Cretaceous Of Korea Research Articles

Evidence for a mixed-age group in a pterosaur footprint assemblage from the early Upper Cretaceous of Korea

Here we describe a new pterosaur footprint assemblage from the Hwasun Seoyuri tracksite in the Upper Cretaceous Jangdong Formation of the Neungju Basin in Korea. The assemblage consists of many randomly oriented prints in remarkably high densities but represents a single ichnotaxon, Pteraichnus. Individuals exhibit a large but continuous size range, some of which, with a wingspan estimated at 0.5 m, are among the smallest pterosaurs yet reported from the Upper Cretaceous, adding to other recent finds which contradict the idea that large and giant forms entirely dominated this interval. Unusual features of the tracks, including relatively long, slender pedal digit impressions, do not match the pes of any known Cretaceous pterosaur, suggesting that the trackmakers are as yet unknown from the body fossil record. The Hwasun pterosaur footprints appear to record gregarious behavior at the exact location by individuals of different ages, hinting at the possibility that pterosaurs gathered in mixed-age groups.

A high-density Grallator assemblage from the Haman Formation (Cretaceous), Korea: implications for Cretaceous distribution of grallatorids in east Asia

ABSTRACT Monospecific assemblages of non-avian theropod tracks are relatively rare in the Cretaceous of Korea, where assemblages dominated by the tracks of diverse tetrapods (birds, sauropods, ornithopods, and pterosaurs) are well known and widely distributed in the Haman and Jindong formations (Hayang Group). To date, few high-density assemblages of theropod tracks have been documented. A Haman Formation site on Adu Island reveals a small high-density assemblage of Grallator tracks (~29 tracks/m2). The tracks, which indicate registration on a sandy substrate infused with microbial mat, are indistinguishable from Grallator tracks known from a few other Lower Cretaceous sites in China and east Asia. Early and Middle Jurassic Grallator-dominated assemblages are common in east Asia, and persist into the Late Jurassic- Early Cretaceous (Neocomian) transition in China, where they are typically only associated with sauropodomorph tracks. Post-Neocomian (Aptian-Albian) Cretaceous assemblages from Korea are much more diverse, and characterised by tracks of sauropod and ornithopod dinosaurs, non-avian and avian theropods (birds), pterosaurs and other tetrapods. Post-Neocomian assemblages dominated by theropod tracks, are rare and no large monospecific grallatorid assemblages are currently known.

Saurischian-dominated tracksites and first Cretaceous lizard trackway from China from the Hekou Group (Lower Cretaceous) of Lanzhou-Minhe Basin, Gansu, Northwest China

ABSTRACT A total of 31 Lower Cretaceous tetrapod tracksites have been reported from four areas in Gansu Province, China: Yanguoshia, Guanshan, Zhongpu and Honggu. Here we report on the previously undescribed track types found at seven of these sites, five of which are sauropod dominated, with one site yielding ornithopod tracks and another one yielding theropod tracks. The Tianjiawan site is of particular significance for having produced the first lizard trackway from the Cretaceous of China and only the fourth global occurrence from this time period. The lizard trackway is tentatively assigned to ?Neosauroides ichnosp. indet., and compared with Neosauroides from the Cretaceous of Korea. As in Korea the Gansu lizard trackway occurs in lake margin sediments suitable for the preservation of the tracks of small tetrapods.

