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Temporal range: 2–0.1 Ma
↓
Pleistocene[1]
Java Man, the holotype of H. erectus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Infraorder: Simiiformes
Family: Hominidae
Subfamily: Homininae
Tribe: Hominini
Genus: Homo
Species:
†H. erectus
Binomial name
†Homo erectus
(Dubois, 1893)

Homo erectus (/ˌhoʊmoʊ əˈrɛktəs/ lit. 'upright man') is an extinct species of archaic human from the Pleistocene, spanning nearly 2 million years. It is the first human species to: evolve a humanlike body and gait, to leave Africa and colonize Asia and Europe, and wield fire. It is the progenitor of all later Homo species, including H. floresiensis, H. luzonensis, H. antecessor, and H. heidelbergensis (the last common ancestor of modern humans, Neanderthals, and Denisovans).

The species was first described by Eugene Dubois in 1893 as "Pithecanthropus erectus" using a skullcap and femur he found in Java, Indonesia. At first he believed he had found a giant gibbon, but in the 1930s, as similar fossils were being discovered in China and other parts of Indonesia, it became clear that the species was an ancient human. At first, they were used to argue that humans evolved in Asia, but in the 1960s, H. erectus fossils were starting to be discovered in Africa which moved the focus there. As such a widely distributed species both geographically and temporally, H. erectus anatomy varies considerably. Though not well-defined, it can sometimes be subdivided into subspecies: H. e. erectus, H. e. pekinensis, H. e. soloensis, H. e. ergaster, H. e. georgicus, and H. e. tautavelensis. East Asian populations can be distinguished as H. erectus sensu stricto ("in the strict sense") and others as sensu lato ("in the broad sense").

The skull usually has a pronounced brow ridge, a protruding jaw, and large teeth. The bones are extraordinarily thickened. H. erectus sensu stricto normally has a much more robust skeleton and bigger brain volume — averaging 1,000 cc (61 cu in), within the range of variation for modern humans. Nonetheless, H. erectus probably had a faster non-human apelike growth trajectory, lacking the extended childhood required for language acquisition. Reconstructed adult body dimensions range from 148–167 cm (4 ft 10 in – 5 ft 6 in) in height and about 50 kg (110 lb) in weight.

H. erectus invented to Acheulean industry, a major innovation of large, heavy-duty stone tools, which may have been used in butchery, vegetable processing, and woodworking digging sticks and spears. H. erectus was a major predator of large herbivores on the expanding savannas of the Quaternary glaciation, which could be implicated in many of their extinctions, especially of elephant species. It is usually characterized as the first hunter-gatherer, and practiced sexual division of labor. Evidence of fire and cave habitation by H. erectus is sparse, and similarly, populations appear to have preferred warmer climates and usually ate meat raw. The last occurrence of H. erectus is 117 to 108 thousand years ago (H. e. soloensis), when the last savannas in the region were swallowed up by jungle.

Taxonomy

[edit]
See also: Human taxonomy

Research history

[edit]
Ernst Haeckel suggested early humans dispersed from the now-disproven hypothetical continent "Lemuria" (above).[2]

Despite what Charles Darwin had hypothesized in his 1871 Descent of Man, many late-19th century evolutionary naturalists postulated that Asia (instead of Africa) was the birthplace of humankind as it is midway between all continents via land routes or short sea crossings, providing optimal dispersal routes throughout the world. Among the major proponents of "Out of Asia" theory was Ernst Haeckel, who argued that the first human species (which he proactively named "Homo primigenius") evolved on the now-disproven hypothetical continent "Lemuria" in what is now Southeast Asia from a species he termed "Pithecanthropus alalus" ("speechless ape-man"). "Lemuria" had supposedly sunk below the Indian Ocean, so no fossils could be found to prove this.[2]

Nevertheless, Haeckel's model inspired Dutch scientist Eugène Dubois to join the Royal Netherlands East Indies Army and search for his "missing link" in Java. At the Trinil site, he found a skullcap in 1891 and a femur in 1892 (Java Man), which he named "Pithecanthropus erectus" in 1893 and unfruitfully attempted to convince the European scientific community that he had found an upright-walking ape-man dating to the late Pliocene or early Pleistocene; they dismissed his findings as some kind of malformed non-human ape.[2]

Franz Weidenreich recognized Java Man as an ancient human by relating it to Peking Man (above).[3]

Dubois would continue to argue that "P. erectus" was a giant gibbon, but in the 1930s, Jewish-German anatomist Franz Weidenreich noticed a striking similarity with ancient human remains recently being unearthed in China (Peking Man, "Sinanthropus pekinensis").[3] This characterization became better supported as German-Dutch palaeontologist Gustav Heinrich Ralph von Koenigswald discovered more Indonesian ancient human remains over the decade at Mojokerto, Sangiran, and Ngandong.[4][5] Weidenreich believed that they were the direct ancestors of the local modern human Homo sapiens subspecies in accord with historical race concepts — that is, Peking Man was a direct ancestor of specifically Chinese people, and Java Man of Aboriginal Australians (polycentricism). He consequently suggested synonymising "Pithecanthropus" and "Sinanthropus" as subspecies of Homo erectus in 1940.[6][7] In the late 20th century, far older H. erectus fossils were discovered across Africa, the first being Kenyan archaeologist Louis Leakey's Olduvai Hominin 9 in 1960.[8] As the human fossil record expanded, the "Out of Africa" theory and monogenism became the consensus, with H. erectus generally considered to be an African species which later dispersed across Eurasia.[9]

Subspecies

[edit]

