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I was cleaning out my pool with a leaf scoop the other day and found a small object, which I assume to be a sort of skull or cartilaginous structure of something that had died.
I live in Sydney, Australia and in the pool there were a large quantity of water boatmen and dragonfly nymphs.
What does this skull belong to, and what is the purpose of the hollow, bulbous mounds next to the eye sockets?
What does this skull belong to? - Biology
The axial skeleton forms the central axis of the body and includes the bones of the skull, ossicles of the middle ear, hyoid bone of the throat, vertebral column, and the thoracic cage (ribcage) (Figure 1). The function of the axial skeleton is to provide support and protection for the brain, the spinal cord, and the organs in the ventral body cavity. It provides a surface for the attachment of muscles that move the head, neck, and trunk, performs respiratory movements, and stabilizes parts of the appendicular skeleton.
Figure 1. The axial skeleton consists of the bones of the skull, ossicles of the middle ear, hyoid bone, vertebral column, and rib cage. (credit: modification of work by Mariana Ruiz Villareal)
The order Carnivora belongs to a group of mammals known as Laurasiatheria, which also includes other groups such as bats and ungulates.   Within this group the carnivorans are placed in the clade Ferae. Ferae includes the closest extant relative of carnivorans, the pangolins, as well as several extinct groups of mostly Paleogene carnivorous placentals such as the creodonts, the arctocyonians, and mesonychians.  The creodonts were originally thought of as the sister taxon to the carnivorans, perhaps even ancestral to, based on the presence of the carnassial teeth.  but the nature of the carnassial teeth is different between the two groups. In carnivorans the carnassials are positioned near the front of the molar row, while in the creodonts they are positioned near the back of the molar row.  and this suggests a separate evolutionary history and an order-level distinction.  In addition recent phylogenetic analysis suggests that creodonts are more closely related to pangolins while mesonychians might be the sister group to carnivorans and their stem-relatives. 
The closest stem-carnivorans are the miacoids. The miacoids include the families Viverravidae and Miacidae, and together the Carnivora and Miacoidea form the stem-clade Carnivoramorpha. The miacoids were small, genet-like carnivoramorphs that occupy a variety of niches such as terrestrial and arboreal habitats. Recent studies have shown a supporting amount of evidence that Miacoidea is an evolutionary grade of carnivoramorphs that, while viverravids are monophyletic basal group, the miacids are paraphyletic in respect to Carnivora (as shown in the phylogeny below).        
†carnivoramorph sp. (UALVP 50993 & UALVP 50994)
†carnivoramorph sp. (UALVP 31176)
†carnivoramorph sp. (WW-84: USNM 538395)
†carnivoraform undet. Genus A (UCMP 110072)
†carnivoraform undet. Genus B (SDSNH 56335)
†carnivoraform sp. (PM 3868)
Carnivoramorpha as a whole first appeared in the Paleocene of North America about 60 million years ago.  Crown carnivorans first appeared around 42 million years ago in the Middle Eocene.  Their molecular phylogeny shows the extant Carnivora are a monophyletic group, the crown group of the Carnivoramorpha.  From there carnivorans have split into two clades based on the composition of the bony structures that surround the middle ear of the skull, the cat-like feliforms and the dog-like caniforms.  In feliforms, the auditory bullae are double-chambered, composed of two bones joined by a septum. Caniforms have single-chambered or partially divided auditory bullae, composed of a single bone.  Initially the early representatives of carnivorans were small as the creodonts (specifically, the oxyaenids) and mesonychians dominated the apex predator niches during the Eocene, but in the Oligocene carnivorans became a dominant group of apex predators with the nimravids, and by the Miocene most of the extant carnivoran families have diversified and become the primary terrestrial predators in the Northern Hemisphere.
The phylogenetic relationships of the carnivorans are shown in the following cladogram:     
†Nimravidae (false saber-toothed cats)
Classification of the extant carnivorans Edit
In 1758 the Swedish botanist Carl Linnaeus placed all carnivorans known at the time into the group Ferae (not to be confused with the modern concept of Ferae which also includes pangolins) in the tenth edition of his book Systema Naturae. He recognized six genera: Canis (canids and hyaenids), Phoca (pinnipeds), Felis (felids), Viverra (viverrids, herpestids, and mephitids), Mustela (non-badger mustelids), Ursus (ursids, large species of mustelids, and procyonids).  It wasn't until 1821 that the English writer and traveler Thomas Edward Bowdich gave the group its modern and accepted name. 
Initially the modern concept of Carnivora was divided into two suborders: the terrestrial Fissipedia and the marine Pinnipedia.  Below is the classification of how the extant families were related to each other after American paleontologist George Gaylord Simpson in 1945: 
- Order Carnivora Bowdich, 1821
- Suborder Fissipedia Blumenbach, 1791
- Superfamily CanoideaG. Fischer de Waldheim, 1817
- Family CanidaeG. Fischer de Waldheim, 1817 – dogs
- Family UrsidaeG. Fischer de Waldheim, 1817 – bears
- Family ProcyonidaeBonaparte, 1850 – raccoons and pandas
- Family MustelidaeG. Fischer de Waldheim, 1817 – skunks, badgers, otters and weasels
- Family ViverridaeJ. E. Gray, 1821 – civets and mongooses
- Family HyaenidaeJ. E. Gray, 1821 – hyenas
- Family FelidaeG. Fischer de Waldheim, 1817 – cats
- Family OtariidaeJ. E. Gray, 1825 – eared seals
- Family OdobenidaeJ. A. Allen, 1880 – walrus
- Family PhocidaeJ. E. Gray, 1821 – earless seals
Since then, however, the methods in which mammalogists use to assess the phylogenetic relationships among the carnivoran families has been improved with using more complicated and intensive incorporation of genetics, morphology and the fossil record. Research into Carnivora phylogeny since 1945 has found Fisspedia to be paraphlyetic in respect to Pinnipedia,  with pinnipeds being either more closely related to bears or to weasels.      The small carnivoran families Viverridae,  Procyonidae, and Mustelidae have been found to be polyphyletic:
- Mongooses and a handful of Malagasy endemic species are found to be in a clade with hyenas, with the Malagasy species being in their own family Eupleridae. 
