Early Triassic vertebrate burrows from the Katberg Formation of the south-western Karoo Basin, South Africa

Abstract

Very large (30-35 cm), uniform diameter cylindrical burrows were found at two localities, 100-110 m above Permo-Triassic boundary in the fluvial Katberg Formation (main Karoo Basin, South Africa). Analysis of their morphology and stratigraphical distribution allows us to improve both the understanding of the ethology of burrowing, and also the reconstruction of the earliest Triassic ecosystems. These burrows have a single opening that leads, via a large, uniform diameter, semi-horizontal tunnel, to a rounded terminus. These 3-m-long structures descend at angles of 30°to a maximum of 1.5 m depth. They are devoid of chambers, branching, cross-cutting, coiling or spiralling. Filled with coarse sediments, some have a <5-mm clay lining, and most have subtle indentations and various scratch marks. These burrows were possibly excavated as resting, hiding or aestivating shelters, and are tentatively attributed to dicynodonts (i.e. Lystrosaurus murrayi and L. declivis). Data suggest that burrowing was widespread after the P ⁄ Tr boundary event, when in this part of Gondwana, dryland fluvial systems had large fluctuations in flow with extended low-flow periods or drought punctuated by high-discharge periods. We hypothesize that these constructed refuges played a role in the biodiversity recovery and maintenance in the Early Triassic (Induan) ecosystem.

Latest Permian paleosols from Wapadsberg Pass, South Africa: Implications for Changhsingian climate

“…A clear, comprehensive description of Karoo Basin paleosols has not heretofore been developed, nor is there agreement amongst authors about paleosol descriptions or classifi cation schemes (Smith, 1995;Retallack et al, 2003;Smith and Botha, 2005;Smith, 2006, 2007;Tabor et al, 2007;Bordy et al, 2011). Smith's (1995) Late Permian (Dicynodon assemblage zone [AZ]; Rubidge, 1995) and Early Triassic (Lystrosaurus AZ) paleosols are described in the context of interpreted landscapes, spatially related to coeval channel deposits.…”

Hettangian tetrapod burrows from the continental Steierdorf Formation at Anina, western Romania

“…Mean while, dur ing pre-Ceno zoic times the wide spread ex am ples of bur row ing mam mals and their im me di ate therapsid an ces tors (e.g., Voorhies, 1975;Smith, 1987;Groenewald, 1991;Groenewald et al, 2001;Miller et al, 2001;Damiani et al, 2003;Hasiotis, 2003;Hasiotis et al, 2004;Colombi et al, 2008Colombi et al, , 2012Tan ner and Lucas, 2009;Sidor et al, 2008;Modesto and Botha-Brink, 2010;Hembree, 2010;Bordy et al, 2011;Tałanda et al, 2011;Liu and Li, 2013 and ref er ences cited therein) were sec onded by dif fer ent groups of "rep tiles" (i.e., sauropsid amniotes) such as lepidosaurs (e.g., Lee, 1998;Kear ney and Stu art, 2004;Martill et al, 2015;Yi and Norell, 2015), procolophonid tur tle an ces tors and tur tles (e.g., Groenewald, 1991;de Braga, 2003;Sidor et al, 2008), or crocodyliforms (e.g., Gomani, 1997;Loope, 2008) as likely can di dates for a bur row ing habit. More re cently, even dino saurs were added to the list of bur row ing Me so zoic tetra pods (Varricchio et al, 2007;Mar tin, 2009;Wood ruff and Varricchio, 2011).…”

“…The old est bur rows are rel a tively sim ple in ge om e try, rep re sented by helically down ward spi ral ling, but oth er wise sim ple, un branched tun nels from the Up per Perm ian, re ferred to the dicynodont Diictodon in South Af rica (Smith, 1987) or to in de ter mi nate, larger-sized dicynodonts in China (Liu and Li, 2013), and are fol lowed by shal lowly dip ping, curvilinear tun nels from the Lower Tri as sic, re ferred to ei ther the dicynodont Lystrosaurus (Groenewald, 1991;Bordy et al, 2011) or to in de ter mi nate therapsids (Miller et al, 2001;Hasiotis et al, 2004;Sidor et al, 2008). Start ing from the Early-Mid dle Tri as sic, therapsid burrow com plex ity in creases; more in tri cate net works of in ter connected tun nels and shafts are de scribed from the Lower Tri assic, re ferred to the cynodont Trirachodon (Groenewald et al, 2001), the Mid dle Tri as sic (therapsids or procolophonids; Voigt et al, 2011), the Up per Tri as sic (in de ter mi nate therapsids; Hasiotis et al, 2004, or cynodonts;Colombi et al, 2012), and the Lower Ju ras sic (in de ter mi nate tritylodontid cynodonts; Lucas et al, 2006;Tan ner and Lucas, 2009).…”

“…Fur ther more, sedimentological fea tures of the Steierdorf For ma tion sug gest that the bur rows were made in a pe riod of in creased arid ity cor re spond ing to the depositional time of the Dealul Budinic Mem ber, pre ced ing the on set of milder, more hu mid cli mates sug gested by the coal-bear ing beds of the Valea Tereziei Mem ber. Sim i larly to the case of the Perm ian/Tri as sic bound ary, when high abun dance of bur row ing tetra pods is re corded in the af ter math of the ex tinc tion event (Smith and Botha, 2005;Bordy et al, 2011;Viglietti et al, 2013), the times around the Tri as sic/Ju ras sic bound ary event ap pear to be also marked by chang ing sea sonal cli mate with pro longed droughts and ex treme mois ture and tem per a ture fluc tu a tions. It may be thus stip u lated that within the first mil lion year in ter val fol low ing the Tri as sic/Ju ras sic bound ary event and un der ad verse en vi ron men tal con di tions, fossorial habit prob ably be came yet again an en dur ance strat egy for the bur row mak ers such as those whose ac tiv ity is re corded in the Lower Ju ras sic de pos its of Anina.…”

“…Re ports of large pen e tra tive tetrapod bur rows in an cient con ti nen tal de pos its are rel a tively rare, how ever, es pecially com pared with the ex ten sive lit er a ture on tetrapod trackways pro duced pri mar ily in the same en vi ron ments. Burrows at trib uted to the ac tiv ity of therapsids are the most commonly re ported such struc tures (e.g., Voorhies, 1975;Smith, 1987;Groenewald, 1991;Groenewald et al, 2001;Hasiotis et al, 2004;Tan ner and Lucas, 2009;Bordy et al, 2011;Tałanda et al, 2011;Voigt et al, 2011). In com par i son, the fos sil re cord of rep tile bur row ing re mains rel a tively sparse (Hasiotis et al, 2004), and only a few am phib i ans (mainly from the Perm ian) are known to have pro duced bur rows pre served in the fos sil record (e.g., Olson, 1971).…”