Information

What kind of skull is this?


We found this skull on a beach in southwestern Sweden, and are curious as to what kind of animal it was.


It's definitely a bird pelvis (synsacrum). Based on the size (~30 cm), it came from a very large bird. Unfortunately, comparative images of bird pelves are rare on the internet. Some possibilities (large birds of Sweden possibly found on the coast):

  • Great northern loon
  • Golden eagle
  • Common crane

A loon skeleton (from http://paolov.wordpress.com/2011/08/05/friday-mystery-object-107/) shown below.


The Types of Skull in the Human Being

The types of skulls of the human being can be classified according to the evolution, according to the race and finally, according to the genetic formation.

The skull is a bony structure that forms the head in most vertebrates, acting as a"box"for vital organs such as brain , Or sensory as the eyes and the tongue. Within the cranial structure are integrated the elements that make up the Central Nervous System .

The human skull is divided into two major parts: the neurocranium, which corresponds to the upper and posterior part and houses most of the cerebral and nervous components And the viscerocratic (or facial skeleton), which mainly contains the facial bones, the jaw being its largest bone piece.

The structure of the human skull, as well as other vertebrates, can be considered an adaptive part of a cephalization process, due to the accumulation of tissue and sensory receptors resulting in a central nervous system and crucial organs.

The structure of the human skull is divided by bones, with the exception of the mandible are united by osseous sutures Cavities, such as those responsible for housing the brain, eyes and nostrils And foramina, as small openings in the skull that allow the blood flow (veins, arteries) and cellular level of the bone at the muscular or facial level.

The differences between the skull of man and woman have been the subject of quite extensive discussions, with historical, anthropological and cultural aspects that have given continuity to the physical superiority of man over women.

However, it has been concluded that, although the skull of man may present a greater volume and robustness, the female skull has a greater thickness in its neurocranial part, providing greater protection to the brain.


Skull

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Skull, skeletal framework of the head of vertebrates, composed of bones or cartilage, which form a unit that protects the brain and some sense organs. The upper jaw, but not the lower, is part of the skull. The human cranium, the part that contains the brain, is globular and relatively large in comparison with the face. In most other animals the facial portion of the skull, including the upper teeth and the nose, is larger than the cranium. In humans the skull is supported by the highest vertebra, called the atlas, permitting nodding motion. The atlas turns on the next-lower vertebra, the axis, to allow for side-to-side motion.

In humans the base of the cranium is the occipital bone, which has a central opening ( foramen magnum) to admit the spinal cord. The parietal and temporal bones form the sides and uppermost portion of the dome of the cranium, and the frontal bone forms the forehead the cranial floor consists of the sphenoid and ethmoid bones. The facial area includes the zygomatic, or malar, bones (cheekbones), which join with the temporal and maxillary bones to form the zygomatic arch below the eye socket the palatine bone and the maxillary, or upper jaw, bones. The nasal cavity is formed by the vomer and the nasal, lachrymal, and turbinate bones. In infants the sutures (joints) between the various skull elements are loose, but with age they fuse together. Many mammals, such as the dog, have a sagittal crest down the centre of the skull this provides an extra attachment site for the temporal muscles, which close the jaws.


Cranial Bones: Anatomy

  • Skull or cranium: all bones of the head, from the top of the head to the hyoid bone (tongue bone). The cranium is the sum of the cranial and facial bones, as well as the bony part of the larynx.
  • Neurocranium: the top part of the skull that covers and protects the brain.
  • Viscerocranium: the bottom part of the skull that makes up the face and lower jaw.
  • Chondrocranium or cartilaginous neurocranium: so-called because this area of bone is formed from cartilage (endochondral ossification). More descriptive terms include skull base and cranial floor.
  • Cranial vault, calvaria/calvarium, or skull-cap. Together, the cranial floor and cranial vault form the neurocranium

The front of the cranial vault is composed of the frontal bone. This bone forms the ridges of the brows and the area just above the bridge of the nose called the glabella. The frontal bone extends back over the curved line of the forehead and ends approximately one-third of the way along the top of the skull.

This single bone articulates (joins) with the nasal bones, some orbit bones, and the zygomatic bone. At the side of the head, it articulates with the parietal bones, the sphenoid bone, and the ethmoid bone.

The two parietal bones continue the shape of the cranial vault these are quadrilateral, smooth, and curved bony plates. They articulate with the frontal, sphenoid, temporal, and occipital bones, as well as with each other at the top of the head (see the final image in the five views below).

The sides of the neurocranium are formed by the parietal, temporal, and sphenoid bones. The temporal bone provides surfaces for both the cranial vault and the cranial floor. It articulates with the mandible by way of a synovial joint. Each temporal bone has sutures with a greater wing of the sphenoid bone and its neighboring parietal bone.

The sphenoid is occasionally listed as a bone of the viscerocranium. However, it also provides important structures at the side and base of the neurocranium. The irregularly-shaped sphenoid bone articulates with twelve cranial and facial bones.

The ethmoid bone, also sometimes attributed to the viscerocranium, separates the nasal cavity from the brain. Like the sphenoid, it is very irregular in shape. It articulates with fifteen cranial and facial bones.

The final bone of the cranial vault is the occipital bone at the back of the head. The occipital bone – located at the skull base – features the foramen magnum. This is a large hole that allows the brain and brainstem to connect to the spine.