- The African palm civet is a basal cat-like carnivoran. 
- The linsang is more closely related to cats. 
- Pandas are not procyonids nor are they a natural grouping.  The giant panda is a true bear  while the red panda is a distinct family. 
- Skunks and stink badgers are placed in their own family, and are the sister group to a clade pertaining Ailuridae, Procyonidae and Mustelidae sensu stricto. 
Below is a table chart of the extant carnivoran families and number of extant species recognized by various authors of the first and fourth volumes of Handbook of the Mammals of the World published in 2009  and 2014  respectively:
Carnivora Bowdich, 1821 Feliformia Kretzoi, 1945 Nandinioidea Pocock, 1929 Family English Name Distribution Number of Extant Species Type Taxon Image Figure Nandiniidae Pocock, 1929 African Palm Civet Sub-Saharan Africa 1 Nandinia binotata (J. E. Gray, 1830) Feloidea G. Fischer de Waldheim, 1817 Family English Name Distribution Number of Extant Species Type Taxon Image Figure Felidae G. Fischer de Waldheim, 1817 Cats Americas, Africa, and Eurasia (introduced to Madagascar, Australasia and several islands) 37 Felis catus Linnaeus, 1758 Prionodontidae Horsfield, 1822 Linsangs Indomalayan realm 2 Prionodon linsang (Hardwicke, 1821) Viverroidea J. E. Gray, 1821 Family English Name Distribution Number of Extant Species Type Taxon Image Figure Viverridae J. E. Gray, 1821 Civets, genets, and oyans Southern Europe, Indomalayan realm, and Africa (introduced to Madagascar) 34 Viverra zibetha Linnaeus, 1758 Herpestoidea Bonaparte, 1845 Family English Name Distribution Number of Extant Species Type Taxon Image Figure Hyaenidae J. E. Gray, 1821 Hyenas Africa, the Middle East, the Caucasus, Central Asia, and the Indian subcontinent 4 Hyaena hyaena (Linnaeus, 1758) Herpestidae Bonaparte, 1845 Mongooses Iberian Peninsula, Africa, the Middle East, the Caucasus, Central Asia, and the Indomalayan realm 34 Herpestes ichneumon (Linnaeus, 1758) Eupleridae Chenu, 1850 Malagasy mongooses and civets Madagascar 8 Eupleres goudotii Doyère, 1835 Caniformia Kretzoi, 1945 Canoidea G. Fischer de Waldheim, 1817 Family English Name Distribution Number of Extant Species Type Taxon Image Figure Canidae G. Fischer de Waldheim, 1817 Dogs Americas, Africa, and Eurasia (introduced to Madagascar, Australasia and several islands) 35 Canis familiaris Linnaeus, 1758 Ursoidea G. Fischer de Waldheim, 1817 Family English Name Distribution Number of Extant Species Type Taxon Image Figure Ursidae G. Fischer de Waldheim, 1817 Bears Americas and Eurasia 8 Ursus arctos Linnaeus, 1758 Phocoidea J. E. Gray, 1821 Family English Name Distribution Number of Extant Species Type Taxon Image Figure Odobenidae J. A. Allen, 1880 Walrus The North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere 1 Odobenus rosmarus (Linnaeus, 1758) Otariidae J. E. Gray, 1825 Eared Seals Subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans and the southern Indian and Atlantic Oceans 15 Otaria flavescens (Linnaeus, 1758) Phocidae J. E. Gray, 1821 Earless Seals The sea and Lake Baikal 18 Phoca vitulina Linnaeus, 1758 Musteloidea G. Fischer de Waldheim, 1817 Family English Name Distribution Number of Extant Species Type Taxon Image Figure Mephitidae Bonaparte, 1845 Skunks and stink badgers Americas, western Philippines, and Indonesia and Malaysia 12 Mephitis mephitis (Schreber, 1776) Ailuridae J. E. Gray, 1843 Red Panda Eastern Himalayas and southwestern China 1 Ailurus fulgens F. Cuvier, 1825 Procyonidae J. E. Gray, 1825 Raccoons Americas (introduced to Europe, the Caucasus, and Japan) 12 Procyon lotor (Linnaeus, 1758) Mustelidae G. Fischer de Waldheim, 1817 Weasels, otters, and badgers Americas, Africa, and Eurasia (introduced to Australasia and several islands) 57 Mustela erminea Linnaeus, 1758
Craniodental region Edit
The canine teeth are usually large and conical. The canines are thick and incredibly stress resistant. All of the terrestrial species of carnivorans have three incisors on the top and bottom row of the dentition (the exception being is the sea otter (Enhydra lutris) which only has two lower incisor teeth).   The third molar has been lost. The carnassial pair is made up by the fourth upper premolar and the first lower molar teeth. Like most mammals the dentition is heterodont in nature, though in some species like the aardwolf (Proteles cristata) the teeth have been greatly reduced and the cheek teeth are specialised for eating insects. In pinnipeds the teeth are homodont as they have evolved to grasp or to catch fish, and the cheek teeth are often lost.  In bears and raccoons the carnassial pair is secondarily reduced.  The skulls are heavily built with a strong zygomatic arch.  Often a sagittal crest is present, sometimes more evident in sexual dimorphic species like sea lions and fur seals, though it has also been greatly reduced seen in some small carnivorans.  The braincase is enlarged and the frontoparietal is position at the front of it. In most species the eyes are position at the front of the face. In caniforms the rostrum is usually longer with many teeth, where in comparison with felifoms the rostrum is shorter and have fewer teeth. The carnassial teeth in feliforms, however is more sectional.  The turbinates are large and complex in comparison to other mammals, providing a large surface area for olfactory receptors. 
