12 - Lucas et al (Tr Eubrontes).p65
Transcription
12 - Lucas et al (Tr Eubrontes).p65
Harris et al., eds., 2006, The Triassic-Jurassic Terrestrial Transition. New Mexico Museum of Natural History and Science Bulletin 37. 86 TRIASSIC-JURASSIC STRATIGRAPHIC DISTRIBUTION OF THE THEROPOD FOOTPRINT ICHNOGENUS EUBRONTES SPENCER G. LUCAS1, HENDRIK KLEIN2, MARTIN G. LOCKLEY3, JUSTIN A. SPIELMANN1, GERARD D. GIERLINSKI4, ADRIAN P. HUNT1 AND LAWRENCE H. TANNER5 1 New Mexico Museum of Natural History and Science, 1801 Mountain Road NW, Albuquerque, NM 87104; 2 Rübezahlstrasse 1, D-92318 Neumarkt, Germany; 3 Dinosaur Tracks Museum, University of Colorado at Denver, PO Box 173364, Denver, CO 80217; 4 Polish Geological Institute, Rakowiecka 4, PL00-975, Warsaw, Poland; 5 Department of Biology, Le Moyne College, 1419 Salt Springs Road, Syracuse, NY 13214 Abstract—Eubrontes is an ichnogeneric name applied to relatively large (pes length > 25 cm) tridactyl tracks of a bipedal theropod dinosaur. Eubrontes tracks are well known from Lower Jurassic strata, especially in southern Africa, western Europe, eastern North America and the American Southwest, and some have advocated that the lowest occurrence (LO) of Eubrontes corresponds to the Triassic-Jurassic boundary. However, there are well documented Late Triassic records of Eubrontes in Australia, southern Africa, western Europe, Greenland and North America. Indeed, the LO of Eubrontes in the Newark Supergroup of eastern North America, long considered to be equivalent to the base of the Jurassic, is demonstrably of Late Triassic age based on radioisotopic ages and microfossil biostratigraphy. Furthermore, body fossils of Late Triassic theropods large enough to make Eubrontes tracks are known from Europe and North America. The theropod footprint record across the Triassic-Jurassic boundary indicates a gradual increase in theropod maximum body size across the system boundary. The idea of a sudden appearance of Eubrontes trackmakers at the beginning of the Jurassic, the result of a rapid (thousands of years) evolutionary response by the theropod survivors of a mass extinction (“ecological release”), can be rejected. INTRODUCTION Eubrontes is an ichnogeneric name long applied to some relatively large, bipedal and functionally tridactyl tracks of early Mesozoic age, widely considered to have been made by a theropod dinosaur (Fig. 1). Since the 1980s, some workers have argued that the lowest occurrence (LO) of Eubrontes coincides with the Triassic-Jurassic boundary (TJB). This idea has been important to placement and correlation of the TJB in nonmarine strata. However, the LO of Eubrontes does not coincide with the base of the Jurassic, as there are various well-documented Triassic Eubrontes records (Lucas, 2003; Lucas et al., 2005b, c). Here, we review these records to establish the biostratigraphic distribution of Eubrontes and to discuss its implications for theropod dinosaur evolution across the Triassic-Jurassic boundary. ICHNOTAXONOMY AND TRACKMAKER We use the ichnogeneric name Eubrontes E. Hitchcock, 1845, as redefined by Olsen et al. (1998). Their diagnosis of Eubrontes reads: Large (>25 cm long) bipedal, functionally tridactyl ichnite with a relatively short digit III, a broad pes, and a hallux which is rarely, if ever, impressed. Divarication of outer digits averaging 25o-40o (Olsen et al., 1998, p. 590). Several authors have argued (most recently Rainforth, 2005) that Eubrontes and the smaller Grallator should be the same ichnogenus, as they are only reliably distinguished on the basis of size (Fig. 1). While we agree with this in general, we still use Eubrontes here because of the biostratigraphic significance that has been attached to this ichnogenus, understood as a Grallator-like pes imprint larger than 25 cm long. As noted by Olsen (1980), Lockley (1999) and Milner et al. (this volume) Grallator tracks are more elongate, with a greater anterior projection of digit III, than Eubrontes. This is what Weems (1992) refers to as “toe extension.” Placing Grallator in the same ichnogenus as Eubrontes, as suggested by Rainforth (2005), requires an allometric argument that implies “lumping” or synonymy. Such an approach explicitly allows the synonymy of two morphologies that represent end members of a FIGURE 1. Eubrontes (left) and Grallator (right) showing possible configurations of phalanges based on congruence (A) or incongruence (B) of pads and phalanges. Not to scale; after Thulborn (1990). Grallator-Anchisauripus-Eubrontes plexus, originally proposed by Olsen (1980) under the double barreled “sub-ichnogenus” labels Grallator (Grallator), Grallator (Anchisauripus) and Grallator (Eubrontes). This cumbersome and ichnologically-unprecedented scheme also has some merit for fans of allometry, and has been accepted by some authors and discussed by others (Gierlinski, 1991; Weems, 1992; Gierlinski and Ahlberg, 1994; Lockley, 2000). It provides ample food for ongoing debate on the perennial problems of theropod track ichnotaxonomy between the lumper versus splitter factions. Although it is outside the scope of this paper to undertake a taxonomic revision of the plexus, we note that Olsen et al. (1998), who undertook the most recent and thorough investigation of the problem, still maintain the Grallator-Eubrontes distinction, which moves away from the implied synonymy of the original