Publications by authors named "Randall Nydam"

15 Publications

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A new vertebrate fauna from the Lower Cretaceous Holly Creek Formation of the Trinity Group, southwest Arkansas, USA.

PeerJ 2021 21;9:e12242. Epub 2021 Oct 21.

Department of Geosciences, University of Arkansas at Fayetteville, Fayetteville, Arkansas, USA.

We present a previously discovered but undescribed late Early Cretaceous vertebrate fauna from the Holly Creek Formation of the Trinity Group in Arkansas. The site from the ancient Gulf Coast is dominated by semi-aquatic forms and preserves a diverse aquatic, semi-aquatic, and terrestrial fauna. Fishes include fresh- to brackish-water chondrichthyans and a variety of actinopterygians, including semionotids, an amiid, and a new pycnodontiform, sp. nov. Semi-aquatic taxa include lissamphibians, the solemydid turtle , a trionychid turtle, and coelognathosuchian crocodyliforms. Among terrestrial forms are several members of Dinosauria and one or more squamates, one of which, gen. et sp. nov., is described herein. Among Dinosauria, both large and small theropods (, , and ) and titanosauriform sauropods are represented; herein we also report the first occurrence of a nodosaurid ankylosaur from the Trinity Group. The fauna of the Holly Creek Formation is similar to other, widely scattered late Early Cretaceous assemblages across North America and suggests the presence of a low-diversity, broadly distributed continental ecosystem of the Early Cretaceous following the Late Jurassic faunal turnover. This low-diversity ecosystem contrasts sharply with the highly diverse ecosystem which emerged by the Cenomanian. The contrast underpins the importance of vicariance as an evolutionary driver brought on by Sevier tectonics and climatic changes, such as rising sea level and formation of the Western Interior Seaway, impacting the early Late Cretaceous ecosystem.
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http://dx.doi.org/10.7717/peerj.12242DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8542373PMC
October 2021

Musculoskeletal ultrasound training encourages self-directed learning and increases confidence for clinical and anatomical appreciation of first-year medical students.

Anat Sci Educ 2022 May 20;15(3):508-521. Epub 2022 Jan 20.

Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, Arizona, USA.

Best-practice guidelines have incorporated ultrasound in diagnostic and procedural medicine. Due to this demand, the Arizona College of Osteopathic Medicine initiated a comprehensive integration of ultrasound into its first-year anatomy course attended by more than 280 students. Ultrasound workshops were developed to enhance student conceptualization of musculoskeletal (MSK) anatomy through visualizing clinically important anatomical relationships, a simulated lumbar puncture during the back unit, carpal tunnel and shoulder evaluations during the upper limb unit, and plantar fascia, calcaneal tendon, and tarsal tunnel evaluations during the lower limb unit. A 5-point Likert scale survey evaluated if ultrasound improved students' self-perceived anatomical and clinical comprehension of relevant anatomy, improved students' ability to orient to ultrasound imagery, and prompted further independent investigation of the anatomical area. Ultrasound examination questions were added to the anatomy examinations. Two-tailed one-sample t-tests for the back, upper limb, and lower limb units were found to be significant across all Likert survey categories (P < 0.001). Positive student responses to the Likert survey in conjunction with examination question average of 84.3% (±10.3) demonstrated that the ultrasound workshops are beneficial to student education. Ultrasound enhances medical students' clinical and anatomical comprehension and ability to orient to ultrasound imagery for MSK anatomy. This study supports early ultrasound education as a mechanism to encourage students' independent learning as evidenced by many undertaking voluntary investigation of clinical concerns associated with MSK anatomy. This study establishes the successful integration of MSK ultrasound into a large medical school program and its benefit to student clinical education.
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http://dx.doi.org/10.1002/ase.2145DOI Listing
May 2022

Evaluating for a correlation between osteopathic examination and ultrasonography on thoracic spine asymmetry.

J Osteopath Med 2021 Oct 13;122(1):31-43. Epub 2021 Oct 13.

Department of Anatomy, Midwesetern University, Arizona College of Osteopathic Medicine, Glendale, AZ, USA.

Context: The thoracic spine is a common area of focus in osteopathic manipulative medicine (OMM) for a variety of conditions. Thoracic spine somatic dysfunction diagnosis is achieved by palpating for asymmetry at the tips of the transverse processes (TPs). Previous studies reveal that instead of following the rule of threes, the TPs of a given thoracic vertebra generally align with the spinous process (SP) of the vertebra above. Ultrasonography has been widely utilized as a diagnostic tool to monitor musculoskeletal conditions; it does not utilize ionizing radiation, and it has comparable results to gold-standard modalities. In the case of thoracic somatic dysfunction, ultrasound (US) can be utilized to determine the location of each vertebral TP and its relationship with the SP. Previous studies have investigated the correlation between OMM and ultrasonography of the cervical, lumbar, and sacral regions. However, there has been no study yet that has compared osteopathic structural examination with ultrasonographic examination of the thoracic vertebral region.