Postcranial region Edit
Aside from an accumulation of characteristics in the dental and cranial features, not much of their overall anatomy unites them as a group.  All species of carnivorans have quadrupedal limbs with usually five digits at the front feet and four digits at the back feet. In terrestrial carnivorans the feet have soft pads. The feet can either be digitigrade seen in cats, hyenas and dogs or plantigrade seen in bears, skunks, raccoons, weasels, civets and mongooses. In pinnipeds the limbs have been modified into flippers. Unlike other marine mammals, such as cetaceans and sirenians which have fully functional tails to help them swim, pinnipeds use their limbs underwater for locomotion.
In earless seals they use their back flippers sea lions and fur seals use their front flippers, and the walrus use all of their limbs. This resulted in pinnipeds having significantly shorter tails. Aside from the pinnipeds, dogs, bears, hyenas, and cats have distinct and recognizable appearances. Dogs are usually cursorial mammals and are gracile in appearance, often relying on their teeth to hold to prey bears are much larger and rely on their physical strength to forage for food. Cats in comparison to dogs and bears have much longer and stronger frontlimbs armed with retractable claws to hold on to prey. Hyenas are dog-like feliforms that have sloping backs due to their front legs being longer than their hindlegs. The raccoon family as well as the red panda are small, bear-like carnivorans with long tails. The other small carnivoran families Nandiniidae, Prionodontidae, Viverridae, Herpestidae, Eupleridae, Mephitidae and Mustelidae have through convergent evolution maintained the small, ancestral appearance of the miacoids, though there is some variation seen such as the robust and stout physicality of badgers and the wolverine (Gulo gulo).  Male carnivorans usually have bacula, though they are absent in hyenas and binturongs. 
Depending on the environment the species is, the length and density of their fur varies. In warm climate species the fur is often short in length and lighter. In comparison to cold climate species the fur is either dense or long, often with an oily substance to keep them warm. The pelage coloration comes in many colors, often including black, white, orange, yellow, red, and many shades of gray and brown. There can be colored patterns too, such striped, spotted, blotched, banded, or otherwise boldly patterned. There seems to be a correlation between habitat and color pattern as for example spotted or banded species tend to be found in heavily forested environments.  Some species like the grey wolf is a polymorphic species with different individual variation in colors. The arctic fox (Vulpes lagopus) and the stoat (Mustela erminea) the fur goes from white and dense in the winter to brown and sparse in the summer. In pinnipeds, polar bears, and sea otters have a thick insulating layer of blubber to help maintain their body temperature.
Lateral View of the Skull
It is primarily consisting of the large and round brain case above and the upper and lower jaws. The areas are separated by the zygomatic arch the bridge of bone.
- Zygomatic arch – it is the bony arch on the side of the skull. It starts from the cheek area to the area above the ear canal.
- Temporal fossa – It is a shallow space in between the side of the braincase and above the zygomatic arch level.
- Infratemporal fossa – It is an area below the zygomatic arch level and deep to the vertical part of the mandible.
Meckel's cartilage, located within the first pharyngeal arch mandibular prominence, forms a cartilage "template" besides which the mandible bone develops by the process of intramembranous ossification. It is important to note that this cartilage template does not ossify (endochondral ossification) but provides a transient structure where the mandible will form, and later degenerates.
See also the 1957 historic paper on temporomandibular joint development. Ε]
The first fossils were discovered in 1972 along Lake Turkana (at the time called Lake Rudolf) in Kenya, and were detailed by Kenyan palaeoanthropologist Richard Leakey the following year. The specimens were: a large and nearly complete skull (KNM-ER 1470, the lectotype) discovered by Bernard Ngeneo, a local a right femur (KNM-ER 1472) discovered by J. Harris an upper femur (proximal) fragment (KNM-ER 1475) discovered by fossil collector Kamoya Kimeu and a complete left femur (KNM-ER 1481) discovered by Harris. However, it is unclear if the femora belong to the same species as the skull. He classified them under the genus Homo because he had reconstructed the skull fragments so that it had a large brain volume and a flat face, but did not assign them to a species. Because the horizon they were discovered in was, at the time, dated to 2.9–2.6 million years ago (mya), Leakey thought these specimens were a very early human ancestor.  This challenged the major model of human evolution at the time where Australopithecus africanus gave rise to Homo about 2.5 mya, but if Homo had already existed at this time, it would call for serious revisions.  However, the area was redated to about 2 mya in 1977 (the same time period as H. habilis and H. ergaster/H. erectus),  and more precisely to 2.1–1.95 mya in 2012.  They were first assigned to the species habilis in 1975 by anthropologists Colin Groves and Vratislav Mazák. In 1978, in a joint paper with Leakey and English anthropologist Alan Walker, Walker suggested the remains belong in Australopithecus (and that the skull was incorrectly reconstructed), but Leakey still believed they belonged to Homo, though they both agreed that the remains could belong to habilis. 
