Saturday, January 20, 2018

Sphenisciformes: the Penguins

Penguins are flightless, marine birds belonging to the order Sphenisciformes in the family Spheniscidae. They have existed since the beginning of the Cenozoic with roots possibly dating back to the late Cretaceous, and they appear to have always been restricted to the Southern Hemisphere; both modern penguins and their extinct relatives are distributed along the coasts of Antarctica, Australia, New Zealand, sub-Saharan Africa, and South America.
A pair of Emperor Penguins (Aptenodytes forsteri) tobogganing across
an Antarctic snowscape. Wiki.
The Paleogene fossil record of penguins has been intensively studied in the last few decades with numerous new taxa having been described during that time, with argueably the most interesting discoveries coming out of New Zealand. Although the penguin lineage is believed to have split away from other birds as early as the late Cretaceous (71mya), the earliest-known and most basal penguins date back to the early to middle Paleocene (62 to 58mya) and belong to the genus Waimanu from New Zealand. The South American genus Perudyptes and a slightly older, unnamed taxon, demonstrate that penguins had expanded their range to encompass the entire southern Pacific Ocean by the middle Eocene and were probably present throughout the Atlantic Ocean as well. There are four accepted penguin subfamilies (discussed below), only one of which is still alive today.

Map showing the collective distribution of modern penguins.
 Penguins throughout their evolutionary history appear to have
been confined to the Southern Hemisphere, so this distribution
map is also applicable to fossil penguins. Wiki.
The Palaeeudyptinae, or “giant penguins”, are the most well-studied of the extinct penguin subfamilies. The earliest known member, Crossvallia unienwillia, lived during the late Paleocene (59.2–56mya) in what is now Antarctica, and therefore would have coexisted with basal penguins like Waimanu. The group persisted throughout the Paleogene and until the late Oligocene, and potentially even lasting until the middle Miocene if the tentatively placed Anthropodyptes proves to be a true member. Palaeeudyptines differ from modern penguins in a number of aspects. For example, the forelimb had not yet developed into a rigid flipper and would have retained a degree of flexibility. The beak also differs from those of modern penguins in being relatively long and spear-like, similar to that of a heron.

By far the most frequent topic addressed when discussing members of Palaeeudyptinae, is body size. True to their colloquial name, these early Cenozoic penguins were quite large by modern standards; the 20 species of modern penguin range in size from the 40cm tall and 1kg Little Blue Penguin (Eudyptula minor), up to the 110cm tall and 35kg Emperor Penguin (Aptenodytes forsteri). The early palaeeudyptine Crossvallia unienwillia was only slightly larger than an Emperor Penguin with much larger penguins, with body lengths of over 130cm, occurring from the middle Paleocene to the late Oligocene. Due to the often fragmentary and incomplete nature of penguin fossils, physical aspects such as body size and mass must be calculated by measuring individual bones and scaling them against modern specimens. Through this method, lengths of 180cm and 160cm have been calculated for Anthropornis nordenskjoeldi and Palaeeudyptes klekowskii respectively, both being widely regarded as the largest penguins known to have ever lived (the latter even being given the common name of “Colossus Penguin”).

Giant penguins appear to have become extinct early in the Neogene. The reason for their disappearance is not currently understood, although a likely explanation may be a combination of climatic changes and feeding competition from pinnipeds (seals, sea lions, and walruses) which were undergoing an adaptive radiation at the time these giant penguins had declined.

Palaeospheniscinae & Paraptenodytinae
Smaller than the large-bodied palaeeudyptines with whom they coexisted for a time, the Palaeospheniscinae and Paraptenodytinae may have been the ecological analogues of the modern spheniscine penguins, though they were probably not directly ancestral to them. Both subfamilies are relatively poorly understood at the timing of this blog post. Palaeospheniscines, also known as “slender-footed penguins”, contain five species within the genus Palaeospheniscus. They were small to medium-sized penguins that ranged in body length from 50 to 75cm, and occurred from the early Miocene to early Pliocene of southern Africa and South America. Paraptenodytines, also known as the “stout-footed penguins”, contains four known species within the genera Arthrodytes and Paraptenodytes. These occurred from the late Eocene to the middle Miocene of South America

The group containing all modern penguins, all of which belong to the subfamily Spheniscinae, arose during the late Paleogene and recognizable members of today’s genera began to appear during the middle Miocene (14 to 13mya). The radiation of this group appears to correspond to two episodes of global climatic cooling.

Examples of each of the modern genera within the penguin subfamily Sheniscinae.
From left-to-right and top-to-bottom: King Penguin (Aptenodytes patagonicus),
Adelie Penguin (Pygoscelis adeliae), Megallanic Penguin (Spheniscus magellanicus),
Little Blue Penguin (Eudyptula minor), Macaroni Penguin (Eudyptes chrysolophus),
Yellow-eyed Penguin (Megadyptes antipodes).

Among modern penguins, the genus Aptenodytes (“great penguins”) are the most basal, with DNA evidence showing that these birds split from other spheniscines around 40mya. The earliest known fossil evidence for this genus comes from the early Pliocene of New Zealand and ascribed to the species A. ridgeni. The two modern members of the genus are characterized by yellow-orange neck, breast, and beak patches. Chicks are almost naked upon hatching and brooding adults incubate their eggs on their feet beneath a specialized fold of skin.

