Ostrich (Struthio camelus) syrinx morphology and vocal repertoire across postnatal ontogeny and sex: Implications for understanding vocal evolution in birds.

Vocal production in birds has been the target of considerable research that mostly has focused on phylogenetically well-nested songbirds. Anatomical descriptions and recordings of many non-songbirds have often only focused on a single ontogenetic stage or sex. While basic morphology of the vocal organ (syrinx) of ostrich (Palaeognathae, Struthio camelus) has been known since the 1800s, descriptions of its vocal repertoire and syrinx anatomy since then have been incomplete or inconsistent. New toolkits now enable detailed qualitative description of internal anatomy and meristic data and allow it to be compared to vocal production. Here we describe the anatomy of the syrinx in Struthio camelus for three post-hatching ontogenetic stages and both an adult male and female utilizing dissection and contrast enhanced X-ray computed tomography (diceCT). We find changes in ring geometry and spacing through ontogeny as well as lateral labia thickness. We document a small unpaired, midline, cartilaginous structure, a "pessuliform process" at the tracheobronchial juncture present throughout ontogeny and in both males and females. Investigation of the vocal repertoire of ostriches across ontogeny using a new dataset of 77 recordings led to identification of four vocalizations not previously reported in the literature, including the simultaneous production of a hiss and tonal. We find syrinx morphology largely consistent across ontogeny and in male and female adults. Both are capable of producing long duration tonal calls, but these may be more frequent in male birds. Closed-mouth boom calls remain unique to males. A detailed understanding of diversity in parts of early diverging clades is pivotal in attempting to estimate features of the ancestral syrinx in birds and how avian vocalization evolved.

Comparison of embryonic development, from HH21 to HH40, between ostrich (Struthio camelus) and chicken (Gallus gallus).

BACKGROUND: The chicken has been a representative model organism to study embryonic development in birds, however important differences exist among this class of species. As a representative of one of oldest existing clades of birds, the African ostrich (Struthio camelus), has the largest body among birds, and has two toes. Our purpose is to establish the corresponding stages in ostrich embryo development that match the well-established HH system of the chicken to facilitate comparative studies between the ostrich and other birds to better understand differences in development. RESULTS: Here we describe in detail the middle period of embryonic development using microscopic images and skeletal staining. We found that clear morphological differentiation between the ostrich and the chicken begins at stage 26. Bird limb cartilage first form in stage 25, while the development of the limb skeletons differs after stage 31. Calcification of limb skeletons in the chicken was completed faster. The first and second toes of the ostrich disappear at stages 36 and 38, respectively. CONCLUSIONS: This study should greatly aid ostrich-related developmental and morphological research and provide a reference for studying the development and evolution of avian limb skeletons, including molecular research. Questions that can now be addressed include studies into the fusion of tarsometatarsal skeleton, ossification, and digit loss.

Anatomy, ontogeny, and evolution of the archosaurian respiratory system: A case study on Alligator mississippiensis and Struthio camelus.

The avian lung is highly specialized and is both functionally and morphologically distinct from that of their closest extant relatives, the crocodilians. It is highly partitioned, with a unidirectionally ventilated and immobilized gas-exchanging lung, and functionally decoupled, compliant, poorly vascularized ventilatory air-sacs. To understand the evolutionary history of the archosaurian respiratory system, it is essential to determine which anatomical characteristics are shared between birds and crocodilians and the role these shared traits play in their respective respiratory biology. To begin to address this larger question, we examined the anatomy of the lung and bronchial tree of 10 American alligators (Alligator mississippiensis) and 11 ostriches (Struthio camelus) across an ontogenetic series using traditional and micro-computed tomography (µCT), three-dimensional (3D) digital models, and morphometry. Intraspecific variation and left to right asymmetry were present in certain aspects of the bronchial tree of both taxa but was particularly evident in the cardiac (medial) region of the lungs of alligators and the caudal aspect of the bronchial tree in both species. The cross-sectional area of the primary bronchus at the level of the major secondary airways and cross-sectional area of ostia scaled either isometrically or negatively allometrically in alligators and isometrically or positively allometrically in ostriches with respect to body mass. Of 15 lung metrics, five were significantly different between the alligator and ostrich, suggesting that these aspects of the lung are more interspecifically plastic in archosaurs. One metric, the distances between the carina and each of the major secondary airways, had minimal intraspecific or ontogenetic variation in both alligators and ostriches, and thus may be a conserved trait in both taxa. In contrast to previous descriptions, the 3D digital models and CT scan data demonstrate that the pulmonary diverticula pneumatize the axial skeleton of the ostrich directly from the gas-exchanging pulmonary tissues instead of the air sacs. Global and specific comparisons between the bronchial topography of the alligator and ostrich reveal multiple possible homologies, suggesting that certain structural aspects of the bronchial tree are likely conserved across Archosauria, and may have been present in the ancestral archosaurian lung.