allometric plexus argument of Olsen (1980). We follow this more 87 recent position (Olsen et al., 1998) in maintaining the Grallator-Eubrontes distinction. Eubrontes, as used here, also encompasses other large grallatorid ichnotaxa from the Triassic-Lower Jurassic, such as Kayentapus, Dilophosauripus and Gigandipus, considered by some authors as distinct from Eubrontes, as well as several forms described under separate names from the Elliot Formation of South Africa (Ellenberger, 1970, 1972, 1974). Full agreement on the synonymy of these ichnogenera has not been reached, and Kayentapus is still used by at least one of us (GG). We consider Anchisauripus, an ichnotaxon that was originally described by Lull (1904) and redefined by Olsen et al. (1998) as grallatorids of intermediate size (15-25 cm length) and morphology between Grallator and Eubrontes, to be a junior synonym of Eubrontes (also see Rainforth, 2005). The name is not used here, but we adhere to the minimum 25-cmlong pes to define Eubrontes because this is the definition of Eubrontes that is of supposed biostratigraphic significance. Olsen et al. (1998) and Rainforth (2005) illustrate a range of extramorphological variation in Eubrontes tracks that subsumes all tracks that are here referred to Eubrontes. There is virtually universal agreement that the Eubrontes trackmaker was a relatively large, early Mesozoic theropod dinosaur, such as the ceratosaur Dilophosaurus. Weems (2003) argued that a Plateosaurus-like prosauropod was the Eubrontes trackmaker, but the disparity between prosauropod foot structure and Eubrontes tracks is so great that we dismiss Weem’s contention, as have others. TRIASSIC RECORDS OF EUBRONTES Here, we review Triassic records of Eubrontes tracks (Fig. 2). Australia Staines and Woods (1964) reported a trackway found in roof shales of the Striped Bacon Coal Seam at Rhonda Colliery in the Sydney basin of eastern Australia (Fig. 3). The best-preserved track is 43 cm long (31 cm long for the digitigrade portion) and 38 cm wide, and the stride of the trackway is 2 m (Hill et al., 1965; Bartholomai, 1966; Molnar, 1991; Thulborn, 1998; Lucas and Tanner, 2004). The tracks closely resemble tracks of Eubrontes giganteus from the Newark Supergroup as redescribed by Olsen et al. (1998). The Australian tracks are from the Blackstone Formation of the Ipswich Coal Measures near Dinmore in southeastern Queensland, a unit of well-established Triassic age (probably late Carnian: Balme and Foster, 1996). Thulborn (2003) argued that the Australian Triassic record of Eubrontes refutes the notion that its LO is at the base of the Jurassic. Olsen et al. (2003), nevertheless, claimed that the Australian Eubrontes tracks are actually tridactyl underprints of a pentadactyl chirothere track. FIGURE 2. Map of Late Triassic Pangea showing Eubrontes locations discussed in the text. Localities are: 1, Sydney basin, Australia; 2, southern Africa; 3, Great Britain; 4, France, Germany and Poland-Slovakia; 5, Scania, Sweden; 6, eastern Greenland; 7, eastern North America; 8, American Southwest. However, the footprint of Eubrontes is mesaxonic (symmetrical around its long axis), as are the Australian Eubrontes tracks (Fig. 3). Tridactyl underprints of chirotheres are paraxonic (asymmetrical around their long axis). Therefore, the Eubrontes tracks from the Upper Triassic of Australia are correctly identified. Southern Africa Relatively large tetrapod tracks from the Triassic of southern Africa were documented in detail by Ellenberger (1970, 1972). They come from footprint-rich red beds of the Lower Elliot Formation, which is Norian in age (Lucas and Hancox, 2001). Ellenberger, following his own ichnological concept, assigned new ichnogeneric names such as Quemetrisauropus, Prototrisauropus or Deuterotrisauropus to the pes imprints of large bipedal dinosaurs from these strata. The morphology and size (pes length up to 35 cm) of these tracks support assignment to Eubrontes (Fig. 4). Moreover, the grallatorid footprint pattern and digit proportions of these lower Elliott theropod tracks preclude their identification as incomplete chirothere tracks, which are also present on the same surfaces. Similar theropod footprints are found in the upper Elliot Formation, which is Lower Jurassic (Ellenberger, 1970, 1972, 1974). Thus, the southern African records of Eubrontes encompass Upper Triassic and Lower Jurassic strata. Great Britain An archosaur track assemblage composed of grallatorid and chirothere imprint forms is known from 88 trackways and numerous isolated tracks from different coastal exposures of Wales (Thomas, 1879; Sollas, 1879; Bassett and Owens, 1974; Tucker and Burchette, 1977; Lockley et al., 1996). The tracks come from a marginal facies of the Mercia Mudstone Group (Norian-Rhaetian), which is overlain by the marine Penarth Group. On the track surfaces, tridactyl grallatorid footprints of varied sizes, showing the characteristic pattern of digit proportions and preserved pads, are common. Although few measurements have been published, in some cases large tracks are as much as 26 cm long, reaching the lower size range of Eubrontes. Switzerland Thirteen trackways of large theropods with Eubrontes-like imprints have been observed on a steeply-inclined surface at the Piz dal Diavel in the Swiss Alps (Furrer, 1993; Lockley and Meyer, 2000). They are preserved in a limestone bed that belongs to the Diavel Formation of the Hauptdolomit Group (Norian). The trackway pattern shows a narrow trackway width and stride lengths up to 2.2 m. The size of the FIGURE 3. Australian Triassic Eubrontes trackway (after Staines and Woods, 1964) and photograph of cast of track (after Bartholomai, 1966). 