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DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539CALIFORNIA STATE POLYTECHNIC UNIVERSITY, POMONAPROJECT & THESIS ELECTRONIC SUBMISSION FORMSubmission Type:XThesisProjectSpring2020Submitted: TermYearSTUDENT INFORMATIONFull Namethein htunEmail Addresstzawhtun@cpp.eduBronco ID009142029Master’s ProgramGeologyLIBRARY FORMAT REVIEWER APPROVALChecked and approved byLibrary Reviewer:GSO - Signature Form16Date:6/15/2020Revised April 2020,Graduate Studies Office

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539CALIFORNIA STATE POLYTECHNIC UNIVERSITY, POMONATHESIS ELECTRONIC SIGNATURE PAGESpring2020Submitted: TermYearTHESIS INFORMATIONTHESIS TITLEALLOMETRIC TRENDS IN THE ONTOGENTIC GROWTH OF VARIOUS PLEISTOCENE NORTH AMERICAN PRAUTHORthein htunDEPARTMENTGeological SciencesSIGNATURESJon NourseCommittee Chair NameThesis Committee ChairPosition6/15/2020Geological se@cpp.eduBryan P. MurrayCommittee Member 2 NameCo-AdvisorPosition6/17/2020Geological ationEmailDonald ProtheroCommittee Member 3 NameAdvisorPosition6/15/2020Geological prothero@att.netUpload Thesis Attachment:Revised April 2020,Graduate Studies Office

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539ALLOMETRIC TRENDS IN THE ONTOGENTIC GROWTH OF VARIOUSPLEISTOCENE NORTH AMERICAN PROBOSCIDEANS AND THEDWARFING OF COLUMBIAN MAMMOTH (Mammuthus columbi) THECHANNEL ISLANDS PYGMY MAMMOTH, (Mammuthus exilis)A ThesisPresented to theFaculty ofCalifornia State Polytechnic University, PomonaIn Partial FulfillmentOf the Requirements for the DegreeMaster of ScienceInGeological SciencesByThein Htun2020

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539SIGNATURE PAGETHESIS:ALLOMETRIC TRENDS IN THE ONTOGENTICGROWTH OF VARIOUS PLEISTOCENE NORTHAMERICAN PROBOSCIDEANS AND THEDWARFING OF COLUMBIAN MAMMOTH(Mammuthus columbi) THE CHANNEL ISLANDSPYGMY MAMMOTH, (Mammuthus exilis)AUTHOR:Thein HtunDATE SUBMITTED:Spring 2020Department of Geological SciencesDr. Jonathan A. NourseThesis Committee ChairGeological SciencesDr. Donald R. ProtheroGeological SciencesDr. Bryan P. MurrayGeological Sciencesii

DocuSign Envelope ID: SI would like to thank my advisor, Dr. Donald Prothero for taking me as one of hisstudents, and therefore giving me an opportunity to advance my career in paleontology.I would also like to thank all of the faculty members of the Geological Sciencesdepartment for their patience and willingness to put up with my shortcomings.I would like thank all of the museum staff members who helped us collect data,which was a massive undertaking with all of the measurements we had to do.iii

DocuSign Envelope ID: netic growth and phyletic dwarfing are both forms of body size alterations.Despite the former being an example of intraspecific, and the latter, interspecific sizechange, they are both subject to similar proportional changes known as allometry. Theycan become more robust or negatively allometric, gracile or positively allometric orundergo very little proportional change, also known as isometry. According to paststudies, isometric growth trends are the most commonly observed in mammals, withpositive allometry as the second most common. Furthermore, instances of phyleticdwarfing are often isometric or negatively allometric. Using methods devised byKilbourne and Makovicky (2012) and Prothero and Sereno (1982), I tested for allometryin various North American proboscideans, more specifically, in the growth trends of theAmerican mastodon, M. americanum, and the Channel Islands mammoth, M. exilis, andthe dwarfing of the Columbian mammoth, M. columbi to the Channel Islands mammoth. Icompared my results to similar past studied from which I found some unexpected results.I expected isometric growth in both the forelimbs and rear limbs of the Americanmastodon, but found that only the forelimbs were isometric, and the that the bones of therear limbs grew with positive allometry in the humerus, and negative allometry in thetibia; which is a stark contrast from past studies, such as the one done by Kilbourne andMakovicky (2012) on modern African elephants, where they found that elephant limbsgrew primarily with isometry. I reasoned it was the lack of the smaller neonates in mymastodon sample set as Kilbourne and Makovicky (2012) explained that a limited sizerange in a study can cause growth slopes to seem negatively allometric. I also found thatthe Channel Islands mammoth, while having isometric ontogenetic growth, becameiv

