Refers to events that occurred at the same time and are associated with each other.

Members of this group of mammals (which includes humans) carry the developing fetus in the uterus, where the placenta facilitates the exchange of nutrients and wastes between the mother and the fetus.

These turtles are related to modern snapping turtles and have a similar morphology. They had large heads and long tails.

These are floodplain deposits made when the river broke through its natural flood banks. Heavier sediments are deposited closer to the river channel, while lighter sediments, such as sand and silt, are deposited farther away from the channel.

These are single-celled, bottom-dwelling organisms that live on or within the carbonate-rich sediment surface. https://www.biointeractive.org/classroom-resources/foraminiferaearths-microscopic-recordkeepers

https://ucmp.berkeley.edu/fosrec/Wetmore.html

S. Burgess stresses that knowledge of the cause or causes of mass extinctions can inform understanding of how the biosphere responds to dramatic environmental change and can help to validate hypotheses about probable outcomes of anthropogenic changes. Both the asteroid impact and large-scale volcanic eruptions as the cause of the K-Pg extinction are credible. Now, with more accurate dating techniques, it appears that most of the large-scale eruptions occurred after the impact, delaying recovery.

This is one of the two groups angiosperms are traditionally divided into. A number of traits distinguish dicots from the other group, the monocotyledons (monocots). The seeds of dicots contain two embryonic seed leaves; monocot seeds contain one.

This is one of the largest volcanic areas on Earth. Its lava flows cover an area of about 500,000 square kilometers.

This stage of the geologic timescale refers to the North American faunal stage, spanning from 66,000,000 to 63,300,000 years BP (Before Present).

Basins located in the eastern Rocky Mountains of the United States were the primary area of interest. Maps showing the location of several of these basins can be seen at the following sites: Map of Williston Basin https://serc..edu/details/images/35362.html

Map of San Juan Basin https://www.mapsofthepast.com/san-juan-basin-usgs-1959-2941-x-23.html

Map of Hanna Basin https://www.researchgate.net/figure/Map-showing-the-Hanna-Laramie-and-Shirley-Basins-Wyoming-including-major-structural_fig1_284185996

Map of the Denver Basin https://www.researchgate.net/figure/Map-of-the-Denver-Basin-within-Colorado-Wyoming-and-Nebraska-with-structure-contours-on_fig1_265508368

J. Rolland et al. reported in Nature Ecology and Evolution that climate change could have a greater impact on reptiles than mammals and birds. By reconstructing historical shifts in geographical ranges and climatic niches, they learned that niche shifts occurred more rapidly in mammals and birds than in cold-blooded species.

Read more in Nature Ecology and Evolution: https://www.nature.com/articles/s41559-017-0451-9

Earlier research showed that the Corral Bluffs area has a relatively continuous K–Pg boundary stratigraphic sequence. It is the most extensive surface exposure in the Denver Basin and allows for the opportunity to interpret fossil collections in the context of K–Pg boundary extinction and recovery.

An important step in the authors' research was the determination of the body masses of the fossil mammals they unearthed. Body mass was estimated by measuring the length × width (L×W) of the first lower molar. This has been found to be an accurate indicator of body mass through comparisons to molar size and the body mass of living mammals. This data is important to the authors since body mass has been linked with characteristics such as energy expenditure, gestational period, temperature regulation, and niche ecology. When reconstructing life during the time period being studied, body mass distributions in mammalian communities can be used to infer ancient environmental conditions. Therefore, determining the body mass of a fossil mammal is an important step toward understanding its paleoecological role. Brain size (cranial size) usually increases with the size of the animal. However, the relationship is fairly inaccurate, as cranial size does not correlate as closely to body mass as the area of the first molar does.

Mass extinctions often result in the loss of entire branches of the tree of life. Pincelli Hull argues that macroevolution is shaped as much by the species that survive a mass extinction as by those that do not. He contends that more than 99% of all species that have ever lived are now extinct and that the losses have not been random.

Wilf et al. differentiate between climatic change and asteroid impact effects on biodiversity. They determined there was a cooling trend during the final 0.1 m.y. of the Cretaceous. This likely accounts for some loss of biodiversity from its peak during the earlier warm interval and makes inaccurate the observation that the asteroid impact alone resulted in the loss of 70%–90% of macrofossil species.

The authors tested the hypothesis that an impact winter following the asteroid impact selected against slow-growing evergreen species. Using fossil leaf collections crossing a 2-million-year interval spanning the K-Pg boundary, they assessed both carbon assimilation rate and carbon investment using leaf vein density and leaf mass per area as proxies. They learned that species that survived the K-Pg extinction had fast-growth strategies with high assimilation rates and low carbon investment.

