Dinosaur Footprints from the Dakota Group of Eastern Colorado L

Dinosaur Footprints from the Dakota Group of Eastern Colorado l

Martin G. Lockley 2

ABSTRACT Dlnosaur footprlnts f rom the Dakota Group In eastern Colorado are known from at least eight different locations buta re essentially undocumented, andu nprotected. Detarleda nalysis reveals t hat trackways from two sites rnclude front foot (manus) ~mpression so f ornithopods, which are probably the most drstrnctrve yet described The tracks shed l ight on the morphologya nd g ait of large ornithopods, which were probably o f iguanodontid affinity The tracks can be assrgned to the ichnogenus C arir~chn~u wmh ich also occurs in South Amerrca The lack of skeletal remarns ~n th e Dakota Group and the good quallty of many tracks suggests that footprlnts should be examined more care- fully for the useful p aleoecologic census rnformation they provrde In s ome cases they may be used for local stratr- graphic correlation.

lN TRODUCTION D~nosau fr ootprlnts are well known from the Dakota Group in the v~clnit yo f Denver, Colorado (Markman, 1938 and 196 1; McKenz~e ,1 968 and 1972; Chamberlain, l976a and 1976b; Lockley, 1985a, l985b, l986a and 1986b) but they have never been studled in any detall. In fact they have been subject to the worst vandal~sm min flicted on any dmosaur tracks In the state. S~m~lar loyc,c urrences elsewhere in the state (Flg 1) are virtually undocumented desp~t eth e fact that tracks and trackways from Lamar and Baca countles are on display ~n nt he Denver Museum (D.M N H. #1608, Reinhe~me ,1 939; and D.M.N H #I7 724 re- spectlvely). The purpose of this paper is therefore to prov~d ea thorough account of the available trackway information and consider ~t si m pllcat~ons .It IS also poss~bl eto compare the Colorado data wlth other recently descr~be dtr acks from the Dakota Group of New Mex~c o( G~llett ea nd Thomas, 1983 and 1985; T homas and G~llette ,1 985) and contemporaneous (Apt~an-Albian )tr acks in Brazll (Leo- nard~ ,1 984a and 1984b), Canada (Currle, 1983; Currle and Sarjeant, 1979) and elsewhere. The recent resurg- ence of interest in dinosaur footprlnts from Colorado (Lockley, 19 84a, 19 84b, l985a, l985b, l986a, l986b, 1986c; and Lockley et al, 1983) and elsewhere In the Rocky Mountain region (Currle, 1983; Mossman and Sarjeant, 1983) is mdicatlve of their value in providing useful rnor- phoiogical, behaworal and paleoenv~ronment ael vidence wh~c hh as been overlooked in the past. In this context, Dakota footprints from the Alameda local~t ya re partlcu- larly significant because they include one of the best sets of ornithopod ( ?iguanodont m anus ( front foot) impress~on yet described. Another distinctive manus track from the Lamar trackway IS also considered to represent an iguanodont~d ,a s are several other pes (hind foot) tracks from localities in this same area.

'M Manuscr~p recelved S eptember 10. 1986. revrsed May 20. 1987. accepted May 27. 1987

'~eologyD epartment Un~vers~otfy C oloradoa t Denver, 1100 14th St. Denver. CO 80202 The Mountarn Geologrst Vol 24. No 4 (October, 1987) p 107-12 2 I I l. . - .- -.-.-. - .- -- -.-.- - - -.-. -..-.- --.- -1.. . ,.-.-., .-.-.-.-. . i a i I ;!f 1* . 1!I

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4 lSOLATED TRACKS ONLY I!!I () TRACKWAYS OR MULTIPLE TR A C K W A Y S !

Figure 1. Location of dinosaur track and trackway srtes rn the Dakota Group of Eastern Colorado and NE New Mexico.

Historical Background In 1866, Mudge reported tracks from the Dakota Group of Kansas (see Mehl, 1931 for stratlgraph~ cd es~gnation) Th~ swa s evidently the first report of ?dinosaurIan tracks In the western USA. These so called "ornithichnites" (bird tracks), indicate sizes and digital divarication angles qu~t different from known blrd tracks of this age (Mehl, 1931). Since 1866, the Dakota Group has yielded tracks In many regions (Snow, 1887; Branson and Mehl, 1932; and others) thus llvlng up to the early Indications of a great ~chnolog ical potential. In Colorado, Mehl (1931) described a re-

ROCKY MOUNTAIN ASSOCIATION OF GEOLOGISTS

MARTIN G LOCKLEY Figure 2. DfotMrifoe raonndro tk oahsmfefta rpeua rnfrro o M'gostr catoreKprceisrkignnssitznio f ilareonlo . c bmm1aula9 tit7 pthri2 eeon.sa f Aa:dt nrslvaaedecm erCkt eiewhndansaatmely yAstb lv CNeee)rlofn atf o uror1ne u.sa trln1 ot#u9dc4a7 a2t l6r rranotas yn at sr wonaecfdee t ksnh1wt re9 naos7 y f1e6 D9 6Nlo3)eoc 8Sn a.ve1H tere. oreI F.nn nAi sAg hu i ) iumsnmr erubae ne5iln prafe outtrrdrboal d tncrresa ktthcowaek oialdssuy font rcbofo rettmoraeap rsrc ii onkhgfgweh b a atee tyxldosspsl o.eo I 1mfsn taus eiennraetd t s 8h 2tuoe)r ( se msdhdoioro uetwdhtcihse fsopra coern bitehtwopeeond sr ig(bhlta acnkd) alenfdt t rcoaecklusr soshoauwnrs h (ewrher btee)t ween the dotted lrnes Rose diagram shows trackway orientations ROCK Y MOUNTAI N ASSOCI ATION N O F GEOLOGIST ©2005 The Rocky Mountain Association of Geologists DI NOSAUR FOOTPRI NTS, EASTERN COLORADO Figure 3. Attemptedphotographic benchmark showing the Alameda road cut exposures in 1938 ( July 1 1th) and 1984. Both photographs taken about 0.45 (0.72 km) north of hairpin turn which cuts through hogback. Coincidentally, the recent photograph (below) shows the Dakota Sandstone sign.

