The basic differences between different dog species are their head shapes and skull sizes. Dog skull types are based on two main factors, the skull width and the length of the muzzle. These features can be traced back to the dog’s root word, cephalos, meaning “head.”
Canine craniofacial diversity
This diagram illustrates the incredible morphologic diversity in Canis familiaris. The skull base of different breeds is nearly parallel, but notable differences in skull shape are noted. The length of the cranial base and the position of the palate relative to the cranial base are also noteworthy. The cranial base is not completely parallel across breeds, and this causes the rostrum to be distorted in some cases.
Scientists analyzed the genetic data of dogs and their unaffected family members to determine the causative genes. Genetic variants found in afflicted family members are causal for the syndrome, but also co-exist in the unaffected family members. Linkage analysis models the coinheritance of makers and tests for significance of diagnostic status. Linkage analysis has provided much of the current knowledge on the genes responsible for craniofacial deformities.
Interestingly, canine craniofacial diversity is highly correlated with breeds with similar morphologies. Studies using mice have demonstrated the influence of intergenic variation on craniofacial morphology, while zebrafish are better suited to modeling the impact of genetic variation on craniofacial morphogenesis. In addition, mice are useful because of their rapid development. Finally, they are amenable to gene knockdown and overexpression, enabling researchers to better understand the effects of genetic variation on craniofacial morphology.
In addition to determining the genetic basis for avian craniofacial variation, research on canine craniofacial development has demonstrated that patterns of variation in pigeons are predictive of those seen in birds. In addition, these patterns of variation may be a result of structural limitations in the shared embryonic bauplan. Therefore, this research is extremely useful in understanding the genetic basis of craniofacial diversity in the canine species.
Patterns of cranial suture closure
The development of cranial sutures influences overall cranial morphology and function, and the patterns of closure among different types of skulls may reflect these functions. Suture development also shapes the diversity of cranial morphology among different taxa. This study reviewed suture development from an evolutionary developmental biology perspective and integrated it into a comparative evolutionary framework to understand the morphological and functional significance of different cranial types.
Previously, the sutures were classified by different techniques. In the case of human skulls, for example, cranial sutures were classified as either preadhesive or postadhesive. The former is characterized by numerous blood vessel holes and calcified matrix fiber bundles aligned in a parallel pattern. The latter displays an irregular pattern, and scattered calcium globules are often observed.
The suture morphology can reveal a wealth of information. Suture complexity, timing, and development, as well as suture fusion, can help us understand how these alterations influence cranial form. Suture morphology and cranial form are related across a number of scientific fields. In fact, the relationship between suture closure and cranial form is still poorly understood.
During the growth stage, the spheno-occipital synchondrosis may be prematurely closed, affecting the angulation of the craniospinal junction. This premature closure of spheno-occipital synchondrosis alters the angulation of the skull base and cervical vertebrae. The occipital condyles rotate rostrally and ventrally. In both cases, the craniocervical junction is rotated ventrally, causing a lateral deviation of the neck.
When the brain is developing, the skull grows to accommodate its growing mass. The growth of the cranial sutures determines the final shape of the skull. They develop at the sites of dural reflections. The inner dural layer descends into the brain and forms septa, dividing it into compartments. The dura responds to mechanical stresses in the expanding brain by secreting morphogenetic peptide growth factors.
Patterns of cranial suture closure in brachycephalic bulldog-type
The bred’s cranial shape and short nose are common occurrences among small brachycephalic breeds. While they are extremely popular and are often bred to be show dogs, these brachycephalic dogs have numerous health issues. Among these are: brachycephaly, a condition that can cause respiratory problems and impairs the ability of the dog to breathe properly; and a hiatus hernia. Some other common problems in brachycephalic dogs include: ear diseases, decreased hearing, corneal ulcers, and pigmentary keratitis.
Upper airway obstruction in brachycephalic dogs is common, with the English bulldog being the most severely affected breed. The shortened facial features constrict airflow, forcing affected dogs to exert excessive effort to breathe. The resulting condition is known as brachycephalic airway syndrome (BAOS).
