First report of Ignotornidae (Aves) from the Lower Cretaceous GatesFormation (Albian) of western Canada, with description of a newichnospecies of Ignotornis, Ignotornis canadensis ichnosp. nov.
Lisa G. Buckley a, *, Richard T. McCrea a, Lida Xing b
a Peace Region Palaeontology Research Centre, Tumbler Ridge, British Columbia V0C 2W0, Canadab School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
a r t i c l e i n f o
Article history:Received 1 August 2017Received in revised form21 November 2017Accepted in revised form 23 November 2017Available online 24 November 2017
Ignotornidae is an avian vertebrate ichnofamily known from the Lower to middle Cretaceous (Aptian e
Cenomanian) of North America (Colorado) and South Korea. The ichnogenus Ignotorniswas first describedfromNorth America; however, in the eight decades since no Ignotornidae have been described fromNorthAmerica, and hitherto none have been reported from Canada. Here we describe the first ichnospecies ofIgnotornis, Ignotornis canadensis ichnosp. nov. (Gates Formation, Lower Cretaceous, Albian), the first newichnospecies of Ignotornis to be described from North America since the original description of Ignotornismcconnelli, and the first report of Ignotornidae from Canada. Ignotornis canadensis ichnosp. nov., whilemorphologically similar to Ignotornis mcconnelli, is larger and has a relatively longer digit I impression thanIgnotornis mcconnelli, and has digit I impressions with a similar orientation to those of the ichnogenusGoseongornipes. Discriminant analyses show that Ignotornis canadensis ichnosp. nov. is most similar to theichnogenera Goseongornipes and Hwangsanipes due to the divarication of digits IeII and IIeIII. Theapparent sinusoidal digit III impression in Ignotornis canadensis and other Ignotornidae is due to watersaturated sediment not completely preserving digital pad impressions, rather than a morphologic featureof digit III. While the majority of ichnospecies of Ignotornidae are from South Korea, and while Asiacurrently contains the largest diversity of avian ichnotaxa from the Cretaceous Period, the apparent lowerdiversity of Cretaceous avian ichnotaxa from North America may be preservationally controlled, and willbe resolved with a greater focus on Early Cretaceous ichnofauna in North America.
Ignotornis mcconnelli was the first bird track described from theMesozoic (Mehl, 1931; Lockley et al., 1992) from the upper part ofthe regressive-transgressive cycle of the Kassler Sandstone and VanBibber Shale of the Dakota Sandstone (Lockley et al., 1992). Theunique morphology of Ignotornis mcconnelli (wide divarication,asymmetric semipalmate webbing traces attached more mesiallyon digit impressions IIIeIV than on digit impressions IIeIV, prom-inent posteriomedially-directed digit I) prompted establishing anew ichnofamily, Ignotornidae, in to which Goseongornipes mark-jonsei (Lockley et al., 2006), Hwangsanipes choughi (Yang et al.,1995), Ignotornis gajinensis (Kim et al., 2012), and Ignotornis yangi
y).
(Kim et al., 2006), were assigned. Ignotornidae was established todistinguish these ichnotaxa from other tetradactyl Mesozoic birdtracks, as Koreanaornipodidae have an inconsistently preserved,short digit I impression (Lockley et al., 2006; Xing et al., 2016) Todate, only one ichnospecies of Ignotornidae, Ignotornis mcconnelli,has been described from North America (Table 1).
1.1. History of avian track descriptions from western Canada
The first avian track type described from Canada was Aqua-tilavipes swiboldae from the Gaylard Member of the Gething For-mation of British Columbia (Currie, 1981). The Gething Formation(Lower Cretaceous: Aptian) is stratigraphically below the GatesFormation. Aquatilavipes swiboldae is a small tridactyl avian trace:to date, no hallux impressions have been described from any ich-nospecies of Aquatilavipes (Buckley et al., 2016). An ichnospecies ofAquatilavipeswas described from the Grande Cache Member of the
Table 1Geographic distribution of Ignotornidae from the Cretaceous.While Ignotornis mcconnelli (Mehl, 1931) was first described fromNorth America, the majority of Ignotornidae areknown from Lower Cretaceous deposits of South Korea, with the exception of Hwangsanipes choughi (Upper Cretaceous.) The Uhangri Formation is described by Yang et al.(1995) as being Upper Cretaceous, and the deposits from which Hwangsanipes choughi was recovered refined by Kim et al. (2006) as being Cenomanian or younger.Although AptianeCenomanian deposits are not uncommon in North America, Ignotornidae (and Cretaceous bird tracks in general) remain underreported.
Ichnotaxon Geographic Location Formation, Age
Hwangsanipes choughi Hwangsan Basin, South Korea Uhangri Formation, Upper Cretaceous (Cenomanian)Goseongornipes markjonesi Kosong County, South Korea Jindong Formation, Lower Cretaceous (Albian)Ignotornis mcconnelli Golden, Colorado, USA Dakota Group, Lower Cretaceous (AptianeCenomanian)Ignotornis canadensis ichnosp. nov. Peace Region, northwest Alberta and
northeast British Columbia, CanadaGates Formation (Grande Cache Member), Lower Cretaceous(Albian)
Ignotornis gajinensis Gajin, South Korea Haman Formation, Lower Cretaceous (Aptianemiddle Albian)Ignotornis yangi Changseon and Sinsu Islands, South Korea Haman Formation, Lower Cretaceous (Aptianemiddle Albian)
Institutional abbreviationsdPRPRC, Peace Region Palaeontology Research Centre, Tumbler Ridge, British Columbia, Canada; TMP, Royal Tyrrell Museum of Palaeontology,Drumheller, Alberta, Canada; UCM, University of Colorado at Boulder Museum, Denver, Colorado, USA.