Anatomy of the Tarsometatarsal Region and Digits in the Ostrich (Struthio Camelus): A Computed Tomography and Cross-Sectional Study.

The ostrich is the largest living bird and has unique characteristics in its locomotor system that differentiate it from other bird species. The purpose of this study was to provide a reference atlas of reference-interval computed tomography (CT) and cross-sectional anatomy of the tarsometatarsal region and digits in the ostrich (Struthio camelus). The pelvic limbs of 25 ostriches were used for this imaging study. The transverse CT images were obtained from the middle third of the tarsometatarsal bone to the distal end of the third digit. The specimens were frozen and sectioned with an electric band saw at 1.5-2 cm intervals. The CT images were compared with the corresponding frozen cross sections. The bones, ligaments, and tendons were identified and labeled at each 1.5-2 cm intervals. The CT images provided anatomic details of the tendons and ligaments in the tarsometatarsal region and digits of the ostrich. The transverse CT images provided an excellent depiction of the anatomic structures of the leg and foot when compared with the corresponding frozen cross sections. The information presented in this study may be used as an initial reference when evaluating the CT images of an ostrich's tarsometatarsal region and digits. Moreover, the information provided in this report may be helpful in determining definitive diagnoses of musculoskeletal disorders affecting the lower leg in this species.

Sex-related differences of bone properties of pelvic limb and bone metabolism indices in 14-month-old ostriches (Struthio camelus).

1. Sex-related differences of long pelvic limb bones and serum bone metabolism indices were evaluated in 14-month-old female (N = 7) and male (N = 7) ostriches of similar body weights. 2. Densitometric parameters of femur, tibia and tarsometatarsus were determined using quantitative computed tomography (volumetric bone mineral density, calcium hydroxyapatite density and mean volumetric bone mineral density) and dual energy X-ray absorptiometry (bone mineral density and bone mineral content) methods. Geometrical parameters such as cortical bone area, cross-sectional area, second moment of inertia, mean relative wall thickness and cortical index were determined in the midshaft of bones. Mechanical properties of bones (maximum elastic strength and ultimate strength) were evaluated using three-point bending test. Serum concentrations of free amino acids, osteocalcin, N-terminal propeptide of type I procollagen, C-terminal telopeptides of type II collagen and total antioxidative capacity were also determined. 3. Bone weight and relative bone weight of all bones were significantly higher in males than in females. Significantly lower values of trabecular bone mineral density and calcium hydroxyapatite density were found in the trabecular bone of tibia in males. The highest number of the sex-related differences was observed in the tarsometatarsus where bone length, bone mineral content, cortical bone area, cross-sectional area and ultimate strength were higher in males. Serum concentrations of taurine, hydroxyproline, valine and isoleucine were significantly higher in males. 4. Higher loading of the tarsometatarsus in comparison to femur and tibia may be an important factor interacting with sex hormones in regulation of bone formation and mineralisation processes. Sex-related differences of bone properties were associated with increased serum concentration of selected amino acids in males.

Radiographic Anatomy of the Metatarsophalangeal Joint and Digits of the Ostrich (Struthio camelus).

The aim of this study was to develop a detailed and accessible set of reference images of the normal radiographic anatomy of the digits of the ostrich (Struthio camelus), with emphasis on the metatarsophalangeal joint and its arthrography. The distal excised pelvic limbs of 10 normal ostriches of different ages (ranging from 10 to 365 days of age) obtained from an abattoir were radiographed, and 2 arthrograms were performed. To illustrate the normal radiographic anatomy of the tarsometatarsal bone, 39 images were selected, labelled, and presented along with detailed descriptions and corresponding images of the bony skeleton. These results provide a valuable dataset to assist in understanding the normal anatomy of the ostrich metatarsophalangeal joint and digits and allow comparison of abnormal corresponding structures in clinical cases in ostriches.

Phenotypic and genetic variability for body weight of ostriches (Struthio camelus).

