Karl F. Hirsch

Contemporary and Fossil Chelonian Eggshells

Although fossil turtle eggs were first reported over 100 years ago, their shell structure is still poorly understood. The calcareous layer of turtle eggshells, unlike those of any other amniote, is composed of aragonite. While contemporary chelonian eggshells vary from relatively flexible to rigid, the fossil record is probably limited to the most easily preserved rigid-shelled eggs. These shells have either an unaltered aragonitic structure or an aragonitic layer which has been partially or completely replaced by calcite. Unaltered or partially altered chelonian fossil eggshells can be recognized by the spherulitic basic units composed of needle-like aragonite crystallites. Under polarized light these units display an extinction cross; in completely altered specimens the basic units are not spherulitic and extinguish totally. In nonchelonian eggs the individual columns or wedges of the basic units rather than the entire unit become extinct under polarized light and thus have no resemblance to the calcitic shell structure of nonchelonian eggs.

Parataxonomy of fossil egg remains (Veterovata): principles and applications

ABSTRACT The tremendous increase in fossil egg and eggshell discoveries throughout the last decade necessitates the establishment of uniform methods for description and for a parataxonomical system for classification of fossil eggs. Principles and applications of fossil egg parataxonomy, which have been developing slowly over the last decades, are summarized in this paper. Adoption of these principles is advocated. A list of all described egg parataxa, ordered into respective oofamilies and oogenera, is presented. A simplified chart shows basic types of eggshell organizations, structural morphotypes, parataxonomical families, and corresponding higher order taxonomic relations. Familial and lower level correlation between fossil vertebrate taxa and egg parataxa are limited to the rare finds of identifiable embryos within their eggs.

Parataxonomic classification of fossil chelonian and gecko eggs

ABSTRACT The probability of fossil preservation of eggs with a soft or pliable shell or of small eggs with a thin hard shell layer is very poor. As result, their structural and parataxonomic classification has been almost non-existant. To fill this gap, the following parataxonomic groups have been established: 1) for chelonian eggs two oofamilies Testudoolithidae and Testudoflexoolithidae with the oogenera Testudoolithus and Testudoflexoolithus and three oospecies, and 2) for gecko eggs one oofamily Gekkoolithidae, with the oogenus Gekkoolithus and one oospecies. This paper also provides some condensed background information about amniote eggshell, its identification, structural and parataxonomical classification, and the potential of eggshell to fossilize.

Crocodilian and avian eggshells from the Middle Eocene of the Geiseltal, Eastern Germany

ABSTRACT Well preserved eggs and eggshell from the Middle Eocene lignite beds of the Geiseltal (Eastern Germany) can be assigned to crocodilians and birds on the basis of their histostructure. Because a specific assignment of the crocodilian eggshell is not yet possible, its parataxonomic similarity to Krokolithes wilsoni Hirsch 1985 has supported establishing the new parataxonomic family Krokolithidae, including the new species, Krokolithes helleri. The avian eggshell of the Geiseltal is subdivided into three types, representing both palaeognathous and neognathous birds. The one specimen with a palaeognathous morphotype, has been assigned to the new parataxonomic family Medioolithidae with the type genus and species Medioolithus geiseltalensis. The eggshell, although fragmented, is excellently preserved, displaying color lines and impressions of decayed organic fibers in both the crocodilian and bird eggshell. Fragmentation may be due to transport and modern day weathering.

Late Cretaceous Peruvian eggshells and their relationships with laurasian and eastern Gondwanian material

Abstract The eggshell material from some Late Cretaceous Peruvian sites is reevaluated in light of the results ofeggshell research in the last years. As a preliminary step, a new oospecies is first described from the Aix Basin (France): Megaloolithus pseudomamillare . The eggshells from the Bagua Basin Peru are divided into six types [1, Dinosauroid spherulitic type, Tubospherulitic morphotype and Angusticanaliculate pore system ( M. pseudomamillare ); 2, Dinosauroid spherulitic, undetermined morphotype; 3, Ornithoid type, Ratite morphotype, Angusticanaliculate; 4, Ornithoid type, Ratite morphotype; 5, Ornithoid type, Ratite morphotype or dinosauroid type, Angustispherulitic morphotype; 6, ? Geckonoid type]. Because of presumable loss of the main part of the material, it was not possible to make additional studies on the eggshells from Laguna Umayo. We can only assess that the tuberculate fragments described by Kerourio & Sige (1984) belong to Megaloolithus , and that the type 2 of this locality could be the same as the type 5 of the Bagua basin. The family Megaloolithidae is thus recorded in Europe, India and South America; it seems that the same oospecies exists in these three areas, in Late Cretaceous deposits. The available biochronological data discussed here support the tentative correlation of the Umayo Formation with the Fundo et Triunfo Formation.

