Hettangian tetrapod bur rows from the con ti nen tal Steierdorf For ma tion at Anina, west ern Ro ma nia
Zoltán CSIKI-SAVA1, *, Artur KĘDZIOR2, Grzegorz PIEŃKOWSKI3 and Mihai E. POPA1
1 Uni ver sity of Bu cha rest, Fac ulty of Ge ol ogy and Geo phys ics, Lab o ra tory of Palae on tol ogy, 1, N. Bălcescu Ave., 010041, Bu cha rest, Ro ma nia
2 Pol ish Acad emy of Sci ences, In sti tute of Geo log i cal Sci ences, Kraków Re search Cen tre, Senacka 1, 31-002 Kraków, Po land
3 Pol ish Geo log i cal In sti tute – Na tional Re search In sti tute, Rakowiecka 4, 00-975 Warszawa, Po land
Csiki-Sava, Z., Kędzior, A., Pieńkowski, G., Popa, M.E., 2016. Hettangian tetrapod bur rows from the con ti nen tal Steierdorf For ma tion at Anina, west ern Ro ma nia. Geo log i cal Quar terly, 60 (2): 395–406, doi: 10.7306/gq.1278
Very large, sparsely dis trib uted, sin u ous, gently dip ping and oc ca sion ally branch ing tun nels with sub or di nate swells, as well as pos si ble cham bers and scratches, are de scribed from the Hettangian Dealul Budinic Mem ber of the Lower Ju ras sic con ti - nen tal Steierdorf For ma tion at Anina in the South Carpathians, Ro ma nia, and are in ter preted as tetrapod bur rows. No bone re mains have been found in as so ci a tion with these struc tures. The mor phol ogy and large di men sions of the bur rows sug gest that the trace-mak ers were sauropsid amniotes, most prob a bly ei ther crocodyliforms or small-sized basal neornithischian di - no saurs, al though their therapsid af fin i ties, de spite be ing less likely, can not be dis carded ei ther. The age, large size and prob a ble or i gin of these bur rows add im por tant in for ma tion to a poorly doc u mented pe riod of the evo lu tion of tetrapod fossoriality. It may be sug gested that within a rel a tively short time in ter val fol low ing the Tri as sic-Ju ras sic ex tinc tion event, when en vi ron men tal con di tions were still marked by strongly sea sonal cli mate with pro longed droughts as well as ex treme mois ture and tem per a ture fluc tu a tions, fossorial habit prob a bly be came yet again an en dur ance strat egy for bur row mak ers.
Key words: Tetrapod bur rows, therapsids, crocodyliforms, di no saurs, Lower Hettangian, Steierdorf For ma tion.
INTRODUCTION
Tetra pods pro duce bur rows for va ri ety of rea sons that in - clude es cap ing en vi ron men tal fluc tu a tions and harsh con di - tions, find ing food, evad ing pred a tors, or rear ing of young (e.g., Voorhies, 1975; Hildebrand, 1985; Miller et al., 2001; Varricchio et al., 2007). 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 pe - cially 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. Bur - rows at trib uted to the ac tiv ity of therapsids are the most com - monly 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 re - cord (e.g., Olson, 1971). Re cently, a spec tac u lar find of Mid-Cre ta ceous trace and body fos sil ev i dence of bur row ing in
a di no saur ex panded the known range of non-avialan di no saur be hav iour to fossoriality (Varricchio et al., 2007; Fearon and Varricchio, 2015).
As yet, Lower Ju ras sic strata yielded only few ev i dences of fossorial be hav iour in tetra pods, and these came ex clu sively from red beds formed in an arid cli mate (Lucas et al., 2006;
Tan ner and Lucas, 2009). The Lower Ju ras sic con ti nen tal beds of the Reşiţa Ba sin at Anina, Ro ma nia, grouped in the Steierdorf For ma tion (Figs. 1–3) rep re sent, how ever, a case of de pos its ac cu mu lated un der a moister cli mate than those yield - ing the Early Ju ras sic tetrapod bur rows from North Amer ica, as the Anina suc ces sion re cords a switch ing from semi-arid to sea sonal/mon soonal and fi nally to more hu mid con di tions up-sec tion. Ver te brate body fos sils have yet not been found in these de pos its, most prob a bly be cause of un fa vour able preservational po ten tial. For tu nately, the pres er va tion of dif fer - ent trace fos sils within these con ti nen tal de pos its al lows a more com plete un der stand ing of the lo cal palaeoecosystem. These trace fos sils in clude in ver te brate traces and tetrapod tracks (Popa, 2000c; Pieńkowski et al., 2009). Popa and Kędzior (2006) briefly re ported pos si ble ver te brate bur rows oc cur ring in the Steierdorf For ma tion, dis tin guish ing two morphotypes of bur rows: lin ear and spi ral ones. How ever, the so-called “spi ral bur rows” ap pear to rep re sent a mere diagenetic phe nom e non, as so ci ated with ox i da tion of si der it ic nod ules. More de tailed de - scrip tion and in ter pre ta tion of these bur rows is the aim of cur - rent pa per.
* Corresponding author, e-mail: zoltan.csiki@g.unibuc.ro Received: October 10, 2015; accepted: February 17, 2016; first published online: February 18, 2016
GEOLOGICAL SETTING
The bur rows de scribed herein were dis cov ered in the Colonia Cehă Quarry, an open cast mine in Anina, Caraş-Severin County (Fig. 2). The open cast mine, dug in N–S di rec tion along the west ern flank of the Anina Anticline, re - vealed a spec tac u lar sec tion of the Steierdorf For ma tion (Hettangian–Sinemurian) with both of its sub units, the lower Dealul Budinic and the up per Valea Tereziei mem bers. The Colonia Cehă Quarry lays be tween two ma jor faults, transversal to the Anina Anticline, the Ponor Fault to the south and the Raimund Fault, north wards. Ad di tion ally, in the Colonia Cehă Quarry, both the flank of the Anina Anticline and the de pos its of the Steierdorf For ma tion are cut by nu mer ous trans verse, par - al lel, nor mal and re verse faults into a se ries of small tec tonic blocks (Figs. 2 and 5C). The beds crop out al most ver ti cally.
