Gary S. Morgan

Exceptionally well preserved late Quaternary plant and vertebrate fossils from a blue hole on Abaco, The Bahamas

We report Quaternary vertebrate and plant fossils from Sawmill Sink, a “blue hole” (a water-filled sinkhole) on Great Abaco Island, The Bahamas. The fossils are well preserved because of deposition in anoxic salt water. Vertebrate fossils from peat on the talus cone are radiocarbon-dated from ≈4,200 to 1,000 cal BP (Late Holocene). The peat produced skeletons of two extinct species (tortoise Chelonoidis undescribed sp. and Caracara Caracara creightoni) and two extant species no longer in The Bahamas (Cuban crocodile, Crocodylus rhombifer; and Coopers or Gundlachs Hawk, Accipiter cooperii or Accipiter gundlachii). A different, inorganic bone deposit on a limestone ledge in Sawmill Sink is a Late Pleistocene owl roost that features lizards (one species), snakes (three species), birds (25 species), and bats (four species). The owl roost fauna includes Rallus undescribed sp. (extinct; the first Bahamian flightless rail) and four other locally extinct species of birds (Coopers/Gundlachs Hawk, A. cooperii/gundlachii; flicker Colaptes sp.; Cave Swallow, Petrochelidon fulva; and Eastern Meadowlark, Sturnella magna) and mammals (Bahamian hutia, Geocapromys ingrahami; and a bat, Myotis sp.). The exquisitely preserved fossils from Sawmill Sink suggest a grassy pineland as the dominant plant community on Abaco in the Late Pleistocene, with a heavier component of coppice (tropical dry evergreen forest) in the Late Holocene. Important in its own right, this information also will help biologists and government planners to develop conservation programs in The Bahamas that consider long-term ecological and cultural processes.

Late Neogene Oceanographic Change along Florida's West Coast: Evidence and Mechanisms

Evidence from vertebrate and invertebrate fossil assemblages and isotopic analyses supports the hypothesis that during the Pliocene biological productivity in the eastern Gulf of Mexico was considerably higher than during the Pleistocene and Recent. Late Pliocene faunal changes in the eastern Gulf, Western Atlantic, and possibly elsewhere may have resulted, at least in part, from this shift in productivity conditions. Even if marine temperatures declined, paleontological and isotopic data appear to require a change in productivity in the Late Pliocene. This putative productivity decline may have been caused by some combination of causes at three geographic scales: (1) globally-marine productivity may have fallen due to changes in continental weathering; (2) regionally-North Atlantic productivity may have fallen as a result of initiation of North Atlantic Deep Water formation (possibly a consequence of formation of the Central American Isthmus, CAI) and resulting net transfer of nutrients to the Pacific; (3) locally-productivity may have fallen only in the eastern Gulf, due to circulation changes assisted with the formation of the CAI, and an accompanying decline in upwelling. The relative importance of processes at these three geographic scales remains unclear. The probable role of the formation of the CAI in two of the three, however, points to the importance of further investigation of the paleoceanographic consequences of this event for Late Cenozoic biological communities of the region.

First North American fossil monkey and early Miocene tropical biotic interchange

New World monkeys (platyrrhines) are a diverse part of modern tropical ecosystems in North and South America, yet their early evolutionary history in the tropics is largely unknown. Molecular divergence estimates suggest that primates arrived in tropical Central America, the southern-most extent of the North American landmass, with several dispersals from South America starting with the emergence of the Isthmus of Panama 3–4 million years ago (Ma). The complete absence of primate fossils from Central America has, however, limited our understanding of their history in the New World. Here we present the first description of a fossil monkey recovered from the North American landmass, the oldest known crown platyrrhine, from a precisely dated 20.9-Ma layer in the Las Cascadas Formation in the Panama Canal Basin, Panama. This discovery suggests that family-level diversification of extant New World monkeys occurred in the tropics, with new divergence estimates for Cebidae between 22 and 25 Ma, and provides the oldest fossil evidence for mammalian interchange between South and North America. The timing is consistent with recent tectonic reconstructions of a relatively narrow Central American Seaway in the early Miocene epoch, coincident with over-water dispersals inferred for many other groups of animals and plants. Discovery of an early Miocene primate in Panama provides evidence for a circum-Caribbean tropical distribution of New World monkeys by this time, with ocean barriers not wholly restricting their northward movements, requiring a complex set of ecological factors to explain their absence in well-sampled similarly aged localities at higher latitudes of North America.