The genus Pygoscelis (“brush-tailed penguins”) are the next to diverge with DNA evidence showing that a split occurred at about 38mya and are said to most closely resemble the common ancestor of the Spheniscinae in physical form. Fossils from the genus date to the late Miocene of South America and New Zealand. There are three modern species which breed in Antarctica and southern South America.

The oldest fossils of the genus Spheniscus (“banded penguins”) date back to the middle Miocene. There are four modern species distributed through southern Africa and the southern and western coasts of South America up to the equatorial islands of Galapagos. Members of the genus are characterized by a single band of black that runs around their bodies bordering their black dorsal coloring, black beaks with a small vertical white band, distinct spots on their bellies, and a small patch of unfeathered or thinly feathered skin around their eyes that can be either white or pink. All members of this genus raise their young in nests situated in burrows or natural depressions in the earth. They are also renowned for their loud, braying vocalizations which earn them the nickname of the "jack-ass penguins".

The genus Eudyptula (“little penguins”) contains three modern species which are distributed through southern Australia and New Zealand. They are burrow-nesters distinguished by their small body size and iridescent dorsal plumage which gives them a bluish-black appearance.

Members of the genus Eudyptes (“crested penguins”) are characterized by their hair-like yellow ornamental head feathers and their reddish-colored beaks. This is the most specious of the modern penguin genera, containing eight species. These form a clade with the New Zealand endemic genus Megadyptes, which has a single living species and one recently extinct after first contact with the Maori. The two genera apparently diverged from each other during the middle Miocene (15 or 14mya) and the modern species of Eudyptes all radiated between the late Miocene and late Pliocene (about 8 to 3mya).

Skeleton & Movement
Penguins are superbly adapted for an aquatic environment and are remarkably swift and agile when traveling through the water (video). Unlike volant (flying) birds which have lightweight, hollowed bones to reduce body weight, penguin bones are solid and heavy which decreases buoyancy, making diving easier. Unlike other flightless birds, the penguin sternum is keeled to support well-developed pectoral musculature. The flight stroke of the wings has been modified into a swimming stroke, enabling these birds to “fly” through the water. The wings of their ancestors have been modified into rigid flippers, which has been achieved by the broadening, flattening, and densification of the bones of the forelimb. While swimming, the feet and tail trail backwards and function as steering aids or rudders. The body itself is fusiform in shape for streamlining.
Articulated skeleton of the Magellanic Penguin (Sheniscus magellanicus)
shown in swimming posture. Wiki.

In contrast to their efficient aquatic locomotion, terrestrial locomotion can be rather slow and clumsy (video). Penguins primarily adopt an upright waddling gait during terrestrial locomotion during which they use their flippers and tails to maintain balance and an upright stance. A hopping motion is utilized for travel over uneven or rocky terrain. The penguin tarsometatarsus (the fusion of three metatarsals and some of the tarsal bones in birds) is very distinctive in that it is extremely short, broad, and flat. possibly to strengthen the foot. This unique shape was present in penguins by the middle Paleocene, as demonstrated by Anthropornis. This shape may correlate functionally with the aforementioned upright posture and gait adopted by modern penguins. The one known subversion of this morphology is the very basal genus Waimanu, which was contemporaneous with Anthropornis but had a tarsometatarsus that was morphologically more comparable to that of a cormorant. This suggests that these archaic penguins had a somewhat different style of terrestrial locomotion and that they probably relied more on their feet for propulsion.

Foot bones of three penguin genera, two extinct and one modern. Compare
and contrast the morphology of the tarsometatarsi between
Anthropornis (a-c), Waimanu (f-g), and Aptendytes (j-k).
Figure 1 from Mayr et al. (2017).

Skin & Feathers
Modern penguins possess a layer of fat, or blubber, several centimeters thick for insulation in cold waters. Given the largely tropical to subtropical conditions of the Paleogene, it is hard to say whether early penguins such as the giant palaeeupytines would have needed this extra layer of insulation. If not, these penguins would have appeared relatively slender compared to modern penguins despite many of them being considerably larger. What is almost certain is that, like their modern relatives, fossil penguins had a dense covering of short, rigid feathers. This plumage insulates penguins against cold air and water by trapping air near the skin. Waterproofing is achieved through the application of a special oil during grooming. When hot, penguins ruffle their feathers to allow cool air to reach their skin, thus lowering the body temperature.

Preserved skin and feathers are known for the late Eocene species Inkayacu paracasensis confirms that the penguin feather morphology was in development very early in the group’s evolutionary history. The feathers of the flipper and body, which were densely packed together, had large shafts that made them very rigid. The feathers were also short compared to those of modern penguins, with a maximum length of 3cm. This, again, may reflect the warm Paleogene environment in which these early penguins lived and the need for insulation; I. paracasensis was a larger animal which lived in tropical waters, while modern penguins are smaller and, with the exception of the Galapagos Penguin (Spheniscus mendiculus), generally inhabit colder Antarctic and Subantarctic waters.

Photograph showing the wing feathering of the late Eocene Inkayacu paracasensis
(scale = 1 cm). Figure 2 from Clarke et al. (2010).

All modern penguins have a countershaded color scheme as adults, with black or dark brown dorsal plumage and white ventral plumage. This coloration provides camouflage when viewed from the top and bottom; a predator looking up from below has difficulty distinguishing between a white penguin underside and the reflective water at the surface, while the dark plumage on the back blends the darker water seen at deeper depths. The known feathers for I. paracasensis are different in that they appear to have been gray or reddish-brown in color as determined by the shape and structure of the melanosomes. It is unclear how these colors were distributed; they may have covered the whole body or perhaps this penguin was similar to the modern Aptenodytes in having special identifying markings while the rest of the body was the more conventional black-and-white pattern. Nonetheless, this fossil eludes to the potential variability that could have existed in the plumage of fossil penguins.

