboramphuswumizusume, Aethia pygmaea). Forty-six skeletal measurementswere employed, most of which were describedpreviously (Livezey METHODS and Humphrey !984, !986) and !! of which were illustrated by Spring (!97!; measurements2, 6, 7, 12, Specimensand related data.--I collecteddata from 1! 13, !4, !6, 38, 39, 40, 4!). All skeletal measurements mounted skin specimensof the Great Auk. In addi- were made with dial calipers to 0.! mm. Sexual di- tion, colleaguesprovided comparabledata from an morphismwas consideredto be smallin extantspecies additional!4 mountedPinguinus skins (see Acknowl- of alcid (Storer!952), and in this studysexual differ- edgments).At least20 study skins(usually !0 of each enceswere found to be negligible.This similarity of sex) of each of the 22 extant speciesof Alcidae were the sexes,and the lack of information on sexfor spec- sampledfor comparisons.I measured total length (ex- imens of Pinguinusand the fossil species,prompted tended specimensonly, from bill to tail, feet exclud- the pooling of the sexesin the morphometric com- ed), culmen length (exposed,on midline), bill height parisons. (at gonys),wing length (chord of unflattened wing), Statisticalanalyses.--Linear measurements and log- tarsuslength (cranial surface),digit-III (middle-toe) transformed(base e) wing-loadings and skeletalratios length (excluding nail), and tail length (roedial arc) were comparedusing analysisof variance (ANOVA) (Baldwin et al. 193!). and analysisof covariance(ANCOVA). Spearmancor- Data on body massof extant alcids were collected relation coefficients(r) were used to measurebivariate from specimen labels and published compilations associations. (Johnson!935, !944; Belopol'skii!96!;