88 FIGURE 4. Eubrontes tracks from southern Africa (Lesotho) in the Ellenberger collection, lower Elliott Formation (“Molteno” zones A2 [B-C] and A4 [A]). A, LES 44.2. B, LES 6.1. C, LES 6.2. footprints (pes is 25-30 cm long: Furrer, 1993) as well as their overall morphology support assignment to Eubrontes. France From the Keuper strata of d’Anduze (Norian) of southern France, Ellenberger (1965) and Ellenberger et al. (1970) described large tridactyl footprints that are associated with chirothere tracks. Several trackways appear on in situ track surfaces in a riverbed near Anduze (département Gard). Unfortunately, most of the material was destroyed by a flood a few years ago (P. Ellenberger, personal commun., 2005). However, Ellenberger’s figures clearly show the grallatorid morphology (digit three longest) of the imprints, which reach a length of 50 cm, and a narrow trackway pattern with stride lengths up to 3 meters. Hence the determination and identification as Eubrontes or Eubrontes-like theropod footprints is justified. Indeed, Haubold (1971) referred these tracks to Eubrontes. The track layer is about 25 m below the base of the Rhaetian, in strata that yield the conchostracan Euestheria minuta, and are considered to be of Norian age (Ellenberger, 1965). Another possible Triassic record of Eubrontes from France at Vendée was documented by Lapparent and Montenat (1967). These are numerous tridactyl tracks, some more than 40 cm long, from strata of likely Rhaetian age (Demathieu et al., 2002). If this age is correct, then this is one of the best documented and most extensive Triassic records of Eubrontes. Germany From the TJB (“Rhätolias”) strata of northern Bavaria, Kuhn (1958) described and illustrated a large pes imprint under the name Coelurosaurichnus sassendorfensis (also see Haubold, 1971, fig. 42.4) The specimen was not collected, but the sketch and published measurements indicate an obvious similarity to Eubrontes. The tridactyl, grallatorid pes imprint (25.6 cm long) is digitigrade with digit three longest, and has large, tapering claws. However, the exact stratigraphic position of the track-bearing sandstone block within a siliciclastic succession comprising the Triassic-Jurassic transition is not certain, so its age is not clear. According to Kuhn (1958), this could be uppermost Rhaetian or lowermost Liassic. Poland-Slovakia The Tomanová Formation in the Tatra Mountains of Poland and Slovakia yields large tridactyl theropod tracks assignable to Eubrontes (Fig. 5A), as revised by Michalik and Kundrat (1998), and by Gierliñski and Sabath (2005). These tracks are associated with characteristic Triassic ichnogenera listed by Gierlinski and Sabath (2005) as “Tetrasauropus” (= Eosauropus: Lockley et al., this volume) and “Pseudotetrasauropus” (=Evazoum Nicosia and Loi, 2003; = Brachychirotherium: Klein et al., this volume). The age of the Tomanová Formation is latest Triassic (Rhaetian) based on macrofloral and palynological analyses (Michalik et al., 1976; Fijalkowska and Uchman, 1993). Sweden Bölau (1952) first documented large (up to 38 cm long pes) tridactyl dinosaur tracks from the Höganäs Formation in northwestern Scania (Fig. 5B). Bölau (1952) made no ichnotaxonomic assignment, but Haubold (1971, 1986) assigned the Swedish tracks to Eubrontes. Gierlinski and Ahlberg (1994) redescribed this record, which is from the roof beds of coal mines in the Bjuv Member of the Hogänäs Formation. This interval is assigned a latest Triassic (Rhaetian) age based on sequence stratigraphy, plant biostratigraphy and the presence of a Triassic amphibian body fossil (e.g., Nilsson, 1934; Pienkowski, 1991). The best-preserved tracks are tridactyl and up to 32 cm long, and certainly referable to Eubrontes (Fig. 5B). A stratigraphically higher level in the Hettangian portion of the Höganäs Formation also yields large theropod tracks assigned to Grallator (Eubrontes) soltykovensis by Gierlinski and Ahlberg (1994), later revised as Kayentapus soltykovensis (Gierlinski, 1996), so in Scania the stratigraphic range of large theropod tracks encompasses the TJB. Greenland Theropod trackways from the Ørsted Dal Member of the Fleming Fjord Formation (Norian) of Jameson Land in east Greenland were described by Jenkins et al. (1994) and Gatesy et al. (1999). Jenkins et al. (1994) report that the grallatorid imprints reach a maximum length of 28 cm, which is within the size range of Eubrontes. 