A gia nt Upper J urassic turtle revealed by its trackways

CHRISTIAN GAILLARD, PAUL BERNIER. GEORGES BARALE, JEAN-PAUL BOURSEAU, ERIC BUFFETAUT, RUBEN EZQUERRA, JEAN-CLAUDE GALL, FRANCE DE LAPPARENT DE BROIN. SABINE RENOUS AND SYLVIE WENZ

LETHAIA

~ Gaillard, C .. Bernier, P .. Barale. G .• BoursC;"au, J.-P .. Buffctaut, E .• Ezqucrra, R .• Gall, I.~C., dt> Lapparent Je Broin, F., RenOU>, S. & Went, S. 2003 12 12: A giant Upper Jur· assic turtlc revealcd hy ils trackwJys. l..~tlwin, Vol. 36, pp. 31S-J22. Oslo. ISSN 0024-11 M .

ExccptionaJ fossili1.ation uf large tclrapod swimming trace..• occurs in th<' Cerin Lager­stalle (lum Mountains. France}. Thesc trackways arc imprim~l in Jurassk ( lat<' Kim­mcridgian) lngoonal finc-graincd limcstoncs and .trc auributcd to gia nt tu nies, which swam with a simullancous muvcmcnl of thcir forclimb.~ likc the modem ~1n<!s. The~ turt lcs l>'wnm in very shallow waters dose hl l.md, perhaps near a ~'ling area. As a major consc<1uencc, thcsc new ichnologic data place the origin of true large marine tur­tles during the lurnssic pcriod and not during the Cretaceous period as previous.Jy con· sidcrcd on the basis of skcletul remains. D l..itlwgmphic limestone, swimmmg traces, tmtkw11ys. turth·. Uppa /lll'tWic.

Christitlll (;ailla rd {Cirristiwi.Gaillard(o/rmiv·lyoll /.frf, Paul Brrnier 1 Ptmi.Bcmier@ulliv­lyorll fr/. Ct•org<'S Ha mie /Gcorgc.<.Btmlle@lunii··IJ'OIII fr/. jean-Paul lloursl.'all {Jea11-Pau/. &mrS<'llll@mliv-1)'011/.frj mul Rubt•n EZ1Jiœrm /Migud.Esqul.'rra@uuiv-lyoul.fr/, UMR CNRS 5115. Pnle'omviroui/CIIIC/It$ ct {Ja/iobi<>splrùt'. Uni•'t'Tsiti Claude Bemard. Lyou-1. Cé01lr, 1 rue Rt~plrad fJulwis. FR-69622 Vill<'urbtlmlc Cedex. Eric /Jufft~ttllll f Eric.Buffetaut @wamtdoo.M. CNRS, /6 Wlff de Liégat, FR-75013 P11ris. /ean-Cia11de Gall (jcgal/@illitc. ll·slmsbg.frJ, f:cof<o 1!1 Observdloire des Scie11ces d<' lu Terre, Uuivcrsiti l.ouis P11sl1'11r, Stmsb<•urg-1, 1 rur 8/essig, FR-67084 Stms/11mrg C!•de.'\. Frnuce dr Lapparr/11 rie Broiu ffdclnp@lcimrsl.nmltn.fr/•md Sylvie \Venz {weuz@mnlm.fi'/. UMR CNRS 8569, Lilbom­toirt• d,• Paléontologie, Muscwu Natiotwl d'Histoirl.' Nmurc•/11', Il rue Buffnn. FR·7S005 P11ris. Sa/nue RMwus {renom@cimrsl .llmlm.frJ, UMJ~ CNUS 8570, /.a/;ormoire d'AIIatO­mir Comparle, MI~S<:IIm Nntiom1l d'Histoire· Nuturdlc•, 55 me Bttf{nll, PU-75005 f>11ris; !8th Fcbnmry 2002. TI!Visct14t!J Mcty 2003.