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Gates Formation, Aquatilavipes curriei (McCrea and Sarjeant, 2001).However, as Aquatilavipes curriei is a trace from a larger trackmakerthan that of Aquatilavipes swiboldae, and because the only similaritybetween the two track types is the lack of hallux impressions,McCrea et al. (2014) reassigned A. curriei to a new ichnofamily(Limiavipedidae) and ichnogenus (Limiavipes). To date, there areonly two avian ichnotaxa known from the Cretaceous-age depositsof Canada: Aquatilavipes swiboldae and Limiavipes curriei. One slabwith two prints of Limiavipes curriei was found in the GaylardMember of the Gething Formation (McCrea et al., 2014). A specimenof Aquatilavipes swiboldae was also identified from the GladstoneFormation (¼ Gething Formation) along the highway outside ofGrande Cache, Alberta (McCrea et al., 2014 and references therein).
There are more Cretaceous avian ichnotaxa known from west-ern North America, but the number is still low in comparison toother Cretaceous-age localities worldwide, especially in Asia(Lockley and Harris, 2010; Xing et al., 2016). In addition to Ignotornismcconnelli (Cretaceous: AlbianeCenomanian, Mehl, 1931; Lockleyet al., 1992), Gruipeda vegrandiunus from the Cantwell Formationof Denali National Park (Upper Cretaceous: Campanian-Maastrichtian, Fiorillo et al., 2011) and Sarjeantopus semipalmatusfrom the Lance Formation of Wyoming, as well as unnamed aviantracks (Upper Cretaceous: Maastrichtian, Lockley et al., 2004) havebeen described from North America. There are reports of Kore-anaornis ichnosp. from the Dakota Group of Utah (Cretaceous:Albian-Cenomanian, Anfinson et al., 2009). Aquatilavipes ichnosp.has been reported from the Poison Strip Member of the CedarMountain Formation of Utah (Early Cretaceous: Aptian; Lockleyet al., 2015), and the Lakota Formation (Lower Cretaceous, Lockleyet al., 2001a). The first description of the ichnogenus Magnoavipes(Magnoavipes lowei, Lee, 1997) described it as the track of a largeavian trackmaker. However, Lockley et al. (2001b) describe Mag-noavipes as an ichnogenus of non-avian theropod in their descrip-tion of Magnoavipes caneeri. Fiorillo et al. (2011) describeMagnoavipes denaliensis as the track of a large avian trackmaker.However, Matsukawa et al. (2014) demonstrate that the ichnogenusMagnoavipes is most likely from an ornithomimid trackmaker. Also,based on comparisons of ranges of total divarication and footprintlength to pace length ratios of bird and theropod trackways, theichnogenus Magnoavipes is most likely that of a non-aviantheropod (McCrea et al., 2014; Xing et al., 2015).
McCrea (2000) and McCrea et al. (2014) outlined several novelavian track types from the Lower Cretaceous (AptianeAlbian) ofwestern Canada whose descriptions are in progress. One specimenis a track-bearing block from the former Grande Cache Coal Minenear the community of Grande Cache, Alberta (Fig.1). The specimen(TMP 2016.036.003, Figs. 2e3) was collected in September 2016.Two avian ichnotaxa are present on the track slab: a small tridactyltrack type and a slightly larger tetradactyl track type. A secondspecimen was collected in August 2014 (PRPRC 2014.05.001) that
preserves several small tridactyl avian tracks. During furtherinvestigation, a second track type was identified that, while heavilyeroded, has digit I impressions (Fig. 4).
2. Materials and methods
2.1. Specimen collection and documentation
PRPRC 2014.05.001 was discovered prior to 2000 (Helm, 2000,2001) near the summit of Roman Mountain, northeastern BritishColumbia. It was not until 2014 that the slab was recovered byhelicopter airlift. The slab is deposited at the PRPRC. TMP2016.036.0003 was discovered in the fall of 2016 at the base of theW2 track site the footwall of a former open pit coal mine (Fig. 1).Specimen data (Table 2) was collected as outlined in McCrea et al.(2014). Photogrammetric images of TMP 2016.036.003 (Fig. 2)were obtained using multiple images (61 photographs taken at anaverage of 0.472m altitude from the subject) with a Canon EOS 70Dcamera (focal length 18 mm, resolution 5472 � 3648, pixel size0.00417 � 0.00417 mm). The photographs were processed by Agi-soft Photoscan Professional (v.1.0.4) with the model having an errorof less than 0.152 pix. These models were converted to colortopographic profile images using CloudCompare (v.2.5.3).