89 FIGURE 5. Triassic Eubrontes from Slovakia and Sweden. A, Eubrontes from Tomanová Formation (Rhaetian), Ticha Dolina (Slovakia). B, Eubrontes cf. E. giganteus, specimen LO 5462t from Höganäs Fm. (Middle Rhaetian), “Gustaf Adolf” coal mine in Scania (Skane), Sweden. The scale bar above the hypex beween digits II and III equals 5 cm. Eastern North America The idea that the LO of Eubrontes corresponds to the base of the Jurassic has almost become doctrine for those who work on the tetrapod track record of the Newark Supergroup in eastern North America (e.g., Olsen, 1983; Olsen and Galton, 1984; Silvestri and Szajna, 1993; Szajna and Silvestri, 1996; Olsen et al., 1998, 2002a, b, 2003; Szajna and Hartline, 2003). Nevertheless, the LO of Eubrontes in the Newark basin, which is just below the lowest basalt sheet of the Newark extrusive zone, does not correspond to the Triassic-Jurassic boundary (Fig. 6). This is because the palynological criteria that supposedly placed the TJB below the lowest basalt sheet do not identify the TJB, and radioisotopic dating of the TJB in marine strata indicate it is no older than 200 Ma, which is younger than the 201 Ma age of the lowest basalt sheet (Lucas and Tanner, 2004; Kozur and Weems, 2005). Recent conchostracan biostratigraphy of Newark Supergroup strata that encompass the TJB also indicates the system boundary is above the lowest basalt sheet and thus above the LO of Eubrontes (Kozur and Weems, 2005). Weems (1987, p. 16-17, fig. 4, pl. 1B) documented relatively large (~27 cm long pes) tridactyl tracks of a biped (a 14 footfall trackway) that he assigned to Eubrontes from the Balls Bluff Siltstone (Norian) at the Culpeper Crushed Stone Quarry in the Culpeper Basin of Virginia. Weems (1992) reported measurements of all the tridactyl tracks at the Culpeper Crushed Stone Quarry, indicating that there are many such tracks with pes lengths greater than 25 cm. Smoot and Olsen (1989, fig. 4A) illustrated one of these tracks as a “possible Grallator,” despite its size, and further argued that this and the other tracks Weems (1987) described from the Culpeper Crushed Stone Quarry are indeterminate. The tracks Weems (1987) assigned to Eubrontes are quite similar to Eubrontes tracks illustrated by Olsen et al. (1998, fig. 4F-G), so we assign them to the ichnogenus. American Southwest There is one possible record of Eubrontes from Upper Triassic strata of the Chinle Group in the American Southwest (e.g., Lockley and Hunt, 1995). Virtually all Chinle Group theropod tracks have been assigned to Grallator (Lucas, 1997), but a possible exception is a report of a tridactyl theropod track that is ~ 26 cm long by Martin and Hasiotis (1998, fig. 5). This track is from the Blue Mesa Member of the Petrified Forest Formation (upper Carnian) in the Petrified Forest National Park, Arizona, but is a single, incompletely preserved track, so its ichnotaxonomic identity is uncertain. Likewise, as noted below, unnamed tracks reaching 25 cm in length (the minimum for Eubrontes) have been reported by Lockley and Hunt (1993) from the Sloan Canyon Formation of northeastern New Mexico. In the American Southwest, the LO of abundant Eubrontes is in the Dinosaur Canyon Member of the Moenave Formation on Ward’s Terrace in northeastern Arizona, approximately 35 m above a tracksite in a tongue of the Wingate Sandstone that yields Triassic tracks (Lucas et al., 2005a, fig. 4). Eubrontes also is present in the top of the Wingate Sandstone, and in the Whitmore Point Member of the Moenave Formation, strata of well-established Early Jurassic age (Milner and Lockley, 2006; Milner et al., this volume) (Fig. 7). Eubrontes tracks are very abundant in the overlying Lower Jurassic Kayenta Formation and Navajo Sandstone (e.g., Rainforth and Lockley, 1996; Lockley et al., this volume). In the American Southwest, Eubrontes tracks do not co-occur 90 FIGURE 6. Different definitions of the TJB in the Newark Supergroup of eastern North America, with respect to the LO of Eubrontes. The definition on the right is consistent with radioisotopic ages and microfossil biostratigraphy. with any unambiguous Triassic age indicators. Thus, it is possible that the LO of Eubrontes in the American Southwest is an earliest Jurassic event. However, until a more precise placement of the base of the Jurassic can be achieved, the most that can be said is that the LO of abundant Eubrontes appears to be a possible Jurassic biostratigraphic datum in the American Southwest (Fig. 7). TRIASSIC THEROPODS AS EUBRONTES TRACKMAKERS FIGURE 7. Lithostratigraphy of the TJB interval on the Colorado Plateau with respect to the LO of Eubrontes. See Lucas et al. (2005a) for discussion of position of TJB. Most Late Triassic theropods were of small to moderate size and thus potential trackmakers of Grallator (pes length generally < 15 cm). However, a handful were significantly larger, and thus are potential trackmakers of Eubrontes. Based principally on published reports and illustrations we reconstruct the pes size of selected relatively large Late Triassic theropods (Fig. 8). These reconstructions are based on the length from the tip of the central digit to the distal articular ends of metatarsals 2 and 4. The inclusion of these articular ends allows us to estimate the length of the “heel” of the footprint (Fig. 1), which would be generated either by the ends of these metatarsals or a fleshy pad, the plantar aponeurosis, directly beneath these metatarsals. The pedes of both Coelophysis bauri and Megapnosaurus rhodesiensis are well known, especially the pes of C. bauri, which is known from dozens of specimens. However, the pedes of both taxa are significantly smaller (14 and 15 cm) than would be needed to make Eubrontes tracks. Thus, their pes sizes would allow them to make Grallator tracks. Liliensternus liliensterni is known from an incomplete skeleton that includes a complete pes. This pes, at 22 cm, is almost the size needed to make a Eubrontes track. Because L. liliensterni is known from only