Saturday, August 20, 2016

More than one way to be a carnivore: an exposition of carnivory

From an early age, many of us are introduced to the terms carnivore, herbivore, and omnivore; animals which consume other animals, plants, or both animals and plants respectively. These terms, while useful, are highly generalized and may overlook the often significant complexity in the diet of a given species. Many animals often considered to be ‘carnivorous’, for example, may ingest particular types of plants depending on the situation. Similarly, many animals traditionally thought of as ‘herbivores’ have been observed feeding on other animals, albeit in small quantities. This shows that animal feeding behaviors are not as fixed as we are taught in school and, in some instances, it may be necessary to use alternate means of classification. To simplify matters, most animals may be grouped into one of three categories based on the amount of animal matter that they consume: hypercarnivore, mesocarnivore, and hypocarnivore*.

*The following descriptions will focus exclusively on mammals, but the aforementioned terms still apply for other animal groupings.
 
Modern examples of a hypercarnivore (Jaguar), mesocarnivore (Red Fox),
and hypocarnivore (Red Panda). Scale represents the percentage of animal
matter which makes up the diet within each respective level of carnivory, note
that this varies between species.
A hypercarnivore is an animal for whom over 70% of the diet consists of animal matter, with non-animal matter (plants, fungi, or algae) being consumed rarely as a dietary supplement if at all. The prefix hyper- comes from the Greek language and in simplest terms translates to “over”. Thus, the word hypocarnivore describes an animal that is highly predacious and requires a huge amount of animal protein to sustain itself. Some hypercarnivores, such as cats, have a reduced ability to digest sugars or carbohydrates, and must therefore rely entirely on animal matter (the term “obligate carnivore” may also be used in this instance).

Hypercarnivory in terrestrial mammals is often, but not always, accompanied by a suite of changes to the skull and dental morphology. The face may be shortening and/or deepening of the face may occur in association with the reduction or loss of pre- and post-carnassial dentition. The carnassials themselves (pictured to the right), laterally compressed cheek teeth adapted for cutting through flesh, are often lengthened to expand the slicing surface while reducing the capacity for crushing. Hypercarnivorous taxa are relatively easy to identify in the fossil record because of these adaptations. Notable mammalian hypercarnivores include all members of Felidae (cats), Phocidae (seals), Otariidae (sea lions), and Cetacea (whales), as well as most members of Mustelidae (weasels), Herpestidae (mongooses), Chiroptera (bats), and Eulipotyphla (shrews).

Additionally, some hypercarnivores may be specialized in taking certain types of prey and are often categorized accordingly: insectivores (invertebrate-eaters), piscivores (fish-eaters), or molluscivores (mollusk-eaters) to name a few examples. It should be noted, however, that animals tend to be opportunists, very rarely limiting themselves to a single food source. River otters, for example, are adapted to a mostly fish-based (piscivorous) diet but will readily feed on many other types of animals including crustaceans, frogs, birds, and small terrestrial mammals whenever they are encountered.
 
Most otters, like this Giant Otter (Pteronura basiliensis), are piscivores;
hypercarnivores that specialize in eating fish (wiki).
A mesocarnivore is any predatory animal for whom animal matter comprises 31-70% of the diet. These animals actively feed on animal matter but will readily feed on non-animal foods such as fruits and fungi, hence the prefix meso- which means “middle”. Compared to hypercarnivores, mesocarnivores may be more numerous in a given terrestrial ecosystem due to their diet being more adaptable. Furthermore, the proportion of animal to non-animal matter may vary depending on location and seasonality. Red Foxes, for example, may feed almost exclusively on small animals for much of the year but may shift to a more plant-based diet during the autumn months in some parts of their range. Mesocarnivorous mammals often have relatively elongate skulls with a more compete dentition adapted for dedicated to piercing, slicing, and crushing.
 
The African Civet (Civettictis civetta) is a mesocarnivore which typically
feeds on small animals and carrion, but also readily feeds on fruits. Note
the expanded grinding area of the carnassials and molars (wiki).
The prefix hypo- means “below” or “beneath”. Thus, the term hypocarnivore describes an animal for whom animal matter makes up 30% or less of the total diet. To extract as much nutrients as possible from the plants they eat, hypocarnivores have expanded the grinding aspect of their dentition, having either reduced or lost those areas dedicated to slicing. Also, the stomach and intestines may be longer and more complex. Notable hypocarnivores among the Carnivora include most bears, raccoons, palm civets, and the Red Panda. These animals independently evolved from mesocarnivorous ancestors that became specialized for a more plant-based diet. Other examples include all primates, peccaries, pigs, fruit bats, and most rodents.
 
