Hypuronector, COLBERT & OLSEN, 2001

COLBERT, EDWIN H. & OLSEN, PAUL E., 2001, A New and Unusual Aquatic Reptile from the Lockatong Formation of New Jersey (Late Triassic, Newark Supergroup), American Museum Novitates 3334, pp. 1-24 : 9-11

Hypuronector , new genus

Figures 6–14

TYPE AND ONLY SPECIES: Hypuronector limnaios , new species

ETYMOLOGY: From the Greek ηψπo (hypo), deep; υpo (uro), tail; νeĸTop, (nektor), the swimmer, meaning the ‘‘deep tailed swimmer’’, the new reptile’s informal name for more than 20 years. Name suggested by Donald Baird.

DIAGNOSIS: Small (<18 cm) drepanosaurid with uniquely deep tail consisting of extremely elongated chevrons or hemal spines and proximally high neural spines; the longest hemal spine being equivalent in length to 11 articulated caudal vertebrae. Limbs long and slender; humerus equal to femur in length, radius and ulna about two­thirds length of humerus and longer than tibia and fibula. Differs from Megalancosaurus in having notochordal centra and a distally edentulous lower jaw and lacking the peculiarly enlarged anterior dorsal neural spines. Differs from Dolabrosaurus and Megalancosaurus in lacking the distally expanded tips of the neural spines. Differs from Megalancosaurus in having amphicoelous rath­ er than procoelous vertebrae. Differs from Drepanosaurus in showing greater fusion of the ribs to the centra, lacking the extreme enlargement of the ungual phalanx digit II of the manus and the greatly broadened ulna, and lacking the ‘‘spine’’ on the tip of the tail. Differs from both Drepanosaurus and Megalancosaurus in lacking massively enlarged neural spines in the shoulder region and the fenestrate or bifurcate proximal chevrons.

Hypuronector limnaios , new species

Figures 6–14

HOLOTYPE: AMNH 7759 , a partially articulated skeleton lacking the skull (fig. 6). Most vertebrae, present including 11 presacrals, two possible sacrals and 38 caudals in close articulation, numerous ribs, shoulder girdle, forelimbs, pelvis, both femora, left tibia and fibula, distal ends of right tibia and fibula. Both pedes and manus incomplete. The holotype was prepared by the air abrasive technique.

ETYMOLOGY: Greek λιμναιoơ (limnaios), of the lake, referring to the lacustrine environment in which the animal lived.

REFERRED MATERIAL: From the Granton Quarry: AMNH, 1721, anterior thoracic region including pectoral girdle; AMNH 7205, 5 presacral ribs, fragments of a pelvis, and 13 anterior caudal vertebrae; AMNH 7755, 3 cervical vertebrae, AMNH 1998, 7 caudal vertebrae; AMNH 2080, a dentary with 7 teeth; AMNH 2076, vertebrae; NJSM 19701, partial mostly articulated posterior trunk and anterior tail; NJSM 19702, proximal caudal vertebra and chevron. From Weehawken: YPM 8641, proximal caudal vertebra and chevron; YPM 56385, limb bone; YPM 56386, distal end of humerus; YPM 56387, caudal vertebrae with chevron and?humerus; YPM 56388, left mandible; YPM 56389, caudal vertebra and partial chevron; YPM 56390, three associated caudal vertebrae with chevrons; YPM 56391, obliquely preserved caudal vertebra and partial chevron; YPM 56392, isolated sacral vertebra; YPM 56393, isolated forelimb. All of the Granton material has been prepared by air abrasion or left unprepared, while all of the Weehawken material has been negatively prepared with hydrochloric acid.

HORIZON AND LOCALITY: Lockatong Formation of the Newark basin portion of the Newark Supergroup , Late Triassic. The ho­ lotype is from the Granton Quarry , North Bergen , New Jersey,? Ewing Creek Member , cycle ‘‘G7’’. Other referred specimens from the Granton Quarry are also from the Ewing Creek Member. Those from Weehawken , New Jersey, are from cycle W­5 of the Nursery Member .

