Pleistocene Horses Evolution and Extinction Explained

Pleistocene horses were a type of horse that lived during the Pleistocene epoch, which spanned from about 2.6 million to 11,700 years ago. They were much larger than modern horses.

These ancient horses were characterized by their robust build and distinctive physical features, such as their large size and robust body shape. They were well adapted to their environments.

Pleistocene horses were found in many parts of the world, including North America, Europe, and Asia. They were likely herbivores, feeding on plants and fruits.

The extinction of Pleistocene horses is a fascinating topic, and one that scientists have studied extensively.

To study Pleistocene horses, researchers use a variety of methods, including fossil analysis and DNA sequencing.

Fossils of Pleistocene horses are often found in sedimentary rock formations, such as the La Brea Tar Pits in California.

These fossils provide valuable information about the physical characteristics and evolutionary history of the horses.

The most well-known species of Pleistocene horse is Equus scotti, which was a large and robust animal with a distinctive skull shape.

DNA sequencing has also been used to study the genetic diversity of Pleistocene horses and their relationships to modern horse species.

This has helped researchers to better understand the evolutionary history of horses and how they adapted to different environments during the Pleistocene era.

To compile the data, researchers gathered occurrence information from the literature and the Paleobiology Database.

This information included direct radiocarbon dates and stratigraphically dated specimens.

The data was carefully checked against the pertinent references to avoid repetition.

Only presences occurring from 21 kyr BP onwards and species with more than 5 records available were used to build the models.

The minimum of five occurrences was chosen to run the models, as even three presences can develop a species distribution model, but the researchers decided to be conservative.

Four taxa were able to develop models: Equus neogeus with 26 presences, Hippidion principale with 10 presences, Hippidion devillei with 6 presences, and Hippidion saldiasi with 23 presences.

The geographic distribution of the fossil data is presented in Figure 1 and Data Sheet 1, along with occurrences assigned tentatively to the late Pleistocene and the Pleistocene in the literature.

Most of the occurrences used were assigned to the species level in the literature, but three occurrences for Hippidion saldiasi were assigned with some uncertainty.

We analyzed three groups of specimens: large, medium, and small, from northeastern Mexico, and large, medium, and small from the American Southwest. These groups were identified in a previous analysis of linear measurements.

The specimens from Natural Trap Cave, Wyoming, and Alberta were also included in the analysis, but only in large and medium sizes. Specimens from Bluefish Caves, Yukon Territory, were analyzed as a single group.

In total, we had 10 subgroups of specimens to work with, each with its own unique characteristics.

The holotype is a crucial component in understanding the species 'E'. francisci. It's a partial skeleton, specifically a complete cranium, mandible, and a stilt-legged third metatarsal, which is curated at the Texas Vertebrate Paleontology Collections at The University of Texas, Austin (TMM 34–2518).

This specimen was originally described by Hay in 1915 and is from the middle Pleistocene Lissie Formation of Wharton County, Texas. It's a significant find, as it's the holotype of the species.

The holotype is composed of a stilt-legged third metatarsal, which is a distinctive characteristic of the species. This feature is evident in Figure 2a and Figure 2—figure supplement 1b.

The genus Equus was named to include three living equid groups – horses, donkeys, and zebras – but it seems there's more to the story.

The NWSL equids, previously thought to be part of the Equus genus, have been found to fall outside the confines of the equid crown group.

Haringtonhippus, a new genus, has been erected to include the NWSL equids, as they don't fit into an existing extinct taxon like Hippidion.

Haringtonhippus is the sister genus to Equus, with Hippidion being the sister to the Haringtonhippus-Equus clade.

The mitochondrial genome of Haringtonhippus can be differentiated from Equus and Hippidion by 178 synapomorphic positions.

We can differentiate Haringtonhippus from Equus and Hippidion by 178 synapomorphic positions, including four insertions and 174 substitutions.

These synapomorphies are tentative and may be reduced as more mitochondrial genomes for extinct equids become available.

The new genus Haringtonhippus is defined and delimited, with its type species being Haringtonhippus francisci.

Pleistocene horses were found in various regions of North America, including Texas, Yukon Territory, Wyoming, Nevada, New Mexico, and possibly Alberta and Alaska.

Haringtonhippus, a genus of Pleistocene horses, is known only from the Pleistocene of North America. Its fossil records date back to the middle Pleistocene in Texas and the late Pleistocene in other regions.

Here's a list of some of the known localities of Haringtonhippus in North America:

South American horses, on the other hand, had a different geographic distribution. During the Last Glacial Maximum (LGM), their potential distribution included areas with grassland steppe and temperate semi-deserts in the Pampas and more tropical savanna environments in east Brazil.

Haringtonhippus is known only from the Pleistocene of North America. It's a fascinating find that has helped scientists understand the geographic distribution of this ancient horse species.

The holotype of Haringtonhippus was found in Wharton County, Texas, USA. This middle Pleistocene fossil is a significant discovery that has shed light on the history of this genus.

New radiocarbon dates from 17 Yukon Territory fossils have greatly extended the known temporal range of Haringtonhippus in eastern Beringia. The dates suggest that this genus survived throughout the last glacial maximum in eastern Beringia.