KNM-ER 1470 was much larger than the Olduvai remains, so the terms H. habilis sensu lato ("in the broad sense") and H. habilis sensu stricto ("in the strict sense") were used to include or exclude the larger morph, respectively.   In 1986, English palaeoanthropologist Bernard Wood first suggested these remains represent a different Homo species, which coexisted with H. habilis and H. ergaster/H. erectus. Coexisting Homo species conflicted with the predominant model of human evolution at the time which was that modern humans evolved in a straight line directly from H. ergaster/H. erectus which evolved directly from H. habilis.  In 1986, the remains were placed into a new species, rudolfensis, by Russian anthropologist Valery Alekseyev  (but he used the genus Pithecanthropus, which was changed to Homo three years later by Groves).  In 1999, Kennedy argued that the name was invalid because Alekseyev had not assigned a holotype.  Pointing out that this is in fact not mandatory, Wood the same year nevertheless designated KNM-ER 1470 as the lectotype.  However, the validity of this species has also been debated on material grounds, with some arguing that H. habilis was highly sexually dimorphic like modern non-human apes, with the larger skulls classified as "H. rudolfensis" actually representing male H. habilis.   In 1999, Wood and biological anthropologist Mark Collard recommended moving rudolfensis and habilis to Australopithecus based on the similarity of dental adaptations. However, they conceded that dental anatomy is highly variable among hominins and not always reliable when formulating family trees. 
In 2003, Australian anthropologist David Cameron concluded that the earlier australopithecine Kenyanthropus platyops was the ancestor of rudolfensis, and reclassified it as K. rudolfensis. He also believed that Kenyanthropus was more closely related to Paranthropus than Homo.  In 2008, a re-reconstruction of the skull concluded it was incorrectly restored originally, though agreed with the classification as H. rudolfensis.  In 2012, British palaeoanthropologist Meave Leakey described the juvenile partial face KNM-ER 62000 discovered in Koobi Fora, Kenya noting it shares several similarities to KNM-ER 1470 and is smaller, she assigned it to H. rudolfensis, and, because prepubescent male and female bones should be indistinguishable, differences between juvenile H. rudolfensis and adult H. habilis specimens support species distinction. She also concluded that the jawbone KNM-ER 1802, an important specimen often used in classifying other specimens as H. rudolfensis, actually belongs to a different (possibly undescribed) species,  but American palaeoanthropologist Tim D. White believes this to be premature because it is unclear how wide the range of variation is in early hominins.  The 2013 discovery of the 1.8 Ma Georgian Dmanisi skulls which exhibit several similarities with early Homo have led to suggestions that all contemporary groups of early Homo in Africa, including H. habilis and H. rudolfensis, are the same species and should be assigned to H. erectus.   There is still no wide consensus on how rudolfensis and habilis relate to H. ergaster and descendent species. 
Beyond KNM-ER 1470, there is disagreement on which specimens actually belong in H. rudolfensis as it is difficult to assign with accuracy remains that do not preserve the face and jaw.   No H. rudolfensis bodily elements have been definitively associated with a skull and thus to the species.  Most proposed H. rudolfensis fossils come from Koobi Fora and date to 1.9–1.85 mya. Remains from the Shungura Formation, Ethiopia, and Uraha, Malawi, are dated as far back as 2.5–2.4 mya, which would make it the earliest identified species of Homo. The latest potential specimen is KNM-ER 819 dating to 1.65–1.55 mya.  : 210
Nonetheless, H. rudolfensis and H. habilis generally are recognised members of the genus at the base of the family tree, with arguments for synonymisation or removal from the genus not widely adopted.  Though it is now largely agreed upon that Homo evolved from Australopithecus, the timing and placement of this split has been much debated, with many Australopithecus species having been proposed as the ancestor. The discovery of LD 350-1, the oldest Homo specimen, dating to 2.8 mya, in the Afar Region of Ethiopia may indicate that the genus evolved from A. afarensis around this time. The species LD 350-1 belongs to could be the ancestor of H. rudolfensis and H. habilis, but this is unclear.  Based on 2.1 million year old stone tools from Shangchen, China, possibly an ancestral species to H. rudolfensis and H. habilis dispersed across Asia. 
In 1973, Mr. Leakey had reconstructed the skull KNM-ER 1470 with a flat face and a brain volume of 800 cc (49 cu in).  In 1983, American physical anthropologist Ralph Holloway revised the base of the skull and calculated a brain volume of 752–753 cc (45.9–46.0 cu in).  For comparison, H. habilis specimens average about 600 cc (37 cu in), and H. ergaster 850 cc (52 cu in).  Anthropologist Timothy Bromage and colleagues revised the face again at a 5° incline (slightly prognathic) instead of completely flat, but pushed the nasal bone back directly beneath the frontal bones. He then said it was possible to predict brain size based on just the face and (disregarding the braincase) calculated 526 cc (32.1 cu in), and chalked up the errors of Leakey's reconstruction to a lack of research of the biological principles of facial anatomy at the time as well as confirmation bias, as a flat-faced reconstruction of the skull aligned with the predominant model of human evolution at the time. This was refuted by American palaeoanthropologist John D. Hawks because the skull remained more or less unchanged except for the 5° rotation outwards.  Bromage and colleagues returned in 2008 with a revised skull reconstruction and brain volume estimate of 700 cc (43 cu in). 
Fossils have generally been classified into H. rudolfensis due to large skull size, flatter and broader face, broader cheek teeth, more complex tooth crowns and roots, and thicker enamel compared to H. habilis.  Early Homo are characterised by larger teeth compared to later Homo. The cheek teeth of KNM-ER 60000, a jawbone, in terms of size are on the lower end for early Homo, except for the third molar which is within range. The molars increase in size towards the back of the mouth. The tooth rows of KNM-ER 1470, KNM-ER 60000, and KNM-ER 62000 are rectangular, whereas the tooth row of KNM-ER 1802 is U-shaped, which may indicate that these two morphs represent different species,  or demonstrate the normal range of variation for H. rudolfensis jaws.  In UR 501 from Uraha, Malawi—the oldest H. rudolfensis specimen dating to 2.5–2.3 mya—the tooth enamel thickness is the same as in other early Homo, but the enamel on the molars is almost as thick as Paranthropus molars (which have some of the thickest enamel of any hominin). Such a wide variation in enamel thickness across the cheek teeth is not exhibited in KNM-ER 1802, which may indicate regional differences among H. rudolfensis populations.  