Clyde et al. used several different dating techniques to more precisely determine the age of volcanic ash deposits across the K-Pg boundary in the Denver Basin. The results were compared to data derived from an analysis of fossil spores and pollen from deposits in the same region. They concluded that the interval between the extinction of the dinosaurs and the appearance of the earliest Cenozoic mammals in the Denver Basin lasted ∼185 k.y. and the "fern spike" lasted ∼1 k.y. after the K–Pg boundary layer was deposited, indicating rapid rates of biotic extinction and initial recovery in the Denver Basin.

Wilson’s research concludes that the richness of mammalian species remained relatively stable for most of the last ~1.9 m.y. of the Cretaceous. However, the relative abundance of mammals more closely related to marsupials than to placentals began declining ~500–600 k.y. before the Cretaceous-Paleogene boundary. Based on available fossil evidence, mammalian recovery occurred within ~600–700 k.y. of the Cretaceous-Paleogene event.

Prum and colleagues investigated avian phylogeny with a data set of >390,000 bases of genomic sequence from each of 198 species of living birds. This represents all major avian lineages, and two crocodilian outgroups. The results of their divergence time analyses are congruent with the paleontological record and support a major radiation of crown birds following the Cretaceous–Paleogene (K–Pg) mass extinction.

Evolution cannot take place quickly enough to keep up with the rate at which humans are exterminating animal and plant species. If conservation efforts are not improved, many mammal species will become extinct in the next few decades that it will take 3 to 5 million years to recover the diversity that will be lost. https://phys.org/news/2018-10-mammals-evolve-fast-current-extinction.html

The authors are concerned about the ability of Earth's ecosystems to recover from the effects of climate change, habitat destruction, and species extinction. They have concluded that extinctions are occurring at a rate that might indicate that we are in the beginning of the 6th mass extinction.

The authors discovered that at around 300,000 years after the asteroid impact that (a) the increase in large, flowering plant species leveled off, (b) the average leaf mass area had increased, indicating a greater level of energy capture through photosynthesis, and (c) there was a continuing increase in the diversity of woody plants, resulting in more energy-rich food. Additional evidence indicates that there was an increase in the number of mammal species that fed on these plants. The authors concluded that these events culminated in the observed increase in the body mass of mammals.

The fossil record shows that the latest of the Cretaceous mammals exhibited a great diversity of adaptations to the environment based on their role in the ecosystem. Some were strict carnivores, others were omnivores that fed primarily on plants, and others strict herbivores. Across the K-Pg boundary, there is a pattern of extinction that selected against larger bodied mammals with specialized diets, especially strict carnivores and species with plant-based diets. This suggests that many of the extinctions were due to a decrease in photosynthesis and plant production rather than these species being instantaneously killed.

In their study, MacLeod et al. reported the values of the oxygen-18 isotope (δ18O) in phosphate compounds isolated from sand-sized (~0.1 to 2 mm) remains of fish teeth, scales, and bone from El Kef, Tunisia, that indicate a warming trend of ~5°C beginning at the K-Pg boundary and lasting for ~100,000 years. This supported similar findings by the author of this research article.

Terrestrial climates near the time of the Cretaceous mass extinction are not well known. Temperature estimates from deep-sea sites are more reliable. Through an analysis of fossil pollen and spore samples found in North Dakota sediments and their correlation with foraminifera fossils from deep marine sediments, it has been possible to accurately determine Earth's warming and cooling trends. These trends influence biodiversity.

Tobin et al. analyzed fossil bivalve shells for carbonate-clumped isotopes. Their findings confirmed a decrease in summer temperatures over the last k.y. of the Cretaceous. This cooling trend accounts for declines in vertebrate and invertebrate biodiversity, making the destabilized ecosystem more susceptible to the asteroid impact.

Legumes appeared in the fossil record at the same time as the size of mammals was increasing. The authors concluded that legumes provided a food resource rich in proteins and carbohydrates to support larger mammals.

In communities of present-day mammals, ecological richness is primarily driven by vegetation type. The fossil record shows that some plant groups, such as gymnosperms (pines, spruce, and firs), decreased in diversity as a result of the K-Pg extinction. Angiosperms (flowering plants), on the other hand, underwent a rapid increase in diversity. When becoming dominant, angiosperms allowed for the evolution of a diversity of mammals and other animals.

The fossil record shows that after the K-Pg extinction event, there was an exponential increase in the maximum size of mammals. About 40 million years ago, this size increase leveled off. It is hypothesized that diversification to fill ecological niches was the primary driver of this rapid increase and that environmental temperature and land area have acted to constrain the continued increase.

This mammal was a specialist and was proof that mammals were evolving and becoming larger as they specialized. Increased plant diversity fueled this growth.

Loxolophus is the oldest placental mammal to be discovered. It has teeth for eating both meat and plants, thus adapting it to a recovering ecosystem.