Chapter 12: Mammalian Biochronology of Blancan and Irvingtonian (Pliocene and Early Pleistocene) Faunas from New Mexico

Abstract Significant mammalian faunas of Pliocene (Blancan) and early Pleistocene (early and medial Irvingtonian) age are known from the Rio Grande and Gila River valleys of New Mexico. Fossiliferous exposures of the Santa Fe Group in the Rio Grande Valley, extending from the Española basin in northern New Mexico to the Mesilla basin in southernmost New Mexico, have produced 21 Blancan and 6 Irvingtonian vertebrate assemblages; three Blancan faunas occur in the Gila River Valley in the Mangas and Duncan basins in southwestern New Mexico. More than half of these faunas contain five or more species of mammals, and many have associated radioisotopic dates and/or magnetostratigraphy, allowing for correlation with the North American land-mammal biochronology. Two diverse early Blancan (4.5–3.6 Ma) faunas are known from New Mexico, the Truth or Consequences Local Fauna (LF) from the Palomas basin and the Buckhorn LF from the Mangas basin. The former contains five species of mammals indicative of the early Blancan: Borophagus cf. B. hilli, Notolagus lepusculus, Neotoma quadriplicata, Jacobsomys sp., and Odocoileus brachyodontus. Associated magnetostratigraphic data suggest correlation with either the Nunivak or Cochiti Subchrons of the Gilbert Chron (4.6–4.2 Ma), which is in accord with the early Blancan age indicated by the mammalian biochronology. The Truth or Consequences LF is similar in age to the Verde LF from Arizona, and slightly older than the Rexroad 3 and Fox Canyon faunas from Kansas. The Buckhorn LF has 18 species of mammals, including two rodents typical of the early Blancan, Mimomys poaphagus and Repomys panacaensis. The Buckhorn LF also is similar in age to the Verde LF and has affinities with the Panaca LF from Nevada. Although the Buckhorn and Truth or Consequences LFs have few taxa in common, the similarities of both faunas with the Verde LF suggest they are close in age. Eight faunas from the central and southern Rio Grande Valley are medial Blancan in age (3.6–2.7 Ma), including the Pajarito and Belen faunas from the Albuquerque basin, the Arroyo de la Parida LF from the Socorro basin, the Cuchillo Negro Creek and Elephant Butte Lake LFs from the Engle basin, the Palomas Creek LF from the Palomas basin, the Hatch LF from the Hatch-Rincon basin, and the Tonuco Mountain LF from the Jornada basin. These faunas are characterized by the presence of taxa absent from early Blancan faunas, including Geomys (Nerterogeomys) paenebursarius, Equus cumminsii, E. scotti, and Camelops, and the absence of South American immigrant mammals found in late Blancan faunas. The Pajarito LF is directly associated with a pumice dated at 3.1 Ma. The Cuchillo Negro Creek and Elephant Butte Lake LFs are in close stratigraphic association with a basalt flow of 2.9 Ma. Magnetostratigraphy constrains the age of the Tonuco Mountain LF between 3.6 and 3.0 Ma. The Mesilla A fauna from the Mesilla basin and the Pearson Mesa LF from the Duncan basin are late Blancan in age (2.7–2.2 Ma). Both record the association of Nannippus with a South American immigrant, Glyptotherium from Mesilla A and Glossotherium from Pearson Mesa, restricting their age to the interval after the beginning of the Great American Interchange at about 2.7 Ma and before the extinction of Nannippus ca. 2.2 Ma. Magnetostratigraphy further constrains the Mesilla A and Pearson Mesa faunas to the upper Gauss Chron, just prior to the Gauss/Matuyama boundary. The Mesilla B and Virden faunas occur higher in the same stratigraphic sequences as the Mesilla A and Pearson Mesa faunas, respectively, and are latest Blancan in age (2.2–1.8 Ma). Both faunas contain taxa restricted to the Blancan, including the camels Blancocamelus and Gigantocamelus from Mesilla B, and Canis lepophagus from Virden. The absence of Nannippus, and of Mammuthus and other genera that first appear in the Irvingtonian, support the age. The Tijeras Arroyo fauna from the Albuquerque basin and the Tortugas Mountain and Mesilla C faunas from the Mesilla basin all possess Mammuthus and other mammals indicative of early Irvingtonian age. The association of Mammuthus and Stegomastodon in the Tortugas Mountain LF indicates an age younger than 1.8 Ma, after the arrival of Mammuthus in North America from Eurasia and before the extinction of Stegomastodon at about 1.2 Ma. The co-occurrence of Glyptotherium arizonae, Equus scotti, and the primitive mammoth M. meridionalis in Tijeras Arroyo and Mesilla C is typical of southwestern early Irvingtonian faunas. Fossils of M. meridionalis from Tijeras Arroyo and Mesilla C are both closely associated with dates of 1.6 Ma on pumice from the lower Bandelier tuff, making them among the oldest dated mammoths in North America. A fauna from San Antonio Mountain (SAM) Cave in the San Luis basin of northernmost New Mexico lacks large mammals, but the presence of the microtine rodents Mictomys kansasensis, an advanced species of Allophaiomys, Lemmiscus curtatus, and Microtus cf. M. californicus indicates medial Irvingtonian age, between about 1.0 and 0.85 Ma.

