Phylogenetic relationships of the genus Sibynophis (Serpentes: Colubroidea)

Os resultados apresentados correspondem à primeira análise molecular feita acerca das afinidades filogenéticas do gênero Sibynophis, um colubróideo de origem asiática. Sibynophis aparece como sendo o grupo-irmão do gênero Neotropical Scaphiodontophis. Embora Liophidium esteja por vezes associado a estes dois gêneros, a sua relação é apenas distante. Os caracteres morfológicos compartilhados entre Liophidium, Sibynophis e Scaphiodontophis correspondem a homoplasias que refletem provavelmente os hábitos alimentares especializados semelhantes, presentes nos três gêneros em questão. A tradicional subfamília Sibynophiinae é elevada ao nível de família, enquanto que Scaphiodontophiinae passa para sua sinonímia.We present the results of the first molecular analysis of the phylogenetic affinities of the Asian colubroid genus Sibynophis. We recovered a sister-group relationship between Sibynophis and the New World Scaphiodontophis. Although Liophidium sometimes is associated with these genera, the relationship is distant. Morphological characters that Liophidium shares with Sibynophis and Scaphiodontophis are resolved as homoplasies that probably reflect the similarities of their specialized feeding habits. The traditional subfamily Sibynophiinae is elevated to the family-level, and Scaphiodontophiinae is placed in its synonymy

A second new species for the rare dipsadid genus Caaeteboia Zaher et al., 2009 (Serpentes: Dipsadidae) from the Atlantic Forest of northeastern Brazil

Caaeteboia is a rare and elusive monotypic genus of Neotropical snake, being one of the least known dipsadids of the Brazilian Atlantic Forest. Here, we assess the morphological and genetic diversity of this genus, comparing these results with several other genera of Xenodontinae. Our combined results revealed the presence of an unknown species from the northeastern portion of the Atlantic Forest. The new species is distributed throughout the enclaves of coastal open forests mixed with savanna-like habitat, locally known as “Floresta de Tabuleiro”, and submontane ombrophilous forests in the Brazilian states of Paraíba and Pernambuco. This new species is easily distinguished from C. amarali by its lower number of dorsal, ventral, and subcaudal scales, and a remarkable dark lateral stripe from the nostril up to the anterior third of the body. The new species extends the distribution of the genus in approximately 700 kilometers northwards, reinforcing the importance of the conservation of small remnants of Atlantic Forest in northeastern Brazil, which still harbor high levels of endemicity and diversity.Caaeteboia é um gênero de serpente raro e monotípico da região Neotropical, sendo um dos dipsadídeos menos conhecidos da Floresta Atlântica brasileira. Neste trabalho, avaliamos a diversidade morfológica e genética desse gênero, comparando-o com outros gêneros de Xenodontinae. Nossos resultados combinados revelaram a presença de uma espécie desconhecida da porção nordeste da Floresta Atlântica. A nova espécie se distribui ao longo dos enclaves de florestas abertas costeiras misturadas com habitats savânicos, conhecidos localmente por “Florestas de Tabuleiro”, e florestas ombrófilas submontanas nos estados da Paraíba e de Pernambuco. Essa nova espécie é distinguida de C. amarali pelo menor número de escamas dorsais, ventrais e subcaudais, e por uma evidente linha escura lateral desde o focinho até o terço anterior do corpo. A nova espécie amplia a distribuição do gênero para aproximadamente 700 quilômetros ao norte, e reforça a importância da conservação dos pequenos remanescentes de Floresta Atlântica no nordeste do Brasil, os quais ainda abrigam altos níveis de endemismo e diversidade.Asociación Herpetológica Argentin

A second new species for the rare dipsadid genus Caaeteboia Zaher et al., 2009 (Serpentes: Dipsadidae) from the Atlantic Forest of northeastern Brazil

Caaeteboia is a rare and elusive monotypic genus of Neotropical snake, being one of the least known dipsadids of the Brazilian Atlantic Forest. Here, we assess the morphological and genetic diversity of this genus, comparing these results with several other genera of Xenodontinae. Our combined results revealed the presence of an unknown species from the northeastern portion of the Atlantic Forest. The new species is distributed throughout the enclaves of coastal open forests mixed with savanna-like habitat, locally known as “Floresta de Tabuleiro”, and submontane ombrophilous forests in the Brazilian states of Paraíba and Pernambuco. This new species is easily distinguished from C. amarali by its lower number of dorsal, ventral, and subcaudal scales, and a remarkable dark lateral stripe from the nostril up to the anterior third of the body. The new species extends the distribution of the genus in approximately 700 kilometers