Denver Museum of Nature and Science

Air space proportion (ASP), the volume fraction in bone that is occupied by air, is frequently applied as a measure for quantifying the extent of skeletal pneumaticity in extant and fossil archosaurs. Nonetheless, ASP estimates rely on a key assumption: that the soft tissue mass within pneumatic bones is negligible, an assumption that has rarely been explicitly acknowledged or tested. Here, we provide the first comparisons between estimated air space proportion (where the internal cavity of a pneumatic bone is assumed to be completely air-filled) and true air space proportion (ASPt, where soft tissues present within the internal cavities of fresh specimens are considered). Using birds as model archosaurs exhibiting postcranial skeletal pneumaticity, we find that estimates of ASPt are significantly lower than estimates of ASP, raising an important consideration that should be acknowledged in investigations of the evolution of skeletal pneumaticity and bulk skeletal density in extinct archosaurs, as well as in volume-based estimates of archosaur body mass. We advocate for the difference between ASP and ASPt to be explicitly acknowledged in studies seeking to quantify the extent of skeletal pneumaticity in extinct archosaurs, to avoid the risk of systematically overestimating the volume fraction of pneumatic bones composed of air. This article is part of the theme issue ‘The biology of the avian respiratory system’.

Postcranial skeletal pneumaticity is a phenomenon in birds in which epithelial extensions of the lung–air sac system aerate bones. Detailed development of this phenotype remains largely unknown. Here, we investigate changes in bone, soft tissue and air space volume in the developing humerus of turkeys using computed tomography and micro-computed tomography. Employing a two-phase approach, we first tracked humeral air space development in vivo in domesticated turkeys between week 10 (W10) and W18 post-hatch. In phase 2, we analysed air space and marrow volume change through the first 22 weeks of post-hatch development. Our results indicate that pneumatization of the humerus begins between W2 and W4 post-hatch, with air spaces expanding distally from the proximal humerus. Internal air space expands most rapidly between W7 and W9, with maximal volume reached at W15. Increased marrow growth occurs between W13 and W19, coincident with stabilization and a potential decline in relative air space volume. Our study highlights a dynamic relationship between bone, marrow and pneumatic epithelium, suggesting pneumaticity expression is likely impacted by both within-bone tissue growth dynamics and extrinsic factors related to forelimb function. This work provides the necessary gross anatomical framework for subsequent analyses of tissue-level and cellular mechanisms related to the pneumatization process.This article is part of the theme issue ‘The biology of the avian respiratory system’.

Phosphatic concretions in terrestrial settings are often identified as coprolites based upon their biotic contents and high phosphorus levels. However, recent discoveries have shown that non-fecal origins of fossiliferous phosphatic concretions are more common than originally recognized. Confusion about the taphonomic origin of phosphatic concretions can lead to erroneous paleobiological and paleoenvironmental interpretations, so a set of criteria would be useful to evaluate whether a phosphatic concretion is a coprolite. Here we describe a phosphatic concretion containing a small crocodylian from the Upper Cretaceous Hell Creek Formation and assess its origin, formation, and paleobiological implications. We conducted neutron computed tomography (CT) on the skull-bearing portion of the concretion, and analyzed the geochemical composition of the concretion with electron microprobe, µ-XRF, and fusion ICP-OES. In this study, the completeness and distribution of the skeletal elements present a stronger case for a non-fecal origin. This scenario suggests minimal transport after death and deposition. Neutron CT analysis of the crocodylian skull supports its referral to Brachychampsa montana, and allows inferences regarding body length, age, and dietary habits. Although coprolites and non-fecal concretions can be difficult to differentiate, unique features can reflect differences in origin that offer different types of taphonomic and paleobiological information.

