Sagittal crest

A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exceptionally strong jaw muscles. The sagittal crest serves primarily for attachment of the temporalis muscle, which is one of the main chewing muscles. Development of the sagittal crest is thought to be connected to the development of this muscle. A sagittal crest usually develops during the juvenile stage of an animal in conjunction with the growth of the temporalis muscle, as a result of convergence and gradual heightening of the temporal lines.

Paranthropus aethiopicus
Paranthropus aethiopicus' sagittal crest on top of the head

Function

A sagittal crest tends to be present on the skulls of adult animals that rely on powerful biting and clenching of their teeth, usually as a part of their hunting strategy. Skulls of some dinosaur species, including tyrannosaurs, possessed well developed sagittal crests. Among mammals, dogs, cats, lions, and many other carnivores have sagittal crests, as do some leaf eaters, including tapirs and some apes.

Apes and hominins

Sagittal crests are found in robust great apes, and some early hominins (Paranthropus). Prominent sagittal crests are found among male gorillas and orangutans, and do occur but only rarely in male chimpanzees such as Bili apes.

The largest sagittal crest ever discovered in the human lineage belongs to the "Black Skull", Paranthropus aethiopicus field number KNM WT 17000, the earliest known robust hominid ancestor and the oldest robust australopithecine discovered to date. The prominence of the crest appears to have been an adaptation for the P. aethiopicus' heavy chewing, and the Black Skull's cheek teeth are correspondingly large. Smaller sagittal crests are also present on the skulls of other Paranthropines, including Paranthropus boisei and Paranthropus robustus.

See also

External links

Acostasaurus

Acostasaurus (meaning "Acosta's lizard") is an extinct genus of possibly Thalassophonean pliosaurid known from the Barremian of the Paja Formation, Colombia. The type specimen, UNDG R-1000, is known from a near complete skull, and postcranial elements including a complete hindlimb and various vertebrae. The specimen has an estimated size of around 4 to 5 metres (13 to 16 ft) long.

Andrewsiphius

Andrewsiphius is an extinct remingtonocetid early whale known from the Eocene (Ypresian-Lutetian, 55.8 to 40.4 million years ago) of Gujarat and Kutch, India and Balochistan, Pakistan.Andrewsiphius is similar to but smaller than Kutchicetus (another remingtonocetid); Gingerich et al. 2001 synonymized them, and Thewissen & Bajpai 2009 proposed a new subfamily, Andrewsiphiinae, for the two species. Later authors, however, still accept both as separate genera.

Andrewsiphius and Kutchicetus share several characteristics not present in other remingtonocetids: an elongated snout that is higher than it is wide; foramina (small holes) on the tip of the snout suggesting the presence of whiskers; eyes located dorsally near the cranial midline, resulting in an appearance of a mammalian crocodile; and a very large sagittal crest overhanging the back of the skull. Other characteristics make them distinct: the second and third upper and lower premolars are double-rooted in Andrewsiphius but single-rooted in Kutchicetus; the large diastemata in the former are absent the latter; and the tail vertebrae are more robust in Andrewsiphius.Andrewsiphius is, compared to the remgintonocetids Remingtonocetus and Dalanistes, smaller, has a narrower rostrum, and smaller premolars separated by longer diastemata.The first specimen was collected by Sahni & Mishra 1972 who described it as mandibular fragments of Protocetus sloani. Sahni & Mishra 1975 described two new species, Andrewsiphius kutchensis and A. minor based on their previous material and new mandibular fragments. Later researchers interpreted the same mandibular specimens as belonging to Remintonocetus. Gingerich et al. 2001 reinterpreted these specimens as fragments from maxillae, and determined that the described "confluence of the mandibular canals anteriorly" was in fact the narial passages. Gingerich et al. also determined that the variations in size among proposed species were within the normal variation for a single species and therefore attributed a number of referred specimens as belonging to Andrewsiphius sloani.Gingerich et al. also noted that the type specimen of Kutchicetus minimus came from the same locality as A. sloani and that its distinctive small size was within the variation that could be expected for A. sloani, and Gingerich et al. therefore included K. minimus into A. sloani. Later authors, however, disagreed on this assignment and Kutchicetus is still accepted as a separate genus.Sahni & Mishra 1972 named the type species for Dr Robert E. Sloan, Department of Geology, University of Minnesota.