Body size estimates of H. rudolfensis and H. habilis typically conclude a small size comparable to australopithecines. These largely depend on the H. habilis partial skeleton OH 62 estimated at 100–120 cm (3 ft 3 in–3 ft 11 in) in height and 20–37 kg (44–82 lb) in weight. H. rudolfensis is thought to be bigger than H. habilis, but it is unclear how big this species was as no bodily elements have been definitively associated with a skull.  Based on just the KNM-ER 1470 skull, male H. rudolfensis were estimated to have been 160 cm (5 ft 3 in) in height and 60 kg (130 lb) in weight, and females 150 cm (4 ft 11 in) and 51 kg (112 lb). 
For specimens that might be H. rudolfensis: the femur KNM-ER 1472 which may also be H. habilis or H. ergaster was estimated at 155.9 cm (5 ft 1 in) and 41.8 kg (92 lb), the humerus KNM-ER 1473 162.9 cm (5 ft 4 in) and 47.1 kg (104 lb), the partial leg KNM-ER 1481 which may also be H. ergaster 156.7 cm (5 ft 2 in) and 41.8 kg (92 lb), the pelvis KNM-ER 3228 which may also be H. ergaster 165.8 cm (5 ft 5 in) and 47.2 kg (104 lb), and the femur KNM-ER 3728 which may be H. habilis or P. boisei 153.3 cm (5 ft) and 40.3 kg (89 lb).  It is generally assumed that pre-H. ergaster hominins, including H. rudolfensis and H. habilis, exhibited sexual dimorphism with males markedly bigger than females. However, relative female body mass is unknown in either species. 
Early hominins, including H. rudolfensis, are thought to have had thick body hair coverage like modern non-human apes because they appear to have inhabited cooler regions and are thought to have had a less active lifestyle than (presumed hairless) post-ergaster species, and so probably required thick body hair to stay warm.  The juvenile specimen KNM-ER 62000, a partial face, has the same age landmarks as a 13 to 14 year old modern human, but more likely died at around 8 years of age due to the presumed faster growth rate among early hominins based on dental development rate. 
It is typically thought that the diets of early Homo had a greater proportion of meat than Australopithecus, and that this led to brain growth. The main hypotheses regarding this are: meat is energy- and nutrient-rich and put evolutionary pressure on developing enhanced cognitive skills to facilitate strategic scavenging and monopolise fresh carcasses, or meat allowed the large and calorie-expensive ape gut to decrease in size allowing this energy to be diverted to brain growth. Alternatively, it is also suggested that early Homo, in a drying climate with scarcer food options, relied primarily on underground storage organs (such as tubers) and food sharing, which facilitated social bonding among both male and female group members. However, unlike what is presumed for H. ergaster and later Homo, short-statured early Homo were likely incapable of endurance running and hunting, and the long and Australopithecus-like forearm of H. habilis could indicate early Homo were still arboreal to a degree. Also, organised hunting and gathering is thought to have emerged in H. ergaster. Nonetheless, the proposed food-gathering models to explain large brain growth necessitate increased daily travel distance.  Large incisor size in H. rudolfensis and H. habilis compared to Australopithecus predecessors implies these two species relied on incisors more. The large, Australopithecus-like molars could indicate more mechanically challenging food compared to later Homo. The bodies of the mandibles of H. rudolfensis and other early Homo are thicker than those of modern humans and all living apes, more comparable to Australopithecus. The mandibular body resists torsion from the bite force or chewing, meaning their jaws could produce unusually powerful stresses while eating. 
H. rudolfensis is not associated with any tools. However, the greater molar cusp relief in H. rudolfensis and H. habilis compared to Australopithecus suggests the former two used tools to fracture tough foods (such as pliable plant parts or meat), otherwise the cusps would have been more worn down. Nonetheless, the jaw adaptations for processing mechanically challenging food indicates technological advancement did not greatly affect their diet. Large concentrations of stone tools are known from Koobi Fora. Because these aggregations are coincident with the emergence of H. ergaster, it is probable H. ergaster manufactured them, though it is not possible to definitively attribute the tools to a species because H. rudolfensis, H. habilis, and P. boisei are also well-known from the area.  The oldest specimen of Homo, LD 350-1, is associated with the Oldowan stone tool industry, meaning this tradition had been in use by the genus since near its emergence. 
Early H. rudolfensis and Paranthropus have exceptionally thick molars for hominins, and the emergence of these two coincides with a cooling and aridity trend in Africa about 2.5 mya. This could mean they evolved due to climate change. Nonetheless, in East Africa, tropical forests and woodlands still persisted through periods of drought.  H. rudolfensis coexisted with H. habilis, H. ergaster, and P. boisei. 
That's not a dinosaur: Tiny fossil discovered in 2020 actually belongs to a lizard
Bones were discovered in Australia 15 years ago, and now it's known they belonged to the largest dinosaur ever found in the country. Associated Press
A small skull found inside a piece of 99-million-year-old amber had scientists believing in 2020 that they had discovered the smallest dinosaur to date. But new research has concluded the fossil belongs to a strange-looking lizard.
In early 2020, the Oculudentavis khaungraae was presented as a flying dinosaur given its round, birdlike skull. The creature, roughly the size of a hummingbird, was found in Myanmar and believed to have existed about 100 million years ago.
But some researchers weren't sure whether it was actually a dinosaur or a bird, and the research that had declared it a dinosaur was redacted. Another group of researchers examined a similar fossil found in the area, and their findings published on Monday determined it belonged toa never-before-seen lizard.
"The specimen puzzled everyone involved at first, because if it was a lizard, it was a highly unusual one," said lead researcher Arnau Bolet of the Institut Català de Paleontologia Miquel Crusafont in Barcelona, Spain.
Once thought to be a bird, the Oculudentavis naga turned out to be a small, unique lizard. (Photo: Scientific illustration by Stephanie Abramowicz.)
