Bone healing is an important survival mechanism, allowing vertebrates to recover from injury and disease. Here we describe newly recognized paleopathologies in the hindlimbs of the early tetrapods Crassigyrinus scoticus and Eoherpeton watsoni from the early Carboniferous of Cowdenbeath, Scotland. These pathologies are among the oldest known instances of bone healing in tetrapod limb bones in the fossil record (about 325 Ma). X-ray microtomographic imaging of the internal bone structure of these lesions shows that they are characterized by a mass of trabecular bone separated from the shaft's trabeculae by a layer of cortical bone. We frame these paleopathologies in an evolutionary context, including additional data on bone healing and its pathways across extinct and extant sarcopterygians. These data allowed us to synthesize information on cell-mediated repair of bone and other mineralized tissues in all vertebrates, to reconstruct the evolutionary history of skeletal tissue repair mechanisms. We conclude that bone healing is ancestral for sarcopterygians. Furthermore, other mineralized tissues (aspidin and dentine) were also capable of healing and remodeling early in vertebrate evolution, suggesting that these repair mechanisms are synapomorphies of vertebrate mineralized tissues. The evidence for remodeling and healing in all of these tissues appears concurrently, so in addition to healing, these early vertebrates had the capacity to restore structure and strength by remodeling their skeletons. Healing appears to be an inherent property of these mineralized tissues, and its linkage to their remodeling capacity has previously been underappreciated.

Notosuchia is a group of mostly terrestrial crocodyliforms. The presence of a prominent crest overhanging the acetabulum, slender straight-shafted long bones with muscular insertions close to the joints, and a stable knee joint suggests that they had an erect posture. This stance has been proposed to be linked to endothermy, because it is present in mammals and birds and contributes to the efficiency of their respiratory systems. However, a bone paleohistological study unexpectedly suggested that Notosuchia were ectothermic organisms. The thermophysiological status of Notosuchia deserves further analysis, because the methodology of the previous study can be improved. First, it was based on a relationship between red blood cell size and bone vascular canal diameter tested using 14 extant tetrapod species. Here we present evidence for this relationship using a more comprehensive sample of extant tetrapods (31 species). Moreover, contrary to previous results, bone cross-sectional area appears to be a significant explanatory variable (in addition to vascular canal diameter). Second, red blood cell size estimations were performed using phylogenetic eigenvector maps, and this method excludes a fraction of the phylogenetic information. This is because it generates a high number of eigenvectors requiring a selection procedure to compile a subset of them to avoid model overfitting. Here we inferred the thermophysiology of Notosuchia using phylogenetic logistic regressions, a method that overcomes this problem by including all of the phylogenetic information and a sample of 46 tetrapods. These analyses suggest that Araripesuchus wegeneri, Armadillosuchus arrudai, Baurusuchus sp., Iberosuchus macrodon, and Stratiotosuchus maxhechti were ectothermic organisms.

Coleoid cephalopods exhibited two distinct reproductive strategies, resulting in small pelagic and large demersal hatchlings, both in the geologic past and recently. In ectocochleate cephalopods, the hatching event is recorded in shell structures (e.g., nepionic constrictions, ultrastructural shifts, or ornamentation differences). In contrast, well-defined hatching markers do not exist on coleoid shells. Changes in septal spacing may be evidence of hatching (e.g., some extant sepiids), but not in all fossil groups. In the present study, we subdivide the early ontogenetic shells of phragmocone-bearing coleoids (belemnoids, spirulids, and sepiids) into key architectural stages and describe their reference to the hatching event. Belemnoids exhibit three key stages, the second of which is here considered to occur shortly before or after hatching. In spirulids and sepiids, there is only one key stage. In Mesozoic belemnoids, spirulids, and sepiids, hatching accordingly occurred with a total shell length of less than 2 mm, which corresponds to mantle lengths of small planktonic hatchlings. Production of small pelagic hatchlings and thus small eggs was therefore the dominant reproductive strategy within the Coleoidea. The first evidence of enlarged hatchlings appeared during the Maastrichtian in Groenlandibelus. During the Eocene, the large-egg strategy apparently became more widespread, particularly in belosaepiids.

