Jason R. Bourque

Giant boid snake from the Palaeocene neotropics reveals hotter past equatorial temperatures

The largest extant snakes live in the tropics of South America and southeast Asia where high temperatures facilitate the evolution of large body sizes among air-breathing animals whose body temperatures are dependant on ambient environmental temperatures (poikilothermy). Very little is known about ancient tropical terrestrial ecosystems, limiting our understanding of the evolution of giant snakes and their relationship to climate in the past. Here we describe a boid snake from the oldest known neotropical rainforest fauna from the Cerrejón Formation (58–60 Myr ago) in northeastern Colombia. We estimate a body length of 13 m and a mass of 1,135 kg, making it the largest known snake. The maximum size of poikilothermic animals at a given temperature is limited by metabolic rate, and a snake of this size would require a minimum mean annual temperature of 30–34 °C to survive. This estimate is consistent with hypotheses of hot Palaeocene neotropics with high concentrations of atmospheric CO2 based on climate models. Comparison of palaeotemperature estimates from the equator to those from South American mid-latitudes indicates a relatively steep temperature gradient during the early Palaeogene greenhouse, similar to that of today. Depositional environments and faunal composition of the Cerrejón Formation indicate an anaconda-like ecology for the giant snake, and an earliest Cenozoic origin of neotropical vertebrate faunas.

New Turtles (Chelonia) from the Late Eocene Through Late Miocene of the Panama Canal Basin

Abstract Four distinct fossil turtle assemblages (Chelonia) are recognized from the Panama Canal Basin. The oldest, from the late Eocene–early Oligocene Gatuncillo Formation, is dominated by podocnemidid pleurodires. The early Miocene Culebra Formation includes both podocnemidids and trionychids. The early to middle Miocene Cucaracha Formation includes taxa classified in Geoemydidae (including Rhinoclemmys panamaensis n. sp.), Kinosternidae (represented by Staurotypus moschus n. sp.), large testudinids, trionychids, and podocnemidids, and finally, the late Miocene Gatun Formation records cheloniid sea turtles. These fossils include the oldest known representatives of Rhinoclemmys, the oldest record of kinosternids in Central America with a more extensive southern paleodistribution for Staurotypus and staurotypines in general, early occurrences of giant tortoises in the Neotropics, the oldest occurrence of soft-shell turtles in the tropics, the oldest late Eocene–early Oligocene Neotropical occurrences of podocnemidids. The Panamanian fossil turtles represent clades that are primarily endemic to North America, showing their very early arrival into the Neotropics prior to the complete emergence of the Isthmus of Panama, as well as their first contact with Caribbean-South American pleurodires by the early Miocene.

Fossil Kinosternidae from the Oligocene and Miocene of Florida, USA

Kinosternid remains are generally rare through the Oligocene and Miocene. Fossil material from eight Florida localities is presented here. Specimens discussed include the latest and most southeastern occurrence of the genus Xenochelys (new species), one of the earliest occurrences of Kinosternon, the oldest record of the Kinosternon subrubrum-baurii group in Florida, and the presence of Miocene Kinosternon species either convergent with or closely related to taxa that occur today in the southwestern United States and Central-South America.

Taxonomic assessment of Alligator Snapping Turtles (Chelydridae: Macrochelys), with the description of two new species from the southeastern United States.

The Alligator Snapping Turtle, Macrochelys temminckii, is a large, aquatic turtle limited to river systems that drain into the Gulf of Mexico. Previous molecular analyses using both mitochondrial and nuclear DNA suggested that Macrochelys exhibits significant genetic variation across its range that includes three distinct genetic assemblages (western, central, and eastern = Suwannee). However, no taxonomic revision or morphological analyses have been conducted previously. In this study, we test previous hypotheses of distinct geographic assemblages by examining morphology, reanalyzing phylogeographic genetic structure, and estimating divergence dating among lineages in a coalescent framework using Bayesian inference. We reviewed the fossil record and discuss phylogeographic and taxonomic implications of the existence of three distinct evolutionary lineages. We measured cranial (n=145) and post-cranial (n=104) material on field-captured individuals and museum specimens. We analyzed 420 base pairs (bp) of mitochondrial DNA sequence data for 158 Macrochelys. We examined fossil Macrochelys from ca. 15-16 million years ago (Ma) to the present to better assess historical distributions and evaluate named fossil taxa. The morphological and molecular data both indicate significant geographical variation and suggest three species-level breaks among genetic lineages that correspond to previously hypothesized genetic assemblages. The holotype of Macrochelys temminckii is from the western lineage. Therefore, we describe two new species as Macrochelys apalachicolae sp. nov. from the central lineage and Macrochelys suwanniensis sp. nov. from the eastern lineage (Suwannee River drainage). Our estimates of divergence times suggest that the most recent common ancestor (MRCA) of M. temminckii (western) and M. apalachicolae (central) existed 3.2-8.9 Ma during the late Miocene to late Pliocene, whereas M. temminckii-M. apalachicolae and M. suwanniensis last shared a MRCA 5.5-13.4 Ma during the mid-Miocene to early Pliocene. Examination of fossil material revealed that the fossil taxon M. floridana is actually a large Chelydra. Our taxonomic revision of Macrochelys has conservation and management implications in Florida, Georgia, and Alabama.

