Large-bodied Forms Research Articles

Caenagnathids (Theropoda, Oviraptorosauria) from the uppermost Maastrichtian of the Scollard Formation of Alberta, Canada

Recent work has greatly improved our understanding of the diversity and paleobiogeography of caenagnathids in North America. However, the late Maastrichtian caenagnathid record remains poorly understood, with only two species established from this time interval. Here we describe three isolated elements of caenagnathids recovered from the base of the upper Maastrichtian portion of the Scollard Formation of Alberta, Canada. Two specimens, a metatarsal II and a pedal ungual, represent large-bodied species and are most similar to the same elements in Anzu wyliei (upper Maastrichtian Hell Creek Formation) and Caenagnathus collinsi (upper Campanian Dinosaur Park Formation). The third specimen, a pedal ungual from an immature individual, is most similar to Leptorhynchos gaddisi (upper Campanian Aguja Formation). Preservation of only isolated elements from the Scollard Formation and a scarcity of relevant comparative specimens from the upper Maastrichtian in general, hinders taxonomic assignment of these specimens to the genus level. Regardless, these specimens provide evidence for the widespread and northerly occurrence of caenagnathids, including large-bodied forms, in North America during the last one million years of the Cretaceous.

Macroevolutionary patterns in the pelvis, stylopodium and zeugopodium of megalosauroid theropod dinosaurs and their importance for locomotor function.

During the Mesozoic, non-avian theropods represented one of the most successful clades globally distributed, with a wide diversity of forms. An example is the clade Megalosauroidea, which included medium- to large-bodied forms. Here, we analyse the macroevolution of the locomotor system in early Theropoda, emphasizing the Megalosauroidea. We scored the Spinosaurus neotype in a published taxon-character matrix and described the associated modifications in character states, mapping them onto a phylogeny and using these to study disparity. In the evolution of Megalosauroidea, there was the mosaic emergence of a low swollen ridge; enlargement of the posterior brevis fossa and emergence of a posterodorsal process on the ilium in some megalosauroids; emergence of a femoral head oriented anteromedially and medially angled, and appearance of posterolaterally oriented medial femoral condyles in spinosaurids. The greatest morphological disparity is in the ilium of megalosaurids; the ischium seems to have a high degree of homoplasy; there is a clear distinction in the femoral morphospace regarding megalosauroids and other theropods; piatnitzkysaurids show considerable disparity of zeugopodial characters. These reconstructions of osteological evolution form a stronger basis on which other studies could build, such as mapping of pelvic/appendicular musculature and/or correlating skeletal traits with changes in locomotor function.

A revision and histological investigation of Saltoposuchus connectens (Archosauria: Crocodylomorpha) from the Norian (Late Triassic) of south-western Germany

Abstract Crocodylomorpha is the stem-lineage of modern crocodylians and the only pseudosuchian (i.e. crocodylian-line archosaurs) clade that survived the Triassic–Jurassic mass extinction event. Its earliest members, the non-crocodyliform crocodylomorphs, also known as ‘sphenosuchians’, were terrestrial and mostly small-bodied (<2 m long), although some large-bodied forms are known. Saltoposuchus connectens is one of the first described crocodylomorph species but it remains poorly studied, in part due to its contentious taxonomy. Here, all referred Saltoposuchus specimens are described in detail for the first time and its taxonomy is revised, with additional taxonomic implications for the British crocodylomorph Terrestrisuchus gracilis and the coelophysoid theropod Procompsognathus triassicus. Saltoposuchus connectens is clearly distinguished from Terrestrisuchus gracilis based on both cranial and postcranial features. The phylogenetic analysis finds that Saltoposuchus connectens, Terrestrisuchus gracilis, and Litargosuchus leptorhynchus form a clade of gracile, long-legged crocodylomorphs, identified as Saltoposuchidae Crush 1984. A histological section of a femur reveals highly vascularized fibrolamellar tissue in the second-largest specimen of Saltoposuchus connectens (SMNS 12596), indicating sustained high growth rates. A similar pattern was previously observed in Terrestrisuchus sp., contrasting with slower growth rates in the crocodylomorph Hesperosuchus agilis. These findings suggest that saltoposuchids had a high resting metabolic rate and active lifestyle.