By the middle of the 20th century, human taxonomy was in a state of turmoil, with many different species and genera defined across Europe, Asia, and Africa, which exaggerated how different these fossils actually are from each other.[10] In 1940, Weidenreich was the first to suggest reclassifying "Sinanthropus pekinensis" and "Pithecanthropus erectus" as subspecies of H. erectus.[6] In 1950, German-American evolutionary biologist Ernst Mayr had entered the field of anthropology, and, surveying a "bewildering diversity of names," decided to subsume human fossils into three species of Homo: "H. transvaalensis" (the australopithecines), H. erectus (including "Sinanthropus", "Pithecanthropus", and various other putative Asian, African, and European taxa), and H. sapiens (including anything younger than H. erectus, such as modern humans and Neanderthals), as had been broadly recommended by various priors. Mayr defined these species as a sequential lineage, with each species evolving into the next (chronospecies).[7] Though later Mayr changed his opinion on the australopithecines (recognizing Australopithecus), his more conservative view of archaic human diversity became widely adopted in the subsequent decades.[11]

In the 1970s, as population genetics became better understood, the anatomical variation of H. erectus across its wide geographic and temporal range (the basis for the subspecies distinctions) became better understood as clines — different populations which attained some anatomical regionality but were not reproductively isolated.[9] In general, subspecies names for H. erectus are now used for convenience to indicate time and region rather than specific anatomical trends.[12]

...to paleontologists in general, subspecies are epiphenomena which do not merit the attention paid to species... The pursuit of subspecies in the fossil record is at best fraught with difficulty, and is more probably futile.

— Ian Tattersall, 1986[13]
Reconstructions of H. e. ergaster (KNM ER 3733) left and H. e. pekinensis right

If an author uses subspecies, the ones usually recognized include:[14]

The French Tautavel Man is sometimes classified as H. e. tautavelensis.[15] The ancient Dmanisi hominins from Georgia have variably been classified as a population of H. e. ergaster (sometimes denoted by a quadrinomial H. e. ergaster georgicus)[16] its own subspecies as H. e. georgicus, or elevated to its own species as H. georgicus.[17] Some authors also elevate H. ergaster[18] and H. pekinensis.[19]

Evolution and dispersal

[edit]
See also: Early expansions of hominins out of Africa
H. e. georgicus (above) represents one of the earliest dispersals out of Africa about 1.8 million years ago.[20]

H. erectus is generally considered to have its origins in Africa, evolving from a population of H. habilis (anagenesis).[21] The oldest identified H. erectus specimen is a 2.04 million year old skull, DNH 143, from Drimolen, South Africa, coexisting with the australopithecine Paranthropus robustus.[22] H. erectus dispersed out of Africa soon after evolution, the earliest recorded instances being the Dmanisi hominins 1.85 to 1.78 million years ago[20] and the Indonesian Mojokerto and Sangiran sites 1.8 to 1.6 million years ago.[23][24] Since the species was first defined in East Asia, those populations are sometimes distinguished as H. erectus sensu stricto ("in the strict sense"), and African and West Eurasian populations as H. erectus sensu lato ("in the broad sense").[12]

Once established around the Old World, H. erectus evolved into several different species, including: H. heidelbergensis, H. antecessor,[25] H. floresiensis,[26] and H. luzonensis,[27] H. heidelbergensis, in turn, is usually placed as the last common ancestor of modern humans (H. sapiens), Neanderthals (H. neanderthalensis), and Denisovans.[25] H. erectus is thus a non-natural, paraphyletic grouping of fossils and does not include all the descendants of a last common ancestor.[28] Despite being designated as different species, H. erectus may have been interbreeding with some of its descendant species, namely the common ancestor of Neanderthals and Denisovans ("Neandersovans").[29]

Successive dispersals of   Homo erectus (yellow),   Homo neanderthalensis (ochre) and   Homo sapiens (red, Out of Africa II)

The dispersal of H. erectus is generally ascribed to the evolution of bipedalism, better technology, and a dietary switch to carnivory. Populations spread out via open grassland and woodland savannas, which were expanding due to a global aridification trend at the onset of the Quaternary glaciation.[30] Most H. erectus sensu lato specimens date to 1.8 to 1 million years ago before giving way to other species. H. erectus sensu stricto persisted much longer, with the youngest population (H. e. soloensis) dating to 117 to 108 thousand years ago in Java.[1] This population appears to have died out when the savannah corridors closed in the Late Pleistocene, and tropical jungle took over.[31]

A 2021 phylogeny of some H. erectus fossils using tip dating:[32]

Homo (2.85)

H. habilis (†1.7 Mya)

H. erectus (2.3)
(2.1)

Stw 53 (†1.9)

Dmanisi (†1.8)

Turkana (†1.7)

Olduvai Hominid 9 (†1.5)

Sangiran (†1.4)

(1.1)
(0.8)

Nanjing Man (†0.6)

Peking Man (†0.5)

(0.9)

Hexian (†0.5)

(0.6)

Sambungmacan (†0.2)

Ngandong (†0.1)

H. rhodesiensis/H. heidelbergensis (incl. H. sapiens)

Biology

[edit]

As such a widely distributed species both geographically and through time, the anatomy of H erectus can vary considerably. Among living primates, the degree of regionality achieved by H. erectus (phenotypic plasticity) is only demonstrated in modern humans.[33]

[edit]
Franz Weidenreich's reconstruction of the H. e. soloensis skull

Dubois originally described the species using a skullcap, noting the traits of a low and thickened cranial vault and a continuous bar of bone forming the brow ridge (supraorbital torus),[a] as well as several other traits now considered more typical of H. erectus sensu stricto, such as a strong crest on the mastoid part of the temporal bone, a sagittal keel running across the midline, and a bar of bone running across the back of the skull (occipital torus).[35] The latter traits can be still be found nonetheless in a few H. erectus sensu lato specimens, namely the 1.47 million year old Olduvai Hominin 9.[36] Compared to H. erectus sensu lato, the skullcap of sensu stricto narrows considerably at the front, the face is bigger and presumably more prognathic (it juts out more, but the face is poorly documented), and the molars are larger particularly in Indonesian fossils.[37] H. erectus was the first human species with a fleshy nose, which is generally thought to have evolved in response to breathing dry air in order to retain moisture.[38] Compared to earlier Homo, H. erectus has smaller teeth, thinner enamel, and weaker mandibles (jawbone), likely due to a greater reliance on tool use and food processing.[39]