2.2. Multivariate statistical analyses
Multivariate statistical analyses were performed using Paleon-tological Statistics (PAST, Hammer et al., 2001). Discriminant ana-lyses and multivariate analyses of variance (MANOVA) wereperformed on linear and angular data of Cretaceous tetradactylavian ichnotaxa Hwangsanipes choughi (Yang et al., 1995), Goseon-gornipes markjonesi (Lockley et al., 2006), an unassigned ichno-species of Goseongornipes (Lockley et al., 2006), Ignotornis gajiensis(Kim et al., 2012), Ignotornis mcconnelli (Lockley et al., 1992) Igno-tornis yangi (Lockley et al., 2006), and Uhangrichnus chuni (Yanget al., 1995). Dongyangornipes sinensis (Azuma et al., 2013) isconsidered by Buckley et al. (2016) as a subjective junior synonymof Uhangrichnus chuni, based on the emendation of Uhangrichnuschuni by Lockley et al. (2012a, b) that included a description of ashort posteriormedially-directed hallux impression (Lockley et al.,2012a), and described the slight differences in webbing impres-sions and digit divarication as due to preservational variation(Buckley et al., 2016). Uhangrichnus chuni, although possessingpalmate webbing impressions as compared to Ignotornidae (sem-ipalmate), was included in the analyses based on similarities inoverall size and digit morphology. Although no hallux impressionswere reported for Gyeongsangornipes lockleyi (Kim et al., 2013), itwas also included in the analyses based on similarities in asym-metric semipalmate webbing and digit morphology. Shandongor-nipes muxiai (Li et al., 2005) was not included in the analyses as it is
Fig. 1. Locality map of specimens of Ignotornis canadensis TMP 2016.036.003 from the Grande Cache Coal Pit near Grande Cache, Alberta, and PRPRC 2014.05.001 from RomanMountain, northeastern British Columbia.
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a zygodactyl ichnotaxon, whereas the other Cretaceous avian ich-notaxon are anisodactyl. Ichnospecies of Koreanaornis (Kore-anaornis hamanensis, Koreanaornis lii) were also included due to thepresence (although somewhat inconsistent) of hallux impressions.Koreanaonris dodsoni (Xing et al., 2011) was not included due to theconsistent lack of a hallux impression. However, ichnospecies ofKoreanaornis are morphologically distinct from those of Igno-tornidae due to its relatively smaller size, consistent lack ofwebbing impressions, and relatively short hallux impressions (Kim,1969; Lockley et al., 2006; Xing et al., 2016). Jindongornipes kimiwasincluded in preliminary statistical analyses despite its larger sizeand morphological differences from other Cretaceous tetradactyltracks. For the analyses discussed herein, Jindongornipes kimi wasnot included due to its much larger footprint size, and the smallsample size data (n ¼ 2). Gruipeda vegrandiunus (Fiorrillo et al.,2011) and Sarjeantopus semipalmatus (Lockley et al., 2004) werealso excluded from the analyses due to their small sample sizes.Size as a confounding factor was removed from the data prior toanalyses, as per Farlow et al. (2013): linear data were first log-transformed, and then the mean was subtracted from each of thelog-transformed linear and angular variables.
3. Geological setting
Both TMP 2016.036.0003 (Figs. 2e3) and PRPRC 2014.05.001(Fig. 4) originate from the Gates Formation of British Columbia andAlberta, respectively (Fig. 1). The stratigraphic context of the lo-cality for PRPRC 2014.05.001 is uncertain, as the block was recov-ered ex situ from the summit of Roman Mountain (10U 06313736082782, WGS 84) within the coal lease tenure of the formerPeaceRiver Coal Trend Mine (McCrea et al., 2014). TMP 2016.036.0003was recovered by RTM under the aegis of the Royal Tyrrell Museumin 2016 as an ex situ track slab from the Grande Cache Member ofthe Gates Formation (Lower Cretaceous: Albian). The specimenwas
collected from the W2 Site of the formerGrande Cache Coal oper-ation (McCrea, 2000; McCrea et al., 2014).
The stratigraphy of the Gates Formation is well-documented.The strata of the Gates Formation were deposited in the WesternCanada Foreland Basin during the second of three clastic deposi-tional cycles in the Lower Cretaceous (Plint and Hart, 1988; Leckieand Smith, 1992). The Gates Formation is part of the Fort St. JohnGroup, which conformably overlies the Lower Cretaceous BullheadGroup (Langenberg et al., 1987) (Fig. 5). The Gates Formation isdivided into three members (lower Torrens Member, middleGrande Cache Member, upper Mountain Parks Member), with thevertebrate track-bearing Grande Cache Member as a source ofeconomic coal seams in western Alberta (Langenberg et al., 1987;McCrea, 2000).
In the Grande Cache coal mines of western Alberta, the verte-brate track-bearing layer was exposed after the removal of theNumber 4 Coal Seam in the Grande Cache Member (McCrea andCurrie, 1998; McCrea, 2000). The paleoenvironment is interpretedto be that of a coastal plain or deltaic complex (Langenberg et al.,1987; Leckie and Smith, 1992; McCrea, 2000). The Grande CacheMember of the Gates Formation has been assigned to the lowerAlbian based on the ostracod Cytheridea bonaccordensis(Langenberg et al., 1987). Paleobotanical studies on the Gates For-mation (Wan, 1996) is interpreted as warm with abundant rainfallbut with possible cold seasons (McCrea, 2000).
4. Systematic ichnology
AVES
Ignotornidae (Lockley et al., 2006)
Ignotornis Mehl, 1931; emend. Lockley et al., 1992
Ignotornis canadensis ichnosp. nov.
Fig. 2. Three-dimensional photogrammetric images of TMP 2016.036.0003 showing true color rendering (top) and false color depth image (bottom). Photogrammetric images,presented here were obtained using multiple images (61 photographs taken at an average of 0.472 m altitude from the subject) with a Canon EOS 70D camera (Focal Length 18 mm,resolution 5472 � 3648, pixel size 0.00417183 � 0.00417183 mm). The photographs were processed by Agisoft Photoscan Professional (v.1.0.4) with the model having an error of lessthan 0.151929 pix. These models were converted to color topographic profile images using CloudCompare (v.2.5.3).