Cranial Bone Anatomy: Internal Surface

If you separate the cranial bones from the facial bones and first cervical vertebra and remove the brain, you would be able to view the internal surfaces of the neurocranium.

The midsagittal section below shows the difference between the relatively smooth upper surface and the bumpy, grooved lower surface. The picture also helps us to view the cranial vault in its natural position the cranial floor is at a distinct angle, starting at the level of the frontal sinus and continuing at an angle to include the small pocket that contains the cerebellum. You can see this small indentation at the bottom of the neurocranium.

The inner surface of the vault is very smooth in comparison with the floor. It does feature a few bumps and grooves. For example, the frontal crest – a notch of bone just behind the frontal sinus. The frontal crest is an attachment point for a fold in the membranes covering the brain (falx cerebri).

Just above the occipital bone and close to the midline of the skull cap are the parietal foramina. Just as with all foramina, important blood vessels and nerves travel through them. They are not visible in the above image.

A vertical groove passes through the middle of the cranial vault – the sagittal groove or sulcus – that provides space for the superior sagittal sinus (part of the drainage mechanism for cerebrospinal fluid and blood). The raised edge of this groove is just visible to the left of the above image.

Below, the position of the various sinuses shows how adept the brain is at removing waste products and extra fluid from its extremely delicate tissues.

At the back of the skull cap is the transverse sulcus (for the transverse sinuses, as indicated above).

The cranial floor is much more complex than the vault.

Looking down onto the inner surface of the skull base, the first thing you notice is a series of divisions. These form indentations called the cranial fossae. In the cranial vault, there are three:

  • Anterior cranial fossa: houses the frontal lobe, olfactory bulb, olfactory tract, and orbital gyri (intellectual and emotional expression)
  • Middle cranial fossa: a butterfly-shaped indentation that houses the temporal lobes, features channels for ophthalmic structures, and separates the pituitary gland from the nasal cavity
  • Posterior cranial fossa: contains the cerebellum, pons, and medulla oblongata the point of access between the brain and spinal canal

The inner surface of the skull base also features various foramina. These include the foramen cecum, posterior ethmoidal foramen, optic foramen, foramen lacerum, foramen ovale, foramen spinosum, jugular foramen, condyloid foramen, and mastoid foramen. And let’s not forget the largest of them all – the foramen magnum. A separate Biology Dictionary article discusses the numerous cranial foramina.

Cranial floor grooves provide space for the cranial sinuses that drain blood and cerebrospinal fluid from the lower regions of the meninges (dura mater, arachnoid, and pia mater), the cerebrum, and the cerebellum.

Cranial Bone Sutures

The neurocranium has several sutures or articulations. The first four in the following list are the most important:

  • Coronal suture: between the two parietal bones and the frontal bone
  • Sagittal suture: between the left and right parietal bones
  • Lambdoidal suture: between the top of the occipital bone and the back of the parietal bones
  • Metopic suture: only found in newborns between the two halves of the frontal bone that, once fused (very early in life), become a single bone
  • Squamous suture: between the temporal and parietal bones
  • Sphenosquamous suture: vertical join between the greater wings of the sphenoid bone and the temporal bones.
  • Frontoethmoidal suture: very short suture between the orbital projections of the frontal and ethmoid bones
  • Petrosquamous suture: refers to the join between the petrous and squamous parts of the temporal bone, close to the middle ear and at the skull base
  • Sphenoethmoidal suture: between the sphenoid and ethmoid bones
  • Sphenopetrosal suture: joins the greater wing of the sphenoid bone with the petrous part of the temporal bone


Contents

Humans Edit

The human skull is the bone structure that forms the head in the human skeleton. It supports the structures of the face and forms a cavity for the brain. Like the skulls of other vertebrates, it protects the brain from injury. [3]

The skull consists of three parts, of different embryological origin—the neurocranium, the sutures, and the facial skeleton (also called the membraneous viscerocranium). The neurocranium (or braincase) forms the protective cranial cavity that surrounds and houses the brain and brainstem. [4] The upper areas of the cranial bones form the calvaria (skullcap). The membranous viscerocranium includes the mandible.

The sutures are fairly rigid joints between bones of the neurocranium.

The facial skeleton is formed by the bones supporting the face.

Bones Edit

Except for the mandible, all of the bones of the skull are joined together by sutures—synarthrodial (immovable) joints formed by bony ossification, with Sharpey's fibres permitting some flexibility. Sometimes there can be extra bone pieces within the suture known as wormian bones or sutural bones. Most commonly these are found in the course of the lambdoid suture.

The human skull is generally considered to consist of twenty-two bones—eight cranial bones and fourteen facial skeleton bones. In the neurocranium these are the occipital bone, two temporal bones, two parietal bones, the sphenoid, ethmoid and frontal bones.

The bones of the facial skeleton (14) are the vomer, two inferior nasal conchae, two nasal bones, two maxilla, the mandible, two palatine bones, two zygomatic bones, and two lacrimal bones. Some sources count a paired bone as one, or the maxilla as having two bones (as its parts) some sources include the hyoid bone or the three ossicles of the middle ear but the overall general consensus of the number of bones in the human skull is the stated twenty-two.

Some of these bones—the occipital, parietal, frontal, in the neurocranium, and the nasal, lacrimal, and vomer, in the facial skeleton are flat bones.

