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Comparative Osteology Online

Online resources for the appreciation and comparison of vertebrate (especially tetrapod) skeletons.

Introduction

Pierre Belon's 1555 comparative osteology illustrationThe comparison of vertebrate skeletons is one of the best ways to understand the ways of life, evolutionary histories, and deep relationships within this group of animals - a group in which we of course have membership.

As early as 1555, when Pierre Belon included the illustration at right in his L'Histoire de la nature des oyseaux (Natural History of Birds), it has been recognized that only after stripping away the feathers, scales, fur, and flesh does it become apparent how much apes and birds have in common, and how remarkably similar we are to creatures as different as bats and whales.

This guide organizes an array of resources - all accessible online - to support and encourage the investigation of this fascinating subdiscipline of zoology and anatomy.

Background Information

undefinedThe story of the vertebrates begins hundreds of millions of years ago, in Cambrian seas that may have looked something like the reconstruction at right (from the Smithsonian Institution).

The articles below, from the Routledge Encyclopedia of Paleontology, available online through Credo Reference, provide some background information about the origins of skeletons (which are not unique to vertebrates!) and the general body form the vertebrates inherited from their chordate ancestors. 

Skeletized Organisms and the Origin of Skeletized Tissues

"Skeletized tissues are tissues reinforced by structural materials. Although the uses of skeletons vary widely (e.g., protection, support, locomotion, feeding), the basic functions of skeletization are to make the tissue stiffer (less prone to deformation), tougher (less prone to tearing), or harder (less susceptible to abrasion)." Read more...

Chordate and Vertebrate Body Structure

"The primary characteristics of chordates originated as their Precambrian ancestors adapted to an active life in water. Chordates have an elongate body with distinct head and tail, bilateral (left-and-right-side) symmetry, and dorsoventral (back-to-belly) orientation—all of which favor efficient forward movement." Read more...

undefinedUnderstanding the common origin and shared features of the basic elements common to all vertebrates makes comparison of their structures both easier to conduct and more remarkable to contemplate. The below articles from the Routledge Encyclopedia of Paleontology, online through Credo Reference, cover these basic skeletal domains.

The Skull

"In vertebrates, structures that protect the brain and sense organs, based on a complex arrangement of hard tissue elements, are important. Protochordate animals (those from which the vertebrates are derived) had limited sense organs and small brains that had little or no special support or protection." Read more...

The Axial Skeleton

"The structure and evolution of the vertebral column and its associated structures has been a central theme in vertebrate paleontology." Read more...

Fins and Limbs, Paired

"Fingers and toes have long been considered unique features of tetrapods (amphibians, reptiles, mammals, and birds). As a result, limbs often are viewed as the major characteristic that separates tetrapods from virtually all known types of fishes." Read more...

What methods of thinking are used to draw comparisons between skeletons, and what is done with this knowledge once it is generated? The articles below offer just a few answers to these questions. The first two are from the Routledge Encyclopedia of Paleontology, while the latter two come from the Elsevier Encyclopedia of Archaeology. All are available online through Credo Reference. 

Comparative Anatomy

"Comparative anatomy is the study of similarities and differences in body structure among organisms, usually to understand form, function, variation, and evolutionary relationships. " Read more...

Functional Morphology

"The aim of a functional morphologist is to assess how fossil animals functioned as living machines." Read more...

Archaeozoology

"Zooarchaeologists study animal remains from archaeological sites. The combination of anthropological, archaeological, biological, ecological, and paleontological research focused on animal remains is a defining characteristic of the discipline." Read more...

Vertebrate Analysis

"Identification of archaeologically recovered vertebrate specimens is fundamental to all subsequent zooarchaeological analysis. The task begins with osteological identification within the framework of zoological classification, and also includes recognizing the many possible factors that can influence how our study assemblage preserved" Read more...

 

Classic Works and Illustrations

Before photography and other imaging technology, the only way to illustrate and communicate evidence from osteological specimens was by drawing. These slides show some examples of incredible skeletal illustration and include links to the original works, all available in digitized form online. 

The walrus below comes from Henri-Marie Ducrotay de Blainville's impressively titled Ostéographie, ou, Description iconographique comparée du squelette et du système dentaire des Mammifères récents et fossiles,  published over the course of 25 years starting in 1839. 

Portions of the complex multipart publication digitized by the Internet Archive are brought together reasonably well by the Biodiversity Heritage Library, and a selection of plates may also be seen at the National Library of Medicine History of Medicine Division's Historical Anatomies on the Web exhibit.

de Blainville, walrus skeleton

In 1860 Benjamin Waterhouse Hawkins published his Comparative View of the Human and Animal FrameHawkins used his artistic skill to create scenes in which skeletons of human and other mammalian species took similar poses, allowing for direct and naturalistic comparison of the bones of the respective species. The image below compares humans and camels. That Hawkins was also a serious anatomist in addition to a great artist is evidenced by the insightful written descriptions that accompany his plates. 

Hawkins, comparative view, human and camel

Leter, Benjamin Waterhouse Hawkins joined forces with Thomas Henry Huxley, the biologist and famously vigorous supporter of Darwin, to form a sort of osteological superteam, and in 1864 they released the spectacular Elementary Atlas of Comparative Osteology in Twelve Plates. Plate VI, below, depicts an array of vertebrae, beautifully and fearfully sculpted through eons of selection. 