These are compact masses of mineral matter, usually spherical or disk-shaped. They are carried along by water and become embedded in host rock that has a different composition. Concretions form in sediments before the sediments become rocks. The authors focused on searching for and cracking open concretions.

Fossil pollen reveals how plant species evolved after the K-Pg extinction. The authors compared pollen from both sides of the K-Pg boundary. The authors discovered that immediately after the impact, there were few plants.

To determine the age of some of the rocks in their study area, the authors used uranium-lead dating. It is most often used to date volcanic and metamorphic rock and very old rocks. This technique involves the radioactive decay of U-238 and U-235 into lead (Pb). The 238 and 235 refer to the sum of the number of protons (92) and neutrons in the nucleus of each of these forms of radioactive uranium. The half-life, which is how long it takes half of a sample of the U-238 to undergo radioactive decomposition and become Pb-206, is 4.47 billion years. The time it takes for half of a sample of U-235 to decay into Pb-207 is 704 million years. Since the two different forms of uranium have different half-lives and decompose into different forms of lead, they are a good check when calculating the age of a rock or fossil. This dating technique is best used on rocks that are from 1 million to 4.5 billion years old.

This technique was used by the authors to date rock strata. Chemical Abrasion-Isotope Dilution-Thermal Ionization Mass Spectrometry (CA-ID-TIMS) is a multistep, high-precision technique used to determine the relative amounts of uranium-238 and lead-206 present in zircon crystals. Zircon crystals, formed from volcanic or metamorphic rock, are extremely durable and resistant to chemical breakdown. They can survive major geologic events. Over time, new zircon layers form on top of the original crystal. The center of the zircon remains unchanged, keeping the chemical characteristics of the rock in which it originally formed. Every radioactive element has a decay rate. The length of time it takes half of the radioactive atoms in a sample to decay (form into a different element) is referred to as its half-life. The half-life of uranium-238 to lead-206 is 4.47 billion years. The authors selected zircon crystals from their study area and dated them using CA-ID-TIMS.

Image of thermal-ionization mass spectrometer: https://www.usgs.gov/media/images/usgs-thermofinnigan-triton-thermal-ionization-mass-spectrometer

This is the study of the magnetism in rocks induced by Earth's magnetic field. The minerals in certain rocks lock in the direction and strength of the magnetic field at the time of their formation. The authors used this method to determine the age of their fossil finds.

Several different dating techniques have determined that the K–Pg boundary layer in the Denver Basin overlaps with the age of the K–Pg boundary layer in the Hell Creek Formation in Montana. The age of both these areas is the same as that of tektites from Chicxulub where the asteroid impact occurred. This provides strong support for the contemporaneous deposition of ash and debris across western North America directly after the Chicxulub impact.

The authors spent many years looking for mammal fossils in different locations in the western U.S.

It has been shown that there is a strong relationship between Earth’s geochemical cycles and the biosphere. An example would be that the many volcanic eruptions occurring in the Deccan Traps likely released greenhouse gases that triggered post-KPgE warming periods. These periods resulted in a greater diversity of plant species, which in turn supported larger bodied mammals.

The extinction event that wiped out nearly three-quarters of all plant and animal species on Earth 66 million years ago.

The abbreviation for "kilo annum." It signifies time in thousands of years.

To analyze what happened in these basin areas, the authors used sequence stratigraphy. They looked for variations in the successive layers of sedimentary rocks and the composition of the rocks. The order in which the different layers were deposited was carefully recorded. The chronostratigraphy aspect of their fieldwork involved tracking changes in the character of the rocks through geologic time. Fossils found in each layer can then be better placed in terms of when these organisms evolved, and in some cases, became extinct.

Learn more about stratigraphy from HHMI BioInteractive: https://www.biointeractive.org/classroom-resources/stratigraphic-principles

Refers to the study of rock layers that can be understood over a large area.

Learn more about stratigraphic principles with HHMI BioInteractive: https://www.biointeractive.org/classroom-resources/stratigraphic-principles

There are regulations regarding fossil collecting on public lands. The Bureau of Land Management has rules for casual collecting.

Read more about these policies at https://www.blm.gov/sites/blm.gov/files/documents/files/2014%20Rockhounding_14_web.pdf

The boundary is a thin band of rock with a high concentration of platinum (heavy) metals. L. Alvarez et al. hypothesized that this layer resulted from an asteroid impact. Evidence is based on the concentration of these metals in Earth’s crust as compared to their cosmic abundance. The asteroid impact resulted in both the asteroid and rock from Earth’s crust being pulverized and sent as dust into the atmosphere. This dust was distributed worldwide. By sampling deep-sea sediments, Alvarez et al. found that the boundary rock contained higher concentrations of platinum metals than the surrounding Cretaceous and Tertiary limestones, supporting the asteroid impact hypothesis.

