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Marine tethysuchian crocodyliform from the?Aptian-Albian (Lower Cretaceous) of the Isle ofWight, UK

MARK T. YOUNG1,2*, LORNA STEEL3, DAVIDE FOFFA4, TREVOR PRICE5,DARREN NAISH2 and JONATHAN P. TENNANT6

1Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, The King’sBuildings, Edinburgh EH9 3JW, UK2School of Ocean and Earth Science, National Oceanography Centre, University of Southampton,Southampton SO14 3ZH, UK3Department of Earth Sciences, Natural History Museum, London SW7 5BD, UK4School of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK5Dinosaur Isle Museum, Sandown, Isle of Wight PO36 8QA, UK6Department of Earth Science and Engineering, Imperial College London, London SW6 2AZ, UK

Received 1 February 2014; revised 5 May 2014; accepted for publication 7 July 2014

A marine tethysuchian crocodyliform from the Isle of Wight, most likely from the Upper Greensand Formation(upper Albian, Lower Cretaceous), is described. However, we cannot preclude it being from the Ferruginous SandsFormation (upper Aptian), or more remotely, the Sandrock Formation (upper Aptian-upper Albian). The specimenconsists of the anterior region of the right dentary, from the tip of the dentary to the incomplete fourth alveolus.This specimen increases the known geological range of marine tethysuchians back into the late Lower Cretaceous.Although we refer it to Tethysuchia incertae sedis, there are seven anterior dentary characteristics that suggesta possible relationship with the Maastrichtian-Eocene clade Dyrosauridae. We also review ‘middle’ Cretaceousmarine tethysuchians, including putative Cenomanian dyrosaurids. We conclude that there is insufficient evidenceto be certain that any known Cenomanian specimen can be safely referred to Dyrosauridae, as there are somecranial similarities between basal dyrosaurids and Cenomanian–Turonian marine ‘pholidosaurids’. Future studyof middle Cretaceous tethysuchians could help unlock the origins of Dyrosauridae and improve our understandingof tethysuchian macroevolutionary trends. © 2014 The Linnean Society of London, Biological Journal of theLinnean Society, 2014, 113, 854–871.

ADDITIONAL KEYWORDS: Dyrosauridae – Ferruginous Sands Formation – Pholidosauridae – SandrockFormation – Tethysuchia – Upper Greensand Formation.

INTRODUCTION

Tethysuchian crocodyliforms were a highly successfulgroup, some of which returned to a marine lifestyleduring the latter part of the Mesozoic and earlyCenozoic. Many species superficially resembledextant gharials in having enlarged supratemporalfenestrae, an elongate, tubular snout, and a high

tooth count (e.g. Koken, 1887; Mook, 1933, 1934; Wu,Russell & Cumbaa, 2001; Jouve et al., 2005a, 2006a;Barbosa, Kellner & Viana, 2008). Tethysuchia wasone of several crocodyliform clades that survived theend-Cretaceous mass-extinction event, with thesubclade Dyrosauridae continuing to radiate anddiversify during the Palaeocene and Eocene (e.g.Buffetaut, 1976, 1978, 1982; Jouve, 2005, 2007; Jouveet al., 2005a, 2006a; Jouve, Bouya & Amaghzaz,2005b, 2008; Barbosa et al., 2008; Hill et al., 2008;Hastings et al., 2010; Hastings, Bloch & Jaramillo,2011, in press). However, the origins of this clade are*Corresponding author. E-mail: [email protected]

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Biological Journal of the Linnean Society, 2014, 113, 854–871. With 11 figures

© 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 854–871854

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poorly understood owing to a paucity of fossils fromthe ‘middle’ Cretaceous.

A phylogenetic definition of Tethysuchia wasrecently proposed by Andrade et al. (2011: S102) as:‘the clade composed of Pholidosaurus purbeckensis(Mansel-Pleydell, 1888) and Dyrosaurus phospha-ticus (Thomas, 1893), their common ancestor and allits descendants’. This definition encompassesDyrosauridae and Pholidosauridae, and possiblyElosuchidae. Although curiously, this is not thecase in the phylogenetic analysis of Andradeet al. (2011), as Elosuchidae was recoveredoutside the Pholidosaurus + Dyrosaurus clade.Moreover, Andrade et al. (2011) proposed thatElosuchidae be used for the clade consisting ofElosuchus, Sarcosuchus, and Vectisuchus. Also, aphylogenetic definition of Pholidosauridae wasrecently proposed by Fortier, Perea & Schultz (2011:S259) as: ‘a stem-based group name includingPholidosaurus schaumburgensis (Meyer, 1841) and alltaxa closer to it than to D. phosphaticus (Thomas,1893) or Pelagosaurus typus Bronn, 1841′. No explicitphylogenetic definition has been proposed forDyrosauridae or Elosuchidae.

Phylogenetic analyses consistently findDyrosauridae to be holophyletic (e.g. Wu et al., 2001;Jouve, 2005; Jouve et al., 2005a, 2006a, 2008;Barbosa et al., 2008; Young & Andrade, 2009;Hastings et al., 2010, 2011, in press; Andrade et al.,2011; Fortier et al., 2011). The holophyly ofPholidosauridae, however, is not always recovered.Pholidosauridae has either been found to be aparaphyletic grade of taxa closely related toDyrosauridae (Wu et al., 2001; Jouve et al., 2005a,2008; Barbosa et al., 2008; Young & Andrade, 2009;Hastings et al., 2010, 2011, in press; Andrade et al.,2011), holophyletic (Fortier et al., 2011; and in one ofthe analyses of the Jouve et al., 2006a data set inHastings et al., in press), or holophyletic withElosuchus being outside the clade comprisingDyrosauridae and Pholidosauridae (Jouve et al.,2006a; and in one of the analyses of the Jouve et al.,2006a data set in Hastings et al., in press). Martin &Buffetaut (2012) and Martin et al. (2014b) also foundPholidosauridae to be holophyletic, but as nodyrosaurids were included in those analyses theynever tested whether pholidosaurids constitute anatural group. When Pholidosauridae is found to beparaphyletic, the sister taxon of Dyrosauridae variesbetween Terminonaris (Wu et al., 2001; Jouve et al.,2005a, 2008; Barbosa et al., 2008; Hastings et al., inpress), Oceanosuchus (Young & Andrade, 2009), andElosuchus (Hastings et al., 2010, 2011), althoughOceanosuchus was only included in the analysis ofYoung & Andrade (2009). As such, the internal evo-lutionary relationships of Tethysuchia are in flux.

This has important implications for tethysuchianevolution, in particular for our understandingof dyrosaurid origins, and whether dyrosauridsand the marine ‘pholidosaurids’ Terminonaris andOceanosuchus constitute a single marine radiation orseveral independent ones.

