Randall Lawrence Nydam

• Phd
• Head of Faculty at Midwestern University

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...

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 chondrichthya...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Life restoration of the legged snake Najash from the Cretaceous of Patagonia (by Raúl Orencio Gómez)

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...

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...

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...

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...

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...

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 criti...

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 par...

Late Jurassic lizards from Solnhofen, Germany, include some of the oldest known articulated lizard specimens, sometimes including soft tissue preservation. These specimens are thus very important to our understanding of early squamate morphology and taxonomy, and also provide valuable information on squamate phylogeny. Eichstaettisaurus schroederi...

In the late 1980’s an assemblage of vertebrate material was discovered at the Briar Site Gypsum Mine, the site of extensive sauropod and theropod tracks from the overlying De Queen Limestone outside of Dierks, Arkansas. The assemblage was discovered in an organic-rich, pyrite-bearing dark grey mudstone. Many of the large vertebrate material contain...

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...

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 (Mi...

The previous oldest known fossil snakes date from B100 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 B70 million years (Mi...

The Upper Cretaceous (Santonian) Iharkút terrestrial vertebrate locality in Hungary has already yielded scincomorphan taxa such as the polyglyphanodontines Bicuspidon and Distortodon and the chamopsiid Pelsochamops. Besides these, more lacertilian material is available, including a single right mandible, different from both the abovementioned gener...

Dakotasaurus gilletorum Nydam 2013 was erected for two partial mandibles of a paramacellodid-cordylid grade scincomorphan lizard from the early Late Cretaceous (Cenomanian) of southern Utah (Nydam 2013). However, the genus name Dakotasaurus is a junior homonym of the ichnofossil Dakotasaurus Branson and Mehl 1932. Under Article 23.1 of the Internat...

The Goler Formation is the only rock unit on the West Coast of North America that has yielded a diverse assemblage of Paleocene vertebrates. Intense prospecting of strata representing member 4 of the formation over the past two decades has resulted in recovery of over 70 specimens of eutherian mammals, representing 18 species. All specimens were re...

Squamates from the Mesozoic of North America have been collected since the end of the nineteenth century. To date, the fossils are known to occur in the Late Jurassic, Aptian-Albian, Cenomanian, Turonian, Santonian, Campanian, and Maastrichtian. Most of the records are from the Western Interior in the arid regions associated with the Rocky Mountain...

Schilleria utahensis Evans and Chure, 1999 was erected for an associated partial skeleton of an enigmatic fossil lizard recovered from the Late Jurassic Brushy Basin Member of the Morrison Formation at Dinosaur National Monument in northeastern Utah (Evans and Chure 1999). However, the genus name Schilleria is a junior homonym of the arachnid subge...

New anatomical observations and reinterpretations of previously identified structures have resulted in new taxonomic diagnoses for the fossil hind-limbed marine snakes Pachyrhachis problematicus, Eupodophis descouensi, and Haasiophis terrasanctus. Among the most important conclusions of our study are the following: Haasiophis and Eupodophis show no...

Newly recovered microvertebrate specimens from three closely spaced localities (Makela-French, Put’s Plunder, Boremys Butte; all University of California Museum of Paleontology localities) in the Judith River Formation include numerous jaws, osteoderms, and vertebrae of lizards. The most common lizards recovered are chamopsiids with specimens refer...

ABSTRACT The late Campanian?aged (= Judithian) squamates from the Terlingua Local Fauna of the Aguja Formation, southern Texas, includes four scincomorphans: a new taxon (Catactegenys solaster, gen. et sp. nov.), referable to Xantusiidae, that has massive teeth and tooth crown morphology similar to that of contogeniid lizards; an indeterminate scin...

The Goler Formation is the only rock unit on West Coast of North America that has yielded a diverse assemblage of Paleocene vertebrates. Intense prospecting over the past two decades in member 4a-4b of the formation has resulted in recovery of over eighty specimens of eutherian and metatherian mammals, representing twenty species. The Goler Assembl...

The late Campanian-aged squamates from the Terlingua local fauna of the Aguja Formation of southern Texas are represented by numerous isolated specimens of fragmentary jaws, vertebrae, and osteoderms. The fauna includes four scincomorphans: a new taxon referable to Xantusiidae that has massive teeth with crown morphology similar to that of more del...

Much of the microvertebrate fauna known from the late Mesozoic of North America is based on fragmentary/isolated remains recovered from bulk collection of fluvial-based deposits in Western Interior. The identified fossil remains of squamates are mostly jaws, though other cranial and postcranial elements are also present as are the rare articulated/...

The origin of snakes from within squamate reptiles is an excellent example of a major evolutionary transition. Investigating the origins of a major lineage, such as snakes, is problematic for the simple reason that the processes of macrevolutionary change produce major morphological differences between the studied lineage and its closest relative o...