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539more robust in their forelimbs as they dwarfed form their parent Columbian mammothancestor. This is also different from past studies on dwarf elephants, such as one done byHerridge (2010) where she found that Mediterranean dwarfed with isometry. This trendwas possibly the result of the steep topography of the Channel Islands, and that robustforelimbs are not an uncommon adaptation in mountain-dwelling mammals. I speculatedthat the dwarfing was the result of heterochronic evolution that favored individuals thatmatured during what would be the smaller neonate stage of growth, when they wouldhave more robust limb and reinforced limb bone growth trends, a form ofpaedomorphism. The results of both studies can be further understood with the use ofhistological techniques in future projects, from which it will be possible to ascertaindifferences of characteristics such bone density, ages and structural strength betweendifferent ontogenetic stages and species.v

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539TABLE OF CONTENTSSIGNATURE PAGE . iiAKNOWLEDGEMENTS. iiiABSTRACT. ivTABLE OF CONTENTS. viLIST OF TABLES. viiiLIST OF FIGURES . ixGLOSSARY OF BIOLOGICAL TERMS FOR GEOLOGISTS . xINTRODUCTION . 1ALLOMETRY AND SIZE INCREASE. 1ALLOMETRIC TRENDS IN PROBOSCIDEANS . 4PHYLETIC DWARFING AND ALLOMETRY. 6INSULAR DWARFING . 7DWARFING AND HETEROCHRONIC EVOLUTION OF ONTOGENTICGROWTH . 8EXAMPLES OF INSULAR DWARFING . 9THE SUBJECTS OF THIS PROJECT . 9THE GOALS OF THIS PROJECT. 12GEOLOGICAL SETTING OF THE CHANNEL ISLANDS. 13PALEOCLIMATOLOGY. 15METHODOLOGY . 17RESULTS . 23ERROR ESTIMATION . 23COLUMBIAN MAMMOTH RESULTS. 23CHANNEL ISLANDS MAMMOTH GROWTH TRENDS . 24MAMMOTH DWARFING TRENDS . 24MASTODON RESULTS. 25DISCUSSION . 31ERROR RESULTS DISCUSSION. 31MASTODON RESULTS DISCUSSION . 32MAMMOTH RESULTS DISCUSSION . 34FUTURE PROJECTS . 38vi

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539CONCLUSIONS. 40REFERENCES . 42vii

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539LIST OF TABLESTable 1: Error results .25Table 2: Humeri results.2627Table 3: Ulnae results .27Table 4: Femora results .29Table 5: Tibiae results .29viii