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Type specimensdTMP 2016.035.0003, natural cast track slab con-taining six tetradactyl tracks in a consecutive trackway, depositedat Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta.Referred specimen, PRPRC 2014.005.001, natural mold track slabcontaining five tetradactyl tracks in a consecutive trackway,deposited at Peace Region Palaeontology Research Centre, TumblerRidge, British Columbia.Etymologyd“Ignotornis,” likely a derivative of “ichno” and “ornis”from Mehl (1931), bird trace; “canadensis,” from Canada.
DiagnosisdAnisodactyl tetradactyl avian tracks of large size (foot-print length 39.0 mme57.2 mm; footprint length with hallux63.8 mme71.8 mm), hallux impression posteriomedially directedand larger than 25% of digit III impression length. Digit II and IVimpressions weakly curve towards digit III impression. Claws shortand acuminate. Asymmetric semipalmate webbing, impressionswith larger webbing impressions between digits IIIeIV than IIeIII.Horizon and localitydHolotype specimen is an ex situ block fromthe 12 Mine South, W2 site at base of footwall, about 21 km
Fig. 3. TMP 2016.036.0003, natural cast track slab of type specimen of Ignotornis canadensis ichnosp. nov., from the Gates Formation of western Canada. A, Photograph of trackwayshowing tracks 1e5, with two partial tracks that may be part of the trackway. B, line drawing of TMP 2016.036.0003, showing the type trackway of Ignotornis canadensis ichnosp.nov. (black), and several small tridactyl bird tracks (grey) that are likely Aquatilavipes ichnosp.
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northwest of Grande Cache, Alberta; Grande Cache Member of theGates Formation, lower Albian (Lower Cretaceous) just below theNo. 4 coal seam (Langenberg et al., 1987).DescriptiondUnless otherwise stated, the descriptions are based ontracks from TMP 2016.035.0003, as those are best preserved(Figs. 2e3, 6e7; Table 2). Tracks are between 44.7 mm and 57.4 mmin footprint length (FL). Footprint lengths including the halluximpressions (FLwH) are 65.0 mme65.6 mm. Digit impressions arenarrow with inconsistently preserved digital pads. Digit III im-pressions are the longest, with digit impressions II and IV subequalin length. The distal ends of digit II and IV impressions curveslightly towards the digit III impression (Fig. 5). Digit I impressions,where preserved, are greater than 25% the length of the total tracklength. Digit I impressions are 31.8%e41.7% the lengths of digit IIIimpressions. Average digit I impression is 27.9% of total footprintlength with hallux (FLwH). Digit I impressions are posteriomediallyoriented, with digit IeII divarication between 55� and 71�. Totaldivarication (IIeIV) is between 109� and 129�, with the proximaledge of the track (where the digit impressions converge) appearingas an obtuse angle with a rounded margin, rather than pointed.Webbing impressions are inconsistently preserved. Where
preserved, webbing impressions between digit IIIeIV impressionsextend more distal than webbing impressions between digit IIeIIIimpressions. No webbing impressions are detected between digitsIeII. Individual tracks are weakly rotated towards themidline of thetrackway (footprint rotation (FR), also known as angle of divarica-tion from midline: �7� to 12�). Track placement in the trackway isrelatively straight (pace angulation (PA): 160�e180�). Pace length(PL) is short compared to footprint length (FL) (FL/PL: 0.30e0.48),as is typical with bird tracks and trackways (Xing et al., 2015).Digit III impressions appear sinusoidal in shape for track naturalcasts that preserve the entire depth of the track. However, this si-nusoidal digit III impression is not observed in tracks that havebeen eroded to the level of the track surface: digits are straight withpartially preserved digital pads (Figs. 3, 6).
5. Comparative ichnology
Ignotornis mcconnellidThe emended description of Ignotornismcconnelli (Lockley et al., 1992, 2009) reveals that its morphology issimilar to that of Ignotornis canadensis ichnosp. nov. DivaricationIeII of Ignotornis canadensis ichnosp. nov. (average digit IeII
Fig. 4. PRPRC 2014.05.001, natural mold track slab with faint impressions of a tetradactyl avian trackmaker referred to Ignotornis canadensis ichnosp. nov. A, photograph of trackway,and B, line drawing of trackway. While heavily eroded, the hallux impression is still visible in Track 2. To date only tridactyl avian tracks have been described fromwestern Canada.
Table 2Linear and angle measurements of Ignotornis canadensis, ichnosp. nov. FR, footprint rotation; FL, footprint length; FLwH, footprint length including hallux impression; FW,footprint width; PA, pace angulation; PL, pace length; SL, stride length.
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Fig. 5. Geologic context of Gates Formation in western Canada, from McCrea (2000). Modified from Plint and Hart (1988).
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divarication ¼ 98�) is close to that of Ignotornis mcconnelli (averagedigit IeII divarication ¼ 97.5�; 63�e133�). However, Ignotorniscanadensis ichnosp. nov. is larger (average FL ¼ 48.5 mm) thanthose described for the type of Ignotornis mcconnelli (averageFL ¼ 40.9 mm) by approximately 7.6 mm on average, and 11.4 mmlarger in track length including the hallux impression. The halluximpressions of I. canadensis ichnosp. nov. are relatively longer(average 18.6 mm, N ¼ 4, 45.3% length of digit III impression) thanthose of Ignotornis mcconnelli (average 14.2 mm, 34.7% length ofdigit III impression, N ¼ 58; Table 3).