Chelonians originatcd from a group of terrestriaJ Permian reptiles, the Pareiasauria (Lee 1995). The earliest chelonians known arc from Late Triassic continental deposits in various parts of the world:

Lithographie limestones of Cerin

The trackways studied in this paper come from the exceptional fossil deposit (=Lagerstatte) of Cerin (southcrn Jura Mountains, France) and were dis­covered during the scientific excavation organized by the Earth Sciences Laboratory of the University Lyon 1 (Fig. 1). They are imprinted in very fine-grained and weU-bedded limestones (Cerin Lithographie Lime­stone Formation) (Fig. 2). Ammonites {probably Ikckeri Zone) indicatc !he Late Kimmeridgian age for these deposits (Enay et al. 1994). The palaeoen­vironment corresponds to a tropical shallow marine lagoon lying upon an eroded reef complex (Bernier 1984; Bara le et al. 1985; Bernier et al. 1991 a). The very shallow water depth and frequent emersions are attested by the presence of the annelid burrow Tubularitw litlwgrapllica (Gaillard et al. 1994), mud­cracks, petee structures and other deformation struc­tures of mkrobial mats (Bernier et al. 1991b). The fTequent growth of microbial mats at the top of these very fine-grained deposits provides optimal condi­tions for the preservation of fossils and trace fossils

Argentina (Rougier et al. 1995), Germany (Gaffney 1990), Greenland (Jenkins et al. 1994 ), Thailand (de Broin 1985), and perhaps New Mexico (Lucas et al. 2000). Both environrnental and morphologicaJ evi­dence (such as a heavy armour and short legs) indicate that the most primitive chelonians, such as Progano­cllelys and Palaeochersis, were terrestrial animais. Lacustrine and fluvial environments were apparently coloniz.ed during the Late Triassic. Adequately docu· mented littoral turtles are known from the Late Jurassic of Europe (de Lapparent de Broin 1996) and Argentina (Pernandez & de la Fuente 1993). Skeletal remains of typical marine turtles capable of efllcient swim.ming are known (rom the Late Cretaceous { Hirayama 1994). The aim of this paper is to report the discovery of very unusual late Jurassic trackways probably made by turtles, whicb improvcs this knowl ­cdge and yields an interesting case in which ichnology is more infornlative than skeletal remains.

t:"::\ Taylor& francis ~ f~~frant•iVOilJ)

DOl 10.1080/00241160310004611 11 2003 T;~y1or & Francis

316 Christian Gaillard et al.

ANNECY .... \

•• Pig. 1. location o( the scientilk exçavation of Ccrin (Ain, fr-a,nçe ).

(Gall et al. 1985). Moreover, they give to the sediment a sufficient finn ness to allow the locomotion of large tetrapods such as tortoises the trackways of which are weU preserved (Bernier eJ al. 1982; Bernier et al. 1984). This taphonomic importance of microbial mats is also known for otber tracksites (Kvale et al. 2001).

Trackways analysis

Type-1 trackways

Two specimens, A and B, of type 1 have been observed. The first one is slightly curved and 10 m long, while the second one is straight and 6 m long. They cross on bed 106 (Figs 2, 3). The type-J trackways are very large (extemal trackway width: A = 1.50 m, B = 1.60 m). Two k:inds of tracks are visible. Majn tracks (width 20 to 30 cm) are weil imprinted and show a clear displacement rim back to the impressions of more or Jess distinct five digits (Fig. 4A). A main groove and severa! poorly preserved short grooves occur back to the rim. Otber tracks are more or less distinct (Fig. 3) and only correspond to a slightly curved deep groove (Fig. 48). Tracks are both symmetrically opposed with regard to the trackway axis. The opposed right and left main tTacks are more distant than the groove-shape ttacks.

Type-2 trackway

Only one specimen is known on bed 224 of litho­graphie limestones (Pigs 2, 5). This trackway is straight and 5.40 m long. Only four similarly large tracks (width 35 to 38 cm) are present, two on the rigtlt (MDI, MD2) and two on the left (MG2 and MG3). Tracks MD2 and MG2 are symmetrically opposed with regard to the trackway axis. Wh ile digit number is unclear, very weU-preserved grooves are visible (Fig. 6). A displacement rim partly overlaps these grooves.

