Information

Determination of the species of a skull


Out here in the mid german woods, the kids found this skull:

Now we would like to figure out what it is. Started to look at various google image search results for all kinds of animals that came to our mind, but not only due to bad reception this takes long and lead to no result.

So what is a good structured way to start detrmining what this is?


If you're serious about this (and it appears you are), you'll benefit by starting with a Comparative Osteology book or webiste that discusses all the various characteristics of skulls that give you clues to exactly what you're dealing with.

This page on Amazon has a variety of such books. Pages such as this one begin with the basics and references help you to pursue the subject further.

On your specimen, although the missing teeth would be very helpful, important identifying features include the very large percentage of the cranium given over to the masseters, the eye socket placement, the size, the jaw shape, etc.


Teeth are really important features for mammal identification.

The types of teeth gives an idea of the kind of food they eat.

In the skull you show, I guess that the tooth surface is far from being a "flat" grinder (which would be typical for an herbivorous, especially if old), but neither is there a sharp scissors-like structure (which would be typical of a carnivore). Therefore I will bet the animal is omnivorous.

The size, number, disposition and diversity of the teeth (dental formula) can further help. Some comments pointed to the presence of small nascent canines.

You can then look at a list of mammals that are living in the region of interest, filter it by size, and check what kind of dental formula they have.


Skull-Based Method of Age Determination for the Brown Bear Ursus arctos Linnaeus, 1758

Due to the lack of a proper technique for determining the ages of brown bears, a simple and straightforward method that is based on published data and our own observations is proposed. This method is based on the simultaneous use of the following different skull parameters to more accurately determine the ages of brown bears: size and weight parameters, degree of obliteration of the joints, degree of wear of the teeth, and development of the flanges. The proposed method contributes to non-destructive age determination, allows for the discrimination of immature and adult bears and also classifies the skulls of adult animals into one of the five selected age groups.


Can skull shape and function determine what kind of food was on prehistoric plates?

When paleontologists put together a life history for a long-extinct animal, it's common to infer the foods it ate by looking at modern animals with similar skull shapes and tooth patterns. But this practice is far from foolproof. New modeling and tests based on living species done at the American Museum of Natural History show that the link between animal diets and skull biomechanics is complex, with a stronger influence from ancestry than previously thought.

"Traditionally, when we looked at a fossilized skull with pointy piercing teeth and sharp slicing blades, we assumed that it was primarily a meat eater, but that simplistic line of thinking doesn't always hold true," said John J. Flynn, the Museum's Frick Curator of Fossil Mammals and a co-author on the new work published today in the journal PLOS ONE. "We've found that diet can be linked to a number of factors--skull size, biomechanical attributes, and often, most importantly, the species' position in the tree of life."

Flynn and Z. Jack Tseng, a National Science Foundation and Frick Postdoctoral Fellow in the Museum's Division of Paleontology, looked at the relationship between skull shape and function of five different modern carnivore species, including meat-eating "hypercarnivore" specialists such as wolves and leopards, and more omnivorous "generalists" such as mongooses, skunks, and raccoons. The initial modeling, which mapped bite force against the stiffness of the animal's skull, yielded a surprise.

"Animals with the same diets and biomechanical demands, like wolves and leopards--both hypercarnivores--were not linking together," Tseng said. "Instead, we saw a strong signal driven mostly by ancestry, where, for example, the leopard and the mongoose bind together because they're more closely related in an evolutionary context, although they have very different dietary preferences and feeding strategies."

But once Tseng and Flynn accounted for the strong effects of ancestry and skull size on the models, hypercarnivores and generalists still could be distinguished based on biomechanics, in particular by looking at where along the tooth row the skull is strongest. Meat specialist skulls are stiffest when hunting with front teeth and/or slicing or crushing with back teeth, whereas skulls of generalists show incrementally increasing stiffness when biting sequentially from the front to the back of the tooth row.

The researchers then applied this improved shape-function computer model to two extinct species: Thinocyon velox, a predatory mammal that was part of the now-extinct Creodont group, and Oodectes herpestoides, an early fossil predecessor of modern carnivores,. They found that T. velox likely had a unique hypercarnivorous feeding style that allowed for skull strength at two places: prey capture with its front teeth and powerful slicing and crushing with its back teeth. The biomechanical profile of O. herpestoides, meanwhile, suggests that it was a generalist, but compared to living relatives of similar body size, it might have fed on smaller prey because of its weaker skull.

"Beyond feeding adaptations of extinct species, we also want to decipher how adaptations evolved using reconstructed ancestors of living and fossil forms," Tseng said. "We are applying similar types of skull shape and biomechanical analyses to reconstructed hypothetical ancestor skulls of Carnivora and their relatives to map out and better understand the long history of feeding adaptation of living top predators."


Contents

In biology, the range of a species is the geographical area within which that species can be found. Within that range, distribution is the general structure of the species population, while dispersion is the variation in its population density.

Range is often described with the following qualities:

  • Sometimes a distinction is made between a species' natural, endemic, indigenous, or native range, where it has historically originated and lived, and the range where a species has more recently established itself. Many terms are used to describe the new range, such as non-native, naturalized, introduced, transplanted, invasive, or colonized range. [2]Introduced typically means that a species has been transported by humans (intentionally or accidentally) across a major geographical barrier. [3]
  • For species found in different regions at different times of year, especially seasons, terms such as summer range and winter range are often employed.
  • For species for which only part of their range is used for breeding activity, the terms breeding range and non-breeding range are used.
  • For mobile animals, the term natural range is often used, as opposed to areas where it occurs as a vagrant.
  • Geographic or temporal qualifiers are often added, such as in British range or pre-1950 range. The typical geographic ranges could be the latitudinal range and elevational range.