one, moderately complete skeleton, it is probable that larger indi- 91 FIGURE 8. Pes skeletons and lengths of selected Late Triassic and Early Jurassic theropods. Line drawings of Coelophysis bauri and Megapnosaurus rhodesiensis from Colbert (1989), drawing of Liliensternus liliensterni from Rowe and Gauthier (1990), and drawing of Dilophosaurus wetherilli from Welles (1984). viduals of this taxon could make Eubrontes tracks. Liliensternus airelensis is known from an isolated tooth, various vertebrae, a sacrum, and an incomplete pelvic girdle described by Cuny and Galton (1993). Based on illustrations in Cuny and Galton (1993, fig. 14), L. airelensis has a pelvic girdle that is approximately 1.5 times the size of L. liliensterni based on the length of the acetabular opening (11 cm in L. airelensis versus 7 cm in L. liliensterni). Applying this same ratio to the pes length of L. liliensterni results in an approximate pes size of 33 cm for L. airelensis, which is clearly large enough to make Eubrontes tracks. However, the holotype material of L. airelensis was collected from strata that do not yield a definitive assemblage of Triassic or Jurassic pollen, and thus was assigned to the uppermost Rhaetian transitional zone, but as noted by Cuny and Galton (1993, p. 263), “it is difficult to say if it is in the Triassic or the Jurassic.” The early Norian ceratosaurian dinosaur Gojirasaurus quayi is known from an isolated tooth, various axial skeletal elements, portions of its pectoral and pelvic girdle, a tibia and a metatarsal (Carpenter, 1997). However, based on the size of the tibia, Carpenter (1997) estimated that G. quayi was 5.5 m long. This is considerably larger than Liliensternus liliensterni, which Carpenter (1997) estimated at 3.8 m long. Thus, based on its size, Gojirasaurus quayi could easily have made large Eubrontes tracks. In summary, there were theropods large enough to produce Eubrontes-size tracks in the Late Triassic. A large Liliensternus liliensterni could produce a very small Eubrontes track, while L. airelensis, if it is indeed from the Late Triassic, could produce a moderately-sized Eubrontes track. Gojirasaurus quayi was large enough to produce a very large Eubrontes track. THEROPOD EVOLUTION ACROSS THE TRIASSICJURASSIC BOUNDARY The idea that the theropod dinosaur ichnogenus Eubrontes has its LO at the base of the Jurassic began with Olsen (1983) and Olsen and Galton (1984), who advocated this datum because of the close correspondence between the LO of Eubrontes in the Newark Supergroup and the “palynostratigraphically-defined” TJB. Thus, use of Eubrontes to indicate the base of Jurassic depends entirely on palynostratigraphy, not on the stratigraphic distribution of the tracks themselves. Indeed, previously, in his global review of footprint ichnotaxa, Haubold (1971) considered Eubrontes to be both Late Triassic and Early Jurassic in age. Subsequent to the correlations advocated by Olsen and Galton (1984), most ichnologists considered Eubrontes tracks to be exclusively of Jurassic age but they did not equate the LO of Eubrontes with the TJB (e.g., Haubold, 1986; Lockley and Hunt, 1994, 1995). These authors knew that Eubrontes occurrences are in rocks generally considered Jurassic in age, though there was no way to correlate most of the occurrences to marine strata or, more importantly, they could not demonstrate a close coincidence of the LO of Eubrontes and the TJB as it is defined in marine strata. Olsen et al. (2002a, b) argued that the sudden appearance of Eubrontes, made by a Dilophosaurus-like theropod, in the “earliest Jurassic” strata of the Newark Supergroup indicates a dramatic size increase in theropod dinosaurs at the TJB. They interpreted this as the result of a rapid (thousands of years) evolutionary response by the theropod survivors of a mass extinction and referred to it as “ecological release” (Olsen et al., 2002a, p. 1307). They admitted, however, that this hypothesis could be invalidated by the description of Dilophosaurussized theropods or diagnostic Eubrontes giganteus tracks in verifiably Triassic-age strata. Indeed, their hypothesis is invalidated because theropods large enough to have made Eubrontes tracks have been known from the Late Triassic body-fossil record for decades, and there are Triassic records of Eubrontes, as discussed above. The idea of a sudden size increase of theropod dinosaurs across the TJB also runs counter to data, especially from the American Southwest, that indicate a relatively gradual increase in theropod track size across the TJB (e.g., Lockley, 1991, fig. 9.2; Lockley and Hunt, 1995, fig. 3.28). Thus, most Late Triassic grallatorid tracks are smaller than 20 cm, though a few are as long as 25 cm and thus reach the minimum for Eubrontes size (Lockley and Hunt, 1993, p. 282, fig. 3; 1995, p. 80, fig. 3.10 bottom, p. 105. fig. 3.28). The oldest abundant Eubrontes tracks in the American Southwest (from the Moenave-Wingate interval) are 25-35 cm long, whereas younger Early Jurassic Eubrontes tracks (KayentaNavajo interval) are up to 50 cm long. Thus, in the American Southwest, there appears to be a relatively gradual increase in maximum theropod pes (and body) size across the TJB, though it should be noted that many small theropod tracks (Grallator) are also known in Lower Jurassic strata. The theropod track record thus does not support the concept of