One of the major issues hampering resolution inthese analyses is the paucity of ‘middle’ Cretaceous(Barremian–Turonian) marine tethysuchians, thusaffecting our understanding of character polarity. Inthose phylogenetic analyses in which ‘pholidosaurids’are paraphyletic, all potential dyrosaurid sister taxa(Elosuchus, Oceanosuchus, and Terminonaris) arefrom this time span (see Mook, 1933, 1934; Wu et al.,2001; de Lapparent de Broin, 2002; Hua et al., 2007).Furthermore, the earliest potential dyrosaurids areCenomanian in age (Buffetaut & Lauverjat, 1978;Buffetaut, Bussert & Brinkmann, 1990). Therefore,investigating specimens from the Barremian–Turonian stages will be key to elucidating the earlyevolution of Tethysuchia.

Here we describe a long-known, but previouslyunstudied, tethysuchian crocodyliform. This speci-men, the anterior-most part of a right dentary(NHMUK PV OR36173), is most probably from theUpper Greensand Formation of England (upperAlbian, Lower Cretaceous). Although this specimenwas discovered over 150 years ago, it has only beenbriefly mentioned once in the literature. Furthermore,it is of importance as a result of its unusual morphol-ogy and geological age. The presence of a marinetethysuchian in the late Lower Cretaceous of the UKwould indicate that tethysuchians moved into themarine realm earlier than previously realized.

ABBREVIATIONSINSTITUTIONAL

MIWG, the Museum of Isle of Wight Geology (nowIWCMS – the Isle of Wight County Museum Service,incorporating Dinosaur Isle museum and visitorattraction); MNHN, Muséum national d’histoirenaturelle, Paris, France; NHMUK, Natural HistoryMuseum, London, UK.

ANATOMICAL

D1, first dentary alveolus; D2, second dentary alveo-lus; D3, third dentary alveolus; D4, fourth dentaryalveolus; for, foramen; rug, rugose patch; sym,symphysis.

HISTORICAL INFORMATION

The anterior right dentary (NHMUK PV OR36173)was purchased by the British Museum (Natural

CRETACEOUS TETHYSUCHIAN FROM UK 855


History) in October 1861 from a Mr Simmons. In theNHMUK specimen register, NHMUK PV OR36173 islisted as an ‘anterior portion of left upper jaw withfour teeth sockets, of a crocodilian reptile. Greensand?Shanklin, I. of Wight’. The only mention of the speci-men we can find in the literature is by Lydekker(1889: 179), who identified NHMUK PV OR36173 asthe pliosaurid, Polyptychodon interruptus, and statesthat it is: ‘apparently the extremity of the leftpremaxilla’. Why he referred NHMUK PV OR36173to Pliosauridae, and thought it might be P.interruptus, was not stated. Amongst the specimenlabels is a note left by Dr Leslie Noé, dated 23 August1999, in which he states: ‘This jaw fragment is notpliosaurian [? crocodilian]’. This taxonomic note iswhat brought NHMUK PV OR36173 to our attention.

GEOLOGICAL INFORMATION

The right partial dentary (NHMUK PV OR36173)was discovered at Shanklin, Isle of Wight, UK. Theexact formation that yielded it is, however, unclear. Itwas referred to the Upper Greensand Formation byLydekker (1889), but the NHMUK specimen registerrefers to it as from: ‘Greensand?’. Therefore, verifyingthat it is actually from the Upper Greensand Forma-

tion, and not from one of the Lower Greensand Groupformations exposed at Shanklin, is important (seeFig. 1). In order to determine this, one of the authors(T.P.) examined the fossils in the MIWG (IWCMS) andthe rocks at Shanklin. Descriptions of the deposits ofthe Lower Greensand and Selborne Groups on theIsle of Wight have been given by White (1921), Wach& Ruffell (1991), Insole, Daley & Gale (1998), andHopson, Wilkinson & Woods (2008).

Numerous marine reptiles are known from theFerruginous Sands Formation (Lower GreensandGroup) of the Isle of Wight. The members of theFerruginous Sands Formation exposed at the lowerpart of the cliffs at Shanklin (Knock Cliff to HopeBeach) are: the Old Walpen Chine Member (XII), theNew Walpen Chine Member (XIII), and Member XIV(un-named). If the provenance of NHMUK PVOR36173 is one of these members, we would expect itto be very dark brown or black in colour with a darkmatrix (this being caused by the iron-rich nature ofthe sediment), as is the case in the exceptionally rareornithopod bones and a number of ichthyosaur verte-brae (e.g. MIWG.5376) from Member VI, which aredark brown/black. However, we cannot discount thatNHMUK PV OR36173 may have come from an iso-lated calcareous lens in one of these members. As

Figure 1. Map of the Isle of Wight showing Shanklin (A), with the geological column of formations exposed there (B). [Aand B are modified from Hopson (2011).] Photographs of the formations exposed near Shanklin, at Luccombe Chine (C),and Knock cliff (D).

856 M. T. YOUNG ET AL.


such, the possibility of a Ferruginous Sands Forma-tion origin cannot currently be completely ruled out.

Overlying the Ferruginous Sands Formation atShanklin is the Sandrock Formation (Fig. 1). Thisformation is a mixture of blue silty clay and yellowsands, and is considered to have been depositedduring a time when cyclical sea-level changes pre-served a number of wide estuaries and near-shoremud flats (see Wach & Ruffel, 1991). Fossil plantsdiscovered from this formation are typically pale(white), fragmentary, and crumble easily. Although wethink it unlikely that the Sandrock Formation is theorigin of NHMUK PV OR36173, the lack of any suit-able reptilian material for comparison means that wecannot entirely discount the possibility.

The final, and highest, formation from the LowerGreensand Group exposed is the Monks Bay Sand-stone Formation (formerly known as the CarstoneFormation of the Isle of Wight) (Fig. 1). This overliesthe Sandrock Formation. It is very gritty, with largeiron-rich sandstone nodules and has a dark-browncoloration. Vertebrate fossils are unreported in thisformation, and along with the iron-rich deposits(which would make fossils darker in colour), weexclude this as the possible origin of NHMUK PVOR36173.

The Lower Greensand Group is overlain by theSelborne Group, with two formations exposed (Fig. 1):the Gault Formation (Albian) and the UpperGreensand Formation (Albian–Cenomanian). TheSelborne Group was deposited in a marine setting,with the Gault Formation forming in a mid- or outer-shelf environment, whilst the Upper Greensand For-mation was formed in a shallow offshore shelf and inlower shoreface zones related to an eastward-prograding shoreline (Hopson, 2011).

At Shanklin, the clays/mudstones of the Gault For-mation are dark in colour, which results in darkfossils. The general coloration and matrix of NHMUKPV OR36173 appears similar to the central part of theUpper Greensand Formation, the ‘Malm Rock’ orFreestone, a pale grey/green glauconitic sandstone/siltstone that contains iron-rich sandy nodules (divi-sion D of Jukes-Browne & Hill, 1900). This thicksequence lies above the basal ‘Passage Beds’ (divisionA of Jukes-Browne & Hill, 1900) and below the ChertBeds (division E of Jukes-Browne & Hill, 1900).