Disjunct distribution occurs when two or more areas of the range of a taxon are considerably separated from each other geographically.

Distribution patterns may change by season, distribution by humans, in response to the availability of resources, and other abiotic and biotic factors.

Abiotic Edit

There are three main types of abiotic factors:

  1. climatic factors consist of sunlight, atmosphere, humidity, temperature, and salinity factors are abiotic factors regarding soil, such as the coarseness of soil, local geology, soil pH, and aeration and
  2. social factors include land use and water availability.

An example of the effects of abiotic factors on species distribution can be seen in drier areas, where most individuals of a species will gather around water sources, forming a clumped distribution.

Researchers from the Arctic Ocean Diversity (ARCOD) project have documented rising numbers of warm-water crustaceans in the seas around Norway's Svalbard Islands. Arcod is part of the Census of Marine Life, a huge 10-year project involving researchers in more than 80 nations that aims to chart the diversity, distribution and abundance of life in the oceans. Marine Life has become largely affected by increasing effects of global climate change. This study shows that as the ocean temperatures rise species are beginning to travel into the cold and harsh Arctic waters. Even the snow crab has extended its range 500 km north.

Biotic Edit

Biotic factors such as predation, disease, and inter- and intra-specific competition for resources such as food, water, and mates can also affect how a species is distributed. For example, biotic factors in a quail’s environment would include their prey (insects and seeds), competition from other quail, and their predators, such as the coyote. [4] An advantage of a herd, community, or other clumped distribution allows a population to detect predators earlier, at a greater distance, and potentially mount an effective defense. Due to limited resources, populations may be evenly distributed to minimize competition, [5] as is found in forests, where competition for sunlight produces an even distribution of trees. [6]

Humans are one of the largest distributors due to the current trends in globalization and the expanse of the transportation industry. For example, large tankers often fill their ballasts with water at one port and empty them in another, causing a wider distribution of aquatic species. [7]

On large scales, the pattern of distribution among individuals in a population is clumped. [8]

Bird wildlife corridors Edit

One common example of bird species' ranges are land mass areas bordering water bodies, such as oceans, rivers, or lakes they are called a coastal strip. A second example, some species of bird depend on water, usually a river, swamp, etc., or water related forest and live in a river corridor. A separate example of a river corridor would be a river corridor that includes the entire drainage, having the edge of the range delimited by mountains, or higher elevations the river itself would be a smaller percentage of this entire wildlife corridor, but the corridor is created because of the river.

A further example of a bird wildlife corridor would be a mountain range corridor. In the U.S. of North America, the Sierra Nevada range in the west, and the Appalachian Mountains in the east are two examples of this habitat, used in summer, and winter, by separate species, for different reasons.

Bird species in these corridors are connected to a main range for the species (contiguous range) or are in an isolated geographic range and be a disjunct range. Birds leaving the area, if they migrate, would leave connected to the main range or have to fly over land not connected to the wildlife corridor thus, they would be passage migrants over land that they stop on for an intermittent, hit or miss, visit.

On large scales, the pattern of distribution among individuals in a population is clumped. On small scales, the pattern may be clumped, regular, or random. [8]

Clumped Edit

Clumped distribution is the most common type of dispersion found in nature. In clumped distribution, the distance between neighboring individuals is minimized. This type of distribution is found in environments that are characterized by patchy resources. Animals need certain resources to survive, and when these resources become rare during certain parts of the year animals tend to “clump” together around these crucial resources. Individuals might be clustered together in an area due to social factors such as selfish herds and family groups. Organisms that usually serve as prey form clumped distributions in areas where they can hide and detect predators easily.

Other causes of clumped distributions are the inability of offspring to independently move from their habitat. This is seen in juvenile animals that are immobile and strongly dependent upon parental care. For example, the bald eagle's nest of eaglets exhibits a clumped species distribution because all the offspring are in a small subset of a survey area before they learn to fly. Clumped distribution can be beneficial to the individuals in that group. However, in some herbivore cases, such as cows and wildebeests, the vegetation around them can suffer, especially if animals target one plant in particular.

Clumped distribution in species acts as a mechanism against predation as well as an efficient mechanism to trap or corner prey. African wild dogs, Lycaon pictus, use the technique of communal hunting to increase their success rate at catching prey. Studies have shown that larger packs of African wild dogs tend to have a greater number of successful kills. A prime example of clumped distribution due to patchy resources is the wildlife in Africa during the dry season lions, hyenas, giraffes, elephants, gazelles, and many more animals are clumped by small water sources that are present in the severe dry season. [9] It has also been observed that extinct and threatened species are more likely to be clumped in their distribution on a phylogeny. The reasoning behind this is that they share traits that increase vulnerability to extinction because related taxa are often located within the same broad geographical or habitat types where human-induced threats are concentrated. Using recently developed complete phylogenies for mammalian carnivores and primates it has been shown that the majority of instances threatened species are far from randomly distributed among taxa and phylogenetic clades and display clumped distribution. [10]

A contiguous distribution is one in which individuals are closer together than they would be if they were randomly or evenly distributed, i.e., it is clumped distribution with a single clump. [11]