Cavities and foramina Edit

The skull also contains sinuses, air-filled cavities known as paranasal sinuses, and numerous foramina. The sinuses are lined with respiratory epithelium. Their known functions are the lessening of the weight of the skull, the aiding of resonance to the voice and the warming and moistening of the air drawn into the nasal cavity.

The foramina are openings in the skull. The largest of these is the foramen magnum that allows the passage of the spinal cord as well as nerves and blood vessels.

Processes Edit

The many processes of the skull include the mastoid process and the zygomatic processes.

Other vertebrates Edit

Fenestrae Edit

The fenestrae (from Latin, meaning windows) are openings in the skull.

The temporal fenestrae are anatomical features of the skulls of several types of amniotes, characterised by bilaterally symmetrical holes (fenestrae) in the temporal bone. Depending on the lineage of a given animal, two, one, or no pairs of temporal fenestrae may be present, above or below the postorbital and squamosal bones. The upper temporal fenestrae are also known as the supratemporal fenestrae, and the lower temporal fenestrae are also known as the infratemporal fenestrae. The presence and morphology of the temporal fenestra are critical for taxonomic classification of the synapsids, of which mammals are part.

Physiological speculation associates it with a rise in metabolic rates and an increase in jaw musculature. The earlier amniotes of the Carboniferous did not have temporal fenestrae but two more advanced lines did: the synapsids (mammal-like reptiles) and the diapsids (most reptiles and later birds). As time progressed, diapsids' and synapsids' temporal fenestrae became more modified and larger to make stronger bites and more jaw muscles. Dinosaurs, which are diapsids, have large advanced openings, and their descendants, the birds, have temporal fenestrae which have been modified. Mammals, which are synapsids, possess one fenestral opening in the skull, situated to the rear of the orbit.

Classification Edit

There are four types of amniote skull, classified by the number and location of their temporal fenestrae. These are:

    – no openings – one low opening (beneath the postorbital and squamosal bones) – one high opening (above the postorbital and squamosal bones) euryapsids actually evolved from a diapsid configuration, losing their lower temporal fenestra. – two openings

Evolutionarily, they are related as follows:

    • Class Synapsida
      • Order Therapsida
        • Class Mammalia – mammals
        • Class Reptilia
          • Subclass Parareptilia
            • Infraclass Anapsida
            • Infraclass Diapsida
              • Class Aves

              Bones Edit

              The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the zygomatic bone or malar bone.

              The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls.

              Fish Edit

              The skull of fishes is formed from a series of only loosely connected bones. Lampreys and sharks only possess a cartilaginous endocranium, with both the upper and lower jaws being separate elements. Bony fishes have additional dermal bone, forming a more or less coherent skull roof in lungfish and holost fish. The lower jaw defines a chin.

              The simpler structure is found in jawless fish, in which the cranium is normally represented by a trough-like basket of cartilaginous elements only partially enclosing the brain, and associated with the capsules for the inner ears and the single nostril. Distinctively, these fish have no jaws. [5]

              Cartilaginous fish, such as sharks and rays, have also simple, and presumably primitive, skull structures. The cranium is a single structure forming a case around the brain, enclosing the lower surface and the sides, but always at least partially open at the top as a large fontanelle. The most anterior part of the cranium includes a forward plate of cartilage, the rostrum, and capsules to enclose the olfactory organs. Behind these are the orbits, and then an additional pair of capsules enclosing the structure of the inner ear. Finally, the skull tapers towards the rear, where the foramen magnum lies immediately above a single condyle, articulating with the first vertebra. There are, in addition, at various points throughout the cranium, smaller foramina for the cranial nerves. The jaws consist of separate hoops of cartilage, almost always distinct from the cranium proper. [5]

              In ray-finned fish, there has also been considerable modification from the primitive pattern. The roof of the skull is generally well formed, and although the exact relationship of its bones to those of tetrapods is unclear, they are usually given similar names for convenience. Other elements of the skull, however, may be reduced there is little cheek region behind the enlarged orbits, and little, if any bone in between them. The upper jaw is often formed largely from the premaxilla, with the maxilla itself located further back, and an additional bone, the symplectic, linking the jaw to the rest of the cranium. [6]

              Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living lungfishes. The skull roof is not fully formed, and consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods. The upper jaw is formed from the pterygoids and vomers alone, all of which bear teeth. Much of the skull is formed from cartilage, and its overall structure is reduced. [6]

              Tetrapods Edit

              The skulls of the earliest tetrapods closely resembled those of their ancestors amongst the lobe-finned fishes. The skull roof is formed of a series of plate-like bones, including the maxilla, frontals, parietals, and lacrimals, among others. It is overlaying the endocranium, corresponding to the cartilaginous skull in sharks and rays. The various separate bones that compose the temporal bone of humans are also part of the skull roof series. A further plate composed of four pairs of bones forms the roof of the mouth these include the vomer and palatine bones. The base of the cranium is formed from a ring of bones surrounding the foramen magnum and a median bone lying further forward these are homologous with the occipital bone and parts of the sphenoid in mammals. Finally, the lower jaw is composed of multiple bones, only the most anterior of which (the dentary) is homologous with the mammalian mandible. [6]

              In living tetrapods, a great many of the original bones have either disappeared or fused into one another in various arrangements.