The brain size of H. erectus varies considerably, but is generally smaller in H. erectus sensu lato, as low as 546 cc (33.3 cu in) in Dmanisi skull 5.[40] Asian H. erectus overall are rather big-brained, averaging roughly 1,000 cc,[33] staying within the range of variation for modern humans.[41] The late-surviving H. e. soloensis has the biggest brain volume with one specimen measuring 1,251 cc (76.3 cu in).[36]

Body

[edit]
Skeleton and reconstruction of Turkana Boy by Mauricio Antón

The rest of the body is primarily only known from three partial skeletons from the Kenyan Lake Turkana site, notably Turkana Boy. Other postcranial fossils attributed to H. erectus are not associated with a skull, making attribution unverifiable. Though the the body plan of earlier Homo is poorly understood, H. erectus has typically been characterized as the first Homo species with a human body plan, distinct from non-human apes.[42][33][43] Fossil tracks near Ileret, Kenya, similarly suggest a human gait. This adaptation is implicated in the spread of H. erectus across the Old World.[44]

Body size differs appreciably among populations, reconstructions ranging approximately 148–167 cm (4 ft 10 in – 5 ft 6 in),[b] with tropical populations typically reconstructed as scoring on the higher end like modern human populations. Adult weight is harder to approximate, but it may have been about 50 kg (110 lb). H. erectus is usually thought to be the first human species with little size-specific sexual dimorphism, but the variability of postcranial material makes this unclear.[33]

It is largely unclear when human ancestors lost most of their body hair. Genetic analysis suggests that high activity in the melanocortin 1 receptor, which would produce dark skin, dates back to 1.2 million years ago. This could indicate the evolution of hairlessness around this time, as a lack of body hair would have left the skin exposed to harmful UV radiation.[46] Populations in higher latitudes potentially developed lighter skin to prevent vitamin D deficiency.[47] Hairlessness is generally thought to have facilitated sweating,[48] but reducing parasite load and sexual selection have also been proposed.[49][50]

Growth and development

[edit]

The dimensions of a 1.8 million years old adult female H. e. ergaster pelvis from Gona, Ethiopia, suggests that she would have been capable of birthing children with a maximum prenatal brain size of 315 cc (19.2 cu in), about 30–50% of adult brain size, falling between chimpanzees (~40%) and modern humans (28%).[51] Similarly, a 1.5 million year old infant skull from Mojokerto had a brain volume of about 72–84% the size of an adult, which suggests a brain growth trajectory more similar to that of non-human apes.[52] This suggests that the childhood growth and development of H. erectus was intermediate between that of chimpanzees and modern humans,[51] and the faster development rate suggests that altriciality (an extended childhood) evolved at a later stage in human evolution.[52] The faster development rate might also indicate a shorter expected lifespan compared to later Homo.[53]

Bone thickness

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Cross sections of H. e. pekinensis humeri (A, B, O, and P) compared to those of modern humans

The cortical bone (the hard outer layer of the bone) is extraordinarily thickened, particularly in Homo erectus sensu stricto, so much so that skull fragments have sometimes been confused for fossil turtle carapaces.[54] The medullary canal in the long bones (where the bone marrow is stored, in the limbs) is extremely narrowed (medullary stenosis). This degree of thickening is usually exhibited in semi-aquatic animals which use their heavy (pachyosteosclerotic) bones as ballasts to help them sink, induced by hypothyroidism.[55]

It is largely unclear what function this could have served. Before more complete skeletons were discovered, Weidenreich suggested H. erectus was a gigantic species. Other explanations include a far more violent and impact-prone lifestyle than other Homo, or pathological nutrient deficiencies causing hyperparathyroidism (such as hypocalcemia).[56][54]

Culture

[edit]

Subsistence

[edit]
See also: Hunting hypothesis
H. erectus overhunting may have led to the extinction of Megalochelys (above).[57]

H. erectus was early-on portrayed as the earliest hunter-gatherer and a skilled predator of big game, relying on endurance running. The gradual shift to "top predator" may have led to its dispersal throughout Afro-Eurasia.[30] Though scavenging may have instead played a bigger role at least in some populations, H. erectus fossils are often associated with the butchered remains of large herbivores,[58] especially elephants, rhinos, hippos, bovines, and boars. The complexities of prey behaviors and the nutritional value of meat have been connected to brain volume growth.[59]

H. erectus is usually assumed to have practiced sexual division of labor much like recent hunter-gatherer societies, with men hunting and women gathering. This ideation is supported by a fossil trackway from Ileret, Kenya, made by a probably all-male band of over 20 H. erectus individuals, possibly a hunting party or (similar to chimpanzees) a border patrol group.[60]

Since common modern human tapeworms began to diverge from those of other predators roughly 1.7 million years ago (specifically the pork tapeworm, beef tapeworm, and Asian tapeworm), not only was H. erectus consuming meat regularly enough for speciation to occur in these parasites, but meat was probably consumed raw more often than not.[61] Some populations were collecting aquatic resources, include fish, shellfish, and turtles at Lake Turkana[62] and Trinil.[63] Underground storage organs (roots, tubers, etc.) were likely also major dietary components, and traces of the edible plant Celtis have been documented at several H. erectus sites.[64]