The origin and evolutionary histories of the two most abundant and diverse genera of invertebrates (Prosserella: Brachiopoda and Syringostroma: Stromatoporoidea) in the Detroit River Group and associated rocks in the vicinity of the Michigan Basin appear to support the models of either allopatric speciation and punctuated equilibria (Eldredge and Gould, 1972) or quantum evolution (Simpson, 1944; 1953). Four morphotypes of Prosserella arose almost simultaneously (a “burst”) just below the base of the Detroit River in sandstone deposited near the axis of the Findlay Arch and persisted without evidence of significant progressive evolutionary change (a “trend”) until their almost simultaneous extinction by lineage termination near the top of the Detroit River. Neither ancestors nor descendants of Prosserella have been recognized and even the familial placement of the genus is uncertain. The genus, its species and morphotypes probably arose by means of very profound genetic or chromosomal “revolutions” that probably took place in small allopatric populations; each population quickly increased in abundance and geographic range and persisted without further significant morphologic modification until its extinction.

S. ristigouchense from the Lower Devonian of New Brunswick is the probable ancestor to six (or seven) species of Syringostroma that appear almost simultaneously (another “burst”) in lower Detroit River carbonate rocks deposited near the eastern margin of the Michigan Basin. Two of these new species are known only from reefs of early Detroit River age (a “crash”), four species persist without significant morphological change to at least the end of Detroit River deposition, and one of these was the probable ancestor to yet another newly evolved species that is abundantly represented in the conformably overlying Columbus Limestone.

The “founding fathers” of chronostratigraphy were pre-Darwinian and based their concepts and methods on assemblages of co-occurring taxa of unknown phylogenetic relations (assemblage-zones, concurrent range-zones and Oppel-zones) rather than on the range-zones of successional species in the same phylogenetic lineage (lineage-zones). Assumptions of these early biostratigraphers concerning the temporal relations of taxa are in close accord with the premises of punctuated equilibria and quantum evolution. The development of the chronostratigraphic system during the 19th century attests to the success of these early methods which depend for their precision on the number of taxa used and determination of the significance of morphologic differences among these taxa and their geographic and stratigraphic distributions.

This study addresses the question of evolutionary tempo and mode in a sequence of Upper Cretaceous bivalves in the genus Pleuriocardia from the Western Interior Basin of North America. Change between species was probably phyletic (without persistence of ancestors). There is some evidence for weak gradual change within the lineage, but most important change is concentrated in short intervals of time. Detailed examination of the differences among samples reveals pronounced geographic variation, whereas temporal variation within localities is generally minor. The relatively rapid episodes of change fit the model of punctuated equilibrium, but the phyletic nature of species-level change does not.

The value of the debate about the punctuated and gradualistic models has been to force a more criticial examination of fossil sequences, but these sequences should not be forced into narrowly defined categories. A variety of evolutionary patterns may exist in the fossil record, and it is this variation in pattern that will inform us of the underlying processes.

The mathematical relationship between species survivorship and duration curves is derived using standard demographic arguments. The result, when applied to the late Cenozoic mammals, suggests that there was an inhomogeneity in the mammalian radiation just before the Wurm, or that the mammalian speciation process has not yet attained the stable-age distribution.

Under favorable circumstances, biogeographic and biostratigraphic data can be combined to identify accurately the time and place of origin of a given taxon, and to reconstruct the pattern of its subsequent radiation. This study considers the dendrasterid sand dollars, which are abundant today along the Pacific Coast of North America. The Neogene sand dollar record in this region is particularly good; in fact, sand dollars have traditionally been used as provincial index fossils.

The dendrasterids originated in central California at the end of the Miocene; the oldest forms are dated at about 6.0–6.5 Ma. They spread south to Baja California during the Pliocene, and then north to Alaska during the Quaternary. This historical pattern is not an artifact of the record; it is consistent with independent paleogeographic evidence. The dendrasterids supplanted an older Mio-Pliocene sand dollar fauna; they are now completely dominant in the temperate coastal waters of the northeastern Pacific. They have reached this position in less than 7 m.y. since their first local appearance. The rapid rise of dendrasterids could be related to their aberrant morphology and behavior; these adaptations allow dendrasterids to suspension-feed, in a manner unique among living echinoids.

Dendrasterids are characterized by “eccentric” test morphologies. Even the oldest species are highly eccentric; transitional forms are unknown. The first dendrasterids appear suddenly in the provincial “Jacalitos Stage,” above an unconformity which represents no more than about 1 m.y. They do not occur in the underlying units, although other fossil sand dollars are abundant. The dendrasterids may have arisen rapidly, through a heterochronic change in the development of older, noneccentric forms. Recent ontogenetic studies have documented the feasibility of this process.

