Ichnos, 14:117–129, 2007Copyright c© Taylor & Francis Group, LLCISSN: 1042-0940 print / 1563-5236 onlineDOI: 10.1080/10420940601010802

Reconstruction of Middle Jurassic Dinosaur-DominatedCommunities from the Vertebrate Ichnofaunaof the Cleveland Basin of Yorkshire, UK

M. A. Whyte, M. Romano, and D. J. ElvidgeDepartment of Geography, University of Sheffield, Sheffield, UK

Globally, skeletal remains of dinosaurs are particularly rarethroughout much of the Middle Jurassic. Thus, other sourcesof evidence, and most importantly ichnofaunas, are importantindicators of the contemporary terrestrial vertebrate communities.The outcrops of the Ravenscar Group (Aalenian—Bajocian) withinthe Cleveland Basin of Yorkshire, UK, which have recently beenrecognised as a megatracksite of global significance, provide onesuch major source of ichnofaunal information of this age. Acomprehensive database on the variety and occurrence of dinosaurand other vertebrate traces within the Ravenscar Group has beenbuilt from a long-term and detailed study of the sequence. Thirtydifferent and distinct morphotypes of vertebrate traces have beenrecognised and are being analysed and further differentiated mor-phometrically. Some of the morphotypes represent behavioural,preservational and perhaps ontogenetic variants of other morpho-types, but nevertheless the range of quadrupedal and bipedal printsallows an overall fauna of sauropod, stegosaurian, ornithopod andtheropod dinosaurs along with crocodiles, pond turtles and fish tobe reconstructed. The distribution and abundance of prints andprint types within the succession shows evidence of environmentalcontrol on the behaviour and distribution of the vertebrates. Casestudies highlight both the advantages and disadvantages of thistype of data in reconstructing palaeocommunities.

Keywords Dinosaur tracks, Middle Jurassic, Ravenscar Group,Cleveland Basin, Yorkshire, communities, ichnofauna

INTRODUCTIONFootprints are the most common vertebrate fossils and

provide unparalleled information about the behaviour of theseanimals in the environments in which they lived. One of theaims of ichnological research must be the reconstruction of theanimal communities represented by the trace fossils. However,with the case of vertebrates in particular, such reconstruction canbe fraught with difficulties, such as problems with identifyingthe trackmakers and their relative abundance. Studies of theichnofauna of the Middle Jurassic of the Cleveland Basin in

Address correspondence to Dr. M. A. Whyte, Department ofGeography, University of Sheffield, Sheffield, S10 2TN, UK. E-mail:M.A.Whyte@Sheffield.ac.uk

Yorkshire illustrate some of these difficulties but also highlightsome of the information that is emerging about the changingpattern of the particular communities they represent. Theinformation that can be deduced from this ichnofauna and othercoeval ichnofaunas is particularly vital for our understanding ofdinosaur community ecology because of the scarcity of skeletalremains of Middle Jurassic age (Romano and Whyte, 2003a).

THE SETTINGThe vertebrate ichnofossils of the Cleveland Basin (Figs. 1, 2)

occur within the Ravenscar Group, which is of Aalenian toBathonian age (Romano and Whyte, 2003a). This unit representsa brief, less than 10 Ma, period of predominantly nonmarinedeposition (Fig. 3) during the otherwise marine history of thebasin (Rawson and Wright, 2000; Romano and Whyte, 2003a).During this interlude the area was occasionally inundated bymarine transgressions and the principal incursions are used tosubdivide the Group into a number of formations and membersof alternating marine and nonmarine character (Fig. 3).

