Onset of maturity in trilobites is generally considered to occur when the last trunk segment is released into the thorax, marking the start of the holaspid stage. Here we describe striking morphological changes that occur within the holaspid ontogeny of Lonchopygella megaspina Zhou in Zhou et al., 1977, which include the effacement of dorsal furrows, the rapid and complete degeneration of pygidial lateral spines, and the increasing prominence of a pygidial axial spine. These notable changes, which are not coincident with the onset of the holaspid phase, emphasize that the onset of maturity in trilobites should be viewed on a character-by-character basis before assessing whether the exoskeleton as a whole can be described as mature. The holaspid pygidial condition in L. megaspina may represent an intermediate step in an evolutionary transition in the number, form, and allocation of segments in the tsinaniid trunk. Pygidial transition from a dynamically changing complement of segments in the meraspid phase to a static complement in the holaspid phase was accompanied by a marked change in the extent to which segment boundaries defined pygidial structure. Attaining this static complement allowed subsequent pygidial development to emphasize its structure as an integrated unit in which internal segmental boundaries became diffuse, a continuous margin to become prominent, and an elongated terminal spine, first evident at onset of epimorphic growth, to develop allometrically. Trilobite body development suggests that while the segmented construction placed constraints on how morphology varied, the influence of these constraints diminished following completion of thoracic segment construction. Selective premium for a distinct posterior tagma might favor the early ontogenetic acquisition of such a structure, and could have been a driver of the repeated trend toward caudalization witnessed among derived trilobite clades.

A phylogenetic analysis was conducted to address evolutionary relationships among the earliest members of the Miacidae (one of two early Cenozoic carnivoran families) and to ascertain the position of an ambiguous taxon, “Miacis” jepseni, with respect to the genera Miacis, Uintacyon, Vulpavus, Vassacyon, and Oödectes. The results of this analysis indicate that “Miacis” jepseni should be referred to the genus Oödectes, and both genus and currently included species are rediagnosed. The phylogenetic relationship of Oödectes to other miacids, and relationships among early Eocene miacids more generally, however, are less well resolved. Support is found for sister taxon relationships between Miacis and Vulpavus and between Uintacyon and Vassacyon, and it is suggested that this latter clade is the sister taxon to all other members of Miacidae.

A deep core from Warren County, Ohio, has yielded numerous fossils of Cambrian age. The specimens, which are among the first recorded from Cambrian rocks of Ohio, suggest revisions in the inferred ages of the Eau Claire and Mount Simon Formations in the Cincinnati Arch region. Trilobites indicative of Dresbachian (late Middle Cambrian to early Late Cambrian) and possibly Franconian (Late Cambrian) age are present in the upper Eau Claire Formation. By implication, the underlying Mount Simon Formation must be of earlier Dresbachian age or perhaps older. Identified trilobites from the Eau Claire Formation seem to be characteristic of inner-shelf lithofacies of Laurentia. Other body fossils from the Eau Claire Formation include inarticulate brachiopods and a graptolite. Body fossils in the lower Knox Dolomite include trilobite sclerites and echinoderm ossicles. Trace fossils are present in both units.

Previously undescribed specimens of Pachycephalosaurus wyomingensis allow partial description of the anterior braincase and a preliminary examination of change of dome shape with age. The two morphs of dome shape recognized in adults are also present in juvenile specimens with dome lengths half that of mature adults. A new specimen of Stegoceras edmontonense in the same geographic and stratigraphic provenance as P. wyomingensis establishes that the two pachycephalosaur genera could exist sympatrically.

Two alternative hypotheses for proximal column growth are tested in Taxocrinus cf. T. whitfieldi, a late Mississippian flexible crinoid. The first hypothesis states that new columnals are added at the base of the proximal column (immediately above the generating columnal), whereas the second hypothesis has columnals of the proximal column inserted beneath the aboral cup. In both hypotheses, middle column columnals are inserted beneath the generating columnal and are independent from the proximal column.