Trackway evidence for large bipedal crocodylomorphs from the Cretaceous of Korea

Large well-preserved crocodylomorph tracks from the Lower Cretaceous (? Aptian) Jinju Formation of South Korea, represent the well-known crocodylomorph ichnogenus Batrachopus. The Korean sample includes multiple, narrow-gauge, pes-only trackways with footprint lengths (FL) 18–24 cm, indicating trackmaker body lengths up to ~3.0 m. Surprisingly, the consistent absence of manus tracks in trackways, with well-preserved digital pad and skin traces, argues for bipedal trackmakers, here assigned to Batrachopus grandis ichnosp. nov. No definitive evidence, either from pes-on-manus overprinting or poor track preservation, suggests the trackways where made by quadrupeds that only appear bipedal. This interpretation helps solve previous confusion over interpretation of enigmatic tracks of bipeds from younger (? Albian) Haman Formation sites by showing they are not pterosaurian as previously inferred. Rather, they support the strong consensus that pterosaurs were obligate quadrupeds, not bipeds. Lower Jurassic Batrachopus with foot lengths (FL) in the 2–8 cm range, and Cretaceous Crocodylopodus (FL up to ~9.0 cm) known only from Korea and Spain registered narrow gauge trackways indicating semi-terrestrial/terrestrial quadrupedal gaits. Both ichnogenera, from ichnofamily Batrachopodidae, have been attributed to Protosuchus-like semi-terrestrial crocodylomorphs. The occurrence of bipedal B. grandis ichnosp. nov. is evidence of such adaptations in the Korean Cretaceous.

A Carcharodontosaurid tooth from the Hasandong Formation (Lower Cretaceous) of South Korea

A large tooth of theropod dinosaur that was recovered from the Hasandong Formation (Lower Cretaceous; Aptian-Albian) in Daedo island, Hadong Couty, South Gyeongsang Province of South Korea is redescribed. Although the tooth was misidentified as a "Prodeinodon"-like megalosaurid theropod at the first time, detailed comparisons with known theropod dentition anatomy strongly indicate that this tooth belongs to an Acrocanthosaurus-like basal carcharodontosaurid theropod. This referral is supported by its combination of large size, ovoid-shaped cervix outline, mesial carina that does not reach the cervix, labially displaced distal carina and large number of denticles. This tooth is different from other carcharodontosaurid teeth from the same formation in several anatomical aspects (e.g., smaller overall size, presence of transverse lines adjacent to the distal carina, presence of interdenticular sulci in distal carina, denticle densities, crown basal ratio), indicating that carcharodontosaurid diversity in the Early Cretaceous of Korea could have been higher, although these differences may represent positional or individual variations. The presence of Acrocanthosaurus-like theropod teeth (e.g., "Prodeinodon", "Wakinosaurus") from early Cretaceous deposits (Valanginian-Cenomanian) of South Korea, Japan, Mongolia and China indicates that North American Acrocanthosaurus atokensis possibly represents a form that immigrated from the Asia.

Exquisitely-preserved, high-definition skin traces in diminutive theropod tracks from the Cretaceous of Korea

Small theropod tracks, ichnogenus Minisauripus, from the Jinju Formation (Cretaceous) of Korea reveal exquisitely preserved skin texture impressions. This is the first report for any dinosaur of skin traces that cover entire footprints, and every footprint in a trackway. Special sedimentological conditions allowed footprint registration without smearing of skin texture patterns which consist of densely-packed, reticulate arrays of small (<0.5 mm) polygons, preserved as both impressions and casts, the latter essentially foot replicas. The skin texture resembles that reported for two Lower Cretaceous avian theropods (birds) from China which had quite different foot morphologies. This is also the oldest report of Minisauripus from Korea predating five reports from the Haman Formation of inferred Albian age. Minisauripus is now known from six Korean and three Chinese localities, all from the Lower Cretaceous. This gives a total sample of ~95 tracks representing ~54 trackways. With >80% of tracks <3.0 cm long, Minisauripus is pivotal in debates over whether small tracks represent small species, as the database suggests, or juveniles of large species.