Regular or uniform Edit

Less common than clumped distribution, uniform distribution, also known as even distribution, is evenly spaced. Uniform distributions are found in populations in which the distance between neighboring individuals is maximized. The need to maximize the space between individuals generally arises from competition for a resource such as moisture or nutrients, or as a result of direct social interactions between individuals within the population, such as territoriality. For example, penguins often exhibit uniform spacing by aggressively defending their territory among their neighbors. The burrows of great gerbils for example are also regularly distributed, [12] which can be seen on satellite images. [13] Plants also exhibit uniform distributions, like the creosote bushes in the southwestern region of the United States. Salvia leucophylla is a species in California that naturally grows in uniform spacing. This flower releases chemicals called terpenes which inhibit the growth of other plants around it and results in uniform distribution. [14] This is an example of allelopathy, which is the release of chemicals from plant parts by leaching, root exudation, volatilization, residue decomposition and other processes. Allelopathy can have beneficial, harmful, or neutral effects on surrounding organisms. Some allelochemicals even have selective effects on surrounding organisms for example, the tree species Leucaena leucocephala exudes a chemical that inhibits the growth of other plants but not those of its own species, and thus can affect the distribution of specific rival species. Allelopathy usually results in uniform distributions, and its potential to suppress weeds is being researched. [15] Farming and agricultural practices often create uniform distribution in areas where it would not previously exist, for example, orange trees growing in rows on a plantation.

Random Edit

Random distribution, also known as unpredictable spacing, is the least common form of distribution in nature and occurs when the members of a given species are found in environments in which the position of each individual is independent of the other individuals: they neither attract nor repel one another. Random distribution is rare in nature as biotic factors, such as the interactions with neighboring individuals, and abiotic factors, such as climate or soil conditions, generally cause organisms to be either clustered or spread. Random distribution usually occurs in habitats where environmental conditions and resources are consistent. This pattern of dispersion is characterized by the lack of any strong social interactions between species. For example When dandelion seeds are dispersed by wind, random distribution will often occur as the seedlings land in random places determined by uncontrollable factors. Oyster larvae can also travel hundreds of kilometers powered by sea currents, which can result in their random distribution. Random distributions exhibit chance clumps (see Poisson clumping).

There are various ways to determine the distribution pattern of species. The Clark–Evans nearest neighbor method [16] can be used to determine if a distribution is clumped, uniform, or random. [17] To utilize the Clark–Evans nearest neighbor method, researchers examine a population of a single species. The distance of an individual to its nearest neighbor is recorded for each individual in the sample. For two individuals that are each other's nearest neighbor, the distance is recorded twice, once for each individual. To receive accurate results, it is suggested that the number of distance measurements is at least 50. The average distance between nearest neighbors is compared to the expected distance in the case of random distribution to give the ratio:

If this ratio R is equal to 1, then the population is randomly dispersed. If R is significantly greater than 1, the population is evenly dispersed. Lastly, if R is significantly less than 1, the population is clumped. Statistical tests (such as t-test, chi squared, etc.) can then be used to determine whether R is significantly different from 1.

The variance/mean ratio method focuses mainly on determining whether a species fits a randomly spaced distribution, but can also be used as evidence for either an even or clumped distribution. [18] To utilize the Variance/Mean ratio method, data is collected from several random samples of a given population. In this analysis, it is imperative that data from at least 50 sample plots is considered. The number of individuals present in each sample is compared to the expected counts in the case of random distribution. The expected distribution can be found using Poisson distribution. If the variance/mean ratio is equal to 1, the population is found to be randomly distributed. If it is significantly greater than 1, the population is found to be clumped distribution. Finally, if the ratio is significantly less than 1, the population is found to be evenly distributed. Typical statistical tests used to find the significance of the variance/mean ratio include Student's t-test and chi squared.

However, many researchers believe that species distribution models based on statistical analysis, without including ecological models and theories, are too incomplete for prediction. Instead of conclusions based on presence-absence data, probabilities that convey the likelihood a species will occupy a given area are more preferred because these models include an estimate of confidence in the likelihood of the species being present/absent. They are also more valuable than data collected based on simple presence or absence because models based on probability allow the formation of spatial maps that indicates how likely a species is to be found in a particular area. Similar areas can then be compared to see how likely it is that a species will occur there also this leads to a relationship between habitat suitability and species occurrence. [19]

Species distribution can be predicted based on the pattern of biodiversity at spatial scales. A general hierarchical model can integrate disturbance, dispersal and population dynamics. Based on factors of dispersal, disturbance, resources limiting climate, and other species distribution, predictions of species distribution can create a bio-climate range, or bio-climate envelope. The envelope can range from a local to a global scale or from a density independence to dependence. The hierarchical model takes into consideration the requirements, impacts or resources as well as local extinctions in disturbance factors. Models can integrate the dispersal/migration model, the disturbance model, and abundance model. Species distribution models (SDMs) can be used to assess climate change impacts and conservation management issues. Species distribution models include: presence/absence models, the dispersal/migration models, disturbance models, and abundance models. A prevalent way of creating predicted distribution maps for different species is to reclassify a land cover layer depending on whether or not the species in question would be predicted to habit each cover type. This simple SDM is often modified through the use of range data or ancillary information, such as elevation or water distance.

Recent studies have indicated that the grid size used can have an effect on the output of these species distribution models. [20] The standard 50x50 km grid size can select up to 2.89 times more area than when modeled with a 1x1 km grid for the same species. This has several effects on the species conservation planning under climate change predictions (global climate models, which are frequently used in the creation of species distribution models, usually consist of 50–100 km size grids) which could lead to over-prediction of future ranges in species distribution modeling. This can result in the misidentification of protected areas intended for a species future habitat.

