Di no saur foot prints from the Up per Cre ta ceous of Mon go lia
Shinobu ISHIGAKI, Mahito WATABE, Khishigjav TSOGTBAATAR and Mototaka SANEYOSHI
Ishigaki S., Watabe M., Tsogtbaatar Kh. and Saneyoshi M. (2009) — Di no saur foot prints from the Up per Cre ta ceous of Mon go lia. Geol.
Quart., 53 (4): 449–460. Warszawa.
We re port new data on 18 di no saur foot print lo cal i ties dis cov ered in the Up per Cre ta ceous of the Gobi Desert of Mon go lia, where we have rec og nized more than 20 000 foot prints of di no saurs. There are at least four types of di no saur foot prints, at trib uted to theropod, ornithopod, ankylosaurid and sauropod trackmakers. We have also rec og nized abun dant foot prints of un iden ti fied trackmakers from each lo cal ity. Co ex is tence of foot prints and many skel e tal re mains in the same and/or nearby beds is a re mark able fea ture of these Mon - go lian sites. Anal y ses of di no saur foot prints and as so ci ated body fos sil re mains for each lo cal ity re veal that even in the same beds, the ichnofauna dif fer from the fauna re con structed on the ba sis of body fos sils of di no saurs. The re sults dem on strate that di no saur fau nal as - sem blages re con structed from body fos sil or foot print ev i dence solely should be con sid ered very care fully.
Shinobu Ishigaki, Hayashibara Mu seum of Nat u ral Sci ences, 1-2-3, Shimoishii, Kita-ku, Okayama 700-0907, Ja pan; e-mail:
isgk@hayashibaramuseum.jp; Mahito Watabe and Mototaka Saneyoshi, Cen ter for Paleobiological Re search, Hayashibara Bio chem i - cal Lab o ra to ries Inc., 1-2-3, Shimoishii, Kita-ku, Okayama 700-0907, Ja pan; Khishigjav Tsogtbaatar, Mon go lian Paleontological Cen - ter, Mon go lian Acad emy of Nat u ral Sci ences, Ulaanbaatar 210351, Mon go lia (re ceive: April 23, 2009; ac cepted: Sep tem ber 9, 2009).
Key words: Mon go lia, Gobi Desert, Up per Cre ta ceous, di no saur, foot print.
INTRODUCTION
Mon go lia is one of the most im por tant coun tries yield ing abun dant di no saur re mains. Ex pe di tion par ties by Amer i can, Rus sian (and the for mer USSR), and Pol ish re search ers in part ner ship with Mon go lian re search ers have dis cov ered large num bers of di no saur skel e tons in the Gobi Desert. The first dis cov ery of di no saur foot prints in Mon go lia was made by Namnandorzhi (1957). In this pa per he re ported the oc cur - rence of 14 tridactyl and 20 oval di no saur foot prints from the Lower Cre ta ceous sand stones at the bot tom of Mt. Sayzhrakh, 250 km west of Ulaanbaatar. Af ter Namnandorzhi (1957), sev eral di no saur foot prints were re ported from the Gobi Desert. Obata and Matsukawa (1996) and Matsukawa et al.
(1997) re ported di no saur foot prints which are 11 oval con - cave de pres sions from the Lower Cre ta ceous of Khuren Dukh, 260 km SSE of Ulaanbaatar. Loope et al. (1998) re - ported di no saur foot prints from the eolian sand de posit of the Ukhaa Tolgod lo cal ity (Up per Cre ta ceous). Cur rie et al.
(2003) re ported foot prints of large or ni tho pods, theropods
and sauro pods at the Nemegt lo cal ity (Up per Cre ta ceous).
Matsukawa et al. (2006) in tro duced the Khuren Dukh and Nemegt tracksites to gether with other Asian Cre ta ceous tracksites. Gierliński et al. (2008) re ported a foot print of Protoceratops in side the field jacket col lected from Flam ing Cliffs in 1965 by the Pol ish-Mon go lian joint ex pe di tion.
In 1995, the Hayashibara Mu seum of Nat u ral Sci ences — Mon go lian Paleontological Cen ter Joint Paleontological Ex pe - di tion (HMNS-MPC Ex pe di tion) dis cov ered abun dant di no - saur foot prints in the Up per Cre ta ceous of Shar Tsav, 275 km east of Dalanzadgad, South Gobi Aimag (Suzuki and Watabe, 2000a). A to tal of about 18 000 foot prints were dis cov ered at Shar Tsav. By the 2008 field sea son, the HMNS-MPC Ex pe di - tion had dis cov ered 18 new di no saur tracksites and more than 20 000 di no saur foot prints from the Up per Cre ta ceous of Mon - go lia (Ishigaki, 1999; Suzuki and Watabe, 2000b; Watabe and Suzuki, 2000a–c; Watabe and Tsogtbaatar, 2004; Watabe et al., 2004; Ishigaki et al., 2004; Ishigaki et al., 2008).