LETHAIA 36 (2003)

>-0

• 0

! ..J 0 ::c 5

MAIN BODY FOSSILS MAIN mACE !Z FeuM Flora FOSSILS 1.11

1

!Id ~ z

1 1 J! i 1 ~ ~ Ill

400 f3

1 ra " ffi

3 :::::!

~ w >-

Il! c m ë

:::::!

-illon

SWIMMING c w mAC ES c

Cil 0 OF w g u

TURTLES ffi LL. :;) .....

b ... ~ c

Bedal224 ~ œ 106 ëil == i

Fig. 2. Stratigraphical and environ mental St!lling of the trackways in the lithographie limes lones of Ccrin (modified from Gaillard et al. 1994).

The longer grooves are slightly curved and can join together the successive tracks (MG2 and MG3). ln adrution, two main straight grooves lie between track alignments (Fig. 5). These are strictly parallel and equidistant from the trackway axis and are the most surprising element.

Trackways interpretation

Beca~e of three main similarities reported below, the two kinds of trackways probably correspond to the same large animal. First, the symmetrical opposition of the main tracks with regard to the trackway axis comprises the main characteristic. Because they are symmetrically opposed, right and left tracks were formed simultaneously. Another resemblance is the presence of a displacement rim posterior to the rugits. This indicates the rear of the tracks and the directjon of locomotion (Figs 3-6). The third resemblaoce is the presence of grooves mainly impressed behind the tracks. They probably correspond to scratch traces and web imprints clearly visible in tracks of type 2

LETHAIA 36 (2003)

0 2m ---====~

--- ->ndlwiy A ----~ lnldtwly B

A gùmt fura.ssic ttlrtle revealed by its trackways 317

BMD3~

Fig; 3. Type-1 trackwayrsketch-ûrip, be<! 106. Two trackways cross on bcd 106 (A: dashed, B: full li ne). Note the alternat ion of main trades (manus, Fig. 4A) and nearer elongate pes imprints (Fig. 48) replacing the simple groove of the type-2 trackway. The arrows indicate each traclcway axis and the direction of movement. Sca.le bar = 2 m.

Fig. 4. Detail of two tracks (manus and pes) from type-1 trackway B. Cerin, bed 106. DA. Track BMD3 (manus). See location i.n Fig. 3. Note the displacement rirn (R), in front, the five fingers (1 to V) and, posteriorly, a simple scratch trace ($).The arrow indicates the direction of movement. Scale bar= 15 cm. 0 B. Track BPGI (pes). See location in fig. 3. This slightly curved shon groove corresponds to the straight continuous groove of type 2 (see Fig. 5). The arrow indicates the direction of movement. Scale b<tr = 15cm. A

t5cm 15 c.n

B

Christian Gaillard et aL

A MG2

~ ........... . ':)?= : .. : ... :: ... ~ _·· ... · -~

MD2 M01

trackway (Figs 5, 6). Digits probably ended in claws and were joined by an interdigital web. The presence of a web shows that the trackmaker is an aquatic animal. The fine impression of the web in the sediment provides solid evidence for considering the trackways as swimming traces. The main scratch traces observed in the type-2 trackway, which join together the successive tracks, display a permanent contact of the animal with the sediment. Because of this·. last observation, the two enigmatic parallel grooves of the type-2 trackway are probably formed by a promlnent part of the animal, which regularly scratched the sediment. These straight grooves are situated at the same place as the narrow elongate ttacks of type-l trackway, which resernble a disrupted groove. Therefore, the two straight parallel grooves were forrned by the extremity of an inactive limb, probably by daws able to scratch deeply into the sediment. This attests that a quadrupedal animal using alterna te movement of fore and hi nd ümbs made the studied trackways. However, as shown by the type-2 trackway, one pair of limbs y<as regularly used and the other one was only occasionally moved. When the latter was not used for locomotion, only the main finger daws scratched the sediment, forming the two straight grooves (type 2). Scratches, which are regular and continuous (type 2) or disrupted (type 1), show

MG3

LETHA1A 36 (2003)

