Spencer G. Lucas

New Mexico Museum of Natural History and Science · Science

Carboniferous tetrapod footprints are mostly of Euramerican origin and have been collected and studied since the 1840s. Very early in that study, Pennsylvanian footprints from North America refuted the idea that no terrestrial tetrapods lived during the Carboniferous, the first example of footprints demonstrating something not known from the tetrap...

Vertebrate trace fossils are footprints, dentalites, regurgitalites, consumulites, gastroliths, coprolites, other bromalites, burrows and nests. Most of the study of these trace fossils has focused on footprints and coprolites and began with the classic work of William Buckland in the 1820s and 1830s. Important research on vertebrate footprints in...

The study of vertebrate ichnology has largely been the study of fossil footprints, but includes studies of fish trails and imprints, bromalites, burrows and nest structures. Despite a nearly 200 year history of research, vertebrate trace fossils have not been regarded as important archives of vertebrate history until relatively recently. And, this...

In their review article in this book, Marchetti et al. (2024) note that Permian tetrapod footprints are abundant, relatively diverse, and widespread in Pangea. They consider 22 ichnogenera to be valid and attributed them to temnospondyls and lepospondyls (Batrachichnus, Limnopus, Matthewichnus), seymouriamorphs (Amphisauropus), diadectomorphs (Ichn...

Of the nine supposed Devonian tetrapod footprint records in the literature, only three can be verified as produced by a tetrapod trackmaker, and one of these may be younger than Devonian. These three are Genoa River, Australia (two trackways), Easter Ross, Scotland (one trackway) and Valentia Island, Ireland (eight trackways). The oldest Devonian t...

Upper Cretaceous-Paleocene stratigraphy and vertebrate paleontology in the Zaysan Basin, Kazakhstan. - J. of Vertebrate Paleontology, 1995, 15, 3: 41A. [Elena G. Kordikova's original data and geological & stratigraphical descriptions.]. Abstract. Upper Cretaceous-Paleocene strata exposed in the Zaysan basin of eastern Kazakhstan are nonmarine silis...

Lower Permian marine strata in the American Southwest (Arizona, New Mexico and Texas, USA) identify three extensive marine seaways, one of Wolfcampian age and the other two of Leonardian age. These are strata deposited on the Mogollon shelf and in the Holbrook basin of Arizona, the Pedregosa basin of Arizona-New Mexico and northern Mexico, the Orog...

Two ichnofacies have been named to encompass inland eolian depositional systems, the Octopodichnus and the Entradichnus ichnofacies, and are often combined into a single, Octopodichnus-Entradichnus ichnofacies. In contrast, coastal dune fields are characterized by a mixture of traces produced by marine and nonmarine organisms attributed to a single...

The Carboniferous Joggins Fossil Cliffs UNESCO World Heritage Site in Nova Scotia, Canada, has long been known for its extensive paleobiodiversity. The ichnofossil record at Joggins is less known than the body fossil record. Amongst the extensive ichnological collections of the late citizen-scientist Donald Reid is a morphologically unique shrimp-s...

Moa tracks were first discovered in New Zealand in 1866, but until the 1990s they received only intermittent study. Now 13 moa track localities are known on the North Island; five were found in the last 20 years. Moa tracks were first found on the South Island in 2019, and two sites are now known. Moa trace fossils are non-randomly distributed betw...

At Clayton Lake in northeastern New Mexico, USA, an extensive dinosaur tracksite is present across the contact of the Lower Cretaceous (upper Albian) Mesa Rica and Pajarito formations. Dinosaur footprints and other trace fossils are found at four stratigraphic levels, two in the uppermost Mesa Rica Sandstone, and two (including the main track level...

Memorial to Daniel Vachard

In southern New Mexico and West Texas, USA, strata of the Hueco Group record Early Permian marine and nearshore paleoenvironments in the equatorial tropics of western Pangea. Age assignments and the correlation of these strata have long been based on fusulinid biostratigraphy, with some other biostratigraphic data based on ammonoids, brachiopods, c...