Here we pres ent an over view of these newly found foot - print lo cal i ties, de scribe the mor phol ogy of rep re sen ta tive foot - prints and in ter pret the pos si ble trackmakers. It is re mark able that in those Mon go lian sites, both bone re mains and foot prints
are rich. Sites with rich bone and track re mains to gether are very rare in the world. Thus we pres ent a pre lim i nary re sult of com par i son be tween ichnofauna and body fos sil re mains from the same bed and lo cal ity.
GEOLOGICAL SETTING
The Up per Cre ta ceous of Mon go lia is sub di vided into four “for ma tions” (“svitas” is the Rus sian strati graphic term):
in as cend ing or der, the Bayn Shire, Djadokhta, Barun Goyot, and the Nemegt for ma tions (Gradziński et al., 1968;
Jerzykiewicz and Rus sell, 1991; Jerzykiewicz, 2000;
Shuvalov, 2000). The Bayn Shire For ma tion is com prised of fluvio-lac us trine de pos its (Jerzykiewicz and Rus sell, 1991;
Jerzykiewicz, 2000). The Djadokhta For ma tion con sists pre - dom i nantly of eolian de pos its with rare in ter ca la tions of fluvio-lac us trine de pos its (Fastovsky et al., 1997;
Jerzykiewicz, 2000). The Barun Goyot For ma tion con sists of eolian and fluvio-lac us trine (playa) de pos its (Gradziński and Jerzykiewicz, 1974; Jerzykiewicz, 2000). The Nemegt For - ma tion is com posed of mainly fluvio-lac us trine de pos its with mi nor eolian de pos its (Gradziński, 1970; Jerzykiewicz and Rus sell, 1991; Ishii et al., 1995; Jerzykiewicz, 2000). The age of each for ma tion has been es ti mated from dino saur ian and in ver te brate fau nas, palaeomagnetic anal y sis and phys i cal data of in ter ca lated ig ne ous rocks (Jerzykiewicz and Rus sell, 1991; Hicks et al., 1999; Jerzykiewicz, 2000; Shuvalov, 2000). The Bayn Shire For ma tion age is es ti mated as be ing from Cenomanian to Santonian; the Djadokhta For ma tion as Santonian to Campanian; the Barun Goyot For ma tion as Santonian to Campanian; and the Nemegt For ma tion as Maastrichtian.
LOCALITIES
In this pa per we re port 18 lo cal i ties of di no saur foot prints.
They are lo cated in the Gobi Desert of South ern Mon go lia (Fig. 1). These are as fol lows: Bayn Shire, Shar Tsav, Tugrekin Shire, Abdrant Nuru, Alag Teg, Udyn Sayr, Khongil, Altan Teg, Yagaan Khovil, Altan Ula III, Altan Ula IV, Ulan Khushu, Gurilin Tsav, Bugin Tsav, Bugin Tsav II, Khermeen Tsav, Shiluut Ula, and Undor Bogd. To re lo cate the geo graph - ical po si tions of these sites, we re fer to Gradziński et al. (1968), Shuvalov and Chkhikvadze (1975), Sochava (1975) and Ivakhnenko and Kurzanov (1988). The names of the foot - print-bear ing for ma tions at each lo cal ity are: the Bayn Shire For ma tion at Bayn Shire; the Djadokhta For ma tion at Abdrant Nuru, Alag Teg, Tugrekin Shire, Khongil and Udyn Sayr; the Barun Goyot For ma tion at Shiluut Ula; and the Nemegt For ma - tion at Shar Tsav, Yagaan Khovil, Altan Ula III, Altan Ula IV, Ulan Khushu, Gurilin Tsav, Bugin Tsav, Bugin Tsav II and Khermeen Tsav (Shuvalov and Nikolaeva, 1985; Jerzykiewicz and Rus sel, 1991; Mikhailov et al., 1994; Jerzykiewicz, 2000;
Shuvalov, 2000). The strati graphic po si tions of the foot - print-bear ing beds in Altan Teg and Undor Bogd are not fully known. Foot prints are pre served in eolian de pos its at Tugrekin
Shire and are pre served in fluvio-lac us trine de pos its at the other lo cal i ties. The geo graph ical in for ma tion of each lo cal ity is shown in Ta ble 1.
DINOSAUR FOOTPRINTS
More than 20 000 di no saur foot prints have been dis cov - ered. We have clas si fied the di no saur foot prints found in these new lo cal i ties into four groups, along with in de ter mi nate forms: Type A, B, C, D and “in de ter mi nate”.
TYPE A
Lo cal i ties: Abdrant Nuru, Alag Teg, in the Djadokhta For - ma tion, and Shar Tsav, Yagaan Khovil, Bugin Tsav, Bugin Tsav II and Khermeen Tsav in the Nemegt For ma tion.
