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9. C. A. Brock, P. Hamill, J. C. Wilson, H. H. Jonsson,K. R. Chan, Science 270, 1650 (1995).
10. J. P. Vernier, L. W. Thomason, J. Kar, Geophys. Res. Lett.38, L07804 (2011).
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12. D. J. Hofmann, J. M. Rosen, Science 208, 1368(1980).
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R. Neely, Geophys. Res. Lett. 36, L15808 (2009).15. T. R. Deshler et al., J. Geophys. Res. 111, D01201
(2006).16. J. P. Vernier et al., J. Geophys. Res. 114, D00H10
(2009).17. J. P. Vernier et al., Geophys. Res. Lett. 38, L12807
(2011).18. J. M. Haywood et al., J. Geophys. Res. 115, D21212
(2010).19. B. Kravitz, A. Robock, J. Geophys. Res. 116, D01105
(2011).20. H. T. Ellis, R. F. Pueschel, Science 172, 845 (1971).21. E. G. Dutton, B. A. Bodhaine, J. Clim. 14, 3255 (2001).
22. C. Wehrli, in WMO/GAW Experts Workshop on a GlobalSurface-Based Network for Long-Term Observations ofColumn Aerosol (WMO Technical Document No. 1287,World Meteorological Organization, Geneva, Switzerland,2005), pp. 36–39; available at http://ftp.wmo.int/Documents/PublicWeb/arep/gaw/gaw162.pdf.
23. L. W. Thomason, S. P. Burton, B.-P. Luo, T. Peter,Atmos. Chem. Phys. 8, 983 (2008).
24. F. Vanhellemont et al., Atmos. Chem. Phys. 10,7997 (2010).
25. See supporting material on Science Online.26. M. Sato, J. E. Hansen, M. P. McCormick, J. B. Pollack,
J. Geophys. Res. 98, 22987 (1993).27. C. M. Ammann, G. A. Meehl, W. Washington,
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(2010).Acknowledgments: The satellite aerosol observations were
analyzed by J.P.V. during his fellowship through theNASA Postdoctoral Program at Langley Research Center,administrated by Oak Ridge Associated Universities. It isalso a part of his Ph.D. thesis financed by the Centre
National de la Recherche Scientifique at LATMOS/Université de Versailles St Quentin. The CALIPSO datawere made available at the ICARE data center (www-icare.univ-lille1.fr/). The authors also acknowledge help fromA. Hauchecorne, J. P. Pommereau, J. Pelon, andA. Garnier in the analysis of the GOMOS and CALIPSOdata sets; J. Barnes for Mauna Loa lidar data; andC. Wehrli for Precision Filter Radiometer data. Fundinghas also been provided by the Atmospheric Compositionand Climate Program of NOAA’s Climate Program.Helpful discussions with J. Gregory and D. M. Murphyare gratefully acknowledged.
Supporting Online Materialwww.sciencemag.org/cgi/content/full/science.1206027/DC1SOM TextFig. S1Table S1References
24 March 2011; accepted 29 June 2011Published online 21 July 2011;10.1126/science.1206027
Viviparity and K-Selected LifeHistory in a Mesozoic MarinePlesiosaur (Reptilia, Sauropterygia)F. R. O’Keefe1* and L. M. Chiappe2
Viviparity is known in several clades of Mesozoic aquatic reptiles, but evidence for it is lackingin the Plesiosauria. Here, we report a Late Cretaceous plesiosaur fossil consisting of a fetuspreserved within an adult of the same taxon. We interpret this occurrence as a gravid femaleand unborn young and hence as definitive evidence for plesiosaur viviparity. Quantitative analysisindicates that plesiosaurs gave birth to large, probably single progeny. The combination ofviviparity, large offspring size, and small brood number differs markedly from the pattern seenin other marine reptiles but does resemble the K-selected strategy of all extant marine mammalsand a few extant lizards. Plesiosaurs may have shared other life history traits with these clades,such as sociality and maternal care.
Viviparity, or birthing live young, is com-mon among reptiles, having evolvedover 80 times among extant clades (1).
