Histological evi de nce of tra u ma i n t us ks of so ut her n Africa n dicy no do nts

§ Megan R. Whitney 1, * , Y u e n Ti n g Ts e 1 & C hristia n A. Si dor 1, 2 1 Depart ment of Biology and Burke Museu m, University of Washington, Seattle, Washington, 98195, U.S. A. 2 Evol utio nary St udies I nstit ute, U niversity of the Wit watersra nd, Joha n nesb urg, So uth Africa Received 11 May 2018. Accepted 20 Dece mber 2018

Dicy no do nts were a cla de of globally- distrib ute d t hera psi ds k no w n for t heir ab u n da nce i n t he fossil recor d a n d for s urvivi ng t he Per mo-Triassic mass exti nctio n. T he gro u p ha d disti nctive de ntal a da ptatio ns i ncl u di ng a beak a n d, i n ma ny s pecies, paire d maxillary t usks. T he f u nctio n of t hese t usks has lo ng bee n of i nterest, yet re mai ns poorly u n derstoo d. We re port here o n t wo i nsta nces of u n us ual morphology in tusk dentine fro m speci mens of: 1) Lystrosa ur us fro m the Karoo Basin of South Africa and, 2) an unidentified dicy no do ntoi d fro m t he Lua ng wa Basi n of Za mbia. I n bot h, t he cross-sectio nal s ha pe of t he t usk root is lobe d a n d i nfol de d, w hic h histological feat ures s uggest is a res ult of ab nor mal de nti ne de positio n. We i nfer t hat t his ab nor mal mor p hology is likely t he co nse - q ue nce of tra u ma give n its re parative nat ure a n d str uct ural si milarities to tra u ma-relate d mor p hologies re porte d i n t he t usks of mo der n ele p ha nts. T his st u dy de mo nstrates t hat histological sa m pli ng of dicy no do nt t usks ca n s he d lig ht o n t he biology of t his i m porta nt cla de of t hera psi ds. Key words : Dicy no do ntia, Triassic, So ut h Africa, Za mbia, Per mia n, pat hology, de nti ne.

Palaeontologia africana 2019. ©2019 Megan R. Whitney, Yuen Ting Tse & Christian A. Sidor. This is an open-access article published under the Creative Co m mons Attrib utio n 4.0 U nported Lice nse ( C C B Y4.0). To vie w a copy of the lice nse, please visit http://creativeco m mo ns.org/lice nses/by/4.0/ . This lice nse per mits u nrestricted use, distrib utio n, a nd reprod uctio n i n a ny medi u m, provided the origi nal a uthor a nd so urce are credited. This article is per ma ne ntly archived at: http:// wiredspace. wits.ac.za/ha ndle/10539/26243

INTRODUCTION dicynodont speci mens were prepared and thin-sectioned Dicy no do nts evolve d o ne of t he most s pecialize d foo d follo wing standard methods (La m m 2013). In both speci- processi ng syste ms wit hi n t he sy na psi d li neage, c harac- me ns, t he t usks were broke n w here t hey e merge fro m t he terize d by a hor n-covere d beak a n d (ofte nti mes) maxillary maxillae, b ut preserve most of t he root portio n of t he tusks, along with a distinctive ja w hinge ( Cro mpton & t usks. T hi n sectio ns were ma de per pe n dic ular to t he lo ng Hotto n 1967; A ngielczyk 2004). E nlarge d, paire d t usks, axis of t he t usk, gro u n d to a t hick ness of a p proxi mately w hic h are t he na mesake of t he cla de, have lo ng i ntrig ue d 100 µ m, and i maged with a Nikon Eclipse L V100P OL palaeontologists with proposed functions including microscope an d NIS-Ele ments soft ware. foragi ng for foo d, sex ual di mor p his m i n so me s pecies a n d b urro wi ng be havio urs (S ulliva n et al . 