The discrete cosine transform (DCT) is a Fourier-related transform widely used in signal processing and well suited to analyzing open outlines such as ammonite ribs. The method is applied here to depict and decipher the ribbing morphospace of a large group of Lower Jurassic ammonites composed of the Oxynoticeratidae and their close ancestors. Because they are clearly associated with buoyancy and/or swimming ability, the usually clearly involute, comparatively smooth and compressed shells of these ammonites may well be misleading taxonomic markers. In this context, quantitative analysis of the ribbing pattern using the DCT may significantly improve our perception of the ornamental patterns expressed within the group. A set of 251 specimens illustrating the worldwide fauna and selected from more than 80 publications is analyzed. Big differences are found in the evolutionary patterns of the two main lineages of Oxynoticeratidae currently accepted in the literature. A previously unsuspected Mediterranean group comprising principally the genus Parasteroceras is identified from its distinctive ornamentation. The northwest European and Mediterranean genera Eparietites, Oxynoticeras, and Parasteroceras do not feature among the American (East Pacific) faunas. This finding calls into question some generally accepted correlations between European and American stratigraphic frameworks. The study shows that the DCT is a valuable tool for discriminating between species within the huge and often puzzling range of ornamental variation of the main genera (e.g., Gleviceras and Radstockiceras).

Genera of montane conifers first appeared in the fossil record in large numbers in the Middle Eocene (47-45 Ma) as widespread volcanism in the Cordilleran region provided scattered, cold upland tracts suited for them. Higher subalpine environments, generally above 2,000 m, probably were confined then to upper slopes of scattered strato-volcanos and basement highs covered with thick pyroclastic deposits. As relief increased in the middle Tertiary, and especially during the Pliocene-Quaternary, the area suited for a subalpine forest zone increased significantly, enabling montane conifers to spread into that higher, colder environment and form a new major forest zone. During glaciations the subalpine zone was much larger and probably from 900-1,000 m lower than at present. Spreading post-glacial warmth and drought account for its retreat to higher levels and for the discontinuous distribution of the forest and its species today. Recency of the subalpine adaptive zone is implied also by the close relations of its varieties and subspecies of herbaceous perennials, a few annuals, and pines to those in vegetation zones below it.

The evolution of thermometabolism in pseudosuchians (Late Triassic to the present) remains a partly unsolved issue: extant taxa (crocodilians) are ectothermic, but the clade was inferred ancestrally endothermic. Here we inferred the thermometabolic regime of two neosuchian groups, Goniopholididae (Early Jurassic to Late Cretaceous) and Dyrosauridae (middle Cretaceous to late Eocene), close relatives of extant crocodilians, in order to elucidate the evolutionary pattern across Metasuchia (Early Jurassic to the present), a clade comprising Neosuchia (Early Jurassic to the present) and Notosuchia (Middle Jurassic until the late Miocene). We propose a new integrative approach combining geochemical analyses to infer body temperature from the stable oxygen isotope composition of tooth phosphate and paleohistology and phylogenetic comparative methods to infer resting metabolic rates and red blood cell dimensions. †Dyrosaurus and †Goniopholis share with extant crocodilians similar lifestyles, body forms, bone tissue organization, body temperatures, metabolic rates, and red blood cell dimensions. Consistently, we infer ectothermy for †Dyrosaurus and †Goniopholis with the parsimonious implication of neosuchians and metasuchians being primitively ectothermic.

Species selection has received a great deal of theoretical attention but it has rarely been empirically tested. It is important to determine the level of selection that operated during a particular extinction event because it can help distinguish between traits that were actually responsible for extinction and those that were merely correlated with it. Here, we present a test that can help distinguish between organismal and species-level selection, which we demonstrate using the high-resolution fossil record of planktonic foraminifera species recorded in deep-sea sediment cores. Our test examines the fate of survivors and victims during the Cretaceous/Paleogene (K/Pg) mass extinction within single geographic regions, where all individuals experience the same selection pressures. Selection at the organismal level implies that individual members of surviving species are more fit than those of victimized species, and therefore should be more likely to survive in affected areas; conversely, selection at the species level implies individuals will suffer equally within an affected area. We find that survivors of the mass extinction suffered very high extirpation rates in cores where the overall extinction rate was high, indicating that individual members of the surviving species were generally no more fit than individual members of extinct species. Rather, these species were able to survive because they possessed advantageous species-level traits, such as larger geographic ranges and greater abundances than victimized species. This geographic pattern of extirpation suggests that selection operated at the species, rather than organismal, level during the K/Pg mass extinction of planktonic foraminifera.