110 MARTIN G. LOCKLEY markable set of bird t racks (Ignotornis m cconnelli U.C.M. 17614) and the tracks of a Uquadruped w lth webbed feet" (Walteria jeffersonensrs) wh~c h e claimed "seems to compare favorably w~t hs ome of the A~g~alosaurida be~n g"w ell on the way to complete aquatic adaptation" In the same year, Johnson (1931, p. 360) referred toUdlno saur tracks in the upper Dakota at Bear Creek water gap just east of Morrison." In 1938, Markman briefly d escribed two dinosaur trackways discovered along the Alameda highway west of Denver. He publ~she da s~mpl es chemat~ c"m ap" using the terms "Alameda No. 1 and No. 2" for the "respective trails" of a larger (48 cm) and a smaller (25 cm) b~peda form (F~g .2 to 4). Neither of these trackways now remains although "a preservative was apphed to the trackway (No. 1) nearest the roadside" and plaster casts and photographs were obtained (Markman, 1961, p. 17). Markman (19 38) noted that trackway No 2 "was not so treated and deterioration of the lmpresslons soon became apparent." In 1945 he wrote on the cast labels that the "originals" were "about destroyed by weathering. Denver Museum archwe photographs, some of which are produced herein (Figs. 3 and 4), show that the outcrop has deter- iorated significantly since 1938 and that the original trackways originated from the higher strat~graph ~hco r~zon exposed at that time. Markman was correct In predicting that "valuable fossil ev~denc em ay be destroyed at any t~me" ;h owever, although trackway No. 1 1s now lost, some of the tracks described herem do appear to include forms resembling Markman's type 2 and they probably originate from the same general locality whch Markman, in his unpublished notes, described as "0.45 mdes north of hairpin turn which cuts through hogback." Th~ sw ould put the outcrop toward the northern end of the ex~stin ge xposures near the present Dakota Sandstone sign (Fig. 3). The following year Reinhelmer( 939) reported that the Denver Museum "obtained a port~o nof (a) t rackway" f rom a Dakota sandstone local~t yo n Willow Creek" a few miles south of Lamar" in southeastern Colorado. The specimen (D. M. N. H. #11608) comprises "a sequence of nine footprints" seven of which are currently on display (Figs. 5d and 6a). Reinheimer (1940) reported that the series of tracks had "been util ized as a floor for the Trachodon skeleton" and that "although the tracks are geologically older than Trachodon, and not pertain~n gto that genus, ~ is apparent that the impressions were made by an animal of approximately the same size and having a similar type of foot." A few additional Dakota footprint casts from southeastern Colorado were donated to the Denver Museum between 1942 and 1976, and tracks contmue to be discovered in the Front Range area, as for example at Turkey Creek(John Warme, personal communication, 1985) and near Boulder (Betty Ann Clark, personal commun~cat~o 1985). In recent years the Alameda trackways have been mentioned in the context of depositional environment re- construct~on sp roposed by McKenzie (19 68, 197 1 and 1972) who photographed the whole sect~o n(1 9 72, Fig. 4), designated the presently exposed trackbearing beds as unit number 2, and interpreted this upper part of the South Platte Formation of the Dakota Group as a tidal flat (McKenzie, 1972, Fig. 2). Weimer and Land (19 72) inter- ROCKY MOUNTAIN ASSOCIATION OF GEOLOGISTS preted the log and root beds as ev~denc eo f a mangrove swamp. Chamberlain (19 76a and 1976b) subsequently confirmed this depositional environment interpretation by describing the dist~nctiv e" nearshore" assemblage of trace fossils from this, and the overlying unit number 1. He also referred to the trackway locations again and recently (Chamberlain, 1985) prov~de da reconstruction showing a trackway following the bank of a t~da aclh annel. Tschudy et a1 (19 84) have also made a valuable contrl- bution by Identifying the first appearance of Nyassapol- len~te sa lbertensis about 20 m below the track bearing beds. This palynomorph consistently appears "at or very near the Albian-Cenomanian b oundary". The current study (Lockley, l984b, l985a, 1985b, l986b and 1986~ h)a s focused specif~call yo n the dinosaur tracks, which have never been studied in any detail. In addition to the fewfootprints exposed alongside the Morrison road, about 3 km south of the Alameda locality (Johnson, 1931), and at Turkey Creek (John Warme, personal communication, 1985), Dakota Group dinosaur tracks are also known from MehI's bird t rack locallty north of Golden, in the vicinity of Deadman's Canyon, southwest of Colorado Springs (see Fig. 4) and from the vicinity of Boulder, Colorado. In the latter area no tracks remain in situ although at least one float specimen is known (Betty Ann Clark, personal communication, 1985) and one natural cast and two plaster replcas are preserved in the museum collection (Fig. 5b). Collectors removed the Boulder tracks (J. Rohner and P. Robinson, personal communication) as has been done at the Alameda locality (see Fig. 2a). The only other Dakota Group trackway in eastern Cole rado, currently known to the author, is in exposures at a water gap southwest of Canon City. Although these are unusual ovoid traces which cannot be assigned to a known group of trackmakers, several present an interesting cross section somewhat reminiscent of the "hoof-print structures in beach sand" described by Van der Lingen and Andrews (19 60). The wide and irregular spacing of these traces could suggest the activity of a partially buoyant animal (Ed Stover, personal communication; cf. Currie, 1983).

The Vandalism Problem The Alameda tracksite has suffered greater vandalism over the years than any other known t racksite in C olorado. As shown in Figure 2a, at least seven tracks have been chiseled out while another three have been partially damaged by collectors. In addition during the course of this study three tracks were obscured by plaster, by persons unknown, in unsuccessful attempts to obtain casts. As the sandstone is porous, casting materials can only be used once adequate precautions are taken to as- sure separation of thecasts. Ideally a preservative s hould be applied before casting with latex, silicon rubber or some other suitable compound. Removal of individual tracks is undesirable for several reasons. Besides accelerating erosion, such activities destroy valuable scientific information including step, stride, pace angulation and rotational dimensions, as well as preventing hip to shoulder length (orglenoacetabular) estimates. Even though individual tracks have often b een

Dl NOSAU R FOOTPRINTS, EASTERN COLORADO

Figure 4. A) Photograph of trackway designated as No. 1 by Markman, taken July 1 1, 1938. Tracks 9- 12 in the sequence are left of picture (also see Figs. 2b and 5f). B) Photograph of trackway designated as No. 2 by Markman, taken July 11, 1938, showing the first five tracks in the sequence (also see Fig. 2b). Evidently the tracks in both pictures were painted before they were photographed. (See text for details of scale.) C) Small tridactyl (coelurosaur) track from the Alameda exposure (see Fig. 2a); length 2 1 cm, width 18 cm. D) Larger tridactyl (coelurosaur) track from the Alameda exposure (Fig. 2a); length 28 cm, width 25 cm. E) Right pes and manus (above) of ornithopod trackway A from Alameda locality (see F ig. 2a and 5a); pes length 34 cm, width 32 cm; manus length 12 cm, width 11 cm. F) Cast of ?ornithopod tracks from Morrison Road outcrops south of Alameda (see Fig. 5g for outline of prominent cast); length and width approximately 30 cm. G) Casts of tridactyl tracks from near Deadman's Canyon southwest of Colorado Springs. Lower track by small tape measure has a length and width of about 32 cm, the more prominent upper track is about the same.