              Birds Edit

              Birds have a diapsid skull, as in reptiles, with a prelachrymal fossa (present in some reptiles). The skull has a single occipital condyle. [7] The skull consists of five major bones: the frontal (top of head), parietal (back of head), premaxillary and nasal (top beak), and the mandible (bottom beak). The skull of a normal bird usually weighs about 1% of the bird's total bodyweight. The eye occupies a considerable amount of the skull and is surrounded by a sclerotic eye-ring, a ring of tiny bones. This characteristic is also seen in reptiles.

              Amphibians Edit

              Living amphibians typically have greatly reduced skulls, with many of the bones either absent or wholly or partly replaced by cartilage. [6] In mammals and birds, in particular, modifications of the skull occurred to allow for the expansion of the brain. The fusion between the various bones is especially notable in birds, in which the individual structures may be difficult to identify.

              The skull is a complex structure its bones are formed both by intramembranous and endochondral ossification. The skull roof bones, comprising the bones of the facial skeleton and the sides and roof of the neurocranium, are dermal bones formed by intramembranous ossification, though the temporal bones are formed by endochondral ossification. The endocranium, the bones supporting the brain (the occipital, sphenoid, and ethmoid) are largely formed by endochondral ossification. Thus frontal and parietal bones are purely membranous. [8] The geometry of the skull base and its fossae, the anterior, middle and posterior cranial fossae changes rapidly. The anterior cranial fossa changes especially during the first trimester of pregnancy and skull defects can often develop during this time. [9]

              At birth, the human skull is made up of 44 separate bony elements. During development, many of these bony elements gradually fuse together into solid bone (for example, the frontal bone). The bones of the roof of the skull are initially separated by regions of dense connective tissue called fontanelles. There are six fontanelles: one anterior (or frontal), one posterior (or occipital), two sphenoid (or anterolateral), and two mastoid (or posterolateral). At birth, these regions are fibrous and moveable, necessary for birth and later growth. This growth can put a large amount of tension on the "obstetrical hinge", which is where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone creating sutures. The five sutures are the two squamous sutures, one coronal, one lambdoid, and one sagittal suture. The posterior fontanelle usually closes by eight weeks, but the anterior fontanel can remain open up to eighteen months. The anterior fontanelle is located at the junction of the frontal and parietal bones it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heart rate by observing the pulse pulsing softly through the anterior fontanelle.

              The skull in the neonate is large in proportion to other parts of the body. The facial skeleton is one seventh of the size of the calvaria. (In the adult it is half the size). The base of the skull is short and narrow, though the inner ear is almost adult size. [10]

              Craniosynostosis is a condition in which one or more of the fibrous sutures in an infant skull prematurely fuses, [11] and changes the growth pattern of the skull. [12] Because the skull cannot expand perpendicular to the fused suture, it grows more in the parallel direction. [12] Sometimes the resulting growth pattern provides the necessary space for the growing brain, but results in an abnormal head shape and abnormal facial features. [12] In cases in which the compensation does not effectively provide enough space for the growing brain, craniosynostosis results in increased intracranial pressure leading possibly to visual impairment, sleeping impairment, eating difficulties, or an impairment of mental development. [13]

              A copper beaten skull is a phenomenon wherein intense intracranial pressure disfigures the internal surface of the skull. [14] The name comes from the fact that the inner skull has the appearance of having been beaten with a ball-peen hammer, such as is often used by coppersmiths. The condition is most common in children.

              Injuries and treatment Edit

              Injuries to the brain can be life-threatening. Normally the skull protects the brain from damage through its hard unyieldingness the skull is one of the least deformable structures found in nature with it needing the force of about 1 ton to reduce the diameter of the skull by 1 cm. [15] In some cases, however, of head injury, there can be raised intracranial pressure through mechanisms such as a subdural haematoma. In these cases the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ("coning") because there is no space for the brain to expand this can result in significant brain damage or death unless an urgent operation is performed to relieve the pressure. This is why patients with concussion must be watched extremely carefully.

              Dating back to Neolithic times, a skull operation called trepanning was sometimes performed. This involved drilling a burr hole in the cranium. Examination of skulls from this period reveals that the patients sometimes survived for many years afterward. It seems likely that trepanning was also performed purely for ritualistic or religious reasons. Nowadays this procedure is still used but is normally called a craniectomy.

              In March 2013, for the first time in the U.S., researchers replaced a large percentage of a patient's skull with a precision, 3D-printed polymer implant. [16] About 9 months later, the first complete cranium replacement with a 3D-printed plastic insert was performed on a Dutch woman. She had been suffering from hyperostosis, which increased the thickness of her skull and compressed her brain. [17]

              A study conducted in 2018 by the researchers of Harvard Medical School in Boston, funded by National Institutes of Health (NIH) suggested that instead of travelling via blood, there are "tiny channels" in the skull through which the immune cells combined with the bone marrow reach the areas of inflammation after an injury to the brain tissues. [18]

              Transgender procedures Edit

              Surgical alteration of sexually dimorphic skull features may be carried out as a part of facial feminization surgery, a set of reconstructive surgical procedures that can alter male facial features to bring them closer in shape and size to typical female facial features. [19] [20] These procedures can be an important part of the treatment of transgender people for gender dysphoria. [21] [22]


              Foramina

              The human skull has numerous holes known as foramina through which cranial nerves, arteries, veins, and other structures pass.