Penguin eyes are specialized for underwater vision and the sense of sight is their primary means of hunting. The sense of hearing is said to be average by the standards of other birds, but nonetheless appears to be sensitive enough for individuals to identify and locate their mates and offspring within huge, densely populated nesting colonies. The first ever study published study to determine the importance of scent for individual recognition in birds demonstrated that Humbolt Penguins (Speniscus humbolti) are able to discern familial and non-familial odors, a finding which holds many implications for penguin social behavior. Interestingly, endocasts of the braincases of multiple genera demonstrate that fossil penguins such as Paraptenodytes had larger olfactory lobes than modern penguins, suggesting that the sense of smell was even more important to them behaviorally.

Endocasts of the brain (blue) and semicircular canals (pink) in several
extinct and modern penguins:
(A) an unnamed fossil from Atarctica
(B) Paraptenodytes antarcticus
(C) Emperor Penguin (Aptenodytes forsteri)
(D) African Penguin (Spheniscus demersus)
(E) Magellanic Penguin (Spheniscus magellanicus)
(F) Little Blue Penguin (Eudyptula minor)
(G) Chinstrap Penguin (Pygoscelis antarctica)
(H) Adélie Penguin (Pygoscelis adeliae)
Figure 9 from Tambussi et al. (2015)

Thanks for reading! If you like what I do here on this blog and want to help me produce more frequent and higher quality content, please consider donating over on my Patreon page. Any amount, even just $1 is a big help and is much appreciated, and in return you get exclusive updates, blog previews and in-progress artwork, and more.

References & Further Reading
Mayr G, De Pietri VL, Scofield PR (2017). "A new fossil from the mid-Paleocene of New Zealand reveals an unexpected diversity of world’s oldest penguins". The Science of Nature 104(9): DOI 10.1007/s00114-017-1441-0 <Abstract>

Mayr G, Scofield PR, De Pietri VL, Tennyson AJD (2017). "A Paleocene penguin from New Zealand substantiates multiple origins of gigantism in fossil Sphenisciformes". Nature Communications 9(1927): DOI: 10.1038/s41467-017-01959-6 <Full Article>

Gavryushkina A, Heath TA, Ksepka DT, Stadler T, Welch D, Drummond AJ (2017). "Bayesian total evidence dating reveals the recent crown radiation of penguins". Systematic Biology 66(1): 57-73 <Full Article>

Tambussi CP, Degrange FJ, Ksepka DT (2015). "Endocranial anatomy of Antarctic Eocene stem penguins: implications for sensory system evolution in Sphenisciformes (Aves)". Journal of Vertebrate Paleontology: e981635 <Abstract>

Coffin HR, Watters JV, Mateo JM (2011). "Odor-based recognition of familiar and related conspecifics: a first test conducted on captive Humbolt penguins (Spheniscus humbolti)". PLoS ONE 6(9): e25003 <Full Article>

Clarke JA, Ksepka DT, Salas-Gismondi R, Altamirano AJ, Shawkey MD, D'Alba L, Vinther J, DeVries TJ, Baby P (2010). "Fossil evidence for evolution of the shape and color of penguin feathers". Science 330(6006): 954-957 <Full Article>

Baker AJ, Pereira SL, Haddrath OP, Edge KA (2006). "Multiple gene evidence for expansion of extant penguins out of Antarctica due to global cooling". Proceedings of the Royal Society B 273: 11-17 <Full Article>

Slack KE, Jones CM, Ando T, Harrison Gl, Fordyce RE, Arnason U, Penny D (2006). "Early penguin fossils, plus mitochondrial genomes, calibrate avian evolution". Molecular Biology and Evolution 23(6): 1144-1155 <Full Article>

Ksepka DT, Bertelli S, Giannini NP (2006). "The phylogeny of the living and fossil Sphenisciformes (penguins)". Cladistics 22(5): 412-441 <Abstract>

Jouventin P, Aubin T, Lengangne T (1999). "Finding a parent in a king penguin colony: the acoustic system of individual recognition". Animal Behavior 57(6): 1175-1183 <Abstract>

Thursday, January 11, 2018

New Year, New Beginnings

Hello and Happy New Year everyone!

This blog post will serve as an announcement for changes to this site and what you can expect from me going forward.

For those who are new to the site, this blog was made to be an accessible source of information covering animals of the Cenozoic Era. Since starting in 2013, I have been writing up such things as detailed overviews of specific animals, morphology, and notable fossil sites. I thank those of you who have stuck with me since from the beginning as I have continued to evolve my writing and art style. I have a few new series in the works which include, but not limited to, documentary and book reviews and comparative anatomy. I am driven by a love of learning new things and a desire to share my knowledge with others, and this blog has been my outlet for doing that.

My paleontological research is currently unpaid, and the amount of money that I make on commissioned artwork is unpredictable from month-to-month. Furthermore, a considerable amount of time goes into research and producing the artwork for a given blog post to ensure an optimal final product. Long-time followers of this blog will note that I have been somewhat prone to extended periods of inactivity. This is not for lack of trying, but due to the demands of everyday life (food and bills) I have been forced to commit more of my time into other, more profitable avenues. Trust me when I say the backlog of rough drafts, concept art, and ideas is vast and ever-growing, it’s just that more often than not I have to leave them on the backburner!