2002; Ra y et al . 2 0 0 5; SYSTE MATIC PALAEO NTOLOGY Mo desto & Bot ha- Bri nk 2010; Bot ha- Bri nk 2017). Des pite Synapsida Osbor n, 1903 this variety of proposed roles, gross morphological T hera psi da Broo m, 1905 evi de nce has provi de d little i nsig ht i nto t he f u nctio n of Dicy no do ntia O we n, 1859 dicy no do nt t usks. Dicynodontoidea O we n, 1859 Here we describe t he histology of t wo t usks a n d t heir surrounding hard tissues in speci mens of Lystrosa ur us Dicy no do ntoi dea i n det. fro m the Karoo Basin of South Africa and an indeter mi - Referred speci me n . N H C C LB836, tusk-bearing left and nate dicynodontoid (possibly Dicy nodo n ) fro m t he ri g ht m a xill a e fr o m o n e i n di vi d u al. Luang wa Basin of Za mbia. Unusually, these speci mens L oc alit y . T his s peci me n was collecte d fro m locality L424, preserve anato my consistent with a develop mental a mediu m-sized outcrop of the upper me mber of the ano maly or pathology, although non-pathological Madu mabisa Mudstone For mation near the southern i nfol de d de nti ne (i.e. plici de nti ne) is see n i n so me border North Luang wa National Park ( Northern Prov - pelycosa ur-gra de sy na psi ds ( Bri nk et al . 2014). Base d o n i nce, Za mbia). Detaile d locality i nfor matio n is available co mparisons with modern tusked ani mals, we conclude fro m N H C C or the authors. t hat tra u ma is t he most likely ex pla natio n for t his a no ma - Lystrosaur us Co pe, 1870 lo us de nti ne a nato my, w hic h ca n provi de i nsig ht i nto t he f u nctio n of t usks i n at least so me dicy no do nts. Lystrosaur us i n d et. Referred speci me ns . S A M-P K- K011603, tusk-bearing right MATERIALS A N D MET H O DS maxilla; S A M- P K- K011604, partial sk ull, i ncl u di ng orbits The tusk and surrounding alveolar ja w bone of the a n d s no ut. * Aut hor for corres po n de nce. E- mail: meg whit @u w.edu L oc alit y . S A M-P K- K011603 was collected near the bound -

Palaeontolo gia africana 5 3 : 7 5 – 8 0 — I S S N 2 4 1 0- 4 4 1 8 [ P al a e o nt ol. afr.] O nli n e o nl y Per manently archived on the 17th of January 2019 at the University of the Wit watersrand, Johannesburg, South Africa T hi s arti cl e i s p er m a n e ntl y ar c hi v e d at: htt p:// wir e d s p a c e. wit s. a c. z a/ h a n dl e/ 1 0 5 3 9/ 2 6 2 4 3

ISS N 2410-4418 P al ae o nt. afr. (2019) 5 3 : 75–80 7 5 ary bet ween the far ms Weltrevreden and Ripple mead f u n nel-s ha pe d p ul p cavity (Fig. 1b), i n dicative of a n ever- ( Nieu Bethesda District, Eastern Cape Province) by Dr gro wing tusk (Steenka mp 2003). Roger S mith as field nu mber RS 337, fro m rocks of the N H C C L B836 i ncl u des associate d left a n d rig ht maxillae Triassic u p per Pali ngkloof Me mber of t he Balfo ur For ma - that contain inco mplete tusks (Fig. 2). The caninifor m ti o n ( Lystrosa ur us Asse mblage Zone; S mith & Botha- Brink processes of t he maxillae are a ngle d slig htly per pe n dic u - 2014). S A M-P K- K011604 was also collected by Dr Roger lar to the dorsoventral axis and more r ugose than the S mit h fro m Lo wer Triassic rocks o n t he far m Do nal d 207 surrounding maxillary bone (Fig. 2a). The left maxilla (Fairy dale) i n t he Bet h ulie District, Easter n Ca pe Prov - includes