              Learning Objectives

              Describe the purpose of foramina in the skull

              Key Takeaways

              Key Points

              • A foramen (plural: foramina ) is an opening inside the body that allows key structures to connect one part of the body to another.
              • The skull bones that contain foramina include the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and occipital.
              • There are 21 foramina in the human skull.

              Key Terms

              • foramina: The openings inside the body that typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body to another.

              Base of the skull (upper surface): This image details the foramina of the skull.

              In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.

              The human skull has numerous foramina through which cranial nerves, arteries, veins, and other structures pass. The skull bones that contain foramina include the frontal, ethmoid, sphenoid, maxilla, palatine, temporal, and occipital lobes.

              Key foramina in the skull include:

              • Supraorbital foramen: Located in the frontal bone, it allows passage of the supraorbital vein, artery, and nerve into the orbit.
              • Optic foramen: Located in the sphenoid, it allows the passage of the ophthalmic artery and nerve from the optic canal into the orbit.
              • Foramen magnum: Located in the occipital bone, it allows the passage of the spinal and vertebral arteries and the spinal cord to pass from the skull into the vertebral column.
              • Foramina of cribriform plate: Located in the ethmoid bone, it allows the passage of the olfactory nerve.
              • Foramen rotundum: Located in the sphenoid bone, it allows passage of the maxillary nerve.

              Contents

              Human evolution from its first separation from the last common ancestor of humans and chimpanzees is characterized by a number of morphological, developmental, physiological, and behavioral changes. The most significant of these adaptations are bipedalism, increased brain size, lengthened ontogeny (gestation and infancy), and decreased sexual dimorphism. The relationship between these changes is the subject of ongoing debate. [9] [ page needed ] Other significant morphological changes included the evolution of a power and precision grip, a change first occurring in H. erectus. [10]

              Bipedalism Edit

              Bipedalism is the basic adaptation of the hominid and is considered the main cause behind a suite of skeletal changes shared by all bipedal hominids. The earliest hominin, of presumably primitive bipedalism, is considered to be either Sahelanthropus [11] or Orrorin, both of which arose some 6 to 7 million years ago. The non-bipedal knuckle-walkers, the gorillas and chimpanzees, diverged from the hominin line over a period covering the same time, so either Sahelanthropus or Orrorin may be our last shared ancestor. Ardipithecus, a full biped, arose approximately 5.6 million years ago. [12]

              The early bipeds eventually evolved into the australopithecines and still later into the genus Homo. There are several theories of the adaptation value of bipedalism. It is possible that bipedalism was favored because it freed the hands for reaching and carrying food, saved energy during locomotion, [13] enabled long-distance running and hunting, provided an enhanced field of vision, and helped avoid hyperthermia by reducing the surface area exposed to direct sun features all advantageous for thriving in the new savanna and woodland environment created as a result of the East African Rift Valley uplift versus the previous closed forest habitat. [14] [13] [15] A 2007 study provides support for the hypothesis that walking on two legs, or bipedalism, evolved because it used less energy than quadrupedal knuckle-walking. [16] [17] However, recent studies suggest that bipedality without the ability to use fire would not have allowed global dispersal. [18] This change in gait saw a lengthening of the legs proportionately when compared to the length of the arms, which were shortened through the removal of the need for brachiation. Another change is the shape of the big toe. Recent studies suggest that australopithecines still lived part of the time in trees as a result of maintaining a grasping big toe. This was progressively lost in habilines.

              Anatomically, the evolution of bipedalism has been accompanied by a large number of skeletal changes, not just to the legs and pelvis, but also to the vertebral column, feet and ankles, and skull. [19] The femur evolved into a slightly more angular position to move the center of gravity toward the geometric center of the body. The knee and ankle joints became increasingly robust to better support increased weight. To support the increased weight on each vertebra in the upright position, the human vertebral column became S-shaped and the lumbar vertebrae became shorter and wider. In the feet the big toe moved into alignment with the other toes to help in forward locomotion. The arms and forearms shortened relative to the legs making it easier to run. The foramen magnum migrated under the skull and more anterior. [20]

              The most significant changes occurred in the pelvic region, where the long downward facing iliac blade was shortened and widened as a requirement for keeping the center of gravity stable while walking [21] bipedal hominids have a shorter but broader, bowl-like pelvis due to this. A drawback is that the birth canal of bipedal apes is smaller than in knuckle-walking apes, though there has been a widening of it in comparison to that of australopithecine and modern humans, permitting the passage of newborns due to the increase in cranial size but this is limited to the upper portion, since further increase can hinder normal bipedal movement. [22]

              The shortening of the pelvis and smaller birth canal evolved as a requirement for bipedalism and had significant effects on the process of human birth which is much more difficult in modern humans than in other primates. During human birth, because of the variation in size of the pelvic region, the fetal head must be in a transverse position (compared to the mother) during entry into the birth canal and rotate about 90 degrees upon exit. [23] The smaller birth canal became a limiting factor to brain size increases in early humans and prompted a shorter gestation period leading to the relative immaturity of human offspring, who are unable to walk much before 12 months and have greater neoteny, compared to other primates, who are mobile at a much earlier age. [15] The increased brain growth after birth and the increased dependency of children on mothers had a major effect upon the female reproductive cycle, [24] and the more frequent appearance of alloparenting in humans when compared with other hominids. [25] Delayed human sexual maturity also led to the evolution of menopause with one explanation providing that elderly women could better pass on their genes by taking care of their daughter's offspring, as compared to having more children of their own. [26]