A new species of Cynomops (Chiroptera: Molossidae) from the northwestern slope of the Andes

Abstract The systematics and taxonomy of the broadly distributed bats of the genus Cynomops has changed considerably in the last few years. Among the major changes, Cynomops abrasus was split into two species of large-bodied forms (Cynomops mastivus and C. abrasus) distributed east of the Andes. However, large Colombian specimens identified as C. abrasus from the western side of the Andes had yet to be included in any revisionary work. Phylogenetic analysis performed in this study, using mtDNA sequences (Cytochrome-b), revealed that these Colombian individuals are more closely related to Cynomops greenhalli. Morphological and molecular data allowed us to recognize populations from western Colombia, western Ecuador and northwestern Peru, as members of a new species of Cynomops. Characters that allow for its differentiation from C. greenhalli include a larger forearm, paler but more uniform ventral pelage, more globular braincase, and well-developed zygomatic processes of the maxilla (almost reaching the postorbital constriction). This study serves as another example of the importance of including multiple lines of evidence in the recognition of a new species. Given its rarity and the advanced transformation of its habitat, this new species is particularly important from a conservation perspective.

Morphological and histological description of small metoposaurids from Petrified Forest National Park, AZ, USA and the taxonomy of Apachesaurus

ABSTRACTMetoposaurids are Late Triassic temnospondyls that are abundant components of freshwater depositional settings. Although metoposaurids are represented by hundreds of specimens in collections around the world, the vast majority pertain to large-bodied, relatively mature individuals, and as a result, the early stages of ontogeny are still poorly characterised. Small-bodied metoposaurids from North America have traditionally been assigned to Apachesaurus gregorii, interpreted as a diminutive taxon, but this interpretation has not been rigorously tested. Here we provide a morphological description of two new small-bodied metoposaurid specimens from Petrified Forest National Park, AZ, USA. Both provide various anatomical details that improve our understanding of small-bodied metoposaurids and their taxonomic placement within Metoposauridae. Furthermore, we perform a histological analysis on associated intercentra of these specimens, which indicates that these are relatively immature individuals. These findings support the growing consensus that Apachesaurus is a juvenile metoposaurid, thereby providing additional data regarding the early stages of metoposaurid ontogeny and evidence of the persistence of large-bodied forms into the late Norian. Accordingly, these findings merit a reevaluation of the taxonomic validity and diagnosis of the taxon and of the previous interpretations of its paleobiology.

Tyrannosauroid integument reveals conflicting patterns of gigantism and feather evolution.

Recent evidence for feathers in theropods has led to speculations that the largest tyrannosaurids, including Tyrannosaurus rex, were extensively feathered. We describe fossil integument from Tyrannosaurus and other tyrannosaurids (Albertosaurus, Daspletosaurus, Gorgosaurus and Tarbosaurus), confirming that these large-bodied forms possessed scaly, reptilian-like skin. Body size evolution in tyrannosauroids reveals two independent occurrences of gigantism; specifically, the large sizes in Yutyrannus and tyrannosaurids were independently derived. These new findings demonstrate that extensive feather coverings observed in some early tyrannosauroids were lost by the Albian, basal to Tyrannosauridae. This loss is unrelated to palaeoclimate but possibly tied to the evolution of gigantism, although other mechanisms exist.

Diverse Aquatic Adaptations in Nothosaurus spp. (Sauropterygia)-Inferences from Humeral Histology and Microanatomy.