Fig. 5. Type·2 trackway. 0 A. Sketch. 0 B. Photo: Cerin, bed 224-. Four large tracks (35 to 38 cm wide) are present, two on the right (MOl, MD2) and two on the left (MG2, MG3). They probably correspond to forelimb ( = manus} imprints. Note the scratch marks nearly connect ing the successive tracks MG2 and MG3. The two straight parallel grooves are probably formed by the daws ending the hi nd foot ( = pes). The arrow indicates the direction of movement. Scale bar = lm.

that the animal swam close enough to the bottom to make contact. W e assume that the pair of lirnbs normally used for swimming was probably the anterior one. Therefore the main tracks correspond to forelimb (manus) imprints and the groove-shape tracks correspond to hindlirnb (pes) imprints. This kind of locomotion may be considered as half­swimming.

Marine turtle as possible trackmaker

These very unusual trackways probably correspond to a large and previously unknown animal. Among large pentadactyl tetrapods, few Turassic animals offer possible candidates. Because of their size and the age of the sediment, a reptile is very probable. Crocodiles are characterized by axial locomotion with undula­tion, whicb is inconsistent with the very straight trackways described here (mainly type 2). Paraxial locomotion is clearly illustrated by the studied track­ways. Sorne marine reptiles such as plesiosaurs also were possible trackrnakers, but their fore- and hindlimbs were sirnilar, probably having had the same action in locomotion and producing no differ­ence between manus and pes imprints. Moreover,

LETHAIA 3€l (2003)

15 cm

Pig. fi. Trnck MG2 (manus) and. on the right, the: ~ronw (pcs. Gl from trackway nf typl' 2- Ccrin, hcd 224. Scrntch tr.tccs (SI .md a wch imprint (W) arc weU preSèrved. A llisplaccmcnt rim ( R) which partly ov~rlaps the web and scratch traces, indi.:ates the b.,.:k of tracks ;md the direction of locomotion (arrow). S.:alc: bar = 15 cm.

Jurassic plesiosaurs have true paddle-like limbs, which are not consistent with the observed tracks.

Aquatic turtles, because they have <l rigid trunk, have true paraxial locomotion. Modern freshwater turtles have discontinuous propulsion using their four limbs alternately. Only marine turtles have pure pectoral paraxial locomotion (Braun & Reif 1982, 1985). The simultaneous movements of their hyper­trophied flapping forelimbs present mechanicaJ advantages in swimming ( Davenport et al. 1984) and even in terrestria.l locomotion (Renous & Bels 1993 ). This characterizes only the turtles, which are the best-adaptcd chelonians for swimming (Wyneken 1997; Renous et al. 2000). ln the subaquatic tlight generated by the forelimbs, the hind limbs, which are smaJier and often motionl~ss, seem to play only the role of rudders.

The most informative comparison may be obtained with the recent species Dcrmodu:lys corincea. Con­sidering the details of these !racks and the inferred simultaneous motion of left and right opposite limbs,

A ~i11111 /urtiHÎc turtle revmletl by its tmckways 319

the trackm;lkers were probably turtles swimming like extanl lurtles. However, the very long scratch traces of the trackway show that the movement of forelimbs is more horizontal than vertical This shows that this ki nd of turtle was doser to a subaqueous rower than a subaqucous flicr. This is an important difference with modern turtles. which are true subaqucous fliers { Davcnport et al. 1984; Wynekcn 1997; Reno us et al. 2000). They differ also from the modern t'lJrtles by the presence of fingers with free claws and interdigital web. During the Ju rassic, turtles like the ones that 111<1de the tracks at Cerin could not yet move with true paddles. By the Late Cretaceous, turtles had forelimbs much larger than hind )jmbs. a modified humerus, elongated and flattened fiogers (particularly digits 2 to 4) and regrcssed claws. Perhaps Jurassic turtles had not yet acquircd ali the necessary physiological adapta­tions to colonjze open sea environments.

These Jurassic giant turtles are knowo only by their traces. Considcring the trackway size, the turtle carapace could be estimated to be 130 to 140 cm in width and 140 to 160 cm in length if they were elongated. These Latc )urassic turtles are the oldest known turtles, which swam with a simultaneous mnvemt•nt of torclimbs, like the movement of modern turtles. As they are giant forms, they most probably derive from earlier smaller ones. The most important event in the his tory of turtJes was successful adaptation to the marine environment and the Cerin trackways provide evidence that this event occurred during the Jurassic period.