Located in present-day Wyoming. Map of the Hanna Basin: https://www.wsgs.wyo.gov/docs/wsgs-web-hanna-basin-geologic-map.pdf

This system established a geologic time scale for the emergence of North American land animals beginning with the late Cretaceous and continuing to the present. These ages, or stages when referring to the rock strata, were established using geographic place names to identify where the fossils were found.

This refers to the analysis of rock strata to determine remanent magnetization. It provides precise information about the polarity of the Earth’s magnetic field at the time of formation of the strata. The time interval between polarity reversals, or chron, is then used to accurately determine when the change occurred and date the strata.

The authors collaboratively planned their investigation to produce data to serve as the basis for evidence, and in the design, decide on the types of data, and the accuracy of the data to produce reliable measurements, and to consider the precision of the data.

They are members of the taxon Multituberculates and are not thought to belong to any of the groups of mammals living today. The anatomy of the pelvis suggests that they did not lay eggs but gave birth to very small, immature young. They had specialized teeth ideal for a vegetarian diet.

Note that the authors' work is built upon the findings of earlier research.

This is a way to determine the temperature based on the principle that the formation temperature of carbonate minerals is proportional to the relative abundance of 13C18O16O in CO₂. The clumped isotope thermometer is based on the measurement of the abundance of 13C-18O bonds in the mineral sample.

The authors developed a model based on evidence to illustrate the relationships between systems and between components of a system.

The fossil record shows that as woody plants increased in number and became more diverse, the diet of many mammal species shifted from being primarily omnivorous or insectivorous to herbivorous. The authors determined that this dietary shift correlated with an increase in the body mass of placental mammals as indicated through an analysis of the size and structure of the fossil mammals’ molars.

Most of the species that have ever lived on Earth did not go extinct during one of the five great mass extinctions. Typically, extinctions occur in small bursts and are followed by a long period of speciation. Since mass extinctions occur on a grand scale, they provide much information about the pacing and duration of change during their aftermath. The re-evolution of species and ecosystems on such a large scale provides an explanation for the pattern and timing of both ecological and evolutionary change observed in the fossil record.

The authors conclude that the distribution of ejecta from the asteroid impact in Chicxulub around the globe provides evidence that the impact triggered the K-Pg mass extinction. The volcanic eruption hypotheses fail to explain the global distribution of ejecta, its composition, the timing of the extinction, and the scale of environmental changes.

The authors conducted a quantitative analysis of megafloral turnover across the K-Pg. They based their work on data from the Williston Basin located in southwestern North Dakota. They relied on previously recovered high-resolution palynological data. Their data confirm that a major plant extinction event occurred in conjunction with the asteroid impact. An estimate of plant extinction, based on species lost that were present in the uppermost 5 m of Cretaceous strata, is 57%.

The authors confirm that current rates of extinction are higher than expected based on the fossil record. He, and other scientists, suggest that a sixth mass extinction may be underway. Conservation efforts must be increased.

Based on skulls, teeth, and other cranial parts, the authors could conclude they had found representatives of sixteen mammalian taxa. This was supported by the work of S. Chester.

The National Geographic article, Rise of Mammals, by Rick Gore discusses how the extinction of dinosaurs opened niches for the tiny mammals that survived the asteroid impact. His descriptions of mammalian adaptations and diversity are based on both fossil and genetic evidence.

Read more in National Geographic https://www.nationalgeographic.com/science/prehistoric-world/rise-mammals/#close

Image of Carsioptychus coarctatus provided by HHMI Tangled Bank Studios shows a rendering of this ancient herbivorous mammal. https://durangoherald.com/articles/300859

Known only to exist in North America, these placental mammals are readily identified by their unique teeth.

This is an extinct clade of turtles that appeared during the Jurassic and disappeared in the Eocene.

The calcium compound that is the main inorganic component of tooth enamel and bones. It gives bones and teeth rigidity.

The Cretaceous land mammal stage dating from 70 Ma to 66 Ma.

Population sizes are stable and remain within a sustainable range. They are in balance.

This is a graphic way to represent the succession of layers over time.

These are the living components of an ecosystem and includes the autotrophs, heterotrophs, and detritivores.

This occurs when biotic and/or abiotic change results in the biosphere or geosphere becoming unbalanced. It provides a way to explain the ecological and evolutionary changes observed in the fossil record.

This occurs when two or more species affect the evolution of each other.

This is an extinct species of hoofed, placental mammals. They are the largest known species of the genus.

Fossils/imprints from the past, referred to as proxies, can be used to determine what the paleoclimate was like. Examples of proxies are coral, pollen, and tree rings. These are analyzed and correlated with current climate conditions.