Thus, in order to make my efforts a bit more sustainable and increase my output, I have established a few means for which you the readers can help make this blog grow.

First off, I have just launched a Patreon page. Patreon, for those who are unaware, is a crowdfunding platform that provides a means to support your favorite authors, artists, and other online content-creators with monthly micropayments. There’s no obligation and, once started, you can quit at any time. In return for your money, you get access to exclusive content, updates, and rewards. Even small amounts can make a huge difference, so any donation you can offer is hugely appreciated. At minimum, patrons who donate $1 per month can expect to have access to in-progress and exclusive artwork related to upcoming blog posts (see the GIF below for an example) and prints, concept art, and other updates. And of course, the more you pledge the more you receive in return.

Another new addition is my store on Redbubble, a global online marketplace for print-on-demand products based on user submitted artwork. The site allows its members to sell their artwork as decoration on a variety of products including T-shirts, posters, mugs, stickers, and many more. I currently have no merchandise to show at the timing of this blog post, but the first designs are planned to be uploaded by late January. From then on, a few new designs will be announced on the last full week of every month.

All of your support will go into helping me with academic activities such as attending conferences and carrying out research projects. It will also free me up to produce better quality work and allow me to keep a more consistent and less sporadic posting schedule (shooting for every other Thursday or Friday at minimum).

This is a transitional period where I am trying to turn my once-hobby into more of a sustainable part-time job of sorts. The idea behind my work has always been to provide a free and accessible source to inform and stimulate curiosity in those who visit my site. There will always be hiccups as I learn to accommodate and adjust. So, as I move forward, please give me your support and patience, and I'll continue to supply you, the viewers, with the content you've enjoyed since 2013.

Thank you all so very much!

Wednesday, November 15, 2017

Documentary Review: Walking with Beasts

Walking with Beasts (WWB) is a 6-episode miniseries which aired in late 2001 as a direct sequel to Walking with Dinosaurs (WWD). It was produced by BBC Natural History Unit and distributed by BBC Worldwide. In the United Kingdom, each of the six episodes aired on a weekly basis from November 15th to December 20th. In the United States, where it was retitled “Walking with Prehistoric Beasts”, these individual episodes were edited together and presented as a single 3-hour long documentary in December of the same year on Discovery Channel. The UK and US broadcast versions of the series were narrated by Kenneth Branagh and Stockard Channing respectively.

As with WWD, the narrative of WWB is presented in the style of a traditional nature documentary. Empty landscapes were filmed in various locations around the world and computer-generated animals were inserted later, shown interacting with the environments and with other animals. Animatronic models were used mostly for closeup shots of the head and life-sized puppets were built for carcasses. Each episode follows the life of a specific animal which serves as a window through which the audience views the world around it and the creatures with which it coexists. The nature documentary style is further reinforced by a few scenes in which the CGI animals interact directly or indirectly with the camera, such as when a young indricothere aggressively charges and knocks over the camera or when a rock thrown by an australopithecine collides with the camera lens cracking it.

Animals featured within Walking with Beasts. Source

While the main focus of the series is on its animal subjects, each episode indirectly addresses an important theme or concept.
  • Episode 1 (New Dawn) touches on the recovery and diversification of mammals after the K/Pg extinction, in the process highlighting some of the adaptations which enabled their success.
  • Episode 2 (Whale Killer) introduces the global climate change that was set in motion largely by the isolation of Antarctica and the subsequent formation of the Antarctic Circumpolar Current, an event which would become a significant driving factor in mammalian evolution through the rest of the Cenozoic.
  • Episode 3 (Land of Giants) shows how mammals recovered and adapted after the Grande Coupure, or the Eocene-Oligocene extinction event, which was likely caused by the aforementioned climatic changes shown in the previous episode.
  • Episode 4 (Next of Kin) depicts the origins of the human lineage as well as establishing how much more familiar the mammalian fauna of the Pliocene would be to us compared to earlier episodes.
  • Episode 5 (Sabretooth) touches on the Great American Biotic Interchange (GABI) by showcasing some of the animals that evolved in isolation on the former island continent of South America and how invading predators from North America changed its ecology.
  • Episode 6 (Mammoth Journey) shows how certain types of mammals have adapted to survive at northern latitudes during glacial cycles, as well as showing how humans have progressed and spread from their ancestral homeland.

Anamatronic entelodont head used in episode 3 of
Walking with Beasts. Source
WWB set a major milestone among paleo-documentaries. While most, including WWD, focused on dinosaurs and other animals of the Mesozoic, WWB places its focus exclusively on the Cenozoic Era. Due to the popularity of (non-avian) dinosaurs, the period after their extinction and the animals that lived during that time have remained relatively unknown to the general public with the exception of more “mainstream” creatures such as sabertooths, mammoths, sloths, and hominids. While much focus is indeed placed on these animals in the latter half of the series, we are also introduced to a variety of interesting creatures which had never before been portrayed on television, or at least not with such attention to detail. In the first episode alone, we are introduced to such creatures as the bipedal mesocarnivore Leptictidium, the walking whale Ambulocetus, and the cat-sized horse Propalaeotherium.

