Geology

Venom delivery systems occur in a wide range of
extant and fossil vertebrates and are primarily based on oral
adaptations. Teeth range from unmodified (Komodo dragons)
to highly specialized fangs similar to hypodermic needles
(protero- and solenoglyphous snakes). Developmental biologists
have documented evidence for an infolding pathway of
fang evolution, where the groove folds over to create the more
derived condition. However, the oldest known members of
venomous clades retain the same condition as their extant
relatives, resulting in no fossil evidence for the transition.
Based on a comparison of previously known specimens with
newly discovered teeth from North Carolina, we describe a
new species of the Late Triassic archosauriform Uatchitodon
and provide detailed analyses that provide evidence for both
venom conduction and document a complete structural series
from shallow grooves to fully enclosed tubular canals. While
known only from teeth, Uatchitodon is highly diagnostic in
possessing compound serrations and for having two venom
canals on each tooth in the dentition. Further, although not a
snake, Uatchitodon sheds light on the evolutionary trajectory
of venom delivery systems in amniotes and provide solid
evidence for venom conduction in archosaur-line diapsids.


Keywords Venom . Uatchitodon . Uatchitodon schneideri .
Evolutionary trajectory . Triassic

Concentrated deposits of small remains from vertebrates, termed microvertebrate sites or vertebrate microsites,
are a unique and detailed source of information about the history of life. Collecting fossils from these sites,
however, presents unique challenges. The most time consuming, and thus most deterring, aspect by far is the
separation of the fossils from the sediment. This study attempts to quantify to what extent the use of sodium
polytungstate (=sodium metatungstate, Na6H2W12O40, abbr. SPT) filtration increases fossil concentration, how
quickly fossils sink in SPT solutions, and what is a good working density for SPT. We do this by generally following
the methodology set out by previous authors, although with some substantial modifications, on an Upper Triassic
deposit dominated by clay minerals and lithic fragments, as well as on a second, smaller quartz sand dominated
microsite. We also provide a revised and detailed guide with our modifications to former practices and our
recommendations to other workers interested in creating a SPT laboratory, including the strong advisory to work
over thin plastic sheets, as SPT can react with metal and adheres strongly to glass when it crystallizes.
Our experiments have shown a significant improvement in fossil concentration (from ~2% of the clasts being
fossils to ~19%) at the main site, with a sample from the other site showing the treated concentrate as 25%
fossil. We have also found very few fossils in the float (<0.5%), but noticeable rates of fossil loss in SPT solutions
above ~2.80 g/mL (up to 16%). Further, we have found that 2.75 g/mL is a good working density for several
lithologies, as it is high enough to float most rock, low enough to sink most fossils, and low enough to be
manageably maintained. SPT has, in processing one particularly rich site, saved many person-hours that otherwise
would have been spent picking through less concentrated sediment.

Located in Santa Fe County, New Mexico, USA, the Lamy amphibian quarry is a Late Triassic (Adamanian)
bonebed stratigraphically low in the Garita Creek Formation of the Chinle Group. Well known for its mass
accumulation of metoposaurid amphibians, it was initially interpreted as a drought-induced death
assemblage. Based on microstratigraphic and sedimentological studies, additional and extensive collecting
at the quarry and a revised understanding of the bonebed, we provide a detailed taphonomic analysis of the
Lamy amphibian quarry that identifies it as a low diversity multitaxic and monodominant bonebed in
pedogenically modified floodplain mudstone. The Lamy bonebed shows no evidence of drought and is
characterized by a high density of completely dissociated bones that show clear alignment by current and
sorting (enrichment of Voorhies Group II and III elements). The bones show no significant abrasion or
weathering (stage 0), preserve virtually no evidence of scavenging and show no evidence of trampling. Based
on skull lengths, the metoposaurid assemblage has a type I survivorship curve and lacks juveniles. We thus
posit that the following sequence of events formed the Lamy amphibian bonebed: (1) aggregation (cause
unknown) of a large number of metoposaurid amphibians at a site different from the location of the bonebed,
though not distant; (2) catastrophic mass mortality; (3) complete disarticulation and disassociation of the
skeletons; and (4) rapid transport of the disarticulated bones onto a floodplain surface that was undergoing
pedogenesis. The Lamy amphibian bonebed is representative of the Late Triassic metoposaurid bonebeds from
Morocco and the western USA, which are monodominant and nearly monotaxic. They indicate that
aggregation (probably of breeding populations) and mass death of metoposaurids were relatively common
across the riverine floodplains of Late Triassic Pangea.