Although the nonmarine units traditionally have been col-lectively referred to as the Estuarine (Fox-Strangways, 1892)or Deltaic (Hemingway, 1949) Series, each of the nonmarinelithostratigraphic units has its own particular character andinternal stratigraphy suggesting that they were each deposited inslightly different environments and with differing environmentalhistories. In general however, these units are typified by thinbedded and repetitive sequences of clays, silts and sands (e.g.,Figs. 4, 5), which in detail show considerable lateral faciesvariations. The finer lithologies were deposited in a range offlood plain, marsh and lacustrine environments. Some of themudrocks are markedly carbonaceous (Fig. 5) and some havebeen worked as impure coals (Hemingway, 1974). Plant beds,with a rich and diverse flora (Black, 1929; van Konijenburg-vanCittart and Morgans, 1999), and plant colonisation surfacesand palaeosols occur throughout the sequence (Figs. 4, 5).Sphaerosiderite is often abundant, indicating prolonged water-logging and gleying of soils, while in contrast desiccation cracksalso occur. Fresh-water unionoid bivalves (Fig. 4) and their

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FIG. 1. Simplified geological map of the Cleveland area of eastern Yorkshire, between Port Mulgrave and Gristhorpe, showing localities mentioned in the textand the principal sites at which dinosaur prints have been recorded (modified from Romano and Whyte, 2003a, fig. 2). The inset map shows the location of thearea.

Lockeia type burrows occur sporadically and attest to lakeand fluvial environments with more permanent water cover.Sheet-like sandstones, which may be single beds or compositeunits and show a variety of small scale sedimentary structures,represent overbank deposits of levees, sheet flood events andcrevasse splays. Occasionally these sands have overwhelmedand preserved in growth position stands of horsetails (Equisetumsp.). In places these bedded sequences are cut into and replacedlaterally by lenticular and usually arenaceous channel deposits.Channel systems may be isolated lenses, or may occasionallybe either vertically stacked (multistorey) or horizontally linked(multilateral) complexes (Alexander, 1992a) (Fig. 4). In additionto cross-bedded bar sandstones, finer grained mudrock orheterolithic plugs may be associated with late stages of someof the channel fills. The Moor Grit Member ( = Prism I ofEschard et al., 1991) at the base of the Scalby Formation(Fig. 3) is a particularly distinctive quartzitic fluvial channelsandstone complex, which rests disconformably on the marineScarborough Formation (Leeder and Nami, 1979) and is locallyabsent. Two other complex lenticular units of fluvial sandstones

(Prisms II and III of Eschard et al., 1991; = Current-BeddedSandstone of Black, 1929) are locally developed in the basal partof the overlying Long Nab Member and are separated from eachother and from underlying (Scarborough Formation or Prism Ior II) and overlying beds (upper part of the Long Nab member,= Level-Bedded Series of Black, 1929) by hiatuses (Fig. 3). TheLong Nab Member is overlain disconformably by the CallovianCornbrash Member (Fig. 3). Lacunae are probably widespreadthroughout the succession. Each of the many horizons at whichfootprints occur, or where there has been plant colonization,indicates at least short time breaks.

Structurally the Cleveland Basin was an east-west trendinghalf graben with a faulted margin between it and the morepositive Market Weighton High (Fig. 2) to the south. Duringthe Middle Jurassic, the relief difference between the two areaswas probably quite small and the high was probably not animportant sediment source. More important sediment sourceslay in the higher grounds of the Pennine Land Mass to the westand the Mid North Sea High to the north, from which the riversystems flowed into and through the basin (Fig. 2). Eastwards

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FIG. 2. Palaeogeographic map of the Cleveland region and adjoining areas inMiddle Jurassic times, showing the extent of the Cleveland Basin and sedimentsources (modified from Romano & Whyte, 2003a, fig. 4). The inset map showsthe position of the area within southern Britain.

the basin linked to NNW-SSE orientated basins in the SolePit Trough (Fig. 2). En echelon NNW-SSE faults within theCleveland Basin cause structural complexities, and the PeakTrough (Milsom and Rawson, 1989) (Fig. 1) appears to havebeen an area of greater subsidence within the basin. The marineincursions, which gave rise to the marine units, came from seasto the south and south east (Rawson and Wright, 2000).

The Cleveland Basin was inverted in the early Tertiary toform the Cleveland Anticline (Rawson and Wright, 2000). Thepresent coastline cuts obliquely across the broadly east-westanticlinal axis (Fig. 1) and provides a section across the basin.The lower parts of the Ravenscar Group succession is best seenin the often spectacular cliff sections (e.g. Fig. 4) on the northernparts of the coast from Staithes to Whitby (Fig. 1) and as farsouth as Hayburn Wyke. The higher parts of the RavenscarGroup sequence are best exposed in the south from Long Naband Burniston to Gristhorpe, where the cliffs are lower (e.g.,Fig. 6). Inland exposures provide information on the more southand westerly part of the basin but, though footprints are known(Romano and Whyte, 2003a) (Fig. 1), these sections seldomprovide the same quality of information as those on the coast.

