G. Lawrence Powell

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• Ph.D.
• Sessional Lecturer at University of Calgary

Lizards of the genus Phrynosoma are distinguished from all other lizards by the presence of an array of cranial horns, but until recently, these have largely been considered to be homologous only in the aggregate. The terminology used to denote them in the descriptive literature has been inconsistent and not based upon a common definition for these...

Members of the genus Phrynosoma all exhibit asperities upon the parietal and squamosal. We examined μ‐CT scans of the dermatocrania of ontogenetic series of all but two of the species of Phrynosoma, and defined parietal and squamosal “horns”, distinguishing them from tubercles. We counted parietal and squamosal horns and used phylogenetic analysis...

PHRYNOSOMA CORNUTUM (Texas Horned Lizard). ABERRANT PARIETAL HORNS. During reptile survey in the northeastern edge of the state of Sonora, Mexico, on 5 August 2022 we encountered an adult female Phrynosoma cornutum (estimated SVL = 103 mm), Municipio de Agua Prieta, ca. 11.6 km WSW of the edge of Agua Prieta (31.285°N, 109.6795°W; WGS 84; 1279 m el...

2018. Incidentally gathered natural history information on Bullsnakes (Pituophis catenifer sayi) in southeastern Alberta. Canadian Field-Naturalist 132(2): Abstract We present observations on Bullsnakes (Pituophis catenifer sayi) gathered during a study of Prairie Rattlesnakes (Crotalus viridis) in a multiple-use, mixed grass landscape adjacent to...

Abstract: We recovered 33 severed heads of Phrynosoma cornutum found in 19 Buteo swainsoni nests at La Reserva de la Biosfera de Janos, Chihuahua, Mexico. We estimated the snout–vent lengths of these lizards by inserting their head lengths into a scaling model relating head length to body length for P. cornutum, derived from an ontogenetic series o...

Postnatal growth patterns within the vertebral column may be informative about body proportions and regionalization. We measured femur length, lengths of all pre‐sacral vertebrae, and lengths of intervertebral spaces, from radiographs of a series of 21 Eublepharis macularius, raised under standard conditions and covering most of the ontogenetic bod...

The role of allometry in producing the variation in autopodial morphology observed among the lizards is not well understood. Allometry of metapodial and digit lengths in the manus and pes of the primitively padless gekkotan (Eublepharis macularius) is explored using maximum-likelihood repeated-measures ANCOVAs with body length as the covariate. Est...

Dermatocranial shape and horn morphology display great disparity among the species of Phrynosoma. Ontogenetic change in dermatocranial shape in a series of 79 specimens of the short-horned Phrynosoma hernandesi (54F: 25M) was examined using geometric morphometric techniques. A multivariate ANCOVA of Procrustes residuals with sex as a factor and ln(...

The lizard tail is well known for its ability to autotomize and regenerate. Physical contact of the tail by a predator may induce autotomy at the location at which the tail is grasped, and upon detachment the tail may undergo violent, rapid, and unpredictable movements that appear to be, to some degree, regulated by contact with the physical enviro...

Tyrannosaurid necks were strong and powerful instruments for wielding the jaws during feeding. Hypotheses of tyrannosaurid neck function are here grounded by observations of neck morphology and function in extant archosaurs. Respectively derived morphologies in birds, crocodilians and tyrannosaurids compromise inferences for some muscles. However,...

Ecomorphological studies of lizards have explored the role of various morphological traits and how these may be associated with, among other things, habitat use. We present an analysis of selected traits of internal morphology of the hind limbs of Neotropical iguanian lizards and their relationship to habitat use. Considering that one of the most w...

Field capture records and observation of wild-caught females indicate that parturition in Alberta populations of Phrynosoma douglassii brevirostre, a viviparous lizard, is synchronized among females, taking place during a short period around the end of July, and generally around noon. Relative clutch mass appears to decrease with female age, and cl...

Scaling of locomotor structures (limb length, scansor area, and intergirdle distance) in three Jamaican Anolis species (A. garmani, A. grahami, and A. opalinus) is examined. Reference to structural-niche use patterns and partitionings typical of these three species is made. Each species represents a separate Anolis ecomorph, differing from the othe...

Both skeletochronology and a somatic growth model based upon mark–recapture data were used to estimate life-span and the relationship between size and age in two populations of long-toed salamanders (Ambystoma macrodactylum krausei) in the upper Bow Valley of southwestern Alberta. Skeletochronologically aged salamanders (n = 170) displayed a sigmoi...

Alberta populations of Phrynosoma douglassi brevirostre display marked sexual size dimorphism, adult females being considerably larger than adult males. Discriminant analyses of whole mensural characters and of scaled mensural characters indicate that this dimorphism is present from birth, although it is more strongly expressed after sexual maturit...