This is a morphological trait used as an indicator of the rates of photosynthesis and respiration. It is a way to link light capture to growth and carbon gain.

Many examples of members of the same genus are present. The area is species-rich.

This is the outer regions of the floodplain.

These were herbivorous mammals.

The saplings are located in their original place.

A skeleton that is all in one piece with the bones arranged in the correct order.

The physical traits of leaves, their morphology, is used to estimate the temperature.

A taxonomic species based only on its physical (morphological) differences from related species.

Flowering plants that have two seed leaves, or cotyledons, in the seed embryo.

Pollen produced by members of the walnut plant family.

Units of sediments deposited by rivers that have similar characteristics based on bedding and texture.

The interbedding of two distinctly different depositional environments.

The analysis of spores, pollen, and other particulate organic matter in sedimentary rock.

The Ma label is the abbreviation for mega annum and signifies time in millions of years.

Earth's north and south magnetic poles have reversed multiple times. Normal polarity occurs when the magnetic north points toward the geographic north pole. The reverse is the opposite. A record of the onset and duration of these reversals has been measured back to the Upper Jurassic.

This basin is located in northern New Mexico and southern Colorado.

Map: https://www.researchgate.net/figure/General-area-map-of-the-San-Juan-Basin-NM-Base-map-adapted-from-Esri-Streets-Data-and_fig1_266569834

This is an area where the underlying rocks are exposed.

These are plants that flower and fruit. They produce seeds enclosed within a female reproductive structure. It includes many non-woody plants, shrubs, and trees.

This is a clade that includes all living bird species and their ancestors, back to the common ancestor and all of the ancestor's descendants that did not evolve to form modern species.

This is a grouping of organisms that includes a single common ancestor and all the species descending from that ancestor, both living and extinct.

The proliferation of species from a single ancestor and their diversification into ecologically different forms.

This refers to things related to the land as opposed to aquatic or marine.

These are cold-blooded dinosaurs, not related to birds.

This refers to a family of plants that have nodules on their roots that contain nitrogen-fixing bacteria. The bacteria transform atmospheric nitrogen gas into nitrogen compounds plants are able to use.

This term refers to large plant species.

This is how an organism fits into the ecosystem—the role it plays. It is how it interacts with other species in a biological community.

The number of different species represented in an ecological community. It is not a count of the number of members of each species, but of the diversity of species present.

Factors that cause an event or phenomenon to occur.

A term used when something that was confusing is made clear.

The earliest of Earth's geologic ages. The Precambrian period extends from when Earth began to form around 4.6 billion years ago to 4 billion years ago. EarthViewer provides an interactive way to work through Earth history.

At the time this article was written, the author stated that the 3.6-million-year-old Laetoli footprints were the earliest evidence of bipedalism in human evolution.

The authors estimated the degree of sexual dimorphism present in Australopithecus afarensis through a systematic, random sampling of skeletal fossils. Simulations using the same sampling strategy with modern humans, chimpanzees, and gorillas confirmed the accuracy of the technique. It was determined that A. afarensis exhibited moderate sexual dimorphism similar to that of modern humans. This, coupled with the presence of a reduced male canine, is consistent with monogamy.

A large assortment bones was unearthed in Laetoli, Tanzania and Hadar, Ethiopa. The authors attribute them to a new species of Australopithecus. The soil types and depth of each bone is described and mapped.

The authors investigated the hotly debated question: "Did early bipeds walk more like humans or more like apes?" Modern humans walk with extended hind limbs whereas apes walk with flexed hind limbs. By comparing the Laetoli trackway prints with those made by modern humans walking along a sand pathway, the authors conclude that A. afarensis walked in an energetically economical way—more like modern humans.

The partial skeleton of A. afarensis specimen KSD-VP-1 was studied to learn more about stature, body mass, and bipedality in the species. KSD-VP-1/1 antedates Lucy (A.L.288-1) by about 0.4 million years. Based on measurements of bones it was determined KSD-VP-1/1 is a larger-bodied specimen than Lucy and likely a male. There is evidence of a high degree of sexual dimorphism and a well-developed thorax different from present-day apes.

There has been much debate over the degree of sexual dimorphism and implied social behavior in Australopithecus afarensis. Previous studies have suffered from limited sample size. The authors present two new resampling techniques that do not rely on template specimen and its associated assumptions. Postcranial size dimorphism is determined measuring the femur, tibia, humerus, and radius in samples of A. afarensis, modern humans, chimpanzees, gorillas, and orangutans. Based on their findings, the authors concluded that postcranial dimorphism in A. afarensis is similar to that of gorillas and orangutans, and significantly greater than in modern humans and chimpanzees. Though not conclusive, the authors feel that there is a strong evidence of behavioral and mating strategies employed by A. afarensis.