1. objective of the present study was to estimate heritability for hatch weight (HW), body weight at 90 (W90) and 180 (W180) d of age in Brazilian ostriches. 2. The heritability estimates were obtained through the restricted maximum likelihood method for an animal model. Least squares method was used to define possible fixed effects for consideration in the analysis model. 3. The estimates of heritability were 0.42 ± 0.05, 0.16 ± 0.04 and 0.24 ± 0.08 for HW, W90 and W180, respectively. 4. Heritability estimates showed that there are sufficient levels of additive genetic variation present in the traits studied, and these traits may respond to selection.

Mechanical and energetic scaling relationships of running gait through ontogeny in the ostrich (Struthio camelus).

It is unclear whether small animals, with their high stride frequency and crouched posture, or large animals, with more tendinous limbs, are more reliant on storage and return of elastic energy during locomotion. The ostrich has a limb structure that appears to be adapted for high-speed running with long tendons and short muscle fibres. Here we investigate biomechanics of ostrich gait through growth and, with consideration of anatomical data, identify scaling relationships with increasing body size, relating to forces acting on the musculoskeletal structures, effective mechanical advantage (EMA) and mechanical work. Kinematic and kinetic data were collected through growth from running ostriches. Joint moments scaled in a similar way to the pelvic limb segments as a result of consistent posture through growth, such that EMA was independent of body mass. Because no postural change was observed, relative loads applied to musculoskeletal tissues would be predicted to increase during growth, with greater muscle, and hence tendon, load allowing increased potential for elastic energy storage with increasing size. Mass-specific mechanical work per unit distance was independent of body mass, resulting in a small but significant increase in the contribution of elastic energy storage to locomotor economy in larger ostriches.

Sex-related differences of morphometric, densitometric, and geometric parameters of tibia and tarsometatarsal bone in 14-month-old ostriches (Struthio camelus).

The aim of the current study was to investigate basic morphometric, geometric, and densitometric parameters of tibia and tarsometatarsus in 14-mo-old male and female ostriches, and interrelationships between these parameters. The study was conducted on 20 tibiae and 20 tarsometatarsal bones of the left pelvic limb derived from 20 healthy 14-mo-old ostriches (Struthio camelus): 10 males and 10 females. The following parameters were determined using peripheral quantitative computed tomography: bone mineral content (BMC), volumetric bone mineral density (vBMD), cortical content (CRT_CNT), cortical density (CRT_DEN), trabecular content, trabecular density (TRAB_DEN), bone area (TOT_A), trabecular area (TRAB_A), cortical area (CRT_A), cortical thickness (CRT_THK_C), periosteal circumference (PERI_C), endocortical circumference (ENDO_C), and strength-strain index (SSI) in the metaphysis and diaphysis of the bones. Statistical evaluation of the obtained results was performed using Student's t-test, and the Pearson correlation coefficient between the investigated parameters was determined. The obtained results have shown significant differences in proximal metaphysis between males and females when evaluating such parameters as CRT_DEN, TOT_A, TRAB_A, PERI_C, SSI in tibia (P < 0.05), and BMC, vBMD, TRAB_DEN, CRT_CNT, TOT_A, TRAB_A, cortical area, PERI_C, ENDO_C, SSI in tarsometatarsus (P < 0.05). Significant differences between the 2 sexes were found in all the investigated parameters of diaphysis of tibia, except for CRT_DEN and ENDO_C (P < 0.05). Significant positive correlations between BW and bone weight were found (P < 0.05). Furthermore, numerous correlations of morphometric, geometric, and densitometric parameters of metaphysis and diaphysis of the tibia and tarsometatarsus were stated (P < 0.05). In conclusion, the present investigation demonstrated sex-related differences in morphometric, densitometric, and geometric properties of tibia and tarsometatarsus in 14-mo-old ostriches. Numerous correleations observed between the investigated parameters have shown that ostrich tibia and tarsometatarsus may present a valuable model for further studies on bone tissue metabolism regulation in breeding birds.

[Structural organization of anterior corneal epithelium of the African ostrich eye].

This investigation was aimed at the histological study of anterior corneal epithelium (ACE) of adult male ostrich Struthio camelus Linnaeus, 1758 (Struthioniformes). The total thickness of ACE was equal to 48.5+/-1.1 microm. The geometry of epithelial cells was investigated. The basal cells had columnar shape; their average height was equal to 21.4+/-1.8 microm, average width - to 5.94+/-0,45 microm, configuration index was 3.84+/-0,50. The intermediate cells were predominantly ellipsoidal in shape; their average height was equal to 6.2+/-0.3 microm, average width - to 12.0+/-0.8 microm, configuration index was 0.54+/-0,06. The superficial cells were squamous, their average height was equal to 3.8+/-0.3 microm, average width - to 22.4+/-1.7 microm, configuration index was 0.18+/-0.02. Index of flattening of epithelial cells of the superficial layer was 5.8+/-0.5. Negative correlation (r+/-m=-0,72+/-0,13) was detected between the height and the width of the epithelial cells.

