Rcv~rede Pale'obiologie, Gen2ve (2004) Vol. spkc. 9 : 143- 149
Isolated theropod teeth from the Ceilomanian of Morocco and their palaeobiogeographical significance Romain ANIIOT1,Eric BUFFETAUT2, Haiyan TONG2,Larbi BOUDAD' & Lahcen KABIR13
Abstract lsolated theropod teeth, from the Cenomanian Kem Kem beds of the Tafilalt region, southern Morocco, are described. Some of these leeth are referred to the species COT-c~harodontosuurus snharicus, and others to the family Dromaeosauridae. This is the first record of this family in northwestern Africa. Whereas Carcharodon~osatcrusseems to have Gondwanan affinities, the I l r o l ~ ~ a e o s a ~ ~ r i d n e can be considered as northern hemisphere faunal elements, which indicate either an episode of faunal interchange bctwccn Luurasia and Gondnana in the Crctaceous. or derivation from an earlier (Jurassic) faunal assemblage with a vast Laurasian-Gondnanan distribution.
Key words Cenomanian, Ci~rrlitrr-odoniosal~r-11s. Dromaeosauridae, Isolated teeth. I<em Kem beds, Morocco, Tafilalt region.
RCsumC DCcouverte de dents isolkes de thkropodes dans le Cknomanien du Maroc ; implications palkobiogkographiques
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Des dents isolCes de thCropodes provenant des Kem Kem beds (Ctnomanien) de la rCgion du Tafilalt (Maroc) sont dCcrites. Certaines d'entre elles semblent appartenir a I'esphce Carchar-odontosuurusscll~uricus.D'autres sont rapportCes aux Dromaeosauridae, et constituent semble Etre un de ce fait le premier enregistrement de cette famille dans le nord-ouest de I'Afrique. Alors que Carrlic~rodoniosartr-11s taxon d'affinitks gondwaniennes, les Dromaeosauridae sont considkrCs comme Ctant d'affinitCs laurasiennes. Deux hypotheses peuvent cxpliquer la prCsence dc ces d e n i e r s au Ma1-OC:( 1 ) Un tpisode dlCchanges fauniques a eu lieu entre la Laurasia et le Gondwana durant le CrCtacC; (2) Ces thkropodes scraient issus d'un assemblage faunique plus ancien (Jurassique) h distribution gkographique Gondwano-Laurasienne.
Mots-clCs CCnomanien, Carcharodoiztosaurus,Drotnaeosauridae, Dents isolCes, Kern Kern beds. Maroc. RCgion du Tafilalt.
l. INTRODUCTION
2. GEOLOGICAL SETTING
The non-marine Kem Kem beds of southern Morocco have been known as a rich source of fossil vertebrates since the pioneering work of LAVOCAT (1954). Kemains of lheropod dinosaurs are not uncommon: but consist mainly of isolated teeth and bones (RUSSELL.1996)> although more complete material has also been reported (SERENO P T U / . , 1996). The peculiar, unserrated and uncompressed teeth of Spirzosaur~rs are especially common. In the present paper, \ye describe theropod teeth of a more "frequent" appearance, including some reminiscent of dromaeosaurids, and discuss the possible palaeobiogeographical significance of the latter.
In the Tafilalt Basin of southern Morocco, non-marine Cretaceous deposits, once described as "Continental Intercalaire" (LAVOCAT. 1954) and now more usuall~. called the Kem Kem Beds (SERENOet al.. 1996). unconformably overlie Palaeozoic deposits. 'I'his formation is generally divided into trio main units: a lo\\,er one consisting of sandstones showing crossbedded stratifications (typically channel fills), and an upper one composed of sequences of sandstone and clay. The Kem Kem Beds are overlain by a thick layer of Cenomano-Turonian marine limestone. These deposits have yielded an abundant continental fossil assemblage including fishes (elasmobranchs, actinopterygians. lungfishes and coelacanths), turtles.