northwards, reinforcing the importance of the conservation of small remnants of Atlantic Forest in northeastern Brazil, which still harbor high levels of endemicity and diversity.Caaeteboia é um gênero de serpente raro e monotípico da região Neotropical, sendo um dos dipsadídeos menos conhecidos da Floresta Atlântica brasileira. Neste trabalho, avaliamos a diversidade morfológica e genética desse gênero, comparando-o com outros gêneros de Xenodontinae. Nossos resultados combinados revelaram a presença de uma espécie desconhecida da porção nordeste da Floresta Atlântica. A nova espécie se distribui ao longo dos enclaves de florestas abertas costeiras misturadas com habitats savânicos, conhecidos localmente por “Florestas de Tabuleiro”, e florestas ombrófilas submontanas nos estados da Paraíba e de Pernambuco. Essa nova espécie é distinguida de C. amarali pelo menor número de escamas dorsais, ventrais e subcaudais, e por uma evidente linha escura lateral desde o focinho até o terço anterior do corpo. A nova espécie amplia a distribuição do gênero para aproximadamente 700 quilômetros ao norte, e reforça a importância da conservação dos pequenos remanescentes de Floresta Atlântica no nordeste do Brasil, os quais ainda abrigam altos níveis de endemismo e diversidade.Asociación Herpetológica Argentin

Catálogo Taxonômico da Fauna do Brasil: setting the baseline knowledge on the animal diversity in Brazil

The limited temporal completeness and taxonomic accuracy of species lists, made available in a traditional manner in scientific publications, has always represented a problem. These lists are invariably limited to a few taxonomic groups and do not represent up-to-date knowledge of all species and classifications. In this context, the Brazilian megadiverse fauna is no exception, and the Catálogo Taxonômico da Fauna do Brasil (CTFB) (http://fauna.jbrj.gov.br/), made public in 2015, represents a database on biodiversity anchored on a list of valid and expertly recognized scientific names of animals in Brazil. The CTFB is updated in near real time by a team of more than 800 specialists. By January 1, 2024, the CTFB compiled 133,691 nominal species, with 125,138 that were considered valid. Most of the valid species were arthropods (82.3%, with more than 102,000 species) and chordates (7.69%, with over 11,000 species). These taxa were followed by a cluster composed of Mollusca (3,567 species), Platyhelminthes (2,292 species), Annelida (1,833 species), and Nematoda (1,447 species). All remaining groups had less than 1,000 species reported in Brazil, with Cnidaria (831 species), Porifera (628 species), Rotifera (606 species), and Bryozoa (520 species) representing those with more than 500 species. Analysis of the CTFB database can facilitate and direct efforts towards the discovery of new species in Brazil, but it is also fundamental in providing the best available list of valid nominal species to users, including those in science, health, conservation efforts, and any initiative involving animals. The importance of the CTFB is evidenced by the elevated number of citations in the scientific literature in diverse areas of biology, law, anthropology, education, forensic science, and veterinary science, among others

Geographical variation in the reproduction and sexual dimorphism of the Boddaert's tropical racer, Mastigodryas boddaerti (Serpentes: Colubridae)

We obtained data on time of sexual maturity, dimorphism, fecundity and on the reproductive cycle of Mastigodryas boddaerti (Sentzen, 1796) through the examination of 321 preserved specimens, of which 221 were collected in the Brazilian Amazon region and 100 in the Cerrado savannas of Central Brazil. The degree of sexual size dimorphism (snout-vent length, SVL) was significantly greater in the specimens from the Cerrado in comparison with those from the Amazon. Females had a significantly larger number of ventral scales, on average, whereas males had more sub-caudal scales. However, there was no intersexual difference in tail length or head width, although the heads of the males were significantly longer, which may reflect dietary differences. Breeding females from the Amazon region contained between one and six eggs (N = 12, mean = 3.0), whereas two females from the Cerrado had four to six eggs (N = 10, mean = 5.0). No relationship was found between the SVL of the Amazonian females and the number of eggs or vitellogenic follicles they contained (Cerrado females were not analyzed here due to small sample size). Males are smaller than their female counterpart when they reach sexual maturity. Even though females from the Amazon reproduce throughout the year, females from the Cerrado breed seasonality

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Thamnodynastes silvai Trevine & Caicedo-Portilla & Hoogmoed & Thomas & Franco & Montingelli & Osorno-Muñoz & Zaher 2021, sp. nov.