Ignotonis yangidIgnotornis yangi is smaller (averageFL ¼ 32.6 mm) than Ignotornis canadensis ichnosp. nov. The halluximpression of Ignotornis yangi (36.1% of digit III impression) issmaller in relative length than that of Ignotornis canadensis ichnosp.nov. Digit IeII divarication of Ignotornis yangi (average digit IeIIdivarication ¼ 83.9�) is smaller than that of Ignotornis canadensis(average digit IeII divarication ¼ 98�); however, there is a largeamount of variation in digit IeII divarication (50�e120�). Indescribed specimens of Ignotornis yangi (Kim et al., 2006) there areobvious webbing impressions between digits IIeIII. Ignotorniscanadensis ichnosp. nov. does have a visible webbing impressionbetween digits IIeIII (Fig. 6), but it is not as robust as in Ignotornisyangi.
Ignotornis gajinensisdIgnotornis gajinensis is smaller in footprintlength (average FL ¼ 58.1 mm) than Ignotornis canadensis ichnosp.nov. (average FL ¼ 66.6 mm); however, there is limited informationavailable on the proportions and the divarication of the halluximpression for Ignotornis gajinensis. Average total divarication(IIeIV) for Ignotornis gajinensis is 137.5� (IIeIII ¼ 73.8�;IIIeIV ¼ 63.7�), whereas the average total divarication of Ignotornis
canadensis ichnosp. nov. is 118.7� (IIeIII¼ 57.6�; IIIeIV¼ 56.9�). Thedivarication between digit impressions IIeIII is relatively larger inIgnotornis gajinensis than in Ignotornis canadensis ichnosp. nov.While the absolute values of digit divarication have potential forlarge variation (Buckley et al., 2015), relative differences in digitdivarications within tracks may be useful. In Ignotornis gajinensis,the divarications between digit IIeIII are consistently larger thandivarication between digits IIIeIV (Table 3). In Ignotornis canadensisichnosp. nov., divarication between digits IIeIII and IIIeIV arealmost equal in size. The relatively larger divarication of digits IIeIII,when compared to divarication of digits IIIeIV, differentiatesIgnotornis gajinensis from both Ignotornis canadensis ichnosp. nop.and Ignotornis mcconnelli. Ignotornis gajinensis also differs fromother described ichnospecies of the ichnogenus Ignotornis in thepresence of feeding traces, similar to that seen in extant spoonbills(Ciconiformes, Kim et al., 2012).
Goseongornipes markjonesidGoseongornipes markjonesi isdifferent from described ichnospecies of Ignotornis in that thehallux impression is consistently shorter in Goseongornipes thanreported for Ignotornis (Kim et al., 2006; Lockley et al., 2006).Average total divarication for Goseongornipes markjonesi is 124.5�
(IIeIII¼ 62.9�; IIIeIV¼ 61.5�; total divarication IIeIV¼ 101�e152�).Ignotornis canadensis ichnosp. nov. also has a large range of totaldivarication (101�e129�). The webbing impressions (when pre-served) are more symmetric between digit impressions IIeIII andIIIeIV in Goseongornipes markjonesi than in Ignotornis canadensisichnosp. nov.
Hwangsanipes choughidYang et al. (1995) described Hwangsa-nipes choughi from a trackway consisting of four consecutive trackson a slab with many other associated Uhangrichnus chuni tracks.
Fig. 6. Close view of tracks 2e4 of TMP 2016.036.003, type trackway of Ignotornis canadensis ichnosp. nov. Aquatilavipes ichnosp. is also present on the track slab (grey.) Comparisonof straight (tracks 2, 4) and sinusoidal (track 3). Incompletely preserved digit III impressions appear to be sinusoidal (B), whereas digit III impressions that have been eroded orbroken to the surface of the slab (the surface that would have been in contact with the upper most level of the track-bearing surface) appear straighter, but with partial digital pads(A, C).
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While larger in size than Ignotornis canadensis ichnosp. nov.,Hwangsanipes choughi has a relatively longer hallux impression,and larger digit divarications IIeIII and IIIeIV. Another morpho-logical difference cited between the ichnogenera Hwangsanipes,Goseongornipes, and Ignotornis, is the size of the webbing impres-sion between digit impressions III and IV. In Hwangsanipes choughi,the digit IIIeIV webbing impression extends more distal on thedigit impressions than in both ichnogenera Goseongornipes andIgnotornis. Based on observations of modern bird tracks, the pres-ence and size of webbing impressions can vary depending onsubstrate consistency. However, the authors have not observedextramorphologic features that would be misinterpreted asmorphologic webbing, as described in Falkingham et al. (2009), inmodern semipalmate and palmate bird tracks.
Jindongornipes kimidJindongornipes kimi (Lockley et al., 2006) isrelatively longer (including the hallux impression) than other ani-sodactyl, tetradactyl bird tracks from the Cretaceous Period(average FLwH ¼ 80 mm). Also, when the hallux impression ispreserved, it is posteriorly directed (180� away from digit IIIimpression), rather than posteromedially directed as in other tet-radactyl bird tracks described from the Cretaceous Period (Lockleyet al., 2006). The main similarity between Ignotornis canadensisichnosp. nov. and Jindongornipes kimi is the relatively long halluximpression; however, the absolute size difference of Jindongornipeskimi as compared to Ignotornis canadensis ichnosp. nov., and thedifferent orientation of the hallux impression, suggests that theseare different track types produced by different trackmakers.