Fossil musk turtles (Kinosternidae, Sternotherus) from the late Miocene–early Pliocene (Hemphillian) of Tennessee and Florida

ABSTRACT The oldest fossil musk turtles, genus Sternotherus, are reported from the Hemphillian of eastern Tennessee and central Florida. Sternotherus palaeodorus, n. sp., is known from five partial shells discovered at the late Miocene—early Pliocene (7–4.5 Ma; late Hemphillian) Gray Fossil Site in Washington County, Tennessee. Sternotherus palaeodorus possesses an enlarged intergular scute, wide first vertebral scute that overlaps peripheral set 1, posteriorly extensive hypoplastron to peripheral 7 contact, and a posteriorly situated inguinal musk duct pore (characteristics more typically seen in Kinosternon). A cladistic analysis recovered S. palaeodorus within crown group Sternotherus in the strict consensus and on the stem of Sternotherus in the majority rule consensus. Sternotherus bonevalleyensis, n. sp., from the Palmetto Fauna (5.5–5 Ma; late Hemphillian) of central Florida was perhaps contemporaneous with S. palaeodorus and is known only from isolated shell fragments. It is morphologically most similar to the Sternotherus minor complex and Sternotherus depressus. Subsequent Blancan fossils from the Suwannee River of Florida represent aff. S. minor peltifer. Additionally, a fragmentary left hyoplastron of cf. Sternotherus from Haile 19A, Alachua County, Florida, could be the oldest record for the genus (ca. 9–8.5 Ma; early Hemphillian). These accounts reveal that Sternotherus was diverse and moderately well distributed geographically by its first known fossil occurrences and support previous hypotheses that the Sternotherus minor complex evolved in the Gulf coastal plain and dispersed throughout that region since at least the latest Miocene-earliest Pliocene.

A fossil mud turtle (Testudines, Kinosternidae) from the early middle Miocene (early Barstovian) of New Mexico

ABSTRACT The nearly complete skeleton of a mud turtle, Kinosternon skullridgescens, n. sp., is described from Santa Fe County, New Mexico. The specimen was collected from the early middle Miocene, early Barstovian, Skull Ridge Member of the Tesuque Formation (16.0–14.9 Ma) and is one of the oldest and most complete fossil representatives of the genus Kinosternon. Phylogenetically, the new taxon is placed on the stem of the flavescens group in conjunction with the extinct Kinosternon pojoaque from the late Barstovian of New Mexico. In addition to the flavescens group, K. skullridgescens shares morphological similarities with members of the subrubrum group (of North America), as well as with Kinosternon herrerai (from gulf drainages of eastern Mexico). Close proximity of the fossils K. skullridgescens and K. pojoaque to Mexico suggests that a small-plastroned ancestor of the extant taxa K. herrerai, Kinosternon angustipons (from lower Central America), and Kinosternon dunni (from northwestern South America) could have dispersed from North America into Central America by the middle Miocene (Barstovian). Phylogenetic results based on morphology suggest that the taxon Kinosternon steindachneri (formerly Kinosternon subrubrum steindachneri) be reinstated at the species level.