A recent study involving seventeen brachycephalic dogs found that the majority of cases had minimal postoperative complications. However, there were a number of postoperative complications, including tracheostomy re-intubation and brachycephalic airway syndrome. The researchers also found that the onset of these problems occurred more commonly among dogs who had a sacculectomy.
In a retrospective study of 248 brachycephalic dogs, 42 of them were cavalier King Charles spaniels, representing 16.9% of the total study population. The medical records of these dogs were reviewed to determine postoperative complications, length of hospitalization, and need for further surgery. The three most common breeds were Pugs, Cavalier King Charles Spaniels, and British Bulldogs. While the bred-type was a risk factor for postoperative complications, the multilevel surgery was associated with substantial improvements in exercise tolerance and heat tolerance.
Another study examined the anesthetic risk factors for brachycephalic dogs. Although the angle of septal deviation was not significantly different between the two breeds, the presence of caudal aberrant nasal turbinates was significantly higher in brachycephalic dogs. In addition, the nasal mucosa was significantly higher in brachycephalic dogs.
Genetics of canine skull shape
The study of dog skull variation has provided important insight into canine skull growth and determines the genetics of canine skull shape. The similarities in genetic conservation between humans and dogs suggests that the regulation of craniofacial development is the same. The discoveries about canine skull growth have important implications for human biology and health. This study provides important information about genetic factors that are associated with canine skull shape, which includes diseases such as Apert syndrome, Crouzon syndrome, and Pfeiffer syndrome, which causes premature skull bones to fuse. Identifying genetic pathways for canine skull shape is critical, as these diseases lead to deformities in both dogs and humans.
Although the morphology of canine skulls has been extensively studied, genetic variation of skull shape is relatively recent. Early efforts to identify genetic variants responsible for canine skull shape focused on brachycephaly. Using candidate genes from humans, future studies will have to consider the origins of canine craniofacial variation. Genetic knowledge of the evolution of canine skull shape may also provide insights into the demographics of the ancestral dogs.
Canine skull shape is a complex trait, but there is good news for dog fanciers: it is a breed-defining trait. Genetic studies have identified multiple QTLs associated with skull length, face shape, and face length. However, they have not identified the genes responsible for skull shape. The study of canine skull shape is currently being conducted to help breeders identify traits that affect the health and appearance of canines.
Differentiation among canine skull shapes is a result of extensive specialized breeding. The morphology of the brain is closely related to dog’s size and shape. The snout and face of modern dogs is elongated while that of gray wolves is compressed. In addition to the size and shape, the cranial base length and palate are broader in dogs than in wolves. Differentiation in brain size may have influenced the shape of canine skulls.
Relationship between skull shape and temperament
The skull structure of dogs can determine a dog’s personality, and scientists have shown that it has a correlation with the dog’s temperament. Dogs with short noses are affectionate and follow commands, and they are more likely to chase lures and exhibit defensive aggression. On the other hand, dogs with long noses have more aggressive tendencies and may be more aggressive toward strangers. Several other factors can also affect the temperament of a dog, including breed, age, and health.
There are roughly 400 breeds of dogs in the world, and morphological variation among them is evident. Skull shape is breed-defining in many breeds, and some canine skull conformations resemble human craniosynostoses. Some breeds have characteristic facial characteristics, including underbite and wide, shallow orbits. But there are also significant breed-specific differences in canine skull shapes.
The variation in skull shape among domestic dogs offers a unique opportunity to study large-scale diversification. For example, the angle between the dog’s palate and neurocranium remains significantly different from the wolf’s throughout its development. Genetic knowledge of this variation may settle the debate about canine skull diversity and reveal the evolutionary mechanisms governing the development of dog skull shapes. Furthermore, it may also shed light on the demographics of ancestral canines.
According to research published in Plos One, the length and shape of the dog’s skull can predict a dog’s behavior. While the physical size of the dog does influence behavior, it has less influence than the shape of the skull. In fact, the size and shape of the skull also influence behavior, but researchers do not yet know whether these differences are due to accidental changes or to functional adaptations. However, a strong correlation is evident among the breeds.