Possibly due to overhunting of the biggest game available, the dispersal of H. erectus may be implicated in the extinctions of large herbivores and the gradual reduction of average herbivore size over the Middle to Late Pleistocene.[65] H. erectus is especially blamed for the extinctions of elephant species (namely in the genera Elephas, Palaeoloxodon, and Deinotherium),[59][66] as well as species of the giant turtle Megalochelys in what is now Island Southeast Asia.[c][57]

Technology

[edit]

Stone tools

[edit]
A handaxe from the Saint-Acheul site at the National Archaeological Museum, France

H. erectus manufactured Lower Paleolithic technologies, and is credited with the invention of the Acheulean stone tool industry at latest 1.75 million years ago. This was a major technological breakthrough featuring large, symmetrical, heavy-duty tools; most iconicly the handaxe. Over hundreds of thousands of years, the Achuelean eventually replaced its predecessor — the Oldowan (a chopper and flake industry) — in Africa, and spread out across Western Eurasia.[67] This sudden innovation was typically explained as a response to environmental instability in order to process more types of food and broaden the diet, which allowed H. erectus to colonize Eurasia. Despite this characterization, the Dmanisi hominins were able to leave Africa despite only manufacturing Oldowan tools,[30][67] and the Acheulean does not seem to have been manufactured commonly in East Asia.[68] This conspicuous pattern was first noted by American archaeologist Hallam L. Movius in 1948, who drew the "Movius Line", dividing the East into a "chopping-tool culture" and the West into a "hand axe culture".[69]

H. erectus seems to have been using stone tools in butchery, vegetable processing, and woodworking (maybe manufacturing digging sticks and spears).[64][70] In Africa, Oldowan sites are typically found alongside major fossil assemblages, but Acheulean sites normally feature more stone tools than fossils, so H. erectus could have been using choppers and handaxes for different activities.[70]

Materials for stone tools were normally sourced locally, and it seems blanks were usually chosen based on size rather than material quality.[67] H. erectus also produced tools from shells at Sangiran[71] and Trinil.[72]

Fire

[edit]

H. erectus is credited as the first human species to wield fire. The earliest claimed fire site is Wonderwerk Cave, South Africa, at 1.7 million years old.[73] While its dispersal far out of Africa has often been attributed to fire and cave dwelling, fire does not become common in the archaeological record until 400,000–300,000 years ago,[74] and cave-dwelling about 600,000 years ago.[75] Therefore, H. erectus may have only been scavenging fire opportunistically. Similarly, H. erectus sites usually stay within warmer tropical or subtropical latitudes,[30] and the dating of northerly populations (namely Peking Man) could suggest that they were retreating to warmer refugia during glacial periods, but the precise age of the Peking Man fossils is poorly resolved.[35][76]

Healthcare

[edit]
The single-toothed H. e. georgicus specimen (above) is the earliest probable example of group care.[77]

Like other primates, H. erectus probably used medicinal plants[64] and infirmed sick group members. The earliest probable example of this is a 1.77 million year old H. e. georgicus specimen who had lost all but one tooth due to age or gum disease (the earliest example of severe chewing impairment) yet still survived for several years afterwards.[77]

Seafaring

[edit]

H. erectus made long sea crossings to arrive on the islands of Flores and Luzon.[78] Some authors have asserted that H. erectus intentionally made these crossings by inventing watercrafts and seafaring so early in time, speaking to advanced cognition and language skills. These populations could have also been founded by natural rafting events instead.[79]

Art and rituals

[edit]
See also: Prehistoric art

In East Asia, H. erectus is usually represented by only skullcaps, which used to be interpreted as widespread cannibalism and ritual headhunting. This had been reinforced by the historic practice of headhunting and cannibalism in some recent Indonesian, Australian, and Polynesian cultures, who at the time were believed to have directly descended from these H. erectus populations. The lack of the rest of the skeleton is now normally explained by natural phenomena.[80]

Engraved Pseudodon shell DUB1006-fL from Trinil, Java

Art-making could be evidence of symbolic thinking. An engraved Pseudodon shell DUB1006-fL from Trinil, Java, with geometric markings could possibly be the earliest example of art-making, dating to 546 to 436 thousand years ago.[72][81][82][83][84] H. erectus was also the earliest human to collect red-colored pigments, namely ochre. Ochre lumps at Olduvai Gorge, Tanzania, associated with the 1.4 million year old Olduvai Hominid 9 may have been purposefully shaped and trimmed by a hammerstone. Red ochre is normally recognized as bearing symbolic value when associated with modern humans.[85][84]

Language

[edit]
See also: Origin of language and Origin of speech

The hyoid bone supports the tongue and makes possible modulation of the vocal tract to control pitch and volume. A 400 kya H. erectus hyoid bone from Castel di Guido, Italy, is bar-shaped—more similar to that of other Homo than to that of non-human apes and Australopithecus—but is devoid of muscle impressions, has a shield-shaped body, and is implied to have had reduced greater horns, meaning H. erectus lacked a humanlike vocal apparatus and thus anatomical prerequisites for a modern human level of speech.[86] Similarly, the spinal column of the 1.6 million year old Turkana boy would not have supported properly developed respiratory muscles required to produce speech,[87][88] and a 1.5 million year old infant H. erectus skull from Mojokerto, Java, shows that an extended childhood to allow for brain growth, which is a prerequisite for language acquisition, was not exhibited in this species.[52]

Nonetheless, given expanding brain size and technological innovation, H. erectus may have been using some basic proto-language in combination with gesturing, and built the basic framework which fully-fledged languages would eventually be formed around.[89]