The Species Distribution Grids Project is an effort led out of the University of Columbia to create maps and databases of the whereabouts of various animal species. This work is centered on preventing deforestation and prioritizing areas based on species richness. [21] As of April 2009, data are available for global amphibian distributions, as well as birds and mammals in the Americas. The map gallery Gridded Species Distribution contains sample maps for the Species Grids data set. These maps are not inclusive but rather contain a representative sample of the types of data available for download:


Reinitiated Consultation

Sometimes after completion of consultation, the project changes, a new species is listed, or critical habitat is designated or revised while the project is ongoing. Other times, take occurs when not exempted, or other relevant new information becomes available (e.g., new research on geographic extent of a species range). Each of these scenarios may result in the need to revise the effects analysis in the Biological Opinion or in an informal consultation letter. Reinitiation of consultation is required and shall be requested by the Federal agency or by us, where discretionary Federal involvement or control over the action has been retained or is authorized by law, and:

  1. If the amount or extent of taking specified in the incidental take statement is exceeded
  2. If new information reveals effects of the action that may affect listed species or critical habitat in a manner or to an extent not previously considered
  3. If the identified action is subsequently modified in a manner that causes an effect to the listed species or critical habitat that was not considered in the biological opinion or written concurrence or
  4. If a new species is listed or critical habitat designated that may be affected by the identified action.

Trigger 1 typically only applies to formal consultations that include an Incidental Take Statement (ITS) within a Biological Opinion, but, if take resulted from an action where it was not exempted and included under an ITS, reinitiation is required immediately. If a project changes, the action agency staff member should contact the section 7 biologist who wrote the consultation letter and/or Biological Opinion. Staff should discuss the changes and the potential need for reinitiation before submitting a request for reinitiation. Reinitiation is not always required if the project changes the changes need to result in the level and/or type of effects to rise beyond the level and/or type of effects that have previously been considered in the consultation. If reinitiation is necessary, the action agency must send us a letter (following the guidelines for requesting consultation) requesting reinitiation of consultation. The request should contain an assessment of the effects of the modified action on listed species and/or critical habitat. If the new determination is that the modified action is “not likely to adversely affect” listed species or critical habitat, an analysis must be provided to support the determination and submitted with a request for our concurrence. If we concur, we will send back a letter which will complete the reinitiated consultation. However, if the modified action is likely to adversely affect listed species and/or critical habitat, then formal consultation is required, and a Biological Opinion will need to be produced (see Formal Consultations for more information).


Development and growth in skulls of three Otariidae species: a comparative morphometric study

We examined the skulls of Arctocephalus australis , Callorhinus ursinus and Otaria byronia with the objectives of (1) estimating the development and growth rates and comparing these parameters among the species (2) describing the development for each linear measure, for each species and sex (3) determining which variables are best correlated with age (4) determining age of physical maturity. We employed traditional and geometric morphometric techniques to study the skulls. In A. australis and C. ursinus , skulls of females mature at about 6 years of age, and those of males at about 8 years. Otaria byronia matures later, at about 9 years. Using geometric morphometric data sets, the rate and constant of growth in A. australis did not differ between the sexes. Callorhinus ursinus and O. byronia showed rates significantly different between sexes concerning growth (and in the constant as well), but only O. byronia differed between sexes in both developmental model parameters (rates and constant). Comparisons between the growth and developmental models showed significant differences in slope and constant. In both treatments employed, a relationship between size and shape dimorphism could be inferred for the skulls of all three species. We conclude that rates or timing of growth and development evolves within a conserved spatiotemporal organization of morphogenesis.


Defending Stephen Jay Gould's Crusade against Biological Determinism

I used to be tough on Stephen Jay Gould, the great evolutionary biologist, who died in 2002. I found him self-righteous and pompous, in person and on the page. In an August 1995 profile of him for Scientific American I summed up his worldview, which emphasizes the role of randomness, or "contingency," in shaping life, as "shit happens."

But I admired Gould's ferocious opposition to biological determinism, which he defined as the view that "the social and economic differences between different groups—primarily races, classes and sexes—arise from inherited, inborn distinctions and that society, in this sense, is an accurate reflection of biology." I loathe biological determinism, too, and so I must defend Gould against charges that he was a fact-fudging "charlatan," as the anthropologist Ralph Holloway of Columbia University put it.

Holloway's slur is based on a critique by him and five other anthropologists of Gould's famous 1981 work The Mismeasure of Man (W. W. Norton & Co., 1981), in which Gould exposed case after appalling case of scientists in the past two centuries "proving" the biological inferiority of certain races as well as criminals, the poor, "imbeciles" and women. One chapter focused on the work of a 19th-century physician, Samuel George Morton, who amassed a collection of almost 1,000 skulls from around the world. Morton estimated the brain size of different racial groups by pouring seed and lead shot into the skulls. He concluded that whites have larger brains on average than blacks, confirming his suspicion that the races did not do not share a common ancestry but stemmed from different evolutionary roots.

Defenders of slavery embraced Morton's work. After he died, an editorial in the Charleston Medical Journal and Review declared, "We in the South should consider him our benefactor, for aiding most materially in giving to the Negro his true position as an inferior race." In Mismeasure, Gould reanalyzed Morton&rsquos skull measurements and concluded that the average sizes of blacks' and whites' skulls were roughly equivalent. Gould suggested that Morton's racial bias had led him, probably unwittingly, to "discover" results consonant with his beliefs.

In "The Mismeasure of Science: Stephen Jay Gould versus Samuel George Morton on Skulls and Bias," published June 7 in PLoS Biology, Holloway and five colleagues from other institutions stated that Gould's own analysis of Morton "is likely the stronger example of a bias influencing results." The group reported that its re-measurements of the skulls in Morton's collection support Morton's conclusions more than Gould's.

Commenting on Gould's claim that bias often influences science, an unsigned editorial in The New York Times snidely remarked, "Right now it looks as though he proved his point, just not as he intended." The anthropologist and blogger John Hawks claims that the "straightforward" analysis of Holloway et al. shows that Gould clearly engaged in "utter fabulation." Hawks added, "Some of Gould's mistakes are outrageous, with others it is hard for me to believe that the misstatements were not deliberate misrepresentations."