Here we report a tooth of a large archosauriform from the Upper Triassic of New Mexico, USA that displays developmental
anomalies of carina formation. This tooth has two supernumerary carinae, both on the lingual side of the tooth. Previously,
carina anomalies of this sort were primarily known from theropod dinosaurs, but always from the labial surface. Integrating
this specimen into a reassessment of the published accounts of carina anomalies in other fossil diapsids reveals that
supernumerary carinae are more widespread throughout Archosauriformes than previously reported. Our interpretation of
this developmental anomaly highlights the present lack of understanding of tooth development in archosaurs, particularly
carina formation, and suggests that crown morphology development in archosauriforms may be constrained differently than
it is in mammals. This developmental constraint may explain the differences observed between the complexity found in
mammal and archosauriform cusp morphology.

The actual abstract (summary) is 2 printed pages.

This monograph is based on my PhD dissertation and describes microvertebrate faunas from seven localities in the lower Chinle Group of Texas, New Mexico, and Arizona. This includes Trilophosaurus quarry 1 (Colorado City Formation, TX), the lower and upper Kalgary localities (Tecovas Formation, TX), the Ojo Huelos locality (Ojo Huelos, NM), L-2739 (Sixmile Canyon, NM), Krzyzanowski bonebed (St. Johns, AZ), and Dying Grounds (Petrified Forest, Arizona). There's a few new taxa here---Diplolonchidion murryi, Palaeollanosaurus fraseri, Planocephalosaurus lucasi, Crosbysaurus harrisae, and Protecovasaurus lucasi. They are a shark, two sphenodontians, and two archosauriforms that may or may not be convergent with early ornithischians or pterosaurs (subperpendicular, offset denticles). I particularly like Crosbysaurus because it has compound denticles and would appear to represent an intermediate stage between fine denticles (serrations) and coarse denticles typical of both Revueltosaurus and many ornithischian dinosaurs.

Coahomasuchus kahleorum, gen. et sp. nov. is a small « 1 m long) aetosaur from the Upper Triassic Colorado City Member of the Dockum Formation in West Texas. The holotype consists of a nearly complete articulated skeleton, including a well-preserved dorsal and ventral carapace. Several postcranial features diagnose Coahomasuchus, including: dorsal paramedian plates considerably (3.25: 1) wider than long, unflexed, lack keels or horns, and bear faint sub-parallel to radial ornamentation, and lateral scutes that are also unflexed, flat, and bear a faint radial pattern of pits and grooves. Coahomasuchus co-occurs with the aetosaur Longosuchus and the phytosaurs Angistorhinus and Paleor- hinus, indicating that it is of Otischalkian (early late Carnian) age.

Detailed phylogenetic analysis reveals that several North American aetosaur taxa are junior subjective synonyms of previously named taxa. Lucasuchus was named from material from the type locality of Longosuchus and is a junior subjective synonym of that taxon. Acaenasuchus is known only from localities that also produce Desmatosuchus and probably represents juvenile individuals of Desmatosuchus. Stegomus, from various localities in the Newark Super- group, is a junior subjective synonym of Aetosaurus, known previously from the German Keuper and Upper Triassic strata in Italy and Greenland. Paratypothorax andressi is properly called P. andressorum and is known from strata of Adamanian (latest Carnian) to Apachean (Rhaetian) age