A simple theoretical argument shows that the evolutionary process will look gradual if it is considered on too fine or too coarse a time scale. There exists an intermediate time scale in which the distribution of evolutionary rates will appear as bimodal.

Knowing the structure and branching order of the evolutionary tree is essential to many studies of the evolutionary process and the history of life. Most attempts to reconstruct evolutionary trees are based on rectangular matrices, in which coded states are assigned for each character and each taxon under study. Everyone who has tried to infer the pattern of evolution from such character-taxon matrices is confronted with a great deal of “noise” and uncertainty. Often, there are multiple “most parsimonious trees” (those requiring the fewest evolutionary steps), which often differ significantly in topology; and many nodes in such trees are poorly supported; that is, there are contradictions and inconsistencies in the data. Some of this noise arises for reasons well known to phylogeneticists. Character states may arise multiple times, evolve in parallel, or reverse (homoplasy); taxa vary insufficiently among themselves; and diversification may be so rapid that data are insufficient to detect the order of branching. Polytomies are regarded as a nuisance rather than as real information. Characters may be coded inappropriately, so that there are too many redundancies, inapplicable character states, and multistate characters, as well as dependence among characters. Moreover, it is highly debatable whether evolution is parsimonious, and there are conflicts about how to establish the polarity of characters (primitive vs. derived). (For reviews and discussion see Sober 1988; Huelsenbeck and Crandall 1997.)

A theoretical morphologic model defining patterns of shell sculptures in Bivalvia is introduced. It is based on the displacement of sculptural elements along the growing shell margin and introduction of new sculptural elements. The kinematics of the sculptural elements are defined in terms of the following parameters: maximum speed of displacement of sculptural elements, position along the growing shell margin where a migrating element attains maximum speed, and position of the divergence axis of the riblets. Computer models successfully mimicked most of the diverse patterns of bivalve shell sculptures. Morphometric analysis revealed that the displacement speed of a sculptural element is not constant but depends on the relative position of the element on the shell margin. It was revealed that the primary component of variation in bivalve shell sculptures could be explained by variation in the displacement speed of sculptural elements around the divergence axis of riblets.

Cheek teeth of some mammalian herbivores exhibit pronounced changes in occlusal size and shape through wear, purportedly caused by strong curvature. Such changes are extreme in the upper cheek teeth of extinct, dentally archaic lagomorphs. Morphologic and taxonomic turnover in lagomorphs suggests that these dentally archaic forms may have been unable to develop hypselodont (ever-growing) cheek teeth. This study investigates how the interaction of tooth shape and wear can cause occlusal size and shape changes, and potentially impose structural constraints on crown height. These constraints may help explain extinction of mammals with teeth like archaic lagomorphs, evolution and diversification of other mammalian herbivores during the late Miocene, and the relative paucity of hypsodont cheek tooth shapes in extant mammals.

I first quantify two-dimensional curvature accounting for shape differences observed in hypsodont teeth, P4s of the archaic lagomorphs Russellagus and Hesperolagomys, which exhibit pronounced change with wear, and Ondatra lower incisors, which show minimal change with wear. Using this quantification, I generate theoretical curvature morphologies and describe a geometric model of tooth wear that generates values for qualitative and quantitative aspects of the occlusal surface at different wear stages. Modeled results of wear surface topography and dimensions closely correspond to observed patterns in Russellagus, Hesperolagomys, and Ondatra. Model results on wear in theoretical tooth morphologies identify two major shape factors influencing wear: orientation of the wear surface (incisor-like or cheek-tooth-like), and tooth curvature (“concentric” or “nonconcentric”). Modeled wear also suggests two geometric constraints on crown height. Teeth with nonconcentric curvatures can have crown height limited by potential tooth area. “Incomplete wear” in any tooth can present severe constraints on increasing crown height, causing structurally untenable morphologies in very tall-crowned to hypselodont teeth.