Suggestions that short-faced members of the Felidae tend to lack the second upper premolar (P2) imply a possible shift in scaling associated with the palate and maxillary tooth row in Lynx, which lacks P2, as compared to felids that retain it. This hypothesis is tested using a scaling model that relates the lengths of the palate, and the upper toot...

of the teeth of western North American tyrannosaurids and its applicability to quantitative classification. Acta Palaeontologica Polonica 50 (4): 757–776. Gross tooth morphology and serration morphology were examined to determine a quantifiable method for classifying tyrannosaurid tooth crowns from western North America. From the examination of tee...

Descriptive, principal component (PCA), and thin-plate spline (TPS) analyses of theropod third metatarsals (MT III) definitively segregate the arctometatarsus from other theropod pedal morphologies and reveal variation within phylogenetic and functional subgroups of metatarsi. PCA indicates that the arctometatarsalian MT III differs in shape from t...

Phrynosoma orbiculare bears one pair of horns on the midline parietal bone (P2), two pairs on each squamosal bone (S1 and S2), and one horn on each frontal bone (F0). Reduced major axis (RMA) regression statistics for the relationship of each horn to head length, and of head length to body length, were estimated and compared for significant differe...

The diet of the Prairie Rattlesnake, Crotalus viridis viridis, in a multiple land use area in southeastern Alberta was investigated by examining the gut contents of 20 road-killed individuals and the composition of eight scats recovered from sequestered individuals. All individuals yielding dietary data were adults. No data on the composition of th...

Ptychozoon kuhli is known for its parachuting/gliding capabilities. In this contribution, we document the allometric scaling properties of its patagium, accessory flaps and folds, and its total body surface area and compare them to similar attributes of the agamine lizard Draco volans. Ptychozoon kuhli has passive patagia that lack skeletal support...

Much is known of the ecology and behaviour of Spermophilus richardsonii (Sabine, 1822) (Richardson's Ground Squirrel), but little has been discussed of its anatomy. Here we document details of its cranial anatomy, based upon 95 specimens from a single locality, focusing primarily on previously undescribed features. This documentation provides the e...

We examined the distribution and abundance of the short-horned lizard Phrynosoma hernandezi in Grasslands National Park, Saskatchewan, Canada. Historical records and anecdotal observations were compiled, and new surveys were conducted in 1995 and 1996. A total of 41 individuals, mostly young-of-the-year, were captured in the West Block of the Park...

EXECUTIVE SUMMARY An intense survey for Ambystoma macrodactylum populations was conducted in the waterbodies of Alberta’s Rocky Mountain’s eastern slopes between 51o 15’ N and the Canada-U.S. border over the three-month period from May to July, 1995. Twenty new population localities were located and illustrated in addition to 57 previously documen...

Short-horned Lizards reach their northern distribution limits in British Columbia, Alberta, and Saskatchewan. Two specimens of the Pygmy Short-horned Lizard (P. douglasi) were reported in 1898 from the vicinity of Osoyoos, British Columbia; there have been no validated sightings since. It was probably found on the sandy lacustrine terraces lining t...

All carnivorans retract and protract their claws. In felids and some viverrids the claws of digits II through V of both the manus and pes have a larger arc of rotation than those of other carnivorans; the claws retract to the lateral side of the middle phalanx rather than onto its dorsal surface as in most other carnivorans. This condition should b...

BAUER, A. M., A. P. RUSSELL and G. L. POWELL. 1996. The evolution of locomotor morphology in the genus Rhoptropus (Squamata: Gekkonidae). Afr. 1. Herpetol. 45(1): 8–30. Reduced major axis regressions of limb skeletal element length against occiput-vent length (OVL) indicate that there are significant differences in the scaling relationships among t...

The eastern short-horned lizard, Phrynosoma douglassii brevirostre, reaches the northern limit of its geographical range in southeastern Alberta. Populations in this area are found in the drainage basins of the South Saskatchewan River, Pakowki Lake and Milk River. The vegetation of the area is typical short-grass prairie. Populations are confined...

Based upon published evidence (Baxter and Stone, 1985), either lizard distributions in Wyoming are extremely patchy or they are not well known. It is apparent that many of the localities for different species are coincidental and clustered in particular areas of the state, suggesting that parts of the state are better collected than others. and tha...

Phrynosoma douglassi brevirostre has a median body temperature (Tb) of 32.9 °C in southeastern Alberta, with a sharply peaked and negatively skewed Tb frequency. The range of the Tb frequency distribution in daylight hours during the active season (activity temperature range) is wide (20.0 °C). The realized thermal niche is approximately 7 °C wide,...

The Alberta populations are less strongly myrmecophagous than the average for the species, when the diet is broken down by prey item counts. Breakdown of the diet by prey dry weight shows that ants, nonsilphid Coleoptera, and Orthoptera are the major components of the diet. The range of prey sizes taken is large, but the species concentrates on a s...

Thesis (M.Sc.) -- University of Calgary, 1982.