<i>Thamnodynastes silvai</i> sp. nov. <p>(Figs. 3–4)</p> <p> <i>Thamnodynastes</i> cf. <i>pallidus</i> Dixon & Soini, 1977: 73; Dixon and Soini, 1986: 132.</p> <p> <i>Thamnodynastes pallidus</i> Bartlett & Bartlett, 2003: 250, fig. 248.</p> <p> <b>Holotype.</b> An adult male, SINCHI-R 2139 (Field Number JSH 948), collected by Juan Silva Haad on Isla Rondinã (no collection date), province of Mariscal Ramón Castilla, district of Ramón Castilla, department of Loreto, Peru (Fig. 3).</p> <p> <b> <i>Paratypes</i> (<i>n</i> =30).</b> Seven adults and one juvenile from Loreto Department, Peru: female, AMNH 52125, collected by Harvey Bassler on March 1931 at Caballococha, Amazon River; male, AMNH 53581, collected by Harvey Bassler on December 16 1926 at Rean Rean, Suhuayo (near Contamana, Ucayali River); male, AMNH 52083 and female, AMNH 55472, without additional information; male AMNH 55643, collected by Harvey Bassler at Monte Carmelo, Requena Province (Uresti), no collection date; female, MHNC 3143 (Field Number 11) from Dos de Mayo (Sarayacu), Ucayali Province; male, USNM 197292 (Field Number AJ 933), collected on November 1970 at Iquitos; young male, CORBIDI 6072, from Requena Province (Jenaro Herrera) without additional information. Twelve adults collected by Dionisio Mafra at Yahuma island, Cayarú, Mariscal Ramón Castilla Province, Ramón Castilla district, Loreto Department, Peru: five females, SINCHI-R 2143 (Field Number JSH 1420), SINCHI-R 2154 (Field Number JSH 1182), SINCHI-R 2148 (Field Number JSH 956), SINCHI-R 2147 (Field Number JSH 1034) and SINCHI-R 2151 (Field Number JSH 1585); and seven males, SINCHI-R 2140 (Field Number JSH 1051), SINCHI-R 2141 (Field Number JSH 1427), SINCHI-R 2163 (Field Number JSH 1062), SINCHI-R 2146 (Field Number JSH 963), SINCHI-R 2149 (Field Number JSH 704), SINCHI-R 2150 (Field Number JSH 1422), and SINCHI-R 2157 (Field Number JSH 1043). Five adults and one juvenile from Leticia, Amazonas department, Colombia: female, IAVH 2046 (Field Number OPM 518), collected by Oscar Pinto-Moreno at Amacayacu Natural National Park; young male, IAVH 854, collected by Juan Silva Haad on August 1978; two males, SINCHI-R 2144 (Field Number JSH 1127) and SINCHI-R 2169 (Field Number JSH 861); and two females, SINCHI-R 2142 (Field Number JSH 819) and SINCHI-R 2159 (Field Number JSH 150). One adult male, USNM 233065 (Field Number 807), collected on May 1952 at Maruma, Morona-Santiago Province, Ecuador (no collector information). Two adult females, SINCHI-R 2153 (Field Number JSH 373) and SINCHI-R 2162 (Field Number JSH 429), from Tabatinga, Amazonas State, Brazil. One adult female, MPEG 18835 (Field Number TCAP 2357), collected on July 29, 1994 by Marinus S. Hoogmoed and Teresa C. Ávila-Pires at the Mamirauá Ecological Station, Araçazinho lake (left bank of Paraná Apara), Uarini, Amazonas state, Brazil.</p> <p> <b>Diagnosis.</b> Venter scattered with sparse dark brown blotches, not forming longitudinal ventral stripes; 12–21 dark brown blotches on the first third of the dorsum of the body, which progressively fade and turn into small brown spots on each side of the paravertebral region (Figs. 3–4); dorsal scale rows smooth, in 17/17/11 (70%, <i>n=</i> 42) or 17/17/13 (22%, <i>n=</i> 13) series; dorsals lacking apical pits; ventrals 124–137 in females and 127–148 in males; and subcaudals 80–97 in females, 83–101 in males (Table 2).</p> <p> <b>Comparisons.