Objectives: To examine the relationship between osteopathic palpation and ultrasonographic measurements of the thoracic spine by creating a study design that utilizes interexaminer agreement and correlation.

Methods: The ClinicalTrials.gov study identifier is NCT04823637. Subjects were student volunteers recruited from the Midwestern University (MWU)-Glendale campus. A nontoxic, nonpermanent marker was utilized to mark bony landmarks on the skin. Two neuromusculoskeletal board-certified physicians (OMM1, OMM2) separately performed structural exams by palpating T2-T5 TPs to determine vertebral rotation. Two sonographers (US1, US2) separately scanned and measured the distance from the tip of the SP to the adjacent TPs of the vertebral segment below. Demographic variables were summarized with mean and standard deviation. Interexaminer agreement was assessed with percent agreement, Cohen's Kappa, and Fleiss' Kappa. Correlation was measured by Spearman's rank correlation coefficient. Recruitment and protocols were approved by the MWU Institutional Review Board (IRB).

Results: US had fair interexaminer agreement for the overall most prominent segmental rotation of the T3-T5 thoracic spine, with Cohen's Kappa at 0.27 (0.09, 0.45), and a total agreement percentage at 51.5%. Osteopathic palpation revealed low interexaminer agreement for the overall most prominent vertebral rotation, with Cohen's Kappa at 0.05 (0.0, 0.27), and 31.8%. Segment-specific vertebral analysis revealed slight agreement between US examiners, with a correlation coefficient of 0.23, whereas all other pairwise comparisons showed low agreement and correlation. At T4, US had slight interexaminer agreement with 0.24 correlation coefficient, and osteopathic palpation showed low interexaminer (OMM1 vs. OMM2) agreement (0.17 correlation coefficient). At T5, there was moderate agreement between the two sonographers with 0.44 (0.27, 0.60) and 63.6%, with a correlation coefficient of 0.57, and slight agreement between OMM1 and OMM2 with 0.12 (0.0, 0.28) and 42.4%, with 0.23 correlation coefficient.

Conclusions: This preliminary study of an asymptomatic population revealed that there is a low-to-moderate interexaminer reliability between sonographers, low-to-slight interexaminer reliability between osteopathic physicians, and low interexaminer reliability between OMM palpatory examination and ultrasonographic evaluation of the thoracic spine.
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http://dx.doi.org/10.1515/jom-2021-0020DOI Listing
October 2021

New skulls and skeletons of the Cretaceous legged snake , and the evolution of the modern snake body plan.

Sci Adv 2019 11 20;5(11):eaax5833. Epub 2019 Nov 20.

Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.

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 on the acquisition of the snake body plan using micro-computed tomography scans of the first three-dimensionally preserved skulls of the legged snake and a new phylogenetic hypothesis. These findings elucidate the initial sequence of bone loss that gave origin to the modern snake skull. Morphological and molecular analyses including the new cranial data provide robust support for an extensive basal radiation of early snakes with hindlimbs and pelves, demonstrating that this intermediate morphology was not merely a transient phase between limbed and limbless body plans.
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http://dx.doi.org/10.1126/sciadv.aax5833DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6867888PMC
November 2019

A New Clevosaurid from the Triassic (Carnian) of Brazil and the Rise of Sphenodontians in Gondwana.

Sci Rep 2019 08 14;9(1):11821. Epub 2019 Aug 14.

Department of Biological Sciences, University of Alberta, Edmonton, Canada.

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 describe the fragmentary remains of an associated skull and mandible of Clevosaurus hadroprodon sp. nov., a new taxon of sphenodontian lepidosaur from the Late Triassic (Carnian; 237-228 Mya) of Brazil. Referral to Sphenodontia is supported by the combined presence of a marginal dentition ankylosed to the apex of the dentary, maxilla, and premaxilla; the presence of 'secondary bone' at the bases of the marginal dentition; and a ventrally directed mental process at the symphysis of the dentary. Our phylogenetic analyses recover Clevosaurus hadroprodon as a clevosaurid, either in a polytomy with the Late Triassic to Early Jurassic Clevosaurus and Brachyrhinodon (under Bayesian inference), or nested among different species of Clevosaurus (under maximum parsimony). Clevosaurus hadroprodon represents the oldest known sphenodontian from Gondwana, and its clevosaurid relationships indicates that these sphenodontians achieved a widespread biogeographic distribution much earlier than previously thought.
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http://dx.doi.org/10.1038/s41598-019-48297-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6694142PMC
August 2019

Giant taxon-character matrices II: a response to Laing et al. (2017).