However, it must be appreciated that a considerableamount of time (over 150 years) has passed sinceNHMUK PV OR36173 was collected. Therefore, theexternal surface may have altered as it dried out andoxidized. Based on general specimen coloration andmatrix, the Upper Greensand Formation seems likethe most probable origin of NHMUK PV OR36173. Asstated above, we cannot preclude the possibility thatNHMUK PV OR36173 originated from the Sandrock

Formation or from an isolated calcareous lens inMember XII, Member XIII, or Member XIV of theFerruginous Sands Formation.

Is NHMUK PV OR36173 reworked from an earlier,Jurassic, horizon? Not only is the morphology ofNHMUK PV OR36173 distinct from any knownJurassic taxon (see the description below), but adrifted block of Jurassic material would needed tohave travelled many kilometres from the nearestexposed Jurassic outcrop to have become entombed inthe marine Greensands. We find this to be an unlikelyscenario.

SYSTEMATIC PALAEONTOLOGYCROCODYLIFORMES BENTON & CLARK, 1988

MESOEUCROCODYLIA WHETSTONE & WHYBROW,1983

NEOSUCHIA BENTON & CLARK, 1988

TETHYSUCHIA BUFFETAUT, 1982

TETHYSUCHIA INCERTAE SEDIS

SpecimenNHMUK PV OR36173, the anterior region of theright dentary.

LocalityShanklin, Isle of Wight, UK.

Horizon and ageMost likely from the ‘Malm rock’ or Freestone, UpperGreensand Formation, Selborne Group (upper Albian,Lower Cretaceous). However, it could be from anisolated calcareous lens from one of three memberswithin the Ferruginous Sands Formation, LowerGreensand Group (upper Aptian, Lower Cretaceous):the Old Walpen Chine Member (XII), the New WalpenChine Member (XIII), or Member XIV (un-named).Moreover, we cannot entirely discount the SandrockFormation, Lower Greensand Group (upper Aptian–lower Albian, Lower Cretaceous), as there are noknown suitable fossils from this formation forcomparison.

DESCRIPTIONDENTARY

Only the anterior region of the right dentary is pre-served. It is approximately 130 mm in anteroposteriorlength. Overall, the preservation is good, other than itbeing broken posteriorly. There is no evidence of post-mortem mediolateral compression or shearing. Theexternal (= lateral and ventral) surfaces of thedentary are gently convex, with numerous large,subcircular foramina that are mostly widely spaced



(Figs 2, 3). The external surface ornamentation com-prises numerous, very small, subcircular pits. Thisornamentation pattern remains constant along theelement. The medial contractions between alveoli(and the raised alveolar rims, especially the D3 andD4) suggest that the premaxillary teeth would haveoccluded lateral to the interalveolar spaces on thedentary (i.e. in an overbite or interlocking manner)(Figs 2–4).

On the dorsal surface of the dentary, the threeanterior-most alveoli are completely preserved, alongwith the anterior section of the fourth (Fig. 4). All ofthe preserved alveoli are very large in proportion tothe overall size of the bone, but vary in size andshape. There is also variation in interalveolarspacing. The first dentary alveolus (D1) is orientateddorsally and slightly anteriorly (Figs 2, 4–5). The D1alveolus is oval in shape, orientated along theanteroposterior axis of the dentary, and has an

anteroposterior length of 48 mm and a mediolateralwidth of approximately 38 mm. Between the D1 andD2 alveoli, there is a minimum interalveolar space of17 mm. The D2 alveolus is notably smaller and alsooval in shape, having an anteroposterior length of25 mm. Between the D2 and D3 alveoli there is aminimum interalveolar space of 14 mm. The D3alveolus is smaller than the D2 alveolus and isslightly more circular in shape, with ananteroposterior length of 21 mm. Between the D3 andD4 alveoli there is a minimum interalveolar space of9 mm. The D4 alveolus is incomplete, but it wouldhave been considerably larger than the D2 and D3alveoli. The D4 alveolus has a transverse width ofapproximately 35 mm. Each alveolus has a slight, ornoticeable, raised rim. In the D1 and D3 alveoli theyare barely noticeable, in the D2 alveolus the rim ismore strongly developed, whilst the D4 alveolius hasa very large and well-developed rim.

Figure 2. Tethysuchia incertae sedis, NHMUK PV OR36173. Anterior region of the right dentary in lateral view: A,photograph; B, line drawing.

Figure 3. Tethysuchia incertae sedis, NHMUK PV OR36173. Anterior region of the right dentary in ventral view: A,photograph; B, line drawing.

Figure 4. Tethysuchia incertae sedis, NHMUK PV OR36173. Anterior region of the right dentary in dorsal view: A,photograph; B, line drawing.



The medial border of the D2 and D3 alveoli areeither in the same sagittal plane, or lateral to, thelateral border of the D1 alveolus (Fig. 4). Overall, thedorsal surface of the dentary is mainly flat, withnumerous large foramina medial to the D2 and D3alveoli. The largest foramen is medial to the D3alveolus.

In lateral view (Fig. 2), the dorsal margin of thedentary is concave between the D1 and D4 alveoli.This results in the D2 and D3 alveoli being ventral inthe transverse plane to the D1 and D4 alveoli. Moreo-ver, the D2 and D3 alveoli are orientated slightlydorsolaterally. When seen in lateral view, the ventralmargin is distinctly curved, and is convex. It risesdorsally anteriorly, and is noticeable ventral to thefirst two dentary alveoli.

In medial view, the preservation is poor but thesymphyseal suture is partially visible (Fig. 6).However, the dentary appears to be ‘hollow’posteroventral to the D3 and D4 alveoli. Anteriorly,the dentary is a solid bone, which would have createda firm mandibular symphysis. Ventral to the D3 thereis a concave surface that forms the boundary from the‘hollow’ and solid regions of the dentary. Posteriorly,bivalve encrustations and bivalve fossils are pre-served within this ‘hollow’ region.

We cannot determine how much of the symphysealsurface is preserved, although it is likely that it

extended posterior to the fourth alveolus. Based on thepreserved region, the dentary appears to be from amesorostrine or longirostrine taxon (based on the long,narrow and dorsoventrally shallow dentary). It issimilar to other tethysuchians such as ‘Elosuchus’felixi (de Lapparent de Broin, 2002) and Dyrosauridae(e.g. Hill et al., 2008; Hastings et al., 2010). There isno trace of the splenial, but we would not expect thereto be because the splenial does not reach as faranteriorly as the fourth alveolus in other tethysuchiantaxa (e.g. de Lapparent de Broin, 2002; Hill et al.,2008; Hastings et al., 2010, 2011; Adams et al., 2011).