The Lower Ju ras sic (Hettangian–Sinemurian) Steierdorf For ma tion is a purely con ti nen tal suc ces sion of siliciclastic, in its up per part also coal-bear ing, sed i ments, formed in an intra - -moun tain de pres sion. This unit forms part of the sed i men tary in fill ing of the Reşiţa Ba sin, also known as the Reşiţa–Moldova Nouă sed i men tary zone, the most im por tant sed i men tary ba sin of the Getic Nappe (Săndulescu, 1984; Bucur, 1991, 1997;
Popa and Kędzior, 2008; Figs. 1–3). The Steierdorf For ma tion un con form ably over lays the Lower Perm ian Ciudanoviţa For - ma tion and it is con form ably over lain by the Pliensbachian–Mid - dle Toarcian Uteriş For ma tion (Bucur, 1991, 1997; Popa and Kędzior, 2008; Fig. 3), a unit that in cludes black, bi tu mi nous shales with si der it ic in ter ca la tions, which were the tar get of open cast min ing.
Fig. 1. Lo cal iza tion of Reêiïa Ba sin and of Anina in the South ern Carpathians, Ro ma nia
Fig. 2. The lo cal geo log i cal struc ture at Anina, em pha siz ing the Anina anticline with Perm ian core and lo cally de vel oped Steierdorf For ma tion coal fields sep a rated by faults, with the Colonia Cehă Quarry marked (sim pli fied from Popa, 2009)
Fig. 3. Syn thetic lithostratigraphic log of the Steierdorf For ma tion
The Steierdorf For ma tion is di vided into two mem bers, the Dealul Budinic Mem ber (?Rhaetian–Hettangian in age), and the Valea Tereziei Mem ber (Hettangian–Sinemurian in age;
Fig. 3; Popa, 2000a, b; Popa and van Konijnenburg-van Cittert, 2006). Age of the fos sil-bar ren Dealul Budinic Mem ber is in - ferred from its strati graphic po si tion and con form able set ting be low the over ly ing fossiliferous Valea Tereziei Mem ber. The Dealul Budinic Mem ber is dom i nated by red and grey-yel low - ish-ol ive con glom er ates, microconglomerates and sand stones with red mudstone in ter ca la tions; the coarser beds orig i nated in al lu vial fans and low-sin u os ity river chan nels, whereas the fine-grained de pos its ac cu mu lated at the co ales cence of the al - lu vial lobes or in top o graphic lows on top of the coarser-grained al lu via (Figs. 3 and 4; Kędzior and Popa, 2013). The up per most part of Dealul Budinic Mem ber is marked by a pyroclastic/tuffitic layer, ma te rial of which the in fill ing of the bur rows re ported in this con tri bu tion is largely made of.
The over ly ing Valea Tereziei Mem ber rep re sents the proper coal mea sure which was heavily mined at Anina for bi tu - mi nous coals since 1792, and is com posed of grey sand stones, clays, coals, con glom er ates and microconglomerates (Fig. 3),
formed in flu vial and lac us trine en vi ron ments. The fos sil re cord of the Valea Tereziei Mem ber in cludes a rich bryophyte, pteridophyte and gym no sperm com pres sive flora, es pe cially in Anina (e.g., Popa, 2000a, b; Popa and van Konijnenburg-van Cittert, 2006), as well as traces of in sect-plant in ter ac tions (Popa, 2009; Popa and Zaharia, 2011). From a phyto stra - tigraphic point of view, the Hettangian age of the lower Steierdorf For ma tion is in di cated by the Thaumatopteris brau - niana as sem blage, while the Acme Zone with Nilssonia cf.
orientalis iden ti fied in its up per part points to the Sinemurian (Fig. 3).
The Dealul Budinic Mem ber, in which the bur rows are dug in, is dom i nated by mas sive, ma trix-sup ported con glom er ates, very coarse- to coarse-grained structureless sand stones and lam i nated siltstones and mudstones (Fig. 4), and is re garded as rep re sent ing largely an al lu vial fan en vi ron ment (Kędzior and Popa, 2013). Depositional pro cesses were dom i nated by high en ergy vis cous flows op er at ing in the prox i mal parts of the al lu - vial fan, ac tive braided chan nel flows de vel oped at mid dle to dis tal reaches, tran si tional flows be tween flu vial and de bris flow pro cesses, and sheet flows oc cur ring dur ing flood ing pe ri ods (Kędzior and Popa, 2013). The pres ence of the fine-grained clastics (mudstones and siltstones) might be re lated to the oc cur rence of lo cal de - pres sions with in ter mit tent wa ter bod ies and other com mon ar eas of fine-grained sed i men ta - tion, usu ally sit u ated at co ales cence zones of in - di vid ual lobes (Neves et al., 2005) or within de - pres sions cre ated on the top of the al lu vial fans (Rachocki, 1981). The de po si tion of the mud might have also oc curred af ter heavy rain falls, thus could be di rectly re lated to mud flows (Rachocki, 1981). Com mon des ic ca tion cracks point to re cur rent wa ter-ta ble fluc tu a tions.
Mas sive or lam i nated red/vi o let mudstones (ca. 180 cm thick) oc cur in the up per part of the Dealul Budinic red bed com plex. These rep re - sent the host sed i ment of the bur rows (Figs. 4 and 5A, C–E). The red colour ing of the sed i - ments is in dic a tive of ox i diz ing con di tions, con - nected with de po si tion of detritic he ma tite un der a warm cli mate with sea son ally dis trib uted rain - falls (van Houten, 1961), and can be linked to mon soonal con di tions as was pos tu lated by Mateescu (1958) and Pieńkowski et al. (2009).
In deed, this area was lo cated be tween 20 and 30° north ern lat i tude dur ing the Early Ju ras sic (Popa and van Konijnenburg-van Cittert, 2006).
The lack of well-pre served plant re mains and lack of pedogenic ho ri zons within the Dealul Budinic Mem ber points to a high ox i da tion level com bined with rapid de po si tion and un sta ble sub strate. Ad di tion ally, pe ri odic and heavy rain - falls lead ing to ero sion might have con trib uted to the wash ing out (re moval) of both the in cip i ent soils and of the plants re mains not yet sta bi lized by well-de vel oped root sys tems.