approxi mately 7.5 c m of tusk and the right is ince, approxi mately 54 metres above the inferred slig htly more co m plete, preservi ng 8.4 c m of t usk i ncl u d - Per mo–Triassic boundary. i ng more of its dorsal portio n. O n bot h si des, t he dorsal portio n of t he maxillae are broke n to ex pose t heir i nterior DESCRIPTI O N a nat o m y as well as t he r o ots of t he t us ks. O n t he ri g ht si de, t his broke n s urface ex poses w hat a p pears to be reg ularly Gross anato my de posite d de nti ne i n a circ ular cross-sectio nal s ha pe. T he S A M-P K- K011603 is an inco mplete right maxilla pre - left si de, ho wever, reveals t hat t he root of t he t usk has servi ng m uc h of t he lateral s urface, i ncl u di ng t he palatal dee ply i nfol de d de nti ne, w hic h is visible macrosco pically ra mus, caninifor m process, and a s mall section of the (Fig. 2b). Esse ntially no ne of t he f u nctio nal t usk is pre - a nterior process (Fig. 1a). Base d o n its size a n d a nato my, ser ve d o n eit her si de, i ncl u di ng pote ntial wear facets. w e r ef er it t o Lystrosa ur us s p., w hic h accor ds well wit h its stratigra p hic positio n, as t here are no ot her dicy no do nt Histolo g y ge nera k no w n fro m t he Triassic portio n of t he Pali ngkloof The tusk of S A M-P K- K011603 is co mposed of dentine Me mber of the Balfour For mation (S mith & Botha- Brink wit h no o uter ca p pi ng tiss ue s uc h as e na mel or ce me nt u m 2 0 1 4). preserved, although the lack of ce mentu m in the E mbe d de d wit hi n t he maxilla is a sectio n of t usk a p prox - preer u ptive root co ul d be preservatio nal. Fro m t he root i mately 5 c m lo ng, alt ho ug h it is o nly visible e mergi ng e n d (i.e. a pex i n sta n dar d de ntal ter mi nology; Fe hre nbac h fro m t he dorsal a n d ve ntral s urfaces of t he bo ne. A p proxi- & Popo wics 2016) to wards the tip of the tusk, the mately 5 m m of erupted cro wn is preserved with not cross-sectio nal s ha pe of t he t usk c ha nges fro m havi ng a n e no ug h material preserve d to exa mi ne wear facets. Base d u n us ual wavier bor der to a more ex pecte d circ ular o ne. o n w hat is visible a n d t he c ur ve of t he ca ni nifor m process, T he wavy margi n is t he s urface ex pressio n of t he i nfol di ng t he root is slig htly rec urve d a n d it ta pers i n dia meter of t he u n derlyi ng de nti ne, w hic h ca n exte n d dee p to near to wards the occlusal surface. The root of S A M-P K- the pulp cavity (Fig. 3a). To wards the tip end, the K011603 is da mage d a pically, b ut a not her, more co m plete i nfol di ngs gra d ually beco me s hallo wer a n d less exagger- Lystrosa ur us speci men (S A M-P K- K011604) was sectioned ate d ( Fi g. 3 b– d) u ntil n o irre g ularities are prese nt ( Fi g. 3 d). lo ngit u di nally a n d reveals a wi de o pe n root wit h a disti nct T he most dra matic i nfol di ng is prese nt o n t he a nterior

Fi g ure 1 . Gross a nato my a n d histology of Lystrosa ur us t us ks. A , Cast of S A M- P K- K011603 i n rig ht lateral vie w. B , Thin section of S A M-P K- K011604 wit h a n o pe n, f u n nel-s ha pe d p ul p cavity i n dicative of a n ever-gro wi ng t usk. Scale bars eq ual: A, 3 c m; B, 5 m m. Abbreviatio ns: ab, alveolar bo ne; d e, d e nti n e; p c, p ul p c a vit y.