Gyeongsangornipes lockleyidAlthough not a tetradactyl avianichnotaxon, Gyeongsangornipes lockleyi is included in thecomparative ichnology because the asymmetric webbing
impressions are similar to those of the ichnogenera Ignotornis andHwangsanipes. Gyeongsangornipes lockleyi is relatively muchsmaller in footprint length (32.1 mm, Deokmyeongri sample;30.8 mm Donghae-myeon sample; Kim et al., 2013) than tracks ofIgnotornis, Hwangsanipes, and Ignotornis canadensis ichnosp. nov.However, Gyeongsangornipes lockleyi is similar in size to Goseon-gornipes markjonesi, but is described as distinct from Goseongor-nipes markjonesi due to Goseongornipes markjonesi possessing aclear hallux impression, web impressions only between digits IIIand IV, and a larger total divarication than Gyeongsangornipeslockleyi (Kim et al., 2013). While smaller than Ignotornis gajiensisand lacking a hallux impression, Gyeongsangornipes lockleyi issimilar to Ignotornis gajiensis in that it has a proportionally largerdigit IIeIII divarication than digit IIIeIV divarication. One of thefeatures consistent in all Ignotornidae is the slight asymmetrybetween the divarication of digits IIeIII and IIIeIV, with thedivarication angle being slightly larger between the impressionsof digits II and III (Table 3).
6. Multivariate analyses
Tracks of Ignotornis canadensis ichnosp. nov. group in morpho-space with Goseongornipes markjonesi based on the relative pro-portions of the divarication of digit impressions IeII, IIeIII, andIIIeIV (Table 4). Ignotornis canadensis is not significantly differentfrom Goseongornipes markjonesi (psame ¼ 0.364), Goseongornipesichnosp. (psame¼ 0.551),Hwangsanipes choughi (psame¼ 0.674), andIgnotornis gajinensis (psame ¼ 0.053) (Fig. 7, Table 5.) However,Ignotornis canadensis ichnosp. nov. is significantly different fromIgnotornis mcconnelli and Ignotornis yangi (Table 4.) The separation
Fig. 7. Discriminant analysis plot of Ignotornis canadensis ichnosp. nov. with tetradactyl avian ichnotaxa from the Cretaceous Period. Ignotornis canadensis shares a morphospacewith Goseongornipes ichnosp. and Hwangsanipes choughi due to the relative proportions of digit divarications IeII and IIeIII. Gyeongsangornipes lockleyi was included due to thesimilarity of the webbing impressions to that of Ignotornidae, but it forms a separate group due to its lack of a digit I impression.
Table 3Comparison of measured data averages for described Ignotornidae. Hwangsanipes choughi, although larger in footprint length with hallux (FLwH) than Ignotornis canadensisichnosp. nov., the webbing impression between digit impressions IIIeIV extends more distal in Hwangsanipes choughi, and a larger digit divarication IIeIII and IIIeIV thanIgnotornis canadensis. DIV, digit divarication; FL, footprint length; FLwH, footprint length with hallux; FW, footprint width.
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of these four ichnospecies from Ignotornis mcconnelli and Ignotornisyangiwas reported by Buckley et al. (2016) based on divarication ofdigit impressions IeII and IIeIII, with Ignotornis mcconnelli andIgnotornis yangi having relatively larger digit IeII and IIeIII divari-cation values (Table 5.) The inclusion of Ignotornis canadensis ich-nosp. nov. shows that this ichnotaxon has relative digit proportionsand digit divarication values consistent with Ignotornidae, and issimilar in said proportions to Ignotornis gajinensis.
Comparison of Gyeongsangornipes lockleyi to IgnotornidaedInitial discriminant analysis shows that Gyeongsangornipes lock-leyi, coded as having hallux data as “missing,” groups separatelyand is significantly different from all other tetradactyl Cretaceousavian ichnotaxa. However, vector loadings indicate that the variablewith the largest amount of variation along Axis 1 is divaricationbetween digit impressions IIeIII (2.82) and IeII (�2.72). The vari-ables along Axis 2 with the strongest loadings are the divaricationvalues between digits IeII (9.27) and digits IIIeIV (1.44). It is alongAxis 2 that Gyeongsangornipes lockleyi separates from the rest of the
tetradactyl Cretaceous bird tracks. Analyzes with digit I dataremoved (in other words, treating all tetradactyl tracks as thoughtheir hallux impressions were not preserved) revealed thatGyeongsangornipes lockleyi shares a morphospace with Ignotornismcconnelli and Ignotornis yangi based on the relative proportions ofdivarication between digit impressions IIeIII and IIIeIV (Fig. 8).Gyeongsangornipes lockleyi is significantly different from bothIgnotornis mcconnelli (psame ¼ 1.13 � 10�41) and Ignotornis yangi(psame ¼ 1.50 � 10�06) (Fig. 8).
Goseongornipes markjonesi, Goseongornipes ichnosp., andHwangsanipes choughi are not significantly different from Ignotorniscanadensis ichnosp. nov. when analyzed after the removal of digit Idata (digit I length, divarication IeII.) However, Ignotornis gajinensisbecomes significantly different from Ignotornis canadensis ichnosp.nov. (psame ¼ 0.005). It is not surprising that there are differentresults obtained by removing of digit I data, as this data contributesthe most variation when included in the previous analyses(Table 4).
