Pheidole praehistorica, Varela-Hernández & Riquelme, 2024

Varela-Hernández, Fernando & Riquelme, Francisco, 2024, Pheidole praehistorica sp. nov., a new addition to spiny ants of the genus Pheidole Westwood, 1839 (Formicidae, Myrmicinae) from Oligo-Miocene Mexican amber, European Journal of Taxonomy 968, pp. 86-97 : 89-92

Pheidole praehistorica sp. nov.

urn:lsid:zoobank.org:act:B6182776-8581-414F-BD67-F5EE483081F0

Figs 1–3

Diagnosis

Pheidole praehistorica sp. nov. differs significantly from the other two Dominican fossil spiny species as follows: P. primigenia has an average size of 2.88–3.56 mm, while P. praehistorica is smaller, with an average total length of 2.3 mm. It also differs by longer pronotal spines in P. primigenia and smaller ones in P. praehistorica . Pheidole praehistorica has a deeper mesonotal groove than P. primigenia ; propodeal spines are curved downwards in P. primigenia but straight in P. praehistorica ; P. primigenia differs markedly by the shape of the anterior edge of the clypeus, which is “slightly prominent in the middle and straight” ( Baroni-Urbani 1995), while it is formed by a median projection with a minute denticle in the middle and a lateral denticle on each side of the median projection in P. praehistorica ( Fig. 1A–E ).

Pheidole tethepa is another fossil species from Dominican amber with pronotal spines similar to those of P. primigenia and P. praehistorica sp. nov. However, P. tethepa has a pair of gular spines not found in P. primigenia or P. praehistorica . In contrast, P. primigenia and P. praehistorica have a well-formed head collar not found in P. tethepa . In addition, P. tethepa differs markedly from P. praehistorica in the shape of the middle of the anterior edge of the clypeus which is convex in P. tethepa , but in P. praehistorica it is formed by a median projection with a tiny denticle at its middle.

Etymology

The specific Latin epithet refers to the fossil (prehistoric) condition of the new species.

Type material

Holotype

MEXICO • Chiapas, Simojovel, Montrecristo mine ; 17°09′11″ N, 92°46′08″ W; CPAL-UAEM, CPAL.464 ( Fig. 1A–C ).

Paratypes

MEXICO • 4 specs; same data as for holotype; CPAL-UAEM, CPAL.465 to CPAL.468 ( Fig. 1 D – E ) .

Remarks

The paratypes are fossil inclusions, complete articulated specimens except CPAL.468, which is disarticulated medially ( Fig. 1E ). All specimens are embedded in a single piece of amber, surrounded by plant remains and soil. They are housed in the Colección de Paleontología (CPAL-UAEM), Morelos, Mexico.

Locality and horizon

Mexico, Chiapas, Simojovel, Montrecristo mine: 17°09′11″ N, 92°46′08″ W. Upper strata of the Simojovel Formation at the late Oligocene and early Miocene boundary ( Riquelme et al. 2024).

Worker description

MEASUREMENTS (n = 1). HL 0.65, HW 0.50, SL 0.85, WL 0.9, CI 76.92, SI 130, PNS 0.15, PPS 0.35 ( Figs 1A , 2A ).

HEAD. Slightly longer than wide; sides subparallel, occipital border straight, post occipital border forming a ‘collar’ ( Fig. 1A–D ). Gena reticule-striated, the occipital border with scattered small bulges, frontal carenas parallel, the area between frontal carenas smooth, posterior margin of clypeus convex, anterior margin discontinuous, formed by a median projection with a tiny denticle at the middle of it, then the margin of clypeus creating a curve to the lateral sides before projecting again as a denticle on each side ( Figs 1A–E , 2B ). Clypeus with four long hairs, two on each side of the median denticle and one on each of the lateral ones ( Figs 1A–C , 2B ). The antenna scape long, surpassing the occipital border of the head by about twice the length of the scape, scape with 12 segments, three-clubbed, club as long as the rest of the funicle ( Figs 1A–B , 2A–B ); antenna covered with long fine erect setae. Mandibles triangular, masticatory and inner border angled, straight, and smooth. Pattern dentition from apical to basal teeth as follows: apical and preapical teeth longer than all other teeth, apical tooth longer than preapical, one tiny denticle, one tooth, three denticles, and a tooth located at the junction of the masticatory and the inner border.

MESOSOMA. Apparently hard, with intricate sculpture, striated and punctured. Pronotum long, forming a long neck in profile view, convex, with a pair of spines that project dorsolaterally. Promesonotal suture slightly marked ( Fig. 1A, C, E ). Mesonotum curved, U-shape margin in profile view so that the posterior extreme of the U connects with the promesonotal suture. The mesonotal groove deep and U-shaped. Propodeum with a pair of long straight spines projecting posteriorly ( Figs 1A, C, E , 2A ), dorsal and declivitous margins well differentiated, forming a 90 degrees angle. The petiole with a long slender stalk, the petiole node relatively short, anterior and posterior faces of the petiolar node form a triangle in lateral view ( Figs 1A, C, E , 2A ).

LEGS. Mid and hind tibiae devoided of spurs, hind femur with minute decumbent hairs.

GASTER. With long, slender, erect setae, setae scattered, dorsum of first gastral tergite finely aciculate.

COLOR. Body with solid cuticle, covered with long erect setae, concolorous light yellow in amber preservation ( Fig. 1A–D ).

Phylogenetic analysis

Results show three most parsimonious cladograms. Here, we present the strict consensus one ( Fig. 3 ). In the cladogram, C. chartifex and F. integroides and D. spurius form independent clades out of the Myrmicinae clade. The Myrmicinae clade is well supported by synapomorphies 8, 22, 23, 24 and 26. There is a polytomy formed by A. mexicana , C. minutus , (( P. primigenia + P. praehistorica ) + Pheidole tethepa ) and all the species of Pheidole ( Fig. 3 ). However, two internal clades are recognized, one of them consists of all species of Pheidole included in this analysis and the other consisting of Pheidole fossil ants, which is well supported by synapomorphies 1, 5, 7, 10, and 21 ( Fig. 3 ). Accordingly, P. praehistorica sp. nov. provides new insights into a spinescence character found in New World species from the late Oligocene and early Miocene boundary.

Figures

Fig. 1. Pheidole praehistorica sp. nov. A–C. Holotype (CPAL.464). A. Profile view. B. Frontal view. C. Closer lateral view of the head and mesosoma. D. Paratype (CPAL.465), latero-frontal view of the head. E. Paratype (CPAL.468), profile view. Abbreviations: acl = antennal club; an = antenna; cly = clypeus; ey = eyes; fl = foreleg; ga = gaster; ha = hairs on clypeus; hd = head; hl = hind leg; mn = mandible; nck = neck; p = petiole; pn = pronotum; pns = pronotal spine; pp = postpetiole; pps = propodeal spine; sc = scape.

Fig. 2. Pheidole praehistorica sp. nov., holotype (CPAL.464), schematic drawing. A. Profile view. B. Frontal view.

Fig. 3. The phylogenetic status of Pheidole praehistorica sp. nov. among fossil and extant congeners inferred from the list of characters (Supp. file 1: Table S1) and the data matrix (Supp. file 1: Table S2), shows the twenty-eight morphological characters to construct the most parsimonious tree. The numbers above the white and black dots represent morphological characters, and the numbers below represent the character encoding. Black dots represent synapomorphies, and white dots represent homoplasies. † represents fossil species from Dominican and Mexican amber. Consistency index = 0.52; retention index = 0.65.