a substantial extinction or evolutionary turnover of these dinosaurs at the TJB. Eubrontes thus has its LO in Upper Triassic strata. The oldest occurrences of the ichnogenus apparently are in Carnian strata of the 92 Sydney basin, Australia and possibly at the Petrified Forest National Park in the American Southwest. African, European and other North American records begin in the Norian and continue into the Early Jurassic. We are hesitant to attribute much significance to the regional diachroneity in the LO of Eubrontes, though Thulborn (2003) suggested it may indicate a Gondwanan origin of the theropod that was the Eubrontes trackmaker. Nevertheless, at this point we are content to establish that the ichnogenus Eubrontes has numerous Triassic records, its LO does not equate to the Triassic-Jurassic boundary, and that the distribution of Eubrontes does not indicate a theropod extinction at the TJB. ACKNOWLEDGMENTS Reviews by Jerry Harris, Andrew Milner and Robert Weems improved the manuscript. REFERENCES Balme, B.F. and Foster, C.B., 1996, Triassic (chart 7), in Young, G.C., and Laurie, J.R., eds., An Australian Phanerozoic timescale: Oxford University Press, Melbourne, p. 136-147. Bartholomai, A., 1966, Fossil footprints in Queensland: Australian Natural History, v. 15(5), p. 147-150. Bassett, M. G. and Owens, R. M., 1974, Fossil tracks and trails: Amgueddfa, Bulletin of the National Museum of Wales (Winter, 1974), p. 2-18. Bölau, E., 1952, Neue fossil funde aus dem Rhät Schunesundihre paläogeographisch-ökologische Auswartung: Gelogiska Föreningens i Stockholm Förhandlingar, v. 74, p. 44-50. Carpenter, K., 1997, A giant coelophysoid (Ceratosauria) theropod from the Upper Triassic of New Mexico, USA: Neues Jahrbuch für Geologie und Paläontologie Abhandlungen, v. 205, p. 189-208. Colbert, E.H., 1989, The Triassic dinosaur Coelophysis: Museum of Northern Arizona, Bulletin 57, p. 1-160. Cuny, G. and Galton, P.M., 1993, Revision of the Airel theropod dinosaur from the Triassic-Jurassic boundary (Normandy, France): Neues Jahrbuch für Geologie und Paläontologie Abhandlungen, v. 187, p. 261-288. Demathieu, G., Gand, G., Sciau, J. and Freytet, P., 2002, Les traces de pas de dinosaures et autres archosaures du Lias Inferieur des Grands Causses, sud de la France: Palaeovertebrata, v. 31, p. 1-143. Ellenberger, F., Ellenberger, P. and Ginsburg, L., 1970, Les dinosaures du Trias et du Lias en France et en Afrique du Sud, d’après les pistes qu’ils ont laissées: Bulletin de la Société Géologiques de France 7, v. 12, p. 151159. Ellenberger, P., 1965, Découverte de pistes de Vertébrés dans le Permien, le Trias et le Lias inférieur, aux abords de Toulon (Var) et d’Anduze (Gard): Comptes Rendus de l’Académie des Sciences de Paris, v. 260, p. 58565859. Ellenberger, P., 1970, Les niveaux paléontologiques de première apparition des Mammifères primordiaux en Afrique du Sud et leur ichnologie. Establissement de zones stratigraphique détaillées dans le Stormberg du Lesotho (Afrique du Sud) (Trias supérieur à Jurassique), in Second Gondwana Symposium, Proceedings and Papers: Pretoria, Council for Scientific and Industrial Research, p. 343-370. Ellenberger, P., 1972, Contribution à la classification des Pistes de Vertébrés du Trias: les types du Stormberg d’Afrique du Sud (I): Palaeovertebrata, Memoire Extraordinaire 1972, 152 p. Ellenberger, P., 1974, Contribution à la classification des Pistes de Vertébrés du Trias : les types du Stormberg d’ Afrique du Sud (II): Palaeovertebrata, Memoire Extraordinaire 1974, 141 p. Fijalkowska A. and Uchman, A., 1993, Nowe dane do palinologii triasu tatrzañskiego (New data on palynology of the Triassic of the Polish Tatra Mts). Przegl¹d Geologiczny, v. 5, p. 373-375. Furrer, H., 1993, Entdeckung und Untersuchung der Dinosaurierfährten im Nationalpark: Cratschla Ediziuns Specialas, v. 1, p. 4-23. Gatesy, S.M., Middleton, K.M., Jenkins, F.A., Jr. and Shubin, N.H., 1999, Three-dimensional preservation of foot movements in Triassic theropod dinosaurs: Nature, v. 399, p. 141-144. Gierlinski, G., 1991, New dinosaur ichnotaxa from the early Jurassic of the Holy Cross Mountains, Poland: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 85, p. 137-148. Gierlinski, G., 1996, Dinosaur ichnotaxa from the Lower Jurassic of Hungary: Geological Quarterly, v. 40, p. 119-128. Gierlinski, G. and Ahlberg, A., 1994, Late Triassic and Early Jurassic dinosaur footprints in the Höganäs Formation of southern Sweden: Ichnos, v. 3, p. 99-105. Gierlinski, G. and Sabath, K., 2005, Dinosaur tracks in the Upper Triassic and Lower Jurassic of central Europe, in Tracking Dinosaur Origins, the Triassic/Jurassic Terrestrial Transition, Abstracts Volume, p. 5. Haubold, H., 1971, Ichnia Amphibiorum et Reptiliorum fossilium: Encyclopedia of Paleoherpetology, Teil 18, 124 p. Haubold, H., 1986, Archosaur footprints at the terrestrial Triassic-Jurassic transition, in Padian, K., ed., The beginning of the Age of Dinosaurs: Cambridge, Cambridge University Press, p. 189- 201. Hill, D., Playford, G. and Woods, J.T., 1965, Triassic fossils of Queensland: Brisbane, Queensland Palaeontographical Society, 32 p. Hitchcock, E., 1845, An attempt to name, classify, and describe the animals that made the fossil footmarks of New England: Proceedings of the 6th Annual Meeting of the Association of American Geologists and Naturalists, New Haven, Connecticut, v. 