THE ICHNOFAUNADinosaur footprints were first definitely recorded from the

Cleveland Basin in the early nineteenth century (Brodrick,1907; Hargreaves, 1913), but the abundance and diversity of thevertebrate ichnofauna of this megatracksite has only recentlybeen appreciated (Romano and Whyte, 2003a, and referencestherein) and continues to be documented and researched. Inparticular, on-going morphometric studies are seeking to refine

FIG. 3. Lithostratigraphy and chronostratigraphy of the Middle Jurassic(Aalenian to Bathonian) rocks of the Cleveland Basin (modified from Romanoand Whyte, 2003a, fig. 24). Marine units are shaded and the vertical linesindicate the principal hiatuses. Three sediment prisms at the base of the ScalbyFormation are indicated with roman numerals, see text for explanation.

and, if necessary redefine, the footprint morphotypes recognizedby Romano and Whyte (2003a) and to compare these withichnotypes recognised and described elsewhere. The Yorkshiremorphotypes (Romano and Whyte, 2003a) were divided amongthree Groups, namely quadrupedal forms (Group A), tridactyl

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FIG. 4. Stratigraphical log of the basal part of the Saltwick Formation, Rail Hole Bight, 700 m east of Whitby Harbour, showing print morphotypes and sourcehorizons (modified from Romano and Whyte, 2003a, fig. 23, column A). The position of the measured section is indicated in the photograph. Note also in thephotograph the channel deposits developed in the upper part of the Saltwick Formation above the logged section and below the Eller Beck Formation, which is thehighest solid rock unit in the cliff. There is a capping of Quaternary boulder clay which makes up the bevelled part of the cliff.

prints (Group B) and a behavioural group of swimming tracksand trackways (Group C).

The quadrupedal dinosaurs include four distinctive printmorphotypes (Ai to Aiv) that have been associated withsauropod dinosaurs (Fig. 7) (Romano et al., 1999; Romanoand Whyte, 2003a). These include morphotypes that have beencompared with the ichnogenera Brontopodus and Breviparopus.The former ichnogenus has been linked with brachiosaur

sauropods, while the latter may indicate a non-brachiosauridsuch as Cetiosaurus. However, the preservation of sauropodprints (Romano and Whyte, 2003a; Romano et al., 2006) is suchthat the vast majority of sauropod tracks cannot be definitelyassigned to any one of these morphotypes and consequentlythey are here considered as a single group. In contrast,the remaining quadrupedal dinosaur morphotype (Fig. 7)is sufficiently distinctive (Whyte and Romano, 1993, 1995,

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FIG. 5. Stratigraphical logs of the Gristhorpe Member, Cloughton Formation,Ravenscar Group at Yons Nab and at Cloughton, showing lithological featuresand print horizons. Key as in Fig. 4.

2001; Romano and Whyte, 2003a) to have been describedas a new ichnogenus and ichnospecies, Deltapodus brodrickiWhyte and Romano, 1995, whose maker has been identified as aprimitive stegosaurian (Whyte and Romano, 2001). To these twodinosaur types may be added another quadrupedal vertebratetype—namely, the walking prints of crocodilians (Romano andWhyte, 2003a) (Fig. 7).

Tridactyl dinosaur prints (Group B of Romano and Whyte,2003a) are widely distributed throughout the sequence. How-ever, because many are seen only as transmitted prints inoblique sections or as partial specimens, the majority cannotbe definitely ascribed to particular track types. Neverthelessit has been possible to recognise 17 morphotypes within this

