Mosasaurus cf. hoffmanni Mantell, 1829

Machalski, Marcin, Jagt, John W. M., Dortangs, Rudi W., Mulder, Eric W. A. & Radwański, Andrzej, 2003, Campanian and Maastrichtian mosasaurid reptiles from central Poland, Acta Palaeontologica Polonica 48 (3), pp. 397-408 : 398-403

Mosasaurus cf. hoffmanni Mantell, 1829

Figs. 2–6 .

Material.—Twoteeth(IGPUWAR−1,IGPUWAR−2),found togetherandpossiblybelongingtoasingleindividual,andone tooth crown (IGPUWAR−3), from the Danian greensand at Nasiłów (redeposited late Late Maastrichtian material). Two toothcrowns(IGPUWAR−4,OGP1254)fromtheupperUp − per Maastrichtian opoka at Nasiłów. A fragmentary jaw and isolated tooth crowns (ZPAL R. I/1–5), representing a single individual, from the Upper Campanian of Maruszów, previously recorded as Mosasaurus sp. (sp. A) by Sulimski (1968: 245,pl.1;pl.2:1–4,refiguredhereinasFigs.4–6).Comparative material from the type Maastrichtian area (type area of Mosasaurus hoffmanni ) includes NHMM 004984−2, 007129, 006684−3b, 1997262, 1997266, and 1997267.

Description.—The best−preserved specimen is an anterior (?premaxillary)tooth,IGPUWAR−2( Fig.2B ),100.3mmin height (including root, with small resorption pit). It is asymmetrically bicarinate, with a deeply U−shaped cross section, and with markedly unequal lingual and buccal surfaces. The buccal surface ismore orlessflat,with2–3 facets (bestvisibleproximally);onthelingualsurfacethefacetsarelesswell developed,andtheirnumbercannotbedeterminedprecisely. Both the anterior and posterior carinae are well developed, with minute serrations over their entire length. The crown has a marked posterior and lingual recurvature. The enamel shows beading, best developed proximally.

IGPUWAR−1 ( Fig. 2A ) is a massive lateral tooth, 89.6 mm in total height (as preserved), including the incomplete root. It has an elliptical cross section, with both buccal and lingual surfaces showing barely visible facets and beading. Both posterior and anterior carinae show minute serrations. Thecrownismoderatelyposteriorlyandlinguallyrecurved.

IGPUWAR−3 (as preserved 57.0 mm in height; see Fig. 2C ) and IGPUWAR−4 (as preserved 51.6 mminheight; see Fig. 3A ) show elliptical cross sections, and appear to have occupied a comparable position in the dental or maxillary ramus.Thesespecimenshavemoreclearlydevelopedfacets, on both the buccal and lingual surfaces, and show distinct beading of the enamel.

OGP 1254 ( Fig. 3B ) is a comparatively small (from a subadult individual?), bicarinate tooth crown (31.5 mm in height,aspreserved),14.2mminwidth(atthebase).Incross sectionitismoreorlesselliptical,withthelingualandbuccal surfacesmarkedlyunequal.Thebuccalsurfaceisfaintlyconvex,with3unequalfacets;onthelingualsurfacethereareup to9suchfacets,narrowerandespeciallymarkedproximally, reaching to just above mid−height; beading is well visible. Bothcarinaearewelldeveloped,theanterioronebeingmore pronounced, withminuteserrationsovertheirentirelengths. The crown is moderately lingually, but more clearly posteriorly recurved.

Teeth and tooth crowns in the Upper Campanian specimen ZPAL R. I/1–5 ( Figs. 4–6 ) show a U−shaped cross section, withboth the buccal and lingual surfaces facetted, with buccal facets wider and more distinct than those on the lingualside.Theyalsoshowwell−developedanteriorandposterior carinae, a slight posterior recurvature and a more pronounced lingual recurvature. Enamel beading is less pronounced than in the Late Maastrichtian specimens, but does occur in patches, both proximally and distally.

Discussion.—Typical anteriorand median−posterior teethof adultspecimens of M. hoffmanni arerobust,bicarinate,have asymmetrical crowns (lingualsidemore inflated)withafew wide “prismatic” facets on the buccal side of the crown, and more numerous facets on the lingual side; they also reveal beading of the enamel ( Lingham−Soliar 1995; Jagt et al. 1995; Kuypers et al. 1998). The posterior teeth are more symmetrical, but are still characterised by beaded enamel and distinct facets (op. cit.). The beading of the enamel was held tobe diagnostic of teeth of M. hoffmanni by Kuypers et al. (1998). However, it occurs in African and Polish specimens herein referred to as “ Mosasaurus (Leiodon) cfr. anceps ”and inone ofthePolishspecimens referred toas M. cf. lemonnieri as well (see below).