The authors employed a new technique, color-rendered optical laser scanning, to decouple the G2/3 Laetoli hominin footprints. Scientists had speculated that the G2/3 print was made by a smaller individual walking in the footsteps of a larger individual. Some had argued that the G2/3 trackway was made by only one individual and not a composite. Until this study, the G2/3 trackway had not been well studied. This article describes how the use of color-rendered optical laser scanning allowed the authors to decouple the G2 and G3 tracks, end the argument, and render the footprints usable for data analyses.

Three lineages of early Homo evolved between 2.5 and 1.5 million years ago. Evidence collected over the past few decades has resulted in a revision in the thinking about how and when adaptations such as our large, linear bodies, long legs, large brains, and reduced sexual dimorphism first appeared. Originally, it was thought these adaptations occurred as a package. Fossil analysis and environmental data indicate that many of the traits associated with Homo sapiens appeared at different times. Some arose earlier and others later. Environmental changes gave a selective advantage to different traits.

The authors based early hominin stature estimates on the length of intact fossil femurs, reconstructed femurs, and femur head diameters.

Read more in Nature.

Homo erectus footprints hint at ancient hunting party. https://www.nature.com/news/homo-erectus-footprints-hint-at-ancient-hunting-party-1.17346

The authors used average footprint length when estimating stature and body mass. They did so to minimize overestimates and underestimates of footprint size and to compensate for poor preservation.

The authors used a regression equation based on walking pace as it relates to the size of the footprint and body mass. Australopithecus afarensis proportions were used rather than those of modern humans.

The authors also estimated the stature of the Laetoli trackmakers using Australopithecus afarensis foot:stature ratios.

Hominin footprints were found near Ileret, Kenya, and are believed to be 1.5 million years old. It is thought the prints were made by Homo erectus.

The authors used two different methods to estimate the stature of the hominin trackmakers. One used modern Homo sapiens body proportions. This was considered to be less accurate since the body proportions of the hominids were likely different from those of modern humans.

The authors gathered the following data on tracks from both G and S.

Converts irregular X,Y,Z data into a regularly spaced grid composed of a series of grid nodes. Each node has a specific X,Y location and associated Z value.

The authors used the same data gathering and visualization techniques on the fiberglass casts as they had used on the tracks at S.

Casts had been made of the original tracks before the site was covered. This protected the original tracks yet made visualization of what they were like.

A set of data points used to represent a surface using X,Y,Z coordinates and serve as a starting point in 3D modeling.

This software processes digital images and generates spatial data required for 3D images.

The authors checked their measurements and used STAR*NET software to combine their conventional observations with GPS vectors. They used the leveling observations the software provided to make 3D adjustments in the footprint images.

Each test-pit was surveyed and photographed in order to determine its relationship to the other test-pits and to Site G.

The authors carefully measured distances between targets so that the location and depth of each of the modeled footprints could be precisely determined.

The authors made 3D models of selected footprints and sets of footprints. Models of some of the footprints were not made due to their poor state of preservation.

A process used to create 3D digital models from a set of photographs. The photographs can be used to measure distances which are then used to develop the models.

Some researchers hypothesized that over time, hominin species increased in stature. This increase coincided with the migration of these species into other regions. This hypothesis is not supported by the authors' work.

Earlier work by other researchers supported a hypothesis that variability in hominin stature was linked to sexual dimorphism or the environment. They also hypothesized that size did not increase over time with Australopithecines exhibiting the same stature as later Homo species including Homo sapiens.

The authors concluded that Australopithecus afaransis males were generally of the same stature as early Homo individuals.

An early hominin that is thought to have evolved from Australopithecus or the earliest of the Homo species. H. erectus first appeared in the fossil record about 1.9 million years ago and shares many of the traits seen in modern humans, including upright posture.

Based on their findings, the authors concluded that Australopithecines were larger in stature than previously thought.

Earlier work determined that the footprints at Site G were located on a specific level of the Footprint Tuff. The authors of this paper question this conclusion since the conclusion is based on an average of all the Laetoli sites and does not provide specific data regarding soil characteristics or photographs.

Based on fossil evidence, the body proportions of Homo sapiens are different from those of Australopithecus. To use these dimensions as the basis for determining the stature, body mass, and walking speed of Australopithecus would not provide an accurate picture.

How weight was distributed along the foot as the individual walked provides information that supports that all the Laetoli footprints were made by Australopithecus afarensis. The footprints also establish a morphology and gait pattern very different from that of non-hominins.

Source: https://corewalking.com/chimpanzee-feet-vs-human-feet/

In humans, this is the non-opposable big toe that is in line with the other toes. The big toe of most other primates points outward, away from the other toes.