Cladistics 2018 Dec 19;34(6):702-707. Epub 2017 Nov 19.

Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, 19555 N. 59th Dr., Glendale, AZ, 85383, USA.

The trend towards big data analyses in evolutionary biology has been observed in phylogenetics via the assembly of giant datasets composed of genomic and phenotypic data. We recently (Simões et al., 2017. Giant taxon-character matrices: Quality of character constructions remains critical regardless of size. Cladistics 33, 198-219) presented a critique of the phylogenetic character concepts used in current morphological datasets, with the caution that giant datasets did not obviate the empirical requirement of rigor in character construction. Laing et al. (2017. Giant taxon-character matrices: The future of morphological systematics. Cladistics, https://doi.org/10.1111/cla.12197) have since argued that we had 'suggested' that large datasets inherently contain flawed characters, and that we had presented a substandard methodology of phylogenetic analysis. Laing et al. concluded by discussing their approach to phylogenetic signal, total evidence and the inevitability of large datasets. We here reply to Laing et al. by reviewing what we actually wrote regarding dataset size, characters and methodology. We show that Laing et al.'s. central premise is unsupported, thus characterizing a Straw Man argument, and deeply misrepresents our original study. In part two, we discuss total evidence and phylogenetic signal issues raised by Laing et al. that are of major consequence to the appropriate construction of large morphological datasets.
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http://dx.doi.org/10.1111/cla.12231DOI Listing
December 2018

X-ray computed microtomography of Megachirella wachtleri.

Sci Data 2018 11 6;5:180244. Epub 2018 Nov 6.

Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, 19555N. 59th Dr., Glendale, AZ 85383, USA.

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 (Middle Triassic, northern Italy), which revealed an important set of features indicating this is the oldest known fossil squamate in the world, predating the previous oldest record by ca. 75 million years. We also compiled a new phylogenetic data set comprising a large sample of diapsid reptiles (including morphological and molecular data) to investigate the phylogenetic relationships of early squamates and other reptile groups along with the divergence time of those lineages. The re-description of Megachirella and a new phylogenetic hypothesis of diapsid relationships are presented in a separate study. Here we present the data descriptors for the tomographic scans of Megachirella, which holds fundamental information to our understanding on the early evolution of one of the largest vertebrate groups on Earth today.
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http://dx.doi.org/10.1038/sdata.2018.244DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6219415PMC
November 2018

A mid-Cretaceous embryonic-to-neonate snake in amber from Myanmar.

Sci Adv 2018 07 18;4(7):eaat5042. Epub 2018 Jul 18.

Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.

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 vertebrae, and details of squamation and body shape; a second specimen preserves a fragment of shed skin interpreted as a snake. Important details of skeletal ontogeny, including the stage at which snake zygosphene-zygantral joints began to form along with the neural arch lamina, are preserved. The vertebrae show similarities to those of fossil Gondwanan snakes, suggesting a dispersal route of Gondwanan faunas to Laurasia. Finally, the new species is the first Mesozoic snake to be found in a forested environment, indicating greater ecological diversity among early snakes than previously thought.
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http://dx.doi.org/10.1126/sciadv.aat5042DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6051735PMC
July 2018

The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps.

Nature 2018 05 30;557(7707):706-709. Epub 2018 May 30.

Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, Glendale, AZ, USA.

Modern squamates (lizards, snakes and amphisbaenians) are the world's most diverse group of tetrapods along with birds and have a long evolutionary history, with the oldest known fossils dating from the Middle Jurassic period-168 million years ago. The evolutionary origin of squamates is contentious because of several issues: (1) a fossil gap of approximately 70 million years exists between the oldest known fossils and their estimated origin; (2) limited sampling of squamates in reptile phylogenies; and (3) conflicts between morphological and molecular hypotheses regarding the origin of crown squamates. Here we shed light on these problems by using high-resolution microfocus X-ray computed tomography data from the articulated fossil reptile Megachirella wachtleri (Middle Triassic period, Italian Alps ). We also present a phylogenetic dataset, combining fossils and extant taxa, and morphological and molecular data. We analysed this dataset under different optimality criteria to assess diapsid reptile relationships and the origins of squamates. Our results re-shape the diapsid phylogeny and present evidence that M. wachtleri is the oldest known stem squamate. Megachirella is 75 million years older than the previously known oldest squamate fossils, partially filling the fossil gap in the origin of lizards, and indicates a more gradual acquisition of squamatan features in diapsid evolution than previously thought. For the first time, to our knowledge, morphological and molecular data are in agreement regarding early squamate evolution, with geckoes-and not iguanians-as the earliest crown clade squamates. Divergence time estimates using relaxed combined morphological and molecular clocks show that lepidosaurs and most other diapsids originated before the Permian/Triassic extinction event, indicating that the Triassic was a period of radiation, not origin, for several diapsid lineages.
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http://dx.doi.org/10.1038/s41586-018-0093-3DOI Listing
May 2018

Giant taxon-character matrices: quality of character constructions remains critical regardless of size.