7 6 ISS N 2410-4418 P al ae o nt. afr. (2019) 5 3 : 75–80 Fi g ure 2 . Gross anato my and thin sections of dicynodontoid ( N H C C L B836). A , Sc he matic re prese nti ng w here sectio ns were take n fro m t he pat ho - logical rig ht t usk a n d t he associate d, nor mal left maxilla i n left lateral vie w. B , Nat ural break s ho wi ng t he pat hological rig ht t usk root wit h a nterior to war ds t he to p of t he page. C , T hi n sectio n s ho wi ng i nfol di ng near root e n d of t usk. D , T hi n sectio n take n near ve ntral e n d of maxilla s ho wi ng less pro no u nce d i nfol di ng. E , Boundary bet ween more co mpact ja w bone and more vascularized alveolar bone. F , Hig h mag nificatio n vie w of t he perio do ntal s pace bet wee n t he t usk root a n d alveolar bo ne. Scale bars eq ual: A– B, 1 c m; C– D, 5000 µ m; E, 250 µ m; F, 50 µ m. Abbreviatio ns: ab, alveolar b o n e; c e, c e m e nt u m; d e, d e nti n e; j b, j a w b o n e; p c, p ul p c a vit y; ps, p eri o d o nt al s p a c e; sf, S h ar p e y’s fi br es. margin of the root an d continues with wavy margins on approxi mately 20 µ m apart, which correspond to the 5- t he me dial a n d posterior e dges (Fig. 3a–c). day i ncre me nts of li nes of vo n Eb ner i n ma m mals (Si m mer T he t wo pre do mi na nt histological feat ures of de nti ne, et al . 2008), are visi ble i n t his s peci me n ( Fi g. 3e–f). B ot h t he dentine tubules and incre mental gro wth marks spaced dentine tubules and lines of von Ebner follo w nor mal

ISS N 2410-4418 P al ae o nt. afr. (2019) 5 3 : 75–80 7 7 Fi g ure 3 . T hi n secti o ns of Lystrosa ur us s p. (S A M- P K- K011603) take n at fo ur locatio ns alo ng t he a pical- occl usal axis. A – D , T hi n sectio ns detaili ng t he c ha nges i n u n us ual de nti ne mor p hology fro m t he a pical- most sectio n wit h t he most dra matic irreg ularities ( A) to t he occl usal- most sectio n wit h reg ular mor p hology ( D). E , Boxe d portio n of sectio n ( A) at hig h mag nificatio n detaili ng de nti ne i nfol di ng a n d perio do ntal s pace. F , Boxe d portio n of sectio n ( B) at hig h mag nificatio n detaili ng re d uce d b ut co nti n ue d i nfol di ng. Scale bars eq ual: A– D, 2 m m; E–F, 500 µ m. Abbreviatio ns: ab, alveolar b o n e; d e, d e nti n e; p c, p ul p c a vit y; ps, p eri o d o nt al s p a c e. patterns in non-lobed portions of the tusk with the (i. e. fi br ol a m ell ar b o n e se ns u Fr a n cill o n- Vi ell ot et al . 1990) tubules radiating out fro m the pulp cavity and gro wth with longitudinally oriented canals and evidence of marks co nce ntrically orga nize d aro u n d t he t usk. I n t he extensive re modeling. A periodontal space is present abnor mal portions of the root, ho wever, both features bet ween the tusk and the surrounding alveolar bone mirror t he s ha pe of its fol de d a n d irreg ular circ u mfere nce. ranging in thickness fro m 90 µ m to 500 µ m. In sections The surrounding alveolar bone is co mposed of highly taken both apically and to wards the erupted end of the vascularized woven-fibred bone with pri mary osteons root, Sharpey’s fibres running perpendicular to the

7 8 ISS N 2410-4418 P al ae o nt. afr. (2019) 5 3 : 75–80 perio do ntal s pace are ab u n da nt a n d provi de evi de nce of a suggests that nor mal dentine deposition had occurred soft-tiss ue perio do ntal liga me nto us toot h attac h me nt. e arli er i n t h e i n di vi d u al’s lif e. T h us, a c o n g e nit al a n o m al y U nlike t he left t usk of N H C C L B836, w hic h a p pears to c a n b e r ul e d o ut. have reg ular de nti ne (Fig. 2a), t he rig ht si de dis plays a n We suggest that trau ma is the likely cause for the irreg ular, i nfol di ng of de nti ne si