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539LIST OF FIGURESFigure 1: Histological diagram of horse metacarpals at different ontogenetic stages,demonstrating changes in osteons per area. A. 54 day old neonate . B, 1-year-old juvenileC, 6-year-old adult (Adapted from Stover SM, et al.: Histological features of the dorsalcortex of the third metacarpal bone mid-diaphysis during postnatal growth inthoroughbred horses, J Anat 181:455, 199 .2Figure 2: Left: Growth series demonstrating proportional changes in allometric growth.Right: Growth series representing little proportional change in isometric growt(Adaptedfrom Roselló-Díez, Alberto, and Alexandra L. Joyner. “Regulation of Long BoneGrowth in Vertebrates; It Is Time to Catch Up.” Endocrine Reviews, vol. 36, no. 6, 2015,pp. 646–680., doi:10.1210/er.2015-1048) .3Figure 3: Diagram of a mammoth forelimb, demonstrating columnar profile (Adaptedfrom Larramendi, A. 2016. Shoulder height, body mass, and shape of proboscideans.Acta Palaeontologica Polonica 61 (3): 537–574.) .5Figure 4: Comparison of M. exilis and M. columbi((Adapted from Semprebon, Gina &Rivals, Florent & Fahlke, Julia & Sanders, William & Lister, Adrian & Göhlich, Ursula.(2016). Dietary reconstruction of pygmy mammoths from Santa Rosa Island ofCalifornia. Quaternary International. 406. 10.1016/j.quaint.2015.10.120.) .10Figure 5: Comparison of M. americanum other proboscideans(Adapted fromEncyclopedia Britannica).11Figure 6: Phylogeny of Proboscidea; note the divergence in the middle Oligocene(Adapted from Shoshani (Jul 2001) Proboscidea (Elephants). In: eLS. John Wiley & SonsLtd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001575]).11Figure 7: Map of the Channel Islands(Adapted from USGS maps) .13Figure 8: Map of the Transverse range mountains. The Channel Islands are circled inblack. Note the East-West orientation(Adapted from USGS maps) .14Figure 9: Chronology of the relative plate motions and rotation (Adapted from NPSgeology animations).14Figure 10: Map of the Channel Islands during glacial and interglacial periods (Adaptedfrom NPS geology animations .16Figure 11: The different limb bones; with scale bar and line that marks approximates thelandmarks on the diaphyseal suture used for measurements .18Figure 12: Measuring loose disarticulated bones.19Figure 13: Measuring a Channel Islands pygmy mammoth directly from the display .29Figure 14: RMA regression plots for mastodon bones .30Figure 15: Dwarfing and growth plots for mammoths .30ix

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539GLOSSARY OF BIOLOGICAL TERMS FOR GEOLOGISTS sOntogeny: The growth and development of an organism throughout its lifeHeterochrony: Pertains to the timing of development of certain traits throughout thegrowth of an organismAllometry: The rates at which parts of an organism’s body grows, and the associatedchanges in proportionIsometry: Little to no change to proportion as an organism growsHistology: Study of the structure of biological tissue at the microscopic levelPaedomorphism: Juvenile traits retained in adultsProboscidea: The taxonomic order that includes all elephantsPhylogeny: Pertains to the evolutionary relationships between organismsDiaphysis: The length of the shaft of a bone between the articular endsTaxon: One or more populations of organisms that comprise a singular biological unitHumerus: Upper arm bone that articulates with the scapula on the proximal(closer) endand with the radius and ulna on the distal(farther) endUlna: Lower arm bone that articulates with the humerus on the proximal end and carpalson the distal end; found in conjunction with the radius boneFemur: Upper rear limb bone that articulates with the pelvis on the proximal end and thetibiae on the distal endTibia: Lower rear limb bone that articulates with the femur on the proximal end and thetarsal bones on the distal endOsteon: cylindrical structural units that bones are comprised ofx

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539Artiodactyl: Mammalian taxonomic group defined by their even number of toesInsular: Pertaining to islandsxi

DocuSign Envelope ID: LOMETRY AND SIZE INCREASEWhen terrestrial tetrapods grow throughout their ontogeny, they undergo variousphysiological alterations in response to their size increase. For instance, their skeletalstructure experiences growth in linear dimensions and density. As a result, their bonesundergo modifications such as an increase in the number of osteons (Fig. 1) per area andgreater cross-section thickness to provide stronger structural support, as the larger sizewill increase the biomechanical stress act on the bones (Carrier 1983; Gould 1966). Thenature of these changes, such as the degree to which proportions change throughoutgrowth, can vary between different taxonomic groups and different ontogenetic growthstages within a species. The change in proportion throughout its growth is also known asallometry. Positive allometry is when the bones grow longer faster than they grow thick,in which they become more gracile, and negative allometry is when they grow thickfaster than they grow longer, in which they become more robust (Fig. 2). When anorganism undergoes little to no proportional change, this phenomenon is known asisometry, or isometric growth (Fig. 2).1