Cladistics 2017 Apr 24;33(2):198-219. Epub 2016 Apr 24.

Department of Anatomy, Arizona College of Osteopathic Medicine, Midwestern University, 19555 N. 59th Dr., Glendale, AZ, 85383, USA.

Giant morphological data matrices are increasingly common in cladistic analyses of vertebrate phylogeny, reporting numbers of characters never seen or expected before. However, the concern for size is usually not followed by an equivalent, if any, concern for character construction/selection criteria. Therefore, the question of whether quantity parallels quality for such influential works remains open. Here, we provide the largest compilation known to us of character construction methods and criteria, as derived from previous studies, and from our own de novo conceptualizations. Problematic character constructions inhibit the capacity of phylogenetic analyses to recover meaningful homology hypotheses and thus accurate clade structures. Upon a revision of two of the currently largest morphological datasets used to test squamate phylogeny, more than one-third of the almost 1000 characters analysed were classified within at least one of our categories of "types" of characters that should be avoided in cladistic investigations. These characters were removed or recoded, and the data matrices re-analysed, resulting in substantial changes in the sister group relationships for squamates, as compared to the original studies. Our results urge caution against certain types of character choices and constructions, also providing a methodological basis upon which problematic characters might be avoided.
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http://dx.doi.org/10.1111/cla.12163DOI Listing
April 2017

Reacquisition of the lower temporal bar in sexually dimorphic fossil lizards provides a rare case of convergent evolution.

Sci Rep 2016 Apr 13;6:24087. Epub 2016 Apr 13.

Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.

Temporal fenestration has long been considered a key character to understand relationships amongst reptiles. In particular, the absence of the lower temporal bar (LTB) is considered one of the defining features of squamates (lizards and snakes). In a re-assessment of the borioteiioid lizard Polyglyphanodon sternbergi (Cretaceous, North America), we detected a heretofore unrecognized ontogenetic series, sexual dimorphism (a rare instance for Mesozoic reptiles), and a complete LTB, a feature only recently recognized for another borioteiioid, Tianyusaurus zhengi (Cretaceous, China). A new phylogenetic analysis (with updates on a quarter of the scorings for P. sternbergi) indicates not only that the LTB was reacquired in squamates, but it happened independently at least twice. An analysis of the functional significance of the LTB using proxies indicates that, unlike for T. zhengi, this structure had no apparent functional advantage in P. sternbergi, and it is better explained as the result of structural constraint release. The observed canalization against a LTB in squamates was broken at some point in the evolution of borioteiioids, whereas never re-occuring in other squamate lineages. This case of convergent evolution involves a mix of both adaptationist and structuralist causes, which is unusual for both living and extinct vertebrates.
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http://dx.doi.org/10.1038/srep24087DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4829860PMC
April 2016

The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution.

Nat Commun 2015 Jan 27;6:5996. Epub 2015 Jan 27.

Fundación Félix de Azara, CEBBAD (CONICET), Universidad Maimónides, Buenos Aires 1405, Argentina.

The previous oldest known fossil snakes date from ~100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation. We report here on snake fossils that extend the record backwards in time by an additional ~70 million years (Middle Jurassic-Lower Cretaceous). These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.
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http://dx.doi.org/10.1038/ncomms6996DOI Listing
January 2015

Dakotaseps gen. nov., a replacement name for the lizard genus Dakotasaurus Nydam 2013, a junior homonym of the ichnotaxon Dakotasaurus Branson and Mehl 1932.

Authors:
Randall L Nydam

Zootaxa 2014 Dec 19;3900(1):150. Epub 2014 Dec 19.

Department of Anatomy, Midwestern University, 19555 N 59th Avenue, Glendale, Arizona, USA.; Email:

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http://dx.doi.org/10.11646/zootaxa.3900.1.11DOI Listing
December 2014

Schillerosaurus gen. nov., a replacement name for the lizard genus Schilleria Evans and Chure, 1999 a junior homonym of Schilleria Dahl, 1907.

Zootaxa 2013 Nov 11;3736:99-100. Epub 2013 Nov 11.

Department of Cell and Developmental Biology, University College London, Gower Street, London, United Kingdom.; Email:

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http://dx.doi.org/10.11646/zootaxa.3736.1.6DOI Listing
November 2013
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