Leptictidium is one of many animals to be depicted on television
for the first time in Walking with Beasts. Source
Watching this series as a young paleontology enthusiast had a profound impact on me. I was captivated by the selection of animals being depicted, most of which I had never heard of before. WWB series sparked in my then 13 year old mind a desire to learn more about these creatures and ultimately led me to shift my research interests away from dinosaurs and toward Cenozoic mammals. Apart from the improved visual effects and storytelling, I found the WWB soundtrack to be much more enjoyable than that of WWD, and to this day I often play it on loop while drawing or writing. In fact, the animals presented within WWB are generally more anatomically accurate in their movement and appearance because most of them have living relatives that could be used as analogues. The series has aged relatively well and is a good introduction to Cenozoic paleontology despite its flaws/inaccuracies, most of which can be attributed to budgetary constraints or limited knowledge at the time of production. These will be elaborated upon in smaller posts in which I will review each episode on its own merits. I will, however, briefly mention a few general problems that I noticed throughout the series;
  • The Paleocene and Miocene are completely skipped over in WWB. While this omission is unfortunate, the decision to do so is understandable from a practical standpoint. The Paleocene is the least understood portion of the Cenozoic. Meanwhile, the Miocene comprises a massive 18 million year gap with many interesting and well-known faunas across the world to choose from, and is thus probably deserving of its own documentary unto itself.
  • As with all the Walking with miniseries, WWB regularly utilizes recycled animation or repurposed creature models. At numerous points, specific clips may be repeated two or more times over the course of a given episode. At others, CGI models may be given a different skin and reused in a later episode. Similarly, the juveniles of some species are simply shrunken down replicas of the adult models. Such “cloning” is fortunately mostly limited to those animals to which less screen time is given and much more differentiation can be seen in those that are on screen most frequently, with some even showing sexually dimorphic traits. Other problems with the models include some shrink-wrapping in the more short-haired/feathered animals, and keen-eyed viewers will note some minor differences in appearance between the CGI animals and their animatronic counterparts.
  • What I found most memorable about the Discovery Channel broadcast of WWB were the brief and informative paleontology segments that were interspersed before commercial breaks and between episodes. In these segments, scientists would give brief explanations of the fossil evidence, thus providing additional information and credibility to what was being portrayed in the main program. These segments were, unfortunately, not included in the DVD release of the series. The decision to not include these segments always confused me, especially since later programs like When Dinosaurs Roamed America and Dinosaur Planet have shown that such a format works quite well (though it should be noted that these programs were produced by Discovery Channel and not BBC).

Side-by-side comparison between the Smilodon mode used in episode 5 and
the Cave Lion from episode 6. Source1 & Source2
These problems do not distract from the stories being presented. It is a worthy successor to its critically acclaimed predecessor WWD and improves upon the formula in many ways. In terms of its coverage and portrayal Cenozoic animals, WWB greatly outclasses older documentaries such as Paleoworld (1994-1997) and Extinct (2001), the latter of which dabbled in CG animated storytelling. Overall, I recommend WWB to anyone who is interested in prehistoric life and I will be using this series as a benchmark when reviewing other paleo-documentaries.

Other Reviews

Sunday, April 16, 2017

Minorca Giant Rabbit (Nuralagus rex)

The Minorca Giant Rabbit (Nuralagus rex) lived on the island of Minorca off the coast of Spain during the Pliocene. Among other unique characteristics, this species holds the record as the largest lagomorph yet discovered. It was also the only lagomorph to become the largest mammalian herbivore of its environment.

Reconstruction of Nuralagus rex based on a selection of bones with
best-fitting articular surfaces. Shown alongside the modern European Rabbit
(Oryctolagus cuniculus) for scale. Figure 3 from Quintana et al., 2011.

The Minorca Giant Rabbit was described in 2011 and is known from abundant skeletal remains. Nura is the ancient Phoenician name for the island of Minorca, and lagos is the Greek word for hare or rabbit. Its species name rex is the Latin word for king, which is a reference to this species great size compared to other lagomorphs. “The King Rabbit of Minorca”. For the purposes of this blog I will be referring to this species as the “Minorca Giant Rabbit” or simply “Minorca Rabbit”.

Habitat & Distribution
Thought to have descended from mainland European rabbits of the genus Alilepus, Minorca Rabbits were, as their name suggests, endemic to the small island of Minorca in the Mediterranean Sea off the coast of Spain. Evolving on a small island which lacked large predators or large-bodied competing herbivores allowed these rabbits to rapidly grow in size and become the largest herbivores in their habitat. The species is known from Pliocene deposits and is thought to have become extinct by the early Pleistocene.

Physical Attributes
Minorca Rabbits differed in numerous ways to modern rabbits, the most obvious difference being its great size. It stood about 50cm high at the shoulder and had an estimated average body mass of 12kg (27lbs), making it more than 10 times heavier than the largest modern rabbits and over 2 times heavier than the largest hares. The modern Amami Rabbit (Pentalagus furnessi) from Japan shares many physical traits with its extinct cousin, albeit to a lesser degree. Most notably, the cursorial adaptations possessed by their mainland relatives have been lost. The hindlimbs were shorter and more robust with broad, plantigrade feet: modern rabbits have long hindlimbs with narrow, shock-absorbing feet. The vertebral column of the Minorca Rabbit was also shorter and less flexible which would further reduce its stride length. When it needed to move quickly it would do so in more of a loping conventional gait probably similar to that of a large mustelid rather than utilizing the hopping gait employed by other rabbits. Furthermore, the body was bulky and the volume of the ribcage shows that the heart and lungs were proportionally small: in cursorial mammals, the ribcage is typically expanded and these organs are often enlarged to maximize circulation and airflow during a run. The skull, eyes, and ears are all notably smaller in proportion to the rest of the body than it is in modern rabbits, suggesting that vision and hearing was somewhat reduced; this is not a severe handicap in an environment which lacks large predators. Large, curved claws and robust forearm bones indicate that Minorca Rabbits were particularly skilled at digging.

