[Paleontology • 2019] Convolosaurus marri • A New Basal Ornithopod (Dinosauria: Ornithischia) from the Early Cretaceous of Texas, USA ---ScRaBBlE

Convolosaurus marri

Andrzejewski, Winkler & Jacobs, 2019

 DOI: 10.1371/journal.pone.0207935

Abstract

Material from a minimum of twenty-nine individuals of a new ornithopod, represented by nearly every skeletal element, was recovered from the Proctor Lake locality in the Twin Mountains Formation (Aptian) of north-central Texas. This material includes various ontogenetic stages, providing insight into the growth patterns of this species. The new ornithopod, Convolosaurus marri gen. et sp. nov., is recovered outside of Iguanodontia, but forms a clade with Iguanodontia exclusive of Hypsilophodon foxii. The presence and morphology of four premaxillary teeth along with a combination of both basal and derived characters distinguish this taxon from all other ornithopods. Basal characters present in C. marri including the presence of premaxillary teeth, the shape of the dentary teeth, and position of the pterygoid wing on the quadrate, whereas the presence of opisthocoelous cervical vertebrae, large proximal caudal neural spines, and curved maxillary tooth roots suggest C. marri is more derived than 80% of the basal neornithischians included in this analysis.

Fig 2. Convolosaurus marri, articulated specimens.
 (A) SMU 70456, articulated subadult individual on display at the Proctor Lake Corps of Engineers Office. Scale arrow equals 10 cm. (B) Composite skeleton on display at the Perot Museum of Nature and Science. Scale bar equals 10 cm. (C) SMU 75379 and SMU 75380, partial articulated skeletons found stacked on one another. Scale bar equals 5 cm.

Fig 4. Skull reconstruction. Skull reconstruction of Convolosaurus marri based on available specimens.

Abbreviations: A-articular, BO-basioccipital, D-dentary, F-frontal, J-jugal, L-lacrimal, MX-maxilla, N-nasal, OP-opisthotic, P-parietal, PD-predentary, PF-prefrontal, PMX-premaxilla, PO-postorbital, Q-quadrate, QJ-quadratojugal, SA-surangular, SOB-supraorbital, SQ-squamosal.

Fig 6. SMU 72834 anterior skull. (A) SMU 72834, anterior skull in right lateral view. (B) Illustration of SMU 72834, in right lateral view (David Baker).

Abbreviations: D-dentary, L-lacrimal, MX-maxilla, PMX-premaxilla, PD-predentary, QJ-quadratojugal. Scale bar equals 5 cm.

Systematic Paleontology

DINOSAURIA Owen, 1842

ORNITHISCHIA Seeley, 1887

NEORNITHISCHIA Cooper, 1985

CERAPODA Sereno, 1986

ORNITHOPODA Marsh, 1881

Convolosaurus marri gen. et sp. nov. 

Holotype: SMU 72834, a skull and partial articulated skeleton with 9 cervical vertebrae; 15 dorsal vertebrae; 6 sacral vertebrae; 23 caudal vertebrae; right and partial left scapula; right and partial left coracoids; left and partial right humeri; left ulna; left radius; partial left manus; articulated pelvis including the left and right ilia, proximal left and right ischia, partial prepubic rods; proximal and distal ends of the left and right femora and the mid-part of the left shaft; proximal left and right tibiae; and proximal left fibula. The type specimen, SMU 72834, is the largest individual in the sample measuring approximately 2.5–3 m in length; however, this skeleton does not represent a full grown adult, thus the adult size of this species in unknown.

Diagnosis: The presence of four premaxillary teeth with proximodistally oriented sulcus on the buccal surface distinguishes Convolosaurus marri gen. et sp. nov. from all other ornithopods. Further, it can be distinguished from other basal ornithopods by a unique combination of primitive and derived character states. Primitive character states include the presence of premaxillary teeth and two supraorbitals that extend across the entire orbit. Derived character states include: curved maxillary tooth roots; opisthocoelous cervical vertebrae; sacral neural spines twice the height of the sacral centra; proximal caudal neural spines 1.5 times the height of the centrum; expanded ischial ‘foot’; shallow intercondylar groove on the anterior surface of the femur; and a laterally compressed prepubic process.

Etymology: The generic name Convolosaurus translates from Latin meaning “flocking lizard” referring to clusters of juvenile specimens. The species name marri is in honor of Dr. Ray H. Marr who produced the Society of Vertebrate Paleontology videos “We are SVP” and “About the SVP Logo” posted on the SVP website (vertpaleo.org), and who is a strong proponent of students at Southern Methodist University (SMU).

Fig 30. Strict consensus tree produced from phylogenetic analysis. Strict consensus tree of 96 most parsimonious trees recovered from phylogenetic analysis. Bootstrap support values >50% listed beneath nodes.

   

Conclusions: 

The Proctor Lake fossil locality contains a wealth of specimens providing not only nearly complete individual skeletons, but also insight into ontogeny and population structure. The femoral length distribution of 29 individuals from the Proctor Lake locality indicates a high mortality rate among the smallest and presumably youngest individuals. Clusters of individuals of varying sizes suggest individuals flocked together long after hatching perhaps for protection against predators. The specimens recovered from Proctor Lake reveal a new species of basal ornithopod with a unique set of both basal and derived characters. Characters including an expanded ischial foot, curved maxillary tooth roots, and opisthocoelus cervical vertebrae position Convolosaurus marri in a clade exclusive of most basal ornithischians including Hypsilophodon foxii [Galton, 1974], but characters such as the presence of premaxillary teeth, shape of the frontals, and the position of the pterygoid wing on the quadrate position C. marri outside of Iguanodontia. Thus, this new species provides crucial information on the evolution of basal neornithischians.

 Kate A. Andrzejewski, Dale A. Winkler and Louis L. Jacobs. 2019. A New Basal Ornithopod (Dinosauria: Ornithischia) from the Early Cretaceous of Texas.  PLoS ONE 14(3): e0207935. DOI: 10.1371/journal.pone.0207935

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