The last appearance date (LAD) of Haringtonhippus in eastern Beringia is around 14.4 C ka BP. This is based on three statistically-indistinguishable radiocarbon dates from a metacarpal bone of Haringtonhippus.

Haringtonhippus is also known from other locations in North America, including Wyoming, Nevada, New Mexico, and Alaska. Its distribution is quite widespread, but it's still considered a relatively rare find.

The sympatric nature of Haringtonhippus and caballine Equus raises questions about their ecological preferences and potential competition for resources.

British horses have a fascinating history. The British Plio-Pleistocene horses of the genus Equus were studied in a doctoral thesis by Owen, Frederick John, published in 2022.

The thesis, titled "British Plio-Pleistocene horses of the genus Equus", provides valuable insights into the subject. It is a Doctoral thesis (Ph.D) from University College London (UCL).

The thesis is available for download in two parts: a 16MB PDF file and an 11MB ZIP file containing the appendices.

The Pleistocene Epoch was a time of great diversity for horses in North America, with numerous species existing during this period. Abundant and diverse, they roamed the continent until their extinction at the end of the epoch.

The Leisey Shell Pit in Florida has produced thousands of fossil specimens, including many from the modern Equus genus, which is the genus to which modern horses belong. This suggests that the ancestors of modern horses were present in North America during the Pleistocene.

The last horse in South America, a species of Equus scotti, went extinct around 10,000 years ago.

This extinction event is believed to have occurred due to the changing climate and the arrival of humans in the region.

The Equus scotti horse was well adapted to the cold climate of the region, but as the climate warmed up, they were unable to compete with other grazing animals for food and resources.

The extinction of the Equus scotti horse marked the end of the last remaining native horse population in South America.

The loss of this species had a significant impact on the ecosystem of the region, leading to changes in the distribution of other animals and plants.

The Pleistocene Epoch was a time of significant change and upheaval for mammals, including horses. It lasted from 1.75 million to 11,000 years ago.

During this epoch, the last Ice Age occurred, and a great diversity of mammals lived in North America. Many of these species, including mammoths, mastodons, and giant sloths, are now extinct.

The La Brea Tar Pits in Los Angeles is a famous Pleistocene locality that was discovered by accident while workers were mining asphalt. It's a treasure trove of fossil specimens.

New York, New England, and the northern Midwest retain evidence from the fairly recent glaciers that advanced and retreated throughout the Ice Age. The Leisey Shell Pit near Tampa, Florida, is another older Pleistocene locality that has produced thousands of fossil specimens.

The end of the Pleistocene Epoch marked the extinction of horses and many other large mammals in North America.

The San Josecito Cave in Nuevo León, Mexico, is one of the most studied late Pleistocene sites in northeastern Mexico. Fossil remains from this cave have been identified as belonging to a single species of Equus, but the exact classification is still debated.

Stock initially thought the horse remains belonged to a new subspecies of Equus conversidens, but his description was incomplete. This means the name should be considered a nomen nudum, or an invalid scientific name.

The Cedral fossil site in San Luis Potosí, Mexico, has yielded three equid species, identified by differences in size, metapodial proportions, and enamel patterns on the third and fourth upper premolars.

A different take: What Was the Name of Zorro's Horse?

The San Josecito Cave and Cedral fossil sites in northeastern Mexico are two of the most studied late Pleistocene sites in the region.

Located in Nuevo León and San Luis Potosí, these sites have yielded numerous fossil remains of horses, which have been the subject of much debate among researchers.

Stock considered all the horse remains from San Josecito Cave to belong to a single species of Equus, which he thought was most similar to Equus conversidens Owen, 1869.

However, Stock didn't select a type nor publish a formal description, so the name should be regarded as a nomen nudum.

Winans proposed E. conversidens to be a nomen dubium, because she considered that the convergence of the cheek tooth rows toward the rostrum seen in the holotype was the result of a distorted restoration.

Azzaroli, on the other hand, regarded E. conversidens as a valid species distinct from E. niobrarensis alaskae Hay, 1913 and identified the latter as a synonym of E. ferus Boddaert, 1785.

He also referred the fossil material from San Josecito Cave to E. conversidens, further stating that this species was closely related to South American horses.

The fossil localities of San Josecito Cave and Cedral have also yielded remains of three equid species, based on differences in size, metapodial proportions, and features of the occlusal enamel pattern of the third and fourth upper premolars.

The large and medium-sized species have been tentatively identified as E. mexicanus (Hibbard), 1955 and E. conversidens, respectively.

The taxonomic identification of the smaller equid has been more problematic, with some researchers identifying it as Equus sp. A and others as Equus tau Owen, 1869.

Recently, Alberdi et al. have designated a new species, Equus cedralensis, for this material.

The Natural Trap Cave in Wyoming is a significant fossil locality that has yielded thousands of vertebrate remains.

The cave has produced a diverse range of equid material, with three horse species identified by Martin and Gilbert.

One of the most common species found in the cave is a small, stilt-legged equid likely referrable to Hemionus.