A new ichnotaxon, Ambulopisces voigti (ichnogen. et ichnosp. nov.), from the early Permian (Wolfcampian) Robledo Mountains Formation (Hueco Group) of south-central New Mexico, is described and shown to represent a fish walking on a muddy substrate. A. voigti is a compound ichnotaxon comprising alternating left and right pectoral fin impressions tha...

The Lower-Middle Triassic Moenkopi Group/Formation in the southwestern USA has yielded a famous tetrapod skeletal and ichnofossil fauna. A new locality in the Holbrook Member of the Moenkopi Formation (Anisian) of northeastern Arizona appears to be the most extensive Middle Triassic tetrapod tracksite in North America. The ichnofossil-bearing level...

Late Cretaceous-Early Palaeocene geo-climatic events played an important role in the diversification of the modern ichthyofauna. Lepisosteiformes and Siluriformes are two diverse clades of freshwater fishes, poorly known from India in this time interval. Their fossil record documents their early diversification and can be used to reconstruct palaeo...

We review the record of Late Triassic and Jurassic dinosaurs from India to determine their geological ages and palaeobiogeographic significance. The oldest Indian dinosaur, the basal saurischian Alwalkeria maleriensis, is from the early Late Triassic (Otischalkian/Carnian) lower Maleri Formation. The archosaur-dominated Upper Maleri Formation (Adam...

A critical review of the reported Devonian tetrapod footprints indicates that there are only three records that can be verified as produced by a tetrapod. These tracks include the oldest fossils of tetrapods. The tracks document that hindlimb-propelled, lateral-sequence walking by tetrapods with larger hindlimbs than forelimbs had appeared in the M...

The Lower Mississippian Blue Beach and Hurd Creek members of the Horton Bluff Formation at Blue Beach, Nova Scotia, Canada, yield an extensive fossil record, including the earliest terrestrial tetrapod fauna, several taxa of associated fishes, nonmarine and marine invertebrates, and an early flora containing nearshore and terrestrial plants. Trace...

In a little over 20 years the need to redefine, and even move, at least two of the Guadalupian GSSPs is clear. How did this unworkable Guadalupian chronostratigraphy come to be? The answer lies in politics and in the use of conodonts in chronostratigraphy. Indeed, the Guadalupian chronostratigraphy provides an excellent example of how the GSSP meth...

Tyrannosaurid dinosaurs dominated as predators in the Late Cretaceous of Laurasia, culminating in the evolution of the giant Tyrannosaurus rex, both the last and largest tyrannosaurid. Where and when Tyrannosaurini (T. rex and kin) originated remains unclear. Competing hypotheses place tyrannosaurin origins in Asia, or western North America (Larami...

A slab of sandstone of the Upper Cretaceous (Cenomanian) Paguate Member of the Dakota Formation has a highly unusual ichnoassemblage preserved on the surface. The traces are: (1) abundant Thalassinoides that form branching, polygonal networks; (2) several trails of Cruziana; (3) four specimens of Zoophycos; and (4) an area with undertracks of the h...

Recent fieldwork has recovered fossils of clawed lobsters of the genus Hoploparia from the Upper Cretaceous (Cenomanian and middle Turonian) strata in the southeastern San Juan Basin near San Ysidro, Sandoval County, New Mexico. Hoploparia is a well known, extinct clawed lobster genus that persisted from the Early Cretaceous to the Early Miocene, w...

The lower Permian strata of the Abo Formation consist of siliciclastic red beds found across much of New Mexico. Deposition of most of these red beds took place on an extensive alluvial plain across which paleoflow was southward to the shoreline of the Hueco seaway. The overall geometry of the Abo Formation deposits in parts of northern and souther...