112 MARTIN G. LOCKLEY removed from various localities, few sites have been damaged or neglected as much as the Alameda site. This s~tuatio nis regrettable and we hopet hat eff orts to improve public awareness will lead to preservation, (Martin, 1986; Lockley, 1986d; Stich, 1986). The history of deterioration or destruction at known track localities necessitatest he documentation of existing sites before further search is undertaken. Reinheimer (19 39) observed that the Lamar trackway representsUthe third series of footprints from thls horizon to be found in eastern Colorado during recent years." His observation suggests other trackway sites exlst in the Dakota Group of Colorado, possibly in Baca County, where there is no shortage of material.

Dakota Group and Equivalent Tracks in Other States Dinosaur tracks are also reported from the Dakota Group in New Mexico (Gillette and Thomas, 1983 and 1985; T homasand Gillette, 1985) A rizona(Gries, 1962 ~ n Weishampel a ndW eishampel, 1983), i nthe time equivalent Lakota Formation of South Dakota (Anderson, 1939) and in the time equivalent Gething Formation of British Col- umbia(Currie, 1983). T hey arealso known from the Dakota Group of Kansas (Mudge, 1866; Snow, 1887), Wyoming (Branson and Mehl, 1932), Arizona and Utah (Jim Kirk- land, personal communicat~on .T he Denver Museum Ar- chives contain an historic photograph of Dakota tracks from Kansas which was sent to Markman by C. M. Stern- berg. McAllister (19 86) and Lockley (19 86b) report similar trackways from this region.

THE PRESENT STUDY Despite the loss of information through weathering and vandalism, trackways are still recognizable and mapable at three adjacent locations alongside Alameda road (Fig. 2c). The existing tracks provide valuable information not alluded to in Markman's brief descriptions (19 38); however, his records in the Denver Museum Ar- chives provide useful and reliable data to supplement the present account. Since Chamberlain (19 76a and 1976b, Fig. 3) described the trace fossil assemblages from this locality, it is possible to view the track bearing beds in their proper stratigraphic and depositional environment context. The Lamar trackway slab(D.M.N.H. # 1608) also bene- fits from a proper description and can be compared in several respects with the Alameda material (Fig. 5). Sim- ilarly, other material from southeastern Colorado sheds light on the overall picture. In all cases, available trackways were photographed, measured and mapped in detail using brunton and tape or tracing paper overlay (Figs. 2 and 5).

The Alarneda Parkway Locality Single short trackway segments occur at the two northern localities shown by Chamberlain ( 1 9 76a and 1976b, Fig. 3). The northernmost one (Fig. 5c herein) was made by a large biped a bout the same size as the makero f trackway B from the southern exposure (Fig. 2a) and Markman's original trackway No. 1 (Fig. 2b). The tracks occur only as brown iron-stained traces on the upper surface of a light

ROCKY MOUNTAIN A SSOCIATION OF GEOLOGISTS buff-colored sandstone bed which lacks any obvious bio- turbation. When traced laterally, the same bed appears to be the mud-cracked un~ tw hich crops out immediately below the root-bearing log bed exposed to the south (see Chamberlain, 1976aa nd 1976b; Fig. 3, and Fig. 2c herein, for location of log bed 2b; also McKenzie, 1972, Fig. 5g). The trackway consists of five consecutive large t ridactyl prints, of which three are complete and easily measured indicating a large biped with feet about as long (52 cm) as wide (50 cm) with a short step (10 5 cm) indicative of slow progression (Fig. 5c) in a southward direction. Although the mid-toe impression ( #Ill) tapers to a fairly narrow point, the overall shape of the foot, the very broad digits, and negative (inward) rotation( sensu, Leonardi, 1987) of about 20 degrees are all indicative of a large herbivorous ornithopod( cf. A mbydactylus gethingi, Currie, 19 83, Fig. 1). It also appears that the outer digit (#IV) isslightly largerand more divergent than #I1 as would be expected from skeletal an- atomy (cf. Dodson, 1980, Fig. 1 for Camptosaurus; Hooley, 1925, Casier, 1960, or Norman, 1980, for Iguanodon; or Lull and Wright, 1942, for hadrosaurs). The greater diver- gence of the outer digit helps stabilize an erect walking biped which puts one foot in f ront of another leaving a narrow parasaggital trackway. Until recently, the preservation o f trackswhich consist only of coloration patterns has been poorly understood. However recent work by Kuban (1986a, 1986b and 1986c) has shown that even where no impression (con- cave epireliefs) exist, tracks may be clearly visible, because of "oxidation of Iron o n the surface." In s ome cases, as at Alameda, the tracks may appear slightly raised (con- vex hyporeliefs) because the iron-stained areas are more resistant to eroslon. Such coloration is not a primary or early diagenetic feature, because it develops only once the lithified track bearing beds are exhumed and subject to weathering. However, the coloration does reflect primary differences in substrate porosity, permeability, watersaturation and chemistry resulting from the pressure applied by the trackmakers (Farlow, 1986a). In the case of the steeply dipping Alameda outcrops, the coloration cannot be attributed to ponding of water and detritus in the tracks. The second of the two isolated trackways occurs in a bed immediately below the one just described (Chamber- lain, 1976a and 1976b, Fig. 3; and McKenzie, 1972, Fig. 5g). It represents a smaller bipedal ornithopod which was walking northwestwards parallel to the axis of what later became a small channel (McKenzie, 1972; Chamberlain, 1985). The trackway demonstrates a footshape (length 36 cm, width 36 cm) similar to the larger form described above. The corresponding step (79 cm) indicates a slow progression like the former example and suggests no obvious difference (see Table I), e xcept size, between the two track makers. ~egative(inward r)o tation is also noted in this trackway. The southern exposure of trackways (Fig. 2a; and McKenzie, 1968, Fig. 3e) presents a somewhat different picture. In addition to providing evidence of both ornithopods and theropods (coelurosaurs) the ornithopod trackways contain manus (hand) impressions indicating that they were capable of walking quadrupedally. In other words, they were facultative rather than obligatory bipeds.

