Michael D. Gottfried

The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana

Fossil crocodyliforms discovered in recent years have revealed a level of morphological and ecological diversity not exhibited by extant members of the group. This diversity is particularly notable among taxa of the Cretaceous Period (144–65 million years ago) recovered from former Gondwanan landmasses. Here we report the discovery of a new species of Cretaceous notosuchian crocodyliform from the Rukwa Rift Basin of southwestern Tanzania. This small-bodied form deviates significantly from more typical crocodyliform craniodental morphologies, having a short, broad skull, robust lower jaw, and a dentition with relatively few teeth that nonetheless show marked heterodonty. The presence of morphologically complex, complementary upper and lower molariform teeth suggests a degree of crown–crown contact during jaw adduction that is unmatched among known crocodyliforms, paralleling the level of occlusal complexity seen in mammals and their extinct relatives. The presence of another small-bodied mammal-like crocodyliform in the Cretaceous of Gondwana indicates that notosuchians probably filled niches and inhabited ecomorphospace that were otherwise occupied by mammals on northern continents.

First record of gars (Lepisosteidae, Actinopterygii) on Madagascar: Late Cretaceous remains from the Mahajanga Basin

ABSTRACT Gars (Lepisosteidae, Actinopterygii) are reported from Madagascar for the first time, from exposures of the Upper Cretaceous (?Campanian) Maevarano Formation in the Mahajanga Basin, northwestern Madagascar. The material includes relatively common isolated scales, and vertebral centra, teeth, fin rays, and dermal cranial elements, all assigned to Lepisosteus sp. This new record from Madagascar adds to previously documented Cretaceous Gondwanan gar occurrences in India, Africa, and South America, as well as in Laurasia. The overall pattern points to a Pangean distribution in the Cretaceous and a Jurassic or earlier origin for the gar clade. The extant endemic fishes of Madagascar are not phylogenetically close to gars or to other Late Cretaceous fishes known from the island, suggesting that the ichthyofauna now there likely evolved from post-Mesozoic colonizers.

AN ASSOCIATED SPECIMEN OF CARCHARODON ANGUSTIDENS (CHONDRICHTHYES, LAMNIDAE) FROM THE LATE OLIGOCENE OF NEW ZEALAND, WITH COMMENTS ON CARCHARODON INTERRELATIONSHIPS

Abstract An associated specimen of the large fossil lamnid shark Carcharodon angustidens from the Late Oligocene of New Zealands South Island preserves approximately 165 teeth, and 32 vertebral centra, making it one of the most complete Tertiary lamnids recovered to date, and the most complete fossil shark known from New Zealand. The well-preserved dentition allows for a more thorough description and revised interpretation of the dental morphology of this relatively poorly known species, and the partial vertebral column permits the unequivocal relating of teeth and centra for this taxon. Based on dental and vertebral morphology, C. angustidens is here considered to be properly assigned to the genus Carcharodon, which also includes several other “great-toothed” Tertiary shark species and C. carcharias, the extant Great White Shark. According to this interpretation, Carcharodon has a record extending back to the early Tertiary; this is in sharp contrast to an opposing view, which holds that the genus evolved much more recently, at the Miocene–Pliocene boundary, and that C. angustidens and the other great-toothed forms should be placed in a separate genus (“Carcharocles”).

An anthropoid primate humerus from the Rukwa Rift Basin, Paleogene of southwestern Tanzania

