Camelids

Camelids are typically herbivorous mammals with long, slender necks and legs and an even number of toes (either two or four). They constitute the only extant family Camelidae under the suborder Tylopoda. This family comprises two genera: Camelus and Lama. Camelus (also called Old World camelids) has three extant species, namely the dromedary, Bactrian, and the wild Bactrian camel, whereas Lama (also New World camelids) consists of four extant species: llama, guanaco, alpaca, and vicuna.

Often called pseudoruminants, these animals are hind-gut fermenters with three-chambered stomachs, unlike ruminants (suborder Ruminantia), where it is four-chambered. Moreover, camelids retain their upper incisors, which are either reduced or absent in the other group.

These mammals first appeared in North America during the Middle Eocene Epoch (around 50 to 40 million years ago) but are currently spread across South America, South Asia, and the Middle East. They occupy a wide range of habitats, such as hot and cold deserts, mountains, and coastal rainforests. Llamas, alpacas, and Bactrian camels are domesticated groups and do not exist in the wild.

Description

Size

New World camelids are larger, weighing on average between 992 and 1433 lb (450 and 650 kg), while the Old World relatives range from 77 to nearly 220 lb (35 to 100 kg). The Bactrian camel is the largest camelid, which measures up to 2,200 lb (1000 kg), whereas the vicuna, the smallest camelid, measures around 77 to 143 lb (35 to 65 kg).

Body Plan

While camelids vary between slender to stocky, they all have small heads, long, slender necks, and elongated legs. Their upper lip is cleft into two distinct and separately mobile parts. 

They have two splayed toes, each ending in a toenail, and soft, leathery footpads instead of hooves. These footpads bear most of their weight and expand in surface area as the animal’s speed increases, helping to distribute pressure more evenly across each foot.

The third and fourth metapodial bones of the limbs are fused proximally to form the cannon bone. The ulna and fibula are considerably reduced, but the phalanges of the toes are distinct.

Their legs are connected to their body only at the top of the thigh, unlike most mammals, whose leg connections extend from the knee upward through skin and muscle. As a result, these animals can only lie down by resting on their knees.

Skull and Dentition

Camelids have skulls that feature an elongated rostrum, a prominent sagittal crest, and a complete postorbital bar. Unlike some mammals, they lack outward projections such as horns or antlers. 

They have selenodont cheek teeth, which are characterized by low crowns and crescent-shaped cusps. Unlike ruminants, this group has retained their upper incisors, with the third incisor modified to resemble canine tusks. In addition to true canines, camelids also possess tusk-like premolars, which are distinctly separated from the molars by a gap known as the diastema.

The dental formula for Old World camels is 1.1.3.3/3.1.1-2.3 = 32-34, while that for New World camels is 1.1.2.3/3.1.1.3 = 30.

Taxonomy

The name of the suborder Tylopoda means ‘padded foot’ in Greek. It refers to the soft and leathery sole pads that characterize the members of this group.

The 7 extant species of camelids are grouped under two genera, Lama and Camelus, both belonging to the only subfamily, Camelimnae.

• Subfamily: Camelinae
  • Tribe: Lamini
    • Genus: Lama
      • Species: Lama glama (Llama)
      • Species: Lama guanicoe (Guanaco)
      • Species: Lama pacos (Alpaca)
      • Species: Lama vicugna (Vicuna)
    • Genus: Hemiauchenia
    • Genus: Palaeolama (Extinct)
  • Tribe: Camelini
    • Genus: Camelus (Camels)
      • Species: Camelus bactrianus (Bactrian camel)
      • Species: Camelus dromedarius (Dromedary)
      • Species: Camelus ferus (Wild Bactrian camel)
      • Species: Camelus moreli (Extinct)
      • Species: Camelus sivalensis (Extinct)
      • Species: Camelus knoblochi (Extinct)
    • Genus: Camelops (Extinct)
    • Genus: Paracamelus (Extinct)
  • Subfamily: Poebrotheriinae (Extinct)
  • Subfamily: Miolabinae (Extinct)
  • Subfamily: Stenomylinae (Extinct)
  • Subfamily: Floridatragulinae (Extinct)

The taxonomic position of the wild Bactrian camel is debated, as it is considered a subspecies (Camelus bactrianus ferus) by a group of scientists.