Aetosaur scutes assigned to Acaenasuchus geoffreyi Long and Murry, 1995,are juvenile scutes of Desmatosuchus haplocerus (Cope, 1892), so A. geoffreyi is a junior subjective synonym of D. haplocerus. Scutes previously assigned to Acaenasuchus lack anterior bars and a strong radial pattern of elongate
pits and ridges, but do possess an anterior lamina and a raised boss emanating from the mid-dorsal surface of the scute. Desmatosuchus is the only aetosaur with this combination of features, and the replacement of the anterior bar with a lamina is an autapomorphy of Desmatosuchus. Other characters
used by previous workers to distinguish Acaenasuchus from Desmatosuchus include deeply incised pitting on the dorsal scutes and the division of the raised boss posteriorly into two lateral flanges in Acaenasuchus. We interpret the deeply incised pitting as an artifact of ontogenetic variation. The more
exaggerated pits and thin grooves on the scutes of "Acaenasuchus" represent a juvenile stage of development/
an ontogenetic feature we have observed on other aetosaurs, notably Aetosaurus. The divided boss is the most unique characteristic of "Acaenasuchus," but even this feature could also represent immature development. Further, of the four localities (the Blue Hills, the Placerias quarry and the Downs'
quarry-all near St. John'S, AZ, and another locality near Winslow, AZ) that have produced scutes assigned to Acaenasuchus, two (the Placerias and Downs' quarries) also produce abundant adult specimens of Desmatosuchus, and all four localities are in strata of equivalent (latest Carnian) age. Thus, in all critical details of morphology, except size, scutes assigned to Acaenasuchus appear to represent scutes
of Desmatosuchus. The apparent rarity and limited geographic and stratigraphic range of Acaenasuchus relative to Desmatosuchus are artifacts of preservational and collecting biases.

Keywords: Aetosaur, juvenile, taxonomy, Upper Triassic, Desmatosuchus, Acaenasuchus

Aetosaur scutes from the Upper Triassic Bull Canyon Formation of the Chinle Group in east-central New Mexico closely resemble specimens of the early-middle Norian index taxon Aetosaurus arcuatus (MARSH) to which they are assigned. Previously, the Aetosaurus biochron of early-middle Norian age could be recognized in the eastern U.S.A., Greenland, Germany, and Italy. Recognition of Aetosaurus in the Bull Canyon Formation thus confirms earlier correlations of the Revueltian land-vertebrate faunachron to the early-middle Norian.

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The aetosaur genus Coahomasuchus HECKERT & LUCAS, 1999 is known from a single specimen from the Colorado City Formation (Upper Triassic, Late Carnian) of the Chinle Group. New data on the braincase and mandible, as well as a
revised diagnosis, are presented. The preserved braincase region includes all or parts of the parasphenoid, basisphenoid, basioccipital, and opisthotic, all of which are described here. The preserved mandible includes a small fragment of the dentary, splenial, angular, surangular, articular, and prearticular. This new cranial description is intended to provide more information on this taxon for future studies on the interrelationships of the Aetosauria. We document that some characters used to discriminate some aetosaurian taxa, such as the presence or absence of a ventral depression on the basisphenoid and a laterally exposed splenial, should not be used in future phylogenetic analyses of aetosaurs.

Brachychirotherium is the common ichnogenus of Late Triassic chirothere footprints well known from western Europe, North America, Argentina and South Africa. Although it has long been agreed by most workers that the trackmaker of Brachychi- rotherium was a derived crurotarsan archosaur, the trackmaker has been identified as either a rauisuchian or an aetosaur, and some workers attribute it to a primitive crocodylomorph (sphenosuchian). New knowledge of the osteology of the manus and pes of a large aetosaur, Typothorax coccinarum, indicates a close correspondence between the manus and pes structure of aetosaurs and the morphology of Brachychirotherium. Furthermore, func- tional analysis of complete skeletons indicates aetosaurs plausibly placed their feet in the narrow gauge, nearly the overstepped walk characteristic of Brachychirotherium. Brachychirotherium and aetosaurs have matched distributions, that is, they were Pangea- wide during the Late Triassic. The manus and pes morphology of rauisuchians and early crocodylomorphs (sphenosuchians) deviate from Brachychirotherium footprint morphology in key features, thus excluding their identification as trackmakers. Aetosaurs made Brachychirotherium footprints.