Upper dentition (P4, M1, & M2) of the Red Panda (Ailurus fulgens), a hypocarnivore
which descended from a predatory ancestor. Note loss of the shearing blade on the
carnassial, broadening of the molars, and the addition of extra grinding cusps
for processing tough plants such as bamboo. 
Like hypercarnivores, some hypocarnivores may specialize in feeding on particular types of foods, in this case non-animal matter, and may be categorized accordingly: frugivores (fruit-eaters), folivores (leaf-eaters), granivores (seed-eaters), and nectarivores (nectar-eaters), and fungivores (fungus-eaters). As with mesocarnivores, hypocarnivores may show considerable versatility in their diets depending on location and season. The diets of Black Bears and Brown Bears, for example, generally consist of 90 to 95% non-animal foods for much of the year. Immediately following winter hibernation, however, the bulk of their food intake may consist of winter-killed ungulates and other animals that failed to survive the winter. Other spikes in carnivory are associated with the spawning or birthing seasons of certain types of fish and ungulates respectively. The Polar Bear is a rare instance of a hypercarnivorous species evolving directly from a hypocarnivorous ancestor.
 
Most modern bears such as this Black Bear (Ursus americanus), shown here
feeding on dandelions, are hypocarivores whose diets are mostly plant-based.
However, these animals display extreme versatility and may become more
carnivorous depending on the season or other environmental factors. The
Polar Bear (Ursus maritimus) is a rare example of a hypercarnivore which
evolved directly from a hypocarnivorous ancestor.

Furthermore, virtually all animals which we traditionally think of as ‘herbivores’ will feed on small amounts of animal matter on occasion and would thus be more accurately considered to be hypocarnivores. Duikers, for example, are small antelopes endemic to the forests of Africa that are well-known to feed on numerous types of small animals such as insects, frogs, and birds in addition to their more regular diet of soft leaves and fallen fruits. There are numerous other examples carnivory among herbivores, some of which have been caught on film as provided below; 
  • River Hippopotami, which feed almost exclusively on grasses, have been filmed scavenging from the carcasses of animals which have either drowned or were killed by large predators (video). 
  • Giraffes, which normally feed on leaves and fruits high above the ground, are known to chew on the bones of other animals when they stumble upon them (video). 
  • Deer, cattle, and horses have also been filmed eating dead or unattended bird chicks (video1, video2, video3, video4). 

These behaviors may seem unusual to the casual observer, but they are likely the result of animals attempting to compensate for the lack of certain nutrients which may be lacking in an otherwise plant-based diets. Although these particular animals lack the physical attributes necessary to actively hunt and kill live prey animals, they will clearly take advantage of animal protein when they can obtain it.


References & Further Reading
Roemer GW, Gompper ME, Valkenburgh BV (2009). “The ecological role of the mammalian mesopredator”. BioScience 59: 165-173 <Full Article>

Valkenburgh BV (2007). “Déjà vu: the evolution of feeding morphologies in the Carnivora”. Integrative and Comparative Biology 47(1): 147-163 <Full Article>

Holliday JA, Steppan SJ (2004). “Evolution of hypocarnivory: the effect of specialization on morphological and taxonomic diversity”. Paleobiology 30(1): 108-128 <Full Article>

Valkenburgh BV (1988). “Trophic diversity in past and present guilds of large predatory mammals”. Paleobiology 14(2): 155-173 <Full Article>