In posterior view, the bone is exposed in crosssection (Fig. 7). As noted by Lydekker (1889: 179)there are large cancelli in the diploë. The dentary ishighly cancellous, with thicker cortical bone along theventral and lateroventral margins of the bone,whereas the dorsal and dorsolateral margins havevery thin cortical bone. Adjacent to the cortical bone,the cancelli immediately internal to the thickest cor-tical bone are larger than those adjacent to thinnercortical bone.

DENTITION

Only two, incomplete, in-situ tooth crowns are pre-served (Fig. 4). The in-situ tooth crowns are in thefirst and third alveoli. In the first alveolus there is an

Figure 5. Tethysuchia incertae sedis, NHMUK PV OR36173. Anterior region of the right dentary in anterior view; A,photograph; B, line drawing.

Figure 6. Tethysuchia incertae sedis, NHMUK PV OR36173. Anterior region of the right dentary in medial view: A,photograph; B, line drawing.



erupting replacement tooth crown. The crown is onlypartially visible, with only the apical half of thelingual surface exposed. In the third alveolus there isa cross section through the base of a fully eruptedtooth crown. The crown has a diameter of 11–12 mm.

Based on the two in-situ tooth crowns, the dentitionwould have been caniniform in morphology (i.e. singlecusped and labiolingually compressed). The basalsection is oval in cross section, being widermesiodistally than labiolingually. The incompletepreservation of the crowns makes it impossible tomake any further comments on the carinal or overallcrown morphologies.

DISCUSSIONEXCLUDING NHMUK PV OR36173

FROM PLESIOSAURIA

We agree with Dr Leslie Noé that the referral ofNHMUK PV OR36173 to Pliosauridae andP. interruptus is incorrect. There are a number ofplesiosaurian characteristics that are lacking inNHMUK PV OR36173, allowing us to exclude, withconfidence, NHMUK PV OR36173 from Sauropterygia.These include the following.

1. The pattern of large-to-small teeth in NHMUK PVOR36173 (in which the first and fourth dentaryalveoli are considerably larger than the second andthird alveoli; Fig. 4) is unknown in Plesiosauria. Toour knowledge there is no known plesiosaurian inwhich the first dentary alveous (D1) is larger thanthe second and third alveoli. In fact, in allplesiosaurian dentaries, the D1 is smaller (or atleast subequal) than the immediately posterioralveoli. This is seen in Rhomaleosauridae (Smith,2007), Pliosauridae (Andrews, 1913; Tarlo, 1960;Albright, Gillette & Titus, 2007a; Benson et al.,2011; Ketchum & Benson, 2011; Sassoon, Noé &Benton, 2012), Leptocleididae (Druckenmiller &

Russell, 2008), and Polycotylidae (Carpenter, 1996;Albright, Gillette & Titus, 2007b).

2. Eosauropterygians have a distinctive tooth-replacement pattern. Their replacement teethoriginate in separate temporary alveoli, recogniz-able by aligned foramina on the dorsal surface ofthe dentaries. Developing teeth grow within these,until the temporary and functional alveoli fuse(Owen, 1840; von Huene, 1923; Rieppel, 2001;Shang, 2007). The erupting teeth grow in ashallow groove medial to each functional alveolus.The separation between primary and secondaryalveoli can be short or large. However, toothreplacement in thecodont groups (includingCrocodylomorpha) involves development of thereplacement teeth in shallow pits in the lingualside of the functional alveolus, and then migrationinto the primary tooth pulp cavity through resorp-tion pits in the old base (Edmund, 1960, 1969;Kieser et al., 1993). Consequently, and in contrastto eosauropterygians, the entire process remainshidden inside the dentigerous bone. An exceptionto this pattern is in polycotylids, in which thesecondary alveoli are placed below the functionalteeth and so are hidden within the bone(O’Gorman & Gasparini, 2013). NHMUK PVOR36173 is clearly thecodont, with a replacementtooth erupting within the first dentary alveolus(Fig. 4).

3. No plesiosaurians have a symphyseal region of thedentary that is as large and continuously flat as inNHMUK PV OR36173 (Fig. 4). In plesiosaurians,the alveoli occupy the largest part of the dorsalsurface. There is usually a groove medial to thealveoli, although sometimes the alveoli and grooveare separated by paradental plates (e.g. Bensonet al., 2011; Ketchum & Benson, 2011). InPliosauridae, replacement alveoli develop withinthe symphyseal groove. Only medial to the grooveis there a flat dorsal surface. The lack of a

Figure 7. Tethysuchia incertae sedis, NHMUK PV OR36173. Anterior region of the right dentary in posterior view: A,photograph; B, line drawing.



symphyseal dorsal groove in NHMUK PVOR36173, and its large flat dorsal surface, does notsupport referral to Pliosauridae.

NHMUK PV OR36173 WITHIN CROCODYLOMORPHA

The most commonly discovered marine crocodylo-morph clade from the Mesozoic is Thalattosuchia.However, the Aptian–Albian age of NHMUK PVOR36173 makes a thalattosuchian identificationunlikely. Teleosaurids are currently only knownfrom the Jurassic, as the only definitive Lower Cre-taceous specimen (from the Valanginian of France)was recently redescribed and reidentified as ametriorhynchid (Young et al., 2014). Moreover, theanterior dentary morphologies of teleosaurids do notmatch NHMUK PV OR36173 (Fig. 8). In teleosauridsthe anterior region is as follows: spatulate, with themaximal width being present at the level of the D3alveolus; the D3 and D4 alveoli are closely set; thereare no enlarged foramina medial to the alveoli; andthe alveolar margin is convex at the D3–D4 region,resulting in those alveoli being positioned dorsal tothe D1 and D2 alveoli (e.g. Fig. 10C; Andrews, 1913;Hua, 1999; Lepage et al., 2008; Martin & Vincent,2013). Accordingly, we can safely disregard ateleosaurid origin for this specimen.

However, at least four lineages of the otherthalattosuchian clade, Metriorhynchidae, survivedinto the Early Cretaceous (Young et al., 2014), andthere is an indeterminate specimen from theBarremian of Spain (Parrilla-Bel et al., 2012). We canexclude NHMUK PV OR36173 from pertaining toany of these lineages (Cricosaurus, Dakosaurus,Geosaurus, and Plesiosuchina) as they all have thefollowing dentary characteristics: the D1 and D4alveoli are not enlarged relative to the other anterioralveoli; festooning along the alveolar margin is eitherabsent or only subtle; no enlarged foramina arepresent medial to the alveoli; and the dentary alveolilack raised rims (e.g. Fig. 8B; Fraas, 1902; Gasparini& Dellapé, 1976; Pol & Gasparini, 2009; Young &Andrade, 2009; Young et al., 2012; Herrera, Gasparini& Fernández, 2013). Therefore, there is no reason toassume a thalattosuchian origin for NHMUK PVOR36173.