Upper Paleozoic (Mississippian, Pennsylvanian, and Permian) strata are exposed around the Sierra Nacimiento, San Pedro Mountains, and Jemez Mountains in northern New Mexico. At scattered outcrops, the Mississippian rocks are assigned to the Arroyo Peñasco Formation, overlain locally by the Log Springs Formation. In the Guadalupe Box area, the Lower...

Triassic and Jurassic strata are prominently exposed by faults and folds in the nexus of the San Ysidro area in Sandoval County, New Mexico. The Triassic strata are assigned to the Middle Triassic Moenkopi Formation overlain by the Upper Triassic Chinle Group, a section of mostly siliciclastic red beds about 582 m thick. The Jurassic strata are ass...

The first known tetrapod footprint assemblage from the Abo Formation in the Jemez Mountains is from New Mexico Museum of Natural History locality 10325, in a 1.3-m-thick bed of ripple-laminated sandstone about 44 m below the upper contact of the Abo Formation with the overlying De Chelly Sandstone of the Yeso Group. The footprints are associated wi...

Zoophycos is a distinctive trace fossil, interpreted as the deposit-feeding trace of a marine worm that is found in marine deposits throughout the Phanerozoic, but it has rarely been reported from New Mexico. We describe an extensive assemblage of Zoophycos traces from the Middle Pennsylvanian (Atokan) Sandia Formation at Guadalupe Box in the Jemez...

For the first time, a complete study of sauropod trackways has been carried out in the lower part of the Djoua series in the In Amenas region (southeastern Algeria). Several locomotion tracks have been discovered in this area. In the present work, we report the discovery of sauropod tracks exposed on a bedding surface of the Lower Formation attribu...

On Glorieta Mesa in San Miguel County, northern New Mexico, the lower Permian Glorieta Sandstone contains numerous sandstone cylinders from two areas and two stratigraphic intervals of interdunal sedimentary deposits in the lower part of the formation. Most of these cylinders are perpendicular to bedding, although some are slightly oblique to the l...

Ancient human footprints have been known from Managua, Nicaragua, since the 1880s. The main footprint site, long preserved in the Acahualinca Tracks Museum ( Huellas de Acahualinca ), reveals hundreds of human footprints that represent a minimum of 12 clearly-defined trackways and a trampled trail or path. Deer, opossum, and bird tracks are also pr...

Numerous investigations have described the rudist bivalve “Ichthyosarcolites” coraloidea Hall and Meek, 1856, from the Upper Cretaceous strata of western North America. Among the well-dated examples is one from the middle-Campanian Lewis Shale in the San Juan Basin of New Mexico, 75.76 + 0.34 Ma. However, contemporary perspectives suggest that this...

Road building in the Franklin Mountains exposed an outcrop of Mancos Formation that is ~ 4.5 m thick and is mainly calcareous shale. These strata contain a low diversity invertebrate fossil assemblage consisting of the bivalves Ostrea beloiti Logan, Inoceramus arvanus Stephenson, I. prefragilis Stephenson and Pinna petrina White, and the ammonoids...

The Bureau of Land Management (BLM) Ojito Wilderness Area in southern Sandoval County, New Mexico, is located in the southeastern San Juan Basin. Most of the strata exposed in the Ojito are of Jurassic age, but its western third exposes outcrops of the intertongued Dakota-Mancos succession of early Late Cretaceous (Cenomanian) age. At the top of th...

A low diversity fauna of upper Turonian ammonites and inoceramids occurs in the Montezuma Valley Member of the Mancos Shale and the overlying Gallup Sandstone near Herrera in Bernalillo County in west-central New Mexico. The ammonites Forresteria (Forresteria) peruana (Brüggen, 1910), Baculites yokoyamai Tokunaga and Shimizu 1926 and Scaphites (Sca...

We report fossil plants and traces from the Arroyo de Alamillo Formation of the Yeso Group, a lithologic succession of siltstone, sandstone, and minor dolostone and gypsum of early Permian (early Leonardian/late Artinskian) age. These Yeso strata formed under a semi-arid to arid climate regime on a vast coastal plain, conditions generally unfavorab...