Monday, April 11, 2016

Perissodactyla: Odd-toed Ungulates

Perissodactyla is the order of mammalian herbivores which includes modern tapirs, rhinos, and horses. This group is characterized by having limbs in which the third digit of each foot is enlarged and reinforced to carry the main body weight. As a result, these animals have a tendency to reduce the number of functional toes from five to just three (as in modern rhinos) or one (as in modern horses). For this reason, members of this group are commonly referred to as the “odd-toed ungulates”. Artiodactyls, the “even-toed ungulates”, differ in that the main weight of the body is distributed equally through the third and fourth digits with the number of functional toes being four or two. The name Perissodactyla was coined by renowned English scientist Sir Richard Owen in 1848.
Representatives of six families of perissodactyls, living (top) and extinct (bottom).
Left to right/top to bottom: the tapir Tapirus terrestris, the horse Equus ferus
the rhino Ceratotherium simum, the brontothere Brontotherium hatcheri
the palaeothere Palaeotherium magnum, and the chalicothere Morpus elatus.
Evolution
Paleogene- The earliest definitive perissodactyls are known from the early Eocene of Europe and probably descended from a phenacodontid codylarth, a group archaic herbivores which may have been perissodactyls themselves according to some experts. This relationship, if correct, would push the origin of Perissodactyla back nearly 10 million years to the early Paleocene. Perissodactyls underwent an explosion in diversity shortly after this initial appearance: the horse, rhino, tapir, chalicothere, paleothere, and brontothere were already well-established by the early-middle Eocene. The first representatives of each of these families were all small animals comparable in size to house cats, with rhino-sized animals appearing by the middle Eocene. The largest perissodactyls, the indricotheres of Oligocene Eurasia, were true giants with one species growing up to 5m tall at the shoulder and weighing nearly twice as much as the largest modern elephants.

Neogene- Perissodactyls dominated the terrestrial herbivore communities of the Northern Hemisphere for much of the Paleogene and the first half of the Neogene. However, the group has undergone a noticeable decline in diversity from the middle Miocene onward, an event which seems to coincide with the continued radiation of artiodactyls. The group remained largely successful as a whole however. After brontotheres became extinct at the beginning of the Oligocene, rhinos became the dominant group of giant herbivores in all terrestrial ecosystems, second only to elephants. Chalicotheres, which never seem to have been particularly abundant, had a broad distribution throughout the Northern Hemisphere and eventually reached Africa by the middle Miocene. The extinction of chalicotheres in North America by the late Miocene (Hemphillian) seems to coincide with the introduction of megalonychid ground sloths to the continent. Tapirs have retained a specialized lifestyle as forest-dwelling browsers and have changed very little throughout the Neogene: tapirs from the early Miocene would have differed very little from their modern counterparts. Horses remained diverse and prominent elements of terrestrial faunas throughout the Neogene and, together with tapirs, became the only perissodactyls to colonize South America when the Isthmus of Panama was formed during the Pliocene.

Quaternary- Perissodactyls were significantly more specious during the Pleistocene with at least twice the number of species than there are today. As a whole however, the group had been reduced to a smaller remnant of their former glory due mostly to the replacement of many types of horses with various deer, antelopes, and pronghorns. The mass extinction which took place at the end of this epoch saw the complete extinction of horses from the New World, of tapirs and rhinos from the temperate regions of North America and Eurasia respectively, and of the last surviving chalicotheres in Africa. At present, there are 3 modern families with 17 species between them ranging in size from 150 to 3,500kg, all of which are either threatened or endangered in the wild do to human activities such as poaching and habitat alteration.

Defining Characteristics
From the beginning of their evolution, perissodactyls developed a specialized tarsal configuration which was specialized for running. A saddle-saped astragalus* forms a pulley-like articulation with the tibia which prevents lateral rotation of the foot, enabling stronger and more efficient forward propulsion. The clavicle (collar bone) has been greatly reduced or lost to enable unhindered motion of the forelimbs during running and to maximize the stride. The first digit (the equivalent of our thumbs and big toes) are absent in all species. All perissodactyls are hindgut fermenters, that is, digested food which has left the stomach is stored in an enlarged cecum* where it is further broken down by bacteria to release the nutrients. Compared to the more complex digestive system found in ruminants*, this method is relatively inefficient and may partly explain the aforementioned decline of perissodactyls throughout the latter half of the Cenozoic. An enhanced ability to obtain nutrients combined with faster reproductive rates could have potentially made ruminants able to exploit new niches and food sources more readily, particularly in the face of environmental changes which would have placed greater stresses on competing herbivores.
The hindfeet of the three modern perissodactyl families: tapir (left), rhino (center), 
and horse (right). Note that the middle digit of each foot is the largest and bares most 
of the body weight, or all the weight in the case of modern horses.
Families
There are two main suborders within the Perissodactyla; (1) Ceratomorpha, which includes tapirs and rhinos, and (2) Hippomorpha, which includes horses, paleotheres, brontotheres, and chalicotheres. Occasionally, chalicotheres are placed in a third suborder Ancylopoda.
  • Phenocodontidae: early Paleocene to middle Eocene
  • Anthracobunidae: early to middle Eocene
  • Tapiridae (tapirs): early Eocene to present
  • Rhinoceratidae (rhinos): middle Eocene to present
  • Palaeotheriidae (paleotheres): early Eocene to late Oligocene
  • Equidae (horses): early Eocene to present
  • Brontotheriidae (brontotheres): early Eocene to early Oligocene
  • Chalicotheriidae(chalicotheres): early Eocene to late Pleistocene

