Michael Wayne Caldwell

Michael Wayne Caldwell
University of Alberta | UAlberta · Department of Biological Sciences and Department of Earth and Atmospheric Sciences

Ph.D, B.Sc., B.P.Ed., FRCGS

About

274
Publications
74,043
Reads
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Introduction
I am an evolutionary biologist and systematist who uses data from the fossil record of squamate reptiles blended with data from the modern fauna to address questions on the deep evolution of these tetrapods. I am particularly interested in snake lizards and the marine lizard group known as mosasaurs and their extinct kin. However, my research questions are expanding to other clades of squamates as my grad students and postdoctoral fellows move forward on new research problems. I have also developed a long term research program on the evolution and development of teeth in squamates that has moved well beyond these animals and is now investigating the origins of teeth in vertebrates broadly speaking.
Additional affiliations
July 2008 - June 2019
University of Alberta
Position
  • Chair
July 2000 - present
University of Alberta
Position
  • Professor
April 1998 - present
Canadian Museum of Nature / Musée canadien de la nature
Position
  • Research Scientist/Research Associate
Education
September 1991 - November 1995
McGill University
Field of study
  • Vertebrate Paleontology
September 1987 - April 1991
University of Alberta
Field of study
  • Vertebrate Paleontology
September 1982 - April 1986
University of Alberta
Field of study
  • Physical Education and Sport Studies