African early Tertiary paleontological sites are notoriously patchy, both spatially and temporally. The vast majority of Paleogene primate fossils have been recovered from sites in the northern portion of the continent (e.g., Thomas et al., 1991; Godinot and Mahboubi, 1992; Hartenberger and Marandat, 1992; Godinot, 1994), with the most extensive record from the Fayum Depression of Egypt (e.g., Osborn, 1908; Simons and Kay, 1983; Simons et al., 1994; Simons, 1995; Simons and Rasmussen, 1995; Simons et al., 2001). Sub-equatorial deposits are relatively sparse, and no primate postcranial remains have been described from Paleogene deposits in sub-Saharan Africa. The rarity of Paleogene strata from much of Africa poses problems not only for understanding the geographical extent and evolutionary significance of faunas occupying the majority of the continental landmass, it also provides obstacles to reconstructing biogeographic histories of a variety of clades, including primates (Stevens and Heesy, 2000; Ducrocq, 2001; Gunnell and Miller, 2001; Heesy et al., in press). In contrast, numerous sites in East Africa have provided a wealth of information concerning the Neogene primate record (e.g., Fleagle and Simons, 1978; Leakey et al., 1995; Harrison, 1997; MacLatchy and Pilbeam, 1999; Kingston et al., 2002). Until relatively recently, the earliest Tertiary faunas reported from East Africa were Miocene in age. New finds from older Tertiary sites suggest that this region also holds keys to understanding issues deeper in paleontological history (e.g., Leakey et al., 1995b; Murray, 2000; Harrison et al., 2001; Gunnell et al., 2002; Kappelman et al., 2003; Stevens et al., 2004). Here we describe a diminutive anthropoid primate humerus recovered from Paleogene deposits in southwestern Tanzania. In many features this specimen resembles basal anthropoids described from the Paleogene Jebel el Qatrani Formation of Egypt, constituting the first primate postcranial record from the Paleogene of sub-Saharan Africa.

First Mesozoic Record of the Stingray Myliobatis wurnoensis from Mali and a Phylogenetic Analysis of Myliobatidae Incorporating Dental Characters

New specimens, including the first record of lower dental plates, of the extinct myliobatid Myliubatis wurnoensis were recovered from the Maastrichtian (Late Cretaceous) of the Iullemmeden Basin, Mali, and are the oldest record of the taxon. We evaluated the phylogenetic position of this taxon with reference to other myliobatids (extinct and extant) using osteology and dentition. Our results indicate that Myliobatinae and Myliobatis are each paraphyletic, and that Aetobatus and Rhinoptera are monophyletic. We also found that taxa known only from the Cretaceous, Brachyrhizodus and Igdabatis, are highly nested within Myliobatidae. The phylogenetic position of these taxa unambiguously extends the origin of Myliobatidae and most of its representative taxa into the Mesozoic.

A new freshwater crab (Decapoda: Brachyura: Potamonautidae)from the Paleogene of Tanzania, Africa

Discovery of numerous fragmentary remains of freshwater crab in Paleogene, probably Oligocene, sediments in Tanzania, Africa, permits the description of a new genus and species, Tanzanonautes tuerkai. The fossils represent the oldest freshwater crabs known.

Stable Isotope Values of Bone Organic Matter: Artificial Diagenesis Experiments and Paleoecology of Natural Trap Cave, Wyoming

Abstract The presence of original organic matter and retention of an indigenous isotopic signal in fossils have been disputed for years. An experiment was conducted to evaluate the influence of diagenesis on bone-protein isotope values, analyses were conducted on Holocene and Pleistocene fossils from Natural Trap Cave (NTC), Wyoming. Modern cow, Bos taurus, bone was heated with and without excess water for up to 195 hours at 100°C in an inert atmosphere. Collagen and non-collagenous proteins (NCP) were extracted and analyzed isotopically. Under dry conditions, carbon and nitrogen isotope values change by less than 0.4‰ during the 0 to 195 hour interval. In the presence of excess water, carbon and nitrogen isotope values change by no more than 1.0‰ and 0.5‰, respectively, over 192 hours. The relative abundance of amino acids of collagen from heated bone differs by less than 10% from that of unheated collagen. Protein preservation is indicated by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) that strongly indicates a portion of the original osteocalcin exists intact in samples heated for 195 hours. Good preservation of collagen in NTC fossils is implied by high collagen yields, C:N, and realistic trophic structures based on isotope values. Carbon and nitrogen isotope values of ancient collagen increase with trophic level, allow dietary assessments to be made, and differentiate between ruminant and non-ruminants. The results indicate that isotope values are resilient during simulated diagenesis and suggest that an indigenous isotopic signal can exist in well-preserved fossils such as those from NTC.