Squamates (lizards/snakes) are a common component of the microvertebrate faunas from the Campanian of western North America. Generally these fossils are disarticulated and fragmentary remains of jaws, vertebrae, and skull elements recovered through bulk sampling and screen wash concentration. The taxa recovered include ?Iguania, Cordylidae/Paramace...

The Cretaceous-aged portion of the sedimentary rocks in southern Utah form a nearly continuous series of terrestrial and interbedded marine facies that are becoming increasingly well-known for producing a spectacular and highly diverse fauna of fossil vertebrates. With regard to squamates (lizards and snakes) the most intensely studied faunas have...

New material of borioteiioidean lizards (Squamata: Scincomorpha) from west-central Alberta, Canada, represent the first and northernmost record of multiple articulated skull elements from the Cretaceous of North America. Specimens were recovered from the fluvial beds of the Wapiti Formation (Campanian) within a bentonitic paleosol exposed at the Kl...

Previous biogeographic studies of late Cretaceous (late Campanian) vertebrate faunas in the Western Interior Basin (WIB) of North America have suggested the presence of faunal and floral provincialism, characterized by distinct northern and southern ‘biomes.’ However, the “provincialism hypothesis” has been questioned based largely on the contentio...

New material of borioteiioidean lizards (Squamata: Scincomorpha) from northern Alberta, Canada, represents the earliest and northernmost record of multiple articulated skull elements from the Cretaceous of North America. Specimens were recovered from a bentonitic paleosol of the Wapiti Formation (Campanian) exposed at Kleskun Hill Park, east of the...

Based on diagnostic jaw and dental material from the Cenomanian–middle Paleocene of the western U.S.A., we erect a new fossil lizard taxon, Contogeniidae taxon nov., that contains the following species: Contogenys sloani Estes, 1969 (Maastrichtian–early Paleocene, Montana); Contogenys ekalakaensis sp. nov. (middle Paleocene, Montana); Palaeoscincos...

Teiid-like scincomorphan lizards from the Late Cretaceous (Campanian) of the Kaiparowits Formation of southern Utah include Chamops cf. Chamops segnis, cf. Leptochamops, a new species of Meniscognathus, and a new taxon with well-developed tricuspid teeth. These taxa comprise some of the only confirmed reports of these types of lizards from Late Cre...

The Kaiparowits Formation (KF), at approximately 75 millions years old (late Campanian), is the youngest of the Cretaceous-aged units in Kaiparowits Plateau region of southern Utah. These thick mudstone deposits are rich in fossil vertebrates, particularly microvertebrates that have been recovered through underwater screen washing. Specimens recove...

Abstract for poster

New material of polyglyphanodontine lizards from the Late Cretaceous has been found in various localities in western North America. Several transversely oriented teeth representing a new species of Dicothodon were recovered from the Turonian of southern Utah. These specimens necessitate reassignment of Polyglyphanodon bajaensis to Dicothodon (Polyg...

Polyglyphanodon sternbergi Gilmore, 1940 is a large-bodied lizard from the Late Cretaceous of North America distinguished by its transversely oriented, interlocking teeth. Initially the teeth of P. sternbergi were described as smooth and blade-like, but recent discoveries of new specimens from the type locality and re-examination of the original ma...

A diverse fauna of lizards has been recovered from the Cedar Mountain Formation (Albian–Cenomanian boundary) of central Utah. These lizards are a component of the now recognized Mussentuchit local fauna and, like many of the other vertebrate groups within this fauna, show striking similarities to their North American Late Cretaceous (Campanian–Maas...

Recent discoveries from the Aptian–Albian Antlers (Oklahoma) and Cloverly (Montana, Wyoming) formations provide significant additions to the Early Cretaceous record of lizards in North America. The lizards from the Antlers Formation include two teiids (one named), an anguimorphan, and a series of fragmentary jaws with “paramacellodid”-like teeth. T...

A heretofore unknown teiid lizard, recovered from the Cedar Mountain Formation (Albian-Cenomanian boundary) of Emery County, Utah, is the oldest teiid that is represented by numerous specimens. This new taxon has a heterodont dentition with conical anterior teeth and transversely oriented bicuspid posterior teeth that are distinct from those of Pen...

A new platynotan lizard, Primaderma nessovi, gen. et sp. nov., from the Mussentuchit Local Fauna, Cedar Mountain Formation (Albian–Cenomanian) of Utah is unique in having a premaxillary process of the maxilla that forms a vertical flange and fine serrations on anterior and posterior edges of the maxillary teeth. Primaderma is the oldest-known terre...

Describes an advanced anguimorph lizard from the Albian (Early Cretaceous) of Utah. The taxon lacks at least one important feature (retracted nares) of Varanoidea, and for this reason is referred to the Necrosauridae, a fossil group characterized by a combination of anguoid and varanoid characters. Nonetheless, the fossil bears several advanced cha...