The manus impressions are of particular interest since they are wel preserved and have apparently not been noticed before except perhaps by McKenzie (119 68 p 5) Al the trackways whlch exh~b bm~atn us impressions(A B and C of Fig 2a) have associated pes impressions which resemble those descr~be dfr om the outcrops to the north and show little significant d~fferenc ein foots~z eo r step dimenson Manus impressions appear throughout trackway A and much of trackway B and C w hile the step remains c onstant. The absence of a few manus impressions In trackways B and C may be due t o lack of preservat~o no r overlap rather than switching between quadrupeda and bipeda progression. However no part~ aol verlap has been observed, and the manus-pes distance IS consistent in most of the Alamedafootprints. Manus ~mpression sin t rackway A are particularly dist~nctiv eIn having an inwardly dlrected digit impression wh~ eth e remainder of the handprint 1 s a cres- cent shaped hoof-like track (Fig 5a) In this respect, the tracks differ from those associated with Ambydactylus which, accord~n gto Currle (119 83) revea "no evidence" of aspecial~ze ddi git Io r"spiken a s in I guanodon However ~ tis poss~b leth at the d~g iimt pressions ss een here are those of digit I(cf Norman 11985 for Iguanodon; and Osborn

1191 12 , and Lul and Wright 11942 PI 9 for hadrosaurs) Severa l authors have recentlyc oined names for ornithopod pes tracks. Alonso (19 80) named Hadrosaurrchnus aus- tralis from the late Cretaceous of Argentina, while Llompart et a (119 84) named Ornithopodlchnites magna based on larger tracks from the Late C retaceous of Spaln To avoid unnecessary proliferation of names e ither or both of these ichospecies could have been compared with existing ornithopod (pes) ~chnotax ali ke lguanodon (Beckles 11854 Dollo 11883 and 11905) Gypsichnrtes or Amblydactylus (Sternberg, 11932) However few authors have described quadrupeda trackways attributable to ornithopods. Apart from the trackway referred to Iguano- don by Norman (19 80) the most d~stinctiv et rackway is Caririchnium magnificum recentlyd escribed by Leonard (119 84a) from the Lower Cretaceous o f Brazil Fortunately Dr Leonard ~h as had the opportunity to examine the Alameda tracks and favors designating them as Caririch- nrum The following short systematic account represents minor emendation of the ichnogeus diagnosis and a description of the Alameda materia lu ndera new ichnospecies

Systematic lchnology Emended d~agnosiso f the chnogenus Carlrrchnlumm ag- nlfrcum Leonard~1, 984.T ype species Carrrrchniumm ag nificum Leonardi, 11984 Quadrupeda trackway, charac- terized by the remarkable difference between the large tr~dact ylh ind footprints and the small subeliptical hoof like fore footprints. H~g hpa ce angulation, trackway quite narrow inner width with negative value Smal eliptica foreprint wlth long axis directed antero-posteriorly or slightly antero- medianly to postero-laterally. Hind footprints large trl- dacty with a plantar pad separated from the toes by skin wrinkles. Toes thlck and stumpy with feet showing negative inward rotation Carlrlchnium leonard~rn ew species. D~agnos~ofs ~ ch nosDecles As for lchnoaenus e xcept In d eta ~ol f the manus and manus pace angulation. Manus shows medially directed ~mpressio no f a d ~g gw~ ht ic h is shallower than the remainder of the forefoot impress~o nM. anus impressions situated anteriorly and slightly latera to the pes Impres sion resulting in pace angulat~o nv alues of about 1145" which are less than those obtained for the pes

Discussion on Affinity of Trackmakers Caririchnium leonardi differs from the Brazll~a nty pe specles C magnlflcum mainly in having better preserved manus lmpresslons which show the hoof-hke nature of the foot and medially d~recte dd ig~ tT he differences in ga~ indicated by the smaller pace angulation values suggest that the Colorado trackmaker cannot conf~dent yb e assigned to C magnificum even though it undoubtedly be- longs to the lchnogenus Carirlchnium. have therefore ass~gne d~ tt o the new specles C. leonardi in honor of Dr Giuseppe Leonard ~,o ne of the world's leading vertebrate ichnologists The above descript~o nis based on trackway A of Figure 2 (see Fig 4e and 5a for detailed il- lustration), but other topotype trackways exist as in B and C of Figure 2a. Iis interesting to note that C magnrficum from the Rio do Peixe Group of Brazi is approximately the same age as C leonardi ifrom the Dakota G roup. However the Colorado trackways suggest that Leonardi's (119 84a) interpretatlon of the trackmakeras a stegosaur is no longer tenable. He agrees with the ornithopod interpretat~o presented herein (persona communication, 11986) Given that the maker of trackway A had a hoof-shaped manus with an inwardly directed first digit, the question arises as to what type of ornithopod could have left such tracks. For a number of reasons ~ ta ppears that an early hadrosaur is a poss~b ec andidate Although Kaye and Russel (119 73) regard the oldest hadrosaurs as Santonian in age Currie (119 83) cons~de rsth at the Peace Rwert racks are indicatwe of the presence of hadrosaurs sduring the Aptian-Albian Th~ sin terpretation would seem to be supported by Gillette and Thomas (119 83 and 11985 who record " hadrosaur" tracks In the Dakota Sandstone of northeastern New Mexico In deposits such as the Dakota where skeleta remains are virtually absent, footprints assume an added importance as a means of assessing the fauna Based o n current footprint evidence particularly the smal manus there seems to be no good reason for d~smissin gth e possibihty of early hadrosaurs during the Aptian-Albian-Cenomanian , especially now that Importan denta materia is emerglng from Cenomanian age Dakota depos~ sin Utah (Jeff Eaton persona communication, 11985) An alternat~v ee xplanation might be that the trackmaker is an iguanodontid of some type. Certainly tracks from southeast Colorado resemble those assigned to Iguanodon The problem with exploring thls interpretation IS that there is a l ack of diagnostic manus impressions associated with the so called "lguanodon" trackways; e.g. Dollo (119 05) Delairand Lander (19 73) Delalr( l981 1)f or England ,a nd Leonardi( 1 19 79) , and Casam~quelaan d Fasola (119 68) for South America Only Norman (19 80) has reported undiagnostic manus ~mpression sof an l guanodon (possibly I.b ernissartensrs) He Inferred that thls specles

114 MARTIN G. LOCKLEY

Figure 5. ROCKY MOUNTAIN ASSOCIATION OF GEOLOGISTS

DINOSAUR FOOTPRINTS. EASTERN COLORADO

Figure 5. Deta1 1o f tracks and trackways mentioned i n text. A) Alameda trackway A - (see Fig. 2a) with estimate of glenoacetabular distance (ga).

B) Boulder specimens (UCM collections). C) Ornithopod trackway from northern locality along Alameda Avenue (see Fig. 2c for location) D) Denver Museum of Natural Hlstory trackway speclmen # 1608 from Lamar, Colorado with detail of manus impressions

from track #2 in the 7 track sequence E) Ventral view of manus of lguanodon bernissartensis modlhed after Norman (1980).

F) Outline of right pes impression # 1 in the original trackway (No 1) described b y Markman Cast is in D. M. N.H G) Outline by Markman of track exposed at the Morrison Road locality, drawn from enlarged p hotograph.