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lhc distal end of the cro\vn base. A diagnostic fealure proposed b~ SE KEN^ et al. (1996), and observed here. is the morphology of the distal ~narginof the cro\\,n \\,hich is sligtitl!. conca1.e at mid-length and convex to\\.rird the a1)c.x. The other diagnostic rcat~ireconcerning enamel ornamentatioii (trans\.erse bands and arcuate \l8rinkles near cro\vn niargin) \vas not o b s c r ~ ~ con d al1 specirnens [M-CH-O03 (PI. 1. lig. 1 ) lacks these characteristics]. Both the labial and linglial sides rire conIrex, the mesial and distal carinae are strong and lie in the midlinc. The 3. T E E T H DESCRIPTIONS denticles of both mcsial and distal carinae have the samc \\,idth (anterior scrration dcnsity: 2.6 denticles per mm; The theropod teeth described hcre comc frorn nine posterior serratiori ciensit~,:2.7) so that DSDI is close to localities in the Kcm Kcm Beds. and \vere reco~,ci-ed by 1. Denticles are usually perpendicular to the tooth asis, surrace collecting. Tootti maicrial dcscribed i11 this papcr but tliis is subjcct to variation (specimen M-TA-032 is dcpositcd at the Facultk des Sciences et Iechniques (Pl. 1, fig. 2) has dcnticlcs on the distal carinae tending to of Errachidia IJniversitl., Morocco. All the specimens point toward the tooth apex). All the diagnostic featlircs folind may be shed tccth. as the! were isolatcd and are observed on the large C. saharicus teeth, but not ruotless. A detailed study bascd on general shape, sj.ste~naticallyon the smaller specimens. We suggest cross section, morphology and dcnsit). of the dcnticlcs, that some of these features (e.g., enamel ornamentation) and the measurement or the Fore-Aft Basal Lcngth may ha1.e appeared later during theropod ontogeny, and et al., 1990), Basal Widtti (BW). Lateral (FABL. CURRIE that the smallcr tccth may belong to juvenile individuals. Compression Indes (LCI = FABLIBW. GRIGORESCLJ. Ho\\,e~>cr, as few sn~rilltccth identified as C. sahuricus 1984) and Dcnticlc Size Difference Indice (DSDI, \vcrc found, this hypothesis cannot be tested on the basis RAUHUT & WERNER> 1995) allo~vedus to recognise three of currcnt data. main morphotlpes (Table 1). the standard terrninology proposed b!, SMITH & DODSON (2003) is uscd for tcetli 2. Velociraptorine-like dromaeosaurids description. lizards, crocodilians. dinosri~ii-sand pterosaurs (LAVOCAT, 1954 : I i i ~ s s ~ i ~1906 i ~ . : S E R ~ etN (11., ~ 1996 : TorĂźc & B ~ I F F E T A1996 ~ I T ;. WEI,I>NHOFER & BIJFF~.I.ALIT : 1999, C A V IPNT r l l . , 2001). The Kein Kcin Beds has I-ariously becn considered as Alhiaii cir Cenomanian in agc. Faunal and stratigrriphic el-idence indicatcs an carIl, Cenomanian agc (sec re\.ie\v i n WEI>I~NHOFEK & B U ~ ~ F T A1999). UT.
1. Carcharodontosaur~tssaharicus Material: M-CH-003 ; M-TA-032 (Pl. 1, Fig. 1 &2). As C. salzaricus \\.as one of the largest prcdators of the Crctaccous. its teeth are ger-ierrill!- larger than those of the othcr Kcm Ken1 thei-opods (cxccpt those of spinosaurids). Teeth arc laterall cciinpressed (I,CI=O.j). As in al1 other C. salzal-iciis tcech fouiid, they arc slightly recurved so that the tooth apc\ only reaches the level of
Material: M-CH-009; M-JQ-012: M-KS-015; M-ZAO14 (Pl. 1, fig. 4, 5 & 6). Tccth rcfcrrcd to the Vclociraptorinae range from IO to 16 mm in lcngth (from the apey to the base of the cro\\,n), with a FABL ranging ĂŽrom 4.0 to 7.9 mm. They are sharply pointed. labio-ling~ially compressed (LCI ranges froin 0.4 to 0.6), and strongly recurved distally so that the tooth ripe\ cxtcnds behind the level of the base of the cro\vn. Bolh lingual and labial sides are conves.
Table 1 : FABI,. BW, LCI and DSDI lalues for Moroccrin theropods used in this studg.
Sample
Tason
FABL (mm)
BW (mm)
LCI
DSDI
DSDI mean
M-TA-032 M-CH-O03
Crrrclzrr~-oclo~~to.rc~r~rl~.c. .c.crlzcrricrrs Crrr.cllrr~-orlo~~tosarrl-irs solzai-iclrs
10.27 12.00
-5.12 5.90
0.50 0.49
1 .O7 0.96
11 .O1
hl-CH-009
Velociraptorinae
3.95
2.12
0.54
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hl-.IQ-O 12 M-KS-O 15
Vclociraptoiinac Velocii-aptorinac
5.11 6.64
2.21 3.8 1
0.43 0.57
1.11 1.32
hl-ZA-O I J
Vclocii-apioi-inae
7.8.5
3.90
0..50
1.42
M-ZA-O 17
I>i-oiiiacosu~iridneindci.
7.27
4.08
0.6
0.93
1
1.28
lsolated theropod teeth from the Cenomanian of Morocco
Both carinae arc scrrated except in speciinen M-CH009 (1'1. 1, fig. a), \vhich has no scrrations on the mesial carinae. When present, denticles of the mesial carinac arc perpendicular to the tooth asis. and the distal oncs arc slightly oblique and point to\\,ard the tooth apex. Distal deiîticles are wider at their base (2.4 to 3.8 denticles per mm) than the mesial oncs (3.4 to 4.0 per mm). and seem to bc about t\\ice as tall (if \vear is considered to be equivalent on both mesial and distal carinac). Rclated DSDI range from 1.1 to 1.4. Interdenticle slits arc relativcly deep and parallel to the longitudinal axis of the dcnticlcs. Among Dromaeosaurids, characterised by the follo\ving synapomorphics (OSTROM, 1990) : strongly laterally compressed teeth both serrated mcsially and distally. \\,ith mesial denticles half as large as the distal ones, Vclociraptorines are diagnosed b), sharp distal curvaturc so that the apes extend behind the base of the crown, and inore elongated and pointed denticles, slightly hooked and pointing to\vard the tooth apes (CURRIE et al., 1990). All these features were observed on these Moroccan specimens, with LCI and DSDI matching publishcd vclociraptorine values range. The only exception is the hooked morphology of their denticles unobservable on these specimcns because of their denticles tips being partly worn.