Live birth has also been documented in severalgroups of Mesozoic aquatic reptiles, includingichthyosaurs (2), mosasauroids (3), choristoderans(4), and nothosaur-grade sauropterygians (5).However, to date no evidence exists for viviparityin the sauropterygian clade Plesiosauria, despitean excellent fossil record and a collection his-tory spanning almost 200 years. This lack ofevidence for viviparity is enigmatic given thatplesiosaurs were large animals whose bodieslacked a firm connection between the appendic-ular and axial skeleton, a condition impeding theterrestrial nesting required in an oviparous am-niote (5–7). Viviparity was documented recent-ly in basal, amphibious eosauropterygian clades
(5), even though these clades have shorter andless intense collecting histories. However, the sin-gle published claim of plesiosaur embryonic ma-terial (8) was shown to be misinterpreted shrimpburrows (9), and until now no pregnant plesiosaurfossil has been reported. In this paper, we presentfossil evidence of a gravid plesiosaur; furthermore,analysis of the fetus demonstrates that plesiosaursexhibited a reproductive pattern unique amongmarine reptiles.
LACM 129639 (Natural History Museum ofLos Angeles County) was discovered in 1987 byCharles Bonner on the Bonner Ranch in LoganCounty (Kansas, USA) at the base of the PierreShale [Sharon Springs Member, Campanian (10)].The fossil consists of the largely articulated skel-etal remains of two plesiosaur individuals, anadult and a juvenile displaying features at veryearly stages of development (Fig. 1). The adultis a large, short-necked plesiosaur referable toPolycotylus latippinus Cope, complete save forthe head and anterior 16 cervical vertebrae. Mea-surement of the adult vertebral column allows aconfident length estimate of 470 cm (11). The
juvenile consists of a mass of poorly ossifiedand largely disarticulated bones spilled from thebody cavity of the adult, intermingled with pha-langes of the adult right fore-paddle (Fig. 2).
Some ambiguity exists concerning the orig-inal orientation of the fossil because no quarrymap was kept of the excavation. However, aconfident reassembly was possible on the basisof the position of elements within each jacket,with subsequent evaluation and validation bythe original excavator, Charles Bonner (Fig. 1)(11). Of the 12 jackets, three contain a mixtureof adult and juvenile elements (Fig. 2). The ele-ments of the juvenile pelvis are near life po-sition, and the juvenile right pubis and leftischium are adhered to the visceral (internal) sur-face of the adult right coracoid by gypsum andmatrix. The presence of phalanges from the rightforelimb in the two jackets containing the ba-lance of the juvenile material indicates that theiroriginal position was in the vicinity of the rightforelimb. The position of this limb relative tothe thorax was established on the basis of thelocation of the pectoral girdle and an associatedpaddle bone in the thorax jacket. The rest of themount was laid out in approximate articulation,and the resulting mount was certified as accurateby the original excavator (11).
Multiple lines of evidence indicate that thejuvenile specimen is an in situ fetus. First, thepartially articulated fetal pelvis adhered tothe visceral surface of the right adult coracoidestablishes that the juvenile was both articulatedand within the adult body cavity at the time ofdeposition, before burial (Fig. 2). Second, bothspecimens are referable to the same species, P.latippinus, on the basis of their possession of thattaxon’s distinctive humerus. This humerus has ashaft that is narrow and strongly curved relativeto other plesiosaurs and also possesses fourdiscrete facets on its distal edge for articulationwith the radius, ulna, and two additional ossifi-cations (11–13). Third, the juvenile skeleton ispoorly ossified and displays numerous embryonic
1Department of Biological Sciences, Marshall University,Huntington,WV25755, USA. 2Dinosaur Institute, Natural HistoryMuseum of Los Angeles County, Los Angeles, CA 90007, USA.