H) 0 M N. H. specimens # 164 1 (above) and # 1620 (below) from Nmavlew, Colorado I) Natural casts of inferred iguanodontid footprints from near Campo, Colorado (drawn from photographs) JI Outline of lguanodon footpnnt impressions from trackways near Bexhill, England. K) Natural c ast of lguanodon footpnnt from the Bexhill M useum (J and K both courtesy of Ken Woodhams andJ ohn Hines).

was Umos tp robably a quadruped." If th~ sln terpretatlon IS correct, then one might conslder ~ m ore probable that the Alameda trackmakers were ~guanodontid sH owever, the manus lmpresslons from this locality appear Incon- s~sten wt ith Norman's (19 80) reconstructions (F~g .7 8 and 84) which show that d~ g gI ~mt a de no contact with the ground, whereas diglts Il-IV diverged s~gnif~can alyn d would presumably be expected to leave separate Impres- sions (cf. Lockley, 1985a, Fig. 2). Norman (19 85) and Shlpman (19 86, p. 102) also illustrate restored Iguan- ondontids w~t hd iverg~n gm anus digits. On balance, the Alameda impressions would thus appear to f ~ ~at m anus of the type illustrated by Osborn (19 12), and Lull and Wright (19 42, PI. 9) for the famous mumm~f~ ehad drosaur. The Alamedap es impressionsa lso differ from those from southeast Colorado in bemg broader toed (cf., Currie, 1983 and Lockley et al, 1983 for hadrosaurs) and less obv~ousl reminiscent of so called lguanodontld tracks whch fre- quently show a more prominent posterlor heel (metatarsal) pad. The designation of Caririchnium, a relatively broad footed form, suggests a trackmakerwhich may have been different from Iguanodon. However, the above arguments may be misleading. Paul (in Bird, 1985) has restored the Peace Rlver trackmaker (Currie, 1983) as an iguanodontid with digits 11 , 111 and IV enclosed In a hoof-like integument. He has ex- panded on th~ sin terpretation In a current study (Paul, In press) and prefers an iguanodont interpretation over an early hadrosaur for the Alameda trackmaker. The alternative interpretations hmge to a large degree on the interpretation of the manus and the fact that in some hadrosaurs a mummified hoof-like forefoot is known. The lack of such mummified iguanodont remains is in no small measure responsible for the existing differences in m anus restoration and the ambiguity over trackway interpretation. Analysis of the AlamedaA t rackway permlt1san) ) es timate of the animal's size. Based on a foot length ( 1)of 3 4 cm, it IS possible, according to Alexander (19 76), to estimate a hip height (h) of 41 1= 136 cm. (Other methods of esti- mating h are available; see Thulborn and Wade, 1984, p. 432-4 for discussion). The estimate of h~ phe ight can be checked independently by est~matin gth e glenoacetabular distance (ga) (see Sarjeant, 1975, p. 289) and Leonardi (19 87), when a quadrupedal trackway is available. When this IS done, (Fig. 5a) an estimate of 107 cm IS obtalned, thus providing a ga l 41 ratio of 0.79. This figure agrees falrly well wlth sim~la rra tios about 0.75 - 0.80 obtainedfrom measurmg of reconstructed Edmontosaurus and Iguan- odon respectively (see Lull and Wright, 1942, Fig. 27; and Norman, 1980, F~gs .8 3-84). Similarly, ga estimates of 130 and 132, respectively, for trackways B and C are consistent with the larger footprints and suggest ga l 4 1 ratios of 0.68 and 0.77. Larger ga estimates are obtained when assuming an alternate pace (e.g. 150 cm for trackway A; see Leonardi, 1987) but produce very high ga/4R values (1 10). In order to explain such values it is necessary to postulate a h~ phe ight of between 5 1 a nd 61. Thls estimate, whrch is consistent wrth measurements obtained from a hadrosaur (Lockley et al, 1983), may be better than the former method, which, coupled with Alex- ander' s41 rule of thumb, apparently leads to underesti- mates of size. My estimate of head to tail lengths in the range 4.5 to 5.75 m for the makers of trackways A, B and C ( Lockley, 1985a) c ould be Increased by up t o4096 based on the larger glenoacetabular est~mates A few largely isolated theropod tracks, probably attributable to gracile coelurosaurs, are also present at the southern exposure. Although few extensive trackways are present, sufficient information is available to deter- minef oot size and step dimensions. It isclear from the data (Table 1) that these tracks (e.g. Ca) are virtually identical to those referred to as type 2 by Markman (1938) and preserved as plaster casts In the Denver Museum. One specimen (Fig. 4c) is smaller (length 21 cm, width 18 cm) and remin~scen to f the "carn~vorous t ypes figured by Anderson (19 39).

General Observations on the Alameda Trackways Evidently, there are at least two types of bipedal d m- saurs represented by the Alameda trackways, a coelurosaur and at least one species of ornithopod. Markman's trackway #1 may be attributable to a large carnosaur. If only one species of ornithopod IS represented, then it

ROCKY MOUNTAIN ASSOCIA TION Of GEOLOGISTS

116 MARTI N G. LOCKLEY

Track way Pes Pes Speed Inferred Number Length: Width (cm) Step: Stride (cm) (W S ~ Trackmaker

A (Alarneda) 34:32 78 156 1.15 Ornlthopod 6 ( Alarneda) 48:48 100 200 1.15 Orn~thopo C (Alarneda) 43:43 102:204 1 36 Ornithopod Ca (Alarneda) 26:25 1 16.232 3 04 Coelurosaur Nth 1 (N. Alameda) 5250 105.2 10 1..14 Orn~thopo Nth 2 (N. Alarneda) 36.36 79:1 58 1 09 Orn~thopo Markrnan 1 (Alarneda) 48:48 96.1 92 1 08 Xarnosaur Markrnan 2 (Alarneda) 2325 107:2 14 2.78 Coelurosaur DMH.H. #I 608 (Lamar) 14 1 37) (102:204) 1.44 Orn~thopo

Table 1. Statistics tor Dakota drnosuar trackways. was apparently a f acultative biped which could s witch f rom quadrupedal to bipedal progression without any significant changes in length of steplstride. Although the existing ornithopod trackways are all very narrow, Markman (19 38) figured a much wider, possibly?carnosaurian trackway with left- and right-foot impressions splayed significantly apart on either side of the parasaggital plane (Figs. 2b and 4a herein). The accuracy of his map is more than adequately confirmed by his photograph (Markman, 1961; and Fig. 4a herein). Although the foot and stepdirnensions and negative rotation pattern closely resemble those recorded for the existing large trackway B (see Table I), the difference may be partially explained by the following ob servations. 1) The animal may not have been an ornithopod. Mark- man's photos and cast show what appears t o be c arnosaur- like claw marks incised in the floor of the footprints (cf. Thulborn and Wade, 1984, Fig. 12.4a). 2) The animal was not walking straight, but veering to the left. Markman's unpublished measurements of the stride (i.e. left-left and right-right) indicate that the left stride was consistently shorter than the right as expected f or an animal veering to the left. 3) According to Markman (19 38), it's three digits "made deep impressions but left no record of the posterior portion of the foot" (I think his photographs show faint heel pad impressions, see Fig. 4). Thiscould imply that the tracks were made underwater as has been suggested by McKenzie (19 72) for tracks at the southern outcrop. It seems reasonable to conclude that an animal's locomotion pattern would vary according to the substrate conditions it encounters and that this was perhaps the case for Markman's No. 1 trackmaker which may have been progressing through shallow water. Currie (19 83) described a situation where "an animal walking on the muddy bottom of a quiet body of water. ..appears to have been pushing off the bottom with its toes because the mark of the heel pad is very shallow and poorly defined." This description could apply to the tracks figured by Markman, and suggest the same type of interpretation. This inference is supported by one of the archive photographs which displays impressions of the distal portions of toes of smaller tridactyl animals. There is also no good reason to discount the possibility that carnosaurs could