From non-marine Barremian–Aptian deposits of theIsle of Wight, numerous crocodylomorph clades areknown. There is a new bernissartiid (genus and speciescurrently in press), the atoposaurid Theriosuchus sp.,the goniopholidid Anteophthalmosuschus hooleyi, the?goniopholidid/elosuchid/pholidosaurid Vectisuchusleptognathus, the enigmatic neosuchian Leiokarino-suchus brookensis, and the basal eusuchianHylaeochampsa vectiana (see Salisbury & Naish,2011; Sweetman et al., in press). Vectisuchus,

Leiokarinosuchus, and Hylaeochampsa lack the ante-rior dentary, and are thus not comparable withNHMUK PV OR36173. Based on the size and shape ofthe supratemporal fenestrae of L. brookensis, it waslikely to have been a longirostrine form (Salisbury &Naish, 2011).

Although no dentaries are known for H. vectiana,the anterior dentary is known for two Albianhylaeochampsid species: Pachycheilosuchus trinqueifrom Texas, USA, and Pietraroiasuchus ormezzanoifrom the southern Apennines, Italy. Both species areinterpreted as living in shallow, near-shore, brackishenvironments (Rogers, 2003; Buscalioni et al., 2011).However, their dentaries do not resemble theShanklin specimen (NHMUK PV OR36173). Inhylaeochampsids, the anterior tip of the dentary islaterally convex in dorsal view, resulting in a broadanterior dentary (D1–D6 region), with each succes-sive alveolus being lateral to the preceding one(Fig. 8O). Also, their symphyses are short (terminat-ing level to the fourth or sixth dentary alveolus) andthe dentaries lack concavities (i.e. festooning) alongthe alveolar margins. Furthermore, the D1 and D4alveoli are not larger than the D2 or D3 alveoli.Rogers (2003: 132) described P. trinquei as having:‘Rough pitting and grooves sculpture the ventralsurface and a row of nutrient foramina parallels thelabial margin’; this differs from the low-relief orna-mentation pattern and the large foramina that arearranged across the lateral and ventral surfaces ofthe dentaries in NHMUK PV OR36173. As such, wecan confidently exclude NHMUK PV OR36173 fromHylaeochampsidae.

The only longirostrine clade of eusuchians knownfrom the Cretaceous are Gavialoidea. Gavialoids areknown from the Maastrichtian (Late Cretaceous) tothe present day, with numerous ‘thoracosaurine’species known from Maastrichtian–Paleocene marinedeposits (e.g. Brochu, 2004, 2006; Hua & Jouve, 2004;Delfino, Piras & Smith, 2005; Jouve et al., 2006b).The Shanklin specimen, however, does not resemblebasal gavialoids. The anterior region of the dentaryof the Maastrichtian species Eothoracosaurusmississippiensis has circular D1 alveoli; the D2alveoli are larger than the D1, D3, and D4 alveoli; adiastema is present between the D2 and D3 alveoli;the D3 and D4 alveoli are closely set, although theydo not form a ‘couplet’; and large foramina on thedorsal surface of the dentary adjacent to the alveoliare absent (Fig. 8P; Brochu, 2004). The anteriorregion of the dentary of the Palaeocene species,Eosuchus lerichi, has: circular D1 alveoli; D1–D4alveoli of similar diameters, with the D3 alveoli beingslightly smaller; a diastema between the D2 and D3alveoli; and large, widely separated foramina on thedorsal surface of the dentary, immediately medial to



the alveoli (Delfino et al., 2005). The anterior region ofthe dentary of the Paleocene species, Argochampsakrebsi, is poorly preserved. However, the alveolardiameters are similar, with the D2 alveoli beingslightly smaller than the D1, D3, and D4 alveoli(Jouve et al., 2006b). As the anterior dentary mor-

phologies seen in basal gavialoids differ fromNHMUK PV OR36173, combined with the longinferred ghost range, we cannot refer the specimen tothat clade.

The Shanklin specimen (NHMUK PV OR36173)does not resemble any goniopholidid. In

Figure 8. The anterior ends of right dentaries of select crocodylomorphs compared with NHMUK PV OR36173 (some arereversed relative to the original figures); all are shown in isolation from the left dentary. A, NHMUK PV OR36173; B,metriorhynchid Plesiosuchus manselii (after Young et al., 2012); C, teleosaurid Machimosaurus hugii (after Martin &Vincent, 2013); D, ‘pholidosaurid’ Sarcosuchus imperator (after Buffetaut & Taquet, 1977); E, dyrosaurid Phosphatosaurusgavialoides (after Hill et al., 2008); F, dyrosaurid Hyposaurus ‘morphotype 1’ (after Jouve, 2007); G, dyrosauridHyposaurus ‘morphotype 2’ (after Jouve, 2007); H, dyrosaurid Rhabdognathus sp. (after Jouve, 2007); I, ‘pholidosaurid’Terminonaris robusta (after Mook, 1934); J–K, elosuchid Elosuchus cherifiensis (after de Lapparent de Broin, 2002); L,‘pholidosaurid’ ‘Sunosuchus’ thailandicus (after Buffetaut & Ingavat, 1980); M, ‘Goniopholis’ phuwiangensis (afterBuffetaut & Ingavat, 1983); N, goniopholidid Goniopholis baryglyphaeus (after Schwarz, 2002); O, hylaeochampsidPietraroiasuchus ormezzanoi (after Buscalioni et al., 2011); P, gavialoid Eothoracosaurus mississippiensis (after Brochu,2004). The reconstructions are not to scale.



goniopholidids, the anterior tip of the dentary islaterally convex in dorsal view, resulting in itbeing wider than the region posterior to the D4 alveo-lus (Fig. 8M, N; Salisbury et al., 1999; Salisbury,2002; Schwarz, 2002). The D1 alveolus ismediolaterally wider than it is anteroposteriorly long;the D3 and D4 alveoli are both larger than the D1 andD2 alveoli; and the ventral and lateral surfaces of theanterior part of the dentary are covered with small,closely spaced pits (Salisbury et al., 1999; Salisbury,2002; Schwarz, 2002). Additionally, the anterior-mostpart of the dentary is often out-turned ingoniopholidids (e.g. Goniopholis sp. (Fig. 9) andGoniopholis tenuidens; Owen, 1879, Pl. 1, fig. 1;Salisbury 2002 as cf. Goniopholis sp.). In view ofthese marked differences, there is no reason to regardNHMUK PV OR36173 as a member of theGoniopholididae.