Soft tissues influence nasal airflow in diapsids: Implications for dinosaurs.

The nasal passage performs multiple functions in amniotes, including olfaction and thermoregulation. These functions would have been present in extinct animals as well. However, fossils preserve only low-resolution versions of the nasal passage due to loss of soft-tissue structures after death. To test the effects of these lower resolution models on interpretations of nasal physiology, we performed a broadly comparative analysis of the nasal passages in extant diapsid representatives, e.g., alligator, turkey, ostrich, iguana, and a monitor lizard. Using computational fluid dynamics, we simulated airflow through 3D reconstructed models of the different nasal passages and compared these soft-tissue-bounded results to similar analyses of the same airways under the lower-resolution limits imposed by fossilization. Airflow patterns in these bony-bounded airways were more homogeneous and slower flowing than those of their soft-tissue counterparts. These data indicate that bony-bounded airway reconstructions of extinct animal nasal passages are far too conservative and place overly restrictive physiological limitations on extinct species. In spite of the diverse array of nasal passage shapes, distinct similarities in airflow were observed, including consistent areas of nasal passage constriction such as the junction of the olfactory region and main airway. These nasal constrictions can reasonably be inferred to have been present in extinct taxa such as dinosaurs.

A test of the validity of range of motion studies of fossil archosaur elbow mobility using repeated-measures analysis and the extant phylogenetic bracket.

Recent studies have presented range of motion (ROM) data in degrees for dinosaur forelimb joints, usually via physical manipulation of one individual. Using these data, researchers have inferred limb orientations, postures, gaits, ecological functions and even phylogenetic trends within clades. However, important areas of concern remain unaddressed; for example, how does ROM at a forelimb joint change after soft tissues are lost in archosaurs? And are fossil ROM methodologies amenable to reproducibility and statistical analysis? Here, we investigated these questions using the extant phylogenetic bracket of dinosaurs. Repeated measures of elbow joint ROM from Struthio camelus and Alligator mississippiensis forelimbs were statistically analyzed as they were sequentially dissected through five levels of tissue removal treatment. Our data indicate that there are no statistically significant differences in repeated measures of ROM between observers who use the same techniques. Extrinsic soft tissues, such as integument, muscles and ligaments were found to impede ROM at the elbow joint. Intrinsic soft tissues, such as articular cartilage, may increase ROM. The hypothesis that the articular surfaces of the bones within the elbow joints of archosaurs provide a general approximation of mobility is supported. Final ROMs were less than the initial ROMs in both taxa, which suggests that prior reports of elbow joint ROMs in degrees for nonavian dinosaurs may represent conservative estimates. We conclude that if observer bias and other variables are controlled for, ROM studies of fossil archosaur limbs can obtain useful degree data for inferring joint mobility in vivo.

"Ostrich sign" indicates bilateral vertebral artery dissection.

Vertebral artery dissections (VADs) comprise about 2% of ischemic strokes and can be associated with trauma, chiropractic manipulation, motor vehicle collisions, whiplash, amusement park rides, golfing, and other motion-induced injuries to the neck. We present a case of bilateral extracranial VAD as a complication of conducting an orchestra. To our knowledge, this has not been documented in the literature. Conceivably, vigorous neck twisting in an inexperienced, amateur conductor may place excessive rotational forces upon mobile portions of the verterbral arteries, tear the intima, deposit subintimal blood that extends longitudinally, and cause neck pain and/or posterior fossa ischemic symptoms. Magnetic resonance angiography examinations of axially oriented slices of bilateral VADs resemble the face of an ostrich. This observation is similar to the "puppy sign," in which bilateral internal carotid artery dissections resemble the face of a dog. Craniocervical dissections of either the carotid or vertebral arteries have the potential to form an aneurysm, cause artery-to-artery embolism, or completely occlude the parent artery, resulting in an ischemic stroke. Because bilateral VADs in axial magnetic resonance angiographic sections stand out like the eyes of an ostrich, and because the fast identification of VADs is so critical, we eponymize this image the "ostrich sign."

Genetic parameters for eggshell traits in ostriches.