Mid-diaphyseal cortical bone tissue in humeri of Nothosaurus spp. consists of coarse parallel-fibered bone, finer and higher organized parallel-fibered bone, and lamellar bone. Vascular canals are mainly arranged longitudinally and radially in a dominantly radial system. Blood vessels are represented by simple vascular canals, incompletely lined primary osteons, and fully developed primary osteons. Nothosaurus spp. shows a variety of diaphyseal microanatomical patterns, ranging from thick to very thin-walled cortices. In the early Anisian (Lower Muschelkalk), small- and large-bodied Nothosaurus spp. generally exhibit bone mass increase (BMI). In the middle to late Anisian (Middle Muschelkalk) small-bodied nothosaurs retain BMI whereas larger-bodied forms tend to show a decrease in bone mass (BMD). During the latest Anisian to early Ladinian (Upper Muschelkalk), small- and few large-bodied nothosaurs retain BMI, whereas the majority of large-bodied forms exhibit BMD. The stratigraphically youngest nothosaurs document five microanatomical categories, two of which are unique among marine amniotes: One consists of a very heterogeneously distributed spongy periosteal organization, the other of very thin-walled cortices. The functional significance of the two unique microanatomical specializations seen in large-bodied nothosaurs is the reduction of bone mass, which minimizes inertia of the limbs, and thus saves energy during locomotion. Transitions between the various microanatomical categories are rather gradual. Our results suggest that small-bodied Nothosaurus marchicus and other, not further assignable small-bodied nothosaurs seem to have been bound to near-shore, shallow marine environments throughout their evolution. Some large-bodied Nothosaurus spp. followed the same trend but others became more active swimmers and possibly inhabited open marine environments. The variety of microanatomical patterns may be related to taxonomic differences, developmental plasticity, and possibly sexual dimorphism. Humeral microanatomy documents the diversification of nothosaur species into different environments to avoid intraclade competition as well as competition with other marine reptiles. Nothosaur microanatomy indicates that knowledge of processes involved in secondary aquatic adaptation and their interaction are more complex than previously believed.

Locomotion in Extinct Giant Kangaroos: Were Sthenurines Hop-Less Monsters?

Sthenurine kangaroos (Marsupialia, Diprotodontia, Macropodoidea) were an extinct subfamily within the family Macropodidae (kangaroos and rat-kangaroos). These “short-faced browsers” first appeared in the middle Miocene, and radiated in the Plio-Pleistocene into a diversity of mostly large-bodied forms, more robust than extant forms in their build. The largest (Procoptodon goliah) had an estimated body mass of 240 kg, almost three times the size of the largest living kangaroos, and there is speculation whether a kangaroo of this size would be biomechanically capable of hopping locomotion. Previously described aspects of sthenurine anatomy (specialized forelimbs, rigid lumbar spine) would limit their ability to perform the characteristic kangaroo pentapedal walking (using the tail as a fifth limb), an essential gait at slower speeds as slow hopping is energetically unfeasible. Analysis of limb bone measurements of sthenurines in comparison with extant macropodoids shows a number of anatomical differences, especially in the large species. The scaling of long bone robusticity indicates that sthenurines are following the “normal” allometric trend for macropodoids, while the large extant kangaroos are relatively gracile. Other morphological differences are indicative of adaptations for a novel type of locomotor behavior in sthenurines: they lacked many specialized features for rapid hopping, and they also had anatomy indicative of supporting their body with an upright trunk (e.g., dorsally tipped ischiae), and of supporting their weight on one leg at a time (e.g., larger hips and knees, stabilized ankle joint). We propose that sthenurines adopted a bipedal striding gait (a gait occasionally observed in extant tree-kangaroos): in the smaller and earlier forms, this gait may have been employed as an alternative to pentapedal locomotion at slower speeds, while in the larger Pleistocene forms this gait may have enabled them to evolve to body sizes where hopping was no longer a feasible form of more rapid locomotion.