Char ac ter is tics: tridactyl or tetradactyl foot prints with long, slen der and sep a rated dig i tal im pres sions. Digit III im - pres sion is the lon gest. The width/length ra tio of the foot prints is less than 0.9 (Fig. 2A–K).
Fig. 1. Lo cal ity map of newly-dis cov ered di no saur tracksites from the Gobi Desert, Mon go lia
De scrip tion: foot prints with im pres sions of dig its II, III and IV. Digit I im pres sion is pre served in some deeply im - printed me dium sized foot prints (Figs. 2C and 3C). Digit II and IV im pres sions are sim i lar to each other in length. Digit III im - pres sions are the lon gest and straight. Pointed tips are printed at the dis tal end of each dig i tal im pres sion in well-pre served foot - prints. The width/length ra tio of the foot prints ranges from 0.6 to 0.9. In well-pre served foot prints, im pres sions of dig i tal pads counts 2 in the digit II, 3 in the digit III and 3–4 in the digit IV.
Divarication an gles of the dig its II–IV vary from 40 to 70°. The val ues of the divarication an gles of the dig its II–III and III–IV are sim i lar to each other. The length of foot prints ranges from 6 to 70 cm (Fig. 2A–K). Elon gated foot prints with meta tar sal im - pres sions have been dis cov ered in Shar Tsav and Abdrant Nuru (Fig. 2C). Trackway width is small, and the pace angulation ranges from 135 to 170° (Fig. 3A–F). The foot print axis is al - most par al lel or ro tated slightly out wards (less than 10°) from the trackway midline. There is no tail drag ging im pres sion.
Ichnotaxonomy: there are foot prints with Asianopodus- type (Matsukawa et al., 2005) out line (Fig. 2E). How ever, the im pres sion of the heel pad is not iso lated from the digit IV im - pres sion. Thus we must be cau tious be fore at trib ut ing them to Asianopodus. The small foot prints with rel a tively long digit III (Fig. 2F–H and K) from Shar Tsav are Grallator-type (Lull, 1953), and me dium to semi-large sized foot prints (Fig. 2B) are mor pho log i cally Eubrontes-type (Lull, 1953). As Eubrontes and Grallator are es tab lished as Trias–Ju ras sic taxa, we use the
name with “-type” for de scrib ing the out line mor phol ogy of the Type A foot print. The ichnotaxonomy of Type A tracks should be dis cussed pre cisely in the fu ture study us ing the best pre - served ma te ri als.
Trackmaker: mor phol ogy and trackway pat terns of Type A foot prints in di cate that their trackmakers are var i - ously-sized theropod di no saurs. The pre cise tax o nomic po si - tions of the trackmakers are un known. How ever, there are two ex am ples that sug gest iden ti cal re la tion ships be tween foot - prints and body fos sils.
One ex am ple is a group of small foot prints with “tear-drop shaped out lines” from the Shar Tsav lo cal ity and the skel e tal re mains of a small theropod, Avimimus. From the larg est ex - po sure of the foot print-bear ing bed ding plane in Shar Tsav, abun dant small foot prints (10–12 cm in length) with
“tear-drop shaped out lines” have been dis cov ered (Fig. 2G and K). Digit III im pres sion is very long. The divarication an - gle be tween dig its II and IV is small (40°). Digit II and IV im - pres sions are al most the same length. The over all out line of the foot print is sym met ri cal. The skel e tal re mains of Avimimus were dis cov ered in the strati graphic zone just be - low the main foot print-bear ing lay ers of Shar Tsav.
(Kurzanov, 1981, 1987; Watabe and Suzuki, 2000a; Watabe et al., 2004). The mor pho log i cal char ac ter is tics of these small foot prints such as the very long digit III im pres sion and the sym met ri cal mor phol ogy are con cor dant with the pes mor -
T a b l e 1 Newly-dis cov ered di no saur tracksites from the Gobi Desert, Mon go lia
Area in the
Gobi Desert Lo cal ity
Ap prox i mate co or di nate
of lo cal ity Be long ing for ma - tion of foot print
bear ing beds
Depositional en vi ron ments
Quan tity of foot prints
Lat i tude Lon gi tude Type A Type B Type C Type D Indeter
minate
South-east Bayn Shire 44°17’ N 109°55’ E Baynshire flu-lac – 5 – – 5
Shar Tsav 43°34’ N 107°46’ E Nemegt? flu-lac 3 000 – 200 – 15 000
Cen tral
Tugrekin Shire 44°14’ N 103°18’ E Djadokhta eolian – – – – 10
Abdrant Nuru 44°32’ N 103°09’ E Djadokhta? flu-lac 120 2 150 – 100
Alag Teg 44°15’ N 103°18’ E Djadokhta flu-lac 15 – – – 30
Udyn Sayr 44°06’ N 102°55’ E Djadokhta flu-lac – – – – 10
Khongil 44°11’ N 102°47’ E Djadokhta? flu-lac – 3 12 – 20
Altan Teg 44°03’ N 102°45’ E ? flu-lac – – – – 5
Yagaan Khovil 44°04’ N 102°40’ E Nemegt? flu-lac 5 20 – 10 20
West
Altan Ula III 43°36’ N 100°30’ E Nemegt flu-lac – – – – 5
Altan Ula IV 43°36’ N 100°27’ E Nemegt flu-lac – – – – 10
Ulan Khushu 43°29’ N 100°27’ E Nemegt flu-lac – – – – 10
Gurilin Tsav 43°51’ N 100°08’ E Nemegt flu-lac – 300 5 – 50
Bugin Tsav 43°52’ N 100°01’ E Nemegt flu-lac 20 300 30 2 1 000
Bugin Tsav II 43°49’ N 99°59’ E Nemegt flu-lac 10 10 5 – 10
Khermeen Tsav 43°28’ N 99°50’ E Nemegt flu-lac 20 – 10 – 100
South Undor Bogd 42°21’ N 105°59’ E ? flu-lac – – 10 – 10
Shiluut Ula 42°18’ N 105°44’ E Barun Goyot? flu-lac – – – – 100
To tal 3 190 640 422 12 16 495
Grand to tal 20 759
phol ogy of Avimimus. These data sug gest that these small foot prints are at trib ut able to Avimimus.