A CT scan was used to analyze the two species, and although similar, they weren't exactly the same. Both had characteristics that are common in lizards, including teeth fused to the jaw rather than nestled into sockets as in most dinosaurs.
"We concluded that both specimens were similar enough to belong to the same genus, Oculudentavis, but a number of differences suggest that they represent separate species," Bolet said.
Comparison of skulls of the Oculudentavis naga (A) and the Oculudentavis khaungraae (B) from the early 2020 study. Although not completely the same, they both are lizards. (Photo: Courtesy: Current Biology)
The differences in specimens led the team from the most recent study to name the creature Oculudentavis naga in honor of the Naga people in Myanmar where the artifact was found.
Though this Oculudentavis species resembles a lizard, researchers note it doesn't look like anything seen in today's world.
"It's a really weird animal. It's unlike any other lizard we have today," herpetologist Juan Diego Daza of Sam Houston State University said in Florida Museum.
Daza also gave credit to the workers who "who risk their lives to recover these amazing amber fossils." Acquiring Burmese amber, the type of amber where this fossil was found, has become difficult in Myanmar after the country's mines were taken over by the military in 2017.
Bones of the skeletal system can be classified into four major types, categorized by shape and size. The four main bone classifications are long, short, flat, and irregular bones. Long bones are bones that have greater length than width. Examples include arm, leg, finger, and thigh bones.
Short bones are almost the same in length and width and are close to being cube-shaped. Examples of short bones are wrist and ankle bones.
Flat bones are thin, flat, and typically curved. Examples include cranial bones, ribs, and the sternum.
Irregular bones are atypical in shape and can not be classified as long, short, or flat. Examples include hip bones, facial bones, and vertebrae.
The cranium (also known as the neurocranium) is formed by the superior aspect of the skull. It encloses and protects the brain, meninges, and cerebral vasculature.
Anatomically, the cranium can be subdivided into a roof and a base:
- Cranial roof - comprised of the frontal, occipital and two parietal bones. It is also known as the calvarium.
- Cranial base - comprised of six bones: frontal, sphenoid, ethmoid, occipital, parietal and temporal. These bones articulate with the 1st cervical vertebra (atlas), the facial bones, and the mandible (jaw).
Clinical Relevance: Cranial Fractures
Fractures of the cranium typically arise from blunt force or penetrating trauma. When considering cranial fractures, one area of clinical importance is the pterion - a H-shaped junction between the temporal, parietal, frontal, and sphenoid bones.
The pterion overlies the middle meningeal artery, and fractures in this area may injury the vessel. Blood can accumulate between the skull and the dura mater, forming an extradural haematoma.
[caption align="aligncenter"] Fig 2 - Lateral view of the skull, showing the path of the meningeal arteries. Note the pterion, a weak point of the skull, where the anterior middle meningeal artery is at risk of damage.[/caption]
The facial skeleton (also known as the viscerocranium) supports the soft tissues of the face.
It consists of 14 bones, which fuse to house the orbits of the eyes, the nasal and oral cavities, and the sinuses. The frontal bone, typically a bone of the calvaria, is sometimes included as part of the facial skeleton.
- Zygomatic (2) - forms the cheek bones of the face and articulates with the frontal, sphenoid, temporal and maxilla bones.
- Lacrimal (2) - the smallest bones of the face. They form part of the medial wall of the orbit.
- Nasal (2) - two slender bones that are located at the bridge of the nose.
- Inferior nasal conchae (2) - located within the nasal cavity, these bones increase the surface area of the nasal cavity, thus increasing the amount of inspired air that can come into contact with the cavity walls.
- Palatine (2) - situated at the rear of oral cavity and forms part of the hard palate.
- Maxilla (2) - comprises part of the upper jaw and hard palate.
- Vomer - forms the posterior aspect of the nasal septum.
- Mandible (jaw) - articulates with the base of the cranium at the temporomandibular joint (TMJ).
Clinical Relevance: Facial Fractures
Fractures of the facial skeleton are relatively common and most frequently result from road traffic collisions, fist fights, and falls.
The four most common facial fracture types are:
- Nasal fracture - the most common facial fracture, due to the prominent position of the nasal bones at the bridge of the nose. There is often significant soft tissue swelling and associated epistaxis.
- Maxillary fracture - associated with high-energy trauma. Fractures affecting of maxillary bones are classified using the Le Fort classification, ranging from 1 to 3.
- Mandibular fracture - often bilateral occurring directly at the side of trauma, and indirectly at the contralateral side due to transmitted forces. Clinical features include pain at fracture site and misalignment of the teeth (malocclusion)
- Zygomatic arch fracture - associated with trauma to the side of the face. Displaced fractures can damage the nearby infraorbital nerve, leading to ipsilateral paraesthesia of the check, nose, and lip.
Evolution of Primates
The first primate-like mammals are referred to as proto-primates. They were roughly similar to squirrels and tree shrews in size and appearance. The existing fossil evidence (mostly from North Africa) is very fragmented. These proto-primates remain largely mysterious creatures until more fossil evidence becomes available. The oldest known primate-like mammals with a relatively robust fossil record is Plesiadapis (although some researchers do not agree that Plesiadapis was a proto-primate). Fossils of this primate have been dated to approximately 55 million years ago. Plesiadapiforms were proto-primates that had some features of the teeth and skeleton in common with true primates. They were found in North America and Europe in the Cenozoic and went extinct by the end of the Eocene.
The first true primates were found in North America, Europe, Asia, and Africa in the Eocene Epoch. These early primates resembled present-day prosimians such as lemurs. Evolutionary changes continued in these early primates, with larger brains and eyes, and smaller muzzles being the trend. By the end of the Eocene Epoch, many of the early prosimian species went extinct due either to cooler temperatures or competition from the first monkeys.