Specimens of the Eocene turtle Baena arenosa have had a complex taxonomic history of being thought to represent between one and 11 species by various authors over 150 years. For the last 50 years, Baena arenosa was largely considered to be one species with some variability. A recent paper suggested that these variants fall in two distinct morphotyp...

A specimen (skull, lower jaw, partial carapace and other postcrania) of the baenid turtle Goleremys mckennai is described from the Torrejonian NALMA interval of the Paleocene Nacimiento Formation of northwestern New Mexico. This is the first record of Goleremys east of the Sierra Nevada mountain range of California. The overall shell dimensions of...

Adocus kirtlandius is further described based on new specimens from the Kirtland and Fruitland formations of the San Juan Basin, northwestern New Mexico. These new specimens add to our knowledge of the anterior carapace and plastron, limbs and vertebrae of this species. Furthermore, some possible sexual dimorphism is apparent in the posterior-later...

We present a basic assessment of intraspecific variation in the shape of the testudinoid turtle shell. The focus is on two main areas – the plastral sulci and their proportions and the bone morphology of Gopherus agassizii. The plastral proportions of the turtles were measured using images and 13 landmarks collected for each individual. The bone st...

The Satan Member of the Mancos Shale on the eastern side of the San Juan Basin and Chama Basin in Rio Arriba County, New Mexico, contains ammonites and other marine molluscan fossils that date from the Campanian Stage. Definitive age diagnostic fossils representative of the Santonian Stage have not been collected from the study area. The earliest C...

The concept that taxon senescence led to the extinction of the heteromorph ammonite genus Baculites Lamarck, 1799, has a long intellectual pedigree dating to E. D. Cope and the neo-Lamarckian period of American paleontology. Revivified versions of Cope’s basic concept emphasize a unimodal or hat-like, five-phased pattern of diversification among fo...

Reports of Turonian occurrences of Eutrephoceras in North America, which are the oldest reports of the genus from the continent, are exclusively from New Mexico, and these reports as well as global reports of that age are rare. The oldest Eutrephoceras previously reported from New Mexico were from the Prionocyclus quadratus Zone. We document here t...

Numerous fossil bivalves in shale/conglomerate were prepared out of several blocks (~227 kg) of sediment that were excavated from the Upper Cretaceous (upper Campanian) Fossil Forest Member of the Fruitland Formation in the Fossil Forest Research Natural Area (23N, R12W) of San Juan County, northwestern New Mexico. The area also contains numerous v...

We add two new records to the fossil biota of the middle Cenomanian Paguate Member of the Dakota Formation in the southeastern San Juan Basin, New Mexico: (1) numerous small coprolites, assigned to Coprulus oblongus Mayer, 1952, likely made by an annelid worm; and (2) part of the right valve of a rudist bivalve, assigned to Durania sp. These new di...

Echinoid fossils are extremely rare in the Upper Cretaceous strata of the Western Interior, where about 60 records are known to date, most of them represented by only a few tests or isolated spines. Six newly discovered echinoid specimens, belonging to the genus Mecaster Pomel, have recently been recovered from the Upper Cretaceous (Turonian) Prion...

The Pennsylvanian stratigraphic section in Mine Canyon in the southern Caballo Mountains, Sierra County, New Mexico, is 326 m thick and consists of the upper part of the Gray Mesa Formation (42 m) and the entire Bar B Formation (219 m thick) overlain by most of the lower Permian Bursum Formation (65 m thick). Gray Mesa Formation strata are mostly c...

In 1928, N. H. Darton reported tetrapod fossils collected by E. C. Case in the bank of the Arroyo de la Parida northeast of Socorro in central New Mexico. Case had earlier, in 1916, identified these bones as representing taxa of “Permo-Carboniferous” age, but Darton concluded that they came from Triassic strata and thus must be reworked. Darton (19...