A current question being debated with considerable intensity is whether or not certain geographic areas act as centers of evolutionary radiation and supply species to other areas that are less active or less effective in an evolutionary sense. Darwin (1859) was the first to write about centers of origin which he called “single centers of creation.” He argued that each species was first produced within a single region and that it subsequently migrated from that area as far as its powers of migration and subsistence under past and present conditions permitted. Adams (1902), in discussing the influence of the southeastern United States as a center of distribution for the flora and fauna of North America, provided a series of criteria for the determination of “centers of dispersal.” His first, and evidently most important criterion was the location of “the greatest differentiation of a type.”

Electron microprobe analyses of platform (pectiniform Pa) elements of Permian conodonts reveal detailed and systematic chemical element distributions. The crown of the conodont element is more densely mineralized than the basal body and shows evidence of less dense mineralization in areas of rapid growth. Patterns in sodium and sulfur concentrations indicate oral to aboral differentiation within conodont elements. These chemical element patterns support oral exposure during life and functional use as a tooth, and they approximate the erupted and embedded positions of the conodont tooth when the animal was alive. Previously unrecognized spatial distributions of geochemically important chemical elements warrant consideration in future geochemical studies of conodonts.

Although generally considered rare in gastropods, septation has long been noted in turritellids, but functional hypotheses do not survive strong scrutiny. Here we outline a methodology for testing spandrel hypotheses and apply it to the problem of turritellid septa. We follow Gould in using “spandrel” as a term for all features that are nonadaptive sequelae of adaptive features of organisms, including those that are structurally necessary, those that are developmentally correlated, and nondeterministic by-products that are correlated to features under selection.

In turritellids, septa are constructed in microstructural continuity with secondary internal thickening of the shell, are highly variable features infraspecifically, and are strongly associated with degree of shell thickening. We therefore conclude that rather than being themselves adaptive, turritellid septa are spandrels of shell thickening. Turritellid septa are composed of crossed lamellar aragonite, which appears to be constructed by mantle epithelium over the visceral mass. Septation was also found in 22 of 24 gastropod families examined from a broad phylogenetic distribution. Septa thus appear to be a widespread feature of caenogastropods, in strong contrast to previous assertions that septa are less common in modern or high-spired shells.

The excellent fossil record of conodonts represents an ideal, yet underutilized, resource for resolving fundamental issues of pattern and process in evolutionary theory. However, this potential has not been exploited because the quantitative understanding of the evolution of conodont element morphology is limited. This work applies standardized morphometric protocols to skeletal elements belonging to the conodont Pterospathodus, derived from a densely sampled section from Estonia. It has established a robust quantitative framework for morphological variation in Pterospathodus, permitting statistical analysis of the current qualitative hypotheses of evolutionary pattern within this genus for the first time. Apparent directional trends were statistically compared with patterns expected for directional evolution, an unbiased random walk and stasis, using maximum-likelihood model fitting, rescaled range analysis, and the runs test. Results confirmed the presence of trends in size and shape change through time, providing an example of convincing directional morphological change in a fossil lineage. The morphometric analyses have also allowed quantitative investigation of ontogenetic processes in Pterospathodus, suggesting that allometric repatterning was the proximal mechanism responsible for mediating the observed shifts in morphology through time. The results have demonstrated that conodonts represent an important resource for understanding evolutionary pattern and process in the fossil record.

We appreciate Dr. Scott's comments about our paper (Malmgren and Kennett 1981), but wish to clarify some aspects which we hope will help provide a better understanding about the Late Neogene evolution of the Globorotalia (Globoconella) group (Kennett and Srinivasan 1983). We also wish to dispute some of Scott's other criticisms. In effect, Scott's arguments have provided no reason to justify abandonment of our initial contention that this lineage represents one of the best documented cases of phyletic gradualism in any group of fossils.

We support Scott's notion that divergence of the lineage took place near the Miocene-Pliocene boundary, but this divergence is not relevant for our evolutionary study. In fact, the Early Pliocene form resembling Globorotalia conoidea was already recognized by one of us (J.P.K.) 10 yr ago (Kennett 1973). It was distinguished as G. cf. conoidea and not G. conoidea as stated by Scott. In our previous papers (Malmgren and Kennett 1981, 1982) we confined our attention to the evolution that occurred in the primary temperate stock (cool subtropical) water mass—the abundant and dominant forms of Globoconella.