A New Semi-Palmate Bird Track, Gyeongsangornipes lockleyi ichnogen. et ichnosp. nov., and Koreanaornis from the Early Cretaceous Jindong Formation of Goseong County, Southern Coast of Korea

Well-preserved semi-palmate bird tracks and small wading bird tracks from the Early Cretaceous Jindong Formation of Deokmyeongri, Hai-myeon, and Naesanri, Donghae-myeon, Goseong County, South Gyeongsang Province, southern coast of Korea, are herein described as Gyeongsangornipes lockleyi ichnogen. et ichnosp. nov. and Koreanaornis hamanensis, respectively. Gyeongsangornipes lockleyi is a small asymmetrical, strong mesaxonic bird track, about 31–32 mm long and 40–41 mm wide, without a clear hallux impression. Divarication between digits II and III is much larger than that between digits III and IV. Webbing is clearly preserved, and the web between digits II and III is smaller than that between digits III and IV, which shows strong asymmetry of web development. Two different-sized Gyeongsangornipes lockleyi appear to suggest two different-size classes of web-footed birds. Koreanaornis hamanensis is a small sub-symmetrical wading bird track, about 26–28 mm long and 29–39 mm wide, without clear hallux impressions. The divarication between digits II and III (59°–66°)°) is larger than that between digits III and IV (44°– 58°). Divarication between digits II and IV is 103°–123°. Length of digit III (26–28 mm) is longer than those of digits II and III (about 18 mm). These new records shed light on patterns of bird track diversity and abundance in the Cretaceous of Korea and document a diverse avian fauna that flourished during the Cretaceous.

Recent Advances in Korean Vertebrate Ichnology: The KCDC Comes of Age

Vertebrate tracks were first reported from the Cretaceous of South Korea in 1969 by B. K. Kim. His discovery of bird tracks, appropriately named Koreanaornis hamanensis, not only signaled the first bird tracks discovered in Asia and the second formally named avian ichnogenus from the Mesozoic, but it also was an indication of the vast wealth of vertebrate tracks that would be discovered a generation later in the Haman Formation and other Cretaceous formations of Korea, particularly in the large Gyeongsang Basin. This landslide of discovery has resulted in a proliferation of papers on vertebrate tracks from the Cretaceous of South Korea and the growing recognition that as a region it reveals multiple track-rich sequences of unique quality and scientific utility. Because of the outstanding ichnological resources in this region, it has been dubbed the Korean Cretaceous Dinosaur Coast (KCDC). Many sites of national and international significance have been designated as national natural landmarks, and the best of these have been nominated for World Heritage Inscription. In this editorial introduction, we attempt to summarize the present state of tetrapod ichnology after four decades of vertebrate track research. This synopsis serves as an introduction to a dozen short papers that focus attention on new discoveries at key sites. These reports, in turn, provide a promise of abundant material for future decades of research. At the present time, there are at least five ichnological research groups working on vertebrate tracks from the Cretaceous of Korea, both independently and collaboratively. Almost all researchers from these groups have contributed to this volume. The result has been the naming of five new tetrapod ichnospecies (Fig. 1), adding to the ten previously named.

The Trackway of a Quadrupedal Ornithopod from the Jindong Formation (Cretaceous) of Korea

We report the first occurrence of the trackway of a quadrupedal ornithopod from the Jindong Formation (Late Aptian) of Korea. Although trackways of ornithopods are abundant in the Cretaceous of Korea, especially in the Jindong Formation, trackways of a quadrupedal trackmaker have never been reported from Korea. Moreover, the manus shows an unusual morphology with three subcircular indentations arranged in an unusual, elongate arc unlike any seen in other ornithopod ichnospecies. The specimen is clearly different from all other known Korean ornithopod footprints and is herein named as Caririchnium kyoungsookimi. To date, Caririchnium is one of only two ichnogenus names applied with confidence to Lower Cretaceous ornithopod tracks from Asia.