The Shanklin specimen can additionally beexcluded from the semi-aquatic basal neosuchiangroup, Atoposauridae (Gervais, 1871), which per-sisted from the Middle Jurassic to the latest Creta-ceous (Evans & Milner, 1994; Martin, Rabi & Csiki,2010; Martin et al., 2014b). Multiple individuals ofTheriosuchus pusillus (Owen, 1879) are known fromthe Lower Cretaceous of the UK. The mandibularrostrum of one well-preserved specimen (NHMUKPV OR48262) is 10 mm long and has sevenalveoli (Fig. 10). Theriosuchus has a heterodont den-tition, which is visible even without preserved or

erupted tooth crowns, owing to the characteristicshift in alveolar shape/morphology (Brinkmann,1992; Schwarz & Salisbury, 2005; NHMUK PVOR48262). NHMUK OV OR36173 lacks this shift inalveolar shape from subcircular (pseudocaniniformmorphotype) to oval (labiolingually compressed teeth)alveoli. The D1 alveoli border the symphysis at itsmost anterior point; the gap between the D1 and D2alveoli is approximately equal to that between the D2and D3 alveoli; and the D3 to D7 alveoli are conflu-ent. The lateral margin of the anterior snout isheavily ornamented, and has numerous heterogene-ously spaced foramina, all approximately 0.5–1 mmin diameter, as is also the case in the other westernEuropean species Theriosuchus guimarotae (Schwarz& Salisbury, 2005) and Theriosuchus ibericus(Brinkmann, 1992). Theriosuchus differs fromNHMUK PV OR36173 in the relative sizes of thefirst four alveoli, with the D1–3 alveoli all beingequal in size and smaller than the D4 alveoli, andthe aforementioned heterogeneous spacing. Addition-ally, the symphyseal surface has a slight dorsal cur-vature anteriorly, unlike the linear surface ofNHMUK PV OR36173. Based on these marked dif-ferences and the overall size differences, we canexclude NHMUK PV OR36173 from being regardedas a large marine atoposaurid.

The anterior end of the dentary is well preserved inseveral taxa conventionally or putatively consideredas members of the Pholidosauridae. In P.

Figure 9. Goniopholis sp., NHMUK PV R1807. Anterior region of the dentary in dorsal view: A, photograph; B, linedrawing.

Figure 10. Theriosuchus pusillus, NHMUK PV OR48262, referred specimen. Anterior region of the left dentary in dorsalview: A, photograph; B, line drawing.



schaumburgensis from the Berriasian of Germany,the anterior region is spatulate and widest at thelevel of the D2 alveoli (Koken, 1887). There is asizeable gap between the D1 and D2 alveoli and theD2 and D3 alveoli, whereas the D3 and D4 alveoli areclosely set (Koken, 1887). Moreover, the D3 and D4alveoli are only slightly larger than the other dentaryalveoli, all of which are similar in size (Koken, 1887).

In the large-bodied ‘pholidosaurids’, Sarcosuchushartii, Sarcosuchus imperator, and ‘Sunosuchus’thailandicus, the anterior dentaries are spatulatewith the maximal width at the level of the D4 alveoli(Fig. 8D; Buffetaut & Taquet, 1977; Buffetaut &Ingavat, 1984; Martin et al., 2014a). In these taxa,the D1 and D2 alveoli are small, and substantiallysmaller than the D3 alveoli. In ‘S.’ thailandicus theD4 alveoli are greatly enlarged relative to the D1–D3alveoli (Buffetaut & Taquet, 1977; Martin et al.,2014a), whereas in S. hartii and S. imperator the D3and D4 alveoli are both enlarged (Buffetaut & Taquet,1977).

In the marine ‘pholidosaurids’ Terminonaris browniand Terminonaris robusta, the anterior region of thedentary is slightly spatulate in shape, its maximalwidth being at the level of the D3 alveoli (Fig. 8I;Mook, 1933, 1934). The D1 and D2 alveoli are notablysmaller than the D3 and D4 alveoli and the rest of thealveoli adjacent to the symphysis. The anterior regionof the dentary is unknown in the ‘pholidosaurids’Oceanosuchus boecensis (Hua et al., 2007; Lepageet al., 2008) and V. leptognathus (Buffetaut & Hutt,1980; Salisbury & Naish, 2011). However, thespatulate premaxilla of O. boecensis suggests thatthe anterior region of the dentary was also spatu-late, being similar to Terminonaris and other‘pholidosaurids’.

The elosuchid/‘pholidosaurid’ Elosuchus cherifiensisalso has a spatulate anterior dentary region, themaximal width being at the level of the D2 and D3alveoli (Fig. 8J, K; de Lapparent de Broin, 2002). TheD1 alveoli are enlarged compared with the D2–D4alveoli, with the D3 alveoli being the smallest of theanterior alveoli (de Lapparent de Broin, 2002). Theline drawings of de Lapparent de Broin (2002) makethe shape of the D1 alveoli between the differentE. cherifiensis specimens somewhat hard to judge, butthey appear to be subcircular to suboval in shape.

The holotype of ‘E.’ felixi and the two lower jawsreferred to this species, share some similarities withNHMUK PV OR36173. The ‘E.’ felixi specimens andNHMUK PV OR36173 share: (1) a D1 alveolus that islarger than the D2 and D3 alveoli; and (2) noticeablyenlarged D4 alveoli relative to the other alveoli (deLapparent de Broin, 2002; MNHN.F INA 21,MNHN.F INA 22, MNHN.F INA 25). Another sharedcharacteristic is the position of the D4 alveoli in

lateral view, which in both ‘E.’ felixi and NHMUK PVOR36173 is dorsal to the D2 and D3 alveoli. Note thatde Lapparent de Broin (2002: fig. 2N) incorrectlyshowed in a figure the D4 alveolus as being ventral tothe D2 and D3 alveoli, and orientated somewhatposteriorly. This is probably a result of the post-mortem deformation of the holotype (MNHN.F INA25); however, the two other lower jaws are from muchlarger individuals (MNHN.F INA 21 and MNHN.FINA 22) and they share the same D4 position asNHMUK PV OR36173. There are, however, somenoticeable differences between ‘E.’ felixi and NHMUKPV OR36173: (1) ‘E.’ felixi lacks the elongateanteroposterior axis of the D1 alveolus that is foundin NHMUK PV OR36173; (2) the anterior dentary isgladius-shaped in ‘E.’ felixi – the anterior dentary ofthe holotype has a slight concavity along the lateralmargin in dorsal/ventral views, but in the largerspecimen, MNHN.F INA 21, this concavity is muchmore pronounced, and in both specimens the anteriordentary is widest at the level of the D4 alveoli; and (3)the gladius-shaped anterior dentary results in thebone tapering anterior to the D4 alveoli, whereas inNHMUK PV OR36173 the D2–D3 region is almoststraight and is only slightly lateral to the D1.