Cranial morphology of Thyrohyrax domorictus (Mammalia, Hyracoidea) from the early Oligocene of Egypt

The Jebel Qatrani Formation in the Fayum Depression, Egypt, has yielded a diverse hyracoid fauna that includes both small- and large-bodied forms. Thyrohyrax domorictus is one of the most common hyracoids found in the upper sequence of the Formation, from sites dating to between 29 and 31 Ma. The dental morphology of T. domorictus is more similar to that of living hyraxes than other Paleogene species, but additional morphological evidence is needed to test the hypothesis of procaviid affinities. Two fairly complete crania of T. domorictus are now known and provide a number of additional craniofacial characters for phylogenetic analysis. The specimens are comparable in size to other small-bodied Fayum hyracoids and extant procaviids. T. domorictus has a relatively long rostrum that is perforated by a nasomaxillary fossa, which is also present in Miocene Afrohyrax and Prohyrax and older Thyrohyrax pygmaeus. The anterior border of the orbit is positioned above the molars, and the orbital aperture is closed posteriorly by a complete postorbital bar. Compared to other Fayum hyracoids, T. domorictus exhibits relatively derived, and more procaviid-like, cranial morphology. The cranium of T. domorictus is most similar to that of the extant genus Dendrohyrax, and they share similar morphology of the orbit and cranial roof. Phylogenetic analysis including morphological and molecular data from a large sample of living and extinct afrotherians places Thyrohyrax domorictus as the closest known Paleogene relative of Procaviidae and Pliohyracidae, supporting the hypothesis of procaviid affinities that was originally proposed solely on the basis of dental morphology.

The allometry of CNS size and consequences of miniaturization in orb-weaving and cleptoparasitic spiders

Allometric studies of the gross neuroanatomy of adults from nine species of spiders from six web-weaving families (Orbicularia), and nymphs from six of these species, show that very small spiders resemble other small animals in having disproportionately larger central nervous systems (CNSs) relative to body mass when compared with large-bodied forms. Small spiderlings and minute adult spiders have similar relative CNS volumes. The relatively large CNS of a very small spider occupies up to 78% of the cephalothorax volume. The CNSs of very small spiders extend into their coxae, occupying as much as 26% of the profile area of the coxae of an Anapisona simoni spiderling (body mass < 0.005 mg). Such modifications occur both in species with minute adults, and in tiny spiderlings of species with large-bodied adults. In at least one such species, Leucauge mariana, the CNS of the spiderling extends into a prominent ventral bulge of the sternum. Tiny spiders also have reduced neuronal cell body diameters. The adults of nearly all orbicularian spiders weave prey capture webs, as do the spiderlings, beginning with second instar nymphs. Comparable allometric relations occur in adults of both orb-weaving and cleptoparasitic species, indicating that this behavioral difference is not reflected in differences in gross CNS allometry.

A phylogeny of the enigmatic Madagascan geckos of the genus Uroplatus (Squamata: Gekkonidae)

Since its discovery in the 17th century, the morphological peculiarities of the gekkonid lizard genus Uroplatus have generated a great deal of attention. A large number of skeletal, integumentary and visceral features are autapomorphic for the genus and some of the more well-known members of the group possess such aberrant characteristics that a separate family was once recognized to accommodate them. Recent phylogenetic analyses confirm that Uroplatus is a typical gekkonid gecko, but the specific affinities of the genus, as well as its intrageneric relationships have remained unresolved. Both nuclear (RAG-1 and PDC) and mitochondrial (ND2 and cyt b) genes (~3.2 Kb) were sequenced for 10 of 13 recognized species of Uroplatus, as well as two Madagascan and mainland African outgroups. The large-bodied forms of Uroplatus (U. fimbriatus, U. giganteus, U. henkeli, and U. sikorae) form a monophyletic group, and the smallbodied, short-tailed species are also monophyletic (U. ebenaui and U. phantasticus). Uroplatus alluaudi + U. pietschmanni comprise another distinct clade, whereas U. lineatus was weakly supported as the sister taxon of the largebodied clade and U. guentheri was sister to all other members of the genus. Our phylogenetic hypothesis based on combined DNA sequence data is mostly congruent with previous hypotheses based on morphological data. Based on a larger, more inclusive dataset, the closest relatives of Uroplatus are mainland African Afrogecko and Madagascan Matoatoa, suggesting that the diverse Malagasy gecko fauna does not comprise a single evolutionary lineage. A high diversity of new taxa (either representing synonyms to resurrect or undescribed species), morphologically similar either to U. ebenaui/phantasticus or to U. henkeli/sikorae, was apparent from our data. Many of these genetically highly divergent lineages originated from localities in northern Madagascar, which indicates this region as the possible center of diversity and endemism for several subgroups of Uroplatus.