Notes

[edit]
  1. ^ H. erectus fossils typically share these traits, but the Kenyan Koobi Fora skulls notably have thinner skulls and weaker supraorbital tori.[34]
  2. ^ The Turkana Boy specimen was originally estimated in 1993 to have been roughly 165 cm (5 ft) when it died at about 12 years of age, and predicted to reach 177–193 cm (5 ft 10 in – 6 ft 4 in) had it survived past its pubertal growth spurt and into adulthood assuming a humanlike growth curve. A 1998 analysis of the femur instead indicated Turkana Boy was near skeletal maturity (it was almost done growing), and an adult female H. e. ergaster pelvis reported in 2008 similarly indicates a non-human apelike trajectory for this group. Using this, Turkana Boy would have reached its adult height of 163 cm (5 ft 4 in) at the age of 16.[45]
  3. ^ During the Pleistocene, most of Island Southeast Asia was connected to the mainland as a single landmass called Sundaland.[30]

References

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  2. ^ a b c Hsiao-Pei, Y. (2014). "Evolutionary Asiacentrism, Peking Man, and the Origins of Sinocentric Ethno-Nationalism". Journal of the History of Biology. 47 (4): 585–625. doi:10.1007/s10739-014-9381-4. PMID 24771020. S2CID 23308894.
  3. ^ a b Boaz & Ciochon 2004, pp. 59–60.
  4. ^ Boaz & Ciochon 2004, pp. 60–62.
  5. ^ von Koenigswald, G. H. R.; Weidenreich, F. (1939). "The Relationship between Pithecanthropus and Sinanthropus". Nature. 144: 926–929. doi:10.1038/144926a0.
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  10. ^ Boaz & Ciochon 2004, p. 65.
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  15. ^ de Lumley, M.-A. (2015). "L'homme de Tautavel. Un Homo erectus européen évolué. Homo erectus tautavelensis" [Tautavel Man. An evolved European Homo erectus. Homo erectus tautavelensis]. L'Anthropologie (in French). 119 (3): 342–344. doi:10.1016/j.anthro.2015.06.001.
  16. ^ Zollikofer, C. P. E.; Ponce de León, M. S.; Margvelashvili, A.; Rightmire, G. Philip; Lordkipanidze, D. (2014). "Response to Comment on "A Complete Skull from Dmanisi, Georgia, and the Evolutionary Biology of Early Homo"". Science. 344 (6182): 360–b. Bibcode:2014Sci...344..360Z. doi:10.1126/science.1250081. PMID 24763573. S2CID 206554612.
  17. ^ Rightmire, G. Philip; Lordkipanidze, David; Vekua, Abesalom (2006). "Anatomical descriptions, comparative studies and evolutionary significance of the hominin skulls from Dmanisi, Republic of Georgia". Journal of Human Evolution. 50 (2): 140. doi:10.1016/j.jhevol.2005.07.009. PMID 16271745.
  18. ^ Rightmire, G. Philip; Ponce de León, Marcia S.; Lordkipanidze, David; Margvelashvili, Ann; Zollikofer, Christoph P. E. (2017). "Skull 5 from Dmanisi: Descriptive anatomy, comparative studies, and evolutionary significance". Journal of Human Evolution. 104: 51. doi:10.1016/j.jhevol.2017.01.005. PMID 28317556.
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Further reading

[edit]