 Glossary*
Astragalus: the ankle bone which connects the foot to the rest of the leg.
Cecum: a pouch connected at the junction between the small and large intestines.
Ruminant: herbivorous artiodactyls which possess a specialized, multi-chambered stomach.

References & Further Reading
Rose KD (ed). 2006. The Beginning of the Age of Mammals. The John Hopkins University Press, Baltimore, Maryland:243-257 <Book>

Macdonald DW (ed). 2006. The Princeton Encyclopedia of Mammals. Princeton University Press, Princeton, New Jersey <Book>

Augusti J, Anton M (2002). Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe. Columbia University Press, New York: 36-37 <Book>



Monday, November 2, 2015

Dire Wolf (Canis dirus)

The Dire Wolf (Canis dirus) is one of the most well-known predators of Pleistocene North America and recently made famous by the television series Game of Thrones (although the animals depicted in the series are much larger than their real-life counterparts). These were mid-sized predators closely related to the modern Coyote (C. latrans) and Gray Wolf (C. lupus), both of which coexisted with it during the Pleistocene.
Reconstructed and restored Dire Wolf skeleton from Rancho La Brea,
on display at the Perot Museum, Texas. Wiki.
Etymology
The genus name Canis is the Greek word for “dog”. The species name dirus is derived from the Latin word dira, which means “ominous”, “fearful”, or “dreadful”.