ROCKY MOUNTAIN A SSOCIATION OF GEOLOGISTS swim (Coombs, 1980). Alternatively, tracks which display only toe impression can be interpreted to underprints or "ghost" tracks. As suggested above, the Markman trackways probably originate from a high stratigraphic horizon near the northern outcrop described herein. This conclusion is sup ported by Markman's notes. It is therefore interesting to note the general southward trend of both the historical trackways and the majority of those still in existence, including the casts 3 km away at Morrison road (Fig. 4f). Although the small number of recognizable trackways (about 12) IS insufficient for a detailed orientational analysis, it is perhaps worth noting that the animals may have been progressing roughly parallel to the north-south shoreline inferred forthis region during deposition of South Platte deposits (Weimer and Land, 1972, Fig. 8). In his analysis of Hadrosaurian paleoecology, Ostrom (19 64) noted that this group "lived in lowland, coastal plains in warm temperate to sub-tropical climates." It is therefore, not surprising to find footprints in what appears to be a typical hadrosaur or ornithopod habitat, complete with abundant vegetation. Although the data are insufficient for a meaninful analysis, the ornithopod1coelurosaur ratio suggests that the former group appears to have been present in greater numbers, as might be expected from their abundance during the Cretaceous. Elsewhere, trackway sites have been reported w here"carnivorous species" predominate (Anderson, 1939). It is interesting to note t hat Markman's #1 trackway, possibly that of a large carnosaur, apparently occurred in isolation o n the bedding plane on which it was found. (The small toe marks mentioned above cannot be adequately analyzed from the few remaining 1938 photos.) The Alameda trackway data permits an analysis of the speed of both types of dinosaur(and the Lamar trackway for comparison. The data are present in Table 1. Speed estimates (u) are obtained by using the formula:

developed by Alexander (19 76) in which g is acceleration due to gravity, A is stride length, and h is hip height (esti- mated as fow times the foot length). The estimates indi-

D INOSAUR FOOTPR INTS EASTERN COLORADO 117 cate slow progression for r the ornithopods without signifi can differences between those which were progressing bipedally and those moving quadrupedally The coeluro saurs however , were evidently moving faster as migh t be expected from this more typically cursoria group Al l the dinosaurs appear to have been moving a t a f airly constan speed excep t for r the Lama r trackmake rdiscussed below

Lamar Trackway Powers County Colorado As reported by Reinheime r( 1 19 39 and 11940 )t he Den ver Museum obtained a " "portion" of "trackway in the ori g ina sandstone" compris ing "a sequence o nine foot prints" (see Figs . 5d and 6a) In collecting and preparing this trackway for exhibit iwas reduced to a seven foot prin t sequence (see Figs .4 and 5) , then split between track #4 and #5 before this artificially created gap was filled with a 11.5 m long reconstructed portion with two artificia tracks (Fig 5d designed to form the base for the hadro saur mounted above . The Museum contains a leas one other track from this location (D.M .N .H # 1608) which presumably originated from "behind" #1 or "in fron of #7 in the origina sequence Reinheime observed tha the trackmake mus have been "intermediate in size between the two. . . recorded. . . from the Alameda highway. Reanalysis o the trackway confirms the validity of this latter observation and permits the addition of severa more . First , i t is noted tha t the tracks show sligh negative (inward ) rotation typica l o many ornithopod trackways (cf Leonardi ,1987) .T he tracks are less broad t oed than those from Alameda and exhibi a hee impression ; their overal configuration closely resembles "Iguanodon" tracks

(Haubold 1971 1 Fig 54 known from Europe (see Fig . 5) The trackway also appears st o include three manus impres sions associated with tracks 2 3 and 7 (see Fig 5d) lm pressions 3 and 7 consis of circular to subcircular dish shaped indentations abou 112 cm in diameter The size and position relative to the pes impressions s uppor t their interpretation as manus tracks Inferred manus track 2 is particularly interesting since irepresents an antero lat era l to poster0 mediany aligned 'scrape mark ' apparently made by a hoof-like appendage in which two blun digit Figure 6 A) Historic photograph of Lamar trackway in the process of being prepared for exhibit in the Denver Museum, probably taken in 11939 or 1940 Note that the trackway was split between tracks 4 and 5 (see Fig 5d) B-E) Casts of ornithopod tracks from Baca County ,s outheastern Colorado with 1ength:width m easurements of 55:5O cm and 58:50 cm r espectively for B and C D and E show smaller casts with a width range of 25 - 32 cm Note metatarsus impres sion in track at left in D © 2005 The Rocky Mountain Association of GeologistsROCKY MOUNTAIN ASSOCIATION OF GEOLOGISTS

118 MARTIN G. LOCKLEY extremities were l~nke db y some form of interdlgltal In- tegument or "web. Such an tnterpretatlon IS necessary to explain the smoothly scraped area between the shallow grooves made by two of the dtgits, and Implies that the trackmaker had a 'web' between two of its digits. Most specles of Iguanodon exhiblt two dlgtts (ll and Ill) wh~c protrude farther than all others. In the case of the Lamar trackmaker, ~ i s therefore reasonable to Infer an iguan- odontld. If this tnterpretatlon is correct, the impltcation IS that at least some forms possessed interd~g~ ~aln tegu ment (webbing) wh~c hre stricted the movement of manus digits as was evtdently the case with hadrosaurs(Osborn, 1912 ; Lull and Wr~gh ,1 942) Such an Inference IS con- ststent w~t hth e restorations proposed by Paul (tn press) and Norman (19 85). The trackway seems to suggest an animal sw~tch~ between bipedal and quadrupedal progression. Certainly the presence of a scrape mark Implies that the animal was barely touching the substrate at this potnt. The variable step also suggests some alternabon in speed. Unfortun- ately, the picture of progression between step 4 and 5 is obscrued by the reconstruction of the trackway surface beneath the "oversized" hadrosaur skeleton. The Lamar trackway evtdently originated from a settlng similar to that represented by the Alameda locallties The track bearing surface contalns many Rossella burrows, which are also known from the Alameda localtty (Cham- berlain, 1976a and 1976b). Relnhetmer (19 39) also reported the presence of fossil leaves including Ficus. Ster- culra and Dewalguea at the Lamar local~ty .T hese forms are typical of the Dakota and rem~niscen otf the list glven by Johnson (1931) and the hadrosaur habitats d~scusse by Ostrom (19 64). The preclse locatlon of the extracted Lamar trackway is unknown. However, ~ tw as possible to locate Dakota outcrops about 10 k m south of Lamar whlch resemble those in the photographs from the Denver Mu- seum Archives, and are almost certainly the same general locality.