Evolution and Fossil Records

Camelids have a long evolutionary history:

• They first appeared in the Middle Eocene Epoch (around 50 to 40 million years ago) in North America. One of the earliest camelids was Protylopus, which was rabbit-sized and possessed four toes on each foot. 
• By the Late Eocene (around 35 million years ago), members like Poebrotherium, about the size of modern-day goats, had lost two lateral toes.
• These animals continued to diversify and evolved into two tribes, the Camelini and Lamini. These tribes continued to diverge in the Early Miocene Epoch (around 17 million years ago) but remained in North America until about 6 million years ago.
• About 3 to 2 million years ago, members of Paracamelus crossed the Bering land bridge and entered Eurasia. With time, they gave rise to the modern camels. However, a population of Paracamelus remained in North America and evolved into the high arctic camel, which went extinct after the Middle Pleistocene Epoch.
• Members of Hemiauchenia entered South America during the Great American Interchange around 3 million years ago, later giving rise to modern llamas.
• With time, the original camelids of North America disappeared, and only three groups survived: the dromedary of northern Africa and southwest Asia, the Bactrian camel of Central Asia, and the four South American members, llamas, alpacas, guanacos, and vicunas.

Distribution and Habitat

The geographical range of the seven extant species of camelids is given in the table below.

Species	Range
Bactrian Camel	Central and Inner Asia
Dromedary	South Asia and the Middle East, particularly in Africa and the Arabian Peninsula (once found in the wild but now entirely domesticated)
Wild Bactrian Camel	Northwest China and Southwest Mongolia
Guanaco	South America
Llama	South America (domesticated)
Vicuna	South America
Alpaca	South America (domesticated)

Camelids inhabit a wide range of habitats, including hot and cold deserts, mountains, and coastal rainforests. Wild Bactrian camels and dromedaries inhabit hot deserts, whereas guanacos and vicunas occupy grassy pampas and different elevations of the Andes mountain range. Llamas and alpacas, being domesticated varieties, are not found in the wild.

Diet

These animals are primarily herbivorous and feed on grasses, shrubs, trees, and forbs. Llamas and alpacas are fed on a fiber-rich diet, including hay, grains, alfalfa, and concentrates, like pellets.

Behavior

• Wild camelids typically live in polygynous groups called harems, with each group led by a single male who has several potential female mates. In some species, like guanacos, bachelor males live in separate herds. In a battle between males to acquire the females, dominance is usually established by biting.
• All camelids use a unique running pattern known as the ‘running pace gait.’ In this gait, the limbs on the same side of the body move together, with the right-side limbs following the left. This synchronized movement allows all four limbs to be off the ground simultaneously at one point in each stride, avoiding collisions between the forelimbs and hindlimbs when running at high speeds.

Conservation Status

Among all camelids, the wild Bactrian camel is the only species listed as Critically Endangered (CR) on the IUCN Red List. Its population continues to decline due to threats such as hunting, habitat loss, and interbreeding with domestic Bactrian camels. In contrast, all other camelid species are classified as Least Concern (LC).

Interesting Facts

• Camelids possess a unique type of antibodies called single-domain antibodies or nanobodies. Unlike typical mammalian antibodies, which have both heavy and light chains forming a Y-shaped binding site, single-domain antibodies consist only of heavy chains that make up the binding site. These antibodies are easy to engineer and highly valuable in the pharmaceutical industry for treating diseases such as cancer and autoimmune disorders.
• Uniquely enough, the red blood cells of these mammals are elliptical in shape.
• The United Nations (UN) has declared the year 2024 as the ‘International Year of Camelids’ (IYC) to acknowledge the crucial role these animals play in the lives of millions of households across over 90 countries worldwide.