Habitat & Distribution
Dire Wolves were geographically widespread throughout North and South America during the Pleistocene, reported from 136 localities in North America and 3 localities in South America. Whether or not this species originated in North or South America is a matter of much debate. Its range extended from Alberta, Canada to Tarija, Bolivia north-to-south. Its habitat included forested mountains to open grasslands and plains up to 2255m (7400ft). Compared to Pleistocene Gray Wolves, Dire Wolves appears to have favored somewhat wetter environments and their fossils are often found in association with ancient marshes, rivers, and lakes. Most famously, the highly productive site of Rancho La Brea, California has yielded the remains of over 4,000 individual Dire Wolves, which had become mired in the asphalt trap most likely after attempting to hunt or scavenge other animals that died there. These wolves are frequently found at the same localities as the Saber-toothed Cat (Smilodon fatalis).
Physical Attributes
Dire Wolves were comparable to Gray Wolves in terms of linear measurements. However, the Dire Wolf was physically more robust and heavily built than the Gray and could have weighed as much as 20% more than a comparably sized Gray Wolf. The skull in particular is proportionally larger and broader with a more prominent sagittal crest*. The canines and carnassials* are also larger. Measurements of the skull suggest that Dire Wolves had a bite force that was about 20% greater than that of the Gray Wolf. Dire Wolves also had sturdier limbs with shortened metapodials and a longer tail. Although undoubtedly a swift runner, Dire Wolves were not built to pursue fast-moving herbivores over great distances the way that Gray Wolves do. Instead, they may have relied more on ambushing prey, taking turns chasing it, or even by chasing animals into the water where its movements are hindered, all of which are tactics still employed by modern pack-hunting canids.
Ecology & Behavior
Because of their greater biting capacity, Dire Wolves have often been suspected of being bone-cracking specialists similar to modern hyenas of the genus Hyaena and extinct “hyena-dogs” of the genus Borophagus. However, studies of their overall dentition and bite damage of fossil bones have demonstrated that their teeth were no better at breaking bones than its modern relative the Gray Wolf, although it must be noted that these wolves can (and do) damage and ingest considerable amounts of bone during feeding. Furthermore, the crushing aspect of the Dire Wolf dentition is not any more developed than that of its modern relative while the slicing aspect is enhanced. Thus, it may be inferred that the robust skull, stronger bite, and larger teeth of the Dire Wolf, coupled with its sturdier frame, was more of an adaptation for seizing and pulling down and rapidly consuming larger herbivores rather than an adaptation for bone cracking. In this way, the hunting and feeding style of the Dire Wolf was likely more akin to that of modern canids like Dholes (Cuon alpinus) or Bush Dogs (Speothos venaticus) which frequently and efficiently hunt prey that is considerably larger than themselves.
Skeletal comparison of Gray Wolf (left) and Dire Wolf (right). Wiki
This, in turn, hints at the potential niche stratification between the Dire Wolf and the Gray Wolf during the Pleistocene. Gray Wolves were more commonly found in drier and more well-drained environments and can exist at higher altitudes than what the Dire Wolf appears to have tolerated. Pleistocene Gray Wolves would probably have focused more on ungulates weighing 50 to 300kg (110 to 660lbs) as its primary prey base. Modern Gray Wolves struggle to bring down ungulates weighing more than 500kg (1,102lbs), even in winter when such animals are easier to overwhelm, with hunts often lasting hours and with a high incidence of injury. Dire Wolves, on the other hand, were potentially hunting prey as much as 10 times their own weight, with a prey menu that included horses, tapir, large deer, camels, and bison, although they would also have opportunistically hunted smaller animals in their environment such as capybaras, giant beavers, and peccaries as encountered. Given that larger prey animals were a more prominent element of the Dire Wolf diet, it is also likely that these animals occurred in relatively larger packs numbering as many as 20 individuals, as opposed to modern Gray Wolves whose packs average 10 members in most areas.
Display of some of the thousands of Dire Wolf skulls recovered from Rancho La Brea
on display at the Page Museum, California. Wiki.
Glossary*
Carnassial: specialized shearing cheek teeth found in terrestrial mammalian predators.
Sagittal crest: the ridge of bone that runs down the midline of the skull in many mammals.

References & Further Reading
Pardi MI & Smith FA (2015). "Biotic responses of canids to the terminal Pleistocene megafauna extinction". Ecography 38: 1-11 <Abstract>

Anyonage W & Baker A (2006). “Craniodental morphology and feeding behavior in Canis dirus, the extinct Pleistocene dire wolf”. Journal of Zoology 269: 309-316 <Abstract>

Dundas RG (1999). “Quaternary records of the dire wolf, Canis dirus, in North and South America”. Boreas 28: 375-385 <Abstract>

Dire Wolf, Canis dirus (Mammalia; Carnivora; Canidae), from the Late Pleistocene (Rancholabrean) of East-Central Sonora, Mexico <Abstract>

Kurten B & Anderson E. “Pleistocene Mammals of North America”. New York City, New York: Columbia University Press, 1980. 171-172 <Book>

Monday, September 28, 2015

Scaglia’s Terror Bird (Llallawavis scagliai)

Scaglia’s Terror Bird (Llallawavis scagliai) is the most recently discovered member of the terror bird family (Phorusrhacidae). This species known for a single near-complete, fully-articulated skeleton which even includes a preserved windpipe.
Drawing showing the skeletal anatomy of Llallawavis scagliai.
Figure 2 from Degrange et al., 2015.
Etymology
The name Llallawa means “magnificent” in Quechua, in reference to the well-preserved nature of the remains. Avis is the Latin word for “bird”. The species name is after Galileo Juan Scalia, a naturalist and director of the Museo Municipal de Ciencias Naturales in Mar del Plata, Argentina. Fully translated, the binomial name therefore means “Scaglia’s Magnificent Bird”.

Habitat & Distribution
Scaglia’s Terror Bird lived during the late Pliocene in what is now Argentina. Its habitat was likely grassland and open woodland.