Above the red dish mudstone beds, there is a 60–120 cm thick grey mudstone layer con tain ing pyroclastic ma te rial. The grey mudstone is usu - ally mas sive, and spo rad i cally pres ents very faint flat lam i na tion and rip ple-drift cross-lam i na tion.
X-ray anal y sis shows that it is largely com posed of kaolinite (96%) with quartz and feld spar grains. This layer does not cor re spond to a di rect ef fu sive de posit, but in stead rep re sents a re de - Fig. 4. Lo cal strati graphic log of the Dealul Budinic Mem ber
of the Steierdorf For ma tion, with po si tion of the ver te brate bur rows in Colonia Cehă Quarry high lighted
Fig. 5. As pects of the amniote bur rows from the Lower Ju ras sic Steierdorf For ma tion, Anina A – bur row no. 1, sim ple sin u ous tun nel with oc ca sional swells, with an other tun nel run ning un der neath and only partly ex posed; north ern cor ner of the Colonia Cehă Quarry, east ern flank, Anina (length of ham mer, used for scale:
290 mm); B – wind ing, di chot o mously branched bur row no. 2; north ern tip of the Colonia Cehă Quarry, east ern flank, Anina (length of ham mer: 270 mm); C – bur row no. 3 (wind ing) and bur row no. 4 (pos si ble “cham ber”; for de - tails, see Figs. 5D and 6); mid dle part of the Colonia Cehă Quarry, east ern flank, Anina; the red dot ted line rep re - sents a lo cal fault, sep a rat ing two small, lo cal tec tonic blocks; the site oc curs in the prox im ity of the sauropod tracks de scribed by Pieńkowski et al. (2009) from a slightly higher ho ri zon; D – bur row no. 4 (pos si ble “cham ber”-like struc - ture); mid dle part of the Colonia Cehă Quarry, east ern flank, Anina; boxed area marks the po si tion of close-up de - tails shown in Fig ure 6A–C; E – bur row no. 5, wind ing form, show ing swells at the turns; Colonia Cehă Quarry, east ern flank, Anina; scale bar rep re sents 10 cm (B), 20 cm (A, D, E) and 40 cm (C), re spec tively
pos ited ma te rial, as proven by the oc cur rence of sed i men tary struc tures in dic a tive of de po si tion from cur rent (Fig. 4). These tuff-bear ing sed i ments were de pos ited in an in ter mit tent shal - low lake and they pro vided part of the in fill ing ma te rial of the bur rows.
The oc cur rence of grey mudstones with vol ca nic tuffs in the top of the Dealul Budinic Mem ber her alds a ma jor change in depositional sys tems and palaeoclimate. From that level up - wards, the cli mate changes to a more hu mid one as sug gested by the coal-bear ing char ac ter of the over ly ing Valea Tereziei Member.
DESCRIPTION OF THE BURROWS
In to tal, five struc tures iden ti fied as po ten tial bur rows, num - bered in this pa per from 1 to 5 (Fig. 5; see be low), were iden ti - fied ex posed within dif fer ent tec tonic blocks along the east ern flank of the Colonia Cehă Quarry:
– bur row no. 1 is the north ern most oc cur rence, show ing sub or di nate swells (Fig. 5A); a sec ond faintly vis i ble bur - row runs un der neath bur row 1 and is only partly ex - posed. It is fol lowed to wards the south, se quen tially, by – bur row no. 2, a di chot o mously di vided bur row with pos si -
ble scratch-marks (Fig. 5B); then by
– bur row no. 3 which rep re sents the lon gest bur row struc - ture ob served in the field (Fig. 5C); and fi nally by – struc ture no. 4, a ten ta tively iden ti fied, pos si ble bur row
rep re sented by a large, ir reg u lar cham ber-like struc ture (Figs. 5C, D and 6; see be low). Bur rows 3 and 4 oc cur in the same out crop where sauropod foot prints have also been re corded re cently by Pieńkowski et al. (2009). On its turn,
– bur row no. 5, with weak swells, is lo cated again in the north ern end of the Colonia Cehă Quarry, close to bur - row no. 1 (Fig. 5E).
Most of these struc tures are sim ple, lin ear to slightly sin u - ous, very large or gi ant tun nels (ac cord ing to the ter mi nol ogy of Miller et al., 2001), el lip soi dal to cir cu lar in cross-sec tion; oc ca - sion ally, the cross-sec tion is slightly asym met ri cal, with a some - what flat tened sur face (“floor”) fac ing down wards and a rounded “roof”. They are up to 7 m long, and usu ally 10–15 cm wide, reach ing in places about 20 cm (Fig. 5C). These bur rows are not cross-cut ting and lack ev i dence for any coil ing or spi ral - ling. Oc ca sion ally, how ever, the bur rows can be di chot o mously branch ing. In places the bur row di am e ter in creases and swells can be ob served (Fig. 5A, E). The bur rows largely fol low the bed ding plane; in cases they are in clined rel a tive to the bed - ding, the in cli na tion an gle re mains very small. In most in stances the bur rows oc cur along one bed ding plane, but lo cally these can be dis trib uted superposed at two sep a rate lev els (Fig. 5A).
The tun nels are usu ally built by lon ger and straighter seg ments linked by shorter, obliquely ori ented con nect ing parts. While the length of the in di vid ual straight seg ments var ies be tween 40 and over 60 cm, the oblique sec tions, rep re sent ing the turn ing parts of their tra jec to ries, are less than 30 cm long; these sec - tions join the lon ger seg ments at an gles rang ing from about 38 to 55°. In places, knobby lin ing can be ob served (Fig. 5A, E);
this can be at trib uted ei ther to diagenetic shrink age or to the ac - tiv ity of commensal or gan isms (likely, in ver te brates). All bur - rows are filled with a mas sive, structureless, noncalcareous grey mudstone with quartzose sandy ad mix ture. Bur row fill (grey pyroclastic sandy mudstone) is lithologically very dis tinct from the host rock (a red-vi o let mudstone) and is rem i nis cent of the over ly ing mixed pyro-siliciclastic de pos its.