Skeletal remains and tracks of Upper J urassic turtles

Skeletnl remnim

Known Jurassic turtles are certainly not able to produce the studied trackways because aU are smaller and considered as poor swimming littoral turtles. SkeJetal remains of Upper Jurassic turtles are present in the Late Kimmeridgian lithographie Umestones of Cerin. They include Achelo11ia formom, Ewystemtlm crassipes, Hydropelta meyeri, ldiochelys fitzillgcri and aff. So/11/wjia (de Broin 1994). The larges! known carapace r~achcs only 22 cm in length. The 21.5 cm long foreli mb attributcd to Eurystemum crassipes couJd correspond to a carapace rcaching more than 50 cm in length. Skeletal remains are a Iso known in similar Upper Jurassic fossil deposits such as litho­graphie limestones of Solnhofen (Germany, Late Kimmcridgian - Early Tithonian), Canjuers (France, Early Tithonian) and Solothurn (Switzerland, Late Kimmeridgian) but they also correspond to relatively

320 Christian Gaillard et al. LETHAIA 36 (2003)

PRESENT DAY lA TE JURASSIC TRACKWAYS

~~ -0

A c -=-w-----(1 J

Type 1 Type 2

WALKING SWIMMING 0

FiR. 7. Model for trnckway genesi~ in Lhe shallow Jagoonal en\·irnnmenl o[Ccrin. DA-C Oll.~ed modem and fo~'il trackways.m: manus imprint. s: M:ratch mark relatcd to the m anus imprinl, p: pes imprint, G: groove currcsponding ro the pes imprinl. 0 U. Tntcrpretation of the related turtle activity. 0 A. Observcd modern trackways of Dermoclzelys coriacea walking on sand a ft er nesting (nfter Renous et al. 19!19). The fnur limhs arc uscd strongly and simultaneously. OB. C. Fnssil trackways (B: type 1, C: type 2) discovcred in the Laie lu rassic lithographie limestone~ of Cerin. They werc probably emplaeed Îll very shnllow water, which hindered normal swimming. Trpe l correspond,; to a locomotion l'lith active foreHmhs and hi nd limbs thal may hav~;: been intermediate between walking and swimming. Type 2 shows a nearly nornu1l swimming ~ction using rmly forelimhs, while motiunless hi nd limbs scratch the bottom. 0 D. Lcft part: modem sea turtle (Dm11oclrclys .:urinccn) observed walking on a beach (after Renous e/11/. 1989). Right ptlrt: supposee! fossll turtle $Witnnùng in the shalluw lagoon of Ccrin. For the sake of clarity, the appearance of this turtle is the sa me in t h~ righ t part as in th~ le fr. ln fact, however, lt shoLJd ccrta inly be different (the Jurassic tu rtl~ having lacked truc paddle-like Jimbs, web and claws) but its full appearancc is stiJl unknown (absence of fossil .~kdetal remains).

small animals (de Broin 1994; Frickinger 1994; Meyer 1988). Among them, the largesl carapace is Tlu:tlas­semys, 65 cm wide and 64 cm Long. The size difference with the maker of the Ceri n trackways is considerable. Unfortunateiy, the limbs of tbese foss il turùes are generally poorly preserved. Only the eurysternid limbs (Eurysternwn, ldiochelys and aff. Solnhojia) are well known and d isplay the sa me adaptation as observcd in the T itho nian Neustîcemys (Fernandez & de la Fueute l993) and the Early Cretaceous Smztanachelys ( Hira­yama 1998): the humerus is not modified but fingers 3 to 5 are slighùy c1ongated (rather than strongly elongated in digits 2-4 as in present-day species), producing a smali paddle- like hand with free claws. The forelimb is longer thau the hind limb. Sucb morphology is most like the expeded trackmaker. However, the trackmaker was larger and strongly suggests a new La.xon, which b not easy lo place in one of the known Late Jurassic [amities.