An other ex am ple is Tarbosaurus and the large nat u ral casts of foot prints around 55 cm in length found at Bugin Tsav and Bugin Tsav II. The im pres sions of each digit of the foot prints are well sep a rated show ing clear claw marks (Fig. 2I). These foot prints were found in the strati graphic zone that yields many skel e tal and iso lated body re mains of Tarbosaurus (Maleev, 1955; Kramarenko, 1974). Among the theropods de scribed from the Nemegt For ma tion of the Gobi Desert, es pe cially of Bugin Tsav, Tarbosaurus is the only can di date to be a trackmaker of the large foot prints. The char ac ter is tics of the
large foot prints are con cor dant with the pes mor phol ogy of Tarbosaurus. These data sug gest that the foot prints were left by in di vid u als of Tarbosaurus.
TYPE B
Lo cal i ties: Bayn Shire in the Bayn Shire For ma tion, Abdrant Nuru and Khongil in the Djadokhta For ma tion, and Yagaan Khovil, Gurilin Tsav, Bugin Tsav and Bugin Tsav II in the Nemegt For ma tion.
Char ac ter is tics: tridactyl foot prints with three broad dig i - tal im pres sions. The digit III im pres sion is the lon gest. The
Fig. 2. Draw ings and pho tos of Type A foot prints
A, B, D, E, F, G, H, K — con cave molds from Shar Tsav (B is the 2nd foot print in Fig ure 3A, D be longs to one of the par al lel trackways in Fig - ure 3F, F is the 5th foot print in Fig ure 3E); C — sole view of elon gated nat u ral cast with digit I im pres sion from Abdrant Nuru; I — top sur face view of very large nat u ral cast from Bugin Tsav; J — sole view of very well-pre served nat u ral cast from Shar Tsav; scale is 10 cm
foot print is al most sym met ri cal. The width/length ra tio of the foot prints is equal to or slightly larger than 1.0.
De scrip tion: foot prints with digit II–IV im pres sions. Im - pres sions of each digit are broad. The dis tal end of the dig i tal im pres sions show rounded out lines. There are no pointed tips.
Digit II and IV im pres sions are sim i lar in length. Digit III im - pres sion is the lon gest. In side the dig i tal im pres sions, there are no traces of dig i tal pads. The foot print width is equal to or slightly larger than the length. Foot print length var ies from 25–115 cm (Fig. 4A–G), av er ag ing 65 cm. The divarication an - gle be tween dig its II–IV var ies from 40 to 90°, mostly around 50–60°. The val ues of divarication an gles be tween dig its II–III and III–IV are sim i lar. The over all out lines of the foot prints of Type B are al most sym met ri cal. All of the find ings are nat u ral casts of sand stone, or mas sive hard sand stone lay ers (underprints) un der the true prints. An ex cep tion ally large spec i men, 115 cm in both width and length, was dis cov ered in the Nemegt For ma tion at Gurilin Tsav (Fig. 4A).
A foot print axis of this type is ro tated slightly in ward (around 10°) from the trackway midline. The trackway width is small, and the pace angulation ranges mostly from 155–170°
(Fig. 5A–D). No manus prints are ob served. There is no tail drag ging im pres sion.
Ichnotaxonomy: most of the foot prints of Type B in this pa per (Figs. 4 and 5) are pro vi sion ally as signed to the Amblydactylus-type (e.g., Stern berg, 1932; Cur rie and Sarjeant, 1979) which is typ i cally known from North Amer ica.
There are some foot prints with Caririchnium-type char ac ter is - tics such as bilobate heels (Figs. 4D and 5B). How ever, there are no traces of the manus at all.