</b> <i>Thamnodynastes silvai</i> differs from all congeners by having 17/17/13 or 17/17/11 dorsals [vs. 19/19/ 15 in <i>T. almae</i> Franco & Ferreira, 2003; <i>T. chaquensis</i> Bergna & Alvarez, 1993; <i>T. corocoroensis</i> Gorzula & Ayarzagüena, 1996; <i>T. dixoni</i>; <i>T. gambotensis</i> Perez-Santos & Moreno, 1989; <i>T. hypoconia;</i> <i>T. marahuaquensis</i> Gorzula & Ayarzagüena, 1996; <i>T. nattereri</i>; <i>T. paraguanae</i>; <i>T. phoenix</i> Franco, Trevine, Montingelli & Zaher, 2017; <i>T. ramonriveroi</i> Manzanilla & Sánchez, 2005; <i>T. rutilus</i> (Prado, 1942); <i>T. strigatus</i>; <i>T. yavi</i> Myers & Donnelly, 1996; and 19/19/ 13 in <i>T. ceibae</i> Bailey & Thomas, 2007], and ventral color pattern lacking longitudinal stripes (vs. at least some portion of venter with continuous or inconspicuous longitudinal stripes in all other <i>Thamnodynastes,</i> except for <i>T. sertanejo</i>). In addition, from the other species with 17 dorsals at midbody (<i>T. chimanta</i> Roze, 1958, <i>T. duida</i> and <i>T. lanei</i> Bailey, Thomas & Silva Jr., 2005), the new species differs by having 13 series of dorsals on the cloacal region (vs. 15 series in <i>T. chimanta, T. duida</i> and <i>T. lanei</i>); smooth dorsal scales (vs. dorsals markedly keeled in <i>T. lanei</i>); and 80–101 subcaudals (vs. 51–61 subcaudals in <i>T. chimanta,</i> 56 in <i>T. duida</i> and 73–88 in <i>T. lanei</i>) (Table 1). From the species of the <i>T. pallidus</i> group (<i>T. longicaudus</i>, <i>T. pallidus</i> and <i>T. sertanejo</i>), <i>T. silvai</i> differs by a set of characters (Table 2). Besides the absence of longitudinal ventral stripes, it differs from <i>T. longicaudus</i> by having 17/17/13 or 17/17/11 dorsals (vs. 19/19/13); from <i>T. pallidus</i> by divided cloacal (vs. single), the overall dorsal pattern, composed by several blotches on the first third of the body (vs. first third with several spots of lighter scales, yellow and whitish, bordered by dark brown or black markings in the scale interspaces, in a variegated pattern, sometimes forming smaller blotches), and wider and darker postocular stripe and supralabials spots (vs. postocular stripe and labial spots composed only by a thin dark line delineating the border, not colored internally) (Figs. 1, 3). <i>Thamnodynastes sertanejo</i> is the only other member of the genus with a blotched ventral pattern (not forming longitudinal stripes). Even so, <i>T. silvai</i> can be easily differentiated by head length 12.3–17.1 mm (vs. 16.1–25.8 mm in <i>T. sertanejo</i>), lower number of ventral counts, both for male and females (Table 2), and also by the overall dorsal body pattern: transverse dark brown or greyish bands separated by lighter bands (formed by three to five rows of beige scales) on the first third of the body, progressively vanishing into a homogeneous pattern with a few scattered small dark spots in mid-body that continue throughout the tail (vs. generally homogeneous first third of the body in <i>T. sertanejo</i>, with dark broad dorsal blotches separated by transverse bands of two or three rows of white scales, evident from the mid-body to tail) (Figs. 1, 3–4). Additionally, <i>T. sertanejo</i> also exhibits a few scattered black dots on the anterior portion of the venter, which may appear as larger black spots on the ventral posterior region (Fig. 1).</p> <p> <b>Description of the holotype.