“…The avian chondrocranium is characterized by only a few specific features that distinguishes it from that of non-avian sauropsids and which are shared with other archosaurs [ 11 ]. There are descriptions of chondrocranial development of particular species [ 25 , 28 , 45 – 58 ] and several aspects of the development of the bird chondrocranium have been discussed before [ 11 , 44 , 59 , 60 ], but without a consideration of phylogeny as currently understood. Fig.…”
Section: Resultsmentioning
confidence: 99%
“…In birds, the parachordal cartilage is continuous below and above the notochord from its first chondrification on [ 11 ] (Table 1 ), and is therefore occasionally called perichordal [ 46 , 47 , 65 ]. The parachordal cartilage in the kiwi Apteryx australis [ 57 ] was interpreted as being paired [ 44 , 47 , 64 ], despite the detailed description of its formation and its fusion in the precartilage state [ 57 ]. Suschkin [ 48 ] argued that the dye (carmine) used by Parker [ 57 ] was not suitable for staining intercellular substance and that because of the difference in chondrogenesis between the median and lateral part of the parachordal cartilage, the median aspect was less obvious and gave the impression of a paired anlage.…”
Section: The Basal Plate and The Fenestra Basicranialis Posteriormentioning
confidence: 99%
“…In Phalacrocorax [ 61 ], the anlage of the pila antotica was already present when the acrochordal cartilage was still mesenchymal. In other birds, the pila antotica followed the onset of chondrification in the acrochordal cartilage (Table 2 ), since they share the centre of chondrification [ 44 ]. In birds, the pila antotica started to chondrify much earlier compared to the ancestral sequence (Fig.…”
Section: The Orbital Regionmentioning
confidence: 99%
“…Either the planum antorbitale develops from the parietotectal cartilage ( Spheniscus [ 47 ], Gallus [ 69 ]) (Figs. 7 b and 12 ), had its origin in the anterior orbital cartilage ( Melopsittacus [ 49 ]), formed from the trabeculae ( Falco [ 48 ], Gallus [ 64 ]), or developed from the paranasal cartilage ( Streptopelia [ 44 ]). Even the development from an independent chondrification centre was described ( Anas [ 46 ], Euplectes [ 50 ], Coturnix [ 75 ]).…”
Section: The Nasal Regionmentioning
confidence: 99%
“…The latter does not run parallel with the ossification sequence [ 11 ]. The chondrification sequence in birds has not been analyzed, although the chondrocranium of many species has been described [ 44 ]. This is mainly because of questionable homologization, missing analytical methodology, and a stable within-bird phylogeny.…”
Background
Birds exhibit an enormous diversity in adult skull shape (disparity), while their embryonic chondrocrania are considered to be conserved across species. However, there may be chondrocranial features that are diagnostic for bird clades or for Aves as a whole. We synthesized and analyzed information on the sequence of chondrification of 23 elements in ten bird species and five outgroups. Moreover, we critically considered the developmental morphology of the chondrocrania of 21 bird species and examined whether the diversity in adult skull shape is reflected in the development of the embryonic skull, and whether there are group-specific developmental patterns.
Results
We found that chondrocranial morphology is largely uniform in its major features, with some variation in the presence or absence of fenestrae and other parts. In kiwis (Apteryx), the unique morphology of the bony skull in the orbito-nasal region is reflected in its chondrocranial anatomy. Finally, differences in morphology and chondrification sequence may distinguish between different Palaeognathae and Neognathae and between the Galloanserae and Neoaves. The sequence of chondrification is largely conserved in birds, but with some variation in most regions. The peri- and prechordal areas in the base of the chondrocranium are largely conserved. In contrast to the outgroups, chondrification in birds starts in the acrochordal cartilage and the basicranial fenestra is formed secondarily. Further differences concern the orbital region, including early chondrification of the pila antotica and the late formation of the planum supraseptale.
Conclusion
Synthesizing information on chondrocranial development confronts terminological issues and a lack of comparable methods used (e.g., different staining; whole-mounts versus histology). These issues were taken into consideration when assessing differences across species. The summary of works on avian chondrocranial development, covered more than a century, and a comparison of the chondrification sequence among birds could be conducted. Future studies could test the hypothesis that chondrocranial disparity in Aves, in terms of the shape and proportion of individual elements, could be as large as adult skull disparity, despite conserved developmental patterns and the richness of forms in other (dermal) portions of the skull.