Trackmaker: foot print mor phol ogy and trackway pat - terns sug gest that all Type B foot prints are at trib ut able to var i - ous-sized ornithopod di no saurs. Pre cise tax o nomic po si tions of the trackmakers are un known. How ever, there is one ex am - ple that sug gests iden ti cal re la tion ships be tween foot prints and body fos sils. At Bugin Tsav, Bugin Tsav II and Gurilin Tsav, Type B foot prints ex ceed ing 50 cm in length are abun - dant. In those lo cal i ties, abun dant skel e tal re mains of Saurolophus have been un earthed from the same or nearby strati graphic ho ri zons of foot prints (Rozhdestvenskii, 1952, 1957; Maryańska and Osmólska, 1984; Nor man and Sues, 2000; Suzuki and Watabe, 2000a, b; Watabe and Suzuki, 2000c). The char ac ter is tics of those large foot prints are con - cor dant with the pes mor phol ogy of Saurolophus (Rozhdestvenskii, 1952, 1957). This ev i dence sug gests that these foot prints are at trib ut able to Saurolophus. Cur rie et al.
(2003) also re ported nat u ral casts of large ornithopod foot - prints from the Nemegt lo cal ity. They also at trib uted these types of foot prints to Saurolophus.
The larg est foot print of this cat e gory is 115 cm in length and width (Fig. 4A). It was dis cov ered at Gurilin Tsav. The spec i men is a nat u ral cast. It is iso lated and does not form a trackway. The value of the divarication an gle be tween dig its II and IV (90°) is very large among this type. We con sider that the trackmaker of this large print might have spread its dig its widely when step ping on to the muddy sub strate. This be hav - iour might have caused the ex ag ger a tion of foot print size and
Fig. 3. Draw ings and photo of Type A trackways
A, B, D, E — trackways from Shar Tsav; C — trackway with digit I im pres - sion from Abdrant Nuru; F — photo of par al lel trackways from Shar Tsav, foot print length: 28 cm, stride length: 285 cm, B is a draw ing of the part of one trackway in this photo
the large divarication an gle. The mean length and width of this large foot print is es ti mated to be about 90 cm, which is the max i mum size among the foot prints from Bugin Tsav, Bugin Tsav II and Gurilin Tsav be long ing to this type.
TYPE C
Lo cal i ties: Abdrant Nuru in the Djadokhta For ma tion, Shar Tsav and Bugin Tsav in the Nemegt For ma tion.
Char ac ter is tics: oval or round foot prints of a qua dru pe - dal an i mal. Wide gauge trackway. Small pace angulation around 83°.
De scrip tion: oval or round foot prints with foot print length rang ing from 30 to 90 cm. In the case of oval foot - prints, the long axis of the foot prints is al most par al lel to the trackway midline (Fig. 6A). All of the find ings are nat u ral casts or platy hard sand stone blocks with underprints formed in the un der ly ing beds be neath the true prints. Strongly weath ered trackways ap pear as a chain of dam aged step ping stones (Fig. 6B and C). Three blunt im pres sions can be ob - served in the an te rior part of better pre served ma te ri als (Fig. 6C and E) and they are con sid ered as traces of dig its. No manus prints were pre served among the in ves ti gated track -
ways be long ing to Type C. But one iso lated foot print was found at Abdrant Nuru. It is a half-moon-shaped nat u ral cast with five blunt dig i tal im pres sions. Its width is 47 cm and the length is 32 cm (Fig. 6D).
Al most all of the foot prints form trackways. 26 trackways were ob served and 15 trackways have been mapped. Val ues of the pace angulation of the trackways range from 71 to 94°. The av er age value of pace angulation of all trackways is 83°. The trackway is wide (Fig. 6A–C). Some of the trackways are in the cat e gory of “wide gauge” (Farlow, 1992; Wil son and Carrano, 1999). The value of trackway ra tio (T/R) of those trackways ranges from 33 to 45%. This cal cu la tion of trackway ra tio is based on the for mula by Romano et al. (2007). There is no tail-drag ging im pres sion.
Ichnotaxonomy: most of the foot prints be long ing to Type C are poorly pre served and dif fi cult to dis cuss tax o nom i cally.
Only one well-pre served large manus foot print is pro vi sion ally as signed to Tetrapodosaurus (Stern berg, 1932) (Fig. 6D).
Tetrapodosaurus-type foot prints have been re ported from the Lower Cre ta ceous of Ja pan (Fujita et al., 2003), but have not been re ported from China or Ko rea (McCrea et al., 2001;
Matsukawa et al., 2006). So this is the first dis cov ery re port of this type from Con ti nen tal Asia.