milar to t hat see n i n peculiar root morphology observed in these speci mens. S A M-P K- K011603. An open root and the abnor mal Mec ha nistically, t he tra u ma co ul d have res ulte d i n eit her dentine were apparent in the field when the speci men irreg ular origi nal de positio n (i.e. pri mary de nti ne) or was collecte d d ue to breakage of t he maxilla a n d its ex po - re parative de positio n (i.e. seco n dary de nti ne). I n cross- s ure of t he a pical portio n of t he t usk root (Fig. 2b). T he sectio n, t he peri p her y of t he t usks re prese nts t he earliest tusk is co mposed of dentine (Fig. 2c–f) surrounded by site of dentine deposition and thus, the abnor mal and alveolar bone with a thin layer of ce mentu m preserved occasio nally i nfol de d margi n co ul d i n dicate t hat d uri ng (Fig. 2f). A t hi n perio do ntal s pace is a p pare nt aro u n d t he t he o nset of tiss ue de positio n tra u ma res ulte d i n irreg ular t usk wit h S har pey’s fibres i n t he alveolar bo ne i n dicative o do ntoblast activity. Alter natively, seco n dary de nti ne of a go m p hosis (Fig. 2f). T he hig hly irreg ularly de posite d could have been deposited to repair da maged pri mary de nti ne is more exaggerate d i n t he a pex of t he root a n d dentine tissue giving rise to the unusual morphology, t he irreg ular patter ni ng is co nsiste nt o n bot h t he labial wit h eit her sce nario de pe n di ng o n t he ti mi ng of a n i nj ur y. a n d li n g u al m ar gi ns ( Fi g. 2 b). T o w ar ds t h e ti p of t h e t us k, I n eit her case, so me exter nal tra u ma to t he t usk or maxilla t he irreg ular i nfol di ng is restricte d to t he posteroli ng ual wo ul d likely prese nt itself as u n us ual alveolar bo ne wit h as pect of t he t usk (Fig. 2 d). Si milar to t he Lystrosa ur us evidence of reparative bone. Surprisingly, we see no speci men, the unusual dentine shape in N H C C LB836 evi de nce of malfor matio ns or tra u ma to t he maxilla, b ut is r efl e ct e d i n t h e p eri o di c d e p ositi o n al li n es ( als o a p pr o xi - give n t he ra pi d t ur nover rate of alveolar bo ne, it is possi - mately 20 µ m apart) as well as the dentine tubules ble that such evidence has been re modelled a way (e.g. ( Fi g. 2 c). n n Vig nery & Baro n 1980). The folded morphology seen in these speci mens is DISC USSI O N re markably si milar to w hat has bee n describe d i n mo der n Infolded dentine has been recognized in the roots of elephant tusks that have experienced trau ma ( Miles & nu merous groups of a mniotes including Captorhinidae, Grigson 1990) and in many ways, dicynodont tusks are Choristodera, Diadecto morpha, Ichthyosauria, Lepido- co mparable to elephant tusks. The tusks of the Lystro- sauria, Parareptilia and Sphenacodontidae ( Brink et al . sa ur us and the dicynodontoid described here were ever- 2014; Mac Dougall et al . 2014; Max well et al . 2011; Me u nier gro wing and anchored to the maxilla by a periodontal et al . 2013). Ty pically, t he s ha pe of t he i nfol de d de nti ne liga ment (i.e. go mphosis). A mong therapsids, LeBlanc is regular and sy m metrical, and has been ter med plici- et al . (2018) reported evidence for a liga mentous tooth dentine ( O wen 1841; To mes 1878). Although the dentine attach ment in the cynodonts Diade modon , Cynognathus , infol dings observe d here are lobe d like plici dentine, Galesa ur us , t h e t h er o c e p h ali a n B a uri a , gorgonopsians an d the distribution and depth of infoldings around the tapinocephalids, and Jasinoski & Chinsa my (2012b) made cr oss-secti o nal area is hi g hl y irre g ular. A d diti o nall y, l obe d a si milar re p ort f or Trit yl o d o n . T he t usks of ele p ha nts are morphology has not been observed in the tusk roots ever-gro wi ng a n d i n cases of tra u ma, ‘t he portio n of t he of other dicynodont speci mens that have been thin- toot h develo pi ng at t he ti me of a n i nj ury us ually has a sectioned (Thackeray 1991; Green 2012; Jaskinoski & cri nkle d a p peara nce wit h irreg ular for matio n i ncreasi ng Chinsa my-Turan 2012a; LeBlanc et al . 