A NEW BAT (CHIROPTERA: NATALIDAE) FROM THE EARLY MIOCENE OF FLORIDA, WITH COMMENTS ON NATALID PHYLOGENY

Abstract We describe a new extinct genus and species of bat belonging to the endemic Neotropical family Natalidae (Chiroptera) from the Thomas Farm Local Fauna in northern peninsular Florida of early Miocene age (18–19 million years old). The natalid sample from Thomas Farm consists of 32 fossils, including a maxillary fragment, periotics, partial dentaries, isolated teeth, humeri, and radii. A proximal radius of an indeterminate natalid is reported from the I-75 Local Fauna of early Oligocene age (about 30 million years old), also from northern Florida. These fossils from paleokarst deposits in Florida represent the 1st Tertiary records of the Natalidae. Other extinct Tertiary genera previously referred to the Natalidae, including Ageina, Chadronycteris, Chamtwaria, Honrovits, and Stehlinia, may belong to the superfamily Nataloidea but do not fit within our restricted definition of this family. Eight derived characters of the Natalidae sensu stricto are discussed, 5 of which are present in the new Miocene genus. Intrafamilial phylogenetic analysis by parsimony of the Natalidae suggests that the 3 living subgenera, Natalus (including N. major, N. stramineus, and N. tumidirostris), Chilonatalus (including C. micropus and C. tumidifrons), and Nyctiellus (including N. lepidus), deserve full generic rank. The Natalidae apparently evolved in North America before the late Oligocene, went extinct in what is now the Nearctic region (i.e., Florida) after the early Miocene, and survived in tropical Middle America during the remainder of the Tertiary. The presence of 2 endemic genera and 4 endemic species suggests that natalids reached the West Indies by overwater dispersal early in their history (Oligocene or Miocene). The lack of a Tertiary fossil record, marginal distribution, and limited species richness and endemism of natalids in South America are suggestive of a comparatively late arrival on that continent, possibly in the late Pliocene after the beginning of the Great American Faunal Interchange.

Temporal Calibration and Biochronology of the Centenario Fauna, Early Miocene of Panama

New excavations along the Panama Canal have yielded a growing Early Miocene assemblage of mammals referred to as the Centenario Fauna. Despite the area’s proximity to South America, the mammals of the Centenario Fauna have entirely North American affinities. The Centenario Fauna is distributed throughout a ∼115-m stratigraphic interval encompassing the uppermost Culebra and Cucaracha Formations within the Panama Canal basin. Previously published ages constrain the age of the lower limit of the Centenario Fauna to no younger than ∼19 Ma, but the upper limit has remained problematical. A fresh exposure of the Cucaracha tuff, a prominent marker horizon within our measured sections, has yielded two new radioisotopic determinations: (1) an 40Ar/39Ar age of 18.96 ± 0.90 Ma and (2) a U-Pb zircon age of 18.81 ± 0.30 Ma. In addition, magnetostratigraphic data indicate that the Centenario Fauna occurs within chron C5Er, from 18.78 to 19.05 Ma on the geomagnetic polarity timescale of Gee and Kent. These correlations further confirm the calibration of the latest Arikareean (Ar4) to early Hemingfordian (He1) transition in Nebraska, at the base of chron C5Er, at about 19.05 Ma. The Centenario Fauna occurs at the beginning of the Hemingfordian North American Land Mammal Age, i.e., He1. A broad faunal province existed during the early Hemingfordian that can be recognized across a north-south range of 5000 km throughout North America, with the southernmost limits defined by the Centenario Fauna of Panama.