Physical Attributes
This species is known from a single, nearly complete articulated skeleton, the most complete of any terror bird known to date. Discovered in 2010 and described in 2015, the skeleton (shown above) was missing only some of the forelimb bones, toe bones, and the pygostyle*. This specimen is particularly valuable in that it includes the only complete trachea known for any terror bird, as well as intact sclerotic rings*.

Scaglia’s Terror Bird was one of the smaller members of its family, with an estimated body mass of 18kg (40lbs) and a hip height of about 90cm (3ft). When fully erect, it could have stood 120cm (4ft) tall at the top of its head. The body was lightly-built with long, slender legs for fast running. The skull was about 27cm (0.9ft) long with a beak that was relatively shallower and with a less prominent hook than that of other terror birds. Another notable feature of the bird’s head was its narial knob or bump just above its nostrils.

Ecology & Behavior
The structure of the inner ear suggests that Scaglia’s Terror Bird was adapted for very rapid and precise movements of the head and neck in response to visual and audio cues. Its low, narrow beak and lightweight body suggests that its diet consisted of relatively small prey items such as cavimorph rodents and other small mammals, as well as smaller birds and reptiles. It probably hunted in a manner similar to modern seriemas; after a short dash the prey would be pinned down before being picked up and violently slammed into the ground repeatedly. This action not only kills the victim, but also makes it easier to swallow due to the breaking of its bones.
Although it is currently impossible to reproduce the types of sounds Scaglia’s Terror Bird could produce, detailed analysis of its hearing capacity has shown that it could detect frequencies ranging from 380 to 4230 Hz, with a mean sensitivity of 2300 Hz. The bird’s own vocalizations, as well as those of its prey would have fallen within this range.

*Glossary
Hertz (Hz): a unit of frequency
Pygostyle: in birds, the fusion of several caudal (tail) vertebrae into a single bone.
Sclerotic ring: rings of interlocking bones which support the eyeball in several vertebrate groups.

References & Further Reading
Degrange FJ, Tambussi CP, Taglioretti ML, Dondas A, Scaglia F (2015). “A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds”. Journal of Vertebrate Paleontology 35(2): e912656 <Abstract>

Wednesday, September 2, 2015

Phorusrhacidae: the Terror Birds

Life restoration of Phorusrhacos longissimus
by Charles R. Knight, 1901. Wiki
The phorusrhacids, known commonly as the “terror birds”, were a diverse group of predatory flightless birds that inhabited South America from the early Paleocene to the late Pleistocene. The family Phorusrhacidae belongs to a larger order of birds known as the Cariamiformes or Cariamae, which originated during the late Cretaceous and appear to have become specialized for a primarily terrestrial lifestyle very early in their evolutionary history. In addition to South America, close relatives of terror birds were also distributed through Europe, Africa, and Antarctica during the Paleocene and Eocene. By the Oligocene, however, they had become extinct on all other continents except South America where they remained diverse.

Red-legged Seriema (Cariama cristata), one
of two surviving representatives of the
Cariamae. Wiki
The terror birds themselves were prominent components of the carnivore-omnivore guild in South America throughout the Cenozoic together with sebecid* crocodylians and sparassodont* marsupials. At least one species, Titanis walleri, managed to colonize the southern United States after the Isthmus of Panama connected the two Americas during the middle Pliocene. Species within this family range in mass from 5kg to about 400kg (10 to 880lbs). Terror birds continued to thrive in South America until they became extinct at the end of the Pleistocene together with many other types of large birds and mammals. The closest living relatives of the terror birds, and the only surviving representatives of the Cariamae, are the two species of seriema (Cariamidae) from South America. These modern birds are still capable of flight but prefer to hunt on the ground.

Anatomy & Action
CT scan of the skull of the mid-sized terror
bird Andalgalornis steulleti. Wiki
Terror birds had proportionally large heads with deep, laterally flattened beaks with a hooked tip for tearing flesh. The inner structure of the beak was reinforced by bony struts and the skull bones were tightly fused together for strength. The pelvis was especially large to act as a counterbalance. They had long, powerful necks which would have been held in an S-shaped position when at rest. Detailed studies of the neck vertebrae shows that they were particularly well-adapted at making swift movements in the sagittal* plane, which is an ideal motion for striking prey. The caudal* vertebrae also appear to be somewhat more developed than those of modern flightless birds, implying that the tail, though highly reduced, may have been functional as a rudder of sorts during the pursuit of prey. As with all flightless birds, the bones of the forelimbs are greatly reduced in terror birds and were possibly involved in stability and maneuverability while running. The overall skeleton is much heavier and sturdier than what would be expected for a flying bird of the same size.