Publications

Publications (274)
Article
Squamates present a unique challenge to the homology and evolution of tooth attachment tissues. Their stereotypically pleurodont teeth are fused in place by a single “bone of attachment”, with seemingly dubious homology to the three‐part tooth attachment system of mammals and crocodilians. Despite extensive debate over the interpretations of squama...
Article
Snakes—a subset of lizards—have traditionally been divided into two major groups based on feeding mechanics: "macrostomy," involving the ingestion of proportionally large prey items; and "microstomy," the lack of this ability. "Microstomy"—considered present in scolecophidian and early-diverging alethinophidian snakes—is generally viewed as a sympl...
Article
Full-text available
Snake fangs are an iconic exemplar of a complex adaptation, but despite striking developmental and morphological similarities, they probably evolved independently in several lineages of venomous snakes. How snakes could, uniquely among vertebrates, repeatedly evolve their complex venom delivery apparatus is an intriguing question. Here we shed ligh...
Article
The origin of snakes remains one of the most contentious evolutionary transitions in vertebrate evolution. The discovery of snake fossils with well-formed hind limbs provided new insights into the phylogenetic and ecological origin of snakes. In 2015, a fossil from the Early Cretaceous Crato Formation of Brazil was described as the first known snak...
Article
The Antarctic plesiosaurian record is critical for understanding the evolution of elasmosaurids in the southern hemisphere. Elasmosaurids exhibit some of the most remarkable modifications of the vertebrate axial skeleton given their extreme elongation of the cervical region. Despite a considerable amount of information available on vertebral counts...
Article
Amblyrhynchus cristatus, the marine iguana, is unique amongst the ~7000 species of living limbed lizards as it has successfully evolved adaptations that allow it to live in both terrestrial and marine environments. This species is endemic to the Galápagos Archipelago and has evolved a specialized feeding behaviour, consuming primarily the algae tha...
Article
Full-text available
Mosasaur researchers have used varieties of tooth crown ornamentation as diagnostic and phylogenetic characters for decades. Such tooth crown features include facets, flutes, striations, serrated carinae, and coarse anastomosing texture. is study investigates the relative contributions of dentine and enamel to the development of these dental charac...
Article
FHSM VP-5515 is a medium-sized russellosaurine mosasaur collected in the 1970s in Logan County, western Kan-sas, USA. A suite of cranial features are unique to this specimen at the species level. One is a conspicuous lack of a predental rostrum on the premaxilla, whose dentigerous portion is spatula shaped in dorsoventral aspect. Furthermore, the f...
Article
Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Article
We examined a selection of three-dimensionally preserved quadrate bones from representatives of all major clades of mosasauroid reptiles, an extinct group of marine lizards inclusive of aigialosaurs and mosasaurs (Squamata, Mosasauroidea). The quadrate bones appear to be very diverse within and across mosasauroid clades, and show variable combinati...
Preprint
Full-text available
Comparative osteological analyses of extant organisms provide key insight into major evolutionary transitions and phylogenetic hypotheses. This is especially true for snakes, given their unique morphology relative to other squamates and the persistent controversy regarding their evolutionary origins. However, the osteology of several major snake gr...
Article
Comparative osteological analyses of extant organisms provide key insight into major evolutionary transitions and phylogenetic hypotheses. This is especially true for snakes, given their unique morphology relative to other squamates and the persistent controversy regarding their evolutionary origins. However, the osteology of several major snake gr...
Article
Full-text available
Background The vast majority of all life that ever existed on earth is now extinct and several aspects of their evolutionary history can only be assessed by using morphological data from the fossil record. Sphenodontian reptiles are a classic example, having an evolutionary history of at least 230 million years, but currently represented by a singl...
Article
The Upper Cretaceous phosphates of Morocco preserve one of the world’s most diverse assemblages of mosasaurs, reflecting the adaptive radiation of this clade during the Maastrichtian. Herein, we describe a new mosasaur from these deposits. Although the teeth of this specimen resemble those of ‘Platecarpus’ ptychodon, suggesting referral to this spe...
Article
Full-text available
The origin of phenotypic diversity among higher clades is one of the most fundamental topics in evolutionary biology. However, due to methodological challenges, few studies have assessed rates of evolution and phenotypic disparity across broad scales of time to understand the evolutionary dynamics behind the origin and early evolution of new clades...
Article
Full-text available
Squamates have an extremely long evolutionary history with a fossil record that extends into the Middle Triassic. However, most of our knowledge of their early evolutionary history is derived from Laurasian records. Therefore, fundamental questions regarding the early evolution of squamates in the Southern Hemisphere, such as the origins of the ext...
Preprint
Full-text available
Adaptive radiations are long believed to be responsible for the origin of phenotypic diversity and new body plans among higher clades in the fossil record. However, few studies have assessed rates of phenotypic evolution and disparity across broad scales of time to understand the evolutionary dynamics behind the origin of major clades, or how they...
Article
Mammals and reptiles have evolved divergent adaptations for processing abrasive foods. Mammals have occluding, diphyodont dentitions with taller teeth (hypsodonty), more complex occlusal surfaces, continuous tooth eruption, and forms of prismatic enamel that prolong the functional life of each tooth [1, 2]. The evolution of prismatic enamel in part...
Data
Masson’s trichrome staining protocol used for the soft tissue histology
Article
The development of the iliosacral joint (ISJ) in tetrapods represented a crucial step in the evolution of terrestrial locomotion. This structure is responsible for transferring forces between the vertebral column and appendicular skeleton, thus supporting the bodyweight on land. However, most research dealing with the water‐to‐land transition and b...
Data
Life restoration of the legged snake Najash from the Cretaceous of Patagonia (by Raúl Orencio Gómez)
Article
Full-text available
Despite being known from every continent, the geological record of pterosaurs, the first group of vertebrates to develop powered flight, is very uneven, with only a few deposits accounting for the vast majority of specimens and almost half of the taxonomic diversity. Among the regions that stand out for the greatest gaps of knowledge regarding thes...
Article
Full-text available
Snakes represent one of the most dramatic examples of the evolutionary versatility of the vertebrate body plan, including body elongation, limb loss, and skull kinesis. However, understanding the earliest steps toward the acquisition of these remarkable adaptations is hampered by the very limited fossil record of early snakes. Here, we shed light o...
Article