*To whom correspondence should be addressed. E-mail:[email protected]
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features, and its overall state of development iscomparable to known prepartum eosauropterygianembryos (14). Fourth, the juvenile shows no in-dication of having been consumed by the adult:There is no maceration of cartilaginous surfacesby stomach acid as seen in other consumedplesiosaurs (10, 15), and no gastroliths (stomach
stones) or other evidence of a gastric mass (16).The above taphonomic, taxonomic, and onto-genetic evidence establishes that the adult was agravid female containing a fetus.
The fetal skeleton belongs to a single in-dividual considering the lack of duplicate ele-ments, the presence of paired elements of equal
size, and the partial articulation of the pelvis. Thefetal remains comprise a skull fragment; 20vertebral centra, many with associated but un-fused neural arches; numerous ribs and gastralia(belly ribs); both pubes and ischia; one ilium;both scapulae; both humeri, one with associ-ated paddle bones; and the left femur (Fig. 2).
Fig. 1. (A) Photograph and (B) interpretive drawing of LACM 129639, asmounted. Adult elements are light brown, embryonic material is dark brown,and reconstructed bones are white. lc indicates left coracoid; lf, left femur;
lh, left humerus; li, left ischium; lp, left pubis; rc, right coracoid; rf, rightfemur; rh, right humerus; ri, right ischium; and rp, right pubis. [Photo credit:R. Cripps]
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All vertebral centra have deep notochordal pits,and perichondral ossification is restricted to aring encircling the center third of each centrum.Identifiable vertebral centra are all thoracic ex-cept for one cervical, as expected of a reptilianembryo in which thoracic and posterior cervicalcentra ossify earlier than other vertebrae (17).The neural arches are very immature, consist-
ing of unfused bilateral arch elements with openneurocentral sutures, rudimentary zygapophyses,and a complete lack of ossified neural spines.Lack of midline fusion of the neural arch ischaracteristic of eosauropterygian embryos [e.g.,Lariosaurus (14) and Keichousaurus (18)]. Thebelly ribs are well developed, also in concor-dance with the precocial ossification of these in
eosauropterygians (18, 19). Both humeri areshort, with poorly ossified proximal ends butwide distal ends. These and the femur are smallrelative to the rest of the body (11), a conditionconsistent with the small humerus and femurproportions in prenatal eosauropterygian em-bryos [e.g., Lariosaurus (17), Neusticosaurus(19), and Keichosaurus (20)]. The skull frag-ment, consisting of a rounded and poorly de-fined left quadrate encased in a thin sheet ofsquamosal, demonstrates that the skull was pro-portionally large. It was poorly ossified, however,and meaningful quantitative measurements areimpossible.
The fetus is notably large given its onto-genetic stage. By considering axial-propodialproportions and their known scaling relationshipsin eosauropterygian embryos (11), we estimatethat the fetus was at most two-thirds mature. Byusing the preserved vertebral centra, whichgenerally scale isometrically with postnatal bodysize (21), we calculate a conservative minimumbody length estimate of 1.5 m at time of death(11) (32% of the 470-cm maternal length). Lengthat full term would have been significantly lon-ger, given the poor ossification of the fetalskeleton. A minimum estimate of fetus length atbirth is 35% of maternal length, with an upperbound at the 50% estimated length of a youngjuvenile of the short-necked plesiosaur Lepto-cleidus (22) (Fig. 3).
A tabulation of hatchling length relative tomaternal length in eosauropterygians, mosasau-roids, choristoderans, and ichthyosaurs (Table 1)shows that parturition length in these clades
Fig. 2. Maps of the LACM 129639jackets containing fetal material,depicted before mounting. Fetalbones are dark brown; adult bonesare light brown. c, centra; f, femur;g, gastralia; lh, left humerus; li, leftischium; lp, left pubis; rep, rightepipodial; rh, right humerus; ri,right ischium; rp, right pubis; rs,right scapula; and v, vertebrae.
Fig. 3. Reconstructions of female P. latippinus and newborn young. Gastralia were present in both animals but have been omitted for clarity.