External features used to determine points of columnal insertion include wedge-shaped columnals and sharp changes in columnar morphology. Sagittal sections reveal the presence of small columnals, some of which can be interpreted as the last columnals inserted prior to death. Data collected on Taxocrinus cf. T. whitfieldi confirm the first hypothesis. This hypothesis may be applicable to other crinoids with xenomorphic columns.

Predatory drillholes (boreholes) are known from fossils as old as the late Precambrian (Bengtson and Zhao, 1992). The presence of predatory drillholes has been documented in a large number of shelly invertebrates including bivalves, gastropods, scaphopods, crabs, ostracodes, brachiopods, and many others (e.g., Sohl, 1969; Bishop, 1975; Bromley, 1981; Vermeij, 1987; Kabat, 1990; and references therein). We document here, for the first time, a drillhole in a lingulid brachiopod.

A newly discovered locality of aestivation burrow casts containing the lungfish, Gnathorhiza serrata, is reported from the early Permian Arroyo Formation of Wilbarger County, north-central Texas. Remains preserved in the burrow casts provide sections of mummified Gnathorhiza and new information about the postcranial skeleton of this fish. Scales of Gnathorhiza resemble those of the modern lungfishes such as Lepidosiren in their microanatomy. No traces of paddle-like pectoral or pelvic fins were found and paired fins of Gnathorhiza may have resembled those of Lepidosiren. The axial skeleton and median fins of Gnathorhiza seem to resemble those of Lepidosiren except that the tail area and caudal fin of Gnathorhiza were stout and strong rather than slender and tapering. Gnathorhiza, which aestivated tail-down in its burrow, may have required a stout tail for support.

Lower Miocene rocks of the uppermost part of the Pysht Formation and the overlying Clallam Formation on the Olympic Peninsula, Washington have yielded rare fossils of a small crab, Cancer (Metacarcinus) starri, new species. This is the second lower Miocene record of the genus Cancer and the oldest of the subgenus Metacarcinus.

The study of specimens of the retiolitid graptolites Stomatograptus sp., and Agastograptus robustus with a complete or nearly complete periderm permits a better understanding of the growth and development of retiolitids. Incremental layers deposited in more or less concentric layers on skeletal lists are synchronized with the deposition of sheetlike fusellar bands between the lists. Lists, therefore, become progressively more robust, while the periderm of fusellar bands remain single-layered. It appears that before the development of new distal thecal lists and concomitant deposition of fusellar bands can begin, the next proximal-most thecae must be essentially complete. Retiolitid graptolite thecal growth thus appears to mirror that of “normal” graptolites.

Etched slices of the cuticle of the Silurian trilobite Homalonotus rhinotropis Angelin, 1854, from two localities in Skåne, southern Sweden, have been examined with the scanning electron microscope. The two major subdivisions of the cuticle are a “prismatic” (originally laminated) outer layer, about 20-30 μm thick, and a principal layer, 200-300 μm thick, which may be foliated or roughly laminated. The original finely-laminated aspect of the outer layer may sometimes be seen as a continuous layer, but is more frequently detected as “shaped inclusions” set in a prismatic background. These “shaped inclusions” are considered to have been produced by accumulation of minerals around the apices of 3-6 μm perpendicular canals early in calcification and preferentially preserved because of subtle differences from the products of later stages of the process. It is possible that calcification started before ecdysis. The difficulties involved in ascertaining the original structure of the principal layer are outlined, and possible reasons for differences in its preservation from the outer layer are proposed.

The Lower–Middle Ordovician (Ibexian, Whiterockian) sedimentary rocks exposed at Rancho Las Norias includes the informally named Las Norias formation, which consists of an intercalation of carbonate and clastic sediments with abundant marine fauna. These deposits occur as the most austral sedimentary rocks of Ordovician age for Laurentia, providing a critical link to understand the distribution of Ordovician marine faunas of North America. An investigation of the gastropod fauna from the upper portion of the Las Norias formation, Sonora, Mexico, is undertaken for the first time. The gastropod assemblage includes Maclurites acuminatus, ?Monitorella sp., Lecanospira sp., Malayaspira aff. M. rugosa, Lophospira perangulata, and Hormotoma? sp. This assemblage indicates a paleogeographic relationship with Laurentia, including the USA (Nevada), Canada (British Columbia, Newfoundland), Greenland, and the Argentine Precordillera.