Molossid Bats from the Late Tertiary of Florida with a Review of the Tertiary Molossidae of North America

The fossil history of molossids in the North American Tertiary is among the poorest for any family of bats. The oldest definite record is of Wallia scalopidens of middle Eocene (Uintan) age from Saskatchewan, Canada. One of the youngest records is of Eumops cf. E. perotis from the late Pliocene (late early Blancan) of Arizona, USA. New occurrences detailed herein from the middle and late Tertiary of Florida, USA, begin to fill in the 40-million-year gap between the previous records. They are: (1) an abraded upper molar of an indeterminate genus from the Brooksville 2 locality, Hernando County, of late Oligocene (Arikareean) age; (2) a large and a small upper molar pertaining to two congeneric species similar to Tadarida and Mormopterus, from the Thomas Farm local fauna, Gilchrist County, of early Miocene (early Hemingfordian) age; and (3) a distal humerus from a Tadarida of an unknown species that is larger than extant Tadarida brasiliensis and similarly sized but differently proportioned than in the extinct Pleistocene species Tadarida constantinei. The last specimen is from the Macasphalt Shell Pit, Sarasota County, and is of late Pliocene (late Blancan) age.

Ontogeny and Sexual Dimorphism of Glyptotherium texanum (Xenarthra, Cingulata) from the Pliocene and Pleistocene (Blancan and Irvingtonian NALMA) of Arizona, New Mexico, and Mexico

North American glyptodonts originated from South American ancestors during the Great American Biotic Interchange no later than early Blancan North American Land Mammal Age (NALMA). A substantial expansion in population samples from the late Blancan 111 Ranch fauna of southeastern Arizona, several late Blancan faunas in New Mexico, and the early Blancan–Irvingtonian faunas of Guanajuato, Mexico, permit, analysis of sexual dimorphism and ontogeny of Glyptotherium texanum Osborn, 1903. Growth of carapacial osteoderms was allometric, including changes of the external sculpturing. Overall anatomy of the carapace changed with growth, with development of distinctive pre-iliac and post-iliac regions in lateral profile of adults. Skulls of adults possess a unique boss on the anterior surface of the descending process of the zygomatic arch that is not present in juveniles. Sexual dimorphism involves differences in anatomy of lateral and posterior osteoderms. Glyptotherium arizonae Gidley, 1926, is a junior synonym of G. texanum. The temporal distribution of G. texanum extends from early Blancan NALMA to Irvingtonian NALMA, with geographical distribution from Central America and Mexico to southern United States.

A NEW VESPERTILIONID BAT (MAMMALIA: CHIROPTERA) FROM THE EARLY MIOCENE (HEMINGFORDIAN) OF FLORIDA, USA

Abstract A new bat, Karstala silva, gen. et sp. nov., is described from the early Miocene (early Hemingfordian) Thomas Farm local fauna, Gilchrist County, Florida. The new taxon is represented by an upper canine, posterior part of the dentary, isolated upper and lower molars, much of the humerus, and part of the radius. The myotodont configuration and steeply inclined lingual cingulid of m1-m2 separate Karstala from the Molossidae and most Vespertilionidae except Antrozous. Karstala differs from Antrozous in other molar details and from all molossids and North American vespertilionids in having a humerus with the combination of a rounded head, deep supraglenoid pit, long and high pectoral ridge, tiny olecranon fossa, and no notch between the medial side of the trochlea and spinous process. The new species is comparable in size to the larger known species of the Vespertilionidae and is the largest known bat in the Tertiary of North America.

Chapter 15: New Oreodont (Mammalia, Artiodactyla) from the Late Oligocene (Early Arikareean) of Florida

Abstract Exceptionally well-preserved partial skeletal remains representing a minimum of six individuals of an oreodont are described from the White Springs Local Fauna, Columbia County, northern Florida. Although oreodonts are very common from classic Oligocene and early Miocene deposits in the western United States, this group is poorly represented from Florida. The White Springs oreodont pertains to a new species, Mesoreodon floridensis, and is derived, particularly in the development of the auditory bulla, relative to more primitive, closely related species such as Merycoidodon culbertsoni, the latter of which is well known from the badlands of the western United States. Mesoreodon floridensis differs from most other species assigned to this genus in the relative development of the nasal region, possible presence of a facial vacuity, configuration of the preorbital fossa, relatively simple occipital and zygomatic morphology, and imbricated premolar morphology. Based on the associated faunal remains and age determinations, M. floridensis is late early Arikareean (Ar2) in age, ca. 25–24 million years old, and occurs in an interval not well represented in the classic Arikareean sequence of western Nebraska. A mounted skeleton of M. floridensis, on exhibition, is also described.