Table 4Multivariate analysis of variance (MANOVA) results for linear and angular data (Materials and Methods) comparing Ignotornis canadensis to functionally tetradactyl Cretaceous avian ichnospecies of Ignotornidae (Goseongornipesmarkjonesi, Goseongornipes ichnosp., Hwangsanipes choughi, Ignotornis gajinensis, Ignotornis mcconnelli, Ignotornis yangi), Koreanaornipodidae (Koreanaornis dodsoni, Koreanaornis hamanensis, Koreanaornis lii), Uhangrichnus chuni(including Dongyangornipes sinensis), with Gyeongsangornipes lockleyi included because of its morphologic similarity to Ignotornidae despite the absence of hallux impressions. Ignotornis canadensis is not significantly differentfrom Goseongornipes, Hwangsanipes, and Ignotornis gajinensis. Interestingly, the tridactyl Gyeongsangornipes is also not significantly different from Hwangsanipes or Goseongornipes ichnosp., and is morphologically similar toHwangsanipes choughi. Gates, Ignotornis canadensis ichnosp. nov.; GoMa, Goseongornipes markjonesi; Go isp, Goseongornipes ichnosp.; GyLo, Gyeongsangornipes lockleyi; HwCh, Hwangsanipes choughi; IgGa, Ignotornis gajinensis;IgMc, Ignotornis mcconnelli, IgYa, Ignotornis yangi; KoDo, Koreanaonris dodsoni; KoHa, Koreanaornis hamanensis; KoLi, Koreanaornis lii; UhCh, Uhangrichnus chuni.
IgMc IgYa IgGa HwCh Gos isp. GoMa KoDo Ko Ha UhCh GyLo KoLi Gates
Table 5Discriminant analysis loadings for linear and angular data (Materials andMethods) comparing Gates Formation Ignotornidae to functionally tetradactyl Cretaceous avian ichnospecies of Ignotornidae (Goseongornipes markjonesi,Goseongornipes ichnosp., Hwangsanipes choughi, Ignotornis gajinensis, Ignotornis mcconnelli, Ignotornis yangi), Koreanaornipodidae (Koreanaornis dodsoni, Koreanaornis hamanensis, Koreanaornis lii), Uhangrichnus chuni (includingDongyangornipes sinensis), with Gyeongsangornipes lockleyi included because of its morphologic similarity to Ignotornidae despite the absence of hallux impressions. Digit divarication has the greatest amount of variation in thedataset, and are the vectors along which the ichnotaxa group. DL, digit length; DIV, digit divarication; FL, footprint length; FR, footprint rotation; FW, footprint width; PA, pace angulation; PL, pace length; SL; stride length.
Fig. 8. Discriminant analysis of Ignotornis canadensis ichnosp. nov., with tetradactyl avian ichnotaxa from the Cretaceous Period. Removal of the digit I data (digit I impressionlength, digit divarication IeII) shows that, while the ichnospecies of Ignotornidae retain their relative positions in morphospace (including the relationship between Ignotorniscanadensis ichnosp. nov. and Goseongornipes ichnosp.), Gyeongsangornipes lockleyi groups with Ignotornis mcconnelli and Ignotornis yangi. Ignotornis canadensis ichnosp. nov. still notsignificantly different from Goseongornipes markjonesi, Goseongornipes isp., and Hwangsanipes choughi, when analyzed after the removal of digit I impression data (digit I length,divarication IeII.) However, Ignotornis gajinensis becomes significantly different from Ignotornis canadensis (psame ¼ 0.005). It is not surprising that there are different resultsobtained by removal of digit I data, as this data contributes the most variation when included in the previous analyses (Table 4).
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7. Discussion
7.1. Statistical results
The multivariate statistical results (MANOVA) show that Igno-tornis canadensis ichnosp. nov. is not significantly different thanGoseongornipes ichnosp., Hwangsanipes choughi, and Ignotornisgajinensis. This is an opportunity to offer a caveat for multivariatestatistical analyses. While a useful tool for testing hypotheses ofdistinctiveness, they can only use the data that are available. Linearand angular data that capture some distinctive morphologic fea-tures, such as webbing impression shape and digit curvature, haveyet to be collected for all of the taxa discussed herein. As such, thereare morphologic data, traditionally used to differentiate amongavian ichnotaxa, that are missing from these analyses. Other tools,such as landmark analyses, may have potential in future analyses ofavian ichnotaxa.
While Ignotornis canadensis ichnosp. nov. is not significantlydifferent than Ignotornis gajinensis, or ichnospecies of Goseongor-nipes, and Hwangsanipes choughi, there are consistent morphologicdifferences between Ignotornis canadensis ichnosp. nov. and theseichnotaxa that justify their distinction. Ignotornis gajinensis ismorphologically distinct from Ignotornis canadensis ichnosp. nov.by the consistently larger divarication of digit impressions IIeIIIthan digit impressions IIIeIV.Hwangsanipes choughi is distinct from
Ignotornis canadensis ichnosp. nov. in its proportionally longerhallux impressions and larger webbing impressions. Webbing im-pressions between digits IIeIII and IIIeIV are equal in size in ich-nospecies of Goseongornipes, whereas webbing impressionsbetween digits IIeIII are smaller than those between digits IIIeIV inIgnotornis canadensis ichnosp. nov.