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generally conforms to lengths predicted fromempirical analyses of maternal-neonate scalingin extant reptiles derived by Andrews (23) andis always less than 30%. This pattern indicatesan r-selected reproductive pattern in which fe-males gave birth to several relatively small young,as documented in a number of gravid fossilsfrom these clades (2–5). Calculation of the liz-ard regression equation of Andrews (23) foran adult length of 470 cm in LACM 129639yields a predicted neonatal length of 103 cm,or 22% of maternal length, for Polycotylus. Thislength is 10% shorter than the minimum LACM129639 fetal length at time of death and 15%shorter than the estimated length at full term.A 15% increase in neonate length embodiesan ~50% increase in mass; therefore Poly-cotylus young at birth were at least one and ahalf times as massive as those in other, moretypical terrestrial and marine reptile clades. Thepresence of a large, single fetus in LACM129639 therefore documents a K-selected repro-ductive strategy unique among marine reptiles.
The closest extant ecological analogs to short-neck plesiosaurs such as Polycotylus are odon-tocete cetaceans. Despite radically differentlocomotor adaptations, both clades are second-arily aquatic tetrapods with similar body sizeranges and feeding morphologies. A survey ofodontocetes with body lengths comparable to thatof Polycotylus shows they are also K-selected,giving birth to large, single progeny (24) (Table1). Odontocetes are highly social and engage inmaternal care, and one may argue that plesio-saurs displayed similar behaviors on the basisof ecological and reproductive similarity. How-
ever, this comparison is complicated becauseall whales, and all marine mammals, invaria-bly give birth to single, large, and precociousyoung (25). A K-selected reproductive strategymay be an adaptive constraint operating on allmarine mammals (26) that apparently did notapply to marine reptiles (Table 1), except forplesiosaurs.
Among modern reptiles, the plesiosaur-liketrait combination of viviparity, small brood size,and large birth size is rare, but it does occur inthe scincid Egernia species group. The mem-bers of this clade with the largest parturitionsizes also exhibit mammal-like social behaviors,including stable, kin-related group structuresand parental care (27–29) (Table 1). Althoughthis example is from a terrestrial clade, it dem-onstrates another instance where K-selected re-production is associated with social behaviorand maternal care. This example is pertinent be-cause it involves squamate reptiles, which arearguably the closest living relatives of plesio-saurs (30). Post-hatching parental care is alsorare in squamates generally (31).
Because both cetaceans and Egernia-grouplizards are highly social and engage in substan-tial maternal care, plesiosaurs may have behavedsimilarly. We hypothesize that large plesiosaurfetus size may indicate that plesiosaurs lived ingregarious social groups and engaged in pa-rental care. More evidence is needed to test thishypothesis; however, it is certain that plesiosaurlife history differed markedly from that of otherMesozoic marine reptiles and resembled thatof highly social marine mammals and scincidlizards.
References and Notes1. M. Delfino, M. R. Sánchez-Villagra, Semin. Cell Dev. Biol.
21, 432 (2010).2. R. Böttcher, Stuttg. Beitr. Naturkd. B 164, 1 (1990).3. M. W. Caldwell, M. S. Y. Lee, Proc. R. Soc. London 268,
2397 (2001).4. Q. Ji, X.-C. Wu, Y.-N. Cheng, Naturwissenschaften 97,
423 (2010).5. Y.-N. Cheng, X.-C. Wu, Q. Ji, Nature 432, 383 (2004).6. M. A. Taylor, Nature 319, 179 (1986).7. D. S. Brown, Bull. Br. Mus. Nat. Hist. Geol. 35, 253
(1981).8. H. G. Seeley, Annu Rep. Yorkshire Philos. Soc. 1895,
20 (1896).9. R. A. Thulborn, Palaeontology 25, 351 (1982).
10. M. J. Everhart, Oceans of Kansas: A Natural History of theWestern Interior Seaway (Indiana Univ. Press,Bloomington, IN, 2005).
11. Materials and methods are available as supportingmaterial on Science Online.
12. F. R. O’Keefe, J. Vertebr. Paleontol. 24, 326 (2004).13. G. W. Storrs, Paleontol. Contrib. Univ. Kansas 11, 1 (1999).14. S. Renesto, C. Lombardo, A. Tintori, G. Danini, J. Vertebr.