Tracks from Baca County Four tracks from Baca county are on display at the Denver Museum (D.M.N.H. #1724). These are preserved as sandstone casts and have been arranged in a se- quences resembling a trackway. However, their considerable difference in size, and consideration of thelr probable origin, suggests that they could not have formed part of a single trackway sequence. The museum records indicate that these and at least three other specimens ori- glnate from somewhere in Baca county. The author has visited the southwestern part of the county and observed at least one private collection conta~nln go ver 160 casts of ornithopod tracks (Figs. 5i and 6b-e) Some, 1not all the D.M.N.H. material originates from this area The tracks from this area appear to be almost exclus~vel t hose of Iguanodon-like ornithopods.

Tracks from Bent, Las Animas and Otero Counties There is some uncertainty about the exact location of presumed Dakota track locations in this region. D.M.N.H. specimens # I620 and #I6 641 originate from somewhere near Ninaview on the BenVLas Animas county line. There are also unpublished records suggesting that tracks are known from Rule Creek to the north. Morrison Formatton tracks are known from both Otero and Las Animas counties (Lockley, 1986a and 1986b).

DISCUSSION AND CONCLUSIONS Manus impressions attributable to lguanodontlds and/ or hadrosaurs are virtually unknown (see Norman, 1980; and Currie, 1983, respectively). Those described herem therefore, assume considerable importance as they are well enough preserved to provide morphological Informa- t~o no n these ornithopods. As demonstrated by Weis- hampel and Weishampel (19 83) hadrosaurs are very rare in the early Cretaceous (see Flg. 7). Consequently, large ornithopod footprints of this age are usually attr~bute dto iguanodontids (e.g., Delalre, 1981; Norman, 1980; Leo- nard~ ,1 979; Casamiquela and Fasola, 1968; also Hotton, 1980, personal communication, Langston, 1974, and Gr~es ,1 962 in W eishampel and Weishampel, 1983). Re- cently, however, Gillette and Thomas(1 983 and 1985) and Currie (19 83) have attr~bute r espect~v D akota Group and Gething Formation(Aptian-Albian) t rackways to hadrosaurs. If these assumptions are correct then these trackways, like those from the Dakota of Colorado, would be indicative of the earliest hadrosaurs in North America because they substantially predate material previously assigned to the "oldest hadrosaur" category (Kaye and Rus- sell, 1973; Carpenter, 1982; Eaton, personal communlca- tion, 1985). S uch s peculations cannot be proven at present, but ~ tIS known that tracks can provide information on stratigraphic range extensions for important dlnosaur groups (Lockley, 1986b). An alternative explanation is that the Dakota and perhaps other coeval trackways represent an iguanodontid or species in the evoluttonary transition between this family and the descendant hadrosaurs. For the reasons outlined above, the Alameda trackways, like those from southeast Colorado, are thought to resemble those expected by an iguanodont trackmaker. As well as noting the occurrence of Caririchnium in both North and South America, it is interesting to note the close resemblance between pes casts from Baca County and those attributed to Iguanodon from the south coast of England (see Fig. 5; and Delair and Sarjeant, 1985) and the south coast of Korea (Yang, 1982). It seems probable that the same mode of preservation (i.e., natural casts) contributes to t his similarity and that the broader toed nature of the Alameda tracks might simply be due to their preservation as shallow impressions/undertracks on a firmer sandy (mud draped) substrate rather than in softer cohesive sediments which produced well-defined natural casts when the deeper impressions were filled by sand. However, the distinctive outline of the Lamarpes impres- sionsalso resembles the shape of thecasts and suggests that some differences in pes shape are recognizable under different preservation conditions. In either case, a strong argument can be put forward f or regarding the trackmakers from southeast Colorado as very similar to the iguanodontid trackmakers of Europe and Asia. Hence this group of trackmakers was very widespread. There are several instances of iguanodontid and hadrosaurian trackways providing evidence of gregarious

DINOSAUR FOOTPRINTS, EASTERN COLORADO +of occurrences by formation

et al, 1983). The evidence from the Dakota of Colorado may be insufficient to either prove or disprove such a hypothesis. However, at Alameda there are at least two Carirtchnium t rackways parallel tot rackwayA suggesting a group of three animals passing together. The artistic reconstruction (Fig. 8) is based on this group of parallel trackways. It seems reasonable toassume that the relatlve abundance of trackways in a small area might support the conclusion of gregarious behavior for both the Alameda and Baca County sites. The abundance of ornithopod tracks during Dakota time and in e nvironments represented b y Dakota deposits IS also of interest for three other reasons. Firstly, it appears consistent with what is known of the habitat preference of large Cretaceous ornithopods (Ostrom, 1964) which un- derwent marked diversification at the same time as the radiation of the angiosperms (Bakker, 1978). Secondly, it indicates the potentlal of footprints in providing a useful census of particular paleoenvironments. Farlow (19 86) and Leonardi (19 84a and 1984b) have indicated that theropod tracks dominate those of ornithopods at many Lower Cretaceous localities. T his is evidently not the case in environments represented by Dakota deposition or in Cretaceous coastal-plain environments in general (Lock- ley 1986~ .B ecause the Dakota ornithopod tracks are quite distinctive and cannot be confused with theropod tracks, the large proportion of ornithopod tracks represents a real census phenomenon. Thirdly, the tracks appear to be useful in local correlation. Using the panoramic photograph of Dakota outcrops published by McKenzie (1972, Fig. 4) ~ i s possible to show that bed 2, the maln track-bearing horizon (Fig. 2) which is heavily trampled, can be t raced at least 230 m t ot hesouth, where ~ tis recog nizable because of its similar heavily trampled character. tive beds in continental successions is a novel area of sedimentological interpretation (Dodson et al, 1980; Laporte and Behrensmeyer, 1980; Lockley et al, 19 86; and Lockley and Conrad, in press). The example cited herein represents one of the first instances of local stratigraphic correlation using "dinoturbation." The correlation is substantiated by the fact that the tracks found 3 km to the south at Morrison, occur at the s ame stratigraphic level as at the Alameda locality (Weimer and Land 1972, PI. 2, unit 10). S imilarly, t he tracksatTurkeyCreek, another2 km to the south, are also near the top of the Dakota section at approximately the same stratigraphic level. There are also several heavily trampled, "dinoturbated layers at Mehl's bird track locality north of Golden. It has not yet been established whether these correlate pre- cisely with the Alameda locality 15 km to the south, however, it does show that track bearing beds are exposed over a lateral distance of about 20 km in this area. On a regional scale, track bearing Dakota outcrops can be traced for over 350 km from Boulder, Colorado to Clayton, New Mexico. ACKNOWLEDGMENTS Spec~a atlh anks to Giuseppe Leonardi for h~ tsr a nslation o f his own work on Carrrichnium and h~ osb servations o n the Ala- meda site. Thanks to Jack Murphy of the Denver Museum for his considerable help In sifting through valuable archive material, some of which is reproduced herein. Bill Richardson also assisted by providing access to his private collection and Ken Woodhams kindly f urnished information o n "lguanodon" tracks from England. T hanks also to Kent Chamberlain, Jeff Eaton, Mark Jones, Greg Paul, Andy Rindsberg, John Rohner, Peter Robinson and John Warme for useful d~scus sion, museum and field assistance. Pallas Photo Labs Inc. also assisted with partial sponsorship of the photographic costs.