</b> Dorsals smooth in 17/17/11 rows; apical pit absent; ventrals 136 and divided subcaudals 98; cloacal semi-divided (division on half of the scale length); supralabials 8/8, 4–5 th contacting eye; infralabials 10/9, 1–5 th /1–4 th contacting first pair of mentals, 5–6 th /4–5 th contacting the second pair; pair of mental shields, approximately the same size; temporals 2+3/2+3; nasal single; loreal elongate on the right side, slightly square on the left; preoculars 1/1 and postoculars 2/2; SVL 440 mm, TL 237.5 mm, head length 15.3 mm, head height 6.1 mm, head width 8.5 mm; distance between nostrils 2.5 mm, eye height 2.6 mm, eye length 3 mm, distance between eyes 5.4 mm, eye-mouth distance (approximately at the level of the fifth supralabial) 1.2 mm, eye-rostral distance 3.6 mm; internasal scale (length X width): 1.2 X 0.9 mm, prefrontal: 1.7 X 1.5 mm, frontal: 4.4 X 1.7 mm, parietal: 4.5 X 2.2 mm, loreal: 1.1 X 0.6 mm; prediastemal maxillary teeth 9 plus 2 slightly enlarged and grooved fangs.</p> <p>In preservative, dorsal surface of the head with intense brown pigmentation from the supratemporals to internasals, temporals light beige with several small brown dots; brown postocular stripe, extending from the postoculars to the rear corner of the mouth, where it continues as a blotch of seven scales in length; supralabial background light beige with a few small brown dots, brown blotches on the first three supralabials, and a small blotch right under the eye between supralabials four and five; infralabials background light beige with scattered small brown stains, reaching mentals, gulars and preventrals. Sixteen dorsal dark brown bands, two to four scale rows long, more prominent on the first third of the body, progressively losing pigmentation towards the tail, until fading into sparse dark brown spots on each side of the vertebral scale; beige stripe from the distal border of the parietals, extending eight scales onto the neck, bordered by two dark brown stripes (10 scales long) on each side; ventral background light beige with intense pigmentation of minute brown spots, darkening the overall ventral pattern towards the tail; diffuse dark brown blotches, concentrated on the paraventral portion, more evident from the second third of the body; ventral portion of the tail dark brown with more intense pigmentation than body (Fig. 3).</p> <p>The hemipenis of the holotype is unilobed (although with divided retractor muscle), unicalyculate and non-capitated, with very short capitulum covered with small papillate calyces; few spinulate calyces on the proximal portion of capitulum on the asulcate side; hemipenial body covered with a few rows of small spines, 19 slightly larger spines encircling first row; sulcus spermaticus divided at the base of the capitulum, with sulci ending in slightly enlarged area, on approximately half the capitulum length; subtle constriction between base and hemipenial body; base covered with several spines, approximately the same size as the body spines (Fig. 5).</p> <p> <b> Hemipenial morphology (<i>n</i> =15).</b> <i>Thamnodynastes silvai</i> has a hemipenis pattern corresponding fairly well to the overall pattern of the <i>T. pallidus</i> group, more closely resembling the hemipenis of <i>T. longicaudus</i> (Figs. 2, 5). Additional prepared hemipenes exhibited little variation (Fig. 5), such as: capitular spinulate calyces can be more evident on the proximal portion of the capitulum, on the asulcate side (Fig. 5C); the sulci are short, after the sulcus spermaticus division, associated with a short capitulum in all analyzed specimens, and their termination can be slightly closer to the capitulum apex (Fig. 5B–D).</p> <p> <b>Meristic and morphometric variation.