The known material of Echinodon is limited to bones of the skull, but the multiple specimens include at least some of the premaxilla, maxilla, lacrimal, jugal, palatine, ectopterygoid and dentary along with most teeth of both the upper and lower jaws.
Based on proportions of the related genus Heterodontosaurus, the skull of Echinodon would have been 62 mm (2.4 in) long, which is comparable to Tianyulong at 66 mm (2.6 in) but less than adults of Fruitadens at 75 mm (3.0 in) long, making Echinodon the smallest presumably adult heterodontosaur and one of the smallest non-avian dinosaurs.

The main body of both premaxillae are preserved in the lectotype specimen of Echinodon, although fractured and crushed.
A premaxillary foramen is present near the anterior margin of the individual bone, and the fossa it is nested within is more similar in shape to Heterodontosaurus than more derived Hypsilophodon.
The surface of the front of the bone along the toothrow is textured and lacks teeth, distinguishing the bone from that of Lesothosaurus which bears teeth along its entire length.
The premaxilla bore only three teeth, lacking denticles (serrations) present in most basal ornithischians, although all teeth are subequal in size with the third being the largest.

Three maxillae are preserved among the material of Echinodon, preserving almost all the bone including most regions of contact with other cranial bones.
The maxillae are slightly flattened, which minimises the strength of the buccal emargination, a diagnostic character of ornithischians where the maxillary tooth row and bone directly above it is inset from the outer edge of the bone.
The presence of an arched diastema in Echinodon is a topic of disagreement.
While Galton and American palaeontologist Paul Sereno interpret a diastema as present as in Heterodontosaurus, British palaeontologists David B. Norman and Paul M. Barrett concluded in 2002 that, based on the images of Owen prior to later damage of the fossil NHMUK 48209, a diastema was absent.
Sereno reiterated in 2012 that a diastema was present and arched based on the maxilla NHMUK 48211.
Nine teeth are present in the maxilla of Echinodon, the first being an enlarged and slender canine similar to those seen in the premaxilla of Lycorhinus and Heterodontosaurus.
Owen also figured a partial tooth in front of the caniniform, but it has since been lost in damage to the material.
While Norman and Barrett used this as evidence for a second caniniform smaller than the one behind, Galton in 1978 and Sereno in 2012 identified only one canine present.
The first post-caniniform tooth of Echinodon is the largest, although only slightly taller than those following, which are all the same size.
There is a round prominence along the middle of the tooth crowns, but there are no prominent ridges present on the crown.
Eight to ten denticles are present on each side of the tooth crowns.

Little of the lacrimal, jugal, and palatine are preserved, although the margin of the orbit can be identified in the fragment of the lacrimal.
The ectopterygoid bone of the palate is partially complete and preserved in articulation with the maxilla of NHMUK 48210.
Lack of preservation limits the anatomical details that can be identified beyond its resembling the bone known in other ornithischians.

The predentary bone is not preserved in Echinodon, but its presence can be confirmed by the morphology of the anterior end of the known dentaries.
Like in other heterodontosaurids, the predentary was only loosely articulated with the dentary in life, lacking lateral and ventral processes.
The dentary was deep for a basal ornithischian, its height at mid-length being 30% of the total length.
The bone tapers anteriorly along its length, although the margins are subparallel under the middle of the tooth row.
A row of foramina are present along the margin of the buccal emargination, as in the maxilla.
The coronoid process is prominent, unlike other basal ornithischians, although the contact between the dentaries is V-shaped as in basal ornithischians.
There were 11 te
The known material of Echinodon is limited to bones of the skull, but the multiple specimens include at least some of the premaxilla, maxilla, lacrimal, jugal, palatine, ectopterygoid and dentary along with most teeth of both the upper and lower jaws. Based on proportions of the related genus Heterodontosaurus, the skull of Echinodon would have been 62 mm (2.4 in) long, which is comparable to Tianyulong at 66 mm (2.6 in) but less than adults of Fruitadens at 75 mm (3.0 in) long, making Echinodon the smallest presumably adult heterodontosaur and one of the smallest non-avian dinosaurs.
The main body of both premaxillae are preserved in the lectotype specimen of Echinodon, although fractured and crushed. A premaxillary foramen is present near the anterior margin of the individual bone, and the fossa it is nested within is more similar in shape to Heterodontosaurus than more derived Hypsilophodon. The surface of the front of the bone along the toothrow is textured and lacks teeth, distinguishing the bone from that of Lesothosaurus which bears teeth along its entire length. The premaxilla bore only three teeth, lacking denticles (serrations) present in most basal ornithischians, although all teeth are subequal in size with the third being the largest.
Three maxillae are preserved among the material of Echinodon, preserving almost all the bone including most regions of contact with other cranial bones. The maxillae are slightly flattened, which minimises the strength of the buccal emargination, a diagnostic character of ornithischians where the maxillary tooth row and bone directly above it is inset from the outer edge of the bone. The presence of an arched diastema in Echinodon is a topic of disagreement. While Galton and American palaeontologist Paul Sereno interpret a diastema as present as in Heterodontosaurus, British palaeontologists David B. Norman and Paul M. Barrett concluded in 2002 that, based on the images of Owen prior to later damage of the fossil NHMUK 48209, a diastema was absent. Sereno reiterated in 2012 that a diastema was present and arched based on the maxilla NHMUK 48211. Nine teeth are present in the maxilla of Echinodon, the first being an enlarged and slender canine similar to those seen in the premaxilla of Lycorhinus and Heterodontosaurus. Owen also figured a partial tooth in front of the caniniform, but it has since been lost in damage to the material. While Norman and Barrett used this as evidence for a second caniniform smaller than the one behind, Galton in 1978 and Sereno in 2012 identified only one canine present. The first post-caniniform tooth of Echinodon is the largest, although only slightly taller than those following, which are all the same size. There is a round prominence along the middle of the tooth crowns, but there are no prominent ridges present on the crown. Eight to ten denticles are present on each side of the tooth crowns.
Little of the lacrimal, jugal, and palatine are preserved, although the margin of the orbit can be identified in the fragment of the lacrimal. The ectopterygoid bone of the palate is partially complete and preserved in articulation with the maxilla of NHMUK 48210. Lack of preservation limits the anatomical details that can be identified beyond its resembling the bone known in other ornithischians.
The predentary bone is not preserved in Echinodon, but its presence can be confirmed by the morphology of the anterior end of the known dentaries. Like in other heterodontosaurids, the predentary was only loosely articulated with the dentary in life, lacking lateral and ventral processes. The dentary was deep for a basal ornithischian, its height at mid-length being 30% of the total length. The bone tapers anteriorly along its length, although the margins are subparallel under the middle of the tooth row. A row of foramina are present along the margin of the buccal emargination, as in the maxilla. The coronoid process is prominent, unlike other basal ornithischians, although the contact between the dentaries is V-shaped as in basal ornithischians. There were 11 te
Echinodon