Fig. 4. Draw ings and pho tos of Type B foot prints from Bugin Tsav (B–G) and Gurilin Tsav (A) (all nat u ral casts) A, B — draw ings of top sur face view of nat u ral casts; C–E — draw ings of sole view of nat u ral cast;
F, G — pho tos of sole view of nat u ral cast
Fig. 5. Draw ings and pho tos of Type B trackways from Bugin Tsav (all nat u ral casts) A, B — draw ing and photo of the same trackway of large in di vid ual;
C, D — draw ing and photo of the same trackway of a mid dle-sized in di vid ual
Fig. 6. Draw ings and pho tos of Type C trackways and foot prints from Abdrant Nuru (all nat u ral casts) A, B — draw ing and photo of the same trackway; C — draw ing of small trackway (strongly weath ered); ar rows in di cate three
blunt digit marks; D — photo of iso lated nat u ral cast of manus print; E — pho to graph of an te rior part of a pes print from trackway C; ar rows in di cate three blunt digit marks
Trackmaker: the main char ac ter is tics of the Type C trackways are the wide gauge and small pace angulation.
There were no bipedal an i mals that im printed such large (30–90 cm in length) foot prints with such wide gauge trackways in the Up per Cre ta ceous of Mon go lia. There fore the trackmakers of Type C trackways are qua dru pe dal an i - mals. The lack of manus prints in these trackways may have been caused by the over lap ping of pos te rior foot prints on the an te rior ones, as the low pace angulation val ues sug gest. The qua dru pe dal di no saur body re mains from the Up per Cre ta - ceous of the Gobi Desert are sauropod, ankylosaurid and ceratopsid. The pace angulation of sauropod trackways gen - er ally ranges from 100 to 140° (e.g., Thulborn, 1990;
Lockley, 1991; Lockley and Hunt, 1995; Lockley and Meyer 2000; Romano et al., 2007). The pace angulation of Type C is around 83° which is sig nif i cantly less than in sauropod track - ways. There fore, there is less prob a bil ity that sauropod di no - saurs were the trackmakers of Type C foot prints.
The wide gauge, small trackway ra tio and small pace angulation of Type C trackways sug gests that the trackmakers had dorsoventrally flat tened body shapes. An i mals with short limbs and a large dis tance be tween left and right limbs could have left the Type C trackways. The an i mals of this kind of body mor phol ogy might have been large in di vid u als of the Ankylosauria or Neoceratopsia. How ever, body fos sils of the lat ter an i mals have not been re ported from Mon go lia. There - fore the most likely trackmakers of the Type C foot prints are ankylosaurid di no saurs.
Leonardi (1984) re ported a trackway with sim i lar char ac - ter is tics of Type C from the Up per Cre ta ceous in Toro Toro, Bolivia, South Amer ica. Leonardi (1984) and McCrea et al.
(2001) at trib uted them to an ankylosaurid di no saur. McCrea et al. (2001) re ported other trackways that have sim i lar char ac ter - is tics to Type C from the Up per Cre ta ceous of Bolivia, Can ada and the USA, at trib ut ing them to ankylosaurid di no saurs.
There are two other pieces of ev i dence that sup port this at - tri bu tion of Type C foot prints. The ex is tence of three blunt im -
pres sions of digit tips in some better pre served nat u ral casts (Fig. 6C and E) and mor pho log i cal char ac ter is tics of a nat u ral cast of manus (Fig. 6D) are im por tant ev i dence. Three or four blunt digit tips on a pes im pres sion are typ i cal char ac ter is tics of pre vi ously dis cov ered ankylosaurid hind foot prints (McCrea et al., 2001). Half moon-shaped large manus im pres sions with five blunt digit marks are also iden ti fied as ankylosaurid.
Fur ther ev i dence is the co ex is tence of skel e tal re mains of ankylosaurids and Type C foot prints in a sin gle bed. In the Djadokhta For ma tion at Abdrant Nuru, one large skel e ton and many disarticulated bones of ankylosaurids (Pinacosaurus and other forms) were dis cov ered from the same strati graphic lay - ers that yielded rich foot prints of Type C (Watabe and Suzuki, 2000b). These data sug gest that the foot prints are at trib ut able to ankylosaurid di no saurs.
TYPE D
Lo cal i ties: Yagaan Khovil and Bugin Tsav in the Nemegt For ma tion.
Char ac ter is tics: large, oval to semi-tri an gu lar out line, four to five im pres sions of pes dig its in the an te rior rim of the foot - prints.
De scrip tion: sev eral large, thick and mas sive nat u ral casts of hard sand stone were dis cov ered at Yagaan Khovil. The out - line of these foot prints is semi-tri an gu lar (one an gle is at the posteriormost point of the foot print). Foot print length and width are al most the same. One well-pre served nat u ral cast is 65 cm in length, 63 cm in width and 25 cm in thick ness (Fig. 7A and B). Very clear slip ping traces of the claws of dig its I, II and III, and more am big u ous slip ping traces of dig its IV and V are im printed. They are pre served at the lat eral sur face of the an te - rior part of the nat u ral cast. The traces left by the slip ping mo - tion mea sure about 20 cm in length. The slip ping traces are not ver ti cal to the bed ding plane (top sur face of the nat u ral cast) but are in clined lat er ally out wards (Fig. 7B).
