characters (Fig. 1, and figs. S4 to S7): maxilla
with rostral ascending process much lower than
caudal ascending process and maxillary fenestra
larger than antorbital fenestra; jugal with notched
postorbital ramus; postorbital with dorsoventrally expanded caudal ramus; dorsoventrally slender
postacetabular process on ilium; and deep extensor fossae on metatarsals II to IV (15).
It was a small, 1.5-m-long bipedal herbivore,
with a short skull, plant-eating teeth, elongate hindlimbs, short forelimbs, and an elongate tail (Fig. 1).
Phylogenetic analysis (figs. S10 and S11) (15) recovers Kulindadromeus as a basal member of
Neornithischia [all genasaurians more closely related
to Parasaurolophus walkeri than to Ankylosaurus
magniventris or Stegosaurus stenops (16)] and the
sister taxon for Cerapoda [Parasaurolophus walkeri,
Triceratops horridus, their most recent common
ancestor, and all descendants (16)].
The key features of Kulindadromeus relate
to its integument. Numerous, varied, exceptionally preserved integumentary features are associated, often in direct connection, with the
bones and vary in morphology among different
body regions. They comprise three types of
scales and three types of featherlike structures.
Small (<3.5 mm long) imbricated and hexago-
nal scales, resembling the scutella in modern
birds (17), are associated with the distal parts
of the tibiae in Kulindadromeus (Fig. 2A and
fig. S8E). Smaller (<1 mm) rounded and non-
overlapping scales occur around the manus,
tarsus (Fig. 2A and fig. S8E), metatarsus, and
pes (fig. S8F), resembling the reticula along the
plantar face of the pes in modern birds (17).
The tail of Kulindadromeus is covered by at
least five longitudinal rows of slightly arched
scales (Fig. 2, B and C, and fig. S8, A to D). The
largest scales (~20 mm long and 10 mm wide)
occur along the proximal part of the tail. The
caudal scales of Kulindadromeus are thin
(<100 mm), unornamented, and slightly imbri-
cated, each scale covering part of the adjacent
distal one (Fig. 2C and fig. S8, B to D). They are
clearly different from the thicker, sculptured, and
nonoverlapping osteoderms in thyreophoran or-
nithischians (18) and from the proportionally
thicker and smaller scales in iguanodontian
ornithopods (19), more closely resembling epi-
dermal scales. The preservation of the scales as
carbonaceous remains suggests that they are
unlikely to be osteoderms, because the bones
(which also comprise calcium phosphate in vivo)
display a quite different preservational pathway.
Each scale forms a triangular anterior spur that
covers the preceding one, so that adjacent ele-
ments are interconnected by a clip-like system.
Proximally, at the level of the base of the tail
(Fig. 2C), the scales become progressively smaller
and more rounded and do not overlap.
Monofilaments are widely distributed around
the thorax (Fig. 2, G to I), on the back, and
around the head (Fig. 2, D to F). Those above
the head are thin (~0.15 mm in diameter), short
(10 to 15 mm long), and curved, with no preferred
orientation. The thoracic and abdominal filaments are wider (0.2 to 0.3 mm) and longer (20 to
30 mm). These monofilaments are shorter and
thinner than the long bristlelike structures on
the proximal part of the tail in Psittacosaurus (12)
and the filamentous structures in Tianyulong (13).
They more closely resemble the monofilaments
in the basal coelurosaur Sinosauropteryx (20) and
are similar to morphotype 1 in a recent evolutionary model of feathers (21).
Kulindadromeus also shows compound, non-shafted integumentary structures along the humerus and femur (Fig. 3, A to F, and fig. S9).
BA
F
H
IG
ED
C
20 mm 10 mm
20 mm
5 mm 10 mm
10 mm
anterior
10 mm
10 mm
10 mm
I
Fig. 2. Epidermal scales and featherlike structures of Kulindadromeus zabaikalicus. (A) Scales around the distal tibia and the tarsus (INREC K4/57);
(B) double row of scales above the proximal part of the tail (INREC K4/94) in dorsal view; (C) close-up of the left row of caudal scales (INREC K4/117) in
dorsal view; (D) partial skull (INREC K4/22) in right lateral view, with (E and F) detail of areas indicated in (D) and (E) showing filamentous structures; (G)
left part of ribcage (INREC K4/33), with (H and I) detail of areas indicated in (G) and (H) showing filamentous structures.