Some caveats are in order here. First of all, Holloway and his colleagues analyzed fewer than half of the skulls in Morton's collection. Second, their analysis, far from being "straightforward," was highly technical and based on many judgment calls, as were those of Gould and Morton. The divergent results depend in part on whether to include or exclude certain skulls that could unduly skew estimates of brain sizes. Third, neither Morton nor Holloway et al. corrected their measurements for age, gender or stature, all of which are correlated with brain size.

Finally, at least one of the PLoS authors, Holloway, is obviously biased against Gould. The Times quoted Holloway saying: "I just didn't trust Gould. I had the feeling that his ideological stance was supreme." Holloway faulted Gould because he "never even bothered to mention" a 1988 paper by John S. Michael that found Morton's conclusions to be "reasonably accurate." But Holloway and his co-authors stated that the paper by Michael, written when he was an undergraduate at the University of Pennsylvania, "has multiple significant flaws rendering it uninformative."

Maybe Gould was wrong that Morton misrepresented his data, but he was absolutely right that biological determinism was and continues to be a dangerous pseudoscientific ideology. Biological determinism is thriving today: I see it in the assertion of researchers such as the anthropologist Richard Wrangham of Harvard University that the roots of human warfare reach back all the way to our common ancestry with chimpanzees. In the claim of scientists such as Rose McDermott of Brown University that certain people are especially susceptible to violent aggression because they carry a "warrior gene." In the enthusiasm of some science journalists for the warrior gene and other flimsy linkages of genes to human traits. In the insistence of the evolutionary biologist Jerry Coyne and neuroscientist Sam Harris that free will is an illusion because our "choices" are actually all predetermined by neural processes taking place below the level of our awareness. In the contention of James Watson, co-discoverer of the double helix, that the problems of sub-Saharan Africa reflect blacks' innate inferiority. In the excoriation of many modern researchers of courageous anti-determinists such as Gould and Margaret Mead.

Biological determinism is a blight on science. It implies that the way things are is the way they must be. We have less choice in how we live our lives than we think we do. This position is wrong, both empirically and morally. If you doubt me on this point, read Mismeasure, which, even discounting the chapter on Morton, abounds in evidence of how science can become an instrument of malignant ideologies.

Photo courtesy Kathy Chapman and Wiki Commons

The views expressed are those of the author(s) and are not necessarily those of Scientific American.


SPECIAL TOPICS: HOW WE BECAME HAIRLESS, SWEATY PRIMATES

As an anthropology instructor, one question about human evolution that students often ask me concerns human body hair&mdashwhen did our ancestors lose it and why? It is assumed that our earliest ancestors were as hairy as modern-day apes. Today, though, we lack thick hair on most parts of our bodies except in the armpit and pubic regions and on the tops of our heads. Humans actually have about the same number of hair follicles per unit of skin as chimpanzees. But, the hairs on most of our body are so thin as to be practically invisible. When did we develop this peculiar pattern of hairlessness? Which selective pressures in our ancestral environment were responsible for this unusual characteristic?

Many experts believe that the driving force behind our loss of body hair was the need to effectively cool ourselves. Along with the lack of hair, humans are also distinguished by being exceptionally sweaty: we sweat larger quantities and more efficiently than any other primate. Humans have a larger amount of eccrine sweat glands than other primates and these glands generate an enormous volume of watery sweat. Sweating produces liquid on the skin that cools you off as it evaporates. It seems likely that hairlessness and sweating evolved together, as a recent DNA analysis has identified a shared genetic pathway between hair follicles and eccrine sweat gland production (Kamberov et al 2015).

Which particular environmental conditions led to such adaptations? In this chapter, we learned that the climate was a driving force behind many changes seen in the hominin lineage during the Pleistocene. At that time, the climate was increasingly arid and the forest canopy in parts of Africa was being replaced with a more open grassland environment, resulting in increased sun exposure for our ancestors. Compared to the earlier australopithecines, members of the genus Homo were also developing larger bodies and brains, starting to obtain meat by hunting or scavenging carcasses, and crafting sophisticated stone tools.

According to Nina Jablonski, an expert on the evolution of human skin, the loss of body hair and increased sweating capacity are part of the package of traits characterizing the genus Homo. While larger brains and long-legged bodies made it possible for humans to cover long distances while foraging, this new body form had to cool itself effectively to handle a more active lifestyle. Preventing the brain from overheating was especially critical. The ability to keep cool may have also enabled hominins to forage during the hottest part of the day, giving them an advantage over savanna predators, like lions, that typically rest during this time.

When did these changes occur? Although hair and soft tissue do not typically fossilize, there are several indirect methods that have been used to explore this question. One method tracks a human skin color gene. Since chimpanzees have light skin under their hair, it is probable that early hominins also had light skin color. Apes and other mammals with thick fur coats have protection against the sun&rsquos rays. As our ancestors lost their fur, it is likely that increased melanin pigmentation was selected for to shield our ancestors from harmful ultraviolet radiation. A recent genetic analysis determined that one of the genes responsible for melanin production originated about 1.2 million years ago (Jablonski 2012).

Another line of evidence tracks the coevolution of a rather unpleasant human companion&mdashthe louse. A genetic study identified human body louse as the youngest of the three varieties of lice that infest humans, splitting off as a distinct variety around 70,000 years ago (Kittler, Kayser, and Stoneking 2003). Because human body lice can only spread through clothing, this may have been about the time when humans started to regularly wear clothing. However, the split between human head and pubic lice is estimated to have occurred much earlier, about three million years ago (Reed et al. 2007). When humans lost much of their body hair, lice that used to roam freely around the body were now confined to two areas: the head and pubic region. As a result of this &ldquogeographic&rdquo separation, the lice population split into two distinct groups.