Be sides the more com mon, lin ear, sin u ous forms, a large (40 cm in di am e ter), iso lated ir reg u lar struc ture was also found (Fig. 5D). It dif fers from the com mon tun nel-like struc tures de - scribed be fore in that it ap pears to be both shorter and wider, sug gest ing a more “cham ber”-like ar chi tec ture; it shares, how - ever, with the tun nels their sim i lar, chro mat i cally and litho - logically dis tinc tive na ture of the in fill ing sed i ments (see above).
Its spa tial re la tion ship to the lin ear bur rows un for tu nately re -
Fig. 6. De tails of the “cham ber”-like struc ture (bur row 4) from the Lower Ju ras sic Steierdorf For ma tion, Anina A, B – close-up im ages of struc ture 4 (pos si ble “cham ber”; Fig. 5C, D), show ing compactional de for ma tions and ridge-like lon gi tu di nal traces in ter preted as pos si ble dig ging traces (ar rowed); C – in ter pre ta tive line draw ing of the sur face of struc ture 4 (pos si ble “cham ber”), with the most prom i nent oblique ridges (in ter preted as po ten tial dig ging traces; solid line) ar rowed; dot ted lines mark fur ther pos si ble oblique dig ging traces; scale bar rep re sents 10 cm
mains un cer tain, as it oc curs iso lated from, and with out ob vi ous con nec tions to, any of the curvilinear tun nels. The “cham ber”
shows ir reg u lar pro tu ber ances, and in places also pres ents sharp, roughly par al lel lon gi tu di nal ridges (Fig. 6) which may po ten tially rep re sent scratch marks. These ridges are ori ented obliquely to the main axis of the struc ture, and widely spaced (Fig. 6). The mor phol ogy of the crests, to gether with their di - men sion rel a tive to the di am e ter of the struc ture, sug gest that they prob a bly rep re sent marks of the dig ging paws them selves in stead that of the in di vid ual dig its/claws. It must be em pha - sized, none the less, that iden ti fi ca tion of this struc ture should be con sid ered very ten ta tive for the mo ment, pend ing fu ture dis - cov ery of sim i lar, pos si bly better pre served traces.
As pre served and ob served in the field, the dis tri bu tion of the lin ear bur rows is rather patchy; how ever, the tectonized na - ture of the out crops with num ber of faults should be also taken to con sid er ation in that re spect (Fig. 5A). Nev er the less, based on our ob ser va tions con cern ing the larg est ac ces si ble con tin u - ous out crop ping sur face with bur rows, it is clear that these struc tures are widely spaced, and do not form more com plex and crowded sys tems as do some of those de scribed from the Tri as sic–Ju ras sic in other parts of the world (e.g., Groenewald et al., 2001; Hasiotis et al., 2004; Tan ner and Lucas, 2009).
INTERPRETATION AND DISCUSSIONS
To be gin with, we have con sid ered al ter na tive, non-bi o log i - cal “zero hy poth e ses” for the or i gin of these struc tures, such as synsedimentary or ero sional or i gin, or else diagenetic or i gin (i.e., concretions).
These al ter na tive hy poth e ses can be re jected be cause it is hard to con ceive how sed i men tary or ero sional (scour-and-fill) pro cesses could have pro duced such rel a tively reg u lar tun - nel-like shapes, closed from all sides, and filled with sed i ment that is com pletely dif fer ent from the sur round ing ma trix.
Post-depositional com pac tion pro cesses can pro duce in deed load casts (i.e., ball struc tures), but they would not be that long, reg u lar and con tin u ous in de vel op ment as doc u mented by the struc tures ob served at Colonia Cehă Quarry (al though it is cer - tainly pos si ble that com pac tion and post-depositional de for ma - tion could have in flu enced, sec ond arily, the shape of the struc - tures de scribed above). Fi nally, struc tures orig i nat ing through dif fer en tial post-depositional chem i cal ce ment ing of the sed i - ments (i.e., con cre tions) are char ac ter ized usu ally by the oc cur - rence of the same ba sic petrographic type within the con cre - tions and the sur round ing ma trix, which is de fin i tively not the case of the struc tures de scribed in this con tri bu tion. To con - clude, a non-biogenic (pri mary sed i men tary, ero sional, or dia - genetic) or i gin for the Dealul Budinic Mem ber tun nel-like struc - tures can be re li ably dis carded, and these are thus considered in the following discussions as structures of biogenic origin (i.e., burrows).
Af ter es tab lish ing the bi otic or i gin of these struc tures, dif fer - ent or i gins of the bur rows were taken into con sid er ation. Due to the purely ter res trial set ting and the age of the de pos its that host the struc tures, the list of po ten tial trace mak ers is rather short, and it in cludes in ver te brates – mainly ar thro pods such as cray fish, annelids and mol lusks, as well as ver te brates – fishes, am phib i ans and amniotes (e.g., Hasiotis, 2003; Hembree, 2010). Most in ver te brates can be ex cluded as trace-mak ers by the large size of the bur rows and the ab sence of ac tive, meni - scate back fill ing. More over, cray fish bur rows (e.g., Hasiotis and Mitch ell, 1993; Bedatou et al., 2008; Mar tin et al., 2008) con sist of sim ple to com plex ar chi tec tures with vary ing de grees of
branch, cham ber, and chim ney (ver ti cal en trance) de vel op - ment, com bined with a va ri ety of surficial morphologies, in clud - ing knobby sur faces, scratch and scrape traces, mud- and lag-lin ers, pleo pod striae, and body im pres sions, which is not the case in the Colonia Cehă bur rows. Among fishes, lungfish bur row deeply to avoid des ic ca tion dur ing dry pe ri ods, pro duc - ing ver ti cal bur rows about 10 cm in di am e ter (Romer and Olson, 1954) and with en larged basal cham bers (Johnels and Svens - son, 1954), a mor phol ogy strik ingly dif fer ent from those de - scribed herein. Fur ther more, fos sil ex am ples of lungfish bur - rows are com monly re ported to be tied to lac us trine to re gres - sive mar ginal ma rine depositional en vi ron ments (e.g., Surlyk et al., 2008; Gaillard et al., 2013), un like the sed i men tary set ting re ported here for the Anina bur rows.