Restored skeleton of Titanis walleri at the Florida Museum of
Natual History. Wiki
Terror birds were primarily carnivorous, as evidenced by their large heads and massive, hooked beaks. Recent studies have shown that the sense of hearing in terror birds was well-developed and particularly sensitive to low-frequency sounds, suggesting that these birds utilized deep, resonant vocalizations to communicate with one another. CT scans of the brain cavities have shown that the areas of the brain that deal with visual information and problem-solving are also well-developed, while the sense of smell was relatively less so. It seems likely that terror birds hunted using vision and hearing as their primary senses. Once captured and dispatched, smaller prey items would have simply been swallowed whole, while larger meals were torn apart by the birds’ massive beak. Studies of terror bird limb muscular and proportions suggests that they were capable of exceptional feats of speed and agility.

Terror Bird Groups
The family Phorusrhacidae is divided into five subfamilies; Psilopterinae, Brontornithinae, Patagornithinae, Mesembriornithinae, and Phorusrhacinae.
Restored skulls and heads of five terror bird species belonging to each of the subfamilies. 
A. Psilopterus lemoinei (Psilopterinae), B. Paraphysornis brasiliensis (Brontornithinae),
C. Andalgalornis steuletti (Patagornithinae), D. Llawllavis scagliai (Mesembriornithinae),
E. Kelenken guillermoi (Phorusrhacinae).
Psilopterinae
The longest-lived terror bird lineage, the Psilopterinae have a temporal range spanning from the late Paleocene to the early Pliocene. They are characterized by relatively slender, lightweight bodies, proportionally thin hindlimbs, and small overall size. Members of this subfamily range from 5 to 15kg in body mass. Known species include Paleopsilopterus itaboraiensis (early Paleocene), Psilopterus affinis (late Oligocene), P. bachmanni (late Miocene), P. lemoinei (late Miocene), and P. cozecus (late Miocene).

Brontornithinae
The brontornithines were large-bodied terror birds that existed during the Oligocene through to the early Miocene. Over time they appear to have been replaced by the Phorusrhacinae (see below) by the middle Miocene. Known species include Physornis fortis (late Oligocene), Paraphysornis brasiliensis (middle Oligocene to early Miocene), Brontornis burmeisteri (late Oligocene to middle Miocene).

Patagornithinae
Patagornithines were mid-sized terror birds with lean bodies and slender limb proportions. Known species include Andalgalornis steulleti (late Miocene to Pliocene), Andrewsornis abbotti (middle to late Oligocene), Patagornis marshi (middle Miocene).

Mesembriornithinae
The Mesembriornithinae are the shortest-lived and most diverse phorusrhacid subfamily, with a fossil record dating back to the late Miocene to the late Pliocene. Most are relatively small at around 10kg, while a few grew considerably large achieving estimated body weights of up to 70kg. It contains three genera and four species; Procariama simplex (late Miocene to late Pliocene), Llallawavis scagliai (Pliocene), Mesembriornis incertus (late Miocene to Pliocene), and M. milineedwardsi (late Miocene to Pliocene).

Phorusrhacinae
The Phorusrhacinae, together with the Brontornithinae, include some of the largest of the terror birds, with species ranging in mass from 100 to 400kg. This subfamily first appeared during the middle Miocene and persisted to the end of the Pleistocene. Known species include Phorusrhacos longissimus (middle Miocene), Kelenken guillermoi (middle Miocene), Devincenzia pozzi (late Miocene to early Pliocene), Titanis walleri (late Pliocene to early Pleistocene).


*Glossary
Caudal: of or referring to the tail of an animal.
Sagittal: a vertical plane that divides the body into right and left halves.
Sebecidae: an extinct group of terrestrial crocodilians endemic to South America until the late Miocene.
Sparassodonta: an extinct order of predatory mammals endemic to South America until the Pliocene.