Background/Objectives: Arachnids are a megadiverse arthropod group. The present study investigated the chromosomes of pedipalpid tetrapulmonates (orders Amblypygi, Thelyphonida, Schizomida) and two arachnid orders of uncertain phylogenetic placement, Ricinulei and Solifugae, to reconstruct their karyotype evolution. Except for amblypygids, the cytogenetics of these arachnid orders was almost unknown prior to the present study. Methods: Chromosomes were investigated using methods of standard (Giemsa-stained preparations, banding techniques) and molecular cytogenetics (fluorescence in situ hybridization, comparative genomic hybridization). Results and Conclusions: New data for 38 species, combined with previously published data, suggest that ancestral arachnids possessed low to moderate 2n (22–40), monocentric chromosomes, one nucleolus organizer region (NOR), low levels of heterochromatin and recombinations, and no or homomorphic sex chromosomes. Karyotypes of Pedipalpi and Solifugae diversified via centric fusions, pericentric inversions, and changes in the pattern of NORs and, in solifuges, also through tandem fusions. Some solifuges display an enormous amount of constitutive heterochromatin and high NOR number. It is hypothesized that the common ancestor of amblypygids, thelyphonids, and spiders exhibited a homomorphic XY system, and that telomeric heterochromatin and NORs were involved in the evolution of amblypygid sex chromosomes. The new findings support the Cephalosomata clade (acariforms, palpigrades, and solifuges). Hypotheses concerning the origin of acariform holocentric chromosomes are presented. Unlike current phylogenetic hypotheses, the results suggest a sister relationship between Schizomida and a clade comprising other tetrapulmonates as well as a polyploidization in the common ancestor of the clade comprising Araneae, Amblypygi, and Thelyphonida.

Fossils representing Cretaceous lineages of crown clade birds (Aves) are exceptionally rare but are crucial to elucidating major ecological shifts across early avian divergences. Among the earliest known putative crown birds is Vegavis iaai1, 2, 3, 4–5, a foot-propelled diver from the latest Cretaceous (69.2–68.4 million years ago)⁶ of Antarctica with controversial phylogenetic affinities2,7, 8, 9–10. Initially recovered by phylogenetic analyses as a stem anatid (ducks and closely related species)1,2,11, Vegavis has since been recovered as a stem member of Anseriformes (waterfowl)7, 8–9, or outside Aves altogether¹⁰. Here we report a new, nearly complete skull of Vegavis that provides new insight into its feeding ecology and exhibits morphologies that support placement among waterfowl within crown-group birds. Vegavis has an avian beak (absence of teeth and reduced maxilla) and brain shape (hyperinflated cerebrum and ventrally shifted optic lobes). The temporal fossa is well excavated and expansive, indicating that this bird had hypertrophied jaw musculature. The beak is narrow and pointed, and the mandible lacks retroarticular processes. Together, these features comprise a feeding apparatus unlike that of any other known anseriform but like that of other extant birds that capture prey underwater (for example, grebes and loons). The Cretaceous occurrence of Vegavis, with a feeding ecology unique among known Galloanserae (waterfowl and landfowl), is further indication that the earliest anseriform divergences were marked by evolutionary experiments unrepresented in the extant diversity3,11, 12–13.

Cryptic genetic differentiation is being increasingly documented in birds and other organisms using genome‐wide variation. A recent example of cryptic genetic differentiation in a widespread species with conserved morphology is the northern house wren Troglodytes aedon. We found that, despite extremely similar morphology and no documented vocal differences, the two subspecies of the northern house wren, T. a. aedon (eastern) and T. a. parkmanii (western), exhibited both nuclear and mitochondrial genomic differentiation. Individuals present along the Front Range of the Colorado Rocky Mountains possessed nuclear genetic variation intermediate between T. a. aedon and T. a. parkmanii; additionally, both divergent mitochondrial lineages, corresponding to the western and eastern northern house wren populations, occur in Colorado. However, the dynamics of this putative contact zone (i.e. amount of hybridization or introgression) and the degree of differentiation between the two subspecies remain uncharacterized. To expand our understanding of northern house wren population genetic differentiation and explore the possibility of hybridization, we used a double digest restriction‐site associated (ddRAD) approach and sequenced 127 northern house wrens, including 109 individuals from across Colorado and Wyoming, as well as nine individuals each from eastern and western allopatric regions. Our results highlight that T. a. aedon occur significantly further west than previously thought, and provide evidence for weak population structure within the northern house wren, while generally setting the stage for future investigations of northern house wren population genomics and the genetic basis of cryptic speciation.

