Contributions to Geology 28.2

Cranio-Mandibular Anatomy of Haldanodon Exspectatus (Docodonta; Mammalia) from the Late Jurassic of Portugal and its implications to the evolution of mammalian characters

JASON A. LILLEGRAVEN Departments of Geology/Geophysics and Zoology/Physiology, The University of Wyoming, Laramie, Wyoming 82071-3006, U.S.A
GEORG KRUSAT Institut fur Palaontolgie, Freie Universitat Berlin, Schwendenerstrasse 8, D-1000 Berlin 33, Federal

Pages
39-138

Keywords
Portugal, Jurassic, Mammalia, Haldanodon exspectatus

Abstract
Members of the order Docodonta (Mammalia), recorded only from Middle and Upper Jurassic strata of western Holarctica, previously were known solely through remains of teeth and jaws. We provide detailed, bone-by-bone descriptions, along with pertinent comparisons, of all available cranial remains of Haldanodon exspectatus, a fossorial docodont collected from Upper Jurassic coastal swamp deposits preserved in the Guimarota lignite mine at Leiria, west-central Portugal. We use the taxonomic distribution of various states of 149 cranio-mandibular characters to develop a cladogram that expresses probable phylogenetic relationships among: (1) advanced cynodont therapsid reptiles; (2) Sinoconodon; (3) Morganucodontidae; (4) other pertinent early mammals; and (5) Docodonta. Previous interpretations of the phylogenetic source of docodonts unanimously favored derivation from Rhaeto-Liassic morganucodontids. In contrast, we suggest that docodonts represent a cladistically earlier stage of synapsid evolution than morganucodontids; Haldanodon shares many primitive features with advanced cynodonts that exist in more advanced states within morganucodontids and their descendants. Tentatively, we further suggest that Sinoconodon diverged at an intermediate level between docodonts and morganucodontids. The Iberian Peninsula was an island throughout Jurassic time, surrounded by deep and ever-widening arms of marine waters. Much of the evolutionary history of Portuguese docodonts, therefore, probably occurred in isolation from other, relatively nearby centers of European, American, and African terrestrial life. Despite its insular history, we recognize 19 autapomorphous cranio-mandibular characters in H. exspectatus that have homoplasous counterparts in other groups of early mammals; 17 of the features exist in Haldanodon in states more advanced than seen in morganucodontids. All 19 of these autapomorphous (but homoplasous) characters typically are thought of as characteristically "mammalian" advancements. In light of the new anatomical information from H. exspectatus, docodonts become much more interesting to the study of vertebrate phylogeny because of their: (1) cladistically basal nature within the Mammalia; (2) independent derivation of features which imply major, mammal-like advancements in metabolic, neurological, and mechanical adaptation; and (3) mosaicism of primitive retentions along with markedly advanced specializations. We neither endorse nor challenge the idea that the Multituberculata represents a group independently derived from a different cynodont ancestry, but suggest that such polyphyly remains as a distinct possibility within the origin of "Mammalia." Additionally, new cranio-mandibular information from H. exspectatus reinforces the concept that parallel development of similar features was an all-pervasive phenomenon within early evolution of the Mammalia, making the unravelling of phylogenetic relationships among its basic groups a daunting, yet highly interesting, task.

Pseudocoprolites in the Mowry Shale (Upper Cretaceous), northwest Wyoming

J. DAVID LOVE U.S. Geological Survey, P.O. Box 3007, Laramie, WY 82071
DONALD W. BOYD Department of Geology and Geophysics, University of Wyoming, P. O. Box 3006, Laramie, WY 82071-3006

Pages
139-144

Keywords
Mowry, Wyoming, coprolites, burrow

Abstract
Near the southern boundary of Yellowstone National Park, the upper surface of a silica-cemented marine sandstone bed in the Mowry Shale is embossed with thousands of peculiar sinuous ridges that are typically several centimeters in width and several decimeters in length. This distinctive surface, about 37 m below the top of the Mowry, is overlain by Lingula-bearing black shale. The enteroform features are composed of sandstone identical to that below, and most are extensions of it. Although the features superficially resemble some coprolites and burrow casts, several characteristics of the sandstone-shale interface suggest that the embossments formed when sand was injected upward into cracks that opened in the lower few centimeters of cohesive but incompletely compacted mud. The cracking may have been caused by a seismic event, with or without concurrent thixotropic expansion of the sand bed.

Allochthonous rocks from the western part of the Early Triassic miogeocline: Hawley Creek area, east-central Idaho

RICHARD A. PAULL and RACHEL K. PAULL Department of Geosciences, University of Wisconsin-Milwaukee, Milwaukee, Wl 53201

Pages
145-154

Keywords
Triassic, Idaho, Medicine Lodge, Beaverhead Mountains, miogeocline, carbonate

Abstract
Lower Triassic marine rocks within the Medicine Lodge thrust system were first described from the Hawley Creek area in the Beaverhead Mountains of east-central Idaho in 1963, but the age (pre-Smithian), thickness (305 m), lower contact (conformable?), and formational assignment (Dinwoody) were incorrect. Because these rocks are the westernmost record of deposition in the northern part of the Early Triassic miogeocline in the United States, it is important that stratigraphic relations be clarified.

Three sections of Lower Triassic rocks were measured, sampled, and described during this study. Twenty-two carbonate samples were processed for conodonts, and 5 yielded age-diagnostic elements. In addition, Meekoceras zone ammonites, polished slabs, and thin sections were studied.

Our field and laboratory work establish that: (1) Triassic rocks disconformably overlie Upper Permian Tosi Chert with little physical evidence of this major hiatus, although significant local relief may have existed, (2) the thickness of Triassic strata exceeds 620 m, (3) the basal 290 m is Smithian and the remainder is Spathian, and all are assignable to the Thaynes Formation, (4) at least the lower 330 m of black shale and siltstone was deposited under basinal conditions, while the upper part records shallower water carbonate deposition with an influx of coarser terrigenous clastics, (5) the study area was subjected to high heat flow related to intrusive rocks near the base of the Medicine Lodge plate, and (6) these rocks are similar in age and lithology to Triassic rocks in south-central Idaho.

We believe the Triassic rocks at Hawley Creek originally accumulated on the eastern edge of the Lemhi arch. They were transported no more than 80 km eastward during movement of the Medicine Lodge thrust system.