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 iguan- odont~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 i! I Mehl 1031 O* m mDE NVER IiI! j ! j Colorado Springs I! j 6 II iI Lamar I ;i iI;, -. -. - - -.-.-.-.-.-.--.-.C-N.l-ai.n-y.a- tv.o-in.e w+ '' C$ i .._- ma.4.--..--m .-.-;J ..--.- p 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 ©2005 The 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 photo- graphs taken about 0.45 (0.72 km) north of hairpin turn which cuts through hogback. Coincidentally, the recent photo- graph (below) shows the Dakota Sandstone sign. © 2005 The Rocky Mountain Association of Geologists ROCKY MOUNTAIN ASSOCIATION OF GEOLOGISTS 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 track- ways 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 re- mains although "a preservative was apphed to the track- way (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 track- ways 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 un- published notes, described as "0.45 mdes north of hairpin turn which cuts through hogback." Th~ sw ould put the out- crop 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 foot- prints" 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 south- eastern Colorado were donated to the Denver Museum between 1942 and 1976, and tracks contmue to be dis- covered 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.