Ceratosaurus is a large‐bodied non‐avian theropod dinosaur known from the Upper Jurassic Morrison Formation of North America and is remarkable both for its exceptionally fast annual growth rate and its status as the only theropod currently known with postcranial osteoderms. We describe the osteohistology of three hind limb bones, two dorsal ribs, and one osteoderm representing four individuals of Ceratosaurus . In addition to describing the tissues of these bones, we compared the annual growth rates from three individuals in our sample to those of five other ceratosaurians. We fit seven growth models to two of the specimens in our sample and compared the results of the best‐fit model(s) to those of two other ceratosaurians ( Masiakasaurus knopfleri and Majungasaurus crenatissimus ) for which sufficient growth data were available. The bone tissue of hind limbs in Ceratosaurus is highly vascularized, with dense plexiform or reticular vascular complexes and alternating strips of parallel or woven‐fibered matrix. Few lines of arrested growth were recorded in hind limbs prior to specimens achieving asymptotic body size. Both sampled dorsal ribs are highly remodeled, with only small portions of primary bone visible in each section, revealing parallel‐fibered bone with sparse primary osteons. Both dorsal ribs contain numerous lines of arrested growth throughout the cortex that allowed for more accurate estimates of individual age when paired with the data from hind limbs. The osteoderm is composed of a core of large Haversian canals and a perimeter of lamellar bone with dense Sharpey's fibers along the internal surface of the bone. Multiple LAGs are also present within the lamellar bone along the exterior margins. Maximum annual growth rates in Ceratosaurus were on average nine‐fold faster than those of other ceratosaurians. Our sample lacks data from juveniles so confidence in inferred growth models is limited. Thus, to begin to constrain Ceratosaurus growth patterns, we averaged the results of all models that possessed an Akaike Information Criterion score corrected for small sample size (AICc) within 10 of the lowest scoring model. We found that the monomolecular model exhibited the lowest AICc value, with the von Bertalanffy and Gompertz models possessing AICc values within 10 units of it. In contrast, the logistic and Gompertz models were confidently selected for Masiakasaurus and Majungasaurus , respectively. Irrespective of growth model, maximum relative annual growth rates for Ceratosaurus were several‐fold greater than those of Masiakasaurus and Majungasaurus. Both histological and growth model estimates of life history support an evolutionary trend towards more prolonged development in Ceratosauria through evolutionary time.

Planetaria are not autonomous systems that, when left to their own devices, can function. The projectors, buildings and exhibitions require people to perform and people to view their performances. The people featured in this chapter range from the titanic figures who have left an undeniable mark on the sector, to those everyday planetarians still working in the archives, at the front desk, and behind the projector. This chapter is also looking at how the visitors interact with the planetarium, and how the planetarium can interact with the local community.

Cobweb spiders, or Theridiidae, with just over 2500 species, are the fourth largest spider family. They are usually small to medium-sized species that can occur worldwide in all terrestrial habitats. The common name cobweb spider refers to their web type. Occasionally, they are also called tangle-web spiders, but this is a rather vague term (who knows exactly what this means) because there are many theridiids that build other types of webs or none at all.

The yellow sac spider family has a turbulent history, as the classic yellow sac spiders, which are primarily discussed here, have changed their family affiliation three times in the last 30 years. Today, they form their own family, as was already proposed back in 1887. Almost 400 species are currently counted among 14 genera of Cheiracanthiidae.

The family of tube-dwelling spiders, Segestriidae, comprises around 180 species worldwide. They are predominantly small to medium-sized spiders that have only six eyes (which you might only see at a second glance, Fig. 4.9), have a cylindrical body structure, and betray themselves through a characteristic leg position. Three pairs of legs are directed forward, with only one pair toward the back (Fig. 21.1). Especially when the animals are in their retreat and waiting for passing prey, it is remarkable to see these six legs. With this lurking position, a prey animal can probably be caught faster or more securely than if only four legs were stretched forward. However, this would still need to be scientifically tested.

