Doolysaurus

Name and Etymology

The generic name Doolysaurus honors "Dooly the Little Dinosaur" (아기공룡 둘리), an iconic South Korean cartoon character created by artist Soo-Jung Kim in 1983. The name was chosen because the fossil represents a juvenile — a "baby dinosaur" — making it a perfect match for the beloved cartoon character. The suffix -saurus derives from the Greek σαῦρος (sauros, meaning "lizard"). The specific epithet huhmini honors Professor Min Huh, a paleontologist who founded the Korea Dinosaur Research Center (KDRC) at Chonnam National University, has dedicated over 30 years to Korean dinosaur research, and collaborated with UNESCO to preserve dinosaur fossil sites in Korea. Professor Huh is the incumbent Administrator of the Korea Heritage Service (Jung et al. 2026).

Taxonomic Status

Doolysaurus huhmini was formally described as a new genus and species (gen. et sp. nov.) on March 19, 2026, in the international open-access journal Fossil Record. It is registered in ZooBank (genus LSID: urn:lsid:zoobank.org:act:86C724BC-2A9E-47EB-A502-898E4FBAC0BD; species LSID: urn:lsid:zoobank.org:act:895C6714-B565-4100-BE78-0F6AFE1537FE). It is currently the only known species in the genus. Among Korean dinosaur taxa, it joins Koreaceratops hwaseongensis (Lee et al. 2011) and Koreanosaurus boseongensis (Huh et al. 2011) as the third valid species based on skeletal fossils.

Key Significance

First Korean dinosaur fossil to include diagnostic cranial material; first new dinosaur species described from Korea in 15 years; a small-bodied mid-Cretaceous thescelosaurid providing new evidence for the Asian origin of the family.

Age Range

The Ilseongsan Formation is dated to the Albian–early Cenomanian, approximately 113–97 Ma. This age is constrained by multiple lines of evidence. The overlying Maewolli Tuff yielded a U-Pb SHRIMP zircon age of 97.55 ± 0.62 Ma (Kim et al. 2014), establishing a minimum age for the underlying formations. Ostracod biostratigraphy from the overlying Dalido Formation and the stratigraphic range of Macroelongatoolithus dinosaur eggs (earliest global occurrence in the Albian; Simon et al. 2018) further support this dating (Choi et al. 2023). Earlier K-Ar dates of 77–83 Ma (Rhee et al. 2012) are now considered outdated in light of the U-Pb and biostratigraphic evidence.

Formation and Lithology

The Ilseongsan Formation conformably overlies the Injiri Formation and is overlain by the Dalido Formation. The Dalido Formation is in turn unconformably capped by the Maewolli Tuff (Kim et al. 2014). The fossil-bearing lithology consists of reddish-brown, homogeneous, fine-grained sandy mudstones interbedded with gray pyroclastic units. Paleosol profiles with calcareous nodules are well developed within these homogeneous layers (Jung et al. 2026).

Paleoenvironment

The homogeneous sandy mudstones with paleosol profiles and calcareous nodules indicate steady, relatively rapid sedimentation in a distal floodplain environment (Kraus 1999; Kim et al. 2022). Stratified deposits containing bone and eggshell fragments within gravelly sandstone layers are interpreted as crevasse-splay deposits. Comparable depositional settings have been reported from dinosaur egg localities at Boseong (Paik et al. 2004), Wi Island (Kim et al. 2022), the upper Hasandong Formation (Paik 2000), and the Gaogou Formation of Henan Province, China (Liang et al. 2009). The site has also yielded an exceptionally preserved giant theropod egg nest (Macroelongatoolithus; Huh et al. 2014) and diverse other dinosaur egg types.

Holotype

Diagnosis

Doolysaurus is diagnosed by a unique combination of 10 features recovered from analysis of the Fonseca et al. (2024) dataset, including one optimized autapomorphy (marked with ). Key diagnostic features include the following. The lateral condyle of the quadrate is larger than the medial condyle (shared with Orodromeus and Haya). The exits of the hypoglossal nerve (XII) in the exoccipital are confluent into a single opening (shared with Jeholosaurus). The basioccipital contribution to the foramen magnum border exceeds one-third of the basioccipital condyle size (shared with Fona). The apex of the maxillary teeth is positioned posterior to the crown center (shared with Zephyrosaurus). Dorsal ribs display distal anteroposterior thickening (shared with Koreanosaurus, Thescelosaurus neglectus, and Th. garbanii). The lateromedial widths of the crista tibiofibularis and the medial condyle of the distal femur are roughly equal near the base (autapomorphy). The fibular shaft is D-shaped in cross-section (shared with Albertadromeus, Koreanosaurus, Orodromeus, Oryctodromeus, Zephyrosaurus, and Fona). Extensor pits are present on the distal ends of pedal phalanges II–IV (shared with Changmiania, Oryctodromeus, and Changchunsaurus).