6, p. 23-25. Jenkins, F.A., Jr., Shubin, N.H., Amaral, W.W., Gatesy, S.M., Schaff, C.R., Clemmensen, L.B., Downs, W.R., Davidson, A.R., Bonde, N. and Osbaeck, F., 1994, Late Triassic continental vertebrates and depositional environments of the Fleming Fjord Formation, Jameson Land, east Greenland: Meddelelser om Grønland Geoscience, v. 32, p. 1-25. Kozur, H.W. and Weems, R.E., 2005, Conchostracan evidence for a late Rhaetian to early Hettangian age for the CAMP volcanic event in the Newark Supergroup, and a Sevatian (late Norian) age for the immediately underlying beds: Hallesches Jahrbuch für Geowissenschaften B, v. 27, p. 21-51. Kuhn, O., 1958, Zwei neue Arten von Coelurosaurichnus aus dem Keuper Frankens: Neues Jahrbuch für Geologie und Paläontologie Monatshefte, v. 1958, p. 437-440. Lapparent, A.F. de and Montenat, C., 1967, Les empreintes de pas de reptiles de l’infralias du Veillon (Vendée): Mémoires de la Société Géologique de France, Nouvelle Série, v. 107, 41 p. Lockley, M.G., 1991, Tracking dinosaurs: a new look at an ancient world: Cambridge, Cambridge University Press, 238 p. Lockley, M.G., 1999, The eternal trail: a tracker looks at evolution. New York, Perseus Books, 334 p. Lockley, M.G., 2000, Philosophical perspectives on theropod track morphology: blending qualities and quantities in the science of ichnology: Gaia, v. 15, p. 279-300. Lockley, M.G. and Hunt, A.P., 1993, A new Late Triassic tracksite from the Sloan Canyon Formation, type section, Cimarron Valley, New Mexico: New Mexico Museum of Natural History and Science, Bulletin 3, p. 279283. Lockley, M.G. and Hunt, A.P., 1994, A review of Mesozoic vertebrate ichnofaunas of the Western Interior United States: evidence and implications of a superior track record, in Caputo, M.V., Peterson, J.A. and Franczyk, K.J., eds., Mesozoic systems of the Rocky Mountain region, USA: Denver, RMS-SEPM, p. 95-108. Lockley, M.G. and Hunt, A.P., 1995, Dinosaur tracks and other fossil footprints of the western United States: New York, Columbia University Press, 338 p. Lockley, M.G., King, M., Howe, S. and Sharp, T., 1996, Dinosaur tracks and other archosaur footprints from the Triassic of South Wales: Ichnos, v. 5, p. 23-41. Lucas, S. G., 1997, Upper Triassic Chinle Group, western United States: a nonmarine standard for Late Triassic time, in Dickins, J.M., Yang, Z., Yin, H., Lucas, S.G., and Acharyya, S.K., eds., Late Palaeozoic and early 93 Mesozoic circum-Pacific events and their global correlation: Cambridge, Cambridge Univerity Press, p. 209-228. Lucas, S.G., 2003, Triassic tetrapod footprint biostratigraphy and biochronology: Albertiana, v. 28, p. 75-84. Lucas, S.G. and Hancox, P.J., 2001, Tetrapod-based correlation of the nonmarine Upper Triassic of southern Africa: Albertiana, v. 25, p. 5-9. Lucas, S.G. and Tanner, L.H., 2004, Late Triassic extinction events: Albertiana, v. 31, p. 31-40. Lucas, S.G., Tanner, L.H. and Heckert, A.B., 2005a, Tetrapod biostratigraphy and biochronology across the Triassic-Jurassic boundary in northeastern Arizona: New Mexico Museum of Natural History and Science, Bulletin 29, p. 84-94. Lucas, S. G., Gierliñski, G., Haubold, H., Klein, H., Lockley, M.G., Tanner L.H., Hunt, A.P., Heckert, A.B. and Thulborn, T., 2005b, Triassic records of the theropod footprint ichnogenus Eubrontes: Journal of Vertebrate Paleontology, v. 25, p. 85A. Lucas, S.G., Gierliñski, G., Haubold, H., Heckert, A.B., Hunt, A.P., Klein, H., Lockley, M.G., Tanner, L.H., Thulborn, T. and Zeigler, K.E., 2005c, Triassic records of the dinosaur footprint ichnogenus Eubrontes: Geological Society of America, Abstracts with Programs, v. 37, p. 132. Lull, R.S., 1904, Fossil footprints of the Jura-Trias of North America: Memoirs of the Boston Society of Natural History, v. 5, p. 461-557. Martin, A.J. and Hasiotis, S.T., 1998, Vertebrate tracks and their significance in the Chinle Formation (Late Triassic), Petrified Forest National Park, Arizona, in Santucci, V. L., and McClelland, L., eds., National Park Service Paleontological Research: Geological Resources Division Technical Report NPS/NRGRD/GRDTR-98/01, p. 138-143. Michalik, J. and Kundrat M., 1998, Uppermost Triassic dinosaur ichnoparataxa from Slovakia: Journal of Vertebrate Paleontology, v. 18, p. 63A. Michalik, J., Planderova, E. and Sykora, M., 1976, To the stratigraphic and paleogeographic position of the Tomanova-Formation in the uppermost Triassic of the West Carpathians: Geologický zborník – Geologica Carpathica, v. 27, p. 299-318. Milner, A.R.C. and Lockley, M.G., 2006, History, geology and paleontology: St. George Dinosaur Discovery Site at Johnson farm, Utah; in Reynolds, R.E., ed., Making tracks across the Southwest: Zzyzx, California State University, p. 35-48. Molnar, R.E., 1991, Mesozoic vertebrates, in Vickers-Rich, P., Monaghan, J.M., Baird, R.F. and Rich, T.H., eds., Vertebrate palaeontology of Australasia: Melbourne, Pioneer Design Studio, p. 605-702. Nicosia, U. and Loi, M., 2003, Triassic footprints from Lerici (La Spezia, northern Italy): Ichnos, v. 10, p. 127-140. Nilsson, T., 1934, Vorläufige Mitteilungen über einen Stegocephalenfund aus dem Rhät Schonens: Geologiska Föreningens i Stockholm Förhandlingar, v. 56, p. 428-442. Olsen, P.E., 1980, Fossil great lakes of the Newark Supergroup in New Jersey, in Manspeizer, W., ed., Field studies in New Jersey geology and guide to field trips: