Daemonosaurus chauliodus

Nesbitt, Sterling J & Sues, Hans-Dieter, 2021, The osteology of the early-diverging dinosaur Daemonosaurus chauliodus (Archosauria: Dinosauria) from the Coelophysis Quarry (Triassic: Rhaetian) of New Mexico and its relationships to other early dinosaurs, Zoological Journal of the Linnean Society 191 (1), pp. 150-150 : 150-

DAEMONOSAURUS CHAULIODUS SUES ET AL., 2011

Holotype: CM 76821 , nearly complete, transversely crushed skull with mandible and associated anterior cervical vertebrae and ribs ( Figs 2, 3 ).

Locality and horizon: Coelophysis Quarry, Ghost Ranch , 20 km NW of Abiquiú, Rio Arriba County, New Mexico, USA. ‘Siltstone member’ of the Chinle Formation, which is dated to near the end of the Late Triassic (see above).

Revised diagnosis: Daemonosaurus chauliodus can be distinguished by the following combination of character states: skull (estimated length: 145 mm) proportionately deep and narrow, with short antorbital region; premaxillary and anterior maxillary teeth much enlarged relative to those with the dentary teeth; premaxilla with long, broad posterodorsal process; three premaxillary teeth increasing in length anteriorly*; prefrontal large relative to the orbit (~50% the anteroposterior length of the orbit)*; ventral process of lacrimal with slender posterior projection; jugal with prominent lateral ridge that is flat laterally*; postorbital with anterolateral process overhang orbit; first two dentary teeth large and procumbent; alveolar margin of dentary downturned at symphysis; absence of a ridge on the ventral surface of the axis; third cervical vertebra with deep, rimmed, ovoid, rimmed depression anteriorly on lateral surface of centrum* (potential autapomorphies marked with asterisks).

Preservation: The holotype was heavily crushed laterally (thickest portion is about ~ 30 mm thick but most is less than 20 mm thick), but roughly in left and right lateral view ( Figs 2, 3 ). Much of the skull roof is present on both sides but not evenly divided along the midline suture. Most of the skull bones remain in articular context, but some (e.g. left quadrate and both premaxilla) have been slightly displaced. Some disarticulation occurred along sutures (e.g. frontals), whereas the bones of the braincase were disarticulated and scattered around the back of the skull.

The often excellent condition of the bone preserves fine details of many sutural contacts, tiny foramina and articular surfaces. However, the mediolateral compression of the skull has heavily fractured surfaces, making it difficult to distinguish broken surfaces from contacts between cranial elements. Slight displacement of the fractured surfaces also resulted in a number of challenges in determining boundaries of those bones and scoring phylogenetic characters. Therefore, we took a systematic approach when identifying boundaries by using both elements of each skull bone, particularly from the better-preserved left side, made detailed comparisons to other early dinosaurs and close relatives, and used a grey highfidelity epoxy cast to help determine if colour was influencing our interpretation of bone boundaries.

Anatomical description: The lightly built skull is narrow transversely and relatively deep dorsoventrally, with a proportionately large orbit. It has a length of about 140 mm (measured from the tip of the premaxilla to the posterior margin of the quadrate on the right side), of which the antorbital region comprises only about 50% ( Figs 2, 3 ).

The laterally facing external narial fenestra is elliptical (with an anteroventrally oriented long axis) on both sides. The anterior half of the margin of the external naris is formed by the premaxilla, whereas the posterior portion is formed by the nasal. The orbit is proportionately large (with an estimated anteroposterior diameter of 50 mm on the left side) and appears to be subcircular rather than oval as typically in Neotheropoda. The infratemporal fenestra, although incomplete because of the disarticulation of the postorbital, was apparently shorter anteroposteriorly than tall dorsoventrally. The oval to weakly triangular antorbital fenestra is much smaller than the orbit and is more completely preserved on the left side. The maxilla forms the anterior and ventral borders, the jugal forms the posteroventral portion and the lacrimal forms the posterior and dorsal portion of this opening.

Figures

Figure 3. The holotype of Daemonosaurus chauliodus (CM 76821) in left lateral view as an interpretive line drawing with individual bones (e.g. maxilla) or sets of bones (e.g. cervical series, palatal bones) coloured (A) and right lateral view as an interpretive line drawing (B). Light grey = rock matrix. White bones = unidentified fragments or cervical ribs. Scale = 1 cm. Abbreviations: an, angular; aof, antorbital fenestra; anfo, antorbital fossa; at, atlas component; ax, axis; bo, basioccipital; cer#, cervical vertebra number; cp, cultriform process of the parasphenoid; cr, cervical rib; d, dentary; ec, ectopterygoid; en, external naris; ex, exoccipital; f, frontal; j, jugal; l., left; la, lacrimal; mf, external mandibular fenestra; mx, maxilla; n, nasal; op, opisthotic; or, orbit; pa, parietal; pal, palatine; pf, prefrontal; pmx, premaxilla; pmxt, premaxillary tooth; po, postorbital; pra, proatlas; pro, prootic; pt, pterygoid; qj, quadratojugal; qu, quadrate; r., right; sc, scleral plate; sp, splenial; sq, squamosal; su, surangular; vo, vomer. [2 columns]