DIAGNOSIS: As for genus, which has only one known species.

Figures

Fig. 6. Holotype of AMNH 7759 (above) and drawing of holotype (below). Photograph by Chester Tarka.

Fig. 7. Additional Granton Quarry specimens of Hypuronector. A, AMNH 1721, ventral view of trunk and left lateral view of crushed pectoral girdle. B, AMNH 7205, partial trunk, pelvic girdle, and proximal caudal vertebrae. C and D, AMNH 1998, unprepared part and counterpart of midcaudal vertebrae. Photographs by Chester Tarka, except for C and D by Julius Weber (courtesy of G. Case).

Fig. 8. Mandibles of Hypuronector: A, AMNH 2080, left mandible, medial view and associated caudal vertebrae from Granton Quarry; B, close up of mandible in A.; C, YPM 56388, lateral and medial views of negatively prepared specimen. Abbreviations are: d, dentary; ang, angular; ar, articular; sa, surangular;?sp,? splenial. Photograph by P. Olsen.

Fig. 9. Examples of vertebrae of Hypuronector (scale bar 1 mm): A, three associated caudal vertebrae with chevrons (YPM 56390); B, early stages of negative preparation of caudal vertebra and partial chevron (YPM 56389) showing matrix filling notochordal cones (c), shown reversed; C, same vertebra as B, fully prepared; D, negatively prepared, obliquely preserved caudal vertebra and partial chevron (YPM 56391); E, reconstruction of specimen in D; F, three cervical vertebrae in dorsal view (AMNH 7755); G, two successive caudal vertebrae and chevrons from the holotype (AMNH 7759); H, proximal caudal vertebra and chevron in anterior view (YPM 8641); I, isolated caudal vertebra and chevron (YPM 56387); J, isolated sacral vertebra in anterior view (YPM 56392).

Fig. 10. Shoulder girdle of Hypuronector

Fig. 11. Forelimb of Hypuronector. A and B, YPM 56393, isolated forelimb drawings of part and counterpart slabs. C and D, AMNH 7759, forelimbs: (C) left manus, radius, and ulna and (D) right manus, radius and ulna. Identification of radius (r) and ulna (u) is not certain.

Fig. 12. Pelvic girdle of Hypuronector; photograph (A) and drawing (B) of AMNH 7159. p, pubioischiatic plate; il, ilium; lf, left femur; rf, right femur. Photograph by Chester Tarka.

Fig. 13. Distal parts of the hind limb of Hypuronector. A, left hind limb; B, right hind limb.?I, is possible proximal phalanx of digit I.

Fig. 14. Tentative cladogram of relationships within Drepanosauridae. Characters are: 1, caudal vertebrae with anteroposteriorly elongated, bladelike transverse processes through most of tail and with prezygapophyses of proximal caudals extending anteriorly well beyond centrum and postzygapophyses extending posteriodorsally from neural spine base; 2, postcervical vertebrae with zygophyseal facets generally very close to midline; 3, neural spines very long, especially on caudal vertebrae; 4, dorsal ribs firmly attached to centra; 5, hemal arches or chevrons fused to posterior part of anterior threequarters of caudal vertebrae and much greater in depth than height of the neural spines; 6, pectoral girdle with high and rodlike scapula; and 7, pelvic girdle with high, anteriorly directed blade of ilium. 8, Bifurcate or fenestrate chevrons; 9, distinctly enlarged and modified neural spines in shoulder region; 10, dorsal ribs fused to centra; 11, reduced manual and pedal phalangeal formula; 12, ‘‘opposable’’ digit I on pes; 13, giant ungual phalanx on manual digit II; 14, extremely deep tail. Note that Dolabrosaurus has no apparent unique derived characters. Dotted lines indicate less favored relationship indicated by character 10.