Specimen Limitations

Only a single juvenile specimen is known, so adult morphology and any ontogenetically variable features cannot be fully assessed. The premaxilla, nasal, frontal, and other anterior cranial elements are not preserved. The forelimb is incomplete (only partial scapula, coracoid, and humerus). Some diagnostic characters may change during ontogeny (Poole 2023).

Body Size

The estimated total femoral length of the holotype is approximately 12–13 cm (Jung et al. 2026). Based on femoral circumference, the juvenile's body mass is estimated at approximately 8.3 kg (Jung et al. 2026; cf. Campione & Evans 2012), comparable in size to a large turkey. Adults may have grown to approximately twice the juvenile's size, but this remains uncertain without adult material. The researchers informally compared the hypothetical adult body to "a little lamb" in terms of overall build and size.

Skull

The partially preserved left maxilla bears six maxillary teeth and nine alveoli (tooth sockets). The crowns are triangular in both lingual and labial views, slightly asymmetrical, and laterally compressed, with a distinct constriction above the root and a well-developed cingulum (basal ridge) at the crown base. The apex of the posterior teeth is positioned posteriorly rather than centrally — a feature shared with Zephyrosaurus. The left dentary preserves 15 teeth and two replacement teeth, with alveolar arrangement suggesting a total capacity of at least 17 teeth. The coronoid process is well developed, straight, and subtriangular in outline. The quadrate is dorsoventrally elongated and blade-like. The supraoccipital has a rhomboidal posterior surface with a subtle midline elevation rather than a prominent nuchal crest. The fused exoccipital/opisthotic shows a unique confluent exit for the hypoglossal nerve (cranial nerve XII).

Postcranium

The hindlimb is well articulated. The femur is relatively straight with a symmetrical medial condyle at the distal end (similar to Haya and Thescelosaurus assiniboiensis, but unlike the asymmetrical medial condyle of Koreanosaurus). The proximal tibia has a sharply defined lateral condyle and lacks an accessory condyle (present in Koreanosaurus). The fibular shaft is D-shaped in cross-section. Pedal phalanges II–IV bear extensor pits at their distal ends.

Locomotion

As is typical for thescelosaurids, Doolysaurus was a bipedal dinosaur. The relatively long tibia compared to the femur suggests it may have been a reasonably agile runner.

Diet

The holotype preserves 40–50 gastroliths (stomach stones) with a combined mass of approximately 30.7 g. These subrounded stones were swallowed during life to aid in mechanical digestion. The gastrolith-to-body-mass ratio, combined with their morphology, is consistent with an omnivorous diet rather than a strictly herbivorous or granivorous one. The gizzard grinding action appears to have been weaker than that of modern seed-eating birds, suggesting a mixed diet of plants, insects, and small animals (Jung et al. 2026; cf. Wings & Sander 2007). The tooth morphology — triangular crowns with denticles on both mesial and distal margins and wear facets across the entire tooth row — also supports omnivory.

Ecological Context

Doolysaurus inhabited a mid-Cretaceous distal floodplain environment in what is now southwestern South Korea. The same site has yielded giant theropod egg nests (Macroelongatoolithus; Huh et al. 2014), indicating coexistence with large predatory dinosaurs. Close relatives such as Oryctodromeus and Fona are interpreted as semi-fossorial (burrowing) dinosaurs (Varricchio et al. 2007; Avrahami et al. 2024), but no direct evidence for burrowing behavior exists for Doolysaurus.

Integument

Thescelosaurids and other early-diverging neornithischians have been inferred to possess filamentous body covering. The study's co-author Julia Clarke suggested Doolysaurus may have been covered in a "fuzzy coat" of filaments, comparing its probable appearance to "a little lamb." However, this is an inference based on phylogenetic bracketing of related taxa; no direct integumentary evidence was preserved with the specimen.

Known Localities

The only known locality is the southeastern coast of Aphae Island (Aphaedo), Shinan, South Jeolla Province, South Korea. The Ilseongsan Formation at this site has also produced diverse dinosaur egg fossils and the Macroelongatoolithus nest (Huh et al. 2014).