Fig. 7. Pho tos of Type D foot print (nat u ral cast) from Yagaan Khovil
A — top sur face view of nat u ral cast; B — slip ping traces of claws on the same spec i men (lat eral view from front-left di rec tion)
Two large platy nat u ral casts were dis cov ered at Bugin Tsav. Their anteroposterior length is larger than their width.
Their over all shape is oval. The length of the lon gest axis of the foot prints is 75–85 cm. They are slab-like sand stone plates.
Claw im pres sions are ob served at the an te rior part of the foot - prints.
These foot prints from Yagaan Khovil and Bugin Tsav are all iso lated, not form ing a trackway. Manus prints are not pre - served. There are no tail-drag ging im pres sions.
Ichnotaxonomy: the Type D pes prints from Yagaan Khovil are mor pho log i cally of Brontopodus-type (Fig. 7A). In Cen tral Asia, Brontopodus-type foot prints have been re ported from the Lower and Up per Cre ta ceous beds of China (Lockley et al., 2002; Li et al., 2006). They are also re ported from the Cre ta ceous of Ko rea (e.g., Lockley et al., 2006; Lee and Lee, 2006). As the ma te ri als in this pa per are iso lated nat u ral casts of pes prints, there is no manus print in for ma tion or trackway data. To com pare Type D foot prints with ma te rial from other ar eas of the world, it is de sir able to find well-pre served com - plete manus-pes trackways.
Trackmaker: the main char ac ter is tics of the Type D foot - prints are their large size, oval to semi-tri an gu lar out lines and clear im pres sions of claws and dig its count ing 4 or 5 in the an - te rior part of the foot prints. The size and over all mor phol ogy of the foot prints of Type D from Bugin Tsav and Yagaan Khovil are at trib ut able to the pes of sauro pods. The fossiliferous beds of Bugin Tsav and Yagaan Khovil are cor re lated with the Nemegt For ma tion. The sauropod taxa Nemegtosaurus and Opisthocoelicaudia were dis cov ered in the Nemegt For ma tion of the Nemegt Ba sin (Nowiński, 1971; Borsuk-Białynicka, 1977). Foot print-bear ing beds of the Nemegt For ma tion in Bugin Tsav and Yagaan Khovil yield disarticulated bones and teeth of a sauropod. From the Nemegt lo cal ity, Cur rie et al.
(2003) re ported nat u ral casts with sim i lar char ac ter is tics of Type D and also at trib uted them to sauro pods. Those data sup - port the at tri bu tion of Type D foot prints to sauropod di no saurs.
All of the find ings of Type D are, at pres ent, iso lated nat u ral casts, and their trackways have not yet been rec og nized in the field. Fur ther dis cov ery of their trackways and manus foot - prints are very im por tant for the re con struc tion of limb anat - omy, lo co mo tion and behaviour.
INDETERMINATE FOOTPRINTS
Lo cal i ties: in de ter mi nate foot prints oc cur in all four named for ma tions at Bayn Shire, Shar Tsav, Tugrekin Shire, Abdrant Nuru, Alag Teg, Udyn Sayr, Khongil, Altan Teg, Yagaan Khovil, Altan Ula III, Altan Ula IV, Ulan Khushu, Gurilin Tsav, Bugin Tsav, Bugin Tsav II, Khermeen Tsav, Shiluut Ula and Undor Bogd.
Char ac ter is tics: poorly pre served ma te ri als with no iden ti - cal char ac ter is tics of the Types A–D.
De scrip tion and com ments: a large amount of poorly pre - served ma te rial that is unassignable to types A–D ex ist at all 18 of these newly-found lo cal i ties. At the lo cal i ties ex cept Tugrekin Shire, they are pre served as nat u ral casts and as hard sand stone underprints. Based on sedimentological and
ichnological data, it is pos si ble to iden tify them as “foot prints”.
They are abun dant in Shar Tsav and Bugin Tsav where they to - tal more than 16 000 (Ta ble 1). At Tugrekin Shire, the foot - prints are found in fine-grained sorted eolian sand stone beds, which are soft, loose, in clined foreset beds. Due to the spe cial char ac ter of sub strates, the foot prints are am big u ous and can not be cat e go rized into the Types A–D.
DISCUSSION AND CONCLUSION
At the well-known di no saur body fos sil-rich lo cal i ties in the world, it is com mon that there are few or no di no saur tracks.
It is also com mon that the best known di no saur ichnosites yield few or no body fos sils. By con trast, the newly found tracksites de scribed in this pa per have been well-known as di no saur body fos sil sites. Fre quent co ex is tence of foot prints and skel e tal re - mains in the same and/or nearby beds is a re mark able fea ture of these Mon go lian sites. That makes pos si ble the de tailed com - par a tive anal y ses of foot prints and body fos sil re mains. Iden ti - cal re la tion ships be tween body fos sils and foot prints are ob - served in the cases of Tarbosaurus, Avimimus and Saurolophus.