On the other hand, tetrapod bur rows are char ac ter ized by dom i nantly hor i zon tal or subhorizontal branches (tun nels, sensu Hasiotis et al., 2004), gently slop ing ramps and/or spi - ralled branches, with a near-cir cu lar cross-sec tion. Usu ally, these bur rows are dug into palaeosol lev els, al though they can also oc cur in other depositional en vi ron ments such as ephem - eral ponds (Hembree et al., 2005), aban doned braided flu vial chan nels (Mar tin, 2009), chan nel mar gins and overbanks (Hasiotis et al., 2004; Colombi et al., 2012), or sand dunes (Loope, 2006, 2008; Lucas et al., 2006). In all their char ac ter is - tics, the Early Ju ras sic bur rows from Anina cor re spond to the tetrapod bur row type and de part sharply from those of the cray - fishes or lungfishes, leav ing one or an other group of tetra pods as po ten tial trace-mak ers.
Among tetra pods, am phib i ans usu ally dig into the sub stra - tum to avoid body de hy dra tion through evap o ra tive wa ter loss dur ing drought pe ri ods, and such be hav iour – sup ported both by ichnology and by skel e tal ad ap ta tions – is al ready re ported from the fos sil re cord (see re views by Gardner, 1999; Hembree, 2010; Maddin et al., 2013; Roček et al., 2014; Henrici, 2016;
Chen et al., 2016). Ac cord ing to Hembree (2010), there is a re - mark able par al lel ism be tween am phib ian bur rows and those of the lungfishes, both types be ing rep re sented by subvertical shafts ex ca vated into ephem eral pond de pos its (see also Hembree et al., 2005); more over, their sizes are rel a tively small (usu ally not sur pass ing 10 cm in di am e ter). In all these fea tures, am phib ian bur rows dif fer from those re ported herein from Colonia Cehă Quarry, and thus am phib i ans can be also ex - cluded from the list of po ten tial trace mak ers, leav ing only mem - bers of the two ma jor groups of amniotes as po ten tial can di - dates for these: the sauropsids and the therapsids.
Dur ing Ce no zoic times, the most im por tant bur row ing tetra - pod group is that of the mam mals. Mean while, dur ing pre-Ce - no 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., 2008, 2012; Tan 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 lepido - saurs (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 di - no 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).
Ex cept for the procolophonids and the snakes, all the other Me so zoic amniote groups listed above and known to ex hibit
fossorial be hav iour were pres ent in the Early Ju ras sic (see Benton, 1993), and thus rep re sent pos si ble can di dates for the trace maker of the Dealul Budinic Mem ber bur rows. Fur ther nar row ing down this list of po ten tial can di dates is pos si ble tak - ing into ac count the ethol ogy of the bur row ers (as man i fested in the mor phol ogy of the bur rows).
Bur row ing hab its evolved rel a tively early in the therapsid evo lu tion ary line lead ing to mam mals, and was prob a bly one of the main fac tors al low ing dif fer en tial sur vival dur ing the end-Perm ian events (e.g., Smith and Botha, 2005). Ad ap ta - tions for dig ging and bur row ing were iden ti fied, based on func - tional mor phol ogy, in sev eral dif fer ent pre-Ce no zoic therapsid taxa. Such skel e tal ad ap ta tions were re ported in this clade from the Perm ian (the dicynodont Diictodon; Ray and Chinsamy, 2003) to the Late Ju ras sic (the theriimorph Fruitafossor; Luo and Wible, 2005) and the Late Cre ta ceous (in de ter mi nate djadochtatherian multituberculates; Kielan-Jaworowska, 1989);
in deed, bur row ing ap pears to be an an ces tral be hav ioural trait at the level of cynodonts, if not that of more basal therapsids (Damiani et al., 2003).
Synapsid (in clud ing mammaliaform) bur rows are among the best known pre-Ce no zoic tetrapod sub ter ra neous dwell ing traces. These were re ported from de pos its of the Up per Perm - ian (Smith, 1987), the Perm ian/Tri as sic bound ary (Damiani et al., 2003), and the Lower–Mid dle Tri as sic (e.g., Groenewald, 1991; Groenewald et al., 2001; Modesto and Botha-Brink, 2010; Fernandez et al., 2013) of South Af rica, as well as from the Mid dle–Up per Perm ian of China (Liu and Li, 2013), the Lower Tri as sic of Antarctica (Miller et al., 2001; Hasiotis et al., 2004), the Mid dle Tri as sic of north ern Af rica (Voigt et al., 2011), the Mid dle and Up per Tri as sic of South Amer ica (e.g., Colombi et al., 2012; Krapovickas et al., 2013), the Up per Tri as sic of Eu - rope (Tałanda et al., 2011), and the Up per Tri as sic (Hasiotis et al., 2004; Colombi et al., 2008), Lower Ju ras sic (Lucas et al., 2006; Tan ner and Lucas, 2009) and Up per Ju ras sic (Hasiotis et al., 2004) of North Amer ica. The com mon char ac ters of these traces are rep re sented by the rel a tively com plex ge om e try of the bur rows, rang ing from spi rally de scend ing tu bu lar tun nels end ing in an en larged ter mi nal cham ber to net works of in ter - con nected tun nels, shafts, oblique ramps and cham bers; their cross-sec tion is cir cu lar to el lip soi dal, fre quently with a me dian thresh old on the floor of the bur row, giv ing it an in verted U-shape; and the rel a tively small size of the cross-sec tion, with its max i mum di am e ter not sur pass ing 20–25 cm, and of ten av - er ag ing only 10–15 cm.
From the sur vey of the pub lished pre-Ce no zoic therapsid bur row ing re cord it ap pears that there was a cer tain pro gres - sion dur ing time in char ac ters such as de gree of in ter con nec - tions and types of branch ing rep re sented in the bur rows, char - ac ters that ap pear to de velop com plex ity over time. The old est bur rows are rel a tively sim ple in ge om e try, rep re sented by heli - cally 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 bur - row com plex ity in creases; more in tri cate net works of in ter con - nected tun nels and shafts are de scribed from the Lower Tri as - sic, 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). This trend fi nally cul mi nates with sim ple to com plex net works of tun nels, shafts, ramps and cham bers, de scribed from the Up per Ju ras sic and at trib uted to in de ter mi nate fossorial mam mals (Hasiotis et al., 2004).