Figure 1. The howler monkey is native to Central and South America. It makes a call that sounds like a lion roaring. (credit: Xavi Talleda)
Anthropoid monkeys evolved from prosimians during the Oligocene Epoch. By 40 million years ago, evidence indicates that monkeys were present in the New World (South America) and the Old World (Africa and Asia). New World monkeys are also called Platyrrhini—a reference to their broad noses (Figure 1). Old World monkeys are called Catarrhini—a reference to their narrow noses. There is still quite a bit of uncertainty about the origins of the New World monkeys. At the time the platyrrhines arose, the continents of South American and Africa had drifted apart. Therefore, it is thought that monkeys arose in the Old World and reached the New World either by drifting on log rafts or by crossing land bridges. Due to this reproductive isolation, New World monkeys and Old World monkeys underwent separate adaptive radiations over millions of years. The New World monkeys are all arboreal, whereas Old World monkeys include arboreal and ground-dwelling species.
Apes evolved from the catarrhines in Africa midway through the Cenozoic, approximately 25 million years ago. Apes are generally larger than monkeys and they do not possess a tail. All apes are capable of moving through trees, although many species spend most their time on the ground. Apes are more intelligent than monkeys, and they have relatively larger brains proportionate to body size. The apes are divided into two groups. The lesser apes comprise the family Hylobatidae, including gibbons and siamangs. The great apes include the genera Pan (chimpanzees and bonobos) (Figure 2a), Gorilla (gorillas), Pongo (orangutans), and Homo (humans) (Figure 2b). The very arboreal gibbons are smaller than the great apes they have low sexual dimorphism (that is, the genders are not markedly different in size) and they have relatively longer arms used for swinging through trees.
Figure 2. The (a) chimpanzee is one of the great apes. It possesses a relatively large brain and has no tail. (b) All great apes have a similar skeletal structure. (credit a: modification of work by Aaron Logan credit b: modification of work by Tim Vickers)
Dawn of Humanity
Becoming Human Part 1
In August 1856, in the German valley of Neander—Neanderthal in German—men cutting limestone for the Prussian construction industry stumbled upon some bones in a cave. Looking vaguely human, the bones—a piece of a skull, portions of limbs, and fragments of shoulder blades and ribs—eventually made their way to an anatomist in Bonn named Hermann Schaafhausen.
Schaafhausen pored over the fossils, observing their crests and knobs. He noticed that the bones had the overall shape youɽ expect from a human skeleton. But some bones had strange features, too. The skullcap, for example, sported a heavy brow ridge, hanging over the eyes like a boney pair of goggles. It was, at once, human and not.
The Neanderthal Man challenged Schaafhausen with a simple yet profound question: Was it a human, or did it belong to another species?
It's been over 150 years since the bones first emerged from the Neander Valley—a time during which we've learned a vast amount about human evolution. Today, scientists can even scan the genomes of Neanderthals who died 50,000 years ago. And yet the debate still rages. It's a debate that extends beyond Neanderthals, forcing us to ask what it means to be a species at all.
Variations on a theme
The Neander Valley bones were a sensation as soon as Schaafhausen published his report on them in 1857, because nothing like them had been seen before. Earlier in the 1800s, cave explorers had found ancient human bones, sometimes lying next to fossils of cave bears and other extinct animals. Naturalists had a hazy sense from such bones that humanity had been around for quite a long time. But the idea that humans—or any other species—had evolved was scandalous. Darwin would not publish The Origin of Species for another two years. Instead, naturalists saw humans as a species distinct from chimpanzees, gorillas, and all other primate species. We were distinct today, and we had been distinct since creation.
The youngest Neanderthal fossils date to 28,000 years ago.
Within the human species, European anatomists divided people into races. They often ranked Europeans as the noblest race, considering the others barely better than apes. To justify this racist view of humanity, anatomists searched for clear-cut differences between the skeletons of different races—the size of skulls, the slopes of brows, the width of noses. Yet their attempts to neatly sort people into groups were bedeviled by the blurry variations in our species. Within a single so-called race, people varied in color, height, and facial features. Schaafhausen knew, for example, about a skull dug up from an ancient grave in Germany that "resembled that of a Negro," as he wrote.
A barbarian (with sword) attacking a Roman legionary in a second-century relief. Neanderthals wouldn't have been out of place amongst such savage sorts, Schaafhausen believed.
On this confusing landscape Schaafhausen tried find a place for the Neanderthal Man. He decided that its heavy brow didn't disqualify it as a human. To back up this diagnosis, he relied on stories of ancient European savagery. "Even of the Germans," Schaafhausen wrote in his 1857 report on the Neander Valley bones, "Caesar remarks that the Roman soldiers were unable to withstand their aspect and the flashing of their eyes, and that a sudden panic seized his army."
Schaafhausen searched historical records for other clues of Europe's monstrous past. "The Irish were voracious cannibals, and considered it praiseworthy to eat the bodies of their parents," he wrote. In the 1200s, ancient tribes in Scandinavia still lived in the mountains and forests, wearing animal skins, "uttering sounds more like the cries of wild beasts than human speech."
Surely, in such a savage place, this heavy-browed Neanderthal would have fit right in.
A distinctive creature
When Schaafhausen published his report, many other naturalists tried to make sense of the bones for themselves. After Darwin published his theory of evolution in 1859, new possibilities arose: Perhaps humans evolved from Neanderthals, or perhaps they were both descended from a common ancestor.
Thomas Huxley, Darwin's great champion in England, argued that Neanderthals were human, pointing to the thick foreheads of living Australian Aborigines. William King, an Irish geologist, disagreed. In an 1864 paper, "The Reputed Fossil Man of the Neanderthal," he pointed to a long list of traits that separated it from living humans—from its tightly curved ribs to the massive sinuses in its skull. Its braincase was so ape-like that it could not house a human-like brain.
