Wednesday, April 24, 2019

Avian Cnemial Crest

Birds have several mechanisms for aquatic locomotion. Two types of propulsion are employed by divers, this by use of their wings or legs. Underwater use of wings is seen in species such as penguins and auks, whereas foot-propulsion is utilized by loons, grebes and some waterfowl. 

Suggestions of an aquatic lifestyle are often noted in a bird’s skeletal features, especially when fossil interpretation is concerned. 

An Early Cretaceous taxon for which a more aquatic lifestyle is strongly established is in Gansus yumenensis, from the lacustrine deposits of the Xiagou Formation in Gansu Province in China (source: Mayr G. Avian Evolution. 2017).

Gansus is commonly mentioned to possess long feet, which were used aptly for hindlimb propulsion. But the strongest evidence for this type of aquatic behavior may lie in the elongated cnemial crest of the tibiotarsus.

The cnemial crest is a crest-like prominence located at the front side of the head of the tibiotarsus or tibia in the legs of birds and other dinosaurs.

Avian Cnemial Crest Diagram
From Manual of Ornithology, N.S. Proctor 1993.
The crest is most highly developed in the loons and grebes in which it partly encircles the knee joint (Source: Avian Osteology). The greatly elongated cnemial crest serves to enlarge the insertion sites of the hypertrophied leg muscles (source: Mayr G. Avian Evolution. 2017). The main extensor muscle of the thigh is attached to this ridge.

Cnemial crest of an extant loon.
From; Mayr G Avian Evolution. 2017
Surprisingly, the evolutionary relationship between loons, grebes and fossil birds is often found, and better understood, within the development of the crest itself. 

Paleontologist Sankar Chatterjee explains this in his 2006 paper; The Morphology and Systematics of Polarornis, a Cretaceous Loon (Aves: Gaviidae) from Antarctica.  

“The long cnemial crest of Polarornis clearly indicates its foot-propelled diving adaptation. Although Polarornis superficially resemble grebes and hesperornithiforms in the mechanical design of the hindlimbs, the way in which the cnemial crest is developed among different foot-propelled diving birds may be an important phylogenetic character. The cnemial crest of the loon is derived solely from the tibiotarsus, but the patella is lacking. In Hesperornis, the cnemial crest evolved from the development and expansion of the patella. In grebes, on the other hand, both patella and tibiotarsus contribute to the formation of the cnemial crest. If these diving birds were closely related, it is unlikely that the formation of this structure would have evolved along such a very different pathway. It is likely that loons, grebes, and hesperornithiform birds are purely convergent in their adaptations and did not share a common ancestry.”

Morphological variations of cnemial crest among diving birds. 
From; The Morphology and Systematics of Polarornis. Chatterjee, 2006 
Name: Extensor digitorum longus. Origin: Anterior surface of the proximal tibiotarsus. Insertion: Distal phalanges of the digits. Action: Extends the digits.
Proctor, N.S. (1993) Manual of Ornithology: Avian Structure and Function. (See below)

Avian cnemial crest 
From Proctor N.S. (1993) Manual of Ornithology

Avian extensor digitorum longus muscle 
From Proctor N.S. (1993) Manual of Ornithology

Friday, April 12, 2019

Avian Pachyostotic Bones; seeking a clear definition.

The gap between amateur and professional ornithologist is often painfully apparent to me, especially when wording is concerned.

This was the situation the other evening while I was reading Gerald Mayr’s 2017 book, Avian Evolution; The Fossil Record of Birds and its Paleo-biological Significance. In it, I came upon a peculiar word that I never saw, or heard of before.

Mayr starts by writing that the foot-propelled hesperornithiforms were highly specialized diving birds and mainly occurred in the northern latitudes of the Northern Hemisphere, most of which were flightless and lived in marine environments. 

Hesperornis regalis
Photo Credit: Paul Cianfaglione
Within hesperornithiforms a large size was gained several times independently, and in particular some species, like the Late Cretaceous Hesperornis were very large, reaching a length of 1.5 meters.

As an adaptation for their diving habits, the limb bones of hesperornithiforms are pachyostotic; that is, they have very thick bone walls. Pachyostotic bones also occur in other flightless diving birds, such as penguins, and reduce buoyancy by increasing the weight of the bird (source: Mayr, G. 2017 Avian Evolution). 