2018) nor are t hey to war ds t he gro wi ng e n d a n d t he tiss ues s ho wi ng sig ns of visible in the contralateral maxilla of N H C C L B836, defective mi neralizatio n’ ( Miles & Grigso n 1990: 404). I n s uggesti ng t hat t he i nsta nces describe d here are a no ma - elephants, the most co m mon reported sources of trau ma lies. Alt ho ug h not exa mi ne d u n der t hi n sectio n, t he lo ng are falli ng or fig hti ng. I n a d ditio n, t usk abrasio n a n d wear axis of t he t us k of Odo ntocyclops whaitsi ( A M N H 5566) does are frequent causes of da mage in digging ani mals like present so me infolding ( Angielczyk 2002), although it walr uses (Steenka mp 2003). Digging and foraging have appears more regular than the infolding seen in S A M- been proposed as potential uses for dicynodonts tusks P K- K011603 or N H C C LB836. The infolding observed in (e.g. Ki ng 1990; Ki ng & Cl uver 1991) a n d t h us, it is u ns ur - Odo ntocyclops co ul d be a differe nt ab nor mality or a differ - prisi ng t hat t hey wo ul d occasio nally accr ue da mage. ent morphology for med fro m a si milar etiology. Ho w - Des pite bei ng disti nct s pecies se parate d by millio ns of ever, without thin-sectioning, useful co mparisons are years, S A M-P K- K011603 and N H C C LB836 share re mark - li mit e d. ably si milar, albeit u n us ual, de ntal histology, w hic h i n T he pec uliar cross-sectio nal mor p hology of t hese s peci - tur n suggests the potential for si milar behaviour and me ns was for me d by irreg ularities i n t he pat h of o do nto - utilizatio n of t heir t usks. T he li mite d sa m ple here does blasts take n d uri ng t heir de positio n of de nti ne, w hic h is not precl u de alter native f u nctio ns i n differe nt s pecies; evi dence d by the correspon dence of dentine tubules an d ho wever, it does lend support that many – if not most li nes of vo n Eb ner to t he lobe d mor p hology. T h us, t here dicy no do nts – use d t heir t usks to forage a n d dig, a n d t hat is goo d evi de nce t hat t he lobe d a nato my is a de positio - occasio nally t hese activities res ulte d i n tra u ma to t heir nal a n o mal y, yet its eti ol o g y is diffic ult t o deter mi ne defi n - developing dental tissues. Continued analysis of the itively. It is i nteresti ng to note, ho wever, t hat t he lack i nter nal a nato my of dicy no do nt t usks will el uci date more of infoldings to wards the e merging end of the tusks about their evolution and develop ment as well as shed

ISS N 2410-4418 P al ae o nt. afr. (2019) 5 3 : 75–80 7 9 lig ht o n t heir f u nctio nal sig nifica nce. T his st u dy de mo n - Radiatio n, Histology, Biology , 149–176. Bloo mi ngto n, I n dia na U niversity Pr ess. strates ho w give n t he lack of exter nal, gross a nato mical J ASI N OS KI, S. C. & C HI NS A MY, A. 2012b. Mandibular histology and i n dicatio ns of t he ab nor mality note d here, histological gro wth of the non ma m maliafor m cynodont Trit yl o d o n .Jo ur nal of A nat - sa m pli ng is a n i m porta nt tool i n gar neri ng more i nfor ma - o m y 2 2 0 , 564–579. KI N G, G. 1990. The Dicy nodo nts: a St udy i n Palaeobiology . Ne w York, Chap - tio n abo ut t he biology of t hese a ni mals. m a n a n d H all. We thank R. S mith (S A M) for collecting the speci men and Z. Skosan (S A M) for KI N G, G. M. & CL U VE R, M. A. 1991. The aquatic Lystrosa ur us : a n alter na - s peci me n access, K. Bri nk, Y. Hari dy, a n d A. Le Bla nc for usef ul disc ussio ns abo ut ti v e lif est yl e. Hist oric al Bi ol o g y 4 : 323–341. L A M M, E. T. 2013. Pre paratio n a n d sectio ni ng of s peci me ns. I n : P a di a n, t hera psi d de ntal histology as well as K. A ngielczyk a n d J. Bot ha- Bri nk for hel pf ul K. & La m m, E.