</b> Largest male (SINCHI-R 2139) SVL 440 mm and TL 237.5 mm; largest female (AMNH 55472) SVL 388 mm and TL 170 mm; smooth dorsal scales in 17/17/11 (70%, <i>n</i> =42), 17/17/13 (22%, <i>n</i> =13), 15/17/11 (3.3%, <i>n</i> =2), 17/17/12 (3.3%, <i>n</i> =2) or 17/17/10 (1.6%, <i>n</i> =1) series. Sexual dimorphism was reported for both ventrals (<i>t =</i> -8.4707, <i>p<</i> 0.001) and subcaudals (<i>t=</i> -6.0197, <i>p</i> <0.001); ventrals 127–148 (137±4.8, <i>n</i> =27) and subcaudals 83–101 (94± 4.2, <i>n</i> =21) in males, ventrals 124–137 (128±2.9, <i>n</i> =31) and subcaudals 80–97 (87±4.1, <i>n</i> =28) in females; supralabials 8 (98%, <i>n</i> =52) or 8/7 (2%, <i>n</i> =1); 4–5 th supralabials contacting eye (75%, <i>n</i> =38) or 3– 5 th (28%, <i>n</i> =15); infralabials 9 (75%, <i>n</i> =43), 8/8 (8.7%, <i>n</i> =5), 9/8 (5.3%, <i>n</i> =3), 9/10 (3.5%, <i>n</i> =2), 10/9 (3.5%, <i>n</i> =2), 8/9 (1.7%, <i>n</i> =1) or 10/10 (1.7%, <i>n</i> =1); preoculars 1/1 (93%, <i>n</i> =52) or 1/2 (<i>n</i> =1); postoculars 2/2 (86%, <i>n</i> =49), 2/3 (<i>n</i> =1), 3/2 (<i>n</i> =2), or 3/3 (<i>n</i> =2); nasal scale single (98%, <i>n</i> =52) or semi-divided on the right side (<i>n</i> =1).</p> <p> <b>Color pattern variation.</b> In preservative, examined specimens show head usually very pigmented with several small dots, from rostral to temporal scales, almost black in few specimens (USNM 233065, MHNC 3143). Head usually with two dark brown bands right after temporals, extending onto the neck, occasionally merged with first pair of dorsal blotches (USNM 203065, SINCHI-R 2142, 2139) (Fig. 4). These two bands may define a lighter central neck band (SINCHI-R 2153). Postocular stripe very distinguished, the same color as dorsal blotches, ending right after the corner of the mouth, and extending for 2 or 3 scales ventrally (IAVH 2046), or linearly extending on the side of the body (AMNH 52083) (Figs. 3, 4). Venter of the head light beige, with a few scattered brown dots concentrated more on neck region and laterally. Twelve to 21 dorsal bands on the first third of the body, defined into regular transverse bands (CORBIDI 6072, AMNH 52536) or irregularly shaped (e.g. IAVH 2046) (Fig. 4). Final dorsal two thirds of body and tail with more intensely pigmented variegate pattern (AMNH 52083, 53581), or with very subtle pigmentation, almost immaculate (AMNH 52858). All specimens (<i>n</i> =64) lack longitudinal ventral stripes, with ventral brown blotches dispersed throughout the belly and tail (Figs. 3–4). These blotches can be evenly spaced, occupying two ventral scales each (AMNH 53582, 55472), or more irregularly dispersed (IAVH 2046, USNM 233065) (Fig. 4). Most specimens with overall ventral darkening towards the tail, from beige or light cream on the head to an intensely pigmentated brown tail (IAVH 2046).</p> <p> <b>Color in life.</b> The following pattern and coloration description of specimen AMNH 147707, from Pebas, Loreto Department, Peru, is from the field notes of Charles W. Myers (pers. comm. to Robert A. Thomas dated April 14, 1977): “Overall grayish brown above, with a few blackish brown spots and vague yellowish-brown areas that are paler than ground color and that occur at intervals to give an incipient banded pattern. The neck or hood region is banded with brown saddles and lighter brown interspaces (scales in the interspaces have pale yellow bases set in white skin). A pair of vague dark brown lines on rear of head and nape. Underside head and neck white, thence turning an increasingly dark grayish brown on venter, with squarish marks of still darker brown; these marks tend to be broken and/or bordered by streaks of whitish. Iris pale brown; pupil vertical. Tongue overall grayish black except for a broad brown band that encircles the base of fork.”