Pliocene chelonian fossil eggs from Gran Canaria, Canary Islands

ABSTRACT Thirty years ago Macau-Vilar (1958) reported chelonian eggs from Gran Canaria. Analysis of the microstructure of these eggs corroborates this identification. Field studies show that these eggs, which were originally thought to be Miocene in age, are from Pliocene pyroclastic sediments about 3.5–4.5 my old.

Structure of shells from eggs of kinosternid turtles

Shells from eggs of five species of kinosternid turtle (Sternotherus minor, Kinosternon flavescens, K. baurii, K. Hirtipes, and K. alamosae) were examined with light and scanning electron microscopy. Except for possible differences among species in thickness of eggshells, structure of shells from all eggs was similiar. In general, kinosternid turtles lay eggs having a rigid calcareous layer composed of calcium carbonate in the form of aragonite. The calcareous layer is organized into individual shell units with needlelike crystallites radiating from a common center. Most of the thickness of the eggshell is attributable to the calcareous layer, with the fibrous shell membrane comprising only a small fraction of shell thickness. Pores are found in the calcareous layer, but they are not numereous. The outer surface of the eggshells is sculptured and may have a thick, organic layer in places. The outer surface of the shell membrane of decalcified eggshells is studded with spherical cores which presumably nucleate growth of shell units during shell formation. The shell membrane detaches from eggs incubated to hatching, carrying with it remnants of the calcareous layer. Such changes in shell structure presumably reflect withdrawal of calcium from the eggshell by developing embryos.

Upper Jurassic Dinosaur Egg from Utah

The Upper Jurassic egg described here is the first known egg from the 100-million-year gap in the fossil record between Lower Jurassic (South Africa) and upper Lower Cretaceous (Utah). The discovery of the egg, which was found mixed in with thousands of dinosaur bones rather than in a nest, the pathological multilayering of the eggshell as found in modern and fossil reptilians, and the pliable condition of the eggshell at the time of burial indicate an oviducal retention of the egg at the time of burial.

New eggshell of ratite morphotype with predation marks from the Eocene of Colorado

ABSTRACT A large number of eggshell fragments from a single locality of the lower Eocene (?Wa5-Wa6 biochron) DeBeque Formation of northwestern Colorado are interpreted as representing a single, disintegrated avian egg. These eggshells, and eggshells from two other localities within the formation, are of the ratite morphotype within the ornithoid basic type. They are unlike any previously described eggs and are assigned to Incognitoolithus ramotubulus oogen. et oosp. nov. This oospecies is distinguished by its smooth outer surface, assumed ellipsoidal shape, relatively large size, relatively thick eggshell, and presence of both non-branching and branching pore canals. Pore openings are clustered in grooves and pits on the outer surface, exhibiting the “aepyornithid” pore pattern. The eggshell fragments preserve a number of holes that were produced by impact from the outside. These marks are thought to have been produced by a predator, most likely avian. Fractures on many of the eggshell fragments occur on ...

Crocodilian eggs from the middle Eocene Bridger Formation, Wyoming

ABSTRACT Four nearly complete eggs from the middle Eocene Bridger Formation (Wyoming) are assigned to the crocodiloid basic organizational group. Similarity in egg shape and size and in the histological structure of the eggshell with Crocodylus johnstoni and Crocodylus porosus justifies this classification. The biocrystalline layer of the crocodilian eggshell is composed of a zone of shell units formed of fairly coarse wedges of tabular crystalline structure rising from the inner zone of basal plate groups. Diagenetic features of the specimens include a secondary deposit of calcite on the surface, the infilling of the eggs with fine-grained sediment, and the precipitation of calcite and quartz crystals lining a geode-like cavity. Embryonic remains were not detected.