Group (Romano and Whyte, 2003a). One of these (Bxvii,Romano and Whyte, 2003a) is most probably a manus print,but the others, together with an additional more recentlydiscovered morphotype (morphotype Bxviii, Fig. 8), are pesprints of bipedal dinosaurs. Preliminary results of multivariateand morphometric analysis indicate that these morphotypes maybe clustered into a number of categories and subcategories (Fig.8) within a broad spectrum. One category consists of prints,which tend to have relatively robust broad digit prints and to beat least as broad as they are long (Fig. 8). The five morphotypeswithin this category (Bi, Biii, Biv, Bx and Bxvi, Fig. 8) showa wide range in size and, though it is not clear how manyichnospecies are represented, it is possible that there are someontogenetic variants within the category. Similar prints havebeen attributed to herbivorous ornithopod dinosaurs (Moratallaet al., 1988, and references therein). A second category consistsof prints in which the length is normally slightly greater thanthe width, the digit prints are narrow and the outer digits(digits II and IV) may be offset from each other where theyconverge in the heel (Fig. 8; Bii, Bv, Bxii and Bxviii). Inthis latter character particularly, some of the morphotypes inthis category resemble Eubrontes and related footprint typesin the Anchisauripus-Grallator series and like these may beattributed to carnivorous theropod dinosaurs (Moratalla et al.,1988; Thulborn, 1990, and references therein). Size differencesbetween morphotypes may again be at least in part ontogeneticbut might also reflect niche partitioning (cf. Farlow and Pianka,2002). The largest morphotype in this category (morphotypeBxviii) has only been recognized recently and is the largesttridactyl print type to be recorded from the Ravenscar Group. Itresembles in both character and size large prints from Bathonianlimestones at Ardley Quarry in Oxfordshire (Day et al., 2002,2003), which have been attributed to a theropod and tentativelylinked with Megalosaurus. Such large theropod prints hadpreviously been thought to be absent from the Cleveland area(Romano and Whyte, 2003a). The third category is made up ofprints which are small (generally less than 15 cm pes length,maximum pes length of about 20 cm) and are gracile with digitswhich are relatively elongate and narrow (Fig. 8; Bvi—Bix, Bxi,Bxiii—Bxv). This category contains four sub-categories. Oneof these is dominated by the prints included within morphotypeBix, which show an isometric relative growth relationship (Fig.9). Linked to this may be the morphotypes Bxiv and Bxv which,like Bix, have curved terminations to lateral digits but differ frommorphotype Bix principally in having more divergent digits(Figs. 8, 9). Though they do not plot close to the relative growthline (Fig. 9) they may be preservational variants of the Bixmorphotype. Morphotypes Bxi and Bviii are united in a separatesub-category by their showing elongation of the posterior of theprint into an extended heel (Bxi) or metatarsal imprint (Bviii)(Fig. 8). Though morphologically distinct they are probablypreservational or behavioural variants of other small graciletypes; the type of morphotype Bxi might, for instance, linkwith morphotype Bix (Fig. 8). A third sub-category links

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FIG. 6. Outline map of the foreshore of Scalby Bay between High (HWM) and Low (LWM) Water Marks. Outcrop sectors (A to D) of the top of Prism III(lower Long Nab Member) in the upper foreshore are shown together with the breaks in the exposure of this unit. The pie charts show the composition of thevertebrate ichnofauna in the corresponding sector. The boundary between large and small tridactyl prints is taken at a print length of 20 cm. The length of theoutcrop is indicated in the photograph (A–D). The cliffs in this area are largely made up of boulder clay with small outcrops of the lowest parts of the upper LongNab Member (Level-bedded Series) at the base.

morphotypes Bxiii and Bvii, which have rounded heel areasthough differ in the lengths of digit III (Fig. 8). The finalsub-category contains only the single morphotype Bvi, whosedigits are different in proportion from and less divergent thanother smaller gracile forms.

There are several morphologically similar groups of smallornithopods and theropods with which the prints in thesesub-categories might be linked. Whyte and Romano (1981)suggested that the type specimen of morphotype Bix mighthave been made by a small ornithopod, but the presence of claw

imprints on the digits in this form and also in morphotype Bvicould indicate that these are theropods (Romano and Whyte,2003a). However claw or claw-like features can be producedor exaggerated during print formation and preservation (DrS. Jackson, pers. comm.). It is hoped that the on-goingmorphometric studies will help to resolve this situation, whichhas important implications for understanding the compositionand relative abundance of the herbivore and carnivore guildswithin the fauna. The upper size limit (c. 20 cm) of the smallgracile types allows a useful distinction to be made between

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FIG. 7. Morphotype Group A (quadrupedal) prints and putative makers. Top sauropods and below (left) stegosaurian and (right) crocodilian prints. The printsare all drawn to the same scale (vertical bar) except for Avi whose scale is separately indicated and is five times larger. The silhouettes are all drawn to the samescale (horizontal bar).

large and small prints even in prints which cannot be assignedto a particular morphotype (see below).