Paleontol. 23, 957 (2003).15. M. J. Everhart, The Mosasaur 7, 41 (2004).16. F. R. O’Keefe, H. P. Street, J. P. Cavigelli, J. J. Socha,
R. D. O’Keefe, J. Vertebr. Paleontol. 29, 1306 (2009).17. O. Rieppel, J. Herpetol. 28, 145 (1994).18. K. Lin, O. Rieppel, Fieldiana Geol. 39, 1 (1998).19. P. M. Sander, Science 239, 780 (1988).20. Y.-N. Cheng, R. Holmes, X.-C. Wu, N. Alfonso, J. Vertebr.
Paleontol. 29, 401 (2009).21. F. R. O’Keefe, O. Rieppel, P. M. Sander, Paleobiology 25,
504 (1999).22. B. P. Kear, J. Paleontol. 81, 154 (2007).23. R. M. Andrews, in Biology of the Reptilia, C. Gans,
F. H. Pough, Eds. (Academic Press, London, 1982),pp. 273–320.
24. W. F. Perrin, S. B. Reilly, Rep. Int. Whal. Comm. Spec. Issue6, 97 (1984).
25. J. A. Estes, J. Fish. Res. Board Can. 36, 1009 (1979).26. D. J. Boness, P. J. Clapham, S. L. Mesnick, in
Marine Mammal Biology: An Evolutionary Approach,A. R. Hoelzel, Ed. (Blackwell Science, Oxford, 2002),pp. 278–324.
27. D. G. Chapple, Herpetological Monogr. 17, 145 (2003).28. C. M. Bull, Y. Pamula, L. Schulze, J. Herpetol. 27, 489
(1993).29. F. Parker, in Advances in Herpetology and Evolutionary
Biology, A. Rhodin, K. Miyata, Eds. (Museum of ComparativeZoology, Cambridge, MA, 1983), pp. 435–440.
30. R. V. Hill, Syst. Biol. 54, 530 (2005).31. R. Shine, in Ecology B: Defense and Life History,
C. Gans, R. B. Huey, Eds., vol. 16 of Biology of theReptilia, C. Gans, Ed. (Alan R. Liss, New York, 1988),pp. 275–329.
Acknowledgments: The fossil described here (LACM 129639)is reposited in the vertebrate paleontology collectionsof the Los Angeles County Museum and is currently ondisplay in the public gallery. Metric data from thespecimen is listed in tables S1 and S2. We thankPhil Fraley Productions for the skilled preparation andmounting of the fossil that made this study possible.B. Kear provided access to unpublished Leptocleidusdata. Thanks to R. Cripps for the mount photograph inFig. 1 and to D. Trankina for Fig. 1 line art. Many thanks toS. Abramowicz for the life reconstruction art, Fig. 3, andwork on other figures. J. Long provided valuable feedbackon an early version of this manuscript. This material isbased on work supported by the NSF under award no.EPS-1003907.
Supporting Online Materialwww.sciencemag.org/cgi/content/full/333/6044/870/DC1Materials and MethodsFig. S1Tables S1 and S2References (32–34)
16 March 2011; accepted 6 July 201110.1126/science.1205689
Table 1. Brood size and parturition length, stated as percentage of maternal length, for viviparousamniote taxa. Length is body length or snout vent length, depending on the study. Asterisks indicateextinct clades of Mesozoic marine reptiles. Cetacean taxa are extant marine mammals, and Egerniaspecies are extant terrestrial skinks.
TaxonSize at parturition(% maternal length)
Brood size
Ichthyosauria*Stenopterygius quadriscissus (2) 23% Multiple
Mosasauroidea*Carsosaurus marchesetti (3) 15% Multiple
Choristodera*Hyphalosaurus baitaigouensis (4) <20% Multiple
Sauropterygia*Lariosaurus valceresii (17) 26% MultipleNeusticosaurus peyeri (19) 29% MultipleKeichousaurus hui (18) 27% MultiplePolycotylus latippinus (LACM 129639) >40% 1 (?)