1. A study was conducted on ~14000 ostrich eggs to estimate genetic parameters for eggshell traits that could benefit the hatchability of ostrich eggs. Traits measured included the number of pores on the eggshell, the average diameter of these pores, the total area of pores on the eggshell, permeability (pore area/shell thickness) and eggshell thickness. 2. Heritability estimates ranged from 0·16 for total pore area to 0·41 for the natural logarithm of pore count. The heritability estimates for water loss on 21 and 35 d (WL21 and WL35) of incubation were high at 0·23 and 0·24, respectively. 3. On a genetic level, pore count was negatively correlated with average pore diameter (-0·73) and shell thickness (-0·28), whereas it was positively correlated with total pore area (0·58), WL21 (0·24) and WL35 (0·34). The direct and maternal genetic correlations of pore count with total pore area (0·58) and permeability (0·59) were high and significant. Permeability was positively correlated to WL21 and WL35, both on the direct and maternal genetic levels. 4. The estimated genetic parameters indicate that it should be possible to select for the various eggshell traits in ostrich eggs, or for permeability and water loss. However, as a trait with an intermediate optimum, direct selection for permeability and other eggshell traits would not be straightforward, and the possible application of these results to improve hatchability of ostrich eggs in the future needs consideration.

A comparative study on the histological structure of the spleen in the ostrich (Struthio camelus), the kestrel (Falco tinnunculus) and the osprey (Pandion haliaetus).

The spleen structurally and functionally belongs to the hematopoietic organs and is also an important component of the reticuloendothelial system, which is known to play a major role in host defense. The histological structure of the spleen was investigated in the ostrich, a non-flying bird, the kestrel, a raptor, and the osprey, a fish-eating bird of prey (fish eagle). For this purpose, Mallory's modified triple stain, methyl green-pyronin and silver stain were used. Germinal centers were not present in the spleen of the osprey. In the spleen of the kestrel, penicillar arterioles and the surrounding lymphoid tissue were markedly dense. Compared to the other two birds, the red and white pulps were clearly distinguishable in the spleen of the ostrich.

Systematization, description, and territory of arteries that promote vascularization of the midbrain and rhombencephalon in the ostrich (Struthio camelus).

Brain specimens from 30 ostriches were injected with red-dyed latex via the internal carotid arteries (Aa.). The ventral tectal mesencephalic artery (a.), invariably a medium-sized single vessel, was, on the right side, a collateral branch of the caudal branch of the carotid artery (53.4%), a direct branch of the carotid artery (43.3%) and a direct branch of the basilar artery (3.3%) and on the left side, a collateral branch of the caudal branch of the carotid artery (66.7%), a direct branch of the carotid artery (30%), and a direct branch of the basilar artery (3.3%). It vascularized only the ventral half of the optic lobe, with no involvement in cerebellar vascularization on the right (93.3%) and left (80%) sides, extending to the ventrorostral-most cerebellar lobules, which were vascularized on the right (6.7%) and left (20%) sides. The caudal ventral cerebellar arteries were a single vessel on the right (96.7%) and left (93.3%) sides. Its first branch was a common trunk: dorsal spinal-caudal cerebellar on the right (60%) and left (56.6%) sides. Its second branch was the caudal cerebellar artery on the right (76.7%) and left (86.7%) sides. Its third branch was the second component of the caudal cerebellar artery on the right (6.7%) and left (3.3%) sides. The midbrain was vascularized by dorsal and ventral tectal mesencephalic arteries. The cerebellum was vascularized by branches of the caudal ventral cerebellar artery and by the dorsal cerebellar artery.

Ontogenetic endocranial shape change in alligators and ostriches and implications for the development of the non-avian dinosaur endocranium.

Birds and crocodiles show radically different patterns of brain development, and it is of interest to compare these to determine the pattern of brain growth expected in dinosaurs. Here we provide atlases of 3D brain (endocast) reconstructions for Alligator mississippiensis (alligator) and Struthio camelus (ostrich) through ontogeny, prepared as digital restorations from CT scans of stained head and dry skull specimens. Our morphometric analysis confirms that ostrich brains do not change significantly in shape during postnatal growth, whereas alligator brains unfold from a cramped bird-like shape in the hatchling to an elongate, straight structure in the adult. We confirm that birds exhibit paedomorphic dinosaur endocranial traits such as retaining an enlarged and compact brain shape in the adult, whereas crocodiles show peramorphic traits where the brain elongates with growth as the skull elongates. These atlases of ontogenetic stages of modern bird and crocodilian endocrania provide a basis for comparison of non-avian dinosaur endocasts and consideration of the divergence of the "avian" and "crocodilian" modes of brain development and heterochronic change on phylogenies.