A Morphometric Approach for Addressing Tooth-Based Species Delimitation in Fossil Mako Sharks, Isurus (Elasmobranchii: Lamniformes)

ABSTRACT Morphological studies of fossil and extant shark teeth have typically been qualitative in nature, with resulting taxonomic problems due to the complicated forms of heterodonty exhibited by many sharks. This is apparent in the designation of fossil species assigned to Isurus (Lamniformes), where the status of the putative Neogene fossil species Isurus xiphodon and I. hastalis is solely based upon supposed differences in tooth morphology. Here we apply the geometric morphometric techniques of Procrustes superimposition, resampling-based Goodalls F-test, and canonical variates analysis to extant Isurus teeth, with the goal of assessing whether these quantitative analytical techniques provide a more objective basis for taxonomic decisions than do traditional qualitative morphological descriptions. These quantitative techniques are then applied to I. hastalis and I. xiphodon to examine whether I. xiphodon should be considered a junior synonym of I. hastalis or a separate species. Results show that geometric morphometric techniques can differentiate between the two extant species as well as the two extinct species, supporting I. xiphodon as a valid taxon. We suggest that this type of analysis is applicable for examining tooth-based species delimitations of sharks with both extant and extinct members, and has the potential to be applied to other fossil shark species as well.

Dinosaur eggshell from the Red Sandstone Group of Tanzania

Investigations over the last several decades at Gondwanan Mesozoic localities have significantly expanded our knowledge of the diversity and distribution of Southern Hemisphere dinosaurs. These records are primarily based on skeletal remains, but included among them are in- stances of preserved eggshell, notably from Argentina (e.g., Calvo et al., 1997; Chiappe et al., 1998) and India (e.g., Khosla and Sahni, 1995). In general, however, dinosaur eggshell is relatively poorly known from Gondwana, and from Africa in particular. Newly initiated (summer 2002) field research in Cretaceous-age deposits of the Red Sandstone Group in southwestern Tanzania has resulted in the discovery of a rich terrestrial/freshwater vertebrate fauna, which includes lungfishes and teleost fishes, turtles, crocodilians, sauropod and both avian and non- avian theropod dinosaurs, and mammals. Included among the dinosaur specimens are pieces of well-preserved eggshell. This is the first dinosaur eggshell from the Cretaceous of Africa to be studied and described in detail; it is here placed in the Oofamily Megaloolithidae on the basis of its structural details and surface ornament, which closely resemble those of Cretaceous megaloolithid eggshell from a number of other, non-African localities.

Kahawamys mbeyaensis (n. gen., n. sp.) (Rodentia: Thryonomyoidea) from the Late Oligocene Rukwa Rift Basin, Tanzania

[Extract] Paleogene micromammal-bearing deposits from Afro-Arabia have until recently been largely restricted to a limited number of localities in Saharan Africa and Oman (e.g., Osborn, 1908; Wood, 1968; Jaeger et al., 1985; Fejfar, 1987; Thomas et al., 1989; Holroyd, 1994; Seiffert et al., 2008; but see also Gunnell et al., 2002). Research in the Rukwa Rift Basin of Tanzania has begun to reveal a diverse late Paleogene vertebrate fauna below the equator. This work has produced evidence of primate (Stevens et al., 2005), macroscelidean (Stevens et al., 2006a) and hyracoid mammals, and in particular, an interesting array of rodent taxa (Stevens et al., 2008). Teeth attributed to the phiomorph rodent Metaphiomys have been recorded in the study area (Stevens et al., 2006b), along with a number of smaller thryonomyoid rodent specimens, many of which are severely worn, hampering precise taxonomic assessment. The recent discovery of a fairly complete, modestly worn thryonomyoid mandible allows us to recognize the presence of a new taxon from the Rukwa Rift Basin deposits. This find is significant in that it represents the first novel Paleogene rodent genus and species described from East Africa, and documents a critically under-represented temporal gap in African faunal evolution (e.g., Seiffert, 2006).