This time-cor re lated pro gres sion in bur row com plex ity ap - pears to mir ror evo lu tion ary changes as so ci ated with the or i gin of the Mammalia (e.g., Kemp, 2005), and most prob a bly re flects in crease in com plex ity of so cial in ter ac tions, in crease that oc - curred in the line lead ing to mam mals, from asociality- sub - sociality in the Perm ian dicynodont Diictodon (Ray and Chin - samy, 2003), to ag gre ga tion and shel ter shar ing in the Early Tri - as sic (Abdala et al., 2006; Viglietti et al., 2013), and fi nally to ad - vanced gre gar i ous be hav iour in the Mid dle Tri as sic–Ju ras sic (Hasiotis et al., 2004; Voigt et al., 2011; Krapovickas et al., 2013). More over, it seems that dig ging com plex bur row net - works of ad vanced ar chi tec ture, fore shad ow ing those of Neo - gene and Re cent mam mals, be came a com mon be hav iour among synapsids as early as the mid dle of the Tri as sic.
In light of these ob ser va tions, the hy poth e sis of synapsid trace mak ers re spon si ble for the Colonia Cehă Quarry bur rows ap pears weakly sup ported at best; the Early Ju ras sic age of the bur rows stands in con trast to their sim ple mor phol ogy, which is more rem i nis cent of those de scribed from the Lower Tri as sic of South Af rica than of those more com plex ones from the Mid - dle–Up per Tri as sic, let alone from the Ju ras sic. How ever, the dicynodonts, mak ers of the sim pler bur row morphologies of the Perm ian–Early Tri as sic, dwin dled dra mat i cally af ter the Mid dle Tri as sic (e.g., Kemp, 2005; Ruta et al., 2013), and were largely ex tinct by the end of that pe riod, be ing re placed by the more ad - vanced tritylodontids and tritheledontids be sides the de rived mammaliaforms (Ruta et al., 2013). Al though the youn gest pos - si ble mem ber of the dicynodonts was re ported from the Lower Cre ta ceous of Aus tra lia (Thulborn and Turner, 2003), the oc - cur rence of basal eucynodontians, sim i lar to those re spon si ble for South Af ri can Early Tri as sic bur rows, in the Lower Ju ras sic of Eu rope is con sid ered highly im prob a ble, al though not en tirely im pos si ble, and re mains yet to be sup ported by the fos sil re - cord.
Fur ther more, the Colonia Cehă Quarry bur rows are larger (es pe cially in length, and also slightly in cross-sec tional di am e - ter) than bur rows cus tom arily re ferred to de rived mam mal-like rep tiles (cynodonts) and/or early mammaliaforms, and are also sig nif i cantly larger than the max i mum size re ported in Early Ju - ras sic mam mals (Kielan-Jaworowska et al., 2004). This is sig - nif i cant, since bur row di men sions (and es pe cially cross-sec tion size) ap pear to be tightly con trolled by the size (skull width/torso width) of the bur rower (e.g., An der son, 1982; Hickman, 1990;
White, 2005; Wilkins and Rob erts, 2007). Con sid er ing these ob ser va tions, it ap pears un likely that de rived therapsids or prim i tive mam mals were the trace mak ers of the Colonia Cehă Quarry bur rows, al though their more basal therapsid or i gin can - not be de fin i tively dis carded. Nev er the less, their sur pris ingly prim i tive ar chi tec ture, re sem bling those from the Perm ian and Early Tri as sic in sim plic ity, is un ex pected and con sid ered worth not ing (see above).
On the other hand, these tun nels are highly rem i nis cent of the larger, but more sim ple bur rows de scribed from the Mid dle Ju ras sic (Loope, 2008) and Up per Ju ras sic (Hasiotis et al., 2004) of North Amer ica, and re ferred ten ta tively to dif fer ent sauropsid amniotes: to non-spec i fied crocodyliforms, re spec - tively crocodyliforms and/or sphenodontids. Sim i lar i ties be - tween such bur rows and those from Colonia Cehă in clude the sim ple mor phol ogy con sist ing of subhorizontal tun nels; cir cu lar to subcircular cross-sec tion de void of a me dian ridge on the
floor; lengths sur pass ing 1 m; and large di am e ters, rang ing from 15 to more than 50 cm. How ever, these tun nels dif fer from the Ro ma nian bur rows in the more ver ti cally slop ing in cli na tion of the tun nels, reach ing val ues as high as 22 to 25°, so that the tun nels de scend as much as 50 cm into the host sed i ment in - stead of be ing ori ented quasi-par al lel with the bed ding plane.
Nev er the less, nei ther crocodyliforms, nor sphenodontids should be dis re garded as po ten tial trace mak ers at Anina. Both of these groups are known to have orig i nated in the Late Tri as - sic at the lat est (e.g., Benton and Clark, 1988; Ev ans, 2003) and thus their pres ence in the Lower Ju ras sic of the Banat re - gion is de fin i tively con ceiv able. In fact, de spite the gen eral lack of ver te brate body re mains from the coal-bear ing de pos its of the Steierdorf For ma tion, the pres ence of in de ter mi nate crocodyliforms was sug gested pre vi ously, based on the re port of tetrapod tracks iden ti fied as Batrachopus cf. deweyi (Hitch - cock, 1843) by Popa (2000c). Al though the pre served tracks point to a small in di vid ual (torso length es ti mated to about 8–9 cm, width about 7 cm), smaller than the po ten tial trace - -maker of the Anina bur rows, these tracks at test that crocodyliforms were prob a ble com po nents of the lo cal Early Ju - ras sic palaeoecosystem. More over, it is worth not ing that Loope (2008) sug gested the small-sized Mid dle Ju ras sic crocody liform Entradasuchus from the Entrada Sand stone For - ma tion, Utah, to be re spon si ble for the large-scale bur rows re - ported from the same de pos its, de spite size dis crep an cies be - tween bur row di am e ters and es ti mated body size of Entradasuchus. Such a dis crep ancy would be sim i lar to that ex - ist ing be tween the Anina bur rows here de scribed and a trace - -maker cor re spond ing in di men sions to the Batrachopus tracks;
fur ther more, these tracks are re corded from the basal part of the over ly ing Valea Tereziei Mem ber, only a few metres higher in sec tion than the bur row-bear ing lay ers (Popa, 2000c). Sev - eral small-sized Me so zoic crocodyliforms were sug gested to have had bur row ing life styles based on their pres er va tion style, taphonomic con di tions, or pres ence of sup pos edly bur row - ing-re lated an a tom i cal ad ap ta tions, as in the case of Mala - wisuchus (Gomani, 1997), Simosuchus (Buckley et al., 2000), Mariliasuchus (Nobre et al., 2008), Armadillosuchus (Marinho and Carvalho, 2009), or Yacarerani (No vas et al., 2009). Ac - cord ingly, the hy poth e sis of a crocodyliform trace maker for the Colonia Cehă Quarry bur rows is worth con sid er ing.