TheLateMaastrichtianspecimensIGPUWAR−1–4from Nasiłów fall within the range of dental variation of adult specimens of M. hoffmanni from the environs of Maastricht. The single tooth from the upper Upper Maastrichtian opoka of Nasiłów (MZ VIII/Vr−66), referred toby Sulimski(1968) as Mosasaurus sp. (sp.B),alsofallswithintheadultcategory of M. hoffmanni .

Teeth of subadult M. hoffmanni are more slender. Specimen OGP 1254 from Nasiłów may belong here. The size of the tooth crowns of the Upper Campanian specimen ZPAL R. I/1–5 from Maruszów suggests that these remains originatefromasubadultindividualaswell.Itiswellmatchedby smaller sized material of M. hoffmanni from the Maastrichtian type area (e.g., Kuypers et al. 1998: pl. 1: 5, 6).

Stratigraphic and geographic range.—In the Maastrichtian type area, the lowermost well−documented occurrence of M. hoffmanni ,basedonthediagnosticskeletalmaterial,iswithin the upper half of the Lanaye Member (Gulpen Formation, lower Upper Maastrichtian Belemnitella junior Zone ). However, finds of isolated teeth and tooth crowns from the Vijlen Member (Gulpen Formation, Lower Maastrichtian) in the

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Fig.5. Mosasaurus cf. hoffmanni Mantell,1829 ,fromthe Upper Campanian opoka at Maruszów. A. ZPAL R.I/ 4 in lingual(A 1)andanterior(A 2)views. B.ZPALR.I/2inlingual (B 1), anterior (B 2), posterior (B 3), and buccal (B 4) views.

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Haccourt−Lixhearea(Liège,NEBelgium),suggest that M. hoffmanni or a closely related speciesmadeitsfirstappearanceintheareaearlier. The species is fairly common in the Emael and Nekummembers(MaastrichtFormation,Upper Maastrichtian), in particular in the Eben Emael (Bassenge) area (Liège). The type of M. hoffmanni (MNHN AC 9648) is from the upper third of the Nekum Member (Bardet and Jagt 1996). The species ranges up to the K/Pg boundary. Reworked tooth crowns have been recorded from the basal Geulhem Member (Houthem Formation) of Early Paleocene age ( Kuypers et al. 1998).

Other records of M. hoffmanni include the Upper Campanian to Upper Maastrichtian of New Jersey ( USA) ( Mulder 1999 synonymised Mosasaurus maximus Cope,1869 ,with M. hoffmanni ), the uppermost Maastrichtian of Missouri ( Campbell and Lee 2001), the Maastrichtian of Alabama ( Kiernan 2002), Bulgaria

( Tzankov1939;seealsoNikolovandWestphal1976),north−

ernDenmark( Bonde1997;Jagtpersonalobservation), Congo

( Zaire) ( Lingham−Soliar 1994b), Niger ( Lingham−Soliar

1991),andTurkey(BardetandTunoǧlu2002). Persson(1959:

462, fig. 10; pl. 15: 1, 2) recorded M. cf. hoffmanni from the

Lower Campanian of southern Sweden. This material, however, refers to Tylosaurus ivoensis ( Persson, 1963) (see Lindgren and Siverson 2002).

InEurope,well−documentedremainsof M. hoffmanni appear to be confined to Upper Maastrichtian strata. However, the specimen from Maruszów suggests that M. hoffmanni or a closely related (ancestral?) species appeared in Europe as earlyastheLateCampanian.Thismaybeconfirmedonlyby more diagnostic finds.

Figures

Fig.2. Mosasaurus cf. hoffmanni Mantell,1829,fromtheDaniangreensandatNasiłów(redepositedlateLateMaastrichtianmaterial). A.IGPUWAR−1in buccal(A1),lingual(A2),andanterior(A3)views. B.IGPUWAR−2inposterior(B 1)andlingual(B2)views. C.IGPUWAR−3inposterior(C 1),buccal(C2), and anterior (C3) views.

Fig.3. Mosasaurus cf. hoffmanni Mantell,1829,fromtheupperUpperMaastrichtianopokaatNasiłów. A.IGPUWAR−4inposterior(A 1),buccal(A2),anterior (A3), and lingual (A4) views. B. OGP 1254 in lingual (B1), posterior (B2), buccal (B3), and anterior (B4) views.

Fig.4. Mosasaurus cf. hoffmanni Mantell,1829,fromtheUpperCampanianopokaatMaruszów,ZPALR.I/1,partialupperjawinbuccal(A),occlusal(B), and lingual (C) views.

Fig.6. Mosasaurus cf. hoffmanni Mantell,1829,fromthe Upper Campanian opoka at Maruszów. A. ZPAL R.I/1, left−handsidetoothinBin anterior(A1),buccal(A2),and posterior (A3) views. B. ZPAL R.I/1, three tooth crowns preserved in original jaw position (although jaw bone is not preserved).