There are several anterior dentary characteristicswhich suggest a close relationship between NHMUKPV OR36173 and Dyrosauridae:

1. The D1 alveolus is enlarged relative to the D2 andD3 alveoli (Fig. 8). This is also seen in:Arambourgisuchus khouribgaensis (Jouve et al.,2005a), Dyrosaurus maghribensis (Jouve et al.,2006a), Hyposaurus ‘morphotypes 1 and 2’and Rhabdognathus sp. (Jouve, 2007), andPhosphatosaurus gavialoides (Hill et al., 2008).

2. The D1 alveolus is mainly dorsally orientated, butthere is also a slightly/moderate anterior orienta-tion. This is also seen in: Cerrejonisuchusimprocerus (Hastings et al., 2010), D. maghribensis(Jouve et al., 2006a), D. phosphaticus (Jouve, 2005),Hyposaurus ‘morphotypes 1 and 2’, andRhabdognathus sp. (Jouve, 2007). This morphologyis also seen in basal gavialoids such as A. krebsi(Jouve et al., 2006b) and E. mississippiensis(Brochu, 2004).

3. Numerous, large foramina on the lateral andventral surfaces of the dentary that are widelyspaced. This is also seen in: A. khouribgaensis(Jouve et al., 2005a) and D. phosphaticus (Jouve,2005).

4. A concave dorsal margin of the dentary betweenthe D1 and D4 alveoli, resulting in the D2 and D3alveoli being slightly dorsolaterally orientated (i.e.a festooned anterior dentary). This is also seen in:D. phosphaticus (Jouve, 2005), Hyposaurus



‘morphotypes 1 and 2’, and Rhabdognathus sp.(Jouve, 2007).

5. Large foramina on the dorsal surface of thedentary, medial to the D2 and D3 alveoli. This isalso seen in: P. gavialoides (Hill et al., 2008).

6. The external ornamentation on the dentaryis of low relief and not conspicuous. This is alsoseen in: A. khouribgaensis (Jouve et al., 2005a),Hyposaurus ‘morphotypes 1 and 2’, andRhabdognathus sp. (Jouve, 2007).

7. The anterior end of the dentary is not spatulate (asit is in the ‘pholidosaurids’ and teleosaurids dis-cussed above) or gladius-shaped (as in ‘E.’ felixi),and the dentary is not laterally convex indorsal view (which results in a distinctly wideanterior region, such as in goniopholidids andhylaeochampsids, discussed above). NHMUK PVOR36173 has a narrow anterior dentary, like thatof longirostrine dyrosaurids (e.g. Jouve, 2007; Hillet al., 2008) and basal ‘thoracosaurine’ gavialoids(e.g. Brochu, 2004; Delfino et al., 2005; Jouve et al.,2006b) (see Fig. 8).

Note that characteristics 1–5 are also seen inCrocodylus spp. (NHMUK Earth Sciences compara-

tive collection of extant reptiles), and are possiblyrelated to an interlocking dentition and verticallyfestooned tooth row at the anterior-most region of therostrum.

In summation, there were numerous clades ofcrocodylomorphs living during the ‘middle’ Cretaceous(Fig. 11). However, NHMUK PV OR36173 differsconsiderably from the basal eusuchian cladeHylaeochampsidae and the neosuchian cladesGoniopholididae and Atoposauridae in alveolar con-figuration and dentary shape, and thus cannot beconsidered a member of these clades (Figs 8–10).Additionally, the anterior dentary morphology ofbasal gavialoids and metriorhynchid thalattosuchiansdiffers from NHMUK PV OR36173 (Fig. 8). Further-more, NHMUK PV OR36173 also lacks themediolaterally expanded anterior dentary seen in‘pholidosaurids’ and teleosaurids, and also differs inalveolar configuration (Fig. 8). The alveolar configu-ration and dentary shape of NHMUK PV OR36173are similar to those of Dyrosauridae (Fig. 8), andnumerous other characteristics (listed above) suggesta close relationship. There is one anterior dentarycharacteristic shared by dyrosaurids that NHMUKPV OR36173 lacks: a diastema/gap between the D2

Figure 11. Stratigraphic ranges of relevant Lower Cretaceous crocodylomorph lineages, plotted against time andcompared with the possible age range of the Shanklin specimen (NHMUK PV OR36173). Dotted lines represent parts oflineages for which fossils are unreported; arrows show that lineage persisted beyond the end of the Turonian.



and D3 alveoli. In view of this combination of dentarycharacters, we conservatively identify NHMUK PVOR36173 as Tethysuchia incertae sedis. More com-plete material and inclusion within a comprehensivephylogenetic analysis would enable testing of whetheror not NHMUK PV OR36173 is the sister taxon toDyrosauridae, or if it is a ‘pholidosaurid’-grademarine taxon.

‘MIDDLE’ CRETACEOUS MARINE TETHYSUCHIANS

The best known ‘middle’ Cretaceous marinetethysuchians are T. browni and T. robusta fromNorth America (middle Cenomanian–middleTuronian) and O. boecensis (lower Cenomanian) fromFrance (Mook, 1933, 1934; Wu et al., 2001; Hua et al.,2007; Lepage et al., 2008; Adams et al., 2011). Fromthe upper Cenomanian of Bavaria, Germany, a large,incomplete upper jaw from a longirostrine taxon hasbeen referred to Terminonaris cf. browni (Buffetaut &Wellnhofer, 1980). Terminonaris and Oceanosuchusdiffer from dyrosaurids in having: (1) more stronglyornamented skull and lower jaw bones; (2) apremaxilla without an anterodorsally projectingprocess anterior to the external nares; (3) a dorsallyorientated external nares; (4) five premaxillary alveoliinstead of four; (5) a subvertical anterior margin ofthe premaxilla that extends ventrally relative to therest of the element (i.e. the ‘pholidosaurid beak’); (6)absence of the D2–D3 diastema/gap seen indyrosaurids; and (7) absence also of the small D7alveoli seen in dyrosaurids. The anterior region of thedentary is not preserved in Oceanosuchus, but theanterior region of the dentary of Terminonaris isslightly spatulate (Mook, 1933, 1934; Wu et al., 2001;Adams et al., 2011). As such, these taxa still hadclassic ‘pholidosaurid’ characteristics (Hua et al.,2007; Fortier et al., 2011).

It should be noted that some putative pholidosaurid(sensu Fortier et al., 2011) and elosuchid (sensuAndrade et al., 2011) apomorphies are also found inthe basal-most known dyrosaurids Chenanisuchuslateroculi (Jouve et al., 2005b) and a new genus andspecies (Hastings et al., in press). Fortier et al. (2011)stated that the medial margin of the orbit (in dorsalview) is mostly formed by the prefrontal, with thefrontal participating only slightly in the medialmargin, and is a pholidosaurid apomorphy. However,this also occurs in C. lateroculi (Jouve et al., 2005b),gen. et sp. nov. (Hastings et al., in press), andgoniopholidids (see the figures in Andrade &Hornung, 2011). Andrade et al. (2011) stated that thefrontal being concave, with the medial borders of theorbit being upturned, is an elosuchid apomorphy.However, this also occurs in the pholidosaurids P.purbeckensis (Salisbury, 2002), P. schaumburgensis

(Koken, 1887), O. boecensis (Hua et al., 2007; Lepageet al., 2008), and T. robusta (Mook, 1934), and thedyrosaurid C. lateroculi (Jouve et al., 2005b; Hillet al., 2008). Therefore, in some aspects, cranial vari-ation between ‘pholidosaurids’ and basal dyrosauridsis less marked than originally thought.

