Ratites

## About

   palaeognaths, more commonly known as ratites are a group of birds defined by their inability to fly and are classified under the super order palaeognathiae. A more specific feature of ratites is their apparent lack of a keel, a bone that most birds have on their sternum. In most bird species this bone is used to stabilise the body during flight or swimming in the case of waterfowl. Ratites lost this trait because they diversified in environments where they did not need the ability to fly and thus no ratites have re-evolved the ability to fly. This lack of a keel bone is such a significant detail that the word 'ratite' comes from the Latin 'ratis', meaning a raft or vessel with no keel. Ratites also lack an interlining structure to their feathers also known as down feathers. Ratites today consist of main five species, each having subspecies, being the; ostriches, emus, cassowaries, kiwis and rheas. Ratites were a once much more diverse group having many other members such as elephant birds and moas. Unlike their large relatives, kiwis stand out as being noticeably smaller and possess shorter legs. Notably they are also the only of the extant ratites to be nocturnal. Ratites are a very interesting group, as they demonstrate a very unique event of a group experiencing an extreme specialisation to a specific niche. The conditions for ratites to go from small, migrating birds into huge flightless grazers had to be extremely specific. The most credible theory excepted by most modern Paleontologists, is that ratites have become what they are today because of a lack of predators in the places they inhabit. In Australia for example, emus have become a huge grazing terrestrial bird species that is rarely preyed upon by most predators, due to the previous lack of predators on the mainland. This theory is applied to all other ratites as well.

### Historic Classification

ratites were classed in an order known as Struthioformes up until very recently when they were reclassified under the super order, palaeognathiae. This change is due to Struthioformes becoming more recognised as a group only containing ostriches. Palaeognathiae, being a super order also includes the closely related order of Tinamiformes, which consists of the American flighted tinamous.

## Extinct Families

### Dinorthidae

      Dinorthidae is a family of ratites that only includes the moa and its subspecies. It is estimated that there were 10 species of moa each greatly differing in size, from the turkey-sized bush moa ***(Anomalopteryx didiformis)*** to the humongous giant moa ***(dinornis robustus)***. Moas were the tallest birds to have ever existed, with the giant moa (females) standing at 3m (10ft) and weighing 250kg (550lbs). Moas were only known to inhabit the North and South Islands on New Zealand, and would have existed on the Islands up until around 1440-1445. The moas were forced to extinction by a combination of factors caused by human interference. Europeans first discovered New Zealand in 1642, and their settlements would lead to the extinction of the moas, due to the competition they partook in with the native Māori peoples of New Zealand. Due to the immense amount of stress placed on the Māori people by the arrival of European settlers, they began overhunting the birds in order to sustain themselves. Before European contact the Māori people hunted the moas sustainably, to a degree where the birds could not face severe population fluctuation however, once Europeans did arrive the moa population quickly decreased due to a variety of reason including overhunting for food and trophies. Eventually the moa became a symbol for the prevention of the extinction of the extinction of the Māori people themselves, really displaying the cultural significance of the moa, and how impactful this extinction was. Recently the vertebral and cranial anatomy of the moa were more concisely studied, leading to the discovery that moas were more likely to have held their heads low to the ground rather than in an ostrich-like display. Paleontologists hypothesise that moas were however, capable of holding their neck and head erect if needed, but would often hang their heads low in order to more efficiently move through the dense forests of New Zealand, a behavioural trait commonly exhibited in modern cassowaries. Moas are thought to have exhibited reverse sexual dimorphism, with females and males being so vastly different in size, that they were considered different species. Female moas were thought to be the dominant sex possibly fighting with other females in order to access the male moa with the best territory and call. It is also suspected that moas were polygamous, with females mating with multiple males and not playing a role in the incubation or raising of their chicks.