CetaceaPseudorca crassidens (24) 40% 1Orcinus orca (24) 35% (Antarctic 44%) 1Globicephala melaena (24) 35% (NW Atlantic 41%) 1Globicephala macrorhynchus (24) 32% (Indian 36%) 1
Scincidae (Egernia group)Egernia stokesii (27) 46% 1–8Tiliqua rugosa (28) >50% 1–2Corucia zebrata (29) 56% 1
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www.sciencemag.org/cgi/content/full/333/6044/870/DC1
Supporting Online Material for
Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia, Sauropterygia)
F. R. O’Keefe* and L. M. Chiappe
*To whom correspondence should be addressed. E-mail: [email protected]
Published 12 August 2011, Science 333, 870 (2011) DOI: 10.1126/science.1205689
This PDF file includes:
Materials and Methods Fig. S1 Tables S1 and S2 References
Supplementary Online Material
Materials and Methods
Taxonomy Diagnosis of the LACM 129639 adult to Polycotylus latippinus Cope is based on
codings for the cladistic matrix in O'Keefe (32; Figure S1). The relevant characters are: character
16: caudal facets for hemal arches are generally on the posterior vertebral centra, more like the
condition in Dolichorhynchops bonneri; however this character varies significantly along the
caudal series, and both states are present in LACM 129639. Character 17: the humerus shaft is
narrow/constricted. Character 18: the humerus shaft is strongly sigmoid. Character 26:
posterior extensions of coracoid are present. Character 31: ischium length vs. width, the
ischium is long posteriorly. Character 37: the dorsal scapular process is not bent. New
character: the anterior end of the scapula is broadly expanded. The humerus also has four
facets for epipodials (shared with D. bonneri). An illustration of the adult and embryonic humeri
is provided below for taxonomic comparison.
Adult Body Length Calculation of body length of the adult was performed by direct
measurement of the articulated vertebral column from the first dorsal vertebra to the tip of the
tail (277 cm). The length of the full neck and of the head were then scaled from measures of the
more complete Yale specimen of Polycotylus latippinus (YPM 1125) contained in O'Keefe (33).
Scaling was performed relative to the geometric mean of the lengths of the scapula, coracoid,
pubis, ischium, humerus, and femur as described by O’Keefe (33). The LACM specimen was
found to be 112% the size of YPM 1125; this yields a neck length estimate of 125cm, and a head
length estimate of 68 cm. A snout‐vent length of 332 cm was calculated by measurement to the
caudal end of the last sacral vertebra. This length was used in calculating an expected length of
the embryo from the empirically‐derived lizard equation in Andrews (23).
Relative Propodial Dimensions Embryos that are pre‐hatching size for Keichousaurus have a
femur/trunk (F/T) ratio of 0.18, while adult females have a ratio of 0.21, and large adult males
have a ratio of 0.25. Pre‐hatching embryos of Neusticosaurus have a F/T ratio of 0.21, while
adult females are in the 0.22 range, and adult males are in the 0.24 range. Calculation of these
ratios in Lariosaurus embryos is difficult because the published embryos are so immature that
trunk length is not a good predictor of size, and snout‐vent length would be more accurate.
These data are not available; however the ratio of femur/(skull + trunk) is 0.15 for small
embryos, and is 0.17 in both juveniles and adults. Therefore, the F/T ratio is less than the adult
value prior to birth, and approaches the adult value at the time of birth, in several
sauropterygian taxa (data analyzed from Cheng et al. (34), Sander (19), and Renesto et al. (17),
respectively). In LACM 129639, the ratio of the femur to body length in the adult is 0.106, while
the ratio is 0.074 in the embryo. This indicates that the embryo was not close to birth, as the
F/T ratio is not near the adult value. The immature juvenile of Leptocleidus reported by Kear
(22) has propodials that are relatively larger than those of the adult.
Embryo Length Calculation Relative size of adult to juvenile was calculated from length, width,
and height measurements of the dorsal vertebral centra. Of the 20 adult dorsal centra, 17 could
be measured reliably (13 lengths, 5 widths, 12 heights). Only D4 and D9 had all three measures.