Archosauromorpha

Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, lizards, and snakes). Archosauromorphs first appeared during the middle Permian, though they became much more common and diverse during the Triassic period.Although Archosauromorpha was first named in 1946, its membership did not become well-established until the 1980s. Currently Archosauromorpha encompasses four main groups of reptiles: the stocky, herbivorous allokotosaurs and rhynchosaurs, the hugely diverse Archosauriformes, and a polyphyletic grouping of various long-necked reptiles including Protorosaurus, tanystropheids, and Prolacerta. Other groups including pantestudines (turtles and their extinct relatives) and the semiaquatic choristoderes have also been placed in Archosauromorpha by some authors.

Archosauromorpha is one of the most diverse groups of reptiles, but its members can be united by several shared skeletal characteristics. These include laminae on the vertebrae, a posterodorsal process of the premaxilla, a lack of notochordal canals, and the loss of the entepicondylar foramen of the humerus.

Cristatusaurus

Cristatusaurus is a genus of theropod dinosaur that lived during the Early Cretaceous Period of what is now Niger, 112 million years ago. It was a baryonychine member of the Spinosauridae, a group of large bipedal carnivores with well-built forelimbs and elongated, crocodile-like skulls. The type species Cristatusaurus lapparenti was named in 1998 by scientists Philippe Taquet and Dale Russell, on the basis of jaw bones and some vertebrae. Two claw fossils were also later assigned to Cristatusaurus. The animal's generic name, which means "crested reptile", alludes to a sagittal crest on top of its snout; while the specific name is in honor of the French paleontologist Albert-Félix de Lapparent. Cristatusaurus is known from the Albian to Aptian Erlhaz Formation, where it would have coexisted with sauropod and iguanodontian dinosaurs, other theropods, and various crocodylomorphs.

Originally proposed to be an indeterminate species of Baryonyx, the identity of Cristatusaurus has been subject to debate, in part due to the fragmentary nature of its fossils. Some argue that it is probably the same dinosaur as Suchomimus, which has also been found in Niger, in the same sediment layers. In that case the genus Cristatusaurus would have priority, since it was named two months earlier. Others have concluded, however, that Cristatusaurus is a nomen dubium, considering it indistinguishable from both Suchomimus and Baryonyx. Some distinctions between the fossils of Cristatusaurus and Suchomimus have been pointed out, but it is uncertain whether these differences separate the two genera or if they are due to ontogeny (changes in an organism during growth).

Dalanistes

Dalanistes is an extinct genus of remingtonocetid early whale known from the late early Eocene (Lutetian, 48.6 to 40.4 million years ago) of Kutch, India and Punjab and Balochistan, Pakistan. Dalanistes is closely related to Remingtonocetus (the type genus of Remingtonocetidae, a slightly more derived family of early whales), but also shares several characters with Ambulocetus (the type of Ambulocetidae, earlier more primitive whales), and, with its combination of terrestrial and amphibious adaptations, Dalanistes apparently is an intermediate form between these two groups. Isotopic evidence suggest that Dalanistes had a marine diet.Dalanistes is known from several localities and collections. The holotype is a skull and a postcranial skeleton. Additional fossils referred to Dalanistes include crania, several vertebrae and sacra, possible caudals, one side of the pelvis, and a distal femur. The alveoli is all that is left of the dentition, but the dental formula apparently was 3.1.4.33.1.4.3.The vertebral elements of the sacrum are solidly fused and form a well-developed articular surface for the pelvis. The ilium is robust and long, and has a large acetabulum similar to that in Remingtonocetus. The femur had a spherical head, a medial condyle considerably larger than the lateral, and a shallow patellar groove. Taken together this morphology suggests the presence of well-developed hind limbs.Dalanistes is similar to but 20% larger than Remingtonocetus; the external nares are located more anteriorly (above C1); the sagittal crest is much higher; the rostrum is angled down 20° relative to the main axis of the braincase; the mandibular symphysis is relatively open (ends at P3) and the mandibular canals fail to unite at the symphysis. This mandibular morphology is also different from that of Andrewsiphius (another remingtonocetid).Dalanistes was named by contracting "Dalana" and "-istes" to allude to the Greek name platanistes used for (unrelated) South Asian river dolphin. Both the genus and species name refer to local place names near the type locality: Dalana Nala and Basti Ahmed respectively.