### Lithornidae

    Little to nothing is known about lithornids, as they are a possibly paraphyletic family, meaning that the group includes a common ancestor but none of its decedents. lithornids inhabited North America and Europe in the late Cretaceous. (100.5–66mya). It is believed that lithornids were much closer to tinamous than other palaeognaths. This relation is supported by the body structure of lithornids, being considerably smaller than most ratites, having the ability to fly and having long slender bills most likely used for probing however, unlike tinamous, lithornids had sharper toe claws. The well developed olfactory lobe of lithornids, also supports the birds having a nocturnal lifestyle as this is a common characteristic in nocturnal species. Lithornids have been split up into three genera being the lithornis, Paracathartis and Psuedocyptrutus.

### Aepyornithidae

        Aepyornithidae contains three genuses with 8 species spread between them, with the largest and most well known being the elephant bird ***(Verombe titan)*** of Madagascar. The elephant bird was only second in height to the previously discussed moa. Elephant birds were the largest ratites until their extinction in 1000-1200. Interestingly the name of the elephant bird is thought to have originated from an account by the famous Marco Polo in 1298. Marco Polo claimed to have encountered a bird so big it could 'seize and elephant with its talons', though the name elephant bird is usually assigned to this ratite, it is thought that originally Marco Polo was referring to an enormous mythical bird of prey known as a 'Rukh' originating from Persian mythos. It was previously thought that the elephant birds were closely related to common ostriches ***(Struthio camelus)*** due to their geographic proximity however, recent genetic evidence has pointed to the elephant bird being the closest relative of the tiny kiwis of New Zealand. It is thought that the elephant bird and kiwi lineages diverged vastly from each other during the Eocene epoch of 50mya. Similarly to the moa, elephant birds are thought to have been pushed to extinction by humans. During the European arrival of Madagascar elephant birds were pushed to extinction through overhunting, along with all of Madagascar's megafauna. In 2018 scientists used CT imaging technology to observe the greater details of elephant bird skulls. They discovered that the bird's optic lobe (a group of nerves that control vision) was reduced in comparison to other ratites, to the point it was almost non-existent in larger species. This lobe shows similarities to that of the kiwi's possibly suggesting that like the kiwi, the elephant bird was nocturnal. The elephant birds laid the largest eggs of any animal to ever exist, containing 7.5L (2gal) in volume. These rich eggs would have lead to egg poaching by both the Malagasy people and the Europeans.

## Modern ratites

### Aepterygidae

    Aepterygidae includes all five extant species of tiny chicken sized kiwis. Kiwis are unique among modern ratites in that they are not tall, large and stocky animals but rather smaller, quiet and shy. It is clear to anyone observing ratites that kiwis appear as though they are out of place however, kiwis are just as much as a ratite as any ostrich or emu. Interestingly, kiwis seem to have occupied the niche of rodent on New Zealand, even going as far as to evolve wispy feathers around their bills which act similarly to whiskers. Kiwis are also the only birds to have their nostrils situated at the ends of their bills. This adaptation allows the kiwis to take full advantage of their ground based lifestyle, as well as achieve a greater sense of smell. A factor that has gone into the continued decrease of wild kiwis is their smell. Kiwis have evolved a perpetual potent smell, which allows other kiwis to identify them in the dark environment at night. This adaptation has lead to kiwis becoming very easily hunted by introduced stoats, which can hunt down kiwis using their smell, and eat their eggs and chicks. It is believed that the ancestor of the kiwi arrived on New Zealand by flight when the North and South Islands were connected around 2.5mya. Through specialisation due to New Zealand's predator-free environment, these flighted birds would eventually become the flightless kiwis.