Identifying the species of animals that were present helped the authors to establish what the local environment was like during the time Australopithecus inhabited the region.

Numerous researchers have studied the fossil tracks left by various wildlife species. The types of animals present provide additional information about the ecology of the region and helps confirm the age of the trackways.

A flat, 2D surface.

Through an analysis of soil strata, the authors determined that the new set of footprints was left at the same time and in the same layer of volcanic tuff. This is important when using the data obtained from the analysis of the footprints to determine stature and the degree of dimorphism.

It establishes that if the footprints in the original trackway were made by Australopithecus afaransis, the footprints in the newly discovered trackway were also made by A. afaransis.

As the term is used here, these are long, narrow cracks in the Earth.

Refers to the structure of Earth. It includes the forces that cause sections of the crust to move and the results of these movements.

In 1978, Dr. Leakey and colleagues discovered fossils of Australopithecus afarensis at Laetoli. Other hominin fossils had been found in the area during work done in 1938. All together, the bones of about 23 individuals had been unearthed. They dated between 3.76 and 3.46 million years old. The fossil footprints in the volcanic tuff dated to about 3.56 million years ago. Based on the evidence, Dr. Leaky and others attributed the footprints to A afarensis.

Estimates of the body mass and degree of sexual dimorphism of early hominins are based on a limited number of fossils. Often, the fossil evidence (bones and footprints) was referenced to modern humans of known body mass. It is likely that the inferred sizes are inaccurate.

More recent evidence indicates that modern humanlike size first appeared around 3–3.5 million years ago in Australopithecus afarensis.

The topic of body size and degree of sexual dimorphism present in Australopithecus afarensis continues to be hotly debated. The authors' analysis of the newly discovered footprints at Laetoli provides evidence that appears to support pronounced body-size dimorphism.

A sample of a population used to infer the characteristics shared by the individuals making up the population. As it is used in this article, it refers to the fossil remains of Australopithecus afarensis used to determine the traits of of the population.

This genus consisted of three species classified as Australopithecines. Paranthropus lived during the Pliocene and Pleistocene eras dating from about 1.8 to 1.2 million years ago.

This family includes humans, orangutans, gorillas, chimpanzees, and bonobos. https://www2.palomar.edu/anthro/primate/table_primates.htm

Refers to the combination of two different fields of study. Paleontology examines evidence of past life from fossils and biology studies living organisms. Thus, palaeobiology examines the environmental and biological history of Earth.

Chipped stones.

Groups of soil particles that bind to each other. They have a stronger attraction to each other than to surrounding soil particles.

The term applies to crystals that have partially developed faces.

The soil particles have no flat surfaces or cross-section shape.

Hominins are any species of early human that are more closely related to modern humans than chimpanzees.

Hominids refers to all modern and extinct great apes, including humans, chimpanzees, gorillas, and orangutans.

All hominins are hominids, but not all hominids are hominins!

By grouping the Pliocene and Pleistocene epochs, scientists have informally created a time period that runs from about 2.5 to 1.5 million years ago. This is when Australopithecus expanded into East Africa. https://www.grossmont.edu/people/bonnie-yoshida-levine/online-lectures/plio-pleistocene.aspx

The authors discuss the animal tracks at a newly discovered Laetoli exposure and other sites. Animal trackways serve as ecological indicators.

The authors examine the African paleoclimate and tectonics to determine how climate variability provides a framework within which to understand human evolution. The varying East African climate supports the pulsed climate variability hypothesis. Drying trends punctuated by short periods of high humidity may have driven hominin speciation and migration.

Dr. Leakey and associates discovered the footprints left by three hominins in the Laetoli beds. In this article, it is reported that the trackway extends 27 meters and provides evidence of upright, bipedal locomotion. Radiometric dating places the tracks at 3.6 million years ago. There have been no stone artifacts found in the Laetoli area. The earliest evidence of stone tools in the region was found in Olduvai Gorge and dates to about 2 million years ago. Consequently, it can be inferred that bipedalism evolved prior to formalized tool-making.

A statistical calculation to determine the accuracy of predictions made using the regression line.

A form of linear regression used to determine the best fit line.

A survey technique used to determine the location of points. Distances along the sides of a triangle are measured and angles computed. By constructing a series of adjacent triangles, distances between points can be accurately determined.

Here, in situ means "in place." Measurements were made of the actual footprint contours left by the individuals striding along the trackway.

A method of taxonomic analysis involving the external measurement of the form of an object, organism, or landform.

The trackway discovered by Dr. Leakey and colleagues has been covered in order to prevent erosion and the encroachment of plant roots. These measures were taken to guarantee that the footprints will not be destroyed. As a consequence, a careful analysis of the soil layers at Site G cannot be conducted.