Examination of these data show that height is greater than width by 1 to 2 mm only, so that
adult centrum faces are essentially circular. Height was therefore used as a measure of centrum
face circumference. Mean dorsal centrum length for the adult is 64.8 mm (n=13). Mean dorsal
centrum height, and hence circumference, is 88.5 mm (n=12). The ratio of adult centrum length
to adult centrum circumference is 0.732.
The embryo has 20 identifiable centra, 19 of which are dorsal; hence only one dorsal
centrum is missing from the series. Seventeen of these centra had measureable faces (height
and width); twelve had measureable centrum lengths. Width is significantly greater than height
in these centra; therefore centrum circumference was taken as the average of the mean height
and mean width. Mean width for embryonic centra was 39.9 mm (n=17). Mean height was 36.2
mm (n=17). Mean centrum circumference was therefore 38 mm. The mean length of embryonic
centra was 20.8 mm (n = 12). The ratio of embryo centrum length to embryo centrum
circumference is 0.546.
Embryonic centra are therefore short relatively compared to those of the adult.
Therefore, relative size was calculated using the centrum face circumference, and then adjusted
with a correction factor for the shorter embryonic centrum length. This correction factor was
L/CD (length/centrum face dimension). The size estimate is therefore the ratio of CD times the
allometric correction factor L/CDe/ L/CDa, or 0.746 the isometric size measure. The isometric
measure is 0.43 the adult length. This yields:
Embryo body length = adult length * centrum face size ratio * centrum length ratio
Embryo length = 470cm * 0.43 * 0.746 = 151 cm.
However, length covaries with ossification state in the embryo, so that well‐ossified
centra are relatively long. The best‐ossified embryonic centrum (C19) has a length of 25 mm,
although its circumference is slightly less than the mean (37 mm). The length correction factor
used above is therefore very conservative because it does not consider unossified cartilage,
which was not preserved. The calculation is also conservative because of the use of the length
correction factor; a straight calculation of relative size based on the geometric mean of all
centrum measurements gives a relative embryo size of 41%. Our stated embryonic length of
32% material length is therefore a conservative minimum estimate, and the real length was
likely greater than this. This large size is remarkable given the osteological immaturity of the
embryo.
Expected embryo size Andrews (23) presents an empirically‐derived regression equation for
hatchling size versus maternal size, based on a large sample of extant reptiles. The regression
relates maternal size to hatchling size, and can be used to calculate an expected hatchling size
in taxa where only adults are known. The size metric is snout‐vent length. The equation for
lizards = y = 1.16 x^.74.
Figure S1. The taxonomically diagnostic left adult humerus and proximal carpus of LACM
129629, compared to the right embryonic humerus from the same specimen. The right
embryonic humerus photograph has been inverted to facilitate comparison.
Data Tables. Metric measurements taken from LACM 129629, all measurements in mm.
Table S1
ADULT
Vertebra Type Length Width Height
D1 D
D2 D 57 82
D3 D
D4 D 62 83 81
D5 D 64
D6 D 83 84
D7 D 83
D8 D 88 90
D9 D 65 91 92
D10 D 91
D11 D 65
D12 D 67
D13 D 64 91
D14 D 63 90
D15 D 64 90
D16 D 66 91
D17 D
D18 D 68 90
D19 D 72 90
D20 D 65
Humerus Length
Right
Left 476
Femur
Right
Left 501
Table S2
EMBRYO
CentrumID Vert Type Length Width Height
C1 D 23 37 40
C2 D 22 42 38
C3 D
C4 D 19 38 38
C5 D 22 41 39
C6 D 19 38 34
C7 D 39 36
C8 D 39 39
C9 D 20 39 38
C10 D 21 38 38
C11 D 22 43 38
C12 D 36 33
C13 D
C14 D 19 42 36
C15 D 39 32
C16 Cerv.
C17 D 42 33
C18 D 18 42 34
C19 D 25 40 34
C20 D 19 43 35
Humerus
Right 95
Left 98
Femur
Right
Left 109
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