Eutheriodontia

The Eutheriodontia are a clade of therapsids that includes therocephalians and cynodonts.

The clade was named in 1986 by James Allen Hopson and Herbert Richard Barghusen, the name meaning the "True Theriodontia". Within Hopson's system, the Eutheriodontia are the sister group of the Gorgonopsia within the Theriodontia. A close relationship between therocephalians and cynodonts had been recognized for many years. In 2001 the Eutheriodontia were defined as the least inclusive clade including Mammalia and Bauria.Therocephalians and cynodonts are thought to have diverged in the Middle Permian, and each group independently evolved mammal-like features, including a secondary palate and the loss of a postorbital bar (these features were retained in mammals, which are considered a derived group of cynodonts). Mammalian features that both groups inherited from a common ancestor include the loss of teeth on the palate, the expansion of the epipterygoid bone at the base of the skull (an area called the alisphenoid in mammals), and the narrowing of the skull roof to a narrow sagittal crest running between large temporal openings.

Galesaurus

Galesaurus (from the Greek roots for 'weasel' and 'lizard') was a prehistoric carnivorous therapsid that lived between the Induan and the Olenekian age in what is now South Africa. It was incorrectly classified as a dinosaur by Sir Richard Owen in 1859.

Notably, Galesaurus was mentioned in the first issue of Nature in 1869, where T. H. Huxley expressed confidence that it would eventually be shown to be a dinosaur. However, current opinion is that it was not a dinosaur and belongs to a mammal-like group called Cynodonts.

Horopeta

Horopeta is a genus of baleen whale from the Late Oligocene (Chattian) Kokoamu Greensand of New Zealand.

KNM WT 17000

KNM WT 17000 (AKA "The Black Skull") is a fossilized adult skull of the species Paranthropus aethiopicus. It was discovered in West Turkana, Kenya by Alan Walker in 1985.

It is estimated to be 2.5 million years old. It is an adult with an estimated cranial capacity of 410 cc.

Its characteristics include a robust build with a prominent sagittal crest. Its coloration is due to the high manganese content of the material it was embedded in. This fossilized cranium's face projects far outward from the forehead, has wide flared zygomatic arches, and has the largest sagittal crest of any early human. The molar and premolar roots in the jaw are indicative of this early human having massive cheek teeth; an adaptation for heavy chewing. It is the only known adult skull of the species.

Lonchognathosaurus

Lonchognathosaurus was a genus of dsungaripterid pterodactyloid pterosaur from the Albian-age Lower Cretaceous Lianmuqin Formation of Xinjiang, China.

The genus was named in 2004 by Michael Maisch, Andreas Matzke and Sun Ge. The type species is Lonchognathosaurus acutirostris. The genus name is derived from Greek lonchos, "lance", gnathos, "jaw" and sauros, "lizard", in reference to the fact that it is a reptile with pointed jaws. The specific name means "needle snout" in Latin.