Extended content
Cryptodira – 11 families, 74 genera, over 200 species
Family[1] Genera[2]
Carettochelyidae
Boulenger, 1887 (1 genus)
Genus Carettochelys Ramsay, 1886 – one species
Common name Scientific name IUCN Red List Status Range Picture
Pig-nosed turtle C. insculpta
Ramsay, 1886 		VU IUCN Southern New Guinea and northern Northern Territory
A beakless turtle with a snout shaped like that of a pigs
Cheloniidae (sea turtles)
Oppel, 1811 (5 genera)
Genus Caretta Rafinesque, 1814 – one species
Common name Scientific name IUCN Red List Status Range Picture
Loggerhead sea turtle C. caretta
Linnaeus, 1758 		VU IUCN
World's oceans excluding the polar regions
A white turtle with a beak, black eye-spots, and a dark-brown carapace
Genus Lepidochelys (Ridley sea turtles) Fitzinger, 1843 – two species
Common name Scientific name IUCN Red List Status Range Picture
Kemp's ridley sea turtle L. kempii
Garman, 1880 		CR IUCN
The Gulf of Mexico and the eastern coast of the United States
A green turtle with a white underside and beak
Olive ridley sea turtle L. olivacea
von Eschscholtz, 1829 		VU IUCN
Coasts of Oceania, South China Sea, Sea of Japan, the Indian Ocean, Africa (excluding the Mediterranean), and the Americas (excluding the eastern coast of North America and southern South America)
alt=A green turtle with a white underside and beak
Genus Chelonia Brongniart, 1800 – one species
Common name Scientific name IUCN Red List Status Range Picture
Green sea turtle C. mydas
Linnaeus, 1758 		EN IUCN
Tropical and temperate oceans of the world
A dark brown turtle with a beak, a green carapace, and a white underside
Genus Eretmochelys Fitzinger, 1843 – one species
Common name Scientific name IUCN Red List Status Range Picture
Hawksbill sea turtle E. imbricata
Linnaeus, 1758 		CR IUCN
Tropical and subtropical oceans of the world
A turtle with a beak, a black head, flippers, and carapace, a white neck and underside, and serrated scutes on the carapace
Genus Natator McCulloch, 1908 – one species
Common name Scientific name IUCN Red List Status Range Picture
Flatback sea turtle N. depressus
Garman, 1880 		DD IUCN
Around the coast of Australia, stretching to New Guinea and Java, excluding the southern coast
A grey turtle with a white beak
Chelydridae
Gray, 1831(2 genera)
Genus Chelydra (snapping turtles) Schweigger, 1812 – three species
Common name Scientific name IUCN Red List Status Range Picture
Common snapping turtle C. serpentina
Linnaeus, 1758 		LC IUCN
United States east of the Rocky Mountains
An orange-brown tortoise with a grey carapace
Central American snapping turtle C. rossignonii
Bocourt, 1868 		VU IUCN Southeastern Mexico, southern Belize, central Guatemala, and northwestern Honduras
Dermatemydidae
Gray, 1870 (1 genus)
Genus Dermatemys Gray, 1847 – one species
Common name Scientific name IUCN Red List Status Range Picture
Central American river turtle D. mawii
Gray, 1847 		CR IUCN Eastern Mexico, Guatemala, Honduras, and Belize
A green turtle with webbed feet
Dermochelyidae
Fitzinger, 1843 (1 genus)
Genus Dermochelys de Blainville, 1816 – one species
Common name Scientific name IUCN Red List Status Range Picture
Leatherback sea turtle D. coriacea
Vandelli, 1761 		VU IUCN
Oceans of the world
A large black turtle without a bony shell
Emydidae
Rafinesque, 1815 (12 genera)
Genus Clemmys von Ritgen, 1828 – one species
Common name Scientific name IUCN Red List Status Range Picture
Spotted turtle C. guttata
Schneider, 1792 		EN IUCN Great Lakes region
A black tortoise with yellow speckles across the body and carapace
Genus Emys Duméril, 1805 – two species
Common name Scientific name IUCN Red List Status Range Picture
European pond turtle E. orbicularis
Linnaeus, 1758 		EN IUCN
Mediterranean Europe, and around the Caspian Sea
A black tortoise with yellow speckles across the body and carapace
Sicilian pond turtle E. trinacris
Fritz, Fattizzo, Guicking, Tripepi, Pennisi, Lenk, Joger and Wink, 2005 		DD IUCN
Sicily, an island off the coast of Italy
A grey tortoise
Genus Emydoidea Holbrook, 1838 – one species
Common name Scientific name IUCN Red List Status Range Picture
Blanding's turtle E. blandingii
Holbrook, 1838 		EN IUCN
Great Lakes region in the United States
A black tortoise with yellow spots covering the body
Genus Actinemys Baird and Girard, 1852 – one species
Common name Scientific name IUCN Red List Status Range Picture
Western pond turtle A. marmorata
Baird and Girard, 1852 		VU IUCN
Western coast of the contiguous United States
A dark brown turtle with webbed feet, and a yellow-speckled head and neck
Genus Glyptemys Agassiz, 1857 – two species
Common name Scientific name IUCN Red List Status Range Picture
Bog turtle G. muhlenbergii
Schoepff, 1801 		CR IUCN
One population in New England and another population in Virginia, United States
A black turtle with an orange patch on its neck
Wood turtle G. insculpta
Le Conte, 1830 		EN IUCN
New England, Newfoundland, and the Greats Lakes
A black tortoise with a yellow plastron and spots on the head and neck
Genus Terrapene (box turtles) Merrem, 1820 – four species
Common name Scientific name IUCN Red List Status Range Picture
Common box turtle T. carolina
Linnaeus, 1758 		VU IUCN Eastern coast of North America, and the Gulf of Mexico
Eastern box turtle
T. c. carolina 		Florida box turtle
T. c. bauri 		Gulf Coast box turtle
T. c. major
Three-toed box turtle
T. c. triunguis 		Mexican box turtle
T. c. mexicana 		Yucatán box turtle
T. c. yucatana
Coahuilan box turtle T. coahuila
Schmidt and Owens, 1944 		EN IUCN Cuatro Ciénegas, Coahuila, Mexico A dark grey tortoise
Spotted box turtle T. nelsoni
Stejneger, 1925 		DD IUCN Sierra Madre Occidental, Mexico
Terrapene ornata] Terrapene ornata
Agassiz, 1857 		NT IUCN Central United States, including the Mojave desert and the Midwest region Brown tortoises
Ornate box turtle left, Desert box turtle right
Genus Chrysemys Gray, 1844 – one species
Common name Scientific name IUCN Red List Status Range Picture
Painted turtle C. picta
Schneider, 1783 		LC IUCN
United States spilling over into Canada excluding the Mojave desert
Eastern painted turtle
C. p. picta 		Midland painted turtle
C. p. marginata 		Southern painted turtle
C. p. dorsalis 		Western painted turtle
C. p. bellii
A grey tortoise with square patterns on the carapace A brown tortoise A grey tortoise with a single thin, orange line running down the carapace from head to tail and white marks on the head and neck A grey tortoise with yellow stripes running down the neck from the head
Underside view, showing a tan plastron Underside view, showing a tan plastron Underside view, showing a tan plastron and webbed feet Underside view, the plastron is bright red with black and white Rorshach-like patterns
Geoemydidae
Theobald, 1868 		24
Kinosternidae
Agassiz, 1857 		4
Platysternidae
Gray, 1869 		1
Testudinidae
Batsch, 1788 		12
Trionychidae
Fitzinger, 1826 		14
Pleurodira – 3 families, 16 genera, over 60 species
Family Genera
Chelidae
Gray, 1831 		15
Pelomedusidae
Cope, 1868 		2
Podocnemididae
Gray, 1869 		3

References

  1. ^ John B. Iverson; A. Jon Kimerling; A. Ross Kiester. "List of All Families". Terra Cognita Laboratory, Geosciences Department of Oregon State University. Retrieved 26 June 2010.
  2. ^ John B. Iverson; A. Jon Kimerling; A. Ross Kiester. "List of Genera". Terra Cognita Laboratory, Geosciences Department of Oregon State University. Retrieved 26 June 2010.

Further reading

  • David T. Kirkpatrick (November–December 1995). "Platysternon megacephalum". Reptile & Amphibian Magazine. pp. 40–47. Retrieved 26 June 2010.
  • Cogger, H.G.; R.G. Zweifel; D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press. ISBN 1-877019-69-0.