Ontogenetic scaling of locomotor kinetics and kinematics of the ostrich (Struthio camelus).

Kinematic and kinetic parameters of running gait were investigated through growth in the ostrich, from two weeks up to 10 months of age, in order to investigate the effects of increasing body size. Ontogenetic scaling relationships were compared with published scaling relationships found to exist with increasing body size between species to determine whether dynamic similarity is maintained during growth. During the study, ostrich mass (M(b)) ranged from 0.7 kg to 108.8 kg. Morphological measurements showed that lengths scaled with positive allometry during growth (hip height proportional to M(b)(0.40); foot segment length proportional to M(b)(0.40); tarsometatarsus length proportional to M(b)(0.41); tibiotarsus length proportional to M(b)(0.38); femur length proportional to M(b)(0.37)), significantly exceeding the close to geometric scaling observed between mammalian and avian species of increasing body size. Scaling of kinematic variables largely agreed with predicted scaling for increasing size and demonstrated relationships close to dynamic similarity and, as such, ontogenetic scaling of locomotor parameters was similar to that observed with increasing body mass between species. However, the ways in which these scaling trends were achieved were very different, with ontogenetic scaling of locomotor mechanics largely resulting from simple scaling of the limb segments rather than postural changes, likely to be due to developmental constraints. Small deviations from dynamic similarity of kinematic parameters and a reduction in the predicted scaling of limb stiffness (proportional to M(b)(0.59)) were found to be accounted for by the positive allometric scaling of the limb during growth.

Study on bio-inspired feet based on the cushioning and shock absorption characteristics of the ostrich foot.

As the main actuator of high-speed running, the ostrich feet are highly capable of cushioning and shock absorption. In this study, based on the elastic modulus scales and assembly order of the 3rd toe soft tissues and the functions of the metatarsophalangeal (MTP) joint, we designed fourteen bio-inspired feet. The impact process on loose sand was simulated on the finite element software Abaqus. Also the stress distributions and deformations of each component of the bio-inspired feet were clarified. With the peak acceleration as the index, the cushioning performances of the bio-inspired feet were compared on both loose sand and solid ground through height-variable impact tests. The 15-15-15 HA (hardness unit) bio-inspired foot showed lower peak acceleration and thereby better cushioning performance, but larger deformation, less-uniform stress distribution and thereby lower stability than the 15-35-55 HA bio-inspired foot. In fact, the silicon rubbers with different hardness degrees (which simulate the elasticity modulus scales of the digital cushions, fascia and skin) and the spring mechanism (which simulates the functions of the MTP joint) work as an "integrated system" of cushioning and shock absorption.

Primary chondrification foci in the wing basipodium of Struthio camelus with comments on interpretation of autopodial elements in Crocodilia and Aves.

UNLABELLED: The present analysis consists of (1) description of the primary chondrification patterns and their transformation into ossified elements in the basipodium of Struthio camelus; (2) comparison of these with the conditions found in Alligator and Gallus; and (3) interpretation of the autopodial elements of Archaeopteryx. CONCLUSIONS: (1) The existence of five discrete metacarpal condensations in the 16-day embryo of Struthio argues for unique linear patterning process for each, and these are interpreted as digits 2,3,4 originating from metacarpal condensations 2,3,4. Nine chondrogenic foci appear in the Struthio carpus: radiale, centrale, intermedium, ulnare, pseudoulnare, pisiform, distal carpal 2+3, distal carpal 4, and distal carpal 5. It is evident that: (a) the avian "radiale" represents fused chondrogenic foci of the intermedium plus the radiale; (b) a neomorph carpal element, the pseudoulnare (probably avian autapomorphy), replaces the ulnare cartilage in Struthio; (c) the pseudoulnare in Struthio and Hinchliffe's element "X" are not identical to each other. (2) Spatio-temporal conditions of the autopodium are less constrained in the development of Struthio than they are in Gallus. This favors the ostrich model as the more appropriate for interpretation of the autopodial skeleton in the oldest birds and their ancestors. (3) An interpretation of the elements of the hand skeleton of Archaeopteryx is as follows: (a) digits 2,3,4; (b) distal carpal 2+3 (the semilunate); (c) distal carpal 4 (a missing element filling the gap between the semilunate and metacarpal IV); (d) the radiale+intermedium complex (the proximal carpal bone); (e) the pseudoulnare (the proximal carpal bone).