Other explanations have also been suggested for the loss of human body hair. For example, being hairless has other advantages such as making it more difficult for skin parasites like lice, fleas, and ticks to live on us. Additionally, after bipedality evolved, hairless bodies would also make reproductive organs and female breasts more visible, suggesting that sexual selection may have played a role.

Homo erectus in Africa

Although the earliest discoveries of Homo erectus fossils were from Asia, the greatest quantity and best-preserved fossils of the species come from East African sites. The earliest fossils in Africa identified as Homo erectus come from the East African site of Koobi Fora, around Lake Turkana in Kenya, and are dated to about 1.8 million years ago. Other fossil remains have been found in East African sites in Kenya, Tanzania, and Ethiopia. Other notable African Homo erectus finds are a female pelvis from the site of Gona, Ethiopia (Simpson et al 2008), and a cranium from Olduvai Gorge known as Olduvai 9, thought to be about 1.4 million years old with massive brow ridges.

Homo erectus&rsquo presence in South Africa is not well documented, though fossils thought to belong to the species have also been uncovered from the famed South African Swartkrans cave site along with stone tools and burned animal bones.

Regional Discoveries Outside Africa

It is generally agreed that Homo erectus was the first hominin to migrate out of Africa and colonize Asia and later Europe (although recent discoveries in Asia may challenge this view). Key locations and discoveries of Homo erectus fossils, along with the fossils&rsquo estimated age are summarized below, and in Figure 10.12.

Figure (PageIndex<2>): Map showing the locations of Homo erectus fossils around Africa and Eurasia.

Indonesia

The first discovery of Homo erectus was in the late 1800s in Java, Indonesia. A Dutch anatomist named Eugene Dubois searched for human fossils with the belief that since orangutans lived there, it might be a good place to look for remains of early humans. He discovered a portion of a skull, a femur, and some other bone fragments on a riverbank. While the femur looked human, the top of the skull was smaller and thicker than a modern person&rsquos. Dubois named the fossil Pithecanthropus erectus (&ldquoupright ape-man&rdquo), popularized in the media at the time as &ldquoJava Man.&rdquo After later discoveries of similar fossils in China and Africa, they were combined into a single species (retaining the erectus name) under the genus Homo.

Homo erectus has a long history in Indonesia further discoveries of fossils from Java were dated by argon dating to about 1.6 million to 1.8 million years. A cache of H. erectus fossils from the site of Ngandong in Java has yielded very recent dates of 43,000 years, although a more recent study with different dating methods concluded that they were much older&mdashbetween 140,000 and 500,000 years old. Still, the possible existence of isolated, yet-to-be-discovered hominin populations in the region is of great interest to paleoanthropologists, especially given the discovery of the tiny Homo floresiensis fossils discovered on the nearby island of Flores, Indonesia, and the very recent announcement of possible tiny hominin fossils from the island of Luzon in the Philippines.

China

There is evidence of Homo erectus in China from several regions and time periods. Homo erectus fossils from northern China, collectively known as &ldquoPeking Man,&rdquo are some of the most famous human fossils in the world. Dated to about 400,000&ndash700,000 years ago, they were excavated from the site of Zhoukoudian, near the outskirts of Beijing. Hundreds of bones and teeth, including six nearly complete skulls, were excavated from the cave in the 1920s and 1930s. Much of the fossils&rsquo fame comes from the fact that they disappeared under mysterious circumstances. As Japan advanced into China during World War II, Chinese authorities, concerned for the security of the fossils, packed up the boxes and arranged for them to be transported to the United States. But in the chaos of the war, they vanished and were never heard about again. What exactly happened to them is murky&mdashthere are several conflicting accounts. Fortunately, an anatomist named Frans Weidenreich who had previously studied the bones had made casts and measurements of the skulls, so this valuable information was not lost. More recent excavations, at Longgushan &ldquoDragon Bone Cave&rdquo at Zhoukoudian, of tools, living sites, and food remains, have revealed much about the lifestyle of Homo erectus during this time.

Despite this lengthy history of scientific research, China, compared to Africa, was perceived as somewhat peripheral to the study of hominin evolution. Although Homo erectus fossils have been found at several sites in China, with dates that make them comparable to those of Indonesian Homo erectus, none seemed to approximate the antiquity of African sites. The notable finds at sites like Nariokotome and Olorgesaille took center stage during the 1970s and 80&rsquos, as scientists focused on elucidating the species&rsquo anatomy and adaptations in its African homeland. In contrast, fewer research projects were focused on East Asian sites (Qiu 2016).

However, isolated claims of very ancient hominin occupation kept cropping up from different locations in Asia. While some were dismissed because of problems with dating methods or stratigraphic context, the 2018 publication of the discovery of stone tools from China dated to 2.1 million years caught everyone&rsquos attention. Dated by paleomagnetic techniques that date the associated soils and windblown dust, these tools indicate that hominins in Asia predated those at Dmanisi by at least 300,000 years (Zhu et al. 2018). In fact, the tools are older than any Homo erectus fossils anywhere. Since no fossils were found with the tools, it isn&rsquot known which species made them, but it opens up the intriguing possibility that hominins earlier than Homo erectus could have migrated out of Africa. These exciting new discoveries are shaking up previously held views of the East Asian human fossil record.