### Casuariidae

        Casuariidae is one of the largest ratite families, including three species of cassowary and the emu ***(Dromaius novaehollandiae)***, as well as some extinct species between them. Casuariids only occur exclusively in Oceania and were once thought to be the closest relatives to kiwis, due to close geographic proximity. Casuariids are quite diverse and both cassowaries and emus are similar yet different from each other. Emus ***(Dromius novaehollandiae)*** are the only remaining species in the genus Dromaius. There was once three subspecies of emu in addition to the extant emu, with the other three being the Tasmanian emu ***(Dromaius novaehollandiae diemenensis)***, the King Island emu ***(Dromaius novaehollandiae minor)*** and finally, the Kangaroo Island emu ***(Dromaius novaehollandiae baudinianus)*** . Tasmanian emus resembled mainland emus very closely, having the same brownish-tan and black plumage as well as the blue face and neck of their mainland counterparts. Tasmanian emus were so similar to mainland emus that it is still debated whether they were a subspecies at all. King Island emus differ greatly from the two other emus, being considerably smaller and more stocky. King Island emus had noticeably darker black feathers on their necks which hung low, almost like hair, and they also exhibited the blue bare skin of all emus. King Island emus were a great example of Island Dwarfism, when a usually large species becomes smaller on an Island environment due to less food. Possibly the emu with the least information on it is the Kangaroo Island emu. Judging by illustrations and a taxidermised specimen, Kangaroo Island emus were similar in appearance to King Island emus, being smaller than mainland emus. Other than this detail not too much was recorded about the Kangaroo Island emus, as they went completely extinct in 1827, just 25 years after their discovery in 1802. Ultimately all of the Island dwelling emu species went extinct in the 1800's due to a combination of overhunting and habitat fragmentation,leaving only the mainland emus to represent Dromaius. Cassowaries are a group of ratites identified by their very vibrant appearance. Unlike emus, there are still three extant species of cassowary, being the Southern cassowary ***(Casaurius casaurius)***, the Northern cassowary ***(Casuarius unappendiculatus)*** and the tiny dwarf cassowary ***(Casaurius benneti)***. Today, all extant species inhabit the Indonesian Island of New Guinea as well as the Cape York peninsula, Queensland however, the Extinct pygmy cassowary ***(Casuarius iyderreki)*** once inhabited New South Wales during the Pleistocene (2.58-0.012mya). Unlike other large ratites cassowaries inhabit heavily forested tropical regions, as opposed to the drier climates that ostriches and emus inhabit. Although all three species of cassowary are relatively widespread, the Southern cassowary still remains the most well known, exceeding the sizes of the other two species, and also interacting with humans more frequently. Northern cassowaries only have one yellowish-orange wattle, when compared to the two pink wattles of the Southern cassowary. Dwarf cassowaries are the most unique of the three species, being the smallest and also most undocumented species. Dwarf cassowaries also lack any wattles at all, instead having pinkish-red wrinkled skin on the back lower region of their neck. Despite the differences between the three species, all cassowaries share the same wiry black feather, bare blue face and neck skin and their conical wing spines. An interesting feature of cassowaries is their 10cm (4in) sickle-like talon on their foot, which is typically used to defend themselves in pressured situations. Such a defensive adaptation has not been recorded in any other known ratite species. Another unique attribute only exhibited in cassowaries among ratites, is their iconic casque that crowns their head. The exact purpose of this structure has been highly debated, with the top theory stating that the casque acts as a thermal regulator, offloading heat and offering heat depending on the environment. Both emus and cassowaries appear in the fossil record at around 150mya in the Jurassic period, and are thought to share a common ancestor which migrated to Oceania by flight. After the KPG mass extinction (66mya) casuariids would further diversify into the birds we know today, because of the lack of predators and the abundance of food.

### Rheidae

    Rheids are a family of South American ratites that are close in appearance to ostriches. Rheas are the second smallest ratites and the third smallest palaeognaths. Rheidae includes the two species of rhea being the greater rhea ***(Rhea americana)*** and the lesser rhea ***(Rhea pennata)***. It is believed that the rhea's flighted ancestors inhabited the Northern hemisphere along with the Listornids, during the Paleocene and Eocene (66-33.9mya), and eventually these birds would spread Southward. Fossil evidence supports this theory, as fossilised rhea remains have been found in Argentina, dating back roughly 2mya. It is believed that rheidae and timadae are closely related families, both having the same origins and geographic proximity to each other. Rheas are typically differentiated from other ratites by their lighter colouration, having lighter grey, white or tan feathers. Rheas have obtained a bad reputation as they can often be quite aggressive however, this is mostly a myth as rheas are more likely to flee a confrontation with a human rather that partake in a fight. Similar to ostriches and emus, rhea males are larger than females and typically incubate the eggs, however dissimilarly to emus, rheas have long wings which they outstretch while running in order to maintain balance and achieve sharp turns.