The final Group (Group C, Romano and Whyte, 2003a)consists of prints that are morphologically distinguished moreby the maker’s behaviour than by its anatomy. These are theraking prints formed by the swimming activity of dinosaurs(morphotypes Ci to Ciii, Romano and Whyte, 2003a; Whyteand Romano, 2002), crocodilians (morphotypes Civ to Cvi,Romano and Whyte, 2003a) and pond tortoises (morphotypeCvii, Romano and Whyte, 2003a) (Fig. 10). With the exceptionof pond tortoises whose walking prints have not yet beenpositively identified, the other swimming track types probablyhave equivalents in the other morphotype groups. A singleexample of Undichna, the swimming trace of a fish has alsobeen recorded (Romano and Whyte, 2003a) (Fig. 10).

The combined vertebrate fauna of the Ravenscar Groupthus consists of at least two sauropods, a primitive stegosaur,megalosaurid and other theropod dinosaurs and both large andsmaller sized ornithopod dinosaurs together with crocodiles,

pond tortoises and fish (cf. Romano and Whyte, 2003a,fig. 27).

PROBLEMS OF TRACK DISTRIBUTIONThe Ravenscar Group represents a relatively short time

interval (<10 Ma), but the environmental variations, whichcharacterise it, make it imperative that the ichnofauna and itsdistribution in time and space be examined as closely as possiblein order to shed light on the vertebrate communities and on theirstructure, environmental control and evolution.

Fundamental to this process is the detailed logging ofsuccessions and documentation of their print-bearing horizons.In the lower part of the Saltwick Formation at Jump DownBight near Whitby (Fig. 4), for instance, several print-bearinghorizons with different vertebrate ichnofaunas have beendocumented by compiling data from measured sections togetherwith information from fallen blocks (for further details seeRomano and Whyte, 2003a). At each horizon (Figs. 4, 11)

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FIG. 8. Morphotype Group B (tridactyl) prints showing their tentative clustering into categories and sub-categories and a putative maker of a print type in eachcategory. Top ‘ornithopod,’ center ‘theropod’ and below ‘small gracile’ print categories. Prints are drawn to the same scale (vertical bar) and the silhouettes arealso drawn to a common scale (horizontal bar).

FIG. 9. Scatter diagram showing plots of footprint width (W) against footprintlength (L) for specimens of Morphotype Bix. The types of morphotypes Bix,Bxiv and Bxv are also plotted.

the morphotypes represent local populations of the vertebratefauna and the different compositions may reflect, at least in part,environmental and behavioural control of the faunas. However,in a laterally variable sequence such as that of the RavenscarGroup, no single succession can be entirely representative.Though one of these horizons, the ‘Unio Bed’ (Fig. 4), may betraced up to 4 km to the south-east (Hemingway, 1974; Romanoand Whyte, 2003a), another, the “Swimming Bed” (Fig. 4), diesout laterally in both easterly and westerly directions within afew hundred metres of where the section was logged (Romanoand Whyte, 2003a). More problematically the coeval sections atPort Mulgrave, 12 km to the northwest, are entirely made up ofstacked channel sandstones. These latter beds contain importantvertebrate ichnofaunas (Romano and Whyte, 2003a) that includemorphotypes not found in the lower Saltwick Formation atWhitby (Fig. 11) and which lack some of those morphotypesfound at Whitby (Fig. 11). However these ichnofaunas cannotat present be related in stratigraphic detail with those at Whitbynor placed along with other ichnological data in a meaningfultime or rock sequence framework.