Based on the estimated sizes of the Laetoli trackway individuals at Sites S and G, the variability is most likely due to reproductive success. If the males had to compete for a chance to mate with females, larger stature would be a favorable adaptation leading to a high degree of sexual dimorphism.

The authors concluded that hominids did not become larger in size between 3.66 and 3.2 million years ago. By combining data from the two Laetoli sites with those from the Hadar region, it was discovered that African Pliocene hominins varied in size from large-bodied to small. There was no evidence of an increase in overall body size between the older Laetoli and more recent Hadar fossil samples.

Represents a time unit of one million years. 1.0 Ma means one million years before the present.

The authors are confident that the footprints at Sites G and S were made at the same time by the same hominin species.

There are some differences between the soil layers observed at Site S and the layers described for Site G. The authors attribute these differences to environmental factors. Deposition is affected by numerous factors such as the mass and size of particles and the wind.

The authors determined through an analysis of soil layers that the Footprint Tuff in Sites G and S were the same age.

A way to statistically summarize the relationship between two quantitative variables.

The weight would be on the front side of the foot, away from the midline, before it is passed along to the toes. It is when the weight reaches the toes that the foot pushes off the ground.

Analysis of the footprints discovered by Dr. Leakey and colleagues determined that the big toes of the hominids leaving the trail aimed forward and that the toes were not distinctly different from each other. This is not true of the feet of hominids such as the chimpanzee.

Source of image ttps://corewalking.com/chimpanzee-feet-vs-human-feet/

The presence of prints left by the same species of wildlife in Sites G and S helps to confirm that the Laetoli hominin prints in Sites G and S were made at the same time.

These are antelopes such as Kirk's dik-dik.

The branch of science that studies fossilized footprints, animal burrows, and other traces of the existence of an animal and its behavior.

Here, undulating indicates that the upper edge of the soil layer has a continuous up and down shape. It is not flat.

Particles that are of the same kind.

Describes the surface of a rock or mineral that is made up of crystals too small to be seen with without magnification.

A mineral involved in the formation of many igneous and metamorphic rocks.

A large-scale photograph made up of many smaller photographs.

For each test-pit, the authors analyzed the soil profile.This established how the different areas were related geologically and provided information about how to proceed with the analysis of hominin and wildlife print present.

The side of a cliff or a steep slope. It can form as a result of faulting or erosion.

The trackway footprints are extremely fragile. Clearing and preserving them had to be done with the utmost care. Unlike fossil bones that are solid, the footprints are only empty spaces. Depending on the substrate, an incorrect move could cause the soil to crumble and the footprint to be destroyed. The author had to do a careful analysis of the trackway soils to be able to know how to best preserve and analyze each footprint.

Site G is the code used by Leakey to identify the trackway her group discovered. The three individuals leaving the footprints are referred to as G-1, G-2, and G-2. Keeping with this code system, the authors identified the new trackway area as Site S. The footprints are attributed to individuals S-1 leaving foot prints numbered S-1-1 through S-1-7 in location L8. Individual S-1 also traveled through locations M9 and TP2.

A raised flat land area with sides that slope.

Stratigraphy is the study of rock layers. An analysis of a stratigraphic sequence would be looking at the types of sedimentary deposits, their age, and distribution from one area to another.

A soft, porous rock that is formed from volcanic ash and or cinders. Over time it is compacted into solid rock.

The single specimen that is used by the author of an article to describe and name a new species. It could also refer to two or more specimens described by the author when a single holotype is not identified.

Formed when preexisting rocks are subjected to intense heat and pressure. This results in the original rocks changing both physically and chemically. Common examples are marble, slate, and schist.

In this case, a series of fossil footprints made by hominids or other animals.

Modern humans do not exhibit a high degree of sexual dimorphism. However, other hominid relatives, such as gorillas and orangutans, are highly dimorphic. Based on a limited number of fossils, it has been assumed that early hominins were highly dimorphic. Knowing more about the degree of sexual dimorphism would provide information about mating behavior and social organization.

Animals that typically have more than one mate.

Refers to differences in appearance and size between males and females of the same species. Modern humans show a low level of difference in size and appearance. Differences between the sexes is much more pronounced in early hominins and in primates such as gorillas and orangutans.

A period during Earth's history that occurred between 23 million and 5.3 million years ago.

A land surface resulting from erosion that occurred during ancient times.

A country located south of the equator in East Africa. (See the map of Africa in Figure 1 for the location of Tanzania and Laetoli.)

There are several layers of tuff that can be distinguished by color—one on top of the other.

The term mottles is used to identify differences in color patterns in a soil profile. Iron and manganese (Fe/Mn) oxides color the soil.

Only some data were published for site G. As a result, the data are less complete and less reliable. There are some differences in the measurements published by individuals viewing the original G tracks and those made by others using the fiberglass casts.