External links

  • John B. Iverson; A. Jon Kimerling; A. Ross Kiester. "EMYSystems". Terra Cognita Laboratory, Geosciences Department of Oregon State University. Retrieved 26 June 2010.
Extended content

Cetacean anatomy is the study of the form or morphology of cetaceans (whales, dolphins and porpoises). It can be contrasted with cetacean physiology, which is the study of how the component parts of cetaceans function together in these living marine mammals.[1] In practice, cetacean anatomy and cetacean physiology complement each other, the former dealing with the structure of a cetacean, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the latter dealing with how those components function together in the living marine mammal.

The anatomy of cetaceans have common characteristics with other terrestrial mammals, and, in addition, is often shaped by the physical characteristics of aquatic living, the medium in which these mammals live. Water is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.

Body

Skeleton Skull

Unlike toothed whales (left), baleen whales (right) do not have a melon

The skull of all cetaceans is extended, which can be clearly seen in baleen whales. The nostrils are located on top of the head above the eyes. The back of the skull is significantly shortened and deformed. By shifting the nostrils to the top of the head, the nasal passages extend perpendicularly through the skull. The teeth or baleen in the upper jaw sit exclusively on the maxilla. The braincase is concentrated through the nasal passage to the front and is correspondingly higher, with individual cranial bones that overlap. The bony otic capsule, the petrosal, is only cartilaginous when connected to the skull, so that it can swing independently.[2][3]

Vertebrae

The number of vertebrae that make up the spine varies between species, anywhere between 40 and 93 individual vertebrae. The cervical spine, found in all mammals, consists of seven vertebrae which, however, are greatly reduced or fused together. This gives stability during swimming at the expense of mobility. The fins are carried by the thoracic vertebrae, ranging from 9 to 17 individual vertebrae. The sternum is only cartilaginous, but nonetheless strong. The last two to three pairs of ribs are not connected at all and hang freely in the body wall. Behind it is the stable lumbar and tail part of the spine which includes all other vertebrae. Below the caudal vertebrae is the chevron bone; the vortex developed provides additional attachment points for the tail musculature.[2][3]

Limbs

The front limbs are paddle-shaped with shortened arms and elongated finger bones, to support the movement. They are united by cartilage. It also leads to a proliferation of the finger members, a so-called hyperphalangy, on the second and third fingers. The only functional joint is the shoulder joint in all cetaceans except for the Amazon river dolphin. The collarbone is completely absent. The movement of cetaceans on land is no longer necessary nor possible, due to the great body weight and the atrophied hindlimbs. In fact the rear limbs have become a rudimentary internal appendage without connections to the spine.[2][3]

External organs Jaw

The jaws of toothed whales are designed for catching swift prey. Porpoises have spade-shaped teeth, but dolphins have conical teeth. Cetaceans are monophydonts, meaning they have one set of teeth their entire life.[4] Toothed whales use their jaw to recieve pulses for echolocation. Echoes are received using complex fatty structures around the lower jaw as the primary reception path, from where they are transmitted to the middle ear via a continuous fat body.[5] Lateral sound may be received though fatty lobes surrounding the ears with a similar density to water. Some researchers believe that when they approach the object of interest, they protect themselves against the louder echo by quieting the emitted sound. This is known to happen in bats, but here the hearing sensitivity is also reduced close to a target.[6]

As opposed to toothed whales, baleen whales have different jaw designs depending on their feeding behavior. Lunge-feeders, like rorquals, have to expand their jaw to a volume that can be bigger than the whale itself; to do this, the oral cavity inflates to expand the mouth. The inflation of the oral cavity causes the cavum ventrale, the folds (throat pleats) on the throat stretching to the naval, to expand, increasing the amount of water that the mouth can store.[7] The mandible is connected to the skull by dense fibers and cartilage, allowing the jaw to swing open at almost a 90° angle. The mandibular symphysis is also fibrocartilaginous, allowing the jaw to bend which lets in more water.[8] To prevent stretching the mouth too far, rorquals have a sensory organ located in the middle of the jaw to regulate these functions.[9] Gulp-feeders, like right whales, on the other hand swim with an open mouth, filling it with water and prey. This makes their head, which can make up a third of their body weight, huge in order to feed effectively. Not able to expand their mouth like rorquals, right whales must have a head that is large enough to take in enough water and food to feed effectively, carrying their bulk all the time.[10]

Beaked whales have a somewhat similar jaw anatomy as rorquals. The throats of beaked whales have a bilaterally paired set of grooves that are associated with their unique feeding mechanism, suction feeding. Instead of capturing prey with their teeth, beaked whales suck it into their oral cavity. Suction is aided by the throat grooves, which stretch and expand to accommodate food. Their tongue can move very freely. By suddenly retracting the tongue and distending the gular (throat) floor, pressure immediately drops within the mouth sucking the prey in with the water.[11]

Eyes The whale eye is relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes of a whale are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When belugas surface, their lens and cornea correct the nearsightedness that results from the refraction of light; they contain both rod and cone cells, meaning they can see in both dim and bright light, but they have far more rod cells than they do cone cells. Whales do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for colour vision than most mammals.[12] Most whales have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. In water, a whale can see around 10.7 metres (35 ft) ahead of itself, but, of course, they have a smaller range above water. They also have glands on the eyelids and outer corneal layer that act as protection for the cornea.[13] Toothed whales can retract and protrude its eyes thanks to a 2-cm-thick retractor muscle attached around the eye at the equator.[14]

Blowhole

Main article: Blowhole (anatomy)

The blowhole is the hole at the top of a whale's head through which the animal breathes air. When a whale reaches the water surface to breathe, they will forcefully expel air through the blowhole. Mucus and carbon dioxide from the animal's metabolism, which have been stored in the whale while diving, are also expelled. The exhalation is released into the comparably lower-pressure and colder atmosphere, so any water vapor condenses. This spray, known as the blow, is often visible from far away as a white splash, which can also be caused by water resting on top of the blowhole. Baleen whales have two blowholes, causing a V-shaped blow, while toothed whales have only one blowhole. The trachea only connects to the blowhole and there is no connection to the esophagus as with humans and most other mammals. Because of this, there is no risk of food accidentally ending up in the animal's lungs, and likewise the animal cannot breathe through its mouth. Consequently, whales have no pharyngeal reflex.[15]

Skin

Fins

Internal organs

Intestines The small intestines is divided into three sections: the duodenum, the jejunum, and the ileum. The mesentery is thin in baleen whales. The caecum is present in all whales with the exception of the Amazon river dolphins and the right whales, however it is relatively short in baleen whales. The appendix is absent in all cetaceans.