A further graphic illustration of the problems caused byspatial and temporal heterogeneity within the succession isprovided by comparing sections of the Gristhorpe Member atYons Nab and at Cloughton Wyke (Fig. 5). The former localitylies to the east of the Peak Trough (Fig. 1) and the successionhere (Fig. 5) is only half as thick as that at Cloughton (Fig. 5),which lies 13 km north-west within the narrow zone of the

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FIG. 10. Morphotype Group C (swimming) prints and their putative makers. Showing from left to right dinosaur, crocodilian, pond tortoise and fish traces. Theprints are drawn to the same scale (vertical bar). The horizontal scale bar is the common scale for the silhouettes.

FIG. 11. Chart showing distribution (presence-absence) of vertebrate tracks from the Middle Jurassic Ravenscar Group of the Cleveland Basin. The upper partshows the distribution of the ichnofauna of the lithological subdivisions of the Ravenscar Group. The lower part of the chart shows the ichnofauna of selectedhorizons or localities discussed in the text. The marine lithostratigraphic units are shaded.

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trough (Fig. 1). At Yons Nab the local ichnofaunal populationsinclude a horizon with both Deltapodus and theropod prints andothers with both large and small tridactyl prints including thetype for morphotype Bvii (Figs. 5, 11). Neither the sedimentarysuccession nor the ichnofaunal assemblages can be correlatedin detail with the sequence at Cloughton (Figs. 5, 11). Herethe most obvious print bearing horizon is provided by sauropodprints made in an impure coal and infilled with white sandstone(Fig. 5). Small tridactyl prints and an Undichna trace havealso been found on loose blocks which appear to have comefrom the sandstones below the sauropod print horizon. Againbecause of the lateral variation and its attendant correlationproblems it is difficult to integrate the data from the twolocalities within a single time frame. The apparent greaterrelative abundance of print-bearing horizons at Yons Nab maybe a function of relative sedimentation rates at the two localitiesand of there being more and longer breaks in deposition at YonsNab.

The sedimentary facies variation is also compounded by aspatial heterogeneity in the ichnofauna and this problem isexacerbated by the fact that at most localities and horizonswithin the Cleveland region the nature of the outcrop is such thatit is only possible to sample a relatively small area. Thus withinthe Saltwick succession at Whitby (Figs. 4, 11) the absence ofsauropod prints or of Deltapodus from a particular horizon maybe in part a sampling deficiency as much as the manifestationof behavioural or environmental control. One of the few unitsthat can be followed over a reasonably-sized area is Prism IIIof the Scalby Formation (Fig. 3) within its outcrop from ScalbyNess to Long Nab. Here the cross-bedded and cross-cuttingsandstone sets of Prism III, also referred to as the meanderbelt or exhumed meander belt (Alexander, 1987, 1992b; Nami,1976), are well displayed on the foreshore. The laterally accretedunits show many disturbances made by dinosaurs moving oninclined slopes. These have in the past been described as squelchmarks and ascribed to soft sediment deformation (Alexander,1987). Though some de-watering structures are present, mostdeformations show clear evidence of having been made bydownward push from above and of down-slope movement ofsediment. These structures appear to have been made by largerbipedal dinosaurs though some sauropod prints may also bepresent. In places the top of cross-bedded units appears tohave been homogenised by extensive dinoturbation and theirappearance is dominated by a vertical, columnar-like jointing.Elsewhere the uppermost part of Prism III shows palaeosolfeatures and, in the upper foreshore of the Scalby Bay area,provides a unique chance to map the distribution of prints withinthe top 1–2 m of the unit along a 1.1 km transect (Fig. 6). Theoutcrop along this transect is not continuous but is naturallybroken into a number of sectors by modern beaches or bychannel sandstones cutting down from a slightly higher levelwithin the upper Long Nab Member ( = Level Bedded Seriesof Black, 1929) (Black, 1928). A striking feature of the sectorsis that even at a fairly crude level of identification they each