A Paradise of Mesozoic Birds: The World's Richest and Most Diverse Cretaceous Bird Track Assemblage from the Early Cretaceous Haman Formation of the Gajin Tracksite, Jinju, Korea

More than 2,500 well-preserved bird tracks associated with theropod and sauropod tracks are recorded from a dense assemblage in lacustrine deposits of the Early Cretaceous Haman Formation of the Gajin area, Jinju, Korea. These tracks are preserved in the recently constructed Fossil Heritage Hall at the Gyeongsangnamdo Institute of Science Education. Bird tracks are attributed to Ignotornis gajinensis ichnosp. nov., Koreanaornis hamanensis, Goseongornipes markjonesi, and ?Aquatilavipes. Like G. markjonesi, I. gajinensis is a semi-palmate bird track, similar to Hwangsanipes (ichnofamily Ignotornidae) with a postero medially directed hallux and characterized by interdigital angles between digits II and III larger than III and IV. However, Hwangsanipes is a larger morphotype than Ignotornis with a more pronounced semipalmate web. I. gajinensis has associated arcuate to semi-circular, double-grooved, or paired impressions resulting from spoonbill-like feeding behavior. Similar rare but more linear traces occur in one Ignotornis specimen from the Cretaceous of Colorado. The Gajin site represents a record of the world's most-dense assemblage of bird tracks (up to ∼600 per m2) at a single locality and provides striking evidence of the diversity of avian ichnotaxa during the Cretaceous. The Gajin tracksite provides new insight into the morphology of four of the eight ichnogenera known from the Cretaceous of Korea. The Goseongornipes sample is the largest and best-preserved available. In the case of Ignotornis, feeding traces shed new light on behavior and paleoecology of the trackmakers, which appear to have been remarkably convergent with modern shore birds.

Ornithopodichnus and Pes-Only Sauropod Trackways from the Hwasun Tracksite, Cretaceous of Korea

Trackways of small (foot length ∼12–15 cm) robust ornithopods are relatively uncommon in the Cretaceous, where most tracks attributed to iguanodontids and hadrosaurs range in size from ∼20–80 cm. The Hwasun site, previously noted for its abundant theropod trackways, also reveals one horizon (L2) with at least six parallel trackways of small blunt-toed ornithopods with wide tracks, short steps and typical inward rotation of the pes. The site also reveals a second horizon (L4) which yields a single clear trackway of a much larger blunt-toed ornithopod. Although allometric trends in tridactyl track assemblages tend to show increased trackway width and reduced anterior projection of digit III (reduced mesaxonic emphasis) with increasing size, the small Hwasun ornithopods reveal unusually wide tracks with reduced mesaxony. The tracks are herein assigned to the ichnogenus Ornithopodichnus. A map of previously unmapped Level 4 is presented showing the context of the large ornithopod tracks on the same surface as an unusual pes-only trackway with distinctive claw traces and sediment rims. This surface also reveals isolated sauropod manus tracks and various underprints.

Lithographus, an Abundant Arthropod Trackway from the Cretaceous Haenam Tracksite of Korea

Trackways ascribed to Lithographus hieroglypichus and attributed to pterygote insects are described from the Cretaceous Uhangri Formation of Korea. The locality is part of the Haenam Tracksite at the Uhangri Dinosaur Museum Complex, which is famous for dinosaur, pterosaur and bird tracks. This represents the first report of the arthropod trackway Lithographus from the Cretaceous of Korea. The trackways are preserved in cherty mudstones that formed in the margins of an alkaline lake in the vicinity of active volcanoes. Numerous trackways are preserved at a single horizon. This probably reflects a brief period of exposure of balanced-fill lake margin sediments, which provided a window of opportunity for the production and preservation of trackways of insects that inhabited the region rather than a sudden influx of insects into the area related to volcanism and a productivity bloom.

