Glossary

**Ankylosauria** is a clade of herbivorous, quadrupedal dinosaurs within the ornithischian suborder Thyreophora, characterized by extensive dermal armor composed of bony plates and scutes (osteoderms) covering the back, flanks, and often the skull. The group first appeared in the Middle Jurassic (approximately 168–165 million years ago) and persisted until the end-Cretaceous mass extinction (66 million years ago). Ankylosaurs possessed low, broad, box-like skulls with osteoderms fused to the cranial bones, relatively weak jaws with small leaf-shaped teeth, and short, stout limbs adapted for slow, graviportal locomotion. The clade is traditionally divided into two families: Ankylosauridae, distinguished by the presence of a massive bony tail club and broadly encrusted skulls, and Nodosauridae, which lack tail clubs but often bear prominent shoulder and flank spikes. A third lineage, Parankylosauria, comprising basal Gondwanan forms, was proposed in 2021. Ankylosaurs were distributed across all major landmasses, with the richest fossil records from North America, Europe, and Asia, though significant discoveries from South America, Australia, and Antarctica have expanded their known biogeographic range.

Ceratopsidae is a family of large-bodied, quadrupedal, herbivorous dinosaurs within the clade Ceratopsia (Ornithischia: Marginocephalia), first named by Othniel Charles Marsh in 1888. All known ceratopsids are restricted to the Upper Cretaceous (approximately 83–66 Ma), with the vast majority of species recovered from western North America (Laramidia), and a single confirmed Asian representative, Sinoceratops zhuchengensis, from eastern China. Ceratopsids are distinguished from other ceratopsians by a suite of derived cranial features: prominent nasal and supraorbital horns, a greatly expanded parietosquamosal frill extending posteriorly over the neck, a deep rostral bone forming a parrot-like beak, and a highly specialized dental battery composed of double-rooted teeth arranged in tightly packed vertical columns capable of an orthopalinal (combined vertical and backward) slicing motion. The family is divided into two well-supported subfamilies—Chasmosaurinae, generally characterized by elongate frills and long supraorbital (brow) horns, and Centrosaurinae, typically bearing shorter frills with elaborate marginal ornamentation and a prominent nasal horn. Ceratopsidae constitutes one of the most species-rich dinosaur families of the Late Cretaceous, with over 40 named genera. Monodominant bonebeds containing hundreds to thousands of individuals of single centrosaurine species provide strong evidence for gregarious, possibly migratory behavior. The family's rapid speciation, high morphological disparity in cranial ornamentation, and eventual extinction at the Cretaceous–Paleogene boundary make it a key study system for understanding Late Cretaceous terrestrial ecosystem dynamics, ornament-driven evolution, and end-Mesozoic faunal turnover.

Hadrosauridae is an extinct family of large ornithischian dinosaurs within the clade Ornithopoda that flourished during the Late Cretaceous period, approximately 86 to 66 million years ago. Members of this family are commonly called "duck-billed dinosaurs" because the bones of their snouts form a broad, flat structure resembling a duck's bill, which was likely covered in life by a keratinous beak used for cropping vegetation. The family is characterized by several key anatomical features. Most notably, hadrosaurids possessed dental batteries—complex tooth structures in which hundreds of small teeth were stacked vertically and interlocked horizontally within each jaw ramus, with up to 300 teeth per jaw. These batteries functioned as continuously self-replacing grinding surfaces, allowing hadrosaurids to process tough, fibrous plant material with remarkable efficiency. The teeth were connected to one another and to the jawbone by periodontal ligaments, forming a dynamic, flexible grinding system unparalleled in vertebrate evolution. Additional diagnostic features include a predentary bone at the front of the lower jaw, a retroverted pubis typical of ornithischians, and stiffened tails reinforced by ossified tendons. Hadrosauridae is divided into two principal subfamilies: Lambeosaurinae, whose members bore hollow cranial crests formed by extensions of the nasal passages, and Saurolophinae (historically called Hadrosaurinae), whose members had solid crests or lacked crests entirely. Hadrosaurids were among the most abundant and diverse terrestrial herbivores of the Late Cretaceous. Their fossils have been recovered from North America, Asia, Europe, South America, Africa, and possibly Antarctica, making them one of the most geographically widespread dinosaur families. Their ecological success has been attributed to the efficiency of their dental apparatus, facultative bipedal-quadrupedal locomotion, and complex social behaviors including colonial nesting and herding.

**Ornithischia** is one of the two traditionally recognized major clades of Dinosauria, uniting all dinosaurs that share a distinctive pelvic configuration in which the main shaft of the pubis is directed posteroventrally, running parallel to the ischium. This superficial resemblance to the avian pelvis gave the group its name, meaning 'bird-hipped,' though modern birds are actually descendants of saurischian theropods rather than ornithischians. Diagnostic synapomorphies distinguishing Ornithischia include the predentary—a unique, unpaired bone at the tip of the lower jaw found in no other dinosaur group—along with palpebral bones over the orbits, the absence of gastralia (belly ribs), five or more sacral vertebrae, and a lattice of ossified tendons reinforcing the vertebral column. All known ornithischians were herbivorous, having evolved leaf-shaped teeth and toothless horny beaks for cropping and processing plant material. The clade first appeared in the Late Triassic, diversified extensively through the Jurassic and Cretaceous, and was entirely extinguished by the Cretaceous–Paleogene (K–Pg) extinction event approximately 66 million years ago, leaving no living descendants.