</p> <p> <b>Etymology.</b> The specific epithet “ <i>silvai</i> ” is patronymic honoring the late Juan Silva Haad, physician at the hospital of Leticia for many years, who maintained a snake collection for over 50 years. He collected several species from Colombian, Peruvian and Brazilian Amazonia, including several of the <i>Thamnodynastes</i> specimens used in this description. He donated most part of his collection to the Sinchi Institute, with over 2,500 specimens of Amazonian snakes, which represented an immense contribution for the Institute’s collection, and a valuable addition of important data for the study of Amazonian snakes. Unfortunately, he passed away on January 31, 2021, just a few weeks before the final reviewed version of the manuscript was accepted.</p> <p> <b>Distribution and natural history.</b> Six females had three to six developed follicles with visible embryos (possibly in early stages of development due to their small size): SINCHI-R 2142 (3 follicles/embryos), SINCHI-R 2143 (6), SINCHI-R 2147 (4), SINCHI-R 2154 (5), SINCHI-R 2172 (5), and SINCHI-R 2173 (5); and one female (MPEG 18835) had three well-developed follicles with larger visible embryos, confirming a viviparous reproductive mode. The largest pregnant female (SINCHI-R 2147: SVL 323 mm, TL 173 mm) had four embryos. One specimen (AMNH 53582: SVL 321 mm, TL 152 mm) had a small frog (family Hylidae) in the stomach.</p> <p> On July 29, 1994 at 14:15 h, during the flood season in the Amazon, Marinus S. Hoogmoed and Teresa C. Avila-Pires collected a female (MPEG 18835) in an isolated tree, emerging from a floating meadow (mixed vegetation) at the edge of a lake, completely surrounded by floating grassy mats along its banks. The specimen was slowly moving on the branches of a tree at a height of about 2m above the water surface. When collected (and later again when photographed), it flattened its head and anterior part of the body horizontally (forming a hood), which caused the thin skin between the scales to be stretched and exposed, suddenly showing a bold pattern of transverse, dark brown spots on a lighter background (Figs. 6A–B). Within the spots, the edges of the scales were black, forming three to six horizontal short zig-zag lines (about three scales long) within the dark spots. Because of the abrupt change this behavior was interpreted as being defensive. No attempt to bite was made. We also report, for the first time, the same behavior for <i>T. pallidus.</i> Two specimens (SINCHI-R 2528 and 2529) displayed the hood-displaying performance while their photographs were being taken, during fieldwork in San José del Guaviare, Guaviare Department, Colombia, in June 15, 2017 (Figs. 6C–D).</p> <p> <i>Thamnodynastes silvai</i> occurs in forested areas of Amazonia, along the triple frontier of Colombia, Brazil and Peru; extending southwest to the Loreto Department in Peru, northwest to the province of Morona-Santiago in Ecuador, and northeast to Uarini, state of Amazonas in Brazil (Fig. 7).</p>Published as part of <i>Trevine, Vivian C., Caicedo-Portilla, José Rancés, Hoogmoed, Marinus, Thomas, Robert A., Franco, Francisco L., Montingelli, Giovanna G., Osorno-Muñoz, Mariela & Zaher, Hussam, 2021, A new species of Thamnodynastes Wagler, 1830 from western Amazonia, with notes on morphology for members of the Thamnodynastes pallidus group (Serpentes Dipsadidae, Tachymenini), pp. 235-256 in Zootaxa 4952 (2)</i> on pages 242-248, DOI: 10.11646/zootaxa.4952.2.2, <a href="http://zenodo.org/record/4674001">http://zenodo.org/record/4674001</a&gt