Western Eurasia

An extraordinary collection of fossils from the site of Dmanisi in the Republic of Georgia has revealed the presence of Homo erectus in Western Eurasia between 1.75 million and 1.86 million years ago. Dmanisi is located in the Caucasus mountains in Georgia. When archaeologists began excavating a medieval settlement near the town in the 1980s and came across the bones of extinct animals, they shifted their focus from the historic to the prehistoric era, but they probably did not anticipate going back quite so far in time! The first hominin fossils were discovered in the early 1990s, and since that time, at least five relatively well-preserved crania have been excavated.

There are several surprising things about the Dmanisi fossils. Compared to African Homo erectus, they have smaller brains and bodies. However, despite the small brain size, they show clear signs of Homo erectus traits such as heavy brow ridges and reduced facial prognathism. Paleoanthropologists have pointed to some aspects of their anatomy (such as the shoulders) that appear rather primitive, although their body proportions seem fully committed to terrestrial bipedalism. One explanation for these differences could be that the Dmanisi hominins represent a very early form of Homo erectus that left Africa before increases in brain and body size evolved in the African population.

Second, although the fossils at this location are from the same geological context, they show a great deal of variation in brain size and in facial features. One skull (Skull 5) has a cranial capacity of only 550 cc, smaller than many Homo habilis fossils, along with larger teeth and a protruding face. Scientists disagree on what these differences mean. Some contend that the Dmanisi fossils cannot all belong to a single species because each one is so different. Others assert that the variability of the Dmanisi fossils proves that they, along with all early Homo fossils, including H. habilis and H. rudolfensis, could all be grouped into Homo erectus (Lordikipanidze et al. 2013). Regardless of which point of view ends up dominating, the Dmanisi hominins are clearly central to the question of how to define the early members of the genus Homo.

Europe

Until recently, there was scant evidence of any Homo erectus presence in Europe, and it was assumed that hominins did not colonize Europe until much later than East Asia or Eurasia. One explanation for this was that the harsh ice age climate of Western Europe served as a barrier to living there. However, recent fossil finds from Spain suggest that Homo erectus could have made it into Europe over a million years ago. In 2008 a mandible from the Atapuerca region in Spain was discovered, dating to about 1.2 million years ago. A more extensive assemblage of fossils from the site of Gran Dolina in Atapuerca have been dated to about 800,000 years ago. In England in 2013 fossilized hominin footprints of adults and children dated to 950,000 years ago were found at the site of Happisburgh, Norfolk, which would make them the oldest human footprints found outside Africa (Ashton et al. 2014).

At this time, researchers aren&rsquot in agreement as to whether the first Europeans belonged to Homo erectus proper or to a later descendent species. Some scientists refer to the early fossils from Spain by the species name, Homo antecessor.


The role of species competition in biodiversity

Skulls of various Canid genera Vulpes (corsac fox), Nyctereutes (raccoon dog), Cuon (dhole) and Canis (golden jackal) Credit: Wikipedia.

(Phys.org)—Over long spans, biodiversity is a fluid and shifting balance of species and influences. Species diversification occurs in response to a host of complex factors, both biotic and abiotic, and understanding them is a major challenge of evolutionary biology.

A group of researchers in Sweden, Switzerland and Brazil have collaborated on a study of North American canids to show that competition from multiple carnivore clades is responsible for the ultimate demise of two extinct canid subfamilies. They theorize that the competitive processes driving these extinctions are more prevalent in species diversification than previously believed. The study is published in the Proceedings of the National Academy of Sciences.

The North American fossil record provides abundant evidence for the evolutionary history of the dog family Canidae and of other major carnivores. The researchers analyzed around 1,500 fossil occurrences for 120 canid species from around 40 million years ago to the present theorizing that competition from other species was a factor driving extinction rates, they also compiled data for five additional carnivore families including cats, bear dogs, false saber-tooth cats, and bears.

They developed an analytical framework to invesigate whether speciation and extinction rates responded to evolution of body mass—a good approximation of diet for canids. The authors suggest that body size can indirectly correlate with diversification dynamics as increases in size predispose the development of hypercarnivory behaviors and selective feeding. These adaptive constraints place canids in danger of extinction by restricting their possible sources of food.

Via a Bayesian analytic framework, the researchers have determined that the two extinct subfamilies that form the basis of their study were ultimately wiped out by the competitive effects of other carnivore clades, previously considered a rare occurrence, but increasingly regarded as an important influence on biodiversity.

Climate change events are widely believed to be a main driver of extinction and speciation, but the study strongly suggests an important role for competition between different species with similar ecologies. Two biologic mechanisms drive clade replacement: passive replacement and active displacement. In the case of passive replacement, an incumbent carnivore clade prevents a competitor population from radiating. The competitor can only radiate once the incumbent carnivore clade declines.

Active displacement is the process by which a clade's rise in diversity causes the decline of another clade by outcompeting for limited resources. "The demise of nonavian dinosaurs by the Cretaceous-Paleogene meteorite impact around 66 million years ago and the subsequent evolutionary and ecologic diversification of mammals provide an iconic example of passive replacement," the authors write.

The authors found evidence for significant changes in speciation and extinction rates for the two extinct canid subfamilies, Hesperocyoninae and Borophaginae, suggesting strongly that the demise of a clade is driven by both its rate of extinction and its failure to originate.

The researchers report that changes in in the speciation and extinction rates of the two extinct canid groups were strongly correlated with changes in diversity of multiple competitors. "Our results strongly indicate that competition among several clades of canids and other carnivores drove the changes in diversification rates and the replacement of entire clades," they write.