              Encephalization Edit

              The human species eventually developed a much larger brain than that of other primates—typically 1,330 cm 3 (81 cu in) in modern humans, nearly three times the size of a chimpanzee or gorilla brain. [27] After a period of stasis with Australopithecus anamensis and Ardipithecus, species which had smaller brains as a result of their bipedal locomotion, [28] the pattern of encephalization started with Homo habilis, whose 600 cm 3 (37 cu in) brain was slightly larger than that of chimpanzees. This evolution continued in Homo erectus with 800–1,100 cm 3 (49–67 cu in), and reached a maximum in Neanderthals with 1,200–1,900 cm 3 (73–116 cu in), larger even than modern Homo sapiens. This brain increase manifested during postnatal brain growth, far exceeding that of other apes (heterochrony). It also allowed for extended periods of social learning and language acquisition in juvenile humans, beginning as much as 2 million years ago.

              Furthermore, the changes in the structure of human brains may be even more significant than the increase in size. [29] [30] [31] [32]

              The temporal lobes, which contain centers for language processing, have increased disproportionately, as has the prefrontal cortex, which has been related to complex decision-making and moderating social behavior. [27] Encephalization has been tied to increased meat and starches in the diet, [33] [34] [35] and the development of cooking, [36] and it has been proposed that intelligence increased as a response to an increased necessity for solving social problems as human society became more complex. [37] Changes in skull morphology, such as smaller mandibles and mandible muscle attachments, allowed more room for the brain to grow. [38]

              The increase in volume of the neocortex also included a rapid increase in size of the cerebellum. Its function has traditionally been associated with balance and fine motor control, but more recently with speech and cognition. The great apes, including hominids, had a more pronounced cerebellum relative to the neocortex than other primates. It has been suggested that because of its function of sensory-motor control and learning complex muscular actions, the cerebellum may have underpinned human technological adaptations, including the preconditions of speech. [39] [40] [41] [42]

              The immediate survival advantage of encephalization is difficult to discern, as the major brain changes from Homo erectus to Homo heidelbergensis were not accompanied by major changes in technology. It has been suggested that the changes were mainly social and behavioural, including increased empathic abilities, [43] [44] increases in size of social groups, [45] [46] [47] and increased behavioural plasticity. [48] Encephalization may be due to a dependency on calorie-dense, difficult-to-acquire food. [49]

              Sexual dimorphism Edit

              The reduced degree of sexual dimorphism in humans is visible primarily in the reduction of the male canine tooth relative to other ape species (except gibbons) and reduced brow ridges and general robustness of males. Another important physiological change related to sexuality in humans was the evolution of hidden estrus. Humans are the only hominoids in which the female is fertile year round and in which no special signals of fertility are produced by the body (such as genital swelling or overt changes in proceptivity during estrus). [50]

              Nonetheless, humans retain a degree of sexual dimorphism in the distribution of body hair and subcutaneous fat, and in the overall size, males being around 15% larger than females. [51] These changes taken together have been interpreted as a result of an increased emphasis on pair bonding as a possible solution to the requirement for increased parental investment due to the prolonged infancy of offspring. [52]

              Ulnar opposition Edit

              The ulnar opposition—the contact between the thumb and the tip of the little finger of the same hand—is unique to the genus Homo, [53] including Neanderthals, the Sima de los Huesos hominins and anatomically modern humans. [54] [55] In other primates, the thumb is short and unable to touch the little finger. [54] The ulnar opposition facilitates the precision grip and power grip of the human hand, underlying all the skilled manipulations.

              Other changes Edit

              A number of other changes have also characterized the evolution of humans, among them an increased importance on vision rather than smell a longer juvenile developmental period and higher infant dependency a smaller gut faster basal metabolism [56] loss of body hair evolution of sweat glands a change in the shape of the dental arcade from being u-shaped to being parabolic development of a chin (found in Homo sapiens alone) development of styloid processes and the development of a descended larynx.


              Animal Skull ID: Identifying Animal Skulls By Their Teeth

              In my previous post about animal skulls I provided you with some basic animal skull identification resources, but in this post I want to help you begin to narrow down what type of animal skull you might have found. The easiest way to start is by looking at the teeth of of the skull. If the teeth are present, this is easiest, though you can sometimes muddle through by looking at the skull if only the tooth sockets remain. It's also helpful if you have both jaws available,(upper and lower mandibles) though it's not required. Often one or the other is enough to help you.

              Different Types of Teeth

              If you feel around your mouth with your tongue, it becomes apparent that you don't have all the same types of teeth. This is true for most animals. Teeth are specialized to do different jobs, depending on the diet of the creature (if you ever want to see a really weird skull, check out the anteater, they don't have any teeth, just a long bone snout!)

              Incisors (dark blue) are at the front of the mouth and are usually for scraping or biting, so they are scoop shaped and smaller. Canines (green) are usually for ripping or tearing meat, so they are long and pointed. Premolars (pink), are behind the canines, and can be flat for grinding, like in the mouth of beavers, or they can be sharp and serrated like in dogs and canines, for tearing meat. Molars (turquoise) also vary, depending on their use. Often they are for grinding food, like in humans, but in meat eating creatures they too may be serrated and have sharp edges for ripping and tearing meat.

