Excerpted from Evans, S.E., C. Lally, D.C. Chure, A. Elder, and J.A. Maisano. 2005. A Late Jurassic salamander (Amphibia: Caudata) from the Morrison Formation of North America. Zoological Journal of the Linnean Society 143:599-616.
Amphibia, Caudata, Urodela
Iridotriton hechti Evans et al., 2005
DINO 16453 is a small specimen preserving parts of a single skeleton missing only small skull bones, digits and the distal tail. This is the type and only specimen. It was recovered at the Rainbow Park microsite (Dinosaur National Monument No. 96), Utah, USA, and is held in the collections of Dinosaur National Monument. The horizon from which it came is the Brushy Basin Member of the Morrison Formation, Upper Jurassic (c.150-148 Myr, Kowallis et al., 1998: Kimmeridgian or early Tithonian in age). The name Irido – triton comes from two words: iris, irido meaning rainbow (an allusion to the Rainbow Park site); and triton, meaning newt. The species name recognises Max Hecht, formerly of the American Museum of Natural History, New York, who was the first person to describe salamander material from the Morrison Formation.
The specimen preserves a small (snout-sacrum length c.55 mm) fully metamorphosed salamander. DINO 16453 remains in articulation and includes much of the skull, the complete presacral axial skeleton, the sacrum, a small set of postsacrals, and parts of the girdles and the limbs. The skull, forelimbs, and anterior presacral series (DINO 16453a) are preserved in dorsal view, but the posterior presacral region and left hind limb are on a small block (DINO 16453b) detached during collection and prepared in ventral view. Only the anterior block was scanned and is shown in the images here.
The specimen is generally well preserved in three dimensions, with the vertebrae fully articulated, but there has been some disarticulation of the limbs and girdles and of parts from the right side of the skull roof and jaws. It is not possible to get an accurate measurement of the snout-sacral length, but comparison of humeral and femoral lengths with those of similarly proportioned modern analogues suggests a snout-sacrum length of 50-60mm, and a total length (with tail) of between 80-100mm overall. Despite this small size, the specimen appears to represent a metamorphosed individual (dermal roofing bones ossified and in position; squamosal full size; all bones of lower jaw ossified; dorsal process of maxilla ossified; vomer fully formed; otic capsule complete and stapes ossified [Rose, 2003]).
The following combination of characters distinguishes Iridotriton hechti from other fossil and modern salamanders: thin unsculptured skull bones; a fully open Meckelian fossa in the dentary; premaxilla with wide, short alary process having angled lateral edge; prootic, opisthotic and exoccipital form a single unit, although sutural lines separate the opisthotic from the other bones; stapes free; parasphenoid without internal carotid foramina, narrower anteriorly than posteriorly; an estimated 17 presacral vertebrae; simple ectochordal vertebral centra, with small anterior basapophyses but no ventromedian keel; atlas shorter than succeeding vertebrae; spinal nerve foramina in atlas and in tail vertebrae; co-ossified scapula and coracoid, with narrow, waisted scapula and large, heavily ossified coracoid plate perforated by supracoracoid foramen; strongly built forelimbs; radius with expanded distal head; well-ossified tarsus and carpus including fusion of ulnare and intermedium; rib bearers with conjoined heads throughout the column.
Crown group salamanders are currently divided into two groups, Cryptobranchoidea (including cryptobranchids and hynobiids) and Salamandroidea (all remaining salamanders). The balance of characters suggests a position for Iridotriton on the stem of salamandroid salamanders.
Click on the thumbnails below for a detailed description of the specimen in dorsal and ventral views.
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