We report the first example of ossified pelvic vestiges in an anomalepidid snake, Liotyplophs beui, and provide a review of the diversity of limb and pelvic elements within Serpentes. We trace the evolution, homology and reduction of the pelvic elements and hindlimbs from the oldest known snakes through to living forms. Evolutionary analysis of the...
Article
We report the first example of ossified pelvic vestiges in an anomalepidid snake, Liotyplophs beui, and provide a review of the diversity of limb and pelvic elements within Serpentes. We trace the evolution, homology and reduction of the pelvic elements and hindlimbs from the oldest known snakes through to living forms. Evolutionary analysis of the...
Article
We examined the morphological diversity of the quadrate bone in squamate reptiles (i.e. lizards, snakes, amphisbaenians). The quadrate is the principal splanchnocranial element involved in suspending the lower jaw from the skull, and its shape is of particular interest because it is potentially affected by several factors, such as phylogenetic hist...
Article
Full-text available
Non-ophidian ophidiomorphs, colloquially referred to as ‘dolichosaurs,’ are small-bodied aquatic lizards that lived in shallow seaways, rivers, and reef environments during the Late Cretaceous. Preservational, geographic, and taphonomic biases in this group make trends in biodiversity difficult to assess. This is exemplified by the fact that the ma...
Article
Full-text available
The early evolution of lepidosaurs is marked by an extremely scarce fossil record during the Triassic. Importantly, most Triassic lepidosaur specimens are represented by disarticulated individuals from high energy accretion deposits in Laurasia, thus greatly hampering our understanding of the initial stages of lepidosaur evolution. Here, we describ...
Article
Full-text available
Accurate knowledge of skeletal ontogeny in extant organisms is crucial in understanding important morpho-functional systems and in enabling inferences of the ontogenetic stage of fossil specimens. However, detailed knowledge of skeletal ontogeny is lacking for most squamates, including snakes. Very few studies have discussed postnatal development i...
Article
The reassessment of a lower jaw fragment of a mosasaur from the upper Maastrichtian of central Chile(Q.3105) indicates that the specimen does not belong to Plotosaurus, as previously suggested by Frey et al.in 2016. The specimen does not show the characteristics of Plotosaurus, such as the long projection anterior to the anteriormost tooth socket o...
Article
A new genus and species of plesiopedal mosasauroid, Portunatasaurus krambergeri, from the Cenomanian–Turonian (Late Cretaceous) of Croatia is described. An articulated skeleton, representing an animal roughly a meter long was found in 2008 on the island of Dugi Otok. The specimen is articulated, in approximate life position, and is well represented...
Article
Full-text available
Durophagous mosasaurs are rare members of Late Cretaceous marine faunal assemblages and new fossil discoveries can shed light on their anatomy, functional morphology and evolutionary history. Here we describe a new species in the durophagous genus Globidens from the Maastrichtian phosphate deposits of Morocco, based on a partial disarticulated skul...
Article
Full-text available
Tylosaurinae (Williston, 1897), is reconstructed in most analyses as the sister group of the Plioplatecarpinae (Dollo, 1884). The most distinctive characteristic of the group is an elongated edentulous rostrum on the premaxilla. Members of the tylosaurine subfamily are divided into two genera: Tylosaurus (Marsh, 1874), and Taniwhasaurus (Hector, 18...
Article
The limbed snake Najash rionegrina from the Cenomanian (early Late Cretaceous) of the La Buitrera Palaeontological Area (LBPA), northern Patagonia is a key taxon in any study of the origin and early evolution of snakes. The original concept of the taxon was based on the holotype and a number of referred specimens including an isolated partial skull...
Article
Full-text available
Snakes are an extremely modified and long-lived clade of lizards that have either lost or highly altered many of the synapomorphies that would clearly link them to their closest sister-group among squamates. We focus here on one postcranial morphological complex, the intercentrum system which in most non-ophidian squamates is limited to the cervica...
Article
Full-text available
Teeth and dentitions contain many morphological characters which give them a particularly important weight in comparative anatomy, systematics, physiology and ecology. As teeth are organs that contain the hardest mineralized tissues vertebrates can produce, their fossil remains are abundant and the study of their anatomy in fossil specimens is of m...
Article
Full-text available
Understanding the origin and early evolution of squamates has been a considerable challenge given the extremely scarce fossil record of early squamates and their poor degree of preservation. In order to overcome those limitations, we conducted high-resolution X-ray computed tomography (CT) studies on the fossil reptile Megachirella wachtleri (Middl...
Article
We here report on the smallest-known, neonate-sized Tylosaurus specimen, FHSM VP-14845, recovered from the lower Santonian portion of the Niobrara Chalk exposed in Kansas, U.S.A. Lacking any associated adult-sized material, FHSM VP-14845 comprises fragmentary and associated cranial bones, here considered to represent a single neonatal individual wi...
Article
Full-text available
We present the first known fossilized snake embryo/neonate preserved in early Late Cretaceous (Early Cenomanian) amber from Myanmar, which at the time, was an island arc including terranes from Austral Gondwana. This unique and very tiny snake fossil is an articulated postcranial skeleton, which includes posterior precloacal, cloacal, and caudal ve...
Article
Full-text available
A new marine lizard showing exceptional soft tissue preservation was found in Late Cretaceous deposits of the Apulian Platform (Puglia, Italy). Primitivus manduriensis gen. et sp. nov. is not only the first evidence of the presence of dolichosaurs in a southern Italian Carbonate Platform, filling a palaeogeographic gap in the Mediterranean Tethys,...
Article
Mosasaurs assigned to the genus Tylosaurus have been reported from the North Atlantic Circle Basin, including the Western Interior Seaway in North America and Europe, from the Turonian of Chihuahua, Mexico, to the early Maastrichtian of Belgium. The youngest record of Tylosaurus in North America is from the middle Campanian of the Pierre Shale, Sou...
Article
Full-text available
Modern squamates (lizards, snakes and amphisbaenians) are the world's most diverse group of tetrapods along with birds 1 and have a long evolutionary history, with the oldest known fossils dating from the Middle Jurassic period-168 million years ago2-4. The evolutionary origin of squamates is contentious because of several issues: (1) a fossil gap...
Article
Full-text available
Madtsoiids are among the most basal snakes, with a fossil record dating back to the Upper Cretaceous (Cenomanian). Most representatives went extinct by the end of the Eocene, but some survived in Australia until the Late Cenozoic. Yurlunggur and Wonambi are two of these late forms, and also the best-known madtsoiids to date. A better understanding...
Article
The transparency of soft tissue in Xenopus laevis tadpoles and the anterior-posterior orientation of their developing tooth germs in the upper jaw offer a unique opportunity for the in vivo charting of the first 15–20 days of the developing dentition. Twenty-two X. laevis tadpoles were anesthetized daily and their mouths opened to record the first...