Pachyostotic, or Pachyostosis, is further described as a non-pathological condition in vertebrate animals in which the bones experience a thickening, generally caused by extra layers of lamellar bone. It often occurs together with bone densification (osteosclerosis), reducing inner cavities. This joint occurrence is called pachyosteosclerosis. However, especially in the older literature, "pachyostosis" is often used loosely, referring to all osseous specializations characterized by an increase in bone compactness and/or volume (source: Wikipedia).

Removed from the definition of Pachyostosis are two related words, including osteosclerosis and pachyosteosclerosis.

Frustrated, I decided to look deeper into other researcher’s scientific work, and see how they used and defined these terms regarding high bone compactness.

One paper I found titled; Osteosclerosis in the Extinct Cayaoa bruneti (Aves, Anseriformes): Insights on Behavior and Flightlessness (De Mendoza and Tambussi 2015), provided a slightly different description of bone histology in extant and extinct birds.    

De Mendoza and Tambussi write;

“There is a strong association between bone micro-anatomy and lifestyle. In general terms, divers have skeletons with greater bone density due to a thickening of the cortex by higher deposition of periosteal bone which is known as pachyostosis. There may be also a reduction in the medullary resorption, a process called osteosclerosis. Both of these processes may occur in combination.”

“Among wing-propelled divers, several studies showed that penguins have highly osteosclerotic limbs (Ksepka, 2007; Meister, 1962; Cerda et al., 2014). Such high osteosclerosis levels were also verified in foot-propelled divers such as the Cretaceous flightless bird Hesperornis (Marsh, 1872) and the Antarctic Cretaceous loon Polarornis gregorii (Chatterjee, 2002).” 

Even more uncertain was information provided in the 2015 paper, Bone Histology in Extant and Fossil Penguins (Aves: Sphenisciformes), by Daniel T Ksepka. He writes; High bone density in penguins results from compaction of the internal cortical tissues, and thus penguin bones are best considered osteosclerotic rather than pachyostotic.

The author also mentions that penguin limb bones differ from those of nearly all other birds in their greater bone density, near complete lack of pneumatization, unusually thick periosteum and greatly reduced medullary cavities. 

Bone Regions
Image Property:
Thick periosteum and greatly reduced medullary cavities? To the average reader like myself, the last sentence sounds a bit ambivalent, but Ksepka goes on to elaborate by stating;

“The bone structure of penguins has been variably referred to as pachyostotic (Meister, 1962; Mayr, 2005; Ksepka et al. 2006; Livezey & Zusi, 2006), osteosclerotic (de Ricqlès & de Buffrénil, 2001; Ksepka et al. 2008; Cerda et al. 2015) or pachyosteoscleortic (Houssaye, 2009). The term pachyostotic does not apply to penguins, because they do not exhibit periosteal hyperplasy: the external dimensions of the hind limb bones of penguins remain unexpanded, with hind limb bone cross-sectional area remaining within the range observed in similarly sized volant birds (DTK personal observation). Comparisons of the external dimensions of wing bones between penguins and volant birds are more difficult due to the highly flattened and shortened morphology of the penguin flipper. However, Meister (1962) demonstrated that the extremely high bone density of the penguin humerus is achieved solely through compaction of the internal tissues, without expansion of the external circumferential layer. This finding was further supported by observations from an ontogenetic series of Aptenodytes patagonicus specimens by Canoville (2010). Thus, the term ‘osteosclerotic’ is more accurately applied to penguin limb bones (de Ricqlès & de Buffrénil, 2001).”

It is also important to point out why this condition is important to certain bird species. Ksepka continues;

“Dense bone commonly has been interpreted as a means of reducing buoyancy and thus conserving energy during diving (e.g. Nopcsa, 1923; Wall, 1983; Lovvorn et al. 1999). Additionally, increased thickness of the limb bone cortices can enhance resistance to bending or torsional loads, which are substantially higher in wing-propelled diving relative to most conditions encountered during aerial flight (Habib & Ruff, 2008). Because extant penguin wing bones exhibit cortical thickness far above that required for bending resistance alone, it is plausible that this increase in thickness serves both to increase ballast and to increase resistance (Habib, 2010).”