## Struthioniformes

### Struthionidae

Struthionidae is made up of two ostrich species which both belong to the Struthio genus, being the common and Somali ostrich ***(Struthio molybdophanes)***. Ostriches are sexually dimorphic, with males having black and white plumage with pinkish beaks, whereas female ostriches have brownish tan feathers and are much smaller. A common trait that both genders share are their two toed feet, which no other ratites possess. Struthionids are the largest extant ratites and also the Northern most ratites. Though struthionids currently only inhabit Africa they were once spread through Europe and Asia during the Miocene (23.03-5.333mya). Fossils found that have been dated back to the Paleocene (66-56mya) and Eocene Epoch (54.8-33.7mya), as well as the Oligocene (33.9-23.03mya) may also belong to the Struthioniformes. Previously the order that ostriches belong to- Struthioniformes, included all ratites however, after further genetic analysis it was discovered that Struthioniformes only includes the ostriches. This change was due to Struthioniformes being found to be paraphyletic as opposed to monophyletic. Notably, the IUCN still groups all ratites as well as tinamous, in the order Struthioniformes.

## Tinamiformes

Tinamiformes were once considered the sister group of ratites but are now seen more commonly as a part of ratites. Unlike ratites, tinamous are flighted. Tinamous are grouped with ratites or palaeognaths- because tinamous are suspected to mirror the early flighted ancestors of the ratites.

### Timadae

Timadae includes all extant species of tinamou which are all native to regions of the Americas. Unlike ratites, tinamous are flighted and generally much smaller. Though tinamous can fly, they typically prefer a ground-dwelling lifestyle and are commonly found in heavily forested regions. Tinamiformes are by far the largest order in palaeognathae, with an impressive 47 described species. Tinamous resemble other flighted birds such as partridges more closely than other ratites, possessing shorter legs and noticeably different wing structure. Fossils from three tinamou genera have been found in a deposit in Argentina, dating back to the Miocene Epoch (23.03-5.33mya). Most fossilised tinamou remains are fossilised species that are still extant, that have been discovered in South America dating back to the Pleistocene Epoch (2.58-0.012mya).

## Sources

* palaeognathae | Wikipedia - https://en.wikipedia.org/wiki/palaeognathae
* ratite | Wikipedia - https://en.wikipedia.org/wiki/ratite
* struthionidae | Wikipedia - https://en.wikipedia.org/wiki/struthionidae
* Kangaroo Island Emu | Wikipedia - https://en.wikipedia.org/wiki/Kangaroo\_Island\_emu
* lithornidae | Wikipedia - https://en.wikipedia.org/wiki/lithornithidae
* Cassowary Casque | Sci News - http://www.sci-news.com/biology/cassowary-casque-06918.html#
* Moa | Britannica - https://www.britannica.com/animal/moa
* Elephant Bird | Britannica - https://www.britannica.com/animal/elephant-bird
* Tinamous | Britannica - https://www.britannica.com/animal/tinamou
* Save The Cassowary | Rainforest Rescue - https://www.rainforestrescue.org.au/save-the-cassowary/evolution/
* How Kiwi Evolved | Save the Kiwi - https://www.savethekiwi.nz/about-kiwi/kiwi-facts/how-kiwi-evolved/
* Rhea | New World Encyclopedia - https://www.newworldencyclopedia.org/entry/Rhea\_(bird)
* rheidae | Encyclopedia.com - https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/rheas-rheidae