However, one region of the skeleton is profoundlydifferent between the marine ‘pholidosaurids’ anddyrosaurids: the dorsal osteoderms. Like S. hartii, themarine taxa T. robusta and O. boecensis: (1) havesubrectangular paravertebral dorsal osteoderms thatare wider than they are anteroposteriorly long; (2)retain the stylofoveal joint (has a anterolateralprocess); (3) have a longitudinal keel; and (4) do nothave accessory osteoderms (i.e. a biserial series, e.g.Buffetaut & Taquet, 1977; Wu et al., 2001; Hua et al.,2007). Dyrosaurids, however, lack the stylofoveal jointand longitudinal keels, they have accessoryosteoderms lateral to the paravertebral series, andhave a lateral process which creates a joint betweenthe paravertebral osteoderm and the accessoryosteoderm (see Schwarz, Frey & Martin, 2006). Assuch, while cranial variation between ‘pholidosaurids’and basal dyrosaurids is less marked than is initiallypresumed, their difference in dorsal osteoderm mor-phologies are significant. These differences have thepotential to be very useful in identifying dyrosauridssolely, or primarily, based on osteoderms.

Although dyrosaurids are well known from theMaastrichtian onwards, their pre-Maastrichtian fossilrecord is relatively poor. Two maxillary fragmentsfrom the Campanian of Egypt pertain to alongirostrine crocodyliform tentatively referred toDyrosaurus (Churcher & Russell, 1992; Churcher,1995). The earliest potential dyrosaurids areCenomanian in age. A partial dentary (mid-symphyseal region) from the middle Cenomanianmarine deposits of Portugal was noted to be reminis-cent of dyrosaurids (Buffetaut & Lauverjat, 1978).However, its incomplete nature means that no firmconclusions can be drawn as to its affinities. Skullfragments (frontal, parietal, and left postorbital) andincomplete vertebrae from Cenomanian lacustrinedeposits of Sudan were referred to Dyrosauridaeindet. by Buffetaut et al. (1990). The dorsal vertebraehave very large hypapophyses, as is the case indyrosaurids (i.e. blade-like, flattened laterally,rounded ventrally, and anteroposteriorly long) (e.g.see the figures in Storrs, 1986; Jouve & Schwarz,2004; Jouve et al., 2005a; Schwarz et al., 2006).Terminonaris robusta also has noticeablehypapophyses on some vertebrae, but they are muchlower and are a different shape (see fig. 4 in Wu et al.,2001). The skull fragments were considered to befrom a primitive dyrosaurid by Buffetaut et al. (1990),as they have: (1) more strongly ornamented cranial



bones; (2) a smaller anterolateral process on the leftpostorbital than that of other dyrosaurids; (3) abroader intertemporal bar than dyrosaurids (i.e.between the supratemporal fenestrae); and (4) adorsal region of the postorbital pillar that is onlyslightly medially inclined. Unfortunately, theanterolateral process of the left postorbital is broken,so its size cannot be properly judged. However, largeanterolateral processes of the postorbitals are alsoseen in T. browni (Mook, 1933), T. robusta (Wu et al.,2001), and O. boecensis (Hua et al., 2007; Lepageet al., 2008). These examples further highlight howcertain marine ‘pholidosaurid’ and dyrosaurid cranialmorphologies overlap and may be homologous. Assuch, only the vertebrae (which Buffetaut et al., 1990could not be certain were associated with the skullfragments) reliably suggest a dyrosaurid, not indeter-minate tethysuchian, origin for this material. Notethat the presence of the Sudanese material in non-marine deposits does not imply that during theCenomanian some putative dyrosaurids wererestricted to freshwater environments, as there isgrowing evidence that dyrosaurids successfullyexploited both freshwater and saltwater environ-ments (see Khosla et al., 2009 and the referencestherein).

CONCLUSIONS

Herein we describe a tethysuchian crocodyliform fromthe Aptian–Albian (most likely the upper Albian) ofthe UK from Shanklin on the Isle of Wight. The singleknown specimen is the anterior region of a rightdentary, and it increases the known geological rangeof marine tethysuchians back into the late LowerCretaceous. Within Tethysuchia this mandibular frag-ment has certain characteristics that suggest a pos-sible relationship with Dyrosauridae: (1) an enlargedfirst dentary alveolus, relative to the second and thirdalveoli; (2) the first dentary alveolus is mainly dor-sally orientated but is slightly anteriorly orientated;(3) numerous large foramina on the lateral andventral surfaces of the dentary that are widelyspaced; (4) a concave dorsal margin of the dentarybetween the first and fourth dentary alveoli, whichresults in the second and third dentary alveoli beingslightly dorsolaterally orientated; (5) large foraminaon the dorsal surface of the dentary medial to thesecond and third alveoli; (6) external ornamentationon the dentary is of low relief; and (7) anteriordentary is not laterally expanded forming a‘spatulate’ morphology. However, establishing a newtaxon for this specimen must await the discovery ofmore complete remains.

We consider there to be no firm evidence that anyknown ‘middle’ Cretaceous tethysuchian is either a

dyrosaurid or an especially close relative of thatclade, especially as some putative apomorphies for‘Pholidosauridae’/Elosuchidae are also found in thebasal-most known dyrosaurids. Only future studies ofnew discoveries, and/or unrecognized museum speci-mens from this key time span, will elucidate thetethysuchian radiation into the marine realm and theorigin of Dyrosauridae.

ACKNOWLEDGEMENTS

We would like to thank Phil Hurst (Image Resources,NHMUK) for photography of NHMUK PV OR36173,and Ronan Allain (MNHN) for collection access. Wealso thank Alexander Hastings (Halle, Germany) andStéphane Jouve (Marseille, France) for their com-ments on NHMUK PV OR36173, and Leslie Noè(Bogotá, Colombia) for making his taxonomic notewhich highlighted this specimen. We also thank ananonymous reviewer and Steve Salisbury (Universityof Queensland, Australia) whose comments improvedthe quality of this paper. MTY received support fromthe SYNTHESYS Project http://www.synthesys.info/which is financed by European Community ResearchInfrastructure Action under the FP7 ‘Capacities’Program.

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marine tethysuchian crocodyliform from the …...isle of wight have been given by white (1921), wach...

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