The Aetosauria are a monophyletic group of quadrupedal, armored, primarily herbivorous reptiles ranging from 1 to 6 m in body length that are known from Upper Triassic strata in North and South America, Greenland, Europe, Africa, and India. To date, 17 genera and 20 species of aetosaurs have been named, and several new forms are current- ly under study. Of these, we recognize ten valid genera: Aetosaurus, Coahomasuchus, Des- matosuchus, Longosuchus, Neoaetosauroides, Paratypothorax, Redondasuchus, Stago- nolepis, Typotharax, and one other unpublished genus. Most of these genera are monospe- cific, with the exception of Aetosaurus (A. ferratus, A. crassicauda, A. arcuatusi and, pos- sibly, Stagonolepis (S. robertsoni, S. wellesii. Most footprints assigned to the ichnogenus Brachychirotherium are probably of aetosaurs.
A phylogenetic analysis using 60 characters and utilizing the rauisuchians as an out- group produces the following phylogenetic hypothesis: Aetosaurus is the sistergroup to all other aetosaurs, which are divided into two clades a more primitive clade consisting of Stagonolepis + one of the unnamed new taxa, and a more advanced clade consisting of tNeoaetosauroides+«Desmatosuchus+(Typothorax+Redondasuchusi +tLongosuchus + Paratypothoraxiii. We refer Aetosaurus to the Aetosaurinae, n. subfam., the more prim- itive clade to the Stagonolepininae and the more advanced clade to the Desmatosuchinae, both preexisting names. Of the other genera, Stegomus is a junior subjective synonym of Aetosaurus: Aetosauroides, Argentinosuchus, Calyptosuchus, and, Ebrachosaurus (in part) are junior subjective synonyms of Stagonolepis; Lucasuchus is a junior subjective syno- nym of Longosuchus;Acaenasuchusis based on juvenile specimens of Desmatosuchusand thus is a junior subjective synonym of that taxon; Fukangolepis is based on fragmentary dicynodont skull material and thus is not an aetosaur; and Chilenosuchus from the El Bordo Formation in Chile is neither from Triassic rocks nor is it an aetosaur. The holotype of Acompsosaurus wingatensis is lost, and probably represents an individual of Stagonolepis. The German Schilfsandstein reptile Dyoplax is a sphenosuchian, not an aetosaur.
Based on the stratigraphic succession of aetosaurs in the upper Carnian-Rhaetian Chinle Group of the western U.S.A., we identify seven aetosaur biochrons: (1) Longosu- chus biochron of early to late Carnian (late Julian to Tuvalian) age; (2) Desmatosuchus biochron that straddles the Carnian-Norian boundary; (3) Stagonolepis biochron of latest Tuvalian age; (4) Paratypothorax biochron straddling the Carnian-Norian boundary; (5) Typothoraxbiochron of Norian age; (6) Aetosaurus biochron of Norian-Rhaetian age; and (7) Redondasuchus biochron of Rhaetian age. Many of these biochrons correlate strata across much of Pangea. Additionally, a marine occurrence of Aetosaurus from the Calcare di Zorzino in Italy (middle-late Norian =younger portion of the Himavatites columbianus Zone) directly correlates the Aetosaurus biochron, including strata in the U.S.A., Green- land, and Germany, to the global marine timescale. An eighth biochron, the Neoaetosau- roides biochron of late Norian-Rhaetian age, can only be identified in the Los Colorados Formation in Argentina. .
Aetosaur genera were relatively cosmopolitan during the late Carnian, as evidenced by intercontinental correlations based on Longosuchus (from the U.S.A., Morocco, and possiblyIndia)andStagonolepis (fromScotland,theU.S.A.,Argentina,andBrazil).How- ever, with the exception of Aetosaurus, aetosaurs became increasingly provincial in the Norian-Rhaetian, as evidenced by endemic taxa such as Typothorax (North American No- rian),Neoaetosauroides (SouthAmericanlate Norian-Rhaetian), and Redondasuchus (North American Rhaetian). Aetosaurus is known from Germany, Italy, Greenland, the United Kingdom, and both the eastern and western United States.

We describe here an incomplete postcranial skeleton associated with a complete skull and
jaws of the phytosaur Angistorhinus grandis Mehl from the Otischalkian (late Carnian) Colorado City
Formation of the Chinle Group in Howard County, Texas. The skeleton consists of two cervical vertebrae
and parts of others, complete sacrum and pelvis, 12 ribs, 30 gastralia, an incomplete fibula, fragments
of other long bones, and 32 scutes. Particularly interesting features include: (1) the thin neural
spines of the sacral vertebrae; (2) the ilia of Angistorhinus do not appear to differ significantly from that
of Rutiodon (= "Machaeroprosopus"), casting doubt on the taxonomic use of differences in phytosaur ilia;
and (3) Angistorhinus apparently possesses dermal armor that is unique among phytosaurs in having
few pits, most of them small, on the dorsal surface of the primary scutes.
Keywords: phytosaur, postcrania, skeleton, Angistorhinus, Otischalkian, Colorado City Member