Nearly 13% of all spider species are jumping spiders (Salticidae). With over 6500 species, they are the most species-rich family of all. Jumping spiders are found throughout the world and are abundant in all terrestrial habitats. They do not build capture webs but stalk their prey before jumping on it to overpower it (hence their name). This is followed by a bite with the mouthparts, preferably in the head or thorax area, where the large muscle packages and nerve centers of their prey are located and where their venom works particularly quickly.

Ground spiders are generally poorly known, as they are nocturnal and usually live quite cryptically. They are a group of spiders distributed worldwide and, with almost 2500 species, represent the sixth largest family. They are small to medium-sized spiders, most of which are colored in brown and black tones, often with parts of the body covered in velvety hairs.

With nearly 300 species, Uloboridae is a species-poor family of spiders, predominantly found in the subtropics and tropics, with only a few species reaching into the temperate zone. These predominantly small animals of 3–10 mm body length have, as a very special feature among spiders, completely reduced their venom glands. The reasons for this are unknown. It does mean, though, that they cannot envenomate captured prey, instead they must immediately wrap up a captured insect. Uloboridae have, therefore, become true packaging artists who wrap their prey so perfectly that escape is no longer possible. Apparently, the loss of venom glands has been more than adequately compensated in this way.

Linyphiidae comprise nearly 5000 species worldwide, making them the second most common spider family after the jumping spiders. They are web-building spiders with a body length of 1–8 mm (although most species are only 1–3 mm), which are recognizable by their horizontal sheet webs. Ground-dwelling linyphiids build their tiny sheet webs in crevices in the ground, which can be seen early in the morning with dew covering the silk. Aerial webs built by spiders in this family often consist of a horizontal or dome-shaped web sheet, frequently called the canopy due to the way it curves downward at the peripheries. In some species, the web sheet is shaped more like a cup or container; these webs are often referred to as “bowl and doily” webs because of their shape. With a system of suspension and alarm threads, the web sheet is held under tension both above and below and is anchored to the vegetation. Contact with these threads causes approaching animals to create vibrations, which are transmitted to the web sheet. The spider thus receives information about whether it is a potential prey or a predator, allowing it to react accordingly: attack or escape. The eight small eyes, on the other hand, do not facilitate visual orientation (Fig. 4.22).

Dictynidae, with around 500 species, is a globally distributed family of predominantly small spiders. Mesh-weavers belong to the cribellate spiders, which incorporate mesh threads (Chap. 1) into their small webs. These webs usually appear unstructured and are mostly deployed on plants, often around the spider’s retreat.

Funnel-web spiders are a family of medium to large (up to 18 mm) spiders, with almost 1400 species in 100 genera worldwide. They are web-building animals, and their web form also gives them their English name. Their web consists of a retreat open on both sides, with its edge widening on one side to form a catching sheet, so that the whole structure resembles an open-cut funnel (Fig. 5.1). Often, the catching sheet is anchored to the side and above with hanging threads or threads in tension, depending on the possibilities offered by the surroundings.

When we, as spider researchers, talk to laypeople about our favorite animals, two completely different reactions are normal: (1) Ah, these are the animals that build those beautiful webs (they always mean orb webs); or (2) Oh my goodness, these are the big, ugly, hairy creatures that lurk in our bathrooms and are even venomous. We, therefore, regularly experience the fact that we are sure to attract attention, as the fascination with spiders is always there, whether it is positive or negative. But what exactly do spiders look like, and what is so special about them? In this introductory chapter, we describe the most important features of the structure and life of spiders. For those who want to know more about this fascinating group of animals, we are happy to refer you to our introductory book, “All You Need to Know About Spiders.”

In this chapter, we offer various identification aids to determine the house spiders discussed here. We will not go to the species level but will be able to resolve their family affiliation. Such identification keys differ in their difficulty depending on the spider species and your prior knowledge. For this reason, in addition to a classic dichotomous identification key, where you always decide step by step between two characteristics, we also offer identification aids based on how commonly the spiders occur and some of their particularly striking features.