Australian Aborigines have a prominent brow ridge, a fact that helped lead Thomas Huxley to argue that Neanderthals were indeed human.
"I feel myself constrained to believe that the thoughts and desires which once dwelt within it never soared beyond those of a brute," King wrote.
From all this evidence, King concluded that the Neanderthal Man was not simply an ancient European, as Schaafhausen had thought. It was a separate species. He even gave that species a name: Homo neanderthalensis.
King was certainly right that Neanderthals were distinct from living humans. Subsequent generations of fossil-hunters have found remains of Neanderthals from Spain to Israel to Russia. The youngest Neanderthal fossils date to 28,000 years ago. The oldest ones date back over 200,000 years. Like the original Neanderthal Man, they were stocky, with a heavy brow ridge and other singular traits. We can't know exactly what thoughts and desires soared in their heads, but they certainly left behind some telling clues—carefully engineered spear blades and stone knives painted shells that might have been used as jewelry. Neanderthals endured the comings and goings of ice ages in Europe and Asia, hunting for reindeer, rhinoceroses, and other big game.
As the fossils have emerged, paleoanthropologists have revisited the question of whether Neanderthals are part of our own species—call them Homo sapiens neanderthalensis—or a separate Homo neanderthalensis. Some researchers argued that Neanderthals belonged to a single species of humans stretching across the Old World, one that evolved over the past million years from small-brained hominids into our big-brained form.
Europeans and Asians carry a small portion of DNA inherited from Neanderthals.
But some researchers challenged this view. They pointed out that for thousands of years, Europe was home to the burly Neanderthals as well as slender humans. Neanderthals didn't give rise to living Europeans, these scientists argued they were replaced by immigrants expanding out of Africa—perhaps even outcompeted into extinction.
Over the past 15 years, Svante Pääbo, a geneticist at the Max Planck Institute of Evolutionary Anthropology, and his colleagues have uncovered an entirely new source of evidence about the nature of Neanderthals: their DNA. Starting with those fossils from the Neander Valley, they extracted bits of genetic material that had survived tens of thousands of years. Eventually, they were able to assemble the fragments into the entire Neanderthal genome.
Populations of the same species that a river or other barrier divides can become unable to breed successfully with each other. Such an inability never occurred between Neanderthals and humans, who bred successfully at least once.
It's clearly different from the genome of any human alive today, sprinkled with many distinctive mutations. These mutations accumulated in a clock-like way, and by tallying them up, Pääbo and his colleagues estimate that Neanderthals and humans share a common ancestor that lived 800,000 years ago. It's possible that the ancestors of Neanderthals expanded out of Africa then, while our own ancestors stayed behind.
A question of breeding
That's a long time—long enough to reasonably ask if humans and Neanderthals are indeed two separate species. Old species split into new ones when some of their members get isolated from the rest. If a river cuts the range of a species of frog in two, for example, the frogs on one side of the river may only be able to mate with one another. Each population will evolve along its own path. If they are isolated long enough, they will have trouble interbreeding. They may even be unable to interbreed at all.
From these facts of evolution, the biologist Ernst Mayr developed what came to be known as the Biological Species Concept in the 1940s—namely, a species is made up of members of populations that actually or potentially interbreed in nature. Experiments on living animals have shown that barriers to this interbreeding can arise in tens of thousands, or even just thousands, of years.
Once the Neanderthal lineage left Africa 800,000 years ago, did humans and Neanderthals have enough time to become unable to interbreed? Pääbo's research provides an answer: no.
Does the late Ernst Mayr's notion of what constitutes a species, which held sway for many decades, need to be scrapped or substantially revised? Many biologists believe so.
Europeans and Asians carry with them a small portion of DNA inherited from Neanderthals—while Africans do not. The best explanation for our mixed genomes is that after humans expanded out of Africa, they encountered Neanderthals and interbred. Comparing the different Neanderthal-derived genes in different people, Pääbo and his colleagues estimate that this encounter occurred around 40,000 years ago. The tiny amount of Neanderthal DNA has been interpreted by some scientists as evidence that Neanderthals rarely mated with humans—perhaps just once, in fact. But as scientists sequence more genomes from more human populations, they're exploring the possibility that our ancestors mated with Neanderthals several different times.
A matter of survival
The presence of DNA from Neanderthals in human genomes is compelling evidence that humans and Neanderthals could mate and produce fertile offspring. If we stick to the Biological Species Concept, then we are a single species, as Schaafhausen originally thought. But some scientists reject this argument. They think that Mayr's Biological Species Concept has worn out its usefulness.
Homo neanderthalensis and Homo sapiens endured—at least until the Neanderthals became extinct.
With the advent of gene sequencing, scientists have found that many animal species regularly interbreed. It's easy for any safari tourist to tell the difference between olive baboons and yellow baboons that live in Kenya, for example. And yet the two species regularly produce hybrids in the places where their species overlap, and they've been doing it for a long time.
What will it take for experts to agree on whether Neanderthals (foreground) and modern humans are one and the same species?
So why haven't the two baboon species merged into a single hybrid olive-yellow species? The baboons produced by interbreeding may not survive as well as purebred ones. They produce fewer offspring of their own, and so the genes from one species don't spread easily in the other. Thus, despite interbreeding—breaking Ernst Mayr's rule, in other words—the olive and yellow baboons endure as separate species.
Perhaps humans and Neanderthals were the same: They only interbred rarely, and when they did, the hybrid children couldn't fuse the two kinds of humans together. That may be why human and Neanderthal fossils remained so different.
William King would probably have been horrified at the notion of human beings having sex with Neanderthal "brutes." But despite this intermingling, Homo neanderthalensis and Homo sapiens endured—at least until the Neanderthals became extinct, and we survived.
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- Superfamily CanoideaG. Fischer de Waldheim, 1817
- Suborder Fissipedia Blumenbach, 1791