Enigmatic Giant Pterosaur Tracks and Associated Ichnofauna from the Cretaceous of Korea: Implication for the Bipedal Locomotion of Pterosaurs

Enigmatic tracks and dinosaur trackways from lacustrine margin sediments of the Lower Cretaceous Haman Formation of the southern coast of Korea represent a new ichnospecies. Trackways with large, pes-only tracks with lengths up to 39 cm, characterized by elongate, subtriangular outlines, impressions of four digits and a subangular heel, are attributed to plantigrade pterodactyloids and assigned to Haenamichnus gainensis ichnosp. nov. These tracks comprise one of the largest and longest pterosaur trackways hitherto reported and provide intriguing new insight into pterosaur locomotory gait and stance, which has been the subject of a 200-year-long controversy. Associated sauropod tracks, assigned herein to Brontopodus birdi, reach 70 cm in length, are medium-gauged, and show outwardly curved digit impressions. E-W trackway alignments likely indicate shoreline trends but could possibly suggest behavioral hunting scenarios. Pes-only pterosaur tracks at this locality are another example of spoor incorrectly interpreted by creationists as the footprints of humans that coexisted with dinosaurs during the Cretaceous Period. This erroneous interpretation is popular in some circles in Korea.

A fossil spider from the Cretaceous of Korea

A fossil spider from the Cretaceous Jinju Formation of Korea is redescribed as Korearachne jinju, n. gen. n. sp. Previous description of this specimen, the only known fossil spider from Korea, was inadequate, and here we present a more detailed interpretation and illustration of the specimen. The fossil spider is preserved alongside juvenile albuiform fish, Diptera and possible crustaceans, which suggests a mass mortality event. Familial identification of the spider is impossible, but it probably belongs to a guild of wandering spiders, possibly lycosoids.

Unusual Didactyl Traces from the Jinju Formation (Early Cretaceous, South Korea) Indicate a New Ichnospecies of Dromaeosauripus

New didactyl dinosaur tracks from the fine-grained sandstone of the Early Cretaceous Jinju Formation, Namhae area, Korea, are herein described as Dromaeosauripus jinjuensis ichnosp. nov. A trackway about 4.3 m long is composed of 12 consecutive didactyl traces. The tracks average about 9.3 cm long and 6.8 cm wide. Pace, stride, and pace angulation are 40 cm, 80 cm, and 175°, respectively. D. jinjuensis is a small didactyl track characterized by slender digit impressions, very narrow divarication angle between digits III and IV, digit III slightly longer than IV, and sharp claw impressions. D. jinjuensis measurements differ significantly from D. hamanensis in length (only 60% of the latter), width (81%), length/width ratio (0.72), and digit thickness (55%). The didactyl tracks are tentatively interpreted to be formed by a small dromaeosaurid walking bipedally on a lake margin. D. jinjuensis represents the oldest theropod dinosaur tracks described in the Cretaceous of Korea and the second ichnospecies of Dromaeosauripus. It suggests more diversity and wider stratigraphic and paleogeographic distribution of dromaeosaurids. The track morphology may also indicate a more digitigrade gait.

Dinosaur skin impressions from the Cretaceous of Korea: New insights into modes of preservation

Three specimens of sauropod dinosaur skin impressions from footprints in the Lower Cretaceous Jindong and Haman formations are unusual because they are not associated with well-preserved ‘host’ tracks. This suggests a hitherto unreported mode of preservation in which diagnostic but isolated skin traces may appear associated with substrates where only the superficial layers were originally soft. Two specimens from the Haman Formation of Gainri and Sinsu Island reveal large pentagonal to heptagonal scale impressions (size 2.0–2.5 cm). Another specimen from the Jindong Formation of the Deokmyeongri area is an extremely well-preserved, honeycomb-like pattern of hexagonal scale impressions, but an adjacent part reveals pentagonal to heptagonal polygons of variable size. Collectively these skin impressions more than double the sparse record of sauropod skin impressions and show that patterns (morphology) are consistent from the Jurassic to the Cretaceous. Although comprehensive syntheses have yet to be attempted, skin traces are amendable to systematic description using tubercle size, shape, thickness, and inter-tubercle groove thickness. Such features are useful for distinguishing the different morphologies of dinosaurs and other vertebrates that lived in Korea and other regions during the Mesozoic. Dinosaur skin impressions have occasionally been confused with glypogryptids, typical deep sea feeding traces, small desiccation cracks, and small load casts which they superficially resemble. To avoid such confusion we enumerate criteria useful for distinguishing dinosaur skin impressions from similar shaped invertebrate trace fossils and inorganic sedimentary structures. These criteria vary in importance but include preservation, morphology, dimension of morphology, depositional environment, deformation of underlying sediments, uniformity of size and shape of individual scale impressions within single specimens, ornamentation, and geological age.