Ecology & Behavior
Like many modern rabbits and hares, Minorca Rabbits likely inhabited extensive burrow systems, excavated by their well-developed claws and forelimbs. These fossorial attributes were also potentially used to dig for plant roots and other underground food resources. Although it is unknown what plants it habitually preferred, this species was most likely a mixed-feeder that grazed and browsed on most of the plants within all habitats on the island. Minorca Rabbits had no known terrestrial predators, although juveniles were potentially at risk from predatory birds.

References & Further Reading
Quintana J, Köhler M, Moyà-Solà S (2011). “Nuralagus rex, gen. et sp. nov., an endemic insular giant rabbit from the Neogene of Minorca (Balearic Islands, Spain)”. Journal of Vertebrate Paleontology 31(2):231–240 <Full Article>

Thursday, March 30, 2017

March of the Moa Part 2: Anatomy and Action

In addition to being known from multiple complete skeletons, soft tissue remains including skin, feathers, muscle tissue, and organs have been found for moa. Because of this, the life appearances and anatomy of most species is relatively well-known with abundant genetic material. Moa were comparable in in some aspects to modern flightless ratites: all share, for example, a small head mounted on a long neck which is in turn connected to a rigid torso, long legs, with a covering of long strands of fur-like feathers on their bodies. In many aspects, however, moa were quite unique with a number of characteristics not seen in their modern relatives. This blog post will highlight these characteristics.

Side-by-side skeletal mounts of Ostrich (Struthio camelus) and the
North Island Giant Moa (Dinornis novaezealandiae).
Photo taken in 1870. Wiki.

Moa beaks and skulls are larger and broader than those of modern ratites, able to deal with a wider variety of plant matter (this will be addressed in greater detail in part 3 of this series). The orbits were large and the nostrils were located at the base of the beak. moa had exceptionally well-developed sense of smell as indicated by enlarged olfactory lobes, a feature which they share with kiwis. An enhanced ability to process odors suggest that chemical communication and other was an important aspect of moa behavior: note the prominent olfactory nerve (labeled CN1) in CT image of the moa brain in the video below which was generated by WitmerLab.

For as long as moa have been known to science, most skeletal mounts and early artistic portrayals have depicted them with an Ostrich-like posture: the neck being held vertically so that the head was held high above the rest of the body. However, recent examinations of moa vertebral and cranial anatomy indicate that these birds would have carried their heads in a lowered position when at rest: the neck was normally held in a curved position so that the head was level to the back. Modern kiwis and cassowaries adopt a similar position, which is more efficient for traveling through dense forest vegetation. Moa would have only adopted an erect-neck posture when browsing, during threat displays, or when surveying to their surroundings.

Two reconstructions of the Upland Moa (Megalapteryx didinus). The left image,
illustrated by George Edward Lodge in 1907 (source) shows the bird in the outdated,
ostrich-like posture with an erect neck. The left image shows the animal in a more
realistic head-lowered posture.

Moa legs were generally longer and more robust than those of modern ratites with particularly elongated tibiotarsi (in birds, the fusion of the tibia and some of the tarsal bones) and shortened tarsometatarsi (in birds, the fusion of the three main metatarsals and some of the tarsal elements). The feet were also larger and broader with most species having four toes. Small feet and elongated lower limb segments, physical characteristics shared among modern ostriches, rheas, and emus, are associated with cursoriality and maintaining high speeds over long distances. Moa limb proportions, with their shortened distal segments, suggest that they were not built for active running although they could still move reasonably fast when they needed to. However, moa may have been better suited for maneuverability than their more fleet-footed relatives. Modern cursorial ratites, despite their great running speeds, have wide turning circles and their slender limbs make sharp turns relatively difficult: the relatively open environments which these birds tend to inhabit lessens this apparent disadvantage. The sturdier legs and shorter foot bones of moa were potentially more adept at weaving through trees and other obstacles when evading aerial predators like the Haast’s Eagle (Harpagornis moorei). Kiwis have similar limb proportions.

Hindlimb skeletons of eight ratite species scaled  to the same femur length.
From left to right: Ostrich, Heavy-footed Moa, North Island Giant Moa,
Bush Moa, Mantell's Moa, Great Spotted Kiwi, Southern Cassowary, and
Upland Moa. Note that in moa and kiwi the lower limb segments are
proportionately much shorter compared those of other ratites, in which the
tibiotarsus and  tarsometatarsus are about the same length.

All flightless ratites evolved from volant (flying) ancestors which possessed hypertrophied forelimbs (wings) and a keeled sternum which supported enlarged pectoralis muscles to facilitate powered flight. When transitioning to a more terrestrial, flightless lifestyle, the sternum lost its keel with an accompanying reduction of the pectoral musculature and of the forelimb skeleton to varying degrees.
  • Ostriches and rheas demonstrate the least forelimb reduction among flightless ratites: the reason for this is because these birds utilize their forelimbs during visual displays and to stabilize themselves when running.
  • Kiwis, emus, and cassowaries demonstrate a more extreme form of reduction in which the forelimbs have become so small that they serve no obvious function and are almost never visible from within the plumage.
  • Moa have become the only known birds to completely lack any external forelimb structure due to the absence of the tbx5 gene: the gene responsible for forming the pectoral girdle. As a result, the sole remnant of the forelimb skeleton is a tiny vestige of bone known as the scapulocoracoid (the fusion of the scapula and coracoid bones) which lies against the ribcage and is no larger than a human finger.