3. Other deinonychosaurs Material : M-ZA-0 17 (PI. 1, fig. 3). Tooth M-ZA-017 (Pl. 1, fig. 3) shows a peculiar combination of features. The crown is 14 mm long, \vith a FABLof 7.3 mm, laterally compressed (LCI = 0.6) and only slightly rccurved so that the tip does not reach the level of the posterior end of the cro\\,n base. ï h e anterior edge is curved but the posterior one is almost straight. The lingual side of the tooth is slightly concave, and the labial one coiîves. The cross section is Icns-shaped. Both carinae arc serrated: lie in the midline. and thcir denticles point toward the tip of the cro\vn. Mesial and distal denticles are almost the samc size, but larger than those of \,elociraptorines. (2.0 and 2.1 denticles per mm, DSDI > 0.9). Blood grooves estend parallel to the longitudinal asis of the denticles, the), are shallo\ver than those of Vclociraptorincs, and possess a characteristic that can bc obscrved on the tecth or Dronzaeosaurus albertetzsis, viz. a series of pits and bumps along the blood grooves (see CURRIE et al.. 1990). This tooth \\,as initially identified as beloiîging to a troodontid-like thcropod (AMIOTet al., 2002), based on the leiîs-like cross section, the DSDI equal to I , and the size of the denticles. \vhich are larger than thosc of olhcr tceth and beiîd to\\,ard the tip of the tooth. Ho\\,cvcr. accordiiîg to 1.' J. CURRIE (pers. comm.). the loolh is loo narro\v at the cro\vn base and ~ h eserrations inoi-e clos cl^. rcscmble those of di-oinacosaurids. conseq~ientl!. it is hci-c assigncd ~o the Di-onîacosa~ii-idac. bu1 moi-c inalcrial should bc i-cco\.ci-cd
and studied before unambiguously assign this specimen to any deinoiîychosaur group.
4. DISCUSSION 1. Note on the systematic use of isolated theropod teeth Much work has been done on theropod teeth from the rich 1,ate Cretaceous assemblages from Alberta and Montana (CURRIE,1987; C U R R ~etEal., 1990 ; FIORILLO & CURRIE, 1994; B ~ s z i o , 1997). These theropod faunas include deinonychosaurs (dromaeosaurids and troodontids), the maniraptoran Richardoestesia, tyrannosaurids and teeth attributed to the enigmatic Paronychodon. According to CURRIE et al. (1990), these teeth can be identified on the basis of size, shape and denticulation pattern. Consequently these assemblages are often used as a reference for studies of theropod teeth from other localities [(ANTUNES & SIGOGNEAU, 1991, 1992; RAUHUT & WERNER, 1995; CSIKI& GRIGORESCU, 1998; ZINKE,1998)]. However, functional convergences may be involved, as suggested by F A R L ~etWal. (1991). For example, similar serrations can be found among nondinosaurian taxa such as crocodiles, sharks, carnivorous mammals and varanids (sce fig. 14 in F A R L ~ et W al., 1991). Moreover, F A R L ~ W et al. showed that some characteristics usually used for tooth descriptions, such as FABL vs. BW: or FABL vs. serration density, etc., can be correlated. As a result, caution must be exercised when attributing tasonomic significance to isolated teeth, al1 the more so when comparing Laurasian theropods et al. (1996) gave with Gondwanan ones. BUSCALIONI detailed descriptions of isolated theropod teeth from Argentina. They found combinations of features different from those describcd in North American theropods and pointed to the possibility of convergent tooth patterns nithin Theropoda.
2. Palaeobiogeographical implications Carcharodotztosaurus saharicus \\.as first described (as Megalosaurus salzat-icus) by DEPÉRET& SAVORNIN (1927) on the basis of isolated teeth (of possibly Albian agc) from the Algerian Sahara. The generic name Carclzarodontosaurits \vas introduced by STROMER (1931) \vhen he described less fragmentary material from the Cenomanian of Bahariya (Egypt). The affinities of this tason have been partly clarified by the discovery of good skull material in the Kem Kcm beds (SERENO et al., 1996). According to S E R E Net~ al. (1996, p. 988). "the close relations bet\\,cen Carclzarodotztosaurus (Afi-ican). Acrocarzthosa~ir~~s(North Americaiî), and Gigannto.raur~is (South Ainerican) idciîtify a carcharodonlosa~irid radiation lhat had achieved a
Plate I