The oldest record of webbed bird and pterosaur tracks from South Korea (Cretaceous Haman Formation, Changseon and Sinsu Islands): More evidence of high avian diversity in East Asia

Tracks of web-footed birds and pterosaurs from the Lower Cretaceous (Aptian-Albian) Haman Formation of Changseon and Sinsu Islands, respectively (southern coast of Korea), represent the oldest records for these footprint types in Asia. The morphology of the bird tracks, with prominent posteriorly directed hallux impression, semi-palmate web, and small ratio of length to width is similar to Hwangsanipes choughi from the Upper Cretaceous (Cenomanian) Uhangri Formation. However, they about 20–25% smaller, and therefore much closer to the size of North American Ignotornis (size difference less than 10%). The development of the web appears intermediate in size between Hwangsanipes and Ignotornis. This leads us to infer a new ichnotaxon herein named Ignotornis yangi. This is the first Asian report of a named bird track similar to the type material of Ignotornis from North America. Pterosaur tracks consist predominantly of clear impressions of tridactyl mani (length 9–13 cm) characterized by strongly asymmetric digit impressions that outnumber less-clear elongated pes traces by a ratio of about 10 to 1. Clusters of short digit impressions or parallel to subparallel scrape marks indicate incomplete pes traces probably made by swimming animals. The pterosaur tracks, here provisionally identified as Pteraichnus, represent the first record of this ichnogenus from Korea. The track maker represents a species quite different from the giant track maker represented by the ichnogenus Haenamichnus from the Cenomanian Uhangri Formation, but it is similar to recent reports of Pteraichnus-like forms from the Lower Cretaceous of China. These new records shed light on patterns of bird-track diversity and abundance in the “mid” Cretaceous of Korea (Aptian-Cenomanian) and show that at least two quite distinct pterosaurian species existed during this time span with at least six distinct species of track-making birds. When combined with additional reports of bird track ichnotaxa from China, the picture emerges of a remarkably diverse Lower Cretaceous avifauna. Such diversity is consistent with the skeletal record for this region, though the types of birds represented by tracks are “shorebird-like” and therefore distinct from the skeletal avifauna, which consist of birds of the perching type. The ability of tracks to record whole foot morphology including details of web and hallux configuration allows for fine discrimination of foot morphology and comparison with web-footed tracks from other regions and geologic time periods. As is the case with modern shore birds, Cretaceous tracks were probably mostly made by adults whose foot size as well as shape is probably indicative of the identity of the track maker at low taxonomic levels.

Some confierous fossil woods from the Cretaceous of Korea

Thirteen silicified fossil woods were collected from the Cretaceous deposits of Haenam Basin and islands of Gwanmae and Byeongpung, Jeollanam-do as well as from the Cretaceous Dadaepo Formation, Busan, Korea. Anatomical features of all of these specimens showed that they were coniferous woods. On the basis of the detailed anatomical features they were identified asDadoxylon byeongpungense sp. nov.,Cupressinoxylon uhangriense sp. nov.,Taxodioxylon cf.nihongii Nishida et H. Nishida,Taxodioxylon albertense (Penhallow) Shimakura, andMesembrioxylon sp. All of them, exceptMesembrioxylon, are described for the first time from the Korean Peninsula. It should be noted that no dicotyledonous wood has been found from this study. Generally the sampled horizons are considered as Upper Cretaceous with dinosaur footprint fossils. In Japan, the Upper Cretaceous sediments bear abundant dicotyledonous fossils. Therefore further studies should be needed to clarify the age of these horizons and the vegetation in the ancient world with dinosaur.