Tracks

.Mesozoic tracks altribulcd to turtles are rare and correspond to a walk on wet sediment (Haubold 1971, 19H4; Bernier et al. 191:12; Foster et al. 1998; Mazin et al. 2000; Wright & Locklcy 2001 ). Turtle swim.ming traces resembling the studied traces have never becn discovered. The turtlc swimming trace

from the Late Jurassic lithographie limestones of Solnhofen ( AbeJ 1935) is a misinterpretation and corresponds to an ammonite shell roll-mark (Aspido­ceras) moved on the bottom by a current (Seilacher 1963). Sorne interesting similarities to Saltosauropus iatus described from the same fossi l deposit of Gerin also occur. Jo fact, t his taxon may also be a turtle trace as proposed by Lockley ( l991) and th us, possibly, not a questionable hopping dinosaur (Bernier etal. 1984}. The same swimmiog turtle under different condh.ions may even have made it. .But, because of some noticcable differences, this assumptiun nccds to be clcarly demonstrated.

Paleoecological implications

The discovery of these trackways lead-; to intcrcsting ecological and cthological consideralions. As shown by sedimentlllogy and ichno logy, Lhc Cerin lagoon was shallnw and frequently emcrgcd (Bernier et al. 1982, 1991 b; Gaillard et al. 1994). The turtle trackways have been ohscrved on.ly in the lower part of lithographie limestones characterized by donùnant marine influ­ences (fig. 2). These special trackways were probably formcd in a shallow layer of water, which hindcred the normal swimming pallcrn of t urtJes (Fig. 7}. Their half-swimming movement was characterized by fre­quent or perma~ienl contact with the bottom. The

ŒTHAIA 36 (20.03)

locomotion shown by the type-2 trackway only uses the forelimbs, whereas the type-1 trackway shows both active forelimbs and hind limbs. For true terrestrial locomotion. as in modern Dermochelys coriacea, the special structure and the synchronous functioning of the four limbs result in a trackway on sand (Reno us et al. 1989) that shows sorne similarities with the type-1 fossil trackway (Fig. 7). The emerged area, which was very close to the shallow Gerin lagoon (Bernier 1984i Bernier et al. 199la; Barale et al. 1985), may have been a rtesting area for marine turdes. They probably episodically colonized the lagoon for egg Jaying and the traces described herein may have been made by animais swimming in very shâliow areas just before going ashore or just returning to the sea after nesting. The Cerin palaeoenvironment is not only exceptional for trackway preservation but also gives valuable information on the behaviour of marine turt:les that inhabited the biota.

Conclusions

lJnusuallarge trackways from the Late Kimmeridgian Lithographie Limestones of Cerin show: 1 - the active and simultaneous use of wetl-developed anterior limbs; 2 - the occasional use of posterior limbs;. 3 -the presence of fingers ending in claws and joined by an interdigital web; 4- a nearly permanent contact of the animal with the sediment. AJl these data are consistent with a large aquatic quadrupedal animal swimming near the bottom. Among large J urassic pentadactyl tetrapods, oruy turtles are possible track­makers. They swam with a simultaneous movement of their forclimbs like the modem ones. The hind limbs were only occasionally used and scratched the sedi­ment more or less regularly. Trackways are made because these giant turtles swam in shallow waters. The lagoon area characterized by these trackways was close to the land, wblch was pos~ibly a nesting arca for marine turtles. A~ another major coosèquenc~ this ichnologièal discovery places the origin of well­swimmiog turtles earlier thau the Cretaceous period as previously considered on the basis of skeletal remains.

Acknowledgements. - This work was supported by the CI\"RS (UMR 5 125 - Paléoenvironnements et Paléobiosphère) and by the Conseil Général de l'Ain. We thank D.D. Gillettt: for help, R.G. Bromley and an anonymous re\'iewer for constructive criti­cal review of the manuscript, j.C. Reniaud and G. Sirven for technic.1l a.ssistance in the field, A. Armand and N. Podevignr for drawing and photography.

A giant Jurassic t11rtle revealtd by its trad.:ways 321 "

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