show different abundances of different print types (Fig. 6). Thusin some sectors (sectors A and B of Fig. 6) sauropod printsdominate while in other areas they may be absent and tridactylprints are dominant (sectors C and D of Fig. 6). The sauropodtrackway, illustrated by Romano and Whyte (2003a, fig. 26),lies in sector A and other transmitted sauropod prints from thissector are illustrated in Romano et al. (2005, fig. 15). The deeptransmission of these sauropod prints may well have destroyedearlier smaller prints and this may bias the relative faunalabundances (Fig. 6). The apparent absence of non-sauropodsin sector B might also result from this effect. Sector C includesthe well-known Jackson’s Bay Trackway (Romano and Whyte,2003a; Rawson and Wright, 2000), which provided the typefor Morphotype Bi (Romano and Whyte, 2003a) (Fig. 8). Thisis the largest of the possibly ornithopod print types (Fig. 8).Recent movement of modern beach sands adjacent to this trackprovided a temporary view of a trackway of a small dinosaurbelonging to morphotype Bix; one of the few smaller prints inthis sector that can be assigned to a definite morphotype. Theprint assemblages on this transect represent local populationswithin a local community. Though, because of preservationalbiases, they may not simply reflect the relative proportions of themakers within these communities they clearly indicate spatialheterogeneity within their occurrence. Such heterogeneity isalso evident in modern terrestrial print assemblages (Cohenet al., 1993).

EMERGING PICTUREResolution of the problems outlined above may not be

straight forward but, in the interim, a simplified approach can betaken by using the established stratigraphy and its subdivisioninto marine and nonmarine units. Thus the overall ichnofaunaof each of the lithostratigraphic units can be examined andcompared and contrasted with those of other units (Fig. 11).At this level the ichnofauna of units is more representative ofand comparable with metapopulations and metacommunitiesof modern ecological terminology (Hanski and Simberloff,1997; Hanski, 1999; Holt, 1997) or with their temporalequivalents, which might be termed chronometapopulations orchronometacommunities.

The distribution chart thus assembled (Fig. 11) shows therelative dearth of clearly identifiable prints from the CloughtonFormation. This may be partly due to this formation being lessexposed and less accessible than other parts of the RavenscarGroup and having thus received less attention, but may alsoinvolve environmental factors including those discussed abovefor the Gristhorpe Member. A further feature is the occurrenceof prints within some of the marine units (Fig. 11) and, asnoted by Romano and Whyte (2003a), this emphasises that thedistinctions between marine and nonmarine are not as simpleor clear-cut as the lithostratigraphic subdivision would imply.Hints of marine influence within parts of the nonmarine unitshave been suggested on sedimentological (Eschard et al., 1991),

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palynological (Hancock and Fisher, 1981; Fisher and Hancock,1985) and invertebrate trace fossil (Livera and Leeder, 1981;Romano and Whyte, 2003b) evidence.

More importantly, the presence-absence distribution (Fig. 11)shows that there is a strong similarity between the quadrupedaland tridactyl ichnofaunas of the Saltwick Formation and those ofthe upper Long Nab Member. Thus the vertebrate groups withinthe chronometacommunities represented by these ichnofaunasare very similar or have at least not evolved sufficiently forchanges to be detectable from the ichnofauna.

This result can be contrasted with the distribution ofswimming morphotypes (Group C), which show a distinct strati-graphic differentiation and, with two exceptions, are confined tothe Saltwick Formation (Fig. 11). Surfaces, which are heavilybioturbated by swimming dinosaurs or crocodilians (Fig. 12),are also confined to the Saltwick Formation. This behaviouralpattern suggests that extensive surface water habitats were morefrequently developed and more persistent during the depositionof the Saltwick Formation than at later times. Interestingly,charcoal abundances suggest that the climate of the upper partof the Ravenscar Group was more seasonally arid than in thelower part (Morgans et al., 1999). However, even in the upperLong Nab Member, the preservational features of footprintsshows that they were made in soft and waterlogged sediments(Romano and Whyte, 2003a; Dr S. Jackson, pers. comm.). Whilethis may reflect a marked bias in preservation it indicates thatthere were, even in this part of the sequence, wet intervals orhabitats.