A new species complex of Daphnia (Crustacea, Cladocera) from the Pacific Northwest of the United States

The genetic characterization of more than 1500 populations belonging to the Daphnia pulex group from the United States and Mexico revealed nine previously unrecognized species. Three of these taxa, showing morphological and genetic affinities, are newly described in this paper and are assigned membership in a new species complex. These species share a unique configuration of P3 sensilla and a triangular ephippial shape which differs from that of other members of the genus Daphnia. All three species are large-bodied forms showing distinctive setulation of the internal margin of the ventral carapace. All these members of the complex appear to be narrow endemics, restricted to temporary ponds in semi-arid areas of the Pacific Northwest.

Zooplankton structure in the Loosdrecht lakes in relation to trophic status and recent restoration measures

A five-year zooplankton study (1982–86) on three shallow and highly eutrophic lakes in the Loosdrecht area (The Netherlands) did not reveal any significant changes following the considerable reduction in external P-loading (from about 1.0 g to 0.3 g P m−2 year−1) since mid-1984. The recent annual fluctuations in the rotifer and crustacean densities are within the range of those found before the restoration measure became operative. A decrease in the average size of the crustaceans and an absence of large-bodied forms reflects an increased fish predation rather than a change in the quality or quantity of their sestonic food ( < 150 µm) which continues to be dominated by filamentous cyanobacteria and Prochlorothrix hollandica, a prochlorophyte discovered in these lakes recently.

Structure and feeding activities of zooplankton community in Lake Zwemlust, in the two years after biomanipulation

The biomanipulation study in Lake Zwemlust (area 1.5 ha; mean depth 1.5 m) is among the series of such investigations initiated recently in The Netherlands. The effects of the lake's reffilling (after it was first completely drained empty) almost entirely the nutrient-rich seepage water from the River Vecht flowing nearby and of removal of the planktivorous bream (Abramis brama), on zooplankton community structure and feeding activities of crustaceans were monitored for two successive years (1987, 1988). In these years a classical pattern of succession occurred, with the rotifer spring maximum preceding the crustacean maximum by about 3 weeks. Among the fiveDaphnia species, which appeared in quick succession during May–July, two were large-bodied forms (D. magna; D. pulex). OnlyD. pulex persisted and was the important grazer species in the second year, especially in spring. In the first year the crustacean grazing, with several values >100%.d−1, contributed significantly to the lake's improved water clarity, with Secchi-disc transparencies of 1.5 m and more almost throughout the summer, compared with 0.3 m before the biomanipulation. Even though the water clarity climate in the second year was quite similar to that in the first, the causal factor was high macrophytic vegetation, rather than zooplankton grazing. The lake developed a rich littoral flora and fauna in the second year in response to the optimal light and nutrient conditions. Apparently, the predation by the introduced planktivorous rudd (Scardinius erythrophthalmus) on zooplankton was an important factor in the changes in zooplankton structure, and in the reduced role of zooplankton in seston elimination during the second year. There is some evidence from bioassay work that, simultaneously with the littoral development, nitrogen limitation of the phytoplankton also contributed to the improved light situation in the second year.