Sur pris ingly enough, the Colonia Cehă Quarry bur rows also show re mark able re sem blances to Late Me so zoic bur rows at - trib uted to di no saurs. Al though not com monly ac knowl edged, the pres ence of dig ging be hav iour or dig ging ad ap ta tions was sug gested for dif fer ent di no saur taxa based on func tional mor - phol ogy and at trib uted trace fos sils. In many in stances, ad mit - tedly, these dig ging ad ap ta tions were re lated not to bur row ing, but in stead to other be hav ioural traits such as scratch-dig ging used in feed ing, as was ad vo cated in the case of cer tain alvarezsaurids (Senter, 2005) and paravialans (Simpson et al., 2010), or in re pro duc tion, as in the case of nest-dig ging ac tiv i - ties re ported for hadrosaurs (e.g., Hor ner, 1982) or ti tano saurs (e.g., Vila et al., 2010); nev er the less, true bur row ing habit has been also sug gested pre lim i nar ily by Bakker (1996) for the Late Ju ras sic basal ornithopod Drinker.
Re cently, how ever, bur row struc tures, rep re sented by rel a - tively sim ple, subhorizontal tun nels ended by a ter mi nal cham - ber, have been de scribed from the lower Up per Cre ta ceous of North Amer ica (Varricchio et al., 2007; Wood ruff and Varricchio, 2011); these tun nels have a con stant, slightly oval cross-sec tion and a slightly de scend ing, sin u ous tra jec tory, be - ing di vided along their length (210 cm, as pre served) into 60–70 cm long seg ments. Such tun nels were re ferred to the
“hypsilophodontid” – or, more prop erly, basal neornithischian (Boyd et al., 2009; Boyd, 2015) – di no saur Oryctodromeus based on as so ci ated skel e tal el e ments dis cov ered within the ter mi nal cham ber. In sup port of this dis cov ery, the skel e tal mor - phol ogy of this taxon was shown to pres ent dig ging ad ap ta tions (Fearon and Varricchio, 2015), and sim i lar ad ap ta tions for lim - ited bur row ing were also re ported in the basal ornithopod Koreanosaurus from the Up per Cre ta ceous of Ko rea (Huh et al., 2011). Sub se quent to the dis cov ery of the Oryctodromeus bur rows, struc tures of sim i lar size and gross mor phol ogy were re ported from the up per Lower Cre ta ceous of Aus tra lia (Mar tin, 2009), and were sim i larly re garded as be ing pro duced by basal neornithischians (“hypsilophodontids”), a clade whose rep re - sen ta tives are well-rep re sented in con tem po rary de pos its of the same area (Molnar and Galton, 1986; Rich and Vickers-Rich, 1989, 1999). Pre vi ously de scribed bur row struc tures from the Mid dle Ju ras sic of North Amer ica (Loope, 2006) were al ready re ported to have sim i lar gen eral mor phol ogy and di men sions to those re ported by Varricchio et al. (2007), and these might hint at an even ear lier, pre-Late Ju ras sic or i gin of basal neorni - thischian bur row ing hab its.
All these tun nel-like struc tures re sem ble those from Anina in their rel a tively large di men sions in length and cross-sec tion (al though cross-sec tional di am e ter is some what smaller in the Anina bur rows), sim ple subcircular cross-sec tion, and sin u ous, gently de scend ing tra jec tory. They are also iso lated tun nels that do not form com plex net works, show swells at the turns of tun - nels, and can have a roughly par al lel tra jec tory, as was also re - ported in the case of the Aus tra lian bur rows de scribed by Mar tin (2009). Even the pres ence of oc ca sional branch ing was de - scribed in the case of Oryctodromeus bur rows by Varricchio et al. (2007).
Com pa ra ble di men sions of the bur rows sug gest sim i larly sized trace-mak ers, while their largely anal o gous morphologies point to sim i lar dig ging be hav iour of these or gan isms. Con sid - ered to gether, sim i lar i ties in shape and size would sup port the hy poth e sis that the Colonia Cehă Quarry bur rows could have been also ex ca vated by basal neornithischian di no saurs, de - spite the fact that the struc tures from Anina look sim pler than those from the “mid”-Cre ta ceous, with cham bers that are not pres ent, or at least not re corded in the pre served tun nel seg - ments (Fig. 5A, E), ex cept in one ques tion able case (bur row no.
4) which, if cor rectly iden ti fied as a ter mi nal cham ber, ap pears to be not con nected to tun nels (Fig. 5D).