-T. (e ds), Bone Histology of Fossil Tetrapods: Advancing revie ws t hat greatly i m prove d t he ma n uscri pt. We also t ha nk t he 2018 Za mbia fiel d Met ho ds, A nalysis a nd I nterpretatio n , 55–130. Berkeley a n d Los A ngeles, tea m a n d t he Natio nal Heritage Co nservatio n Co m missio n for assista nce i n collect - C alif or ni a, U ni v ersit y of C alif or ni a Pr ess. ing N H C C LB836 and support fro m National Geographic Exploration Grant LEBL A N C, A. R. H., B RI N K, K.S., W HIT NE Y, M. R., AB D AL A, F. & REIS Z, N GS-158 R-18 (a war de d to B. R. Peecook). K. Button an d A. Huttenlocker contrib - R. R. 2018. De ntal o ntoge ny i n exti nct sy na psi ds reveals a co m plex evo - ut e d i niti al t hi n s e cti o ns f or Lystrosa ur us and K. Abra ms prepared N H C C LB836 for l utio nary history of t he ma m malia n toot h attac h me nt syste m. Procee d - sectioning. This research was supported by National Science Foundation PL R- i ngs of the Royal Society B 2 8 5 , 20181792. 1341304 (a warded to C. A. Sidor) and DE B-1701383 (a warded to M. R. Whitney). M AC D O U G ALL, M.J., LEBL A N C, A.R. H. & REISZ, R.R. 2014. Plici - de nti ne i n early Per mia n parare ptile Colobo mycter pholeter , a n d its I NSTITUTI O NAL ABBREVIATI O NS phylogenetic and functional significance a mong coeval me mbers of S A M Iziko South African Museu m, Cape To wn. t h e cl a d e. PL OS O NE 9 ( 5), 1 – 9. N H C C National Heritage Conservation Co m mission, Lusaka. MAX WELL, E.E., CAL D WELL, M. W. & LA M O UREX, D. O. 2011. The str uct ure a n d p hyloge netic distrib utio n of a m niote plici de nti ne. Jo ur - nal of Vertebrate Paleo ntology 3 1 (3), 553–561. § O R CI D i Ds ME U NIE R, F.J., DE M AY RI N C K, D. & B RIT O, P. M. 2013. Presence of M. R. W hit n e y: orci d.org/0000-0002-6671-5127 plici de nti ne i n t he labial teet h of Hoplias ai mara ( Er yt hri ni dae; Y. Ti n g Ts e: orci d.org/0000-0002-5235-3081 Ostari o p h ysi; Tele ostei). Acta Zoologica 9 6 , 174–180. C. A. Si d or: orci d.org/0000-0003-0742-4829 MILES, A.E. W. & G RI GS O N, C. 1990. Colyer’s Variatio ns a nd Diseases of the Teeth of A ni mals (rev. e d n.). Ca mbri dge, Ca mbri dge U niversity Press. M O DEST O, S.P. & B OT H A-B RI N K, J. 2010. A burro w cast with Lystro - REFERE NCES sa ur us skeletal re mai ns fro m t he Lo wer Triassic of So ut h Africa. Pal ai os A N GIEL C Z Y K, K. D. 2002. Redescription, phylogenetic position, and 2 5 , 274–281. stratigraphic significant of the dicynodont genus Odo ntocyclops OS B O R N, H.F. 1903. The reptilian subclasses Diapsida and Synapsida (Synapsida: Ano modontia). Jo ur nal of Paleo ntology 7 6 , 1047–1059. a n d t he early history of t he Dia ptosa uria. Me moirs of the A merican A N GI E L C Z Y K, K. D. 2004. P hyloge netic evi de nce for a n d i m plicatio ns of Museu m of Natural History 1 , 449–507. a dual origin of propaliny in ano modont therapsids (Synapsida). O WE N, R. 1841. On the teeth of species of the genus Labyrinthodon Pale o bi ol o g y 3 0 , 268–296. (Mastodontosaur us of Jaeger), co m mon to the Ger man Keuper for ma- B OT H A-B RI N K, J. 2017. Burro wing in Lystrosa ur us : prea da ptatio n to a tion and the Lo wer Sandstone of War wick and Lea mington. Tra nsac- postexti nctio n e nviro n me nt? Jo ur nal of