The ichnofaunal similarity between the Saltwick Formationand the upper Long Nab Member can also be qualified in anumber of ways. Firstly there are some differences betweenthe tridactyl ichnofaunas of the two units. Some of these maybe more apparent than real. Thus morphotype Bxv, which isabsent from the Saltwick Formation, is only recorded fromthe Long Nab Member by a single specimen. However itmay be more significant and reflective of the environmentaldifferences between the units that the largest ornithopod (Bi)and theropod (Bxviii and Bii) morphotypes are not found in theSaltwick Formation while the smallest morphotypes (Bxvi andBxii) of these two categories are confined to it. Second, evenwhere morphotypes are present in both lithostratigrahic units,their abundances may differ. Deltapodus (morphotype Av), forinstance, is more common in the Saltwick Formation than inother parts of the Ravenscar Group (Fig. 13). This could bedirectly related to the climatic changes within the sequence(Morgans et al., 1999) or may be an indirect effect linked tochanges in vegetation or sedimentary facies. The pes printsof Deltapodus show, like those of morphotype Bix (Fig. 9),an isometric relative growth relationship between pes lengthand width (Fig. 13). The data (Fig. 13) does not howeverindicate any significant size or shape differences between thestratigraphic units. A feature of this distribution is that there isa dearth of footprints smaller than 25 cm long (Fig. 13). Whilepreservational factors will have a role in this it is nevertheless

FIG. 12. Swimming dinoturbation on the base of a loose block of sandstone.Note the strong alignment of traces parallel to the 10 cm scale bar. SaltwickFormation, c. 50 m east of East Pier, Whitby.

difficult to explain since other small (<25 cm long) dinosaurprints are preserved (e.g., Fig. 9). One possibility is that theDeltapodus maker spent the early part of its life outside thebasin and only entered the basin as it matured and perhapseven then only during wetter intervals or seasons. Migratoryhabits may also have affected other elements of the fauna,such as morphotype Bix (Fig. 9) and the sauropods, in whichthere is also a lack of small (juvenile) footprints. Intenselydinoturbated horizons, which might have been produced bysauropod herds are known (Romano and Whyte, 2003a), butthe way in which they are concentrated below some of themarine horizons suggests that other factors such as higherwater tables and reduced sedimentation rates may also bea factor in their occurrence. Isolated sauropod tracks showthat they did not spend the whole time in closely aggregatedherds.

128 M. A. WHYTE ET AL.

FIG. 13. Scatter diagram showing plots of the footprint length (L) against footprint width (W) for 46 specimens of Deltapodus brodricki Whyte and Romano,1995. Specimens collected from the Saltwick, Cloughton and Scalby (Long Nab Member) Formations are indicated and the pie chart shows the proportions ofspecimens from these three lithostratigraphic units. Modified from Romano and Whyte (2003a, fig. 22) with additional data.

CONCLUSIONSBecause of the abundance of its vertebrate tracks and track

bearing surfaces the Cleveland Basin has been recognised as amegatracksite (Romano and Whyte, 2003a). However, as hasbeen demonstrated, the study of these tracks presents manydifficulties linked to the nature of the outcrops, to the characterof the sequence and its lateral facies variations and to thepreservation of tracks and trackways.

Preliminary results indicate that there is a diverse ichnofaunathat is remarkably constant throughout the 10-million-yearinterval represented by the sequence and points to constancyin the vertebrate metacommunities of this time (Aalenian—Bathonian). The detailed occurrence and abundance of partic-ular print morphotypes and the behaviour of their makers is,however influenced by environmental factors, which appear toinclude climate, water levels and sedimentary environments.Possibilities of niche partitioning, herding and migratorybehaviour deserve to be further considered especially as someof these aspects can only be deduced from the ichnofaunalevidence.

The constancy of the overall ichnofauna needs to beconstantly reviewed and reconsidered in the light of new data,but opens up new potential in the ongoing study of thesefootprints and vertebrate communities in the Cleveland Basin,including a more facies-based approach.

ACKNOWLEDGEMENTSThe authors would like to thank all the many people who

have taken an interest in their work and who have in many casesassisted in the field and helped to build the data on which this

paper is based. In particular the authors are very grateful for thesupport of Earthwatch, both for its generous financial supportand for the many enthusiastic volunteers who have taken partin our projects. We thank Simon Jackson for his comments andpractical assistance, and Jim Booth and other past and presentmembers of the Sheffield University Dinosaur Track ResearchGroup. Technical help from Paul Coles, Rob Ashurst and BarryPigott is gratefully acknowledged.

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