Huxley and Hawkins, atlas of comparative osteology, Plate VI (vertebrae)

Another wonderful plate from Hawkins and Huxley. This one, plate IX, compares the forelimb skeletons of a number of mammals, birds, and non-avian reptiles.

Huxley and Hawkins, Plate IX, forelimbs

This schematic illustration of a generalized mammal skull from William Henry Flower's 1876 Introduction to the Osteology of the Mammalia resembles something out of a technical manual. Its simplified forms encourage a conceptualization of the mammal skull that allows one to see the affinities and commonalities (derived from common ancestry) underlying the distinct forms of members of the class.

As this illustration of a wolverine skull and teeth shows, Edmond Hue's 1907 Musée ostéologique étude de la faune quaternaire does a particularly good job of representing dentition, portraying its subjects' teeth in an orderly array in both side and top views. The available reproductions were made by Google so the quality is a bit dodgy, but they're still worth a look. Scans may be viewed on HathiTrust

Edmond Hue, 1907, wolverine skull and dentition

The left page below from Sidney Reynolds' 1913 The Vertebrate Skeleton makes use of the technique, also used in mechanical drawing, of 'exploding' this green sea turtle skull to render visible portions that would otherwise be obscured in the point of view depicted. This method has been employed using newer visualization technology as well (see below, in 3d Models). A section of this same species' skull appears in the page at right below. 

Reynolds, green sea turtle skull

3D Models

The advent of computing brought about the next great wave of osteological visualization in the form of 3d modeling. In some cases, these models are arguably able to convey even more information than would an examination of the physical originals, especially if viewed only in a museum case. This gallery shares some interesting informative innovations used in 3d modeling and provides links to free collections of 3d osteological models online. 

Digital Morphology, or DigiMorph, is hosted at UT Austin and is part of the National Science Foundation Digital Libraries Initiative. It is probably the premier online site for 3d visualizations of vertebrate skeletons and skeletal components.

The skull below appears birdlike - but is it a bird? Click on the animation to learn which creature has this curious cranium.

Credit: Dr. Ted Macrini, 2004, "Zaglossus bartoni" (On-line), Digital Morphology. Accessed May 4, 2020 at http://digimorph.org/specimens/Zaglossus_bartoni/.

Other collections may not match DigiMorph in the extent of their holdings or the depth of their accompanying information, but have added features like manipulability and naturalistic surface coloring.

The Osteologic Atlas from the Museu de Ciències Naturals de Barcelona offers a variety of 3d osteological models, primarily of the skulls and mandibles of mammals and birds. The skull below is of a male hammerhead bat. 

Hammerhead bat skull 3d model

A brown-throated three-toed sloth skull, also from the Museu de Ciències Naturals de Barcelona, showing the remarkable zygomatic bones (cheekbones), which flare out and back from the forward part of the skull and do not reconnect. The 3d model offers particularly useful perspectives for examining these and other unique formations.

3d model of brown-throated three-toed sloth skull

Some institutions create 3d models not only of skulls or other skeletal units, but of entire skeletons. The Idaho Virtual Museum has some examples of this among its collection of 3d models, which is particularly strong in mammals and birds.

The humpback whale whose skeleton was used to create the model below was 44 years old and pregnant when she was struck and killed by a cruise ship in Glacier Bay, Alaska.

3d model, humpback whale skeleton

This image, also from a model from Idaho Virtual Museum, illustrates the particular utility of the 3d model for examining skeletons. From within the shell of a leopard tortoise, it looks out along the spine towards the skull, showing how the shoulders are suspended from and encased within the shell. 3d modeling makes available lines of sight that might be impossible even when examining a physical specimen in one's hand. 

3d model, leopard tortoise skeleton

The University of Dundee in Scotland has a collection of 3d models that is kind of a hodgepodge, with some items with wonderful surface detail like this delightfully strange skull of a dugong. This species is the closest living relative of the great Steller's sea cow.

3d model, dugong skull

The Museum für Naturkunde Berlin has a wonderful collection of 3d ungulate skull models, like this Abyssinian mohr, a kind of gazelle. 

3d model, Abyssinian mohr skull

In addition to an excellent collection of amphibian and non-avian reptile models, the Blackburn Lab at the University of Florida's Florida Museum of Natural History also has a fine selection of forelimb models with each bone color-coded for easy comparison between species. Contrasted below are the forelimbs of a snowy egret (left) and a star-nosed mole (right). The bones are (almost) all the same, conserved from a common ancestor, but alterations in relative size and shape result in very different outcomes and utilities. 

The Witmer Lab at Ohio University employs some interesting features in their 3d models, including embedded vasculature and brain models and, most engagingly, the use of animation. Below are stills from an animation showing how moveable bones in the upper skull of the scarlet macaw allow for a greater range of motion for its bill through a phenomenon called 'cranial kinesis.' The effect is most pronounced in the animation itself, so click on the image below and have a watch. 

In a recapitulation of the method employed by Reynolds with the green sea turtle skull above, the Witmer Lab animation of which stills are shown below 'explodes' the human skull to show its constituent components, reminding us that our skull is in fact made of a large number of individual bones, and in many other species these bones remain functionally distinct and capable of moving in isolation.

3d model 'exploding' human skull