              The number, shape, and size of teeth can help you determine what type of animal skull you've found. Knowing where molars and premolars begin and end can be tricky. There's no hard and fast rule for telling them apart, and often they can look very similar. The other types of teeth are much easier. You'll have to practice skull identification, and looking at different types of teeth to get comfortable. For now, if it helps, focus mostly on the incisors, canines and molars (farthest back two pairs of teeth) if you're not sure.

              The last tidbit you should know, is about bilateral symmetry. All mammals, like you and me, have bodies with mirror halves. The right side of our skeleton, and our external body, matches the left. This means, that when you study the teeth of a mammal you only need to study one side of the mouth, or count teeth on one side of the skull. The other half of the jaw is exactly the same (for dental formulas you then multiply by two). For example, in the image above, there are three incisors, one canine, four premolars, and two molars on one side. You would double that for a full tooth count.

              Remember that animal skulls will not always have the same number of teeth in their upper and lower jaws. This is because each jaw may have a different function. In deer (and sheep, horses, etc.), the upper jaw has no incisors, but the lower jaw has a full set of incisors. This is because they use their lower jaw to "scoop" grass and leaves, and then the vegetation is passed to the back molars for grinding (this scooping action is what animal trackers look at to know the difference between the shearing cuts of rabbit teeth and the ragged scoop of deer teeth on vegetation).

              Deer skull, with clear molars, lower incisors, but no top incisors (Photo: Wiki Commons).

              Narrow Down the Choices: 3 Categories (Carnivore, Herbivore, Omnivore)

              Now that you know the basics, let's try to narrow down the type of animal you have.

              • Carnivores- These are true meat-eating-only animals that have sharp teeth for ripping and tearing. Often their front canine teeth are elongated and sharp and their incisors are often small and reduced in size. Their back teeth, or molars and premolars are what we call " carnassial " meaning that they too are serrated and sharp, like the blades of a saw. This allows them to hold, rip, and tear meat from prey. For this classification I'm going to include insectivores like bats and some voles and moles and pescavores , or fish eaters. These creatures often have very wicked looking teeth, and sharp carnassials as well, just like the other carnivores.

              This is an example of a rodent skull, with bright orange incisors (Photo: Mike Simpson, Flicker Sharing).

              • Omnivores- Omnivores eat both meat and plant material. Their teeth are usually a combination of meat eating and plant eating teeth. A great example can be seen in the dentition of raccoons. In the image below you can see that they have both flat molars for grinding plant matter, and sharp canines for ripping and tearing meat. If your skull has a combination of teeth then you're probably looking at an omnivore.

              DENTITION: COUNT IT OUT

              This is the skull of a raccoon, it is an omnivore, and has teeth for eating meat and plants (Photo: Wiki commons).

              Each type of animal has its own unique dental formula. These formulas can be used by biologists to help accurately identify skulls and to assist in categorizing animals into families and subgroups. In the resources I mention in my other post about good references for skull identification, you'll often find dental formulas listed for each type of animal. My favorite book, "The Wild Mammals of Missouri" has a great combination of pictures of animals, their skull, lower jaw, tracks, descriptions, and a dental formula.

              A dental formula is quite simple, they just use letters to represent each type of tooth :

              After each number you will find two numbers that look like a fraction. These aren't really fractions. The top number represents the number of a particular teeth in the top mandible (or mouth) and the bottom number represents the number of a particular type of teeth in the lower mandible or jaw. For example, here is the dentition of an adult human:

              Adult Human: I - 2/2 C - 1/1 P - 2/2 M - 3/3 = 16 x 2 = 32 total teeth

              Notice that the total number of teeth is counted and then multiplied by two. This is because of what I mentioned earlier, bilateral symmetry. You only need to count the teeth on one side of the animal's skull and jaw, and then double it to get a full count of teeth. It simply saves you some work.

              This is the dental formula of an American beaver (Castor canadensis):

              American Beaver: I-1/1 C- 0/0 P- 1/1 M- 3/3= 10 x2 = 20

              TRY DENTAL FOMULAS YOURSELF

              Try your hand at the dentition of this red fox skull. I'm going to try to stump you here, because this was a relatively young animal when it perished. Look at the lower jaw, you can see that one side has erupted teeth, and one side does not, just behind the canine. Assume that if it had lived, it would have had a complete set of erupted teeth.

              Try your hand at the dentition of this red fox ( vulpes vulpes ). (Photo: Will's Skull Page)

              First, is it a carnivore, herbivore, or omnivore?

              I __/___ C __/___ P __/___ M___/___= ______ x2= _____ total teeth

              You can search the Wildwood Tracking website for the dentition of specific animals of North America if you'd like to see if you're on the right track with your count and ID. Here's the answer if you're not sure: I 3/3, C1/1, PM 4/4, M 2/3 = 21 x 2 = 42.

              The image above came from a great website, called Will's Skull Page. It has great online images of different types of animal skulls, and close ups of teeth.

              INCOMPLETE SKULLS

              Often times you'll find skulls that are missing their lower jaws, teeth have fallen out, or various and sundry things have happened to the skull, so the teeth are hard to count or may be missing. Here are a few examples. See if you can guess the dentition.

              Ok, this opossum skull is rough. It has both upper and lower jaw, but many teeth are missing and the jaw image is from only one direction. Try the dentition yourself first, then scroll to the bottom of the "jaw" image to see if you're correct.