Three grades of forelimb reduction observed in ratites. (A) long and slender
humerus with shortened forearm elements as seen in ostriches and rheas;
(B) short, stubby forearm as seen in most flightless ratites such as emus
and cassowaries; (C) complete absence of external limb elements with the
scapula and coracoid fused to form the scapulocorocoid, a feature which is
unique to moa.

The internal anatomy of moa is still mostly unknown. However, a few unique specimens of the Eastern Moa (Emeus crassus) and Stout-legged Moa (Euryapteryx curtus) have been found with ossified tracheal rings within their body cavities revealing the form and structure of the windpipe. These two species, and potentially other members of Emeidae, possessed a convoluted windpipe. From the neck, the windpipe passed downwards on the left side of the body before doubling back on itself and then backward into the lungs, almost doubling this organ’s length. Modern birds which have this adaptation (swans, cranes, etc) are known for producing deep, resonant vocalizations: the convoluted nature of the windpipe forming a structure analogous to the tubing of certain types of wind instruments. The Tetrapod Zoology blog discusses this adaptation in greater detail hereWe can imply that moa were highly vocal animals that could produce a broad range of situation-specific calls which could be heard over great distances including contact calls, alarm calls, and mating calls. These Sandhill Cranes (video) provide a reasonable analogue for potential moa vocalizations. 

A diagram approximating the shape of the windpipe in the 
Eastern Moa (Emeus crassus).

Moa plumage is particularly well-known thanks to the discovery of numerous desiccated specimens recovered from caves throughout New Zealand. Like modern ratites, moa plumage consisted of long, shaggy, and somewhat hair-like strands for insulation and repelling water. These birds possessed cryptic coloration which was adapted to camouflage them within their respective environments, much like modern kiwis or the Kakapo (Strigops habroptilus), a flightless New Zealand parrot. Base colors ranged from light yellowish-brown to reddish-brown and many feathers were tipped in white, which would have produced a mottled or speckled effect. Such coloration was ideal for concealment and likely evolved as a defensive measure against the keen-eyed flying predators with which these birds coevolved.

Characteristic morphology and color of moa feathers which are identified to
species via ancient DNA sequences. Feathers belong to (from left to right)
Upland Moa, South Island Giant Moa, Stout-legged Moa, and Heavy-footed
Moa. Figure 3 from Rawlence et al., 2009.

The nine known species of moa ranged in size from the diminutive Bush Moa (Anomalopteryx didiformis) to the large yet lanky South Island Giant Moa (Dinornis robustus); a range of 15 to 250kg. In addition, most species display female-biased sexual dimorphism (also known as "reverse dimorphism"), that is, the females grew noticeably larger than the males. For most moa, females typically ranged from 15 to 20% larger, which is typical of modern dimorphic ratites. Members of the genus Dinornis, however, display the most extreme dimorphism seen among any terrestrial vertebrate with females growing up to three times the mass of males. The size difference is so vast, in fact, that the male morph of both Dinornis species was once thought to be a species in its own right: called the Slender Moa (D. struthoides). DNA sequencing in 2003 has since corrected this mistake and several other formerly recognized moa 'species' which had been established based on size differences were also debunked.  

Comparison of coefficients of variation for femora lengths with male:female
body mass in moa. The relative size of male (blue) to females (pink) are given
for the genera Dinornis, Pachyornis, Euryapteryx, and Emeus.
Figure 3 in Huyen et al., 2003.

Part 1: Evolution & History
Part 3: Paleoecology

References & Further Reading
Huynen L, Suzuki T, Ogura T, Watanabe Y, Millar CD, Hofreiter M, Smith C, Mirmoeini S, Lambert DM (2014). "Reconstruction and in vivo analysis of the extinct tbx5 gene from ancient wingless moa (Aves: Dinornithiformes)". BioMed Central Evolutionary Biology 14:75 <Full Article>

Rawlence NJ, Wood JR, Scofield RP, Fraser C, Tennyson AJD (2013). "Soft-tissue specimens from pre-European extinct birds of New Zealand". Journal of the Royal Society of New Zealand DOI:10.1080/03036758.2012.704878 <Full Article>

Rawlence NJ, Wood JR, Armstrong KN, Cooper A (2009). "DNA content and distribution in ancient feathers and potential to reconstruct the plumage of extinct avian taxa". Proceedings of the Royal Society B 276: 3395-3402 <Full Article>

Huynen L, Millar CD, Scofield RP, Lambert DM (2003). "Nuclear DNA sequences detect species limits in ancient moa". Nature 425: 175-178 <Abstract>

Thursday, March 23, 2017

Heavy-footed Moa (Pachyornis elephantopus)

The Heavy-footed Moa (Pachyornis elephantopus) was the largest member of the genus Pachyornis and the third largest species of moa overall. This exceptionally heavily-built species lived in South Island during the Pleistocene and Holocene where it fed on relatively low-quality plant matter.

Heavy-footed Moa skeleton on display at the Exhibit Museum of
Natural History, University of Michigan. Wiki.

The genus name Pachyornis is derived from the Greek words pachys (meaning “thick”) and ornis (meaning “bird”), a reference to members of this genus being particularly heavily-built compared to other moa genera. The species name elephantopus is a combination of the Greek words elephas (meaning “elephant”) and pous (meaning “foot”). Its full scientific name therefore translates as “Elephant-legged Bird” in reference to this species’ robust skeleton with particularly thick limb elements, a trait which is further emphasized by common name “Heavy-footed Moa”.