References & Further Reading
Degrange FJ, Tambussi CP, Taglioretti ML, Dondas A, Scaglia F (2015). “A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds”. Journal of Vertebrate Paleontology 35(2): e912656 <Abstract>

Blanco RE & Jones WW (2013). “Terror birds on the run: a mechanical model to estimate its maximum running speed”. Proceedings of the Royal Society B 272: 1769-1773 <Full Article>

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Saturday, July 4, 2015

Adzebill (Aptornis otidiformis)

Adzebill skull drawn by James Erxleben, 1879 Wiki
Adzebills (Aptornithidae) were predatory flightless birds that lived on the islands of New Zealand. When first discovered, they were thought to have been a type of moa due to their large size. They were later found to be an offshoot of the Gruiformes, the group which contains cranes and rails. The group first appears in the early to middle Miocene (19 to 16mya) with the species Aptornis proasciarostratus from the St. Bathan’s Formation in central Otago. The better-known adzebill of the Pleistocene-Holocene will be the focus of this entry.

Habitat & Distribution
Adzebill fossils are typically found in drier, more open lowland areas of New Zealand. They occurred at altitudes up to 1,000m above sea level but were absent from subalpine environments. Population densities appear to have been relatively low. Two species have been identified; the North Island Adzebill (A. otidiformis, Owen 1844) and the South Island Adzebill (A. defossor, Owen 1871). Physically, these two birds are virtually identical apart from geographic location and size, the South Island form being 20% larger due to the island’s greater land area. Rather than being separate species, the two may instead be subspecies.

Physical Attributes
Adzebills were heavily-built birds about the height of a Wild Turkey (Meleagris gallopavo) but over twice the mass. Because of their size they were believed to be a type of small moa on their initial discovery. However, a genetic study in 2011 revealed them to be a type of Gruiform*. The Adzebill’s most notable characteristic was its large, thick-walled skull and brain case. The powerful, down-curved pointed beak is very stout with thick cutting edges and is much wider at the back, indicating that these birds had a considerable bite force. The neck vertebrae were robust and would have been heavily-muscled in life. The bones of the legs and toes were sturdy with short foot bones, suggesting that these birds were active runners. The wings are highly reduced and were likely not visible within the birds’ feathers.

Ecology & Behavior
Sir Richard Owen, who first described the species, suggested that Adzebills were omnivores. He further noted that the large, powerful beak would have been better suited to picking off small animal prey as well as plant matter. Small sets of gastroliths recovered from two complete skeletons, however, suggest that these birds had a much more predatory lifestyle. Recent isotope analysis of Adzebill bones has confirmed that the birds were indeed active predators that were feeding on considerably large prey, perhaps even larger than themselves. Notable physical characteristics such as a thick-walled skull, a powerful bite, protected braincase, thick neck, and sturdy legs made these birds capable of withstanding considerable torsional forces.

Mounted Adzebill skeleton at Canterbury
Museum. Wiki
The Adzebill’s size would have made it one of the top predators of New Zealand. Prey species would have included many of the terrestrial birds on the islands, including some of the smaller moa. Newly-hatched Adzebills are more likely to have fed on smaller animals like insects, bats, and tuatara, steadily graduating to larger prey as they matured. It would have hunted by dashing after prey and seizing it by the neck with its powerful jaws, either crushing the spine or pulling prey to the ground with powerful jerking motions. These predators were, potentially, even able to hunt cooperatively in small groups as some modern birds are known to do. Scavenged meat would have been another key component of the Adzebill diet, and it may have also scavenged from the kills of New Zealand’s other top predator, the Haast’s Eagle (Harpagornis moorei).

Adzebills were victims of the same pressures that befell other large, flightless birds of New Zealand. Their bones have been recovered from Maori middens, indicating that they were hunted occasionally. The birds’ eggs and chicks were also likely to have been preyed upon by introduced dogs and rats.

-Special thanks goes out to Mike Dickison (@adzebill) for his advise pertaining to the life reconstruction and physical characteristics of this species.

Glossary*
Gruiform: the order of birds containing cranes, rails, and their closest relatives.

References & Further Reading

Lanfear R & Bromham L (2011). “Estimating phylogenies of species assemblages: A complete phylogeny for the past and present native birds of New Zealand”. Molecular Phylogenetics and Evolution 61(3): 958-963 <Full Article>