Stomach In most whales, food is swallowed and travels down through the esophagus where it meets a three-chambered-stomach. The first compartment is known as the fore-stomach; this is where food gets ground up into an acidic liquid, which is then squirted into the main stomach. Like in humans, the food is mixed with hydrochloric acid and protein-digesting enzymes. Then, the partly digested food is moved into the third stomach, in which fat-digesting enzymes, and then mixed with an alkaline liquid to neutralize the acid from the first stomach to prevent damage to the intestinal tract. Once the solution is safe, it is moved into the intestinal tract.

Kidneys Whale kidneys are specially designed for excreting excess salt content. Water is typically gained by the food they eat, however, the invertebrates they consume have the same salt content as seawater. As in other vertebrates, whale salt levels are three times less than that of seawater. However, the kidneys are inefficient at retaining water, and expel much of it while excreting salt.[16]

Spleen Liver The liver in whales is bilobed, as opposed to the five-lobed liver in humans, and they lack a gall bladder. Toothed whales have one bile duct and baleen whales have two. Like other mammals, the liver is located in the right side of the body, just below the diaphragm.

Heart

Swim bladder Weberian apparatus

Reproductive organs Testes Ovaries

Nervous system Central nervous system Cerebellum Identified neurons Immune system

See also

References

  1. ^ Prosser, C. Ladd (1991). Comparative Animal Physiology, Environmental and Metabolic Animal Physiology (4th ed.). Hoboken, NJ: Wiley-Liss. pp. 1–12. ISBN 0-471-85767-X.
  2. ^ a b c Bruno Cozzi; Sandro Mazzariol; Michela Podestà; Alessandro Zott (2009). "Diving Adaptations of the Cetacean Skeleton" (PDF). The Open Zoology Journal. 2: 24–32. doi:10.2174/1874336600902010024. Retrieved 5 September 2015.
  3. ^ a b c A. Thomas, J. (1916). Outlines of Zoology (5 ed.). pp. 766–771.
  4. ^ The Institute for Marine Mammal Studies. "Frequently asked questions". IMMS. Retrieved 17 February 2016.
  5. ^ Webster, D.; Fay, R.; Popper, A. (1992). "The Marine Mammal Ear: Specializations for aquatic audition and echolocation". In Ketten, D.R. (ed.). The Evolutionary Biology of Hearing. Springer-Verlag. pp. 717–750. ISBN 978-1-4612-7668-5.
  6. ^ Au, W.; Fay, R.; Popper, A. (2000). "Cetacean Ears". Hearing by Whales and Dolphins. SHAR Series for Auditory Research. Springer-Verlag. pp. 43–108. doi:10.1007/978-1-4612-1150-1. ISBN 978-0-387-94906-2.
  7. ^ W. Vogle, A.; A. Lillie, Margo; A. Piscitelli, Marina; A. Goldbogen, Jeremy; D. Pyenson, Nicholas; E. Shadwick, Robert (2015). "Stretchy nerves are an essential component of the extreme feeding mechanism of rorqual whales". Current Biology. 25 (9): 360–361. doi:10.1016/j.cub.2015.03.007.
  8. ^ A. Goldbogen, Jeremy (2010). "The Ultimate Mouthful: Lunge Feeding in Rorqual Whales". American Scientist. 98 (2): 124. doi:10.1511/2010.83.124.
  9. ^ Welsh, Jennifer (2012). "Whale's Big Gulp Aided by Newfound Organ". Retrieved 23 January 2016.
  10. ^ Kenney, Robert D. (2002). "North Atlantic, North Pacific and Southern Right Whales". In William F. Perrin, Bernd Wursig and J. G. M. Thewissen (ed.). The Encyclopedia of Marine Mammals. Academic Press. pp. 806–813. ISBN 0-12-551340-2.
  11. ^ Rommel, S. A.; Costidis, A. M.; Fernandez, A.; Jepson, P. D.; Pabst, D. A.; McLellan, W. A.; Houser, D. S.; Cranford, T. W.; van Helden, A. L.; Allen, D. M.; Barros, N. B. (2006). "Elements of beaked whale anatomy and diving physiology and some hypothetical causes of sonar-related stranding". Journal of Cetacean Research and Management. 7 (3): 189–209.
  12. ^ Mass et al. 2007, pp. 701–715.
  13. ^ Reidenberg, Joy S. (2007). "Anatomical adaptations of aquatic mammals". The Anatomical Record. 290 (6): 507–513. doi:10.1002/ar.20541.
  14. ^ Bjerager, P.; Heegaard, S.; Tougaar, J. (2003). "Anatomy of the eye of the sperm whale (Physeter macrocephalus L.)". Aquatic Mammals. 29 (1): 31–36. doi:10.1578/016754203101024059.
  15. ^ Tinker 1988, The Respiratory System, pp.65–68.
  16. ^ Cavendish, Marshall (2010). "Gray whale". Mammal Anatomy: An Illustrated Guide. ISBN 978-0-7614-7882-9.

Further reading

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