“…The avian chondrocranium is characterized by only a few specific features that distinguishes it from that of non-avian sauropsids and which are shared with other archosaurs [ 11 ]. There are descriptions of chondrocranial development of particular species [ 25 , 28 , 45 – 58 ] and several aspects of the development of the bird chondrocranium have been discussed before [ 11 , 44 , 59 , 60 ], but without a consideration of phylogeny as currently understood. Fig.…”
Section: Resultsmentioning
confidence: 99%
“…In birds, the parachordal cartilage is continuous below and above the notochord from its first chondrification on [ 11 ] (Table 1 ), and is therefore occasionally called perichordal [ 46 , 47 , 65 ]. The parachordal cartilage in the kiwi Apteryx australis [ 57 ] was interpreted as being paired [ 44 , 47 , 64 ], despite the detailed description of its formation and its fusion in the precartilage state [ 57 ]. Suschkin [ 48 ] argued that the dye (carmine) used by Parker [ 57 ] was not suitable for staining intercellular substance and that because of the difference in chondrogenesis between the median and lateral part of the parachordal cartilage, the median aspect was less obvious and gave the impression of a paired anlage.…”
Section: The Basal Plate and The Fenestra Basicranialis Posteriormentioning
confidence: 99%
“…In Phalacrocorax [ 61 ], the anlage of the pila antotica was already present when the acrochordal cartilage was still mesenchymal. In other birds, the pila antotica followed the onset of chondrification in the acrochordal cartilage (Table 2 ), since they share the centre of chondrification [ 44 ]. In birds, the pila antotica started to chondrify much earlier compared to the ancestral sequence (Fig.…”
Section: The Orbital Regionmentioning
confidence: 99%
“…Either the planum antorbitale develops from the parietotectal cartilage ( Spheniscus [ 47 ], Gallus [ 69 ]) (Figs. 7 b and 12 ), had its origin in the anterior orbital cartilage ( Melopsittacus [ 49 ]), formed from the trabeculae ( Falco [ 48 ], Gallus [ 64 ]), or developed from the paranasal cartilage ( Streptopelia [ 44 ]). Even the development from an independent chondrification centre was described ( Anas [ 46 ], Euplectes [ 50 ], Coturnix [ 75 ]).…”
Section: The Nasal Regionmentioning
confidence: 99%
“…The latter does not run parallel with the ossification sequence [ 11 ]. The chondrification sequence in birds has not been analyzed, although the chondrocranium of many species has been described [ 44 ]. This is mainly because of questionable homologization, missing analytical methodology, and a stable within-bird phylogeny.…”
Background
Birds exhibit an enormous diversity in adult skull shape (disparity), while their embryonic chondrocrania are considered to be conserved across species. However, there may be chondrocranial features that are diagnostic for bird clades or for Aves as a whole. We synthesized and analyzed information on the sequence of chondrification of 23 elements in ten bird species and five outgroups. Moreover, we critically considered the developmental morphology of the chondrocrania of 21 bird species and examined whether the diversity in adult skull shape is reflected in the development of the embryonic skull, and whether there are group-specific developmental patterns.
Results
We found that chondrocranial morphology is largely uniform in its major features, with some variation in the presence or absence of fenestrae and other parts. In kiwis (Apteryx), the unique morphology of the bony skull in the orbito-nasal region is reflected in its chondrocranial anatomy. Finally, differences in morphology and chondrification sequence may distinguish between different Palaeognathae and Neognathae and between the Galloanserae and Neoaves. The sequence of chondrification is largely conserved in birds, but with some variation in most regions. The peri- and prechordal areas in the base of the chondrocranium are largely conserved. In contrast to the outgroups, chondrification in birds starts in the acrochordal cartilage and the basicranial fenestra is formed secondarily. Further differences concern the orbital region, including early chondrification of the pila antotica and the late formation of the planum supraseptale.
Conclusion
Synthesizing information on chondrocranial development confronts terminological issues and a lack of comparable methods used (e.g., different staining; whole-mounts versus histology). These issues were taken into consideration when assessing differences across species. The summary of works on avian chondrocranial development, covered more than a century, and a comparison of the chondrification sequence among birds could be conducted. Future studies could test the hypothesis that chondrocranial disparity in Aves, in terms of the shape and proportion of individual elements, could be as large as adult skull disparity, despite conserved developmental patterns and the richness of forms in other (dermal) portions of the skull.
Turbinals are bony or cartilaginous structures that are present in the nasal cavity of most tetrapods. They are involved in key functions such as olfaction, heat, and moisture conservation, as well as protection of the respiratory tract. Despite recent studies that challenged long‐standing hypotheses about their physiological and genomic correlation, turbinals remain largely unexplored, particularly for non‐mammalian species. Herein, we review and synthesise the current knowledge of turbinals using an integrative approach that includes comparative anatomy, physiology, histology and genomics. In addition, we provide synonyms and correspondences of tetrapod turbinals from about 80 publications. This work represents a first step towards drawing hypotheses of homology for the whole clade, and provides a strong basis to develop new research avenues.
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