Below is a comparison in weight of two similar sized bones; the humerus of a Miocene Banded Penguin (Spheniscus urbinai), the other of a Pleistocene Wild Turkey (Meleagris gallopavo). Despite the penguin bones smaller dimensions, its weight is nearly double that of the turkeys. 

Banded Penguin and Wild Turkey Humerus
Photo Credit: Paul Cianfaglione
Banded Penguin Humerus Weight in Grams
Photo Credit: Paul Cianfaglione
Wild Turkey Humerus Weight in Grams
Photo Credit: Paul Cianfaglione

Wednesday, April 10, 2019

Avian Inspired Poems. The Cedar-Bird (Cedar Waxwing).

Avian Inspired Poems. The Cedar-Bird (Cedar Waxwing).

Inspired by such works as Land-Birds and Game-Birds of New England by H.D. Minot (1877) and The Birds of New England by Edward A. Samuels (1870), is my attempt to bring their long-forgotten words, and place in time, back to life through a series of short poems and images. 

The Birds of New England by Edward A. Samuels (1870)

Common name in 1877:   The Cedar-Bird

Common name in 2019:   Cedar Waxwing, (Bombycilla cedrorum)

1938 Arm & Hammer Useful Birds of America Series

The Cedar-Bird

Footpaths lined with ornamentals, don their mellow fruits. 

The Cedar-Bird is not a songster, in silence they often loot.

Social are these olive birds, they feast and have their fill.

Returning to the biting sky, with grace and much free will.

Cedar Waxwing (Bombycilla cedorum) 
Photo Credit: Paul Cianfaglione
Cedar Waxwing (Bombycilla cedorum)
Photo Credit: Paul Cianfaglione

Friday, April 5, 2019

Great Blue Heron (Ardea Herodias) Rookery

Here are a couple images from last evening at a local Great Blue Heron (Ardea herodias) rookery.

Great Blue Heron (Ardea herodias) building nest
Photo Credit: Paul Cianfaglione

Great Blue Herons nest communally in "rookeries" or "heronries" containing up to 50 pair. Herons typically use the same rookery every year until eventually the trees collapse.

Great Blue Heron (Ardea Herodias) building nest
Photo Credit: Paul Cianfaglione
Great Blue Heron (Ardea Herodias) nest
Photo Credit: Paul Cianfaglione

The nests are flat platforms made of sticks and lined with moss, pine needles, and other leaf material. The nests are added to each year, eventually becoming very bulky and measuring up to four feet in diameter.


Wednesday, April 3, 2019

Effects of the increased Use and Disuse of Parts, as controlled by Natural Selection. Avian Darwin.

Effects of the increased Use and Disuse of Parts, as controlled by Natural Selection. Avian Darwin. 


“From the facts alluded to in the first chapter, I think there can be no doubt that use in our domestic animals has strengthened and enlarged certain parts, and disuse diminished them; and that such modifications are inherited. Under free nature, we have no standard of comparison, by which to judge of the effects, of long-continued use or disuse, for we know not the parent-forms; but many animals possess structures which can be best explained by the effects of disuse. As Professor Owen has remarked, there is no greater anomaly in nature than a bird that cannot fly; yet there are several in this state. The logger-headed duck of South America can only flap along the surface of the water, and has its wings in nearly the same condition as the domestic Aylesbury duck: it is a remarkable fact that the young birds, according to Mr. Cunningham, can fly, while the adults have lost this power. As the larger ground-feeding birds seldom take flight except to escape danger, it is probable that the nearly wingless condition of several birds, now inhabiting or which lately inhabited several oceanic islands, tenanted by no beast of prey, has been caused by disuse. The ostrich indeed inhabits continents, and is exposed to danger from which it cannot escape by flight, but it can defend itself by kicking its enemies, as efficiently as many quadrupeds. We may believe that the progenitor of the ostrich genus had habits like those of the bustard, and that, as the size and weight of its body were increased during successive generations, its legs were used more, and its wings less, until they became incapable of flight” 

Logger-headed Duck (Tachyeres brachypterus) aka Falkland Steamer Duck
Image Property of: Wikipedia

Charles Darwin

Origin of Species; 1873.

Chapter 6, page 108, Effects of the increased Use and Disuse of Parts, as controlled by Natural Selection.

First edition in which Darwin uses the word evolution. This was also the last edition published during Darwin's lifetime.