Paleogeographic Context

During the mid-Cretaceous (~100 Ma), the Korean Peninsula was situated on the eastern margin of the East Asian continent. Paleogeographic reconstructions (Scotese 2021) place the region at slightly lower latitudes than its present position. The distal floodplain setting and associated pyroclastic deposits suggest a warm, relatively humid subtropical to temperate climate with periodic volcanic activity.

Phylogenetic Analysis Results

Jung et al. (2026) conducted phylogenetic analyses using two morphological data matrices. The primary analysis used the Fonseca et al. (2024) matrix (174 taxa, 900+ characters), and a sensitivity analysis employed the Avrahami et al. (2024) matrix (300+ characters). Parsimony analyses were run in TNT v. 1.6 and Bayesian tip-dated analyses in MrBayes v. 3.2.7 under the Fossilized Birth-Death model.

Both analyses recover Doolysaurus within Thescelosauridae. In the Bayesian analysis and the 50% majority-rule consensus of the parsimony analysis, it is placed as a basal member of the subfamily Thescelosaurinae, alongside Jeholosaurus and Changchunsaurus. The strict consensus parsimony tree leaves its position within the family unresolved. The cladogram below shows the simplified Bayesian result (after Jung et al. 2026):

Thescelosauridae includes two subfamilies: Thescelosaurinae (containing Changmiania, Changchunsaurus, Jeholosaurus, Doolysaurus, Fona, Parksosaurus, Thescelosaurus spp.) and Orodrominae (containing Yueosaurus, Haya, Nevadadromeus, Oryctodromeus, Zephyrosaurus, Albertadromeus, Koreanosaurus, Orodromeus). Doolysaurus is recovered at the base of Thescelosaurinae.

Biogeographic Implications

The recovery of Doolysaurus alongside most other Asian thescelosaurids (Jeholosaurus, Changchunsaurus, Changmiania, Haya) near the base of the family tree provides further support for an Asian origin of Thescelosauridae, with subsequent dispersal to North America.

Relationship to Other Korean Dinosaurs

Koreanosaurus boseongensis is another Korean thescelosaurid from the significantly younger Seonso Conglomerate (Santonian–Campanian, ~81 Ma). Despite limited overlap in preserved elements, the two taxa differ in distal femoral morphology (anterior margin shape, medial condyle symmetry), proximal tibial morphology (presence vs. absence of accessory condyle), and other features. Koreaceratops hwaseongensis is a basal ceratopsian and cannot be directly compared, though cranial features clearly distinguish it from Doolysaurus.

Confirmed

Validity as a new genus and species (10-character diagnostic combination including 1 autapomorphy). Placement within Thescelosauridae. Juvenile ontogenetic status (0–2 years old; femoral histology evidence). First diagnostic cranial material from a Korean dinosaur. Presence of gastroliths.

Strongly Supported Inferences

Omnivorous diet (gastrolith morphology and relative mass + dental morphology). Bipedal locomotion. Adult size approximately twice the juvenile.

Hypothetical / Uncertain

Fuzzy filamentous integument (no direct fossil evidence; inferred from phylogenetic position). Semi-fossorial habits (no direct evidence). Precise adult body mass and body length (no adult specimen). Precise age within the ~113–97 Ma range.

South Korea possesses one of the world's richest records of dinosaur trace fossils — trackways, eggs, and nests — yet skeletal remains are exceedingly rare. Prior to Doolysaurus, only two dinosaur taxa were considered valid based on skeletal material: Koreaceratops hwaseongensis (Lee et al. 2011) and Koreanosaurus boseongensis (Huh et al. 2011). Earlier-named taxa such as Ultrasaurus tabriensis (Chang et al. 1982; Kim 1983) and Pukyungosaurus milleniumi (Dong et al. 2001) are now regarded as nomina dubia due to the absence of diagnostic autapomorphies and insufficient morphological data (Lee & Yang 1997; Park 2016).

The discovery of Doolysaurus demonstrates that micro-CT technology can non-destructively reveal fossils hidden within hard rock matrices. The preservation of small, lightweight gastroliths in situ suggested that additional skeletal elements might remain intact within the block — a hypothesis confirmed by CT scanning. The research team anticipates that Aphae Island and other sites with comparable taphonomic conditions in Korea may yield further dinosaur skeletal fossils, potentially revealing a richer dinosaurian diversity than the trace fossil record alone suggests (Jung et al. 2026).