Abstract
The history of biodiversity is characterized by a continual replacement of branches in the tree of life. The rise and demise of these branches (clades) are ultimately determined by changes in speciation and extinction rates, often interpreted as a response to varying abiotic and biotic factors. However, understanding the relative importance of these factors remains a major challenge in evolutionary biology. Here we analyze the rich North American fossil record of the dog family Canidae and of other carnivores to tease apart the roles of competition, body size evolution, and climate change on the sequential replacement of three canid subfamilies (two of which have gone extinct). We develop a novel Bayesian analytic framework to show that competition from multiple carnivore clades successively drove the demise and replacement of the two extinct canid subfamilies by increasing their extinction rates and suppressing their speciation. Competitive effects have likely come from ecologically similar species from both canid and felid clades. These results imply that competition among entire clades, generally considered a rare process, can play a more substantial role than climate change and body size evolution in determining the sequential rise and decline of clades.


The Birth of the “Neanderthals”

Library archives reveal the Gibraltar skull’s role in the discovery of our sister species.

T here it was—exactly the type of clue I was looking for. I was sitting in the library of the Royal College of Surgeons in London, an elegant, high-ceilinged room lined to the rafters with impeccably organized old books, like a frozen set piece from the 19th century. I was there to examine the papers and photographs of George Busk, a man who was once president of the college. Busk spent much of his working life at the Royal College lecturing on biology, and his papers and other materials have resided in the archives since his death in 1886.

I had been flipping through Busk’s photographs of fossils, many of which were of fragmented cave bear bones, when I came upon an image of the Gibraltar Neanderthal skull. Its large, hollow eye sockets stared up at me. Without thinking, I raised the photo toward my face for closer examination. It was then that a voice from across the room brought me back to reality, reminding me that photos must be kept on the table. These precious images are not to be held or breathed upon. I carefully placed the picture back on the table and continued to stare at it in awe.

I n addition to being a surgeon, a lecturer, and a photographer of cave bear remains, Busk was the man who first introduced Neanderthals to the English-speaking world. The photograph that made me gasp had likely been taken in 1864, when Busk was most engaged in describing the skull. It captivated me not simply because it was a beautiful shot, but also because it was evidence of an important moment in the story of scholarship on Neanderthals. The Gibraltar skull had appeared as a crucial piece of evidence at precisely the moment when scientists were first attempting to discern what a Neanderthal was.

I n 1856, a fossilized skull had been found in the Neander Valley in Germany, and it soon ended up in the hands of the well-regarded German anatomist Hermann Schaaffhausen. The skull looked vaguely human, with a big brain, but also different, somewhat apelike. In order to explain this peculiar skull, which became known as the “Neanderthal man,” many scientists argued that it was merely a diseased idiot who died in a cave. Others maintained that it was truly something novel—a new, humanlike creature never seen before. Busk brought the debate from Germany to the United Kingdom by translating Schaaffhausen’s scholarly paper about the fossil into English, adding his own comments to the translation. He recognized that settling the debate would require more evidence. More fossils needed to be discovered.

The Gibraltar skull signaled that the Neanderthal man remains were not an aberration, but it raised more questions than it answered. Royal College of Surgeons of England

A n answer to Busk’s call appeared almost immediately in the form of the Gibraltar skull. Originally found in 1848, the skull had been sitting in a library cupboard, collecting dust, for over a decade—until Busk’s call to action moved someone to send it to him. The fossil was strikingly similar to the Neander specimen, making it the key to settling the debate. Recognizing the fossil’s significance, Busk quickly published a paper arguing that the Neander fossil was not a “mere individual peculiarity” but instead a new type of creature whose range once stretched “from the Rhine to the Pillars of Hercules.”

T he story of Busk and the Gibraltar Neanderthal zeros in on the moment when scientists first recognized that Neanderthals were something unique. The nature and meaning of the discovery—a new species perhaps, or a new variety of human—were still open. But thanks to the Gibraltar skull, scientists had determined that these creatures were not simply unhealthy humans: They were something worth paying close attention to.

T his is the story that brought me to the reading room in 2014 I was hoping to learn more about this moment in history. Who sent Busk the skull? How did he go about studying it? What measurements did he take, and how did he determine the skull’s similarity to the Neander specimen? The photo gave me a glimmer of hope that I could answer these questions.

I ntertwined with the 19th-century study of Neanderthals were issues of their identity and relationship to modern humans. Busk and other scientists wanted to know: Did Neanderthals have art or language? Were they humans, or were they something else? These questions likely seem familiar. Although our knowledge of Neanderthal anatomy, DNA, and behavior has grown dramatically since the 1860s, many of the questions we ask about our closest relatives are very much the same.

L ike Busk, paleoanthropologists today want to know the extent of Neanderthals’ relationships and similarities with humans. They also want to know how Neanderthals lived, whether or not they had symbolic culture, and how intelligent they were. As a historian and philosopher of science, I maintain that in order to truly understand what we think we know about the Neanderthals, we must also ask, “How do we know?”

A lthough I don’t yet have all the answers for how Busk “knew” the Neanderthals, I have clues. This photo of the Gibraltar skull tells me more about Busk’s recognition of the skull’s importance: Photography was rare at the time, and only truly important things were photographed. A notebook he kept on his trip to Gibraltar, which I also found in his archives, illuminates his attempts to learn more about the skull. By searching through old photographs and scribbled notes, I can answer questions about how Busk and others went about “knowing” the Neanderthals. This in turn can help us appreciate how we have come to understand this sister species.

T he materials buried in libraries give historians clues that help us answer questions about how we know what we think we know. Busk’s archives are a window into how he attempted to understand fossils. By studying his papers, I can view the Gibraltar skull through his eyes, and I can experience some of the wonder and fascination he must have felt when he first lifted it out of a box back in 1864.


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