Mem bers of basal Neornithischia, a phylo gen etic po si tion sug gested for the trace-mak ers of the Late Cre ta ceous North Amer i can bur rows (and con sid ered as po ten tial trace mak ers of the Early Cre ta ceous Aus tra lian bur rows as well), are known to ap pear in the Mid dle Ju ras sic (Nor man et al., 2004). How ever, the sis ter-taxon of Neornithischia (i.e., the least-in clu sive taxon that in cludes “hypsilophodontids”) – that is, ei ther Hetero - dontosauria, ac cord ing to Nor man et al. (2004) or Thyreophora, ac cord ing to But ler et al. (2008; see also Boyd, 2015); as well as basal mem bers of the Neornithischia (Stormbergia; But ler et al., 2008) are al ready known from the Early Ju ras sic, and these oc - cur rences place the or i gin of the line lead ing to “hypsilo - phodontids” also into the Early Ju ras sic. And, al though dino - saur ian body fos sils are ex tremely rare in the Lower Ju ras sic of Eu rope, the dino saur ian track re cord sug gests that cursorial ornithischians (even or ni tho pods) were al ready pres ent in this area at the be gin ning of the Ju ras sic (see Weishampel et al., 2004), in clud ing in Cen tral Po land (Gierliński and Pieńkowski, 1999; Gierliński et al., 2004). It is thus con ceiv able that basal or - ni tho pods (or basal neornithischians) with a life style sim i lar to that of the mem bers of the later-ap pear ing, bur row ing basal
neornithischian clade iden ti fied by Boyd et al. (2009; Orodro - minae of Boyd, 2015) were also pres ent in the Early Ju ras sic eco sys tem of south west ern Ro ma nia, and might be re spon si - ble for the bur rows re ported here.
PALAEOENVIRONMENTAL SIGNIFICANCE OF THE ANINA BURROWS
As re ported here, the Hettangian Dealul Budinic Mem ber of the ter res trial Steierdorf For ma tion, south west ern Ro ma nia, yields a re cord of tetrapod bur rows that is unique in the Me so - zoic of Ro ma nia. These bur rows are at trib uted in this pa per ei - ther to non-mam ma lian therapsids, or, more prob a bly, to crocodyliforms or to basal neornithischian di no saurs with a semi-fossorial habit. Re gard less of their ex act tax o nomic af fin - ity, the pre cise pur pose of dig ging these bur rows re mains un - cer tain, and iden ti fi ca tion of their pur pose de pends largely of the iden tity and ecol ogy of the trace maker. Nev er the less, based on the na ture of the pub lished fos sil re cord of tetrapod bur rows and on the lo cal geo log i cal data, hid ing from weather ex tremes in a ter rain in flu enced by sea sonal, pe ri od i cally harsh con di tions, ap pears to be the most probable explanation for the activity of the trace makers.
Ad verse cli ma tic con di tions ne ces si tate com pen sat ing thermoregulatory be hav iour of the or gan isms, such as us age of di ur nal shel ter, thus we sug gest as a work ing hy poth e sis a sig - nif i cant cli ma tic con trol on the bur row ing be hav iour of Early Ju - ras sic Ro ma nian tetra pods. In deed, many Early Me so zoic fos - sil ver te brate bur rows have been dis cov ered from strata that doc u ment ex tremes in global palaeoclimatic fluc tu a tions (e.g., Smith, 1987, 1995; Damiani et al., 2003; Smith and Botha, 2005; Abdala et al., 2006). Mean while, other bur rows orig i nated in palaeoenvironments marked by sea son ally harsh, ex treme con di tions such as se vere arid ity (e.g., Voigt et al., 2011;
Krapovickas et al., 2013) or pro longed cold pe ri ods (e.g., Mar - tin, 2009).
Based on these cases, all of which doc u ment strong en vi - ron men tal (i.e. cli ma tic) con trol on the pres ence of bur row ing hab its, it can be hy poth e sized that their fossorial be hav iour al - lowed trace mak ers of the Anina bur rows to ame lio rate the strongly sea sonal cli ma tic con di tions of the ear li est Ju ras sic, as were the ones sug gested by the lo cal sed i men tary re cord. It is well-con strained based on phytostratigraphy that the Dealul Budinic Mem ber of the Steierdorf For ma tion was de pos ited dur - ing the ear li est Ju ras sic or near to the Tri as sic/Ju ras sic tran si - tion, and is thus close to the Tri as sic/Ju ras sic bound ary ex tinc - tion event. 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 a - bly 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.
CONCLUSIONS
The ter res trial Steierdorf For ma tion of Early Ju ras sic (Hettangian–Sinemurian) age from the Reşita Ba sin, in the South Carpathians, Ro ma nia, a highly sig nif i cant for its well-pre served and di verse plant fos sil re cord, as well as its re - cently iden ti fied ter res trial trace fos sils. More spe cif i cally, the lower unit of the Steierdorf For ma tion, the Hettangian Dealul Budinic Mem ber, yields tetrapod bur rows that are unique for the Me so zoic of Ro ma nia as well as for the Lower Ju ras sic of Eu - rope. Based on their size, mor phol ogy and pat tern of de vel op - ment, these bur rows are at trib uted in this pa per ei ther to non-mam ma lian therapsids, or, more prob a bly, to small-sized croco dyliforms or basal neornithischian di no saurs with a semi - -fossorial habit. Al though the ex act pur pose of these bur rows re mains un cer tain, it can be hy poth e sized that they con trib uted to the suc cess of the sur vival strat egy em ployed by the trace maker or gan isms in cop ing with the sea son ally arid en vi ron - men tal con di tions that char ac ter ized – ac cord ing to the lo cal sedimentological re cord – the first few mil lion years fol low ing the Tri as sic/Ju ras sic bound ary ex tinc tion event, that is, the time of deposition of the burrow-bearing Dealul Budinic Member.
Ac knowl edge ments. This re search was funded by the CNCSIS (NURC) grant no. 978 (436/1.10.2007 – to ZCs-S, MEP), and by the pro ject fi nanced from re sources of the Pol ish Na tional Sci ence Cen tre, granted on the ba sis of de ci sion no.
DEC-2012/06/M/ST10/00478 (to GP). E. Bordy (Grahams town, South Af rica) is thanked for send ing use ful ref er ences. Fi nally, we are thank ful for the thor ough re views of fered by the re view - ers G. Niedźwiedzki (Uppsala, Swe den) and A. Uchman (Kraków, Po land) that helped us im prove the orig i nal ver sion of the manu script, as well as to han dling Ed i tor A. Wysocka for her as sis tance. This is a con tri bu tion to the IGCP pro ject 632 “Con - ti nen tal Cri ses of the Ju ras sic”.
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