Juvenile specimens of the Paleocene–Eocene pantodont Coryphodon provide more extensive ontogenetic information for this genus than is available for other Paleocene–Eocene mammals. The dental eruption sequence for Coryphodon is: 1) (DC11, DI1–31–3); 2) DP44; 3) DP33; 4) DP22; 5) (M11, I33); 6) DP11, 7) M22; 8) P44; 9) P33; 10) (P22, I11?); 11) C11; 12) (M33, I22) (eruption sequence of tooth positions in parentheses is uncertain). The DP11 of Coryphodon do not have permanent successors. No significant, qualitative morphological variation can be detected in deciduous cheek teeth of Coryphodon, and metric analysis of these teeth failed to detect taxonomically significant differences. The ontogenetically youngest Coryphodon is known from parts of a skeleton of an individual perhaps less than three years old at the time of death. This skeleton and other partial juvenile skeletons suggest that juvenile Coryphodon grew quickly and approached near-adult proportions before the deciduous dentition was lost or the epiphyses of the long bones began to fuse.

A new species of the Pliocene–Pleistocene flat-headed peccary, Platygonus pollenae, has been recovered latest Hemphillian (latest Miocene) localities from Nebraska, Kansas, Colorado, and Texas. It can be distinguished from other tayassuids by its distally rounded wing-like zygomatic process, and its subzygodont cheek teeth. In contrast to more derived species of Platygonus, it is much smaller in size, its molars are relatively more bunodont, the talon and talonid cusps are retained on the premolars of most individuals, and the mandibular symphysis lacks a median keel on the chin. In these characters, it is the earliest and the most primitive species of Platygonus known. It is more primitive than the typical Blancan species, or any of the species from the Pleistocene, and demonstrates the origin of this important Pleistocene mammal in the latest Miocene.

Specimens of the gastropod genus Donaldina are numerous throughout marine units of the Pottsville, Allegheny, and Conemaugh Groups in the Appalachian Basin. Six species of Donaldina from thirteen marine units are described. New species proposed are Donaldina quadroliratus, from Pottsville and Allegheny units, and Donaldina superclivis, from Conemaugh units.

A new genus and species of obolellid brachiopod, Brevipelta chouberti, is described from the Early Cambrian of Morocco. It is a useful index fossil for the upper Choubertella Zone and the Daguinaspis Zone in Morocco. Additionally discussed are taphonomic aspects that lead to the question whether the shell may have been weakly calcified compared to other obolellid brachiopods and the calcareous part may have been composed of aragonite crystallites, or whether the preservation of Brevipelta is due to facile solubility of a calcitic shell substance. Brevipelta chouberti represents not only the oldest described Early Cambrian brachiopod from Africa, but one of the oldest obolellid brachiopods known worldwide.

The development of the trilobite pygidium involves both an articulation process at the frontal part and the formation of new segments at the rear end, and hence the development of the meraspid pygidium entails complicated morphological changes. This study deals with the ontogeny of the Furongian (late Cambrian) ptychaspidid trilobite, Quadraticephalus elongatus (Kobayashi, 1935), from the Hwajeol Formation of the Taebaek Group, Taebaeksan Basin, Korea, with a special focus on the segmentation process during the meraspid pygidial development. Compared to the ontogeny of a ptychaspidid trilobite, Asioptychaspis subglobosa (Sun, 1924), which is assumed to be an ancestral species of Q. elongatus, the convexity of the cranidium of Q. elongatus increased in a slower rate; the yoked free cheek of Q. elongatus splits to form a ventral median suture in a later developmental stage; and, a rim-like ridge, which disappeared in the early holaspid pygidium of A. subglobosa, was maintained in the late holaspid period of Q. elongatus. These morphological changes with growth imply that paedomorphosis was involved in the evolution of Q. elongatus. Eleven stages are recognized for the meraspid pygidial development, which began with an accumulation phase during which the number of segments increased from three to seven, followed by an equilibrium phase with seven segments, and ended up with a depletion phase during which the number of segments within the pygidium decreased to four. During the depletion phase, the pygidial length did not increase or even slightly decreased. The onset of the epimorphic phase, in which the total number of trunk segments does not increase anymore, precedes the onset of the holaspid period, demonstrating that the developmental mode of Q. elongatus is protomeric.