An extinct mud turtle of the Kinosternon flavescens group (Testudines, Kinosternidae) from the middle Miocene (late Barstovian) of New Mexico

ABSTRACT The complete skeleton of a fossil mud turtle, Kinosternon pojoaque, n. sp., is described from the late Barstovian Rodent Pocket, San Ildefonso Locality of Santa Fe County, New Mexico. The new species represents the oldest member of the Kinosternon flavescens group and suggests that this clade first evolved in the southwestern United States, which, along with northern Mexico, is the center of diversity for these turtles today. The new taxon exhibits plastral characters that suggest phylogenetic affinities with Kinosternon angustipons, Kinosternon dunni, Kinosternon herrerai, Kinosternon hirtipes, and Kinosternon sonoriense and is interpreted here as an example of a morphological intermediate between the clade composed of these taxa and the flavescens group. The new fossil, along with other Miocene Kinosternon fossils from New Mexico, provides evidence that the flavescens clade likely diverged from other southwestern, Central, and South American Kinosternon by at least the late Barstovian, 14.3–13.3 million years ago.

Reassessment of a Putative Fossil Stinkpot (Kinosternidae: Sternotherus) from the Late Miocene (Clarendonian) of Kansas

Abstract The oldest paleontological record of the Stinkpot Musk Turtle, Sternotherus odoratus, from the WaKeeney local fauna (approximately 10 million years ago, Mya) is refuted here. Kinosternids from this fauna are represented only by the genus Kinosternon. Kinosternon sp. probably represents a new taxon, but lack of sufficient material hinders a proper description. A gap of between 9 and 12.5 million years now exists between the first occurrences of Sternotherus (at approximately 4.5–7 Mya) and sister group Kinosternon (between 16 and 17 Mya).

New mud turtles (Kinosternidae, Kinosternon) from the middle–late Miocene of the United States

Abstract. Kinosternon Spix, 1824, was widespread in xeric to savanna associated paleowetlands across North America during the middle—late Miocene and steadily diversified following its first occurrences in the Hemingfordian. In the middle Miocene, Kinosternon rincon n. sp. occurred in the late Barstovian Cerro Conejo Formation of north central New Mexico, perhaps concurrently with Kinosternon pojoaque Bourque 2012a from the Tesuque Formation. Subsequent late Miocene kinosternine fossils indicate that at least three potentially contemporaneous species existed throughout the Clarendonian. These are Kinosternon pannekollops n. sp., from the Ogallala Formation of northern Texas; Kinosternon wakeeniense, n. sp., from the Ogallala Formation of northwestern Kansas and Ash Hollow Formation of south-central Nebraska; and Kinosternon notolophus n. sp., from the Alachua and Statenville formations of northern Florida. Kinosternon rincon is phylogenetically nested between the Kinosternon flavescens (Agassiz, 1857) group (= Platythyra Agassiz, 1857) and more derived Kinosternon including the Kinosternon subrubrum (Lacépède, 1788) group (= Thyrosternum Agassiz, 1857). Kinosternon pannekollops is recovered on the stem of the K. subrubrum group and is the oldest and largest member of that lineage. Kinosternon notolophus is readily differentiated from other Miocene Kinosternon in possessing a distinct dorsomedial keel on the nuchal and faint dorsolateral costal carination. The K. subrubrum group probably originated in the late Miocene savannas of the Great Plains and dispersed eastward via the Gulf Coastal Plain. An unnamed kinosternine taxon existed in the coastal plains of the eastern and southeastern United States during the Middle Miocene Climatic Optimum (with fossils from ∼18 to 15 Ma), and disappeared from the region coincident with the end of that megathermal event.

An Extinct Map Turtle Graptemys (Testudines, Emydidae) from the Late Pleistocene of Florida

ABSTRACT Graptemys kerneri, n. sp., from the Suwannee River drainage of north-central Florida, represents the most southeastern occurrence of the genus. This species is morphologically and geographically most similar to the extant Barbours map turtle, Graptemys barbouri. G. kerneri exhibits sexual dimorphism similar to extant G. barbouri, G. ernsti, G. pulchra, and G. gibbonsi, with females being megacephalic and attaining a much larger size than males. The new species possesses a very wide skull and mandible, making it the most blunt-headed member of its clade. Specimens described here include a nearly complete skull, eight mandibles, two epiplastra, 34 neural bones, and an assortment of other shell fragments. Previously reported fossil material from Florida was collected in the 1960s along the Santa Fe River and referred to both the Pliocene and Pleistocene. Rare earth element (REE) analysis of this material is reinterpreted here as being Rancholabrean in age.