We describe a Pennsylvanian stratigraphic section near Lamy in Santa Fe County, New Mexico, where approximately 85 m of Sandia Formation strata are exposed in fault contact with underlying Proterozoic granitic rocks and below an erosional unconformity at the base of the overlying Abo (=Sangre de Cristo) Formation. The Sandia Formation strata are mo...

A recently discovered tracksite in the Abo Formation in the Quebradas region of Socorro County is distinguished by unusually high ichnodiversity and exceptional preservation. This site, NMMNH (New Mexico Museum of Natural History) locality 12617, is north of Tinajas Arroyo in the Cañon de Espinoso Member of the Abo Formation, about 5 meters below t...

Edward Drinker Cope (1840-1897) was the paleontologist on the Wheeler Survey that explored the New Mexico Territory in 1874. He collected a series of Miocene vertebrate fossils from badlands in northern New Mexico north of Santa Fe in the vicinity of the Native American pueblos of San Ildefonso and Pojoaque, from strata he called the “Santa Fé marl...

Cranial sexual dimorphism is common among vertebrates. The array of antlers, crests, beards, wattles, and other sexual display structures is vast, not to mention the many size, shape and color variants that may apply to all parts of the body. Here, we explore another possible sexual dimorphism signal seen in the skulls of at least some temnospondyl...

We have investigated the skull morphology of numerous aquatic and semiaquatic predators, paying particular attention to the rostrum. Cluster analysis, using the ratios of a few skull or mandible measurements, shows that their skull shapes do not exist on a continuum that varies from relatively long to relatively short rostra and/or relatively narro...

The Pennsylvanian stratigraphic section in the Sierra Ladrones of northern Socorro County can be assigned to the (ascending) Sandia, Gray Mesa, Atrasado and Bursum (lower part) formations. The Sandia Formation is 105 m thick and consists of a lower part that is mostly conglomerate, conglomeratic sandstone, sandstone, limestone and covered intervals...

Although the paleontology of the upper Cenozoic Santa Fe Group in New Mexico has been collected and studied since the 1870s, little is known of its ichnofossils. A vertebrate tracksite in the Plio-Pleistocene Ceja Formation at Rio Rancho, Sandoval County, is the most prolific ichnoassemblage now known from the Santa Fe Group. This assemblage is in...

We present an alternative to the original lekking/display arena hypothesis to explain theropod scrapes in the Cretaceous Naturita and South Platte formations in Colorado. Thus, we posit that they are failed attempts by the smaller of two sizes of theropods to dig near-circular bowls to be used as nests. A variety of shapes and sizes in a set of sma...

Heteropolar coprolites are common in the lower Permian of the American Southwest. Previously there were only two occurrences of Megaheteropolacopros sidmcadamsi, from the Vale Formation of Texas and the El Cobre Canyon Formation of New Mexico. We describe two new occurrences of M. sidmcadamsi from Texas and review the localities, ichnotaxonomy and...

Numerous fossil bivalves in shale/conglomerate were prepared out of several blocks (~227 kg) of sediment that were excavated from the Upper Cretaceous (upper Campanian) Fossil Forest Member of the Fruitland Formation in the Fossil Forest Research Natural Area (23N, R12W) of San Juan County, northwestern New Mexico. The area also contains numerous v...

Ermine Cowles Case (1871-1953), known as E. C., was a distinguished American paleontologist of the late nineteenth and early twentieth century who was a leading expert on upper Carboniferous, lower Permian and Upper Triassic vertebrate fossils. He conducted extensive fieldwork in New Mexico from 1894 to 1934. His unpublished memoirs, fieldbooks and...

The Bureau of Land Management (BLM) Ojito Wilderness Area in southern Sandoval County, New Mexico, is located in the southeastern San Juan Basin. Most of the strata exposed in the Ojito are of Jurassic age, but its western third exposes outcrops of the intertongued Dakota-Mancos succession of early Late Cretaceous (Cenomanian) age. At the top of th...