Identification of tracemakers is of primary importance for evaluating the biotic interactions inferred from bore holes in fossil shell assemblages. Domicile bore holes in the subapical whorls of gastropods produced by spionid polychaete Dipolydora sp., supposed to be commensal with hermit crabs, are common in dead gastropod assemblages from deepwater habitats in the Philippines. These holes exhibit unique features and support a new criterion for the interpretation of nonpredatory borings in fossil gastropods. Diagnostic of these bore holes are: small circular to elliptical outer opening, the presence of weak dissolution of the columella beneath the bore hole, and the presence of a hollowed tube composed of detritus held together with mucus within some gastropod whorls anterior to the hole. The two selection factors of subapical whorls and elongate shells are supplementary criteria for recognition of these holes. Bore holes are recognized here in a deepwater gastropod assemblage from the upper Pliocene Shinzato Formation of Okinawa, Japan, and named Polydorichnus subapicalis n. igen. and isp. These holes are identical to modern examples exhibiting similar site and species selectivity. P. subapicalis has its oldest fossil record in the upper Miocene of the Philippines, was common in offshore assemblages from the Miocene onward, and is a good indicator of occupation by a hermit crab and for commensalism between polychaetes and hermit crabs.

Two new species of scutelluine styginid trilobites are described from Frasnian strata in the Virgin Hills Formation in the Canning Basin of Western Australia. They are placed in the genus Telopeltis n. gen., reflecting the fact that their final occurrence in the late Frasnian, up to the latest Frasnian Kellwasser extinction event, is the last known record of scutelluine trilobites. As such, it also represents the youngest record of the order Corynexochida. The two species, Telopeltis woodwardi n. sp. and Telopeltis microphthalmus n. sp., are unlike most other scutelluines in possessing extremely vaulted pygidia and showing trends to eye reduction. Such eye reduction is a common feature of late Frasnian trilobites. The characteristic morphological features of this small genus are indicative of evolution of this last scutelluine by paedomorphosis.

Two new Early Ordovician crinoids have been discovered in Gondwanan rocks of northwest Argentina. Ramseyocrinus argentinus n. sp., among the most complete for the genus, aids in reconstructing key morphology. Ramseyocrinus is unorthodox with just four radials forming the entire cup, these articulating to five arms above and a tetrameric stem below. Evidence is presented radials comprise A, B, D, and E ray elements (C absent) with B and D radials adjoining to form a compound facet for the C arm. Thus the cup entirely lacks posterior plating; an elongate anal sac projects from the CD tegmen region alongside the C arm. Cup synapomorphies closely link Ramseyocrinus and the Middle Ordovician Tetragonocrinus; inclusion of this clade within disparids is tenuous. Quechuacrinus ticsa n. gen. and sp., increases the paleogeographic range of reteocrinid camerates, previously documented only from Laurentia. This taxon expresses synapomorphies characterizing the Late Ordovician Reteocrinus, demonstrating the antiquity of this morphotype.

Cryptolithinid trilobites have been repeatedly described from North America for over 150 years. Earlier work on these forms is here integrated with new information from Oklahoma to form a strong case for the following conclusions: 1) the genus Cryptolithus migrated to (present-day) eastern North America from Europe at a single time in the early Caradoc; 2) it gave rise rapidly to a western North American relative, Cryptolithoides; 3) both genera were restricted to relatively cool-water shelf environments roughly 30 m deep and remained, in general, geographically isolated for several million years. The Viola Group, geographically between these eastern and western occurrences and representing much of Middle and Upper Ordovician time, chronicles the interplay between these two genera over some six million years.

In the biogeographic boundary region formed by Oklahoma, the two supposedly distinct genera showed suprising convergence of fringe pit and other character traits as marine transgression reduced provinciality through Ordovician time. This suprising convergence of genera is interpreted as hybridization of mere subspecies after several million years of incomplete geographic separation.