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539Figure 1: Histological diagram of horse metacarpals at different ontogenetic stages,demonstrating changes in osteons per area. A. 54 day old neonate. B, 1-year-old juvenileC, 6-year-old adult (Adapted from Stover SM, et al.: Histological features of the dorsalcortex of the third metacarpal bone mid-diaphysis during postnatal growth inthoroughbred horses, J Anat 181:455, 199)2

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539."body rauo,Nomroi!ll d oyou11gest 1!il;i:g0He-.aW1aJI ratio,Norm;;ill.rod ,o:,--0ur,g,cs't r!ilu.g,c41 3, 12 111AUometric growthIsometric growthFigure 2: Left: Growth series demonstrating proportional changes in allometric growth.Right: Growth series representing little proportional change in isometric growth.(Adapted from Roselló-Díez, Alberto, and Alexandra L. Joyner. “Regulation of LongBone Growth in Vertebrates; It Is Time to Catch Up.” Endocrine Reviews, vol. 36, no. 6,2015, pp. 646–680., doi:10.1210/er.2015-1048)It was a long-held belief that most mammals exhibit positive allometry, with variousexceptions. Of these exceptions, it was thought that limb bones of large-bodied animalssuch as elephants underwent negative allometry to compensate for higher stress resultingfrom their greater mass. (Christiansen 2007). However, this notion was contradicted byKilbourne and Makovicky (2012). They found that isometry is the most widespread withpositive allometry as a very close second. They also found that the mode of growth oftencorrelates with a variety of intraspecific and interspecific factors, ranging from stage ofontogeny, adult and birth mass, and type of metabolism. For instance, in a study about thegrowth of the bovid, Ovibos moschatus, Heinrich et al. (1999) reasoned that pre-juvenileneonates likely underwent negative allometric growth, then shifted to isometric growthwhen approaching adulthood, indicating that such mode of growth at an early age mayhave been to build up more robust morphology and later growth to maintain such3

DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539proportions to support its large size; this notion is supported by lower structural failureindices in mammalian neonates, as observed by Main and Biewener (2006) on a study ofthe safety factors of goat long bones. This was also observed by Long et al. (2018), whofound that saber-toothed cat juveniles were born robust and grew with the normal trendthat all other cats show until they reached adulthood. It is also pertinent to note that onlya few limb allometry studies take into account the possibility of shifting modes; the fewthat have, have been limited to few species, mainly due to the lack of large sample sizesthat also represent the entire ontogeny. More specifically, there is often a paucity ofjuvenile and neonate specimens. (Herridge 2010; Kilbourne and Makovicky 2012)ALLOMETRIC TRENDS IN PROBOSCIDEANSThis study concerns the postnatal ontogenetic growth of different North American latePleistocene proboscideans. Compared to most other mammalian groups, modern andrecently extinct elephants are unique in that their limbs are kept in a near columnar stanceduring locomotion (Fig. 3). Consequently, their morphology is largely adapted to thislocomotor style. With this gait, the limbs experience more axial stress and have reducedlateromedial bending range. As such, it would be reasonable to believe that to account forthis increased stress, their limbs would grow increasingly more robust, or n

R: Thein Htun DATE SUBMITTED: Spring 2020 Department of Geological Sciences Dr. Jonathan A. Nourse Thesis Committee Chair Geological Sciences Dr. Donald R. Prothero Geological Sciences : Dr. Bryan P. Murray Geological Sciences . ii DocuSign Envelope ID: D2906CB9-5550-4526-8AB1-FFC055885539

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