Habitat & Distribution
Heavy-footed Moa had an extensive late Quaternary fossil record. Their preferred habitat appears to have been lowland to montane grassland, shrubland, herbfields, and forest margin environments in the eastern and southern parts of South Island. The altitudinal limit for this species appears to have been 700m above sea level as no fossils for it have been found above this point. Heavy-footed Moa underwent significant changes in relative abundance and distribution in response to environmental changes during the late Pleistocene and Holocene. Climatic and environmental fluctuations during glacial cycles caused its preferred habitat to expand and contract repeatedly, resulting in two genetically distinct populations in the northern and southern halves of South Island. Like all other moa, it held a relatively constant population size until the arrival of the Maori in the late 13th century.

Physical Attributes
The Heavy-footed Moa is the third largest species of moa behind both species of Dinornis and is the heaviest moa relative to its size. It stood up to 120cm tall at the hips and 180cm tall when fully erect and weighed up to 145kg, with females being larger than the males. The skeleton was robust with relatively thick leg bones and shortened tarsometatarsi (in birds, the foot bone formed by the fusion of the metatersals). This species is known from desiccated soft tissue remains recovered from cave sites which have preserved skin, tendons, and feathers. From these subfossil remains, we know that this species had shaggy, white-tipped feathers which would give the living animal a mottled or speckled appearance and that the skin of its lower legs were covered in non-overlapping scales like those of most birds. The beak was long, sturdy, and downturned and its overall head was shaped somewhat differently from other moa and was adapted to handle particularly tough vegetation.

Ecology & Behavior
Plant remains from within coprolites and among gizzard stones reveal that Heavy-footed Moa were generalized mixed-feeders with a diet consisting of at least 21 species of particularly fibrous grassland, shrubland, and forest margin vegetation. It grazed on various types of herbs and grasses and browsed on the branchlets of trees and shrubs. As with most of the larger moa species, the only predator of adult Heavy-footed Moa was the Haast’s Eagle (Harpagornis moorei) with the smaller Eyle’s Harrier (Circus eylesi) possibly feeding on the smaller juveniles. Evidence from coprolites further shows that this species hosted several types of taxa-specific parasites.

Heavy-footed Moa are thought to have been less abundant than other moa due to its less frequent representation in the fossil record. Females appear to outnumber males at natural fossil assemblages, suggesting that males were even less common in a given population. This relatively low number of males may be due to increased predation by Haast’s Eagles who likely targeted them more regularly due to their smaller size. Heavy-footed Moa eggs were among the largest of any moa and the only known moa embryos are also attributed to this species. The growth rate of this species is not known. It became extinct abruptly due to human overexploitation and habitat alteration.

References & Further Reading
Attard MRG, Wilson LAB, Worthy TH, Scofield P, Johnston P, Parr WCH, Wroe S (2016). "Moa diet fits the bill: virtual reconstruction incorporating mummified remains and prediction of biomechanical performance in avian giants". Proceedings of the Royal Society of London B 283: 20152043 <Full Article>

Wood JR, Wilmshurst JM, Richardson SJ, Rawlence NJ, Wagstaff SJ, Worthy TH, Cooper A (2013). "Resolving lost herbivore community structure using coprolites of four sympatric moa species (Aves: Dinornithiformes)". PNAS 110(42): 16910-16915 <Full Article>

Rawlence NJ, Wood JR, Scofield RP, Fraser C, Tennyson AJD (2013). "Soft-tissue specimens from pre-European extinct birds of New Zealand". Journal of the Royal Society of New Zealand DOI:10.1080/03036758.2012.704878 <Full Article>

Oskam CL, Allentoft ME, Walter R, Scofield RP, Haile J, Holdaway RN, Bunce M, Jacomb C (2012). "Ancient DNA analyses of early archaeological sites in New Zealand reveal extreme exploitation of moa (Aves: Dinornithiformes) at all life stages". Quaternary Science Reviews 52: 41-48 <Full Article>

Rawlence NJ, Metcalf JL, Wood JR, Worthy TH, Austin JJ, Cooper A (2012). "The effect of climate and environmental change on the megafaunal moa of New Zealand in the absence of humans". Quaternary Science Reviews 50: 141-153 <Full Article>

Allentoft ME, Bunce M, Scofield RP, Hale ML, Holdaway RN (2010). "Highly skewed sex ratios and biased fossil deposition of moa: ancient DNA provides new insight on New Zealand’s extinct megafauna". Quaternary Science Reviews 29: 753–762 <Abstract>

Huynen L, Gill BJ, Millar CD, Lambert DM (2010). "Ancient DNA reveals extreme egg morphology and nesting behavior in New Zealand’s extinct moa". Proceedings of the National Academy of Science 107(37): 16201-16206 <Full Article>

Wood JR, Rawlence NJ, Rogers GM, Austin JJ, Worthy TH, Cooper A (2008). "Coprolite deposits reveal the diet and ecology of the extinct New Zealand megaherbivore moa (Aves, Dinornithiformes)". Quaternary Science Reviews 27: 2593–2602 <Abstract>

TH Worthy (1990). "An analysis of the distribution and relative abundance of moa species (Aves: Dinornithiformes)". New Zealand Journal of Zoology 17(2): 213-241 <Full Article>