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Dromaeosauriformipes
Smallest-dinosaur-tracks-5
Name Dromaeosauriformipes
Order Dinosauromorphipeda
Suborder Theropodipedia
Class Reptilipedia
Name Translation Tracks of the Dromaeosauriform
Period Early Cretaceous (Aptian?)
Location South Korea
Diet Freshwater fish and insects?
Size 10 cm (4 in) long, and 5 cm (2 in) at the hips and 10-12 grams in weight
Date of Discovery November 15, 2018

Dromaeosauriformipes (meaning "Tracks of the Dromaeosauriform") is an extinct ichnogenus of South Korean dromaeosauripodid, or dromaeosaurid. It was the smallest known dinosaur having been around the size of a sparrow. The footprints it produced were around 1 cm (0.4 in) in diameter and belonged to a juvenile or diminitive individual. If the trackmaker was a juvenile then that would make Minisauripus and Ashdown Maniraptoran both the joint smallest dinosaurs.[1]

41598 2018 35289 Fig4 HTML

(A) The type trackway of Dromaeosauripus jinjuensis shown as photograph (left) and line drawing (right): (B,C) line drawings of single tracks from the type trackways of D. jinjuensis, D. hamanesis and D. yongjingensis. TA1R and TE3R identify individual tracks in D. yongjingensis sample10; (D) line drawings of the trackways of small Dromaeosauriformipes rarus for scale

The type ichnospecies, Dromaeosauriformipes rarus, was described by Kim et al. in 2018. The tracks are currently being excavated for further study.

The holotype consists of Trackway 1 on Chinju National University of Education (CUE) specimen CUE JI-2E Dr001 (Fig. 2), also represented by University of Colorado Museum of Natural History (UCM) replica UCM 214.309.

Type locality

Dromaeosauriformipes was discovered in the Jinju Formation, Lower Cretaceous (Aptian), Korea National Natural Monument Number 534 in Jinju Innovation City, Gyeongsangnam-do Province, South Korea.

Smallest-dinosaur-tracks-2

Holotype trackway

Etymology

Ichnogenus (Dromaeosauriformipus rarus) named for similarity in “form” (shape) to the didactyl raptor track Dromaeosauripus, previously defined as meaning “dromaeosaur foot.” Ichnospecies from Latin rarus meaning both small and infrequently found.
41598 2018 35289 Fig5 HTML

Illustrations of Dromaeosauriformipes rarus ichnogen. et ichnosp nov. trackway described here at same scale as type Dromaeosauripus jinjuensis with reconstruction of trackmaker anatomy at scale corresponding to footprint sizes. Upper left color inset is photogrammetric image of Trackway 1, and right side photogrammetric color image shows the type trackway of Dromaeosauripus jinjuensis[2]

Description

The holotype slab contains 18 tracks of a diminutive biped, preserved as natural impressions (concave epireliefs). These include the holotype series designated as Trackway 1 (Fig. 2), containing a seven-track sequence, a second three-track, paratype series, Trackway 2, and eight isolated tracks. All are remarkably consistent in size. The holotype averages 10. 33 mm long (L) and 4.15 mm wide (W): L/W 2.49 (N = 7). These mean values are similar to those obtained from Trackway 2 (L 10.5 mm. W 4.00 mm, L/W 2.63, N = 3), for the isolated tracks (means: L 9.53 mm, W 3.35 mm, L/W 2.84, N = 8) and for the sample as a whole (means: L 10.47 mm, W 3.91 mm, L/W 2.68, N = 18).

Holotype dimensions

The dimensions of holotype Trackway 1 reveal a mean step and stride length of 4.62 cm and 10.00 mm, respectively, indicating a step about 4.5 times footprint length and slow progression (0.6 m/sec, or 2.16 km/hr). By contrast paratype Trackway 2 has a mean step or pace length (PL) of 27.82 cm (stride of 55.63/2) indicating steps about 26.49 times footprint length and much higher estimated speed of 10.5 m/sec, or 37.8 km/hr. However, both trackways are very narrow, with correspondingly high pace angulation values (168°–188°).

Diagnosis of the holotype

Didactyl tracks of a diminutive biped more than twice as long as wide, with two equidimensional, elongate parallel traces. Trackway about as narrow as individual tracks, with step length highly variable. Dromaeosauriformipes differs from Dromaeosauripus in size and degree of footprint elongation, and in the absence of any trace of digit II characteristic of other dromaeosaurid ichnotaxa.[3][4][5]

References

  1. (2018) "Smallest known raptor tracks suggest microraptorine activity in lakeshore setting". Scientific Reports 8: Article number 16908. DOI:10.1038/s41598-018-35289-4. PMID 30442900. 
  2. Kim JY, Lockley MG, Woo JO, Kim SH. Unusual didactyl traces from the Jinju Formation (Early Cretaceous, South Korea) indicate a new ichnospecies of Dromaeosauripus. Ichnos. 2012;19:75–83. doi: 10.1080/10420940.2012.664054.
  3. Kim JY, et al. New didactyl dinosaur footprints (Dromaeosauripus hamanensis ichnogen. et ichnosp. nov.) for the Early Cretaceous Haman Formation, south coast of Korea. Palaeogeography, Palaeoclimatology, Palaeoecology. 2008;262:72–78. doi: 10.1016/j.palaeo.2008.02.003.
  4. Zhen S, Li J, Zhang B, Chen W, Zhu S. Dinosaur and bird footprints from the Lower Cretaceous of Emei County, Sichuan, China. Memoirs of Beijing Natural History Museum. 1994;54:106–120.
  5. Xing L, et al. Tetrapod track assemblages from Lower Cretaceous desert facies in the Ordos Basin, Shaanxi Province, China, and their implications for Mesozoic paleoecology. Palaeogeography, Palaeoclimatology, Palaeoecology. 2018;507:1–14. doi: 10.1016/j.palaeo.2018.05.016.

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