Saint Bathans mammal
TheSaint Bathans mammalis a currently unnamed extinct primitivemammalfrom theEarly Miocene(Altonian,18.7 Ma to 15.9 Ma) ofNew Zealand.A member of theSaint Bathans fauna,it is notable for being a late-surviving "archaic" mammal species, neither aplacentalnor amarsupial.It also provides evidence that flightless fully terrestrial mammals did in fact once live inZealandia.This is in contrast to modern New Zealand, wherebats,cetaceansandsealsare the only non-introduced mammals in the otherwisebird-dominated faunas.[1]
Discovery
[edit]The Saint Bathans mammal is currently represented by three specimens inTe Papa:NMNZ S.40958,NMNZ S.41866,andNMNZ S.42214,composed of two lower jaw fragments and a femur respectively. It was part of an assemblage of fossils recovered inSaint Bathansin 1978, in what would later be understood to be the Bannockburn Formation (Manuherikia Group), and first described in 2006.[1]
Description
[edit]Like most small mammal fossils, the Saint Bathans mammal material is rather incomplete, with only a lower jaw fragment and femur being known.
The lower jaws are toothless, though the presence of deep tooth sockets suggests that they were toothed in life and that the teeth were lost post-mortem. They bear a long fusedmandibular symphysis,an evidently procumbent lowerincisor,and five additional sockets that imply adental formulaof one incisor, onecanineand two double-rootedpremolars.
The femur possesses a roundheadand poorly definedneck,oriented slightly dorsomedially with respect to the long axis of the shaft, and separated from thegreater trochanterby a marked trough. The alignment of the femur in life is hard to ascertain, but it is thought that the animal had a semi-sprawling stance, more abducted than intherianmammals but nowhere near as much as inmonotremes.
Phylogeny
[edit]Because of the incomplete material, it is very hard to understand the position of this taxon withinMammaliaformesas a whole. Worthy et al. 2006 tentatively deemed the Saint Bathans mammal as atheriiform,being more derived thanmorganucodontans,eutriconodontsandmonotremesbut not as much asmultituberculates,on the basis of its femoral anatomy. As the phylogeny of non-therianmammals has undergone multiple shifts since its description, new studies might be necessary.
Ecology
[edit]The Bannockburn Formation depicts a warm temperate or subtropical lakeside environment, surrounded by herbaceouspeat–swamps.Casuarinas,araucarias,podocarps,eucalypts,palm treesandsouthern beechesare among the various plant species known to have grown here. As today, the local vertebrate fauna was dominated by birds: earlymoasandadzebillsare represented by unnamed species, as are various representatives of groups such aswaterfowl,flamingos,rails,herons,strigopoideanparrotsand even an earlykiwi,Proapteryx.[2]However, unlike modern New Zealand it also had a variedherpetofauna:besides an earlytuatara,the Saint Bathans fauna also includesmeiolaniidandpleurodireturtlesand possiblymekosuchinecrocodylidsandsnakes.[3]
Besides the Saint Bathans mammal, this fauna also includesmystacinebats, a group still present in modern New Zealand.[4]Like the modern species, these were probably terrestrial foragers,[5]the same general ecological niche proposed for the Saint Bathans mammal. Other bats, including avesper batand several currently unclassified species, also existed.
References
[edit]- ^ab Worthy, Trevor H.; Tennyson, Alan J. D.; Archer, Michael; Musser, Anne M.; Hand, Suzanne J.; Jones, Craig; Douglas, Barry J.; McNamara, James A.; Beck, Robin M. D. (2006)."Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific".PNAS.103(51): 19419–19423.Bibcode:2006PNAS..10319419W.doi:10.1073/pnas.0605684103.PMC1697831.PMID17159151.
- ^Worthy, Trevor H.; et al. (2013).Miocene fossils show that kiwi (Apteryx, Apterygidae) are probably not phyletic dwarves(PDF). Paleornithological Research 2013, Proceedings of the 8th International Meeting of the Society of Avian Paleontology and Evolution. Retrieved 9 March 2014.
- ^Scofield, R. Paul; Worthy, Trevor H. & Tennyson, Alan J.D. (2010)."A heron (Aves: Ardeidae) from the Early Miocene St Bathans Fauna of southern New Zealand."In W.E. Boles & T.H. Worthy. Proceedings of the VII International Meeting of the Society of Avian Paleontology and Evolution. Records of the Australian Museum 62. pp. 89–104.doi:10.3853/j.0067-1975.62.2010.1542
- ^ Hand, Suzanne J.; Worthy, Trevor H.; Archer, Michael; Worthy, Jennifer P.; Tennyson, Alan J. D.; Scofield, R. Paul (2013). "Miocene mystacinids (Chiroptera, Noctilionoidea) indicate a long history for endemic bats in New Zealand".Journal of Vertebrate Paleontology.33(6): 1442–1448.Bibcode:2013JVPal..33.1442H.doi:10.1080/02724634.2013.775950.S2CID85925160.
- ^ Hand, Suzanne J.; Beck, Robin M. D.; Archer, Michael; Simmons, Nancy B.; Gunnell, Gregg F.; Scofield, R. Paul; Tennyson, Alan J. D.; De Pietri, Vanesa L.; Salisbury, Steven W.; Worthy, Trevor H. (2018)."A new, large-bodied omnivorous bat (Noctilionoidea: Mystacinidae) reveals lost morphological and ecological diversity since the Miocene in New Zealand".Scientific Reports.8(1): 235.Bibcode:2018NatSR...8..235H.doi:10.1038/s41598-017-18403-w.PMC5762892.PMID29321543.