ROCKY MOUNTAIN A SSOCIATION OF GEOLOGISTS

MARTIN G. LOCKLEY

Figure 8. Artistic reconstrucbon by John Slbbick ot three iguanodontids walking southeastward along a marine shoreline. Based on trackway A and two parallel trackways of Flgure 2.

REFERENCES Alexander, R. Mc. N., 1976, Est~mate sof the speeds of dm - saurs: Nature, v. 26 1, p 129-1 3 0. Alonso, R. N., 1980, lcn~ta sd e dmosaurias (Ornithopoda, Hadrosauridae) en el Cretac~c S uperior del Norte de Argentina: Acta Geologica L~lloana ,v. 152, p. 55-63 Anderson, S. M., 1939, Dinosaur tracks In the Lakota Sand- stone of the eastern Black Hills, South Dakota: Journal of Paleontology, v. 13, p. 361-364. Bakker, R. T., 1978, Dinosaur feeding behaviorand the origin of flowering plants: Nature, v 274, p. 661-663. Beckles, S. H., 1854, O n the Orn~tho~dichnit eof s th e Wealden: Proceedings of the Geological Soc~et yof London, v. 10, p. 456-464. Bird, R. T., 1985, Bones for Barnum Brown: Texas Christian University Press, 255 p. Branson, E. B., and M. G. Mehl, 1932, Footprmts from the Paleozoic and Mesozoic of Missouri. Kansas and Wyoming: GSA Bulletin, v. 43, p. 383-398. Carpenter, K., 1982, The oldest Late Cretaceous dinosaurs in North America: Mississippi Geology, v. 3, p. 1 1-17 . Casamiquela, R., and A. Fasola, 1968, Sobre pisadas de dmcr saurios del Cretacio inferlor de Colchagua (Ch~le )U: niver- s~da dC hile Facultad Geologia, Fiscas, Matematicas, De- partamento Geologia, v. 30, p. 1-24. Casier, E., 1960, Les lguandons de Bernissart: Brussels. p. 134. Chamberlain, C. K., 1976a, Field guide to the trace fossils of the Cretaceous Dakota hogback along Alameda Avenue. west of Denver, Colorado, in R. C. Epis, and R. J. Weimer, eds.: Colorado School of Mines. Professional Contribu- tions #8, p. 242-250.

ROCKY MOUNTAIN ASSOCIA TION OF GEOLOGISTS

Chamberlain, C. K., 1976b, Field guide to the trace foss~l so f the Cretaceous Dakota hogback along Alameda Avenue, west of Denver, Colorado, in C. K. Chamberlain, and R. W. Frey, eds., Seminar on trace fossils: USGS Golden, Colo- rado, pp. 37-42. Chamberlam, C. K., 1985, The tidal complex of the Muddy Formation at Alameda Parkway, in Environments of deposition (and trace fossils) of Cretaceous sandstones of the Western Interior: SEPM, Rocky Mountain Section Field Guide to Field Trip No. 3, v. 3, p. 131- 1 42. Coombs, W. P., 1980, The swimming ability of carniverous dinosaurs: Science, v. 207, p. 1198-1 2 00. Currie, P. J., 1983, Hadrosaur trackways from the lower Cret- aceous of Canada: Acta Palaeontologica Polonica, v. 28, p. 63-73. Currie, P. J.. and W. A. S. Sarjeant. 1979, Lower Cretaceous dinosaur footprints from the Peace River Canyon, British Columbia: Paleogeography, Paleoclimatology, Paleo- ecology, v. 28, p. 103-1 15. Delair, J. B., 1981. Multiple t rackwaysf rom the Isle of Purbeck: Proceedings Dorset Natural History and Archaeology So- ciety, v. 102. p. 65-68. Delair, J. B., and A. B. Lander, 1973, A short history of the discovery of reptilian f ootprints in the Purbeck b eds of Dorset, with notes o n their stratigraphical d istribution: Proceedings Dorset Natural History and Archaeology Society, v. 94 ,;. 17-20. Delair, J. B., and W. A. S. Sarjeant, 1985, History and bibli- ography of the study of fossil vertebrate footprints in the British Isles: Supplement 1973-1 9 83: Paleogeography. Paleoclimatology, Paleoecology. v. 49. p. 123-1 6 0.

DINOSAUR FOOTPRINTS, EASTERN COLORADO 121

~odson ,P ., 1980, Comparative osteology of the American ornithopods Camptosaurus and Tenontosaurus Memolre of Geologcal Society of France, v. 139, p. 81- 85. Dodson, P., A. K. Behrensmeyer, R . T. Bakker, and J. S. Mcl n- tosh, 1980, T aphonomy and paleoecology of the dmosaur beds of the Jurassic Morr~so Fn ormation: Paleob~ology ,v. 6, p. 208-232. Dollo, L., 1883, Quatrteme Note Sur les Dinosaureus De Bernissart: Bulletin of the Royal Museum of Nat~ona H~stor yof Belgium, v. II, p. 223-252. Dollo, L., 1905, Les. Allures des Iguanodons, dipres les ~mpreinte sd es pieds et de la queue: Bulletm Scientlfique de la France et Belgique, v. 50 (Ser. 4, 9), p. 1-12. Farlow, J., 1986a, Lower Cretaceous dinosuar footprints of Texas: strat~graphi ca nd paleoenv~ronmenta aol ccurrence, morphology, and ~mplicat~o nfsor dmosaur locomotion and behavior, m D. D. 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