Lonchognathosaurus is based on holotype SGP 2001/19, found near Urumqi in the southern Junggar Basin, the front portion of a skull and lower jaws that came from a large individual; the estimated length of the complete skull was about 400 mm (15.75 in). The point of the upper jaw, composed of the premaxilla bones, was slender and had a needle-like tip. The teeth of the upper jaw appeared far back of the tip, and were well-spaced, diminishing in size from front to back; they ended again in front of the nostrils. They were placed in tooth-sockets that had a low bony ridge but were not otherwise elevated from the jaw. Each maxilla only had eight teeth, and the bottom margin of the upper jaw was straight (unlike in other pterosaurs where it is strongly curved). A sagittal crest was present, with grooves and a concave leading margin.

The genus was, after a cladistic analysis, classified as a member of the Dsungaripteridae, as the sister taxon to Dsungaripterus.According to Brian Andres Lonchognathosaurus is a junior synonym of Dsungaripterus weii. David Hone on the other hand, argued in 2017 that the species could not be distinguished from Noripterus.

Mesonyx

Mesonyx ("middle claw") is a genus of extinct, superficially wolf-like mesonychid mesonychian mammal: fossils of the various species are found in Early to Late Eocene-age strata in the United States and Early Eocene-aged strata in China, 51.8—51.7 Ma (AEO).Mesonyx measured about 1.5 m (5 ft) long not including the tail, and weighted an estimated 22.7–34 kg. It was a fast predator from the Middle Eocene of Wyoming, and it probably hunted hoofed plant eaters, moving lightly on its toes. However, instead of claws, Mesonyx's toes ended in small hooves. Its long skull had a relatively large sagittal crest above the braincase to anchor large jaw muscles and give it a powerful bite.

Mesonyx specimens have been unearthed in Colorado, Wyoming, Utah and China. Mesonyx uintensis from the Upper Eocene of Wyoming is described as having a total cranium length of 429 mm. (17 inches) and a facial length of 206 mm (8 inches). Another specimen of Mesonyx uintensis is known from the Upper Eocene of northern Utah. Additional two species – Mesonyx uqbulakensis and M. nuhetingensis – have been described from the early Eocene Arshanto Formation in China.

Neocnus

Neocnus is an extinct genus of ground sloth, whose species ranged across Cuba and Hispaniola (Haiti and Dominican Republic). Neocnus would have resembled a typical megalonychid ground sloth, though much smaller, with a longer tail and a broad trunk, as well as lissome limbs and long claws. This sloth was known for having caudal vertebrae that were broad, a trait shared with other ground sloths, indicating that this animal, like the tamandua of today, likely used its tail to stand upright. The caniniform teeth of the Neocnus were large and triangular, and its skull was deep and had a large, sagittal crest which, when used with the deep mandible likely allowed strong exertion by the masticatory muscles.

The fossils of this sloth were found in Haitian cave deposits. They have been dated to as recently as 4391 BP, calibrated to c. 5000 BP. It is theorized that this sloth, in common with other Antillean sloths, was killed off by humans seeking its pelt and meat. Currently, this species of sloth is being studied by evolutionary historians. Neocnus is suspected of having been semi-arboreal.

Paranthropus robustus

Paranthropus robustus (or Australopithecus robustus) is an early hominin, originally discovered in Southern Africa in 1938. Particularly regarding cranial features, the development of P. robustus seemed to be in the direction of a "heavy-chewing complex". On account of the definitive traits associated with this "robust" line of australopithecine, anthropologist Robert Broom established the genus Paranthropus and placed this species in it.

Paranthropus robustus is generally dated to have lived between 2.0 and 1.2 million years ago. It had large jaws and jaw muscles with the accompanying sagittal crest, and post-canine teeth that were adapted to serve in the dry environment they lived in. The post-canine teeth also commonly display pitting enamel hypoplasia, thought to be caused by a genetic condition, amelogenesis imperfecta, and was likely common due to instability in crucial gene(s) after evolving such large teeth.