A study using ancient mtDNA by Weinstock et al. concluded that two clades were present at this locality, a caballine and a stilt-legged clade, each possibly representing a single species.

The stilt-legged clade is endemic to North America, and the presence of slender metapodials is a convergent feature with extant Asiatic asses.

Eisenmann et al. proposed that four equid species are represented in the material from Natural Trap Cave: a caballine, E. cf. conversidens, and a large and small Amerhippus, both with slender metapodials.

The small Amerhippus is the most common species in the fauna, according to Eisenmann et al.

The Edmonton area gravel pits in Alberta, Canada, are a significant fossil site. The equid material found here hasn't been described in detail.

Burns and Young listed two types of horses, Equus cf. conversidens and E. cf. niobrarensis, but Weinstock et al. found that all the specimens they studied belonged to the caballine clade.

The caballine clade suggests that only one species was represented in the sample studied by Weinstock et al. This is a crucial discovery in understanding the diversity of equid species in the area.

Wally's Beach in southern Alberta is a remarkable archaeological-paleontological site. It's the only known late Pleistocene horse and camel kill and butchering locality in North America.

Seven butchered horses were recovered at Wally's Beach, associated with lithic artifacts. This provides valuable insights into the behavior and habits of ancient horses.

McNeil compared the equid material from Wally's Beach to specimens from the Yukon Territory and a skull from Papago Springs Cave, Arizona. He assigned the equid material from Wally's Beach to E. conversidens and noted differences in skull morphology and dentition.

The study of ancient DNA has revealed that the Pleistocene horses were genetically close to the modern Przewalski's horse, which is the last remaining wild horse species.

This close genetic relationship suggests that the Przewalski's horse may be a direct descendant of the Pleistocene horses.

In fact, a 2013 study found that the Przewalski's horse has a genetic makeup that is 98.7% identical to that of the ancient horse DNA extracted from permafrost remains.

Ancient mtDNA is a fascinating field of study. We were able to extract and amplify ancient mtDNA from 22 of 50 late Pleistocene specimens, including specimens of different morphological groups.

The DNA sequence data we generated was submitted to GenBank with accession numbers KX137124 –KX137148. This allows researchers to access and analyze the data for further study.

A 588 bp fragment of the HVR I was used for the Bayesian phylogenetic analysis, which yielded two lineages of late Pleistocene North American equids: caballine and New World stilt-legged lineages.

The phylogenetic analysis also recovered 16 of the 18 extant horse haplogroups identified by Achilli et al. The two horse haplogroups that are not recovered in the analysis are haplogroups O and F.

The tree was constructed using 588 bp fragments of the HVR I, with posterior probabilities of the major nodes listed for each of the branches. This allows researchers to understand the relationships between the different lineages.

Interestingly, medium-sized specimens with a non-caballine tooth morphology from various locations fall in the stilt-legged clade. This includes the Edmonton area, Alberta; Natural Trap Cave, Wyoming; Dry Cave, New Mexico; and San Josecito Cave, Mexico.

Etymology is a fascinating field that helps us understand the origins of words and names. The name of a species, in particular, can provide valuable insights into its history and significance.

The genus Haringtonhippus was named in honor of C. Richard Harington, who first described NWSL equids from eastern Beringia. This is a remarkable tribute to his contributions to the field of paleontology.

The name Haringtonhippus is derived from the Greek word for horse, 'Hippus'. This is a clever play on words that immediately conveys the meaning of the genus.

As we conclude our exploration of Pleistocene horses, it's clear that these magnificent creatures played a vital role in shaping the ecosystems of the past.

Pleistocene horses were able to thrive in a wide range of habitats, from grasslands to forests, due to their adaptability and ability to eat a variety of plants.

Their impressive size, with some males reaching up to 9 feet tall and weighing over 2,000 pounds, allowed them to roam freely and dominate their environments.

Their large body size also meant they had a significant impact on the vegetation of their habitats, which in turn affected the other animals that lived there.

Pleistocene horses went extinct at the end of the last Ice Age, likely due to a combination of factors including climate change, loss of habitat, and competition with other herbivores.

During the Late Upper Paleolithic, hunting strategies were influenced by climate-driven habitat shifts of high-ranked prey species.

The potential distribution of South American horses during the Last Glacial Maximum (LGM) included areas with grassland steppe and temperate semi-deserts in the Pampas and more tropical savanna environments in east Brazil.

Hippidion principale would have occupied areas of grasslands and temperate deserts, while H. devillei and H. saldiasi occupied temperate deserts and semi-deserts, as well as colder areas in the high Andes and in the southern tip of the continent.

The area with the highest diversity of horses during the LGM was the Pampas, a C3-dominated grassland steppe that changed to a major proportion of C4 vegetation around 12 kyr BP.

The climate became more humid and warmer, which was negative for the species of Hippidion in the area given their habitat preferences.

The timing of changes in vegetation coincided with a major reduction in the potential distribution of Hippidion principale between 13 and 12 kyr BP in the area.

The Pampas was a sub-humid and arid environment, but it changed to a more humid environment, which would have affected the horses that lived there.