We first an tic i pated that the fauna based on body fos sils and the fauna based on foot prints (ichnofauna) from a sin gle lo cal ity might be sim i lar in their tax o nomic com po si tions and also in the fre quency ra tio of oc cur rence in each taxon. How ever, the data re veal that the in ferred di no saur fau nal as sem blages based on foot prints are dif fer ent from those based on the body fos sil re - mains, even in the same strati graphic zone at the same lo cal ity.
For ex am ple, in the foot print-bear ing beds of the Nemegt For ma tion at Bugin Tsav and Gurilin Tsav, Type A (theropod) foot prints are rare while Type B (ornithopod) are abun dant (Ta - ble 1). By con trast, many theropod body fos sils have been un - earthed there, to gether with ornithopod body fos sils in the same layer as con tain the foot prints at these sites (Chudinov, 1966;
Suzuki and Watabe, 2000a). Al though there is no pre cise nu - mer i cal data re gard ing the ex posed body fos sil re mains, theropod fos sils are more abun dant and fre quently ob served than ornithopod fos sils in the field.
At the Shar Tsav lo cal ity, where the foot print-bear ing beds might be cor re lated with the Nemegt For ma tion, the ma jor ity of the foot prints dis cov ered are Type A (theropod) of var i ous sizes (Ta ble 1 and Fig. 1). There are some Type C (ankylosaurid) foot prints, but no Type B (ornithopod) nor Type D (sauropod) foot prints. How ever, no body fos sil re - mains of me dium to large sized theropods or ankylosaurids have been re cov ered from this site. Only small theropods and sauropod body fos sil re mains have been dis cov ered (Kurzanov and Bannikov, 1983; Watabe and Suzuki, 2000a).
At the Abdrant Nuru lo cal ity, both body re mains of ankylosaurids and Type C (ankylosaurid) foot prints are abun - dant. This as so ci a tion seems to be rea son able. How ever, body fos sils of theropods are very rare com pared to the fre quent dis - cov ery of Type A (theropod) foot prints at the same site.
These pre lim i nary ob ser va tions in di cate that, even in the same bed and site, the di no saur fau nal as sem blage based on foot prints dif fers from that on body fos sil re mains. Cur rie et al.
(2003) re ported a sim i lar ex am ple from the Nemegt lo cal ity.
Based on their ob ser va tions at Nemegt, they in ferred bi ases against the fos sil iza tion and re cov ery of hadrosaur skel e tons com pared to theropod skel e tons. Cur rie et al. (2003) noted the pos si bil ity that Tarbosaurus was very ef fec tive at scav eng ing the carcasses of dead hervivores. They suggested that the chem i cal en vi ron ment of the sed i ment in flu ences the rel a tive pres er va tion of ornithopod and theropod bones. Such in ter pre - ta tions could be ap pli ca ble at Bugin Tsav and Gurilin Tsav.
How ever, they may not be ap pli ca ble to other sites. The pro - cesses pre serv ing body fos sils and foot prints must be in flu - enced by many fac tors. The re sults dem on strate that di no saur fau nal as sem blages should be con sid ered very care fully and wher ever pos si ble, in clude ev i dence from both foot prints and body fos sil re mains to form a com plete anal y sis.
Ac knowl edge ments. We are grate ful to the mem bers of Hayashibara Mu seum of Nat u ral Sci ences — Mon go lian
Paleontological Cen ter Joint Paleontological Ex pe di tion for their help through out the field work and re search. We are greatly in debted to K. Hayashibara, Pres i dent of the Hayashibara Group, K. Ishii, Di rec tor of the Hayashibara Mu - seum of Nat u ral Sci ences, R. Barsbold, Di rec tor of the Mon go - lian Paleontological Cen ter and all the gen er ous mem bers of the HMNS, MPC and the Hayashibara Com pany who con sis - tently sup ported the re search. We are also grate ful to the Olym - pus Cor po ra tion, the Mitsubishi Mo tors Cor po ra tion, and the Panasonic Cor po ra tion for their sup port for the field work, and to the “KAMEI Foun da tion for the Pro mo tion of So cial Ed u ca - tion” for fund ing to one of au thors (Ishigaki). We also thank to T. Tsubamoto, Y. Matsumoto, S. Suzuki, P. Narmandakh and Y. Ariunchimeg for in valu able ad vice. M. G. Lockley and C.
A. Meyer re viewed the manu script and gave us im por tant sug - ges tions; we thank them for their kind and con struc tive ad vice.
This pa per con sti tutes Con tri bu tion Num ber 49 of the HMNS-MPC Joint Paleontological Ex pe di tion.
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