The role of ciliated protozoa in pelagic freshwater ecosystems

The abundance and biomass of ciliates are both strongly related to lake trophic status as measured by chlorophylla concentrations. Taxonomic replacements occur with increasing eutrophication such that large-bodied forms (predominantly oligotrichs) are progressively replaced by smaller-bodied ciliates (mainly scuticociliates). Highly acidic lakes display a more pronounced dominance of large-bodied forms when contrasted with less acidic lakes of comparable trophy. Community structure of ciliate populations is determined largely by lake trophy with acidic oligotrophic systems being characterized by reduced diversity and species richness compared with hypereutrophic systems. The temporal and spatial distribution of small (< 100μm) ciliate populations is ascribed to lake thermal regimes which provide localized concentrations of food resources. Likewise, in extremely productive lakes, very large (> 100μm) meroplanktonic ciliates enter the water column during midsummer after the development of thermal stratification and associated profundal deoxygenation. Laboratory studies indicate that large zooplankton (crustaceans) are capable of utilizing ciliates as a food source, but there is little direct evidence from field studies documenting this trophic link. Ciliates can be voracious grazers of both bacterioplankton and phytoplankton, and each species has a distinct range of preferred particle size which is a function of both mouth size and morphology. Myxotrophic ciliates may be important components in some plankton communities, particularly during periods of nutrient limitation or after their displacement from the benthos of eutrophic lakes. Evidence regarding the importance of planktonic ciliated protozoa in nutrient regeneration and as intermediaries in energy flow is discussed.

The distance demersal zooplankton migrate above the benthos: implications for predation

The distance demersal zooplankton (mobile, benthic organisms which periodically emerge from the benthos and move up into the water column) swim vertically above the bottom at night was measured quantitatively on a subtidal sand flat in the Gulf of California during July, 1979. Three patterns of migration were observed: (1) small-bodied animals, including copepods, ostracods and the amphipod Metaceradocus occidentalis, remained within 30 cm of the bottom except at full moon when a significantly higher proportion of these animals swam up at least 1 m into the water column, (2) syllid polychaetes swam up at least 2 m into the water column irregardless of the phase of the moon, and (3) large-bodied forms (animals >2 mm) swam throughout the water column but in gradually decreasing abundances nearer the surface. Since nocturnally foraging planktivorous fishes feed primarily on the large-bodied, readily visible animals, we had predicted that these large forms would remain near the relative safety of the benthos. However, the movement of the larger demersal zooplankton higher into the water column than the smaller, less visible forms, suggests that factors other than predation, possibly dispersal, may be major selective pressures governing the distance demersal zooplankton swim above the benthos.

Speciation in North American Cave Millipeds

with regard to water relations, but actually a wide range exists in their humidity reactions, a range stated by Perttunen (1953) to be as wide as that among insects. Large, heavy-bodied forms tend to be euryhygric and smaller forms stenohygric, but within each size range a great variety exists in the humidity reactions. Measured evidence of this is scarce, for the study of the class Diplopoda is still in the descriptive stage. Millipeds collected in caves fall into three ecological groups, viz., epigean forms that have entered accidentally, facultative cavernicoles, and obligate cavernicoles. It is often impossible to determine to which ecological group a particular form belongs on the basis of morphological characters alone, for millipeds are a conservative group, and cave-induced modifications are seldom spectacular. Bizarre caveadapted forms are rare. The accidental cave entrants usually have pigmented, heavy exoskeletons and include both small-bodied and large-bodied forms. They wander into caves, fall in, are washed in by flood waters, are driven in by drought, or are carried in by other animals. And since caves have been studied so much more thoroughly than most epigean areas, some epigean forms are known only from cave collections. The facultative cavernicoles, or troglophiles, are epigean forms with great moisture requirements that usually live in deep humus, but they are also tolerant of cave conditions and sometimes reproduce there. Some troglophiles have the somatic miodifications that are associated with obligate cave life: reduction of body pigment, elongation of legs and antennae, a thinner exoskeleton, and loss of some or all of the ocelli. Others show these modifications only to a slight degree or 116