Parapapio

Parapapio is a genus of prehistoric baboons closely resembling the forest dwelling mangabeys. Parapapio is distinguished from other Papio by the lack of an anteorbital drop, thin browridges, absence of maxillary fossae or a sagittal crest and only slight sexual dimorphism.There are four recognized species, Pp. jonesi, Pp. whitei, Pp. broomi, and Pp. lothagamensis, but these taxonomic designations have generated some controversy. Traditionally, these species have been distinguished based on molar size with Pp. jonesi being the smallest and Pp. whitei the largest. However, variation in molar size in Pp. broomi overlaps the other two. Pp. jonesi is distinguished as having a more squarish muzzle than Pp. whitei but more rounded than Pp. broomi; however these distinctions are subtle and better diagnostic criteria are needed.Some authors argue for a confused taxonomy in Parapapio but disagree with the reclassification. Since there may be no significant difference between mean tooth sizes or isotopic signatures in Pp. broomi and Pp. jonesi, these may represent a single sexually dimorphic species. However, the ranges of variation in Pp. broomi and Pp. whitei overlap and show no statistical differences based on an ANOVA run on the eleven interlandmark distances used in their analysis, and propose that the two are merely a single variable species. The sample of Pp. jonesi (STS 565) differs enough in facial characteristics that it remains distinctive from other Parapapio species.

Pelictosuchus

Pelictosuchus is an extinct genus of therocephalian therapsids from the Late Permian of South Africa. It is classified in the family Akidnognathidae. The type species Pelictosuchus paucidens was named by South African paleontologist Robert Broom in 1940 from the Dicynodon Assemblage Zone.Pelictosuchus was once classified in the family Nanictidopidae. Pelictosuchus and other therocephalians traditionally classified as nanictidopids have thin postorbital bars forming the back margins of the eye sockets and parietal bones that form a low sagittal crest at the top of the skull. They were thought to be closely related to another family of therocephalians called Scaloposauridae, although they differed from scaloposaurids in having higher, narrower skulls. Pelictosuchus is no longer classified as a nanictidopid, and is instead considered a member of Akidnognathidae.

Riebeeckosaurus

Riebeeckosaurus is an extinct genus of tapinocephalian therapsids from the Guadalupian epoch of Middle Tapinocephalus Zone, lower Beaufort Beds of the Karoo, in South Africa. Only two skulls are known from the type genus.

It was a herbivorous, medium-sized (2.5 metres (8 ft 2 in) in length, 500 kilograms (1,100 lb) in mass) dinocephalian, with a very long, slender snout and a narrow intertemporal region with a narrow sagittal crest.

SK 46

SK 46 is the fossilized partial cranium and palate of the species Paranthropus robustus. It was discovered in Swartkrans, South Africa by local quarrymen and Robert Broom in 1949.

It is estimated to be 1.5-1.8 million years old.

Its characteristics include large cheek teeth and a sagittal crest. The large teeth and crest for attaching chewing muscles indicate a diet consisting mainly of coarse vegetable matter.

Scalopodon

Scalopodon is an extinct genus of therocephalian therapsids from the Late Permian of Russia. The type species Scalopodon tenuisfrons was named in 1999 from the Kotelnichsky District of Kirov Oblast. Scalopodon is known from a single fragmentary holotype specimen including the back of the skull, the left side of the lower jaw and isolated postorbital and prefrontal bones. The skull was found in the Deltavjatia Assemblage Zone, which dates back to the early Wuchiapingian about 260 million years ago. Distinguishing features of Scalopodon include narrow frontal bones and a distinctive sagittal crest along the parietal region at the back of the skull. Scalopodon was originally classified in the family Scaloposauridae, and was the first scaloposaurid found in Russia (scaloposaurids are also known from southern Africa and Antarctica). More recent studies of therocephalians have found scaloposaurids like Scalopodon to be juvenile forms of larger therocephalians and do not consider Scaloposauridae to be a valid group. Scalopodon and most other scaloposaurids are now classified as basal members of Baurioidea.

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