7.2. Occurrences of Ignotornidae and Early Cretaceous avianichnodiversity
The large diversity of avian footprints from the Lower Creta-ceous of China and Korea is suggested as evidence of provincialismand endemism in the Lower Cretaceous track record in Asia(Lockley et al., 2012b). However, it is possible that the currentapparent low diversity of bird tracks in Lower Cretaceous depositsof North America is artificial (Xing et al., 2016), at least in part dueto preservational factors. Reporting and describing avian ichnotaxafrom Lower Cretaceous deposits, inwhat was once thewestern partof Laurasia, is in the process of “playing catch-up” (Xing et al., 2016),as the known diversity of avian footprints from the Lower Creta-ceous of North America is growing. McCrea et al. (2015) describedPaxavipes babcockensis from the Boulder Creek Formation(AptianeAlbian), and Limiavipes curriei (McCrea and Sarjeant,2001; McCrea et al., 2014) was described from the Gates Forma-tion (Albian), both from western Canada. As more research is
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conducted on the avian ichnology of the Lower Cretaceous strata ofNorth America, it is possible the diversity of North American avianichnotaxa may approach that known from the Lower Cretaceous ofChina and Korea. At present, assuming the validity of named ich-notaxa from the two regions, there are some similarities in theLower Cretaceous ichnogenus diversity: i.e., the ichnogeneraAquatilavipes, Koreanaornis, and now Ignotornis, have been found inboth regions. However, Limiavipes curriei and Paxavipes babcock-ensis are known only from North America, while the ichnogeneraGoseongornipes, Gyeongsangornipes, Jindingornipes, Shandongornips,andWupus are known only from Asia, with Limiavipedidae (Wupusagilis, Limiavipes curriei; McCrea et al., 2014; Xing et al., 2015)present in both North America and Asia.
Ignotornis mcconnelli is present in Lower Cretaceous deposits ofNorth America in Colorado (AlbianeCenomanian). The Gates For-mation is early Albian in age and within the age range of Ignotornismcconnelli. However, Ignotornis canadensis ichnosp. nov. is largerthan Ignotornis mcconnelli, indicating that the trackmaker forIgnotornis canadensis ichnosp. nov. was distinct from the track-maker of Ignotornis mcconnelli. The trackmaker of Ignotornis cana-densis ichnosp. nov. also possessed a pes that had digit proportionsand digit divarication similar to that of Goseongornipes ichnosp. andIgnotornis gajinensis.
Fig. 9. Comparison of sinusoidal digit III impressions of Ignotornis canadensis ichnosp. nov. (showing a sinuosity to digit III impressions; B, PRPRC NI2010.004, plaster cast of tracks of thdigit III impression to a digit III impression that is laterally curved. The only difference betwewere made on sediment that was saturated. Scale in centimeters.
7.3. Interpretation of sinusoidal digit III impressions
With only the information provided by tracks of the Ignotorni-dae, there would be justification in assuming that the sinusoidalshape of digit III impressions is due to the morphology of the digit.However, comparisons with neoichology specimens reveal that thesinusoidal appearance of digit III is likely due to preservationalvariability rather than digit morphology. Curved digit impressionsare not unknown in the ichnogenus Ignotornis: Ignotornis yangi isdescribed as having digit III impressions that are straight or slightlycurved (Kim et al., 2006). Ignotornis mcconnelli also shows slightlysinusoidal digits (Fig. 9). Casts of tracks of Actitis macularius(Spotted Sandpiper) show that, when individuals walk on a fine-grained surface with high water content, the sediment does nothave the structural integrity to preserve the shape of the digitalpads, which may differentially collapse. This makes the digit IIIimpression appear as a line that can present as both straight andcurved within the same trackway (Fig. 9).
8. Conclusions
While still small, the number of avian ichnotaxa known from theCretaceous deposits of North America is growing. Here, we describe
Fig. 6) to extinct and extant avian traces. A, UCM 203.5, replica of Ignotornis mcconnelli,e modern Actitis macularius (Spotted Sandpiper), showing the transition from a straighten the tracks is the substrate consistency: the tracks show that the curved digit III traces
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a novel avian ichnotaxa, Ignotornis canadensis ichnosp. nov., whichrepresents the second report of Ignotornidae from North Americaand the first report of Ignotornidae from Canada. Ignotornis cana-densis ichnosp. nov. is larger than other reported Ignotornidae, yetpossesses digit divarication that is similar to that of ichnogeneraGoseongornipes and Hwangsanipes. The apparent sinusoidal digit IIIimpressions, while common in Ignotornidae, is due to preserva-tional variation rather than the morphology of digit III. Compari-sons with neoichnology track casts show that incompletepreservation of digital pads in water-saturated sediment can resultin digit III impressions appearing curved or sinusoidal. A high levelof endemism is hypothesized for the ichnofauna of the LowerCretaceous of Asia (Lockley et al., 2012b). The diversity of birdtracks in Asia, particularly that of South Korea, is likely high basedon optimal preservation conditions (lacustrine basin and lakemargin paleohabitats). In comparison, the Dakota Formation, whilealso optimal for bird track preservation, has fewer bird track sitesthan in South Korea (Lockley et al., 2012b). However, there areseveral Lower Cretaceous bird track sites that await description(McCrea et al., 2014), which may add to the paleodiversity ofCretaceous bird tracks from North America. With increased focuson avian traces from Lower Cretaceous deposits, we will have abetter understanding of the paleogeographic distribution of LowerCretaceous avian ichnotaxa and the global distribution of birds inthe Early Cretaceous.
Acknowledgements
Specimens were collected from the ancestral lands of the Treaty8 First Nations in British Columbia and Kelly Lake First Nations inBritish Columbia, and Kelly Lake, Tsuu T’ina, and AseniwucheWinewak First Nations in Alberta. The authors wish to thank D.Spivak and B. Strilinsky (TMP) for access to TMP 2016.035.0003;Ridge Roters for helicopter support for collection of PRPRC2014.05.001; M. Lockley for access to cast material of Ignotornidae.This manuscript was greatly improved by the contributions of M.Lockley, an anonymous reviewer, and the editorial staff.
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