New York State Geological Association guide to field trips, v. 52, p. 352-398. Olsen, P.E., 1983, Relationship between biostratigraphic subdivisions and igneous activity in the Newark Supergroup: Geological Society of America, Abstracts with Programs, v. 14, p. 71. Olsen, P.E. and Galton, P.M., 1984, A review of the reptile and amphibian assemblages from the Stormberg of southern Africa, with special emphasis on the footprints and the age of the Stormberg: Palaeontologia Africana, v. 25, p. 87-110. Olsen, P.E., Smith, J.B. and McDonald, N.G., 1998. Type material of the type species of the classic theropod footprint genera Eubrontes, Anchisauripus, and Grallator (Early Jurassic, Hartford and Deerfield basins, Connecticut and Massachusetts, U.S.A.): Journal of Vertebrate Paleontology, v. 18, p. 586-601. Olsen, P.E., Kent, D.V., Sues, H.-D., Koeberl, C., Huber, H., Montanari, A., Rainforth, E.C., Fowell, S.J., Szajna, M.J. and Hartline, W., 2002a, Ascent of dinosaurs linked to an iridium anomaly at the Triassic-Jurassic boundary: Science, v. 296, p. 1305-1307. Olsen, P.E., Koeberl, C., Huber, H., Montanari, A., Fowell, S.J., Et-Touhani, M. and Kent, D.V., 2002b. The continental Triassic-Jurassic boundary in central Pangea: recent progress and preliminary report of an Ir anomaly. Geological Society of America, Special Paper 356, p. 505-522. Olsen, P.E., Sues, H.-D., Rainforth, E.C., Kent, D.V., Koeberl, C., Huber, H., Montanari, A., Fowell, S.J., Szajna, M.J. and Hartline, B.W., 2003, Response to comment on “Ascent of dinosaurs linked to an iridium anomaly at the Triassic-Jurassic boundary”: Science, v. 301, p. 169c. Pienkowski, G., 1991, Eustatically-controlled sedimentation in the Hettangian-Sinemurian (Early Liassic) of Poland and Sweden: Sedimentology, v. 38, p. 503-518. Rainforth, E.C., 2005, Ichnotaxonomy of the fossil footprints of the Connecticut Valley (Early Jurassic, Newark Supergroup, Connecticut and Massachusetts) [Ph.D. dissertation]: New York, Columbia University, 1301 p. Rainforth, E. C. and Lockley, M. G., 1996, Tracking life in a Lower Jurassic desert: vertebrate tracks and other traces from the Navajo Sandstone: Museum of Northern Arizona, Bulletin 60, p. 285-289. Rowe, T. and Gauthier, J., 1990, Ceratosauria, in Weishampel, D. B., Dodson, P., and Osmólska, H., eds., The Dinosauria: Berkeley, University of California Press, p. 151-168. Silvestri, S.M. and Szajna, M.J., 1993, Biostratigraphy of vertebrate footprints in the Late Triassic section of the Newark basin, Pennsylvania: reassessment of stratigraphic ranges: New Mexico Museum of Natural History and Science, Bulletin 3, p. 439-455. Smoot, J.P. and Olsen, P.E., 1989, Stop 4.1: Culpeper Crushed Stone Quarry, Culpeper (Stevensburg), VA, in Olsen, P.E., Schlische, R.W. and Gore, P.J.W., eds., Tectonic, depositional, and paleoecological history of early Mesozoic rift basins, eastern North America, field trip guidebook T351: Washington, D.C., American Geophysical Union, p. 60-63. Sollas, W.J., 1879, On some three-toed footprints from the Triassic conglomerate of South Wales: Quarterly Journal of the Geological Society of South Wales, v. 35, p. 511-516. Staines, H.R.E. and Woods, J.T., 1964, Recent discovery of Triassic dinosaur footprints in Queensland: Australian Journal of Science, v. 27, p. 55. Szajna, M.J. and Hartline, B.W., 2003, A new vertebrate footprint locality from the Late Triassic Passaic Formation near Birdsboro, Pennsylvania, in LeTourneau, P.M. and Olsen, P.E., eds., The great rift valleys of Pangea in eastern North America, volume 2: New York, Columbia University Press, p. 264-272. Szajna, M.J. and Silvestri, S.M., 1996, A new occurrence of the ichnogenus Brachychirotherium: implications for the Triassic-Jurassic mass extinction event: Museum of Northern Arizona, Bulletin 60, p. 275-283. Thomas, T.H., 1879, Triassic uniserial ichnolites in the Trias at Newton Nottage, near Porthcawl, Glamorganshire: Cardiff Naturalists’ Society, v. 10, p. 72-91. Thulborn, T., 1990, Dinosaur tracks: London, Chapman and Hall, 410 p. Thulborn, T., 1998, Australia’s earliest theropods: footprint evidence in the Ipswich Coal Measures (Upper Triassic) of Queensland: Gaia, v. 15, p. 301-311. Thulborn, T., 2003, Comment on “Ascent of dinosaurs linked to an iridium anomaly at the Triassic-Jurassic boundary”: Science, v. 301, p. 169b. Tucker, M.E. and Burchette, T.P., 1977, Triassic dinosaur footprints from south Wales: their context and preservation: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 22, p. 195-208. Weems, R.E., 1987, A Late Triassic footprint fauna from the Culpeper Basin, northern Virginia (U.S.A.): Transactions of the American Philosophical Society, v. 77, p. 1-79. Weems, R.E., 1992, A re-evaluation of the taxonomy of Newark Supergroup saurischian dinosaur tracks, using extensive statistical data from a recently exposed tracksite near Culpeper, Virginia: Virginia Division of Mineral resources, Publication 119, p. 113-127. Weems, R.E., 2003, Plateosaurus foot structure suggests a single trackmaker for Eubrontes and Gigandipus footprints, in LeTourneau, P.M. and Olsen, P.E., eds., The great rift valleys of Pangea in eastern North America, volume 2: New York, Columbia University Press, p. 293-313. Welles, S.P., 1984, Dilophosaurus wetherilli (Dinosauria, Theropoda): osteology and comparisons: Palaeontographica Abteilung A, v. 185, p. 85180.