Vertebrate Paleo ntology . tio ns of the Geological Society 2 , 505–513. D OI: 10.1080/02724634.2017.1365080 O W E N, R. 1859. O n t he or der of fossil a n d Rece nt Re ptilia, a n d t heir dis- B RI N K, K.S., LEBL A N C, A. R. H. & REIS Z, R. R. 2014. First record of tri b uti o n i n ti m e. Report of the T we nty- ni nth Meeti ng of the British Associa- plici de nti ne i n Sy na psi da a n d patter ns of toot h root s ha pe c ha nge i n tio n for the Adva nce me nt of Scie nce 1859 , 153–166. early Per mian sphenocodontians. Nat ur wisse nschafte n 1 0 1 , 883–892. R AY, S., C HI NS A MY, A. & B A N DY OPA D HYAY, S. 2005. Lystrosa ur us B R O O M, R. 1905. On the use of the ter m Ano modontia. Records of the m urrayi ( T hera psi da, Dicy no do ntia): bo ne histology, gro wt h a n d life- Albany Museu m 1 , 266–269. style a da ptatio ns. Palaeo ntology 4 8 , 1169–1185. C OPE, E. D. 1870. On the skull of dicynodont Reptilia. Lystrosa ur us STEE N K A MP, G. 2003. Oral biology and disorders of tusked ma m mals. fro ntos us fro m Cape Colony. Proceedi ngs of the A merica n Philosophical I n : Cr ossl e y, D. A. ( e d.), The Veteri nary Cli nics of North A merica, Exotic Societ y 1 1 , 4 1 9. A ni mal Practice 6( 3). P hil a d el p hi a, W. B. S a u n d er C o m p a n y. C R O MPT O N, A. W. & H OTT O N, N. 1967. Functional morphology of the SI M ME R, J.P., S MIT H, J. A. & YA M A K OS HI, Y. 2008. Dentin-pulp co m - masticatory apparatus of t wo dicynodonts ( Reptilia, Therapsida). pl e x. I n : N a n ci, A. ( e d.), Ten Cate’s Oral Histology: Develop ment, Str uc - Postill a 1 0 9 , 1 – 5 1. t ure, a nd Fu nctio n , 1 9 1 – 2 3 8. St. L o uis, M os b y I n c. FR A N CILL O N-VIELL OT, H., DE B UFFRÉ NIL, V., CASTA NET, J., S MIT H, R. M. H. & B OT H A-B RI N K, J. 2014. Anato my of a mass extinc - GÉ R A U DIE, J., ME U NIE R, F.J., SI RE, J.Y., ZYLBE R GE R, L. & DE tion: sedi mentological and taphono mic evidence for drought- RI QLÉS, A. 1990. Microstr ucture and mineralization of vertebrate induced die-offs at the Per mo-Triassic boundary in the main Karoo s k el et al tiss u es. I n : C art er, J. G. ( e d.), Skeletal Bio mi neralizatio n: Patter ns, Basi n, S o ut h Africa. Palaeogeography ,Palaeocli matology ,P alaeoecology 3 9 6 , Processes and Evolutionary Trends , Vol. 1. Ne w York, Van Nostrand 99–118. R ei n h ol d. S ULLI VA N, C., REIS Z, R. R. & S MIT H, R. M. H. 2002. The Per mian ma m - FE HRE NB AC H, M.J. & P OP O WI CS, T. 2016. Illustrated Dental E mbryol - mal-like herbi vore Diict o d o n , the oldest kno wn exa mple of sexually ogy, Histology, and Anato my (4th edn). Maryland Heights, Missouri, di morphic ar ma ment. Proceedi ngs of the Royal Society of Lo ndo n B 2 7 0 , Sa u n ders. 173–178. G R E E N, J. 2012. Bo ne a n d de ntal histology of Late Triassic dicy no do nts T H A C K E R AY, J.F. 1991. Gro wt h i ncre me nts i n teet h of Diict o d o n (Therap - fro m North A merica. I n : Chinsa my-Turan, A. (e d.), Forer u n ners of si d a). Koe doe 3 4 ( 1), 7 – 1 1. Ma m mals: Radiatio n, Histology, Biology , 179–196. Bloo mi ngto n, I n dia na T O MES, C.S. 1878. On the structure and develop ment of vascular U ni versit y Press. d e nti n e. Philosophical Transactions of the Royal Society of London 1 6 9 , J ASI N OS KI, S. C. & C HI NS A M Y-T U R A N, A. 2012a. Biological inferences 2 5 – 4 7. of the cranial microstr ucture of the dicynodonts Oudenodon a n d VI G NE RY, A. & B A R O N, R. 1980. Dyna mic histo morpholoy of alveolar Lystrosa ur us . I n : C hi nsa my-Tura n, A. (e d.), Forerunners of Ma m mals: b o n e r e m o d eli n g i n t h e a d ult r at. The Anato mical Record 1 9 6 , 191–200.

8 0 ISS N 2410-4418 P al ae o nt. afr. (2019) 5 3 : 75–80