              American opossum skull upper mandible (the North American mammal with the most teeth by the way!). Photo: K. McDonald

              American Opossum Dentition: I 5/4 C 1/1 P 3/3 M 4/4 = 25 x 2 = 50

              Here's a really challenging skull. It's a rabbit, specifically a jackrabbit, not a rodent. If you're unsure of the difference, check out my earlier blog post. Notice, some of the back molars are just erupting , and we only have the top mandible.

              Because this is a rabbit, it has an additional set of teeth behind its long front teeth (unique to hares and rabbits, not found in rodents), so the count is: I 2 C 0 P 3 M 3= 8 total or 16 in the top jaw alone.

              Ok, so there you have it, skulls and dentition at a glance. This only touches the tip of the iceberg for identifying skulls, but it's a great place to start, and can help you hone your naturalist skills.


              What is Caucasian skull?

              Definition:

              A Caucasian skull is a skull that is found in people who are of European descent and are Caucasian.

              Features of the cranium and chin:

              The skull shape of a Caucasoid person is generally long and it is narrow when compared to the skull shape that is evident in other race groups of people. The zygomatic bones are less pronounced in Caucasians compared with other ethnic groups of people, and the chins (mental protuberance) are more pronounced in the skulls of European people.

              Features of the eye orbits and brow:

              In Caucasoids, the eye orbits are rectangular in shape but less massive compared with the overall size of the face when compared with Australoid skulls (Aborigines), and eye orbits do appear sloped in European skulls. Caucasian people also have eye orbits that seem to be sloped when seen from the anterior viewpoint. The brow ridges are also less pronounced when compared with the Aboriginal skull ridges but more pronounced than some other races.

              Features of the nasal region:

              The skulls of Caucasian people tend to have a more triangle shape to the opening of the nose compared with the nasal openings seen in the skulls of the other race groups. In addition, European skulls show a more protruding and obvious nasal ridge, and the nose is not flared.

              Features of the jaw and teeth:

              Loss of bone in the alveolar region of the jaw has been found to be less pronounced in the skulls of Caucasoid when compared with that which has been seen historically in the skulls of Negroid and Australoid skulls. The amount of alveolar loss was also noted to decrease by the 19 th century. Teeth are small in size and are arranged closely together in the Caucasoid type of skull. This is different from the other racial groups in which teeth are seen to be much larger in size with teeth spaced further apart by comparison.


              Human skull - Facial muscles

              The facial muscles are a group of striated skeletal muscles that control facial expressions and allow us to chew our food. The muscles located on our skull are the following:

              Occipitofrontalis muscle - the large muscle of the forehead

              Temporalis muscle - a thick muscle that closes the mouth and assists the jaw to move side-to-side to grind up food

              Procerus muscle - a small pyramidal slip of tissue in between the eyebrows, helps flare the nostrils and express anger

              Nasalis muscle - the muscle responsible for "flaring" of the nostrils

              Depressor septi nasi muscle - this muscle arises from the incisive fossa of the maxilla, closes the nasal septum

              Orbicularis oculi muscle - muscle in the face that closes the eyelids

              Corrugator supercilii muscle - muscle functions to move the eyebrow down and inward toward the nose and inner eye, creates vertical lines or wrinkles

              Auricular muscles (anterior, superior and posterior) - the outer ear, external ear, or auris externa is the external portion of the ear, which consists of the auricle (also pinna) and the ear canal. It gathers sound energy and focuses it on the eardrum

              Orbicularis Oris muscle - this muscle brings our lips together so we can pucker up for a kiss

              Depressor anguli oris muscle - facial muscle associated with frowning, starts from the mandible and inserts into the angle of the mouth.

              Risorius - a very thin and delicate muscle that pulls the lips horizontally creating a broad, albeit insincere smile

              Zygomaticus major muscle - draws the angle of the mouth superiorly and posteriorly to allow one to smile

              Zygomaticus minor muscle - it brings the upper lip backward, upward, and outward and is used in smiling

              Levator labii superioris alaeque nasi - this muscle dilates the nostrils and raises the upper lip. It’s often referred to as the ‘Elvis muscle’ in homage to Elvis Presley.

              Depressor labii inferioris muscle - this muscle pulls down the bottom lip allowing us to sulk

              Levator anguli oris - the happy muscle, making the corners of our mouth turn upwards into a smile

              Buccinator muscle - known as the ‘trumpeter muscle,’ the Buccinator’s role is to puff out the cheeks and prevent food from passing to the outer surface of the teeth during chewing

              Mentalis - called the ‘pouting muscle,’ contraction of the Mentalis raises and thrusts out the lower lip to make us pout

              Check out the original article: Cráneo humano: partes, huesos, músculos y anatomía at viviendolasalud.com

              References:

              Carlson, B. M. (1999). Human Embryology & Developmental Biology. Mosby.

              Rouvière, H. & Delmas, A. (1996). Anatomía humana: descriptiva, topográfica y funcional (9ª Ed.), Tomo I. Masson.

              Slater, B. J., Lenton, K. A., Kwan, M. D., Gupta, D. M., Wan, D. C. & Longaker, M. T. (2008). Cranial sutures: a brief